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1 fe-safe 2017 VERITY MODULE IN fe-safe

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3 Contents Contents 1 INTRODUCTION TO VERITY IN FE-SAFE ABOUT FE-SAFE ABOUT VERITY IN FE-SAFE HOW TO USE THIS MANUAL USING VERITY IN FE-SAFE OPENING AN FEA MODEL Selecting the Datasets Defining the Welds Evaluating the structural stresses ANALYSING THE MODEL Defining the Loading Defining the Materials Performing the Analysis INTERFACE REFERENCE WELD DEFINITIONS The Weld Tree The automatic weld finder Spot Weld Parameters Legacy Line Definition Parameters Group selection and editing Model Units Other Options DIAGNOSTICS Structural Stresses Table Worst cycle mean stress and damage parameter contour Log for Items Histories for Items WELD MASTER S-N CURVES THE VERITYSSM METHOD APPROACHES TO EVALUATION OF WELDED JOINTS THE STRUCTURAL STRESS METHOD Shell/Plate Element Procedures Calculation Examples MASTER S-N CURVE FORMULATION Structural Stress Based K Estimation A Two-Stage Growth Model Equivalent Structural Stress Parameter Initial Crack Size Effects S-N DATA CORRELATION A SIMPLE EXAMPLE OF THE STRUCTURAL STRESS METHOD Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 1

4 Contents 4.6 PROPORTIONAL COMBINATION OF NORMAL AND SHEAR EQUIVALENT STRUCTURAL STRESSERROR! BOOKMARK NOT DEFINED. 4.7 MULTIAXIAL COMBINATION OF NORMAL AND SHEAR EQUIVALENT STRUCTURAL STRESSERROR! BOOKMARK NOT DEFINED. 4.8 MULTIAXIAL S-N CURVE NORMALISATION... ERROR! BOOKMARK NOT DEFINED. 4.9 MULTIAXIAL PARAMETER CONFIGURATION... ERROR! BOOKMARK NOT DEFINED. 5 PREPARING FE MODELS FOR USE WITH VERITY SUPPORTED FE PROGRAMS Abaqus Nastran I-DEAS Ansys MODELLING CONSIDERATIONS AND APPLICATIONS Full Penetration Welds Partial Penetration Weld and Root Failures Lap Fillet Weld and Failure Modes Fillet Weld between Two Plates with Dissimilar Thicknesses Weld Line Curvature Modelling Calculations without Modelling Weld TUTORIAL A: SINGLE WELD LINE (USING ABAQUS) INTRODUCTION PREPARATION OPEN THE MODEL Select the Datasets Define the Weld Evaluate the structural stresses ANALYSE THE MODEL Define the Loading Define the Materials Perform the Analysis TUTORIAL B: MULTIPLE WELD LINES (USING ANSYS) INTRODUCTION PREPARATION OPEN THE MODEL Select the Datasets Define the Welds Evaluate the structural stresses ANALYSE THE MODEL Define the Loading Define the Materials Perform the Analysis Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

5 Contents 8 TUTORIAL C: SHELL WELD LINES (USING NASTRAN) INTRODUCTION PREPARATION OPEN THE MODEL Select the datasets Define the materials Define the welds Evaluate the structural stresses ANALYSE THE MODEL Define the loading Define the algorithm Define the Weld material Perform the analysis TUTORIAL D: SPOT WELDS (DETECT ALL CONNECTING ELEMENTS) INTRODUCTION PREPARATION OPEN THE MODEL Select the Datasets Define the Welds Evaluate the structural stresses ANALYSE THE MODEL Define the Loading Define the Materials Perform the Analysis TUTORIAL E: SPOT WELDS (DETECT CONNECTING ELEMENT GROUP) INTRODUCTION PREPARATION OPEN THE MODEL Select the Datasets Define the Welds Evaluate the structural stresses ANALYSE THE MODEL Define the Loading Define the Materials Perform the Analysis TUTORIAL F: AUTOMATIC WELD FINDER FOR SOLID WELDS (USING ABAQUS) INTRODUCTION PREPARATION OPEN THE MODEL Select the Datasets FILLET GROUP DEFINE THE WELD Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 3

6 Contents 11.6 ANALYSE THE MODEL Define the Loading Limit analysis to the verity weld toe groups Perform the Analysis TUTORIAL G: AUTOMATIC WELD FINDER FOR SOLID WELDS (USING ANSYS) INTRODUCTION PREPARATION OPEN THE MODEL Select the Datasets FILLET GROUP DEFINE THE WELDS ANALYSE THE MODEL Define the Loading Limit analysis to the Verity groups Perform the Analysis TUTORIAL H: AUTOMATIC WELD FINDER FOR SHELL WELDS (USING NASTRAN) INTRODUCTION PREPARATION OPEN THE MODEL Select the datasets Define the welds ANALYSE THE MODEL Define the loading Define the algorithm Define the materials Perform the analysis SPECIFIC LINE ANALYSIS Define the line welds Analyse the Model Define the materials Perform the analysis REFERENCES Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

7 Trademarks fe-safe, Abaqus, Isight, Tosca, the 3DS logo, and SIMULIA are commercial trademarks or registered trademarks of Dassault Systèmes or its subsidiaries in the United States and/or other countries. Use of any Dassault Systèmes or its subsidiaries trademarks is subject to their express written approval. Other company, product, and service names may be trademarks or service marks of their respective owners. Legal Notices fe-safe and this documentation may be used or reproduced only in accordance with the terms of the software license agreement signed by the customer, or, absent such an agreement, the then current software license agreement to which the documentation relates. This documentation and the software described in this documentation are subject to change without prior notice. Dassault Systèmes and its subsidiaries shall not be responsible for the consequences of any errors or omissions that may appear in this documentation. Dassault Systèmes Simulia Corp, Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 5

8 Third-Party Copyright Notices Certain portions of fe-safe contain elements subject to copyright owned by the entities listed below. Battelle Endurica LLC Amec Foster Wheeler Nuclear UK Limited fe-safe Licensed Programs may include open source software components. Source code for these components is available if required by the license. The open source software components are grouped under the applicable licensing terms. Where required, links to common license terms are included below. IP Asset Name IP Asset Version Copyright Notice Under BSD 2-Clause UnZip Info-ZIP) (from 2.4 Copyright (c) Info-ZIP. All rights reserved. Under BSD 3-Clause Qt Solutions 2.6 Copyright (c) 2014 Digia Plc and/or its subsidiary(-ies) All rights reserved. 6 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

9 Introduction to Verity in fe-safe 1 Introduction to Verity in fe-safe 1.1 About fe-safe fe-safe is a powerful, comprehensive and easy-to-use suite of fatigue analysis software for Finite Element models. It is used alongside commercial FEA software to calculate: where fatigue cracks will occur; when fatigue cracks will initiate; the factors of safety on working stresses (for rapid optimisation); the probability of survival at different service lives (the warranty claim curve). Results are presented as contour plots which can be plotted using standard FE viewers. fe-safe has direct interfaces to the leading FEA suites. 1.2 About Verity in fe-safe Verity in fe-safe is an add-on module for use with fe-safe fatigue analysis software, that computes equivalent structural stresses based on the Battelle Structural Stress Method, and uses these stresses to calculate fatigue damage and corresponding fatigue lives. Users of Verity in fe-safe are assumed to have a working knowledge of fe-safe, including such techniques as configuring a fatigue analysis and setting properties for different parts of the model, defining the fatigue loading, running an analysis and exporting fatigue results. The use and application of fe-safe is described in the fe-safe User guide, which should be referred to alongside the Verity in fe-safe manual. Features of Verity in fe-safe include: Support for Finite Element solutions from Abaqus FIL and ODB, Nastran OP2, I-DEAS UNV and Ansys RST files.automatic identification of weld line and through-thickness connectivity. Automatic detection of spot weld nuggets and their associated sheets. Support for a wide range of FE dimensionalities. The FE mesh in the vicinity of the weld line may be comprised of 3D solids (either hexahedral/pentahedral or tetrahedral) or 3D mid-surface shells. Beam and 1D solid elements may be used in the mesh, but must not be included in the weld element domain that contributes nodal forces to the nodes along the weld line and is used to derive the weld line connectivity. Consistent structural stress calculations regardless of mesh sizes, element types, or the FE software used (a critical step to realising 6 sigma in CAE applications). Structural stress calculations for both normal and Mode III (in plane) shear forces. Use of a single master S-N curve, eliminating the need to determine weld classification (required by other weld fatigue approaches). Support for element types of any dimensionality that feature linear or quadratic order. The ability to process multiple load cases from multiple results files. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 7

10 Introduction to Verity in fe-safe The ability to process load cases from linear or nonlinear static analyses. User-specified rotations of the weld line local coordinate system (to accommodate structural stress computations on through-thickness sections that are not normal to the plate surfaces). If the reference surface is offset from the mid-surface during an analysis involving 3D shells, this offset may then be input so that the structural stress calculations will account for the offset. User-specified symmetry at either end of the weld line that will de-activate virtual node weld end correction. Support for further improving the accuracy of fatigue life predictions by allowing the user to formulate their own custom, master S-N curve based on proprietary data. Compatibility with tools in PreProcessors such as Ansa that automatically identifies and generates the required weld definitions. 1.3 How to Use This Manual Chapter 2 (Using Verity in fe-safe) provides an overview of the actions required in order to perform Verity or LBF analysis in fe-safe, while chapter 3 (Interface Reference) offers further details of the available options. The Verity Method itself is discussed in chapter 0. The prerequisites for Verity analysis are explained in chapter 0 (Preparing FE Models for use with Verity ). Worked examples of the process are provided in several tutorials. Users new to fe-safe Because this manual assumes some familiarity with fe-safe, it will be necessary to learn a little about the main program first. Work through some of the tutorials in the fe-safe User guide, including at least one demonstrating the use of files from your preferred FEA software, then return here. fe-safe users new to Verity Some understanding of the Verity method is required to make the best use of the software. Chapter 0 provides a description for those unfamiliar with the method. Work through one or more tutorials including at least one demonstrating the use of files from your preferred FEA software. Then read chapter 0 to find out how to prepare your own FE models for use with Verity. Once you have done this, follow the procedure described in chapter 2 with your own models, referring to chapter 3 as necessary. Experienced users of Verity in fe-safe Experienced users are most likely to refer to chapter 3, which provides a detailed interface reference, including descriptions of infrequently-used parameters. 8 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

11 Preparing FE Models for use with Verity 2 Using Verity in fe-safe 2.1 Opening an FEA Model To perform a fatigue analysis using this technique, an FE model must be opened using the File menu item Open Finite Element Model... The model to be read is then selected in an open file dialog box Selecting the Datasets If the model is being read for the first time, fe-safe pre-scans the model to see what it contains. A prescan dialog box is displayed allowing the selection of the stresses and forces to read: Figure 2-1 To perform a Verity based analysis some datasets containing Forces for Verity must be selected in addition to datasets containing Stress. Select the required forces and stresses and click OK. fe-safe will read the selected data and echo to the Message Log a summary of the datasets that have been read. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 9

12 Preparing FE Models for use with Verity Defining the Welds Once the stresses and forces have been read the weld locations should be defined prior to evaluation of the structural stresses. This can be done using the Weld Preparation >> Define and Analyse Weld Geometry menu and a new dialog box will be displayed: Figure 2-2 Remove any unwanted weld definitions using the Delete or Delete All buttons, then add welds as necessary using the Add button. For further options, see section Evaluating the structural stresses Once all weld definitions are complete click the Save and analyse button to start the calculation of the structural stresses. fe-safe will locate the weld line domain and identify the local coordinate system at each weld line node, and then run the Verity module to calculate structural stresses and echo the Verity outputs to the message log, as well as the following information: 10 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

13 Preparing FE Models for use with Verity Processing foces dataset 1.1 at time 2.22e-016. Saving structural stresses to FED file... Verity stress generation and import completed. This tells you that fe-safe is importing the structural stresses calculated by Verity. When subsequently running the analysis if a node/element is part of a Verity group, the stress dataset(s) defined in the loading are used to look up the correct structural stress dataset(s). Once the import is completed the Current FE Models window should show one or more groups beginning with WELD (one for each failure mode) which contain the elements for the weld lines. A summary of the Verity analysis run can be found in the verity-diagnostics.log file (Weld preparation >> View Structural Stress Diagnostics Log menu item) and a table of the structural stresses calculated can be found in the verity-ss.txt file (Weld preparation>> View Structural Stress File menu item). 2.2 Analysing the Model After the import process has completed the WELD groups will appear in the Group Parameters section in the Fatigue from FEA window. These groups have limited configuration options, the algorithm for these groups can be a structural stress method weld analysis for either normal or shear stresses, or Do not analyse. If the algorithm cell for a WELD group is selected then the following dialog box is displayed, from which this selection is made via the respective radio button. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 11

14 Preparing FE Models for use with Verity Defining the Loading To define the type of loading for the analysis, select the Loading Settings tab on the Fatigue from FEA dialog box. Figure 2-3 Remove any unwanted loadings by right clicking on the tree and selecting Clear all loadings, then add the desired loadings using the Add button. When finished click OK Defining the Materials Materials from the verity.dbase are provided for use with the structural stress algorithms. This currently includes 8 materials: Steel Weld (50%) Steel Weld 2SD (2.2%) Steel Weld 3SD (0.12%) Steel Weld/Throat (50%) Steel Weld/Throat 2SD (2.2%) Steel Weld/Throat 3SD (0.12%) Al alloy Weld (50%) Al alloy Weld 2SD (2.2%) 12 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

15 Preparing FE Models for use with Verity The material will default to the steel mean life curve each time a new Verity structural stress calculation is performed. Note that in fe-safe and 2016 versions, there were separate materials for Steel Weld shear. In fe-safe 2017 the Verity materials contain two S-N curves instead: the normal S-N curve and a new attribute storing the T-N curve for the shear response. For the Steel Weld (50%), Steel Weld -2SD and -3SD materials these are equivalent to the S-N curves of the previous respective Steel Weld Shear materials. Fe-safe automatically picks the appropriate curve for the selected algorithm. For other material classes, (Root or Throat failures and aluminium alloy welds) Battelle have not published the shear response data. The T-N curves used in the shear damage calculation have therefore been calculated from the normal S-N curve assuming a Von Mises assumption (as recommended by Dong and Hong in [1]). So in effect in the absence of a published T-N curve for shear, the shear algorithm multiplies the shear amplitude by and then uses the normal S-N curve Performing the Analysis Once the WELD group is configured, click the Analyse button. The FEA Fatigue Analysis Summary dialog box is displayed, showing the parameters that will be used for the analysis: Figure 2-4 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 13

16 Preparing FE Models for use with Verity Click Continue to begin analysis. As the analysis is being performed the worst life calculated so far will be displayed in the Message Log window. Once the analysis is complete, a results file will be produced by default containing the log10 (life) contours. If a node is included in the analysis of more than one weld, the result exported for the node is the worst-case result if no failure mode had been specified, although separate results can be maintained where the mode weld line domains are defined on different elements (see 3.1.4) and failure mode is specified. For example the fusion domain can be defined on the fillet elements of the weld line, and the toe domain on the parent plate side of the line. Note that if the automatic weld finding capability is used then this will automatically happen (but see compact contour mode settings for root mode in 3.1.2). Additional contours export options can be configured in the FEA Fatigue >> Analysis Options dialog box, Export tab: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

17 Preparing FE Models for use with Verity All nodes on an element use element s worst value: all nodes on an element will be assigned the worst contour value of that element. All nodes on an element use element s averaged value: all nodes on an element will be assigned the average contour value of that element. Skipped nodes use element s worst contour value [Default]: nodes not analysed (e.g. those of weld elements which are not part of the weld line) will be assigned the worst contour value of the remaining nodes on element. Skipped nodes use element s averaged contour value: nodes not analysed (e.g. those of weld elements which are not part of the weld line) will be assigned the average contour value of the remaining nodes on element. Skipped nodes use default contour value: nodes not analysed (e.g. those of weld elements which are not part of the weld line) will be assigned the default contour value: Contour Default value Life / Log of Life Infinite life FOS Max FOS FRF 10 Dang Van - radial 10 Dang Van - vertical 10 Dang Van - survived 1 Probabilities -100 SRP PP 0 SRP PC 1 SRP CP 2 SRP CC 3 All other contours 0 Skipped nodes are not exported: nodes not analysed (e.g. those of weld elements which are not part of the weld line) will not be assigned any value. More detailed description of all configuration options can be found in Chapter 5 of the fe-safe User Guide. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 15

18 Preparing FE Models for use with Verity 16 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

19 Preparing FE Models for use with Verity 3 Interface Reference Note that only those interface elements of particular importance for Verity Analysis are described here. 3.1 Weld Definitions The weld definition dialog box can be displayed after the datasets have been read by using the Weld Preparation >> Define and Analyse Weld Geometry menu: Figure The Weld Tree The weld tree is used to define all the welds and the parameters associated with each of the welds. The root tree items with the icon are line welds (either individual lines or groups of automatically located lines defined via a fillet group), while those with the icon represent a set of spot welds. The name of a weld can be edited by selecting the weld and then clicking the Edit button or double-clicking the weld name. The weld names must be unique. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 17

20 Preparing FE Models for use with Verity Prior to fe-safe , each weld line and failure mode combination was defined individually as a separate weld in the tree, and required a domain group and set of line nodes to be explicitly specified. This method is still available, but is now referred to as a Legacy Line Definition. The alternative is to define a set of lines and/or failure modes in a single weld definition in the tree, by providing a weld fillet group, and much of the previously required data is automatically derived by fe-safe (see 3.1.2). For each weld there are a series of children defining the parameters for a weld. Those with a icon are required. The list of the required parameters for a weld is a function of the type of elements used within the FEA model. If the checkbox Show all configuration options for each weld is checked then a series of optional parameters are also shown. These are marked with a icon. The list of optional parameters is affected by the status of the open weld parameter as well as the element type. Buttons to the right of the weld tree allow welds to be modified, stored and retrieved: Add creates a new weld definition using default settings. The type (Line Welds (From Weld Fillet Elements), Spot (Detect All Connecting Elements), Spot (Detect Connecting Element Group) or Legacy Line Definition) is selected from a popup menu. Note: Line Welds has replaced the Solid Weld option prior to fe-safe version 2016, and now includes Shell elements. The new Legacy Line Definition now performs the functionality that was previously termed Line Welds prior to fe-safe version Delete removes the currently selected weld. Duplicate creates a copy of the currently selected weld, which can then be edited. This is particularly useful when there are welds of the same type but with different nodes (for example, the two sides of a weld). Delete All removes all welds. Edit allows the currently selected aspect of a weld Open replaces the current tree with a set of weld definitions stored on disk. Append preserves the current tree, but adds the weld definitions from a file. This will only succeed if there are no duplicate definitions. Save All writes the current tree to a file. Save One writes the currently selected weld to a file. All the possible parameters that can be defined for a weld are documented below. To start editing a parameter select it and then click the Edit button. Text items can be edited in place in the tree control. Items that have a pre-defined list of options will display a dialog box containing the list to select from. 18 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

21 Preparing FE Models for use with Verity The automatic weld finder Weld lines on either solid or shell elements can be defined automatically as an alternative to the legacy weld line method (see Section 3.1.4). The intention is to provide a simpler way of defining the weld domain and weld lines, especially when multiple weld lines are to be analysed, or several different failure modes (Toe, Fusion, Throat, Root). Instead of inputting the weld domain and detailed information on the weld line nodes for each line and failure mode, the fillet group is defined instead. The fillet group may already be available in fe-safe, for example as a Set, Material, or Property group defined in the FE model or it may be a user-defined group in fe-safe. The various weld lines and weld domains are then automatically computed by fe-safe, although it is still necessary to provide a domain group for root failures on solid element welds. Multiple weld fillets in the model can be supplied as a single fillet group, including both solid and shell elements (though a mix of shell and solid elements is not allowed in the same weld), and the software will automatically locate the separate lines in the various fillets, although it is possible that some complex geometries involving intersecting lines in branching fillets may contain some ambiguities, which would require definition of separate fillet groups. fe-safe locates potential weld lines by identifying nodes connected by edges lying along the interface between fillet and non-fillet elements. The root lines are also located, either because these are formed from internal surface nodes in fully penetrative welds, or lie on a fillet-parent material interface where there are two faces with significant change in normal direction. To invoke this option, click the Add button on the main Weld Definition dialog and select Weld Lines (From Weld Fillet Elements) from the resulting popup menu. This will result in the weld definition dialog displayed below. The only compulsory input is the fillet group. Note this group specifies all weld fillet elements, not the weld domain. For toe, fusion, or throat failure modes, the weld domains can be automatically extracted. For root failures the weld domain can be detected automatically for shell welds, but for solid welds a root domain group must be specified. If multiple root lines are to be analysed, this root domain group covers the combined domain of all of them. Note that the specified root domain may be a superset of the actual weld domain; the weld finder will determine which elements from it actually lie on the failure plane. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 19

22 Preparing FE Models for use with Verity Figure 3-3 Double clicking on the value field of the Fillet Group parameter invokes the Group definition dialog (see section 3.1.5), and allows selection of a loaded group or user-defined group in the fe-safe Group Manager. By default only Toe and Fusion failures are automatically analysed; use the optional parameters (Auto-detect Fusion failures, etc) to configure automatic extraction of Toe, Fusion, or Throat modes. Alternatively explicit domains can be defined for any of these. Note that if a Toe or Fusion domain is specified which relates only to one line of a fillet, but auto-extraction is on for that mode, then the other line will still have its domain automatically extracted. If detailed diagnostics are specified on the Weld Definition dialog (see section 3.1.7), then a comprehensive set of groups will be created in the Group Manager (in the list of unused groups) specifying the nodes and elements of each line, and the located domain. 20 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

23 Preparing FE Models for use with Verity Recall that if the checkbox Show all configuration options for each weld is checked then a series of optional parameters are also shown. These are marked with a icon. Descriptions of each parameter are included below. Fillet Group This is a list of elements defining the weld fillet material, (i.e., the filler material added in the process of creating a line weld). Auto-detect Fusion Failures This option can be turned On or Off (default is On), and automatically identifies fusion plane failure modes. Auto-Detect Shell Root Failures This option can be turned On or Off (default is Off), and automatically identifies weld root failure modes (for shell welds only). Auto-detect Throat Failures This option can be turned On or Off (default is Off), and automatically identifies weld throat failure modes. Auto-detect Toe Failures This option can be turned On or Off (default is On), and automatically identifies weld toe failure modes. Compact contour mode This option can be turned On or Off (default is On). It applies to sub-surface line elements on solid welds, namely root failures, or throat failures analysed from the root. When On, this results in fatigue results for the root line solid elements being projected onto the surface line(s) for easier viewing in the Output file i.e. there is no need to view/cut the results, in order to see the life contour. If throat failure mode is analysed, then the root results will be projected onto the surface throat failure line; otherwise they are projected onto both surface weld lines at the edges of the fillet. Note that the same element can have results from several failure modes (eg. a fusion result and a projected compact contour result from root failure), and fe-safe will pick the worst for the final result. If throat failures are analysed from both surface and root using automatic domain identification, and compact contour mode is on, then both results are displayed on different sides of the line (e.g. the domains discussed below in Throat Failure Sense). However if the domain had been explicitly specified then only that one side is available, so only one set of throat results will be displayed which will be the worst of the two. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 21

24 Preparing FE Models for use with Verity Crack Length As in the default value of this parameter is set at crack length = plate thickness. There is a slight difference relating to the default value, due to differences in the plate thickness used as a default for this parameter. In Automatic weld finder for solid welds, the plate thickness parameter may be extracted from the model rather than pre-configured. If this happens the plate thickness may vary somewhat along the length of the weld line, so the maximum plate thickness value is used as default. Domain Constraint This is used in automatic domain location for solid welds, and is ignored when an explicitly specified domain is in use. If left at the default Unconstrained, then the search for through nodes in the weld domain will continue all the way through the model until a surface is reached, or until no further node or element edge is found aligning with the failure plane (which would result in diagnostic warnings). Alternatively use the popup menu after double-clicking on this value field to select Constrained by Plate Thickness, which will terminate the domain search at a maximum distance from the weld line, specified in the Plate Thickness option. Note that in Solid Welds, this plate thickness may not be exactly what is used in the Verity structural stress calculations (see Structual Stress Plate Thickness option below). Failure Plane Co-planarity Tolerance This is used to specify a tolerance in degrees for the angle between the calculated failure plane normal, and that of a candidate element face. This is used to test potential domain solid elements if no candidate nodes are located for that element within the nodal tolerance cone (see also Through Thickness Cone Tolerance). The domain location algorithm would then attempt to find aligned points close to edge intersections which are within the cone tolerance distance of the edge, but only if the edge lies on an element face within this parameter s tolerance of the failure plane. The nodal forces are then interpolated (potentially between a corner and a mid-side node on the edge). Note that solid elements should ideally be meshed so that the weld domain contains a set of elements with faces aligning along the failure plane. However automatic tet meshers are not guaranteed to produce this. This parameter is intended to allow small violations of this co-planarity assumption. However this should not be used to set large tolerance values so that arbitrary meshes can be processed in Verity, as testing indicates that meaningful results can be obtained only if the through-thickness mesh is regular. Fusion Domain Group This is used to override the automatic fusion domain extraction by explicitly specifying the domain. The automatic algorithm will extract a domain on the fillet side of the failure plane. This can be used to place the domain on the parent material side, or to vary the plate thickness along the line. If a domain is specified but some elements are never included, then an unused group is created which consists of all domain group elements which have not been placed in the weld domain (for example their nodes, or faces may not align, see Failure Plane Co-Planarity Tolerance and Through Thickness Cone Tolerance). 22 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

25 Preparing FE Models for use with Verity I(r) Function As part of the fatigue life calculation procedure, Verity uses a dimensionless polynomial function of the bending ratio, (see Section 4.3.3). The following equations are available to the user for analysing normal stresses: which have been designated as Structural Joints / Displacement Control and Small Details / Load Control, respectively. The Structural Joints / Displacement Control equation is the default option in the Verity GUI. This ensures the best possible correlation for the engineering applications that are usually analysed in Verity (as opposed to the less common assessment of test specimens). Note that for backward compatibility with previous versions of Verity the user must set this parameter to Small Details / Load Control. Note that when shear stresses are analysed then this selection is ignored, and instead a fixed shear polynomial I(r) function is used given in section Number of smoothing iterations Sometimes a line weld configuration can yield large structural stress fluctuations. To address this issue a structural stress smoothing algorithm is available, which provides the ability to smooth the resultant structural stress profile. This algorithm is cyclic in nature and up to 10 iterations can be applied. The default value is zero, i.e. the smoothing function is disabled. Plate Thickness The plate thickness may be specified, in the same units as those selected for the FEA model distance units using Loaded FEA Model Properties dialog box accessed from the Current FE Models window in the fe-safe GUI. With shell welds for FE models that do not contain shell thickness this parameter must be specified, for solid welds this is always optional. For solid welds, if a domain has been set it is not necessary to specify this, nor if the desired domain goes all the way through the model to a surface. If set, then this parameter has two potential uses, depending on the selections of the Domain Constrained and Stuctural Stress Plate Thickness settings. The former relates to its use in determining the maximum thickness of the weld domain anywhere along the weld line, whereas the latter determines whether it is used in the Verity structural stress calculations as a constant along the line (rather than the actual distance determined by the local domain thickness). See also Domain Constrained and Stuctural Stress Plate Thickness. Note that if the plate thickness is set, then normally one or both of these options should be changed, as the default will be to ignore this parameter. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 23

26 Preparing FE Models for use with Verity Reference Length The reference length value defines the parameter L used in the virtual node weld end correction, and is used only when this correction is being applied. The reference length is the parameter L in the derivation of the weld end correction. If the specified reference length is not greater than or equal to 2.5 times the crack length, it will be reset to this value. If the weld line is closed or if the symmetry flag has been set at both ends, the reference length is not needed. Root Domain Group If root failures are to be analysed then the root domain (same group for all root lines) must be specified. Note that the selected elements for solid welds must be the ones on the fillet side of the continuation of the parent/fillet interface plane (i.e. directly under the back of the fillet). Although in principle the elements on the other side could be used in the Verity calculations, and the same results should be obtained (if forces are validly balanced), in this context that would create an ambiguity in the algorithm used to determine the failure plane. The root failure plane is aligned to an element s face in the root domain that has an edge on the root line and is adjacent to an element that is neither in the root domain nor the weld fillet. Note that this requires the root domain to be directly under the fillet, not under the continuation of the fusion plane on the parent material side (as the latter would have two such faces, one in each fusion plane, rendering it ambiguous).. Note that the specified root domain may be a superset of the actual weld domain; the weld finder will determine which elements from it actually lie on the failure plane. Rotate LCS After Solve This flag indicates whether the nodal forces and moments along the weld line and through-thickness (if necessary) will be rotated into the local co-ordinate system before solution of the weld line system of equations, or the resultant line forces and moments will be rotated into the local co-ordinate system after system solution. By default, Verity will rotate the nodal forces and moments accumulated at the weld line and throughthickness nodes (if necessary) before the solution of the weld line system of equations and application of the weld end correction. In this case, only the local x and y line forces and moments will be computed during system solution and subjected to the weld end correction (if necessary). If the user specifies that the rotation be performed after the system solution, the global line forces and moments of all components will be computed from the accumulated global nodal forces during system solution. After the system solution and end correction (if necessary), the resultant line forces and moments will be rotated into the local co-ordinate system. In either case, only the computed line forces and moments in the local x and y directions are used to compute the normal and in-plane structural stresses. 24 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

27 Preparing FE Models for use with Verity Start Element or Node (for Symmetry Start) This option is used to resolve ambiguities in weld line sense when Weld Symmetry has been set to Start or End. In the case that weld symmetry is used, Verity needs to know which end to apply the symmetry setting to (see Weld Symmetry). This can only be used when the fillet group contains a single fillet, although there can be multiple (connected) lines induced by large angle changes (in excess of 45 degrees). Either of the surface lines or root line can be used, and the other lines will be automatically aligned in the same sense. Specify either the start element or node corresponding to the end of the weld line corresponding to the Start, for use in applying the Weld Symmetry setting. If the direction changes by more then 45 degrees between two nodes, then a new line is created, but the direction sense will be continued into connected split lines from the line containing the specified start item. However weld ends internal to a series of weld lines, induced by such splitting will always have symmetry on at the junction (and likewise if the end is embedded in the parent material). So for example if a weld line goes from nodes 1,2, 50 followed by a large angle change and a new line from nodes 51 to 100, then specifying Weld Symmetry as Start and start element 1, will result in symmetry on at nodes 1,50 and 51, but not 100. This is the same as specifying Weld Symmetry to End, and setting the Start Node to 100 instead. However note that in automatically determined throat failures this can result in swapping over the domain to the other side of the failure plane, as the choice of element parity depends on the line direction sense, and the lines will be reordered so that they start in the sense of the specified start item. The start item value is first interpreted as an element ID. If no such element exists, or if no line has an end at such an element, then the software tries to reinterpret it as a node ID. If no such node exists either, or it is not the start (or end) of a surface weld line, then an error occurs. If the line consists of a single element then the value must be a node. Note that if Weld Symmetry is Both or None, then there is no need to set this parameter. Structural Stress Plate Thickness This option is used to select what plate thickness is used in the Verity structural stress calculations. By default the determined domain geometry is used to calculate a node-by-node thickness which may vary along the weld line (Derived from Domain Geometry). This popup menu can be used to select the alternative From Configured Plate Thickness option, which will result in Verity using the value specified in the Plate Thickness option for every line node. This is mainly intended as a backwards compatability option with weld lines specified as per section Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 25

28 Preparing FE Models for use with Verity Throat Domain Group If throat failures are to be analysed then the throat domain may optionally be specified. For solid welds the default surface throat line(s) contains central nodes on the fillet surface which are equidistant from two paired surface weld lines (to within a small tolerance). The failure plane direction is from this line to the root line. There should be a sequence of element faces which are aligned with this, so mid-nodes cannot be used, and there should be an even number of elements across the fillet surface for the automatic method. Alternatively if the geometric centre of the fillet is not the desired failure plane, or there is an odd number of elements across the fillet, then the domain can be explicitly specified, and the failure plane will be the set of faces closest to the automatic central plane. Use the popup menu to select the group, if needed. For shell welds the analysis of the throat should occur at both sides of the fillet where the weld line interfaces with the parent material. Throat Failure Sense Solid Weld throat failures can be analysed from either the surface line to the root or vice versa, or in both senses. Use the popup menu to select the sense. The selection of this sense will determine which throat domain is identified (see Figure 3-6 below). The local Verity coordinate system (V x, V y, V z ) as discussed below in Throat Wrap Around Line Angle determines this domain because V z will be inverted, and V x must conform to a right-hand-rule. The default setting for this parameter is From Surface. See also Compact Contour Mode for display of root line results projected onto the surface if From Root or Both is used. Throat Wrap Around Line Angle This angle is used to determine what additional solid elements are included in the domain at the base of a throat failure of a solid weld. This is only used if automatic throat failure location is on and no explicit throat domain group was specified. The normal criteria for including elements in the domain is that they should be on the correct side of the failure plane, which in automatic mode means the side pointed to by the local Verity x-axis (V x ) in a right handed coordinate system where the Verity z-axis (V z ) is the through thickness direction, and the Verity y axis (V y ) is the local line direction. V z is the red vector on Figure 3-5 below, if the failure sense is from surface to root. However at the root nodes which lie on the fillet/parent plane interface, this rotation can be used to further rotate the local x-axis so it points into the root parent plate. Additional elements sharing the root node which also lie below the corresponding rotated plane are included in the weld domain. 26 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

29 Preparing FE Models for use with Verity Note that a negative angle will act to reduce the domain. The positive rotation sense will be selected by the software to be either clockwise or anti-clockwise depending on whether (V x,w) is a left or right handed system respectively, where w is the vector from root to surface (either the V z axis or its opposite depending on failure sense). A small tolerance is applied so that some element nodes can be marginally on the wrong side of the plane, as long as the element centre is on the correct side, and no node is incorrectly positioned by more than 5% of the element scale (mean distance from corners to centroid). Take for instance this example specimen. V z is the red vector on Figure 3-5 below: Figure 3-4 Figure 3-5 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 27

30 Preparing FE Models for use with Verity There are two potential weld throat domains on either side of the theoretical crack path that has been modelled from the middle of the weld throat to the weld root (the red arrow in Figure 3-5 above) where parent material 1 (blue) and parent material 2 (green) meet weld material (grey). Assuming partial penetration, there are no shared nodes between parent material 1 (blue) and parent material 2 (green). The possible domains are shown in side view: Figure 3-6 The weld domain on the left must contain two elements on the parent material 1, whilst the weld domain on the right can only contain one element in the parent material 2. This is because of connectivity in the model and shape/size of each element in the base material. Let s investigate this further: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

31 Preparing FE Models for use with Verity Note that while there is one shared (also referenced as common node or equivalenced) node between the three sets shown above at left, there are still four nodes on the plane between the two parent material groups whose nodes are not shared (unequivalenced nodes with no interaction). The plane containing the four nodes at right is a free surface inside the mesh, and should not be crossed by the weld domain. In order to maintain this convention, the weld domain in Figure 3-6 at right has an angle of -45 while the weld domain in Figure 3-6 at left has an angle of 45 about the weld line. Note that a positive sign always acts to increase the set of elements in the domain, and a negative sign always serves to reduce it, so positive means a rotation away from the domain side of the failure plane, whereas negative means a rotation towards the domain (thus further restricting it). fe-safe automatically calculates whether this requires a clockwise or anti-clockwise rotation, depending on whether (V x,w) is a left or right handed system respectively, where w is the vector from root to surface (either the V z axis or its opposite depending on failure sense). Because there is a small tolerance of 5% of element scale it is not necessary to be absolutely precise on the angle, but for positive rotations with some mesh irregularities, or weld line curvature, it may be better to use a value slightly larger than what is strictly required (e.g. +50 rather than +45) to be sure that the rotated axis fully includes all the required elements. Finally note that in the above example at right the rotation of -45 is not strictly necessary, as the failure plane bisects the next parent material blue element along its diagonal, and so this would not be included even with zero angle. However in a mesh including wedge elements or tetrahedral elements, where the blue element diagonal might form part of an element face, then the -45 rotation would be necessary to exclude them. Through Thickness Tolerance Cone This parameter applies to solid welds and is specified as a proportional displacement (default 0.05) which defines a cone around a weld line node, centred on the through thickness direction vector (normal to the local weld line tangent lying in the failure plane). If the height of the through thickness vector to the current node is h, then the tolerance cone is defined as a search through an angle theta (Θ) where theta is the inverse tangent of the height times the parameter value: Θ=arctan(0.05*h) in the case of the default. This is used to search for through nodes to include in the structural stress computations. Some tet meshes may require a parameter as high as 0.1 in curved sections of the weld line in order to include all the necessary nodes, but increasing this too high may result in spurious extra nodes being included from neighbouring elements, and more accurate results would be achieved by improving the regularity of the mesh. Note that this parameter is used for all solid weld mesh types, but typically tet meshes may need a larger value, as they tend to be less regular than hexahedral (brick) meshes. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 29

32 Preparing FE Models for use with Verity If nodes do not line up with the weld line normal, then virtual nodes will be inserted where the weld line normal passes within this cone tolerance of an element edge, and the forces will be interpolated between the nearest nodes on the edge. See also Failure Plane Co-planarity tolerance above. On curved sections for which high cone tolerances are required because element edges do not quite align with the local normal, one problem can be that additional unwanted through nodes can be acquired from neighbouring elements. Therefore a secondary pruning stage is applied, and where subsets of through nodes are found at a similar projected distance from the weld line (i.e. projected onto the normal), then only the one closest to the normal is retained. The proximity parameter used for grouping the set to be pruned nodes whose inter-node projected distance is below 25% of the median inter-node projected distance in the through node set for the line node. Toe Domain Group If toe failures are to be analysed then the toe domain may optionally be specified. The default toe failure plane is normal to the weld toe face (i.e. the parent material face adjacent to the weld line), and the domain parity selection is in the sense of above the top of the fillet, or right of the the bottom of the fillet (See also Figure 11-9 of Tutorial F below, or Figure 12-9 of Tutorial G below). The automatic search would continue along this plane until the model is traversed and a surface face is reached, or possibly the plate thickness is reached (see Domain Constraint above). Use this option to specify the domain explicitly, which must be done if the failure plane is significantly not normal to the parent material toe face. This also allows for variable domain thickness along the weld line, or for the element parity selection sense to be inverted (note this latter would result in the line results not being visible in the FE model results file without using a view cut or removing the obscuring fillet elements). Weld Symmetry Same as Weld Symmetry in below. Note that if Start or End is selected then it is necessary to specify a start element or node as discussed above in Start Element or Node (for Symmetry Start). Start or End is not available for fillet groups containing multiple sub-fillets, as the application of the start sense then becomes ambiguous. If weld symmetry is required then multiple solid weld definitions must be supplied, one per fillet (with separate fillet groups). Also note that any line end which is not on an open surface will automatically have symmetry on at the appropriate end regardless of the parameter setting. This also includes lines which end because of a large angle change, or if the end of the line is embedded in a parent material surface, or if the line is a closed loop. Symmetry on means that no weld end correction is applied there. 30 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

33 Preparing FE Models for use with Verity Wrap Around Angle This parameter is used to determine what additional elements are included in the domain at the end of the weld line and has a range of [-90,90] degrees, where the zero angle refers to the continuation of the weld line beyond its end (which at the start would be 180 degrees from the weld line direction). The rotation axis is about the through thickness direction vector, with positive sense towards the weld domain. On Toe failure modes, a zero value would include one element beyond the line end; -90 would curtail the domain by excluding this element; whereas +90 results in a wrap around of the domain as illustrated in Figure 3-8 below. An element is included if all of its nodes are on the domain side of the rotated line, or if the centre of the element is so located, and no node is more than 10% of the mean element edge length on the wrong side. Default value is 90 degrees, in line with Verity modelling guidelines. For hexahedral meshes it would be usual to set this to either 0, 90 or -90; but intermediate settings such as 45 degrees can result in partial wrap around in tet meshes. Note that 45 degrees would effectively be the same as 0 degrees in a typical hexahedral mesh, as at least one corner of the partially included element would still be outside. Figure Spot Weld Parameters A spot nugget may be modelled in two ways: as a beam (in Abaqus or Nastran); as an Abaqus (discrete or point-based) fastener where the weld saxial direction is represented by the z-axis of the element s local coordinate system. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 31

34 Preparing FE Models for use with Verity as a Nastran CWELD element where the weld s axial direction is represented by the x-axis of the element s local coordinate system. Note that Nastran CWELD elements defined as point-topoint or point-to-patch are supported for spot weld analysis in fe-safe, but patch-to-patch CWELD element types are not supported It is assumed that nuggets are represented exclusively by beams or fasteners. For a beam or point-based fastener the connection to each sheet must occur at a single node. For a discrete fastener the connection can occur anywhere on the sheet. For a beam the nodal forces are extracted from the associated shell elements. For a fastener the forces are extracted from the associated connector element. Irrespective of nugget representation structural stresses will be calculated for each sheet and each intermediate nugget segment. However, note that only sheet failure is considered during the fe-safe analysis phase as the equivalant structural stress calculations are only applicable to sheet failure. A weld tree item with the icon designates a spot weld definition. The icon can be added by clicking the Add button then selecting one of two spot weld definition options, namely Spot (Detect All Connecting Elements) and Spot (Detect Connecting Element Group). The purpose of Spot (Detect All Connecting Elements) is to allow the user to create a single weld definition for every spot weld in the associated model. This option assumes that the nugget element under consideration, i.e. a beam or fastener, is used exclusively as a nugget element in the FE model. After creating the definition (and after clicking the Save and analyse button): every spot weld nugget is detected; every spot weld sheet is detected; a single nugget diameter value is applied to every spot weld. These extracted values are then used to calculate structural stresses, per spot weld. Only one Spot (Detect All Connecting Elements) definition can be created by the user. The Spot (Detect Connecting Element Group) option creates a definition that instructs fe-safe to find and then process a group (or groups) of spot weld elements. Given a suitably defined group, i.e. a group of beams or fasteners; the resultant procedure ensures that: every spot weld sheet is detected; a single nugget diameter value is applied to every spot weld. The extracted values are then used to calculate structural stresses, per selected group of spot welds. Multiple Spot (Detect All Connecting Group) definitions can be created by the user. Irrespective of definition option the following parameters will be observed under the spot weld definition icon: 32 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

35 Preparing FE Models for use with Verity Connecting Elements Specifies the group of spot nugget elements to be assessed. For the Spot (Detect All Connecting Elements) option no group is required, i.e. every spot weld will be detected and then assessed, so the option is pre-set to All. For the Spot (Detect Connecting Element Group) option the user selects from a list of groups (as defined). Nugget Diameter The diameter of every spot weld nugget. Nugget Diameter Estimate A sheet-thickness dependent nugget diameter estimate that is implemented during the calculation phase (the results of which are displayed in a Verity output file). When this is turned-on the Nugget Diameter option is disabled. I(r) Function As described above Legacy Line Definition Parameters Element Type The FE mesh away from the weld line may be comprised of elements of any type. The elements in the weld element domain that contribute nodal forces to the nodes along the weld line and are used to derive the weld line connectivity must be of the same dimensionality. Editing the element type will display a dialog box allowing the selection of one of the valid element types. Figure 3-2 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 33

36 Preparing FE Models for use with Verity Shells This category refers to 3D mid-surface shell elements that have no through-thickness dimension. At this time 3D continuum shell elements that have an explicitly modelled through-thickness dimension are not supported. If the FE program allows, the user may model the surface of the shell element as being offset from the mid-surface and then specify this offset (see Specify Mid-Surface Offset). It is assumed that orientation of all shell elements along the weld line remains consistent. Solids This category refers to hexahedral (brick) and pentahedral (wedge) 3D solid elements. Tetrahedral elements require special handling and belong to a separate category. The only restrictions on solid mesh topology is that only rectangular element faces may lie upon the through-thickness cut from the weld line and that the mesh be regular on the through-thickness cut. By regular it is meant that corner nodes line up with corner nodes, midside nodes line up with midside nodes, and all nodes lie upon the through thickness direction which is normal to the weld line in the failure plane to the weld toe surface. With respect to the input required by shell meshes, solid meshes require only one more command: to specify the reference normal to the weld toe surface at the start node. Tetrahedrons Tetrahedral elements are 3D solids but because they are often generated by automatic meshers their through-thickness topology may not be regular. The possible irregularity requires special handling. Since through-thickness face nodes may lie anywhere on the through-thickness face, in order to determine the weld line connectivity all nodes lying on the through-thickness cut from the weld line, along the full length of the weld line, must be specified (see Specify Through-Thickness Face Nodes). The locations at which nodal forces are extracted on the through-thickness line is determined by specifying stations on the through-thickness line or by identifying intersections between the throughthickness line and element edges on the through-thickness face (see Through-Thickness Station Points). As with solid meshes, the reference normal at the start node must be specified. Although tetrahedral meshes that are irregular on the through-thickness face are allowed, testing has indicated that meaningful answers can only be obtained if the through-thickness mesh is regular. This is because nodal forces extrapolated to locations other than the nodes are no longer in equilibrium and because if forces from corner nodes and midside nodes are mixed then the equations for processing structural stresses from nodal forces are no longer valid. If tetrahedral elements are employed, the user is strongly encouraged to manage the mesh so that it is regular on the through-thickness face. Plate Thickness The plate thickness must be specified. The specified plate thickness is constant along the weld line and is in the same units as those selected for the FEA model distance units. 34 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

37 Preparing FE Models for use with Verity Weld line nodes This is a list of nodes defining the line of the weld. The nodes may be input in any order. In the tree the weld line is picked from a list of existing node groups. See section for how this is performed. The structural stresses will be calculated along the line of the weld. Weld reference elements This is a list of elements defining the weld line and identifying the elements on through thickness plane of the weld, (i.e., for a weld toe the section where the base metal joins the weld). An element domain at the toe is used for weld toe failure analyses and a similar weld element domain at the throat is used for weld throat failure analyses, etc. For shell elements, a single element defines the through thickness plane, but for solid and tetrahedral elements, the weld element domain must include all of the elements through the thickness, on the plane of the the through-thickness cut on which to analyse weld fatigue. All rows through the thickness are required for solids in order to calculate the moment at the weld line. If a weld line is open (i.e. not a closed circular weld), it is required that up to two additional elements from the Finite Element mesh at the end of the weld line be included in the domain (and all corresponding elements through the thickness as well), if they exist in the mesh. These two elements are not the Start Element (as the start element is on the weld line and contains two nodes in the node domain). The additional elements share a node with the start element (and at the other end of the weld line the end element) and contribute to the force balance at the start or end node. The requirement for weld element domain preparation on solid mesh topology is that only rectangular element faces may lie upon the through-thickness cut from the weld line and that the mesh is regular on the through-thickness cut. By regular it is meant that corner nodes line up with corner nodes, midside nodes line up with midside nodes, and all nodes lie upon the the through thickness direction which is normal to the weld line in the failure plane. Start Node and Element The start node must always be specified. The start node is the first node to be processed along a weld line. If the weld line is closed the choice of the start node is arbitrary; if the weld line is open then the start node must be one of the end nodes. The start element gets the process of automatic determination of the weld line connectivity going by indicating the initial positive direction along the weld line. To be the start element, the element must be connected to the start node, must share the weld toe surface, and must share an edge with the weld line. For 3D solid meshes it is possible to have an element that is connected to the start node but is not in the weld toe surface and/or does not share an edge with the weld line. For 3D shell meshes it is possible for an element to connect to the start node but not to share and edge with the weld line. All of these elements are not valid start elements. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 35

38 Preparing FE Models for use with Verity Shell layer Shell orientation can be configured for the weld line elements. The shell layer option is only required for meshes comprised of 3D shell elements. This specifies which face of the shell is to be considered for structural stress calculations: Top (default), Bottom or Both layers can be specified. It is assumed that orientation of all shell elements along the weld line remains consistent. If a node is included in the analysis of more than one weld, the result exported for the node is the worst-case result. Reference Normal The reference normal is only required for meshes comprised of 3D solids or tet elements. The reference normal is the normal to the weld toe surface at the start node, in the form of a vector. The weld line nodes define the toe of the weld and lie in the weld toe surface. The start node is the user-specified first node along the weld line. The weld toe surface is considered the top surface; the bottom surface is through-thickness. The reference normal should point outward from the weld toe surface, away from the through-thickness direction. If the mesh is comprised of shell elements, the normal to any element along the weld line is well defined (Note that the user is responsible for ensuring that the direction of the shell element normals around the weld line are consistent). All shell element faces by definition lie in the weld toe surface, with the top (toe) surface section being defined as the shell element section on top in the direction of the normal. The reference normal is required for 3D solids and tets because fe-safe has no way of knowing what is the weld toe surface that is, which faces of the elements connected to the weld line constitute the weld toe surface. By supplying the reference normal, fe-safe knows how to determine what is the weld toe surface face of connected elements. To get the reference normal, all the user has to do is create a line perpendicular to the weld toe surface and away from the through-thickness direction in the FE modeller- if the through-thickness direction is parallel to the normal direction then the nodes at the top and bottom surfaces will determine this line. The vector from point 1 to point 2 of this line defines the reference normal. The reference normal is updated automatically by fe-safe as the weld line comprised of 3D solids and tets is traversed; all the user has to supply is the reference normal at the start node to get the process started. Through thickness face nodes The face nodes on the through-thickness section along the entire length of a weld line comprised of 3D solid tetrahedral elements are specified. Through thickness face nodes need only be specified for meshes comprised of 3D solid tetrahedral elements, due to the possible irregularity of tet meshes through the thickness. In the tree the through thickness nodes are picked from a list of existing node groups. See section for how this is performed. 36 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

39 Preparing FE Models for use with Verity Weld type Is the weld open or closed? A closed weld is one that has no ends. Crack Length The default value of this parameter is set at crack length = plate thickness. This is based on the failure criterion of the first appearance of a through-thickness crack. The crack length at failure is used only when the virtual node weld end correction is being applied. The crack length is the parameter L1 in the derivation of the weld end correction. If the weld line is closed or if the symmetry flag has been set at both ends, the crack length is not needed. Failure Mode The weld line can have its associated failure mode specified (Toe, Fusion, Throat or Root), or this can be left at Unspecified. This selection does not affect the structural stress calculations but can affect the subsequent group processing during the fe-safe fatigue calculations, if different failure modes (e.g. Toe and Fusion) are specified for the same nodes. For example the same node can appear in two line specifications: one for a Toe failure and one for Fusion. If no Failure Mode is specified on the weld definition, then only one value will be stored for the node in the structural stress database, which will be the worst of the analysed modes. Later when the weld groups are analysed by the fe-safe fatigue calculation, the associated elements of the node will both have the same fatigue life, even though the intention might have been to have one element having the fusion result and the other having the toe result. In order to achieve individual mode-specific results, it is necessary to specify the failure mode. This will also result in the creation of separate analysis groups for each specified mode. Reference Length Same as this parameter in above. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 37

40 Preparing FE Models for use with Verity Through thickness node search co-planarity tolerance angle When searching into the solid domain for the through thickness nodes that are to be associated with each solid weld line node, the legacy fe-safe algorithm uses element edges for hexahedral or pentahedral elements; note tetrahedral meshes use a different approach to find through nodes aligned within a tolerance cone. At fe-safe 6.5 some additional checks were put in place to ensure that the element edges remain aligned with the weld line normal. It was possible for the original algorithm to deviate onto incorrectly aligned nodes under some circumstances. Firstly the element face containing the putative through node edge to be traversed must be approximately co-planar with the failure plane computed at the line node. This parameter specifies the tolerance threshold on this co-planarity in degrees. If the element face normal deviates by more than this (default 5 degrees) from the weld line normal to the failure plane, then the through node search will terminate (for that line node). If this happens then a warning message will be displayed at the end of the analysis. The diagnostic log will contain further information about the element(s) at which this happened. The weld will still be analysed, but this is likely to result in some inaccuracies as it probably means that some through nodes are missing. This may occur in weld lines with complex curvature. This tolerance parameter may be increased up to a maximum of 30 degrees. However a finer mesh may be a more accurate solution. Through thickness node validation cone tolerance Secondly (following on from the previous parameter), a final validation check is performed on all through nodes from solid hexahedral or pentahedral meshes, to confirm that all through nodes lie within a cone centred on the through thickness normal whose semi-angle is defined via this parameter. The parameter defines the tangent of the cone semi-angle (i.e. allowed deviation distance off the normal as a proportion of the projected distance of the through node from the line along the normal). This is for solid non-tetrahedral meshes similar to the Tet mesh through thickness connectivity parameter defined below, but it is used for final validation rather than location of the through nodes. If located through nodes fail this validation check then the weld line will not be processed and an error message will result. The default value is 0.1 (equivalent to 5.7 degrees). The tolerance parameter may need to be increased for weld lines with complex curvature, but a finer mesh may be a more accurate solution, as there is an implicit assumption in Verity that through nodes lie along the weld line normal. Note that this parameter is not used for tetrahedral meshes, because these have their own cone tolerance parameter which was used to locate their through nodes in the first place. Mid surface offset The offset from a shell element mid-surface to the surface on which the shell is modelled is set. The mid-surface offset is defined as a fraction of the plate thickness. A negative sign indicates that the offset is in the direction opposite to the element normal. For instance, if the shell element is modelled on the top surface of the plate, the offset is 0.5. If the shell element is modelled on the bottom surface of the plate, the offset is The mid-surface offset is used to modify the line moments along the weld line since the computed nodal forces are with respect to the modelled shell surface. 38 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

41 Preparing FE Models for use with Verity Weld symmetry Symmetry end conditions are specified for the weld line. The specification of symmetry has no effect on a closed weld line. If the weld line is open, the end for which symmetry conditions are specified is treated as closed and no virtual node weld end correction is applied. The start end is where the start node is located. The keyword Both causes symmetry conditions to be applied at both ends. If symmetry conditions are applied at both ends then no virtual node weld end correction is applied at either end and there is no need to specify the crack length at failure or the reference length. Through thickness station points The number of station points on a line through-thickness from the top surface to the bottom surface at which to interpolate nodal forces so that structural stresses may be computed from a mesh comprised of 3D solid tetrahedral elements. There are two algorithms used to identify through-thickness locations at which nodal forces are interpolated for meshes comprised of 3D tetrahedral elements: Station Points The user specifies the number of station points. At this number of equally spaced stations through the thickness from a weld line node, nodal forces will be interpolated from surrounding nodes. The interpolated nodal forces will be used to compute line forces and moments at the weld line node. If the through-thickness mesh is regular (see Element Type section above), then if the number of station points equals the number of elements through-thickness the stations will line up with actual nodes and no interpolation is necessary. Edge Intersections The user specifies zero station points. The default is zero, so omission of the station points command will lead to use of the edge intersection algorithm. For this algorithm, a line is extended throughthickness from the top surface to the bottom surface at a weld line node. Where this line intersects element edges, station points will be established to which nodal forces will be interpolated. As before, the interpolated nodal forces will be used to compute line forces and moments at the weld line node. If the through-thickness mesh is regular, the edge intersections will occur at actual nodes and no interpolation is necessary. Meaningful results can be computed from 3D solid meshes comprised of tetrahedral elements only if the through-thickness mesh is regular. As such it is most straightforward to use the station point algorithm by specifying the number of station points to be equal to the number of elements throughthickness. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 39

42 Preparing FE Models for use with Verity Rotate weld line co-ord system (deg.) The angle in degrees by which to rotate the automatically computed weld line local co-ordinate system about the weld line to arrive at the LCS for use in structural stress computations is specified. Specifying a rotation angle for the LCS only affects results for 3D shell elements and should be used to alter the angle of the through thickness plane. For all other elements types the through thickness plane is defined by the element domain. The positive x-axis of the LCS is perpendicular to the weld line, in the weld toe surface, and points into the weld element domain. The positive y-axis of the LCS points along the weld line and proceeds from the start node in the direction of the start element to the end of the weld line. The positive z-axis is the cross product of the x-axis with the y-axis. The positive z-axis can be reversed by reversing the direction in which the weld line is traversed (i.e., change the start element for closed weld lines or the start node and element for open weld lines). In the vast majority of cases, the direction of the cut through the thickness of the plate on which to base structural stress computations is parallel to the weld toe surface normal. As such, the normal is used to identify the weld toe surface and through-thickness faces along the weld line. The local z-axis is then also parallel with the normal, although it may point in the opposite direction. The algorithm to identify the weld line connectivity will work even if the normal and the through-thickness face are roughly parallel (see Tolerances section), although the structural stress computations will proceed on the basis that the two and the local z-axis are parallel. There may be cases where the desired through-thickness direction and the normal are so out of alignment that fe-safe fails to correctly identify the weld line connectivity or that the accuracy of the structural stress computations suffers. In these cases the user may specify an angle by which to rotate the automatically computed weld line local x-axis about the weld line (the local y-axis) so that the cross product produces a local z-axis that is parallel to the through-thickness face. This is the angle between the weld toe surface normal and the through-thickness line from the bottom surface to the top surface. During the determination of the weld line connectivity fe-safe will take this angle into account so that it will be able to correctly identify the through-thickness faces. The resulting structural stresses will then be relative to the angled through-thickness face, not the line through-thickness that is parallel to the weld toe surface normal. The specified plate thickness should be the angled distance from the top surface to the bottom surface. It is valid to specify a rotation angle for meshes comprised of 3D shell elements. Rotation into weld coord system Same as Rotate LCS After Solve in above. 40 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

43 Preparing FE Models for use with Verity Tet Mesh through thickness connectivity tolerance The tolerance for determining tet mesh through-thickness connectivity is used to evaluate when a through-thickness line intersects an element face edge or the location on a through-thickness face that coincides with a station point. The tolerance is given as a fraction of the plate thickness. The more refined the mesh, the less the required tolerance. The default tet mesh tolerance is For coarse meshes of, say, two quadratic elements through the thickness, it may be necessary to set the tet mesh tolerance as high as if there is significant curvature in the through-thickness face along the weld line. Since the only way to produce meaningful structural stresses from a tet mesh is to force the throughthickness mesh to be regular, either the station point or the edge intersection algorithm will produce stations through-thickness at which to extract nodal forces that coincide with nodes (thus eliminating the need for interpolation of nodal forces). It is thus fairly straightforward to examine the debug output file to determine that the appropriate through-thickness nodes are being found. If they are not being found, successively increase the tolerance slightly until all are being found. Number of smoothing iterations Same as this parameter in above. I(r) Function Same as this parameter in above Group selection and editing The group selection dialog box will be displayed whenever a parameter requiring an element or node group is edited. Note that the title depends upon which parameter is being edited: Figure 3-9 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 41

44 Preparing FE Models for use with Verity To pick one of the existing groups, either loaded from the source model or predefined earlier select it and click OK. The Import, Export..., New..., and Edit... buttons in the group selection dialog box are legacy methods for defining and editing groups of nodes or elements to be used in weld definitions. It is now recommended to use the group manager (FEA Fatigue >> Manage Groups... menu) for all operations related to element and node groups instead. See section 5 of the fe-safe User Guide for more details Model Units The units of the FE model are required for two purposes: 1. To evaluate the plate depth in mm this is used to convert the structural stresses to equivalent structural stresses. This is done as part of the Open Finite Element Model process, or in the Current FE Models window as described in section 5 of the fe-safe User guide. 2. To convert the stresses to SI units for use with the master weld S-N curves. This is done when the fatigue analysis is performed Drop down boxes provide a list of commonly used units, but any conversion factor may be applied Other Options Output Extensive Diagnostics Verity diagnostics will be saved to the verity-diagnostics.log file, at the end of the analysis process the user will be asked if they wish to view the debug log. If this checkbox is ticked additional diagnostics relating to the structural stress calculation will be requested. Note that selecting this option can generate a lot of additional data, and increase the overall analysis time Merge All Groups Into WELD Group This option allows to have multiple WELD groups in the Group Parameters control, so that each weld can have individual properties assigned: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

45 Preparing FE Models for use with Verity or to merge all welds into a single WELD group, as below: Figure 3-11 Note that in Line Welds (3.1.2) the WELD group is broken up into groups for different failure modes (e.g. WELD[Toe], WELD[Fusion]. If the node is associated with different element for different modes (e.g. fillet side for fusion, parent plate side for toe), then this sub-typing of the nodal structural stress data means that the separate failure mode results are preserved. If there are multiple results arising from the same node mapped to the same element (possibly after projection from the root to a surface line in compact contour mode), then all such WELD groups are analysed and the final result would then be the worst life arising from any group. 3.2 Diagnostics Structural Stresses Table The calculated structural stresses are exported to the verity-ss.txt file. A sample output (truncated) is shown below. Weld line: elems1_nodes1 Results File: Load case: Step: 1 Increment: 1 Time: Node WL Distance NSS Membrane NSS Bending NSS Total top NSS Total btm TSS Membrane TSS Bending TSS Total top TSS Total btm E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+05 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 43

46 Preparing FE Models for use with Verity Where: WL Distance - Distance along the weld line from the start node. For a closed weld the value of WL Distance for the start node is the total length of the weld line, rather than the distance along the weld line. NSS Membrane - Membrane structural stress normal to the through-thickness plane (σ m ) NSS Bending - Bending structural stress normal to the through-thickness plane (σ b ) NSS Total Top - Total structural stress at the top surface normal to the through-thickness plane (σ T(top) ) NSS Total Bottom - Total structural stress at the bottom surface normal to the through-thickness plane (σ T(bottom) ) TSS Membrane - Membrane shear stress on the through-thickness plane (τ m ) TSS Bending - Bending shear stress on the through-thickness plane (τ b ) TSS Total Top - Total shear stress at the top surface on the through-thickness plane (τ T(top) ) TSS Total Bottom - Total shear stress at the bottom surface on the through-thickness plane (τ T(bottom) ) through-thickness plane Weld S t S Figure 3-12 S structural stress normal to the through-thickness plane: s m b f t y' 6m t x' 2 S Shear stress on through-thickness plane: s m For a more detailed description please refer to Chapter 4.2. b f t x' 6m 2 t y' 44 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

47 Preparing FE Models for use with Verity Worst cycle mean stress and damage parameter contour For fe-safe analysis algorithms that base the fatigue calculation on extracting cycles, the most damaging cycle seen at a node can have its damage parameter exported. The meaning of this contour depends on the selected algorithm, and for Verity the exported contours are the equivalent structural stress (see 4.3.3) mean and amplitude, either the normal or shear form depending on the respective structural stress analysis algorithm (see 2.2). The export is selected via a checkbox (Worst cycle mean stress and damage parameter) on the Contours tab invoked via the Exports... button on the Fatigue from FEA dialog box, as in Figure 3-13 below. See also section 22.1 of the fe-safe user guide. Figure 3-13 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 45

48 Preparing FE Models for use with Verity Log for Items The equivalent structural stress cycles can be written to the log file for a list of specified items. Access to this control is from the Exports... button on the Fatigue from FEA dialog box. The ids defining the nodes to export must be defined on the List of Items tab to enable the export options controls. On the Log for Items tab there is a checkbox to Cycle-by-cycle life table for critical plane. If the ids specified relate to a node within the WELD group then equivalent structural stresses values for each cycle are exported to the log file. The log contains a table with a row for each cycle in each block giving the cycle minimum and maximum equivalent structural stress, the respective point indices of these within the load history, and the life which would be obtained just from that cycle. The format is per the example below: WORST PLANE CYCLE LIFE TABLE for Element e Block 1 (Maximum of 100 most damaging cycles shown, 1 is the first point) 0 degs nf (Repeats) Cycle Pt 1 Pt 2 MPa MPa 1.26e e e e Histories for Items The equivalent structural stress history for the top and bottom of the plate can be exported for a list of specified nodes. Access to this control is from the Exports... button on the Fatigue from FEA dialog box. The ids defining the nodes to export must be defined on the List of Items tab to enable the export options controls. On the Histories for Items tab there is a checkbox to export Load histories. If the ids specified relate to a node within the WELD group then equivalent structural stresses are exported. It should be noted that the ids will be element ids unless nodal averaged stresses are used then they will be nodal ids. You can check what the stresses in your model are by expanding a dataset in the Current FE Models window. 46 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

49 Preparing FE Models for use with Verity The tree item will indicate if the stresses are nodal or elemental: Figure 3-14 When the analysis is performed a history plot file will be created for each node. These are listed towards the bottom of the analysis.log file. These files can be opened using the File menu item Open Data File, and then plotted using one of the options on the View menu or toolbar. Figure 3-15 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 47

50 Preparing FE Models for use with Verity 3.3 Weld master S-N curves The Verity database contains the master S-N curves that are provided for Verity analyses. When defining these curves it should be noted that Stress Range versus Life (rather than Stress Amplitude) is required. The S-N curves can be plotted using the Generate Material Plot Data option on the Material menu. The option to plot Stress Range rather than Stress Amplitude is provided on this dialog box. The master S-N curves for steel and aluminium alloy weldments are based on systematic analysis of test data spanning many industries and many welded joint configurations. Where users have their own test data, it is recommended that they assess the validity of these master curves against their own test results. The database in fe-safe allows users to enter their own fatigue curves in addition to the master curves, should they wish to do so. 48 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

51 Preparing FE Models for use with Verity Note that from fe-safe 2017 the shear T-N curves are also specified in the same database, so each material contains an S-N curve for normal stress and a T-N curve for shear stress. If there is no shear test data available then the default is to assume a Von Mises response, which means that the shear stress will be scaled by and then the normal S-N curve is used. As Battelle have only provided shear curves for Steel Welds for Toe failures [2], the default scaling has been used for other standard Verity materials (aluminium alloys and root/throat failures). Note that earllier versions of fe-safe provided separate shear materials; the new approach is to provide one material with both S-N and T-N curves, and then use the curve appropriate to the selected algorithm. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 49

52 Preparing FE Models for use with Verity 50 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

53 Preparing FE Models for use with Verity 4 The VeritySSM Method The VeritySSM method is based on the mapping of the balanced nodal forces/moments along an arbitrary weld line (available from a typical Finite Element run) into the work-equivalent tractions (or line forces/moments). A complex stress state due to notch effects can then be represented in the form of a simple stress state in structural mechanics, in terms of through-thickness membrane and bending components at each nodal location. The resulting structural stress calculations are mesh-insensitive (assuming the overall geometry of a component is reasonably represented in the Finite Element model), regardless of element size, element type and integration order used. 4.1 Approaches to Evaluation of Welded Joints Stress concentration in welded joints (and notched structures) dominates the fatigue behaviour of welded structures. Traditional Finite Element methods are not capable of consistently capturing the stress concentration effects, due to their mesh-sensitivity at welds (resulting from notch stress singularity). In practice, use of an artificial and subjective radius generates large variability in results. Fatigue design and evaluation of welded joints are typically carried out by a weld classification approach in which a (theoretically infinite) family of parallel nominal stress based S-N curves are used (based upon joint types and loading modes). Extrapolation-based hot spot stress methods offer the potential to reduce the required number of the S-N curves, and these have become increasingly popular in offshore and marine applications. An example of hot spot stress based SCF using three extrapolation techniques shows the variability in results: Figure 4-1 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 51

54 Preparing FE Models for use with Verity One issue with using any extrapolation-based hot spot stress procedures is that the stress gradients are more localised in plate structures than in tubular structures. In Figure 4-2, the surface stresses normal to weld (indicated by arrows) are normalised by the respective nominal bending stresses. The surface stress gradients shown become increasingly localised as the joint type changes from tube-to-tube through tube-to-plate to plate-to-plate joints. As a result, extrapolations using 0.5t/1t, 0.5t/1.5t or nodal value at 0.5t yield a unity in SCF, i.e., the nominal stress. If the Finite Element mesh is not refined enough or not yet converged, extrapolated hot spot stresses tend to vary with the element sizes, types, joint types, and loading mode (as shown in Figure 4-1). Figure 4-2 In all global based stress analysis procedures for fatigue evaluation, the ultimate goal is to identify an appropriate global stress parameter which: a. can be calculated consistently with a minimum mesh-sensitivity (mesh sizes, element shapes, element types, etc.) at a fatigue prone location such as at weld toe; and b. is demonstrably capable of correlating different fatigue behaviours (such as S-N data) observed in various joint types, loading modes, plate thicknesses, etc. 52 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

55 Preparing FE Models for use with Verity Nominal stress definition (if applicable for some joint configurations) satisfies (a) since it can be calculated by simple mesh-insensitive formulae. It does not satisfy (b) since it cannot be used to correlate S-N data from various joint types and loading modes. This is why the IIW recommended the use of a very large family of (essentially parallel) S-N curves with respect to the nominal stress parameter: Figure 4-3 The fact that the IIW S-N curves are essentially parallel to one another suggests that a scaling parameter which correctly measures the stress concentration in various welded joint types and load modes should be able to collapse all the parallel S-N curves into a single master S-N curve. The VeritySSM method uses an effective global stress parameter to establish such a curve. 4.2 The Structural Stress Method The structural stress method is used to analyse stress concentration at a fatigue prone location such as a weld toe, as shown in (a) below: Figure 4-4 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 53

56 Preparing FE Models for use with Verity It was postulated that this can be represented by an equilibrium-equivalent simple stress state (b) and a self-equilibrium stress state (c). The former describes a stress state corresponding to an equivalent far field stress state in fracture mechanics context (or more simply, a generalised nominal stress state at the same location), while the latter can be estimated by introducing a characteristic depth t1 shown by the dashed lines in (c). For displacement-based Finite Element methods, the balanced nodal forces and moments within each element automatically satisfy the equilibrium conditions at every nodal position. Therefore, the equilibrium-equivalent structural stress state (in the form of membrane and bending) can be calculated by using the nodal forces/moments at a location of concern Shell/Plate Element Procedures In order to calculate the structural stresses in terms of membrane and bending components, line forces and moments must be properly formulated by introducing work-equivalent arguments. For an arbitrarily curved, closed weld line (i.e., one with two ends overlapping each other, such as a tubular joint), the nodal forces can be related to line forces along the weld as: ( l1 ln 1) F 1 3 F l 2 1 F Fn 1 ln 1 6 l1 6 ( l1 l2) 3 l l2 6 ( l2 l3) 3... ln2 6 n1 l l 3 f f f.. ) f n2 n1 n1 0 ( l l (1) The weld start node is the same as the weld end, i.e., F n = F 1 and f n = f 1, where f 1, f 2,, f n 1 are line forces along y. In the matrix on the left, l i (i =1, 2,, n 1) represents the element edge length from the i th element projected onto the weld toe line. The corresponding line moments can be calculated in an identical manner by replacing the balanced nodal forces F 1, F 2,, F n 1 in local y direction with balanced nodal moments M 1, M 2,, M n 1, with respect to x in Eq (1). 54 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

57 Preparing FE Models for use with Verity Note that the nodal force Fi in Eq. (1) represents the summation of the nodal forces at node i from the adjoining weld toe elements situated on the positive side of the y axis. Before Eq. (1) can be constructed, coordinate transformation for the nodal forces and nodal moments from the global x-y-z into the local x -y -z system must be performed, with x travelling along the weld line and y being perpendicular to the weld line. The linear system of equations described by Eq. (1) can be solved simultaneously to obtain line forces for all nodes along the line connecting all weld toe nodes. Substituting the corresponding nodal moments into Eq. (1), one obtains line moments in the same manner. Then, the structural stress shown in Figure 4-4 (b) at each node along the weld (such as weld toe) can be calculated as: f y' 6mx' s m b (2) 2 t t For parabolic plate or shell elements, Eq. (1) can be formulated in an identical fashion, as can in-plane shear Calculation Examples Tubular T-Joint A round robin study on fracture assessment collected detailed strain gauge measurements on a tubular T-joint (for deriving hot spot stress based stress concentration at the saddle positions shown). To demonstrate the effectiveness of the present structural stress procedures, four shell element models with drastically different element sizes near the tube-to-tube weld are shown, at approximately 0.25tx0.25t, 0.5tx0.5t, 1tx1t and 2tx2t: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 55

58 Preparing FE Models for use with Verity Note that the weld was not modelled at the tube-to-tube intersection to simplify mesh generation. The four shell models produced the following structural stresses along the weld toe on the chord side: Since the structural stresses along the weld possess the quarter symmetry, only the results for a quarter of the weld length measured from the saddle point are shown. The maximum structural stress concentration occurs at the saddle position. Within the angular span of 90 o along the 3D curved weld from saddle to crown positions, the 2tx2t mesh represents the weld line with only three nodal positions (or about two and half linear elements) as shown by the triangle symbols. Therefore, the difference in the structural stress calculations from the 2tx2t mesh is mainly due to geometric changes at the weld line (tube to tube intersection) resulting from the large linear element sizes used. However, the structural stress based SCF at the saddle position is still within about 5% of the fine mesh case (.25tx.25t). Excluding the 2tx2t mesh, the SCF variations in the other three models are all within 2% of each other. Plate To I-Beam Joint In these models, the box fillet weld was modelled as simple nodal connections between attachment plate edge and I beam. The weld line in this instance is considered as being open-ended. The virtual node method is automatically activated in constructing Eq. (1): 56 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

59 Preparing FE Models for use with Verity Four drastically different element sizes ranging from 0.5tx0.5t to 4tx4t are used in the mesh designs, resulting in the following structural stress distributions (normalised by the nominal bending stress) calculated along the weld toe on the attachment plate side: It can be seen that the variation in the structural stress calculated at the weld end positions is within about 1% for all four cases. The validity of the SCF was demonstrated using models with the fillet weld being properly represented by a row of inclined shell elements. Note that in all four models, the weld is not modelled for simplicity. As the element sizes change at the beam to attachment intersection, the geometric representation remains the same. 4.3 Master S-N Curve Formulation A stress-based scaling parameter to collapse the multiple S-N curves of Figure 4-3 can only be found if fracture mechanics principles apply, so that crack propagation dominates fatigue lives in welded joints. A large amount of S-N test data supports this Structural Stress Based K Estimation The simplest candidate fracture mechanics parameter which can be considered is the stress intensity factor K, but generalised K solutions are not available for welded joints. Fortunately, the structural stress definition of Figure 4-3 (b) is consistent with the far-field stress definition ( ) in fracture mechanics. Therefore, the structural stress calculation process can be viewed as a stress transformation process from an actual complex joint in a structure under arbitrary loading to a simple fracture specimen, in which the complex loading and geometry effects are captured in the form of membrane and bending: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 57

60 Preparing FE Models for use with Verity Figure 4-5 As a result, K for any crack size along the weld can be estimated by using the existing K solution for a simple plate fracture mechanics specimen subjected to both membrane tension and bending, by considering either an edge crack or a surface elliptical crack. Figure 4-6 shows the validation for considering an edge crack in a T fillet weld: Figure 4-6 The case corresponding to W/O notch stress was obtained by directly plugging the structural stress components (membrane and bending) calculated using the present structural stress method into the existing K solution for an edge notch specimen under remote tension and bending, respectively. The case W/ notch stress refers to the use of the self-equilibrating part of the stress state shown in Figure 4-4 (c) which is analytically estimated. 58 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

61 Preparing FE Models for use with Verity It can be seen that without considering the notch stress (or self-equilibrating part of the stress state), the current solution provides an accurate K estimation for crack size a/t larger than about 0.1. With the notch stress effects, K can be calculated for any given infinitesimally small a/t. The current solution in Figure 4-6 is higher for small a/t than the weight function solution from Glinka, since Glinka introduced a small weld toe radius in performing the Finite Element stress calculation to avoid mesh-sensitivity. In the present calculations, the weld toe radius was assumed to be zero, i.e., simulating a sharp notch at the weld toe A Two-Stage Growth Model The non-monotonic K behaviour as a function of a/t shown in Figure 4-6 is characteristic of all joint types investigated. As the crack size a/t becomes smaller than about a/t ~ 0.1, the elevated K is attributed to the dominance of the notch stresses at weld toe. It can then be postulated that both the short crack and long crack growth processes may be characterised by the two distinct stages of the K behaviour as a crack propagates from a/t < 0.1 to a/t > 0.1. Along this line, it can be argued that two stages of stress intensity solutions in the form of the notch-stress dominated K a/t<0.1 and far-field stress dominated K a/t<0.1 can be separated to characterise the full range crack growth behaviour from 0 < a/t < 0.1 ( small crack ) to 0.1 a/t 1 ( long crack ). Here, the term K refers to the stress intensity factor range corresponding to remote stress range. It then follows: da dn C f 1 ( K) a / t0.1 f2( K) a / t0.1 By introducing a stress intensity magnification factor Mkn in dimensionless form and assuming a powerlaw form of the two stage crack growths corresponding to f 1 (K) a/t 0.1 and f 2 (K) a/t>0.1, respectively, Eq. (3) can be re-written as: (3) da dn ) n m C( M kn ) ( K (4) n The terms M kn and K n are defined below: M kn K(with local notch effects) (5) t t K (based on through thickness m and b) n signifying the notch-induced magnification of the stress intensity factors as a/t approaches zero. n represents the constant crack growth exponent for the first stage of the crack growth and m represents the conventional Paris law exponent, both of which are to be determined by experimental crack growth rate data. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 59

62 Preparing FE Models for use with Verity The validation of the two-stage growth model is shown in Figure 4-7. The crack growth data were taken from well-known short crack growth data by Tanaka and Nakai and Shin and Smith. Without relying on any crack closure arguments, all the so called anomalous crack growth data in (a) are collapsed into single straight data band in (b), with a unified slope of m=3.6. Note that the first exponent in Eq. (4) was empirically determined as n=2. Figure Equivalent Structural Stress Parameter The two-stage crack (Eq. 4) with two stage growth exponents being n = 2 and m = 3.6 can be integrated as: N aa f da n m C ( M a kn ) ( K) 0 (6) An extensive investigation of M kn for various joint types showed that it can be approximated by a single curve as a function of a/t for all joint types once the denominator in Eq. (5) is formulated using the mesh-insensitive structural stress. 60 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

63 Preparing FE Models for use with Verity Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 61 Note that the integral in Eq. (6) is not very sensitive to the final crack size a f and can be written in a relative crack length form as: ) ( ) ( 1 ) ( ) ( ) / ( / 0 / r I t C K M C t a td N m s m t a t a m n kn i (7) where I(r) is a dimensionless function of bending r (r = b / s ) after performing the following integration for a given m: 1 / 0 / ) ( ) ( ) ( ) ( ) / ( ) ( t a t a m b m m n kn i t a f t a f r t a f M t a d r I Then, Eq. (7) can be expressed in terms of N once the dimensionless I(r) function is known: m m m m m s N r I t C ) ( (8) Eq. (8) uniquely describes a family of an infinite number of structural stress based S-N curves ( s N) as a function of thickness effects (t), and bending ratio effects r. If Eq. (8) provides a good representation of the fatigue behaviour of welded joints, an equivalent structural stress parameter can be defined by normalising the structural stress range s with the two variables expressed in terms of t and r on the right hand side of Eq. (8): m m m s s r I t S ) ( (9) where the thickness term t (2 m)/2m becomes unity for t =1 (unit thickness), so the thickness t can be interpreted as a ratio of actual thickness t to a unit thickness, rendering the term dimensionless. With this interpretation, the equivalent S s retains a stress unit. It is worth noting that the equivalent structural stress parameter described by Eq. (9) captures the stress concentration effects ( s ), thickness effects (t), and loading mode effects (r) on fatigue behaviour.

64 Preparing FE Models for use with Verity Initial Crack Size Effects Before Eq. (9) can be used to construct a single master S-N curve for welded joints, assumptions in performing the integration and the effects of M kn on I(r) must be quantified. It is well known that initial crack size (a i / t) can make a significant difference to the final life prediction based on fracture mechanics as described in Eqs. (6-8). Figure 4-8 shows the effects of a series of assumed initial crack sizes, using the edge crack based K solution. Note that I(r) is presented as I(r) 1/m after considering the exponent 1/m in Eq. (12) to facilitate the comparison between the two graphs. Without considering the local notch effects, i.e., M kn, different initial crack sizes a i / t produce significantly different I(r) 1/m curves as a function of r. Once M kn is considered, the dependency of the I(r) on initial crack size a i / t becomes insignificant, particularly for the two cases with small initial crack size (a i / t), as shown in Figure 4-8 (b). The increase in I(r) 1/m is about 8.5% as r increases from r = 0 (pure membrane) to r = 1 (pure bending) under load controlled conditions. This implies that with a strong notch effects in typical welded joints characterised by Mkn, the usual initial crack size effects on life predictions observed in typical fracture mechanics specimens without stress riser are significantly diminished in welded joints. Based on Figure 4-8 (b), a i / t = will be used in the rest of this chapter. Figure 4-8 Hong and Forte [2] showed that a similar approach can be used in shear dominated loadings, with some modifications. The parameter m is modified to. A different function is used: 62 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

65 Preparing FE Models for use with Verity And the bending ratio term r is replaced by its shear equivalent Furthermore the equivalent structural stress is scaled by. We then have an equivalent structural stress for shear dominated loading given by 3 s S 2m 1 2m m t I ( r) (10) 4.4 S-N Data Correlation The ultimate test for proving if the equivalent stress parameter (Eq. 9) is valid is to demonstrate if a large amount of experimental S-N data can be collapsed into a single narrow band. In doing so, a massive amount of S-N data (over 800 fatigue tests) from drastically different joint geometries, plate thicknesses, and loading modes were collected from literature and published reports, as highlighted below: Joint G (t=12.7mm) Joint Gb (t=20mm) Joint B(t=12.7mm), Joint B(Kihl)(6.35mm), Joint G (t=12.7mm) Joint Gb (t=20mm) Joint B(t=12.7mm), Joint B(Kihl)(6.35mm), 13/10/8AW(13mm), 50/50/16AW(50mm), 13/10/8AW(13mm), 50/50/16AW(DW)(50mm),100/50/16AW(100mm), 50/50/16AW(50mm), 50/50/16AW(DW)(50mm),100/50/16AW(100mm), 100/50/16AW(QT Steel)(100mm) 100/50/16AW(QT Steel)(100mm) Joint E (t=12.7mm) The Application of Fatigue Design Rules to Large t The Application of Fatigue Design Rules to t Large t t t t t Joint E: Mantaghi, S. and Maddox, S.J., 1993, The Application of Fatigue Design Rules to Large Welded Structures, Joint-Cb(Booth)(t=38mm), TWI. Joint C(t=12.7mm) t Joint-Cb(Booth)(t=38mm), Joint-Cb(Pook)(38mm) Joint D(t=12.7mm) TWI. Joint C(t=12.7mm) Joint-Cb(Pook)(38mm) Joint D(t=12.7mm) t Bell (t=16mm) t t t t t Joint D(t=12.7mm) : Mantaghi, S. t and Maddox, S.J., 1993, The Application of Fatigue Design Rules to Large Joint D: Mantaghi, S. and Maddox, S.J., t 1993, The Application Joint-Cb(Booth)(t=38mm), of Welded Fatigue Structures, Design Rules to Large t = Bell 5-80mm Bell: Bell, R., and Vosikovsky, O., 1993, Fatigue Life Welded Prediction Structures, of Welded Joints (t=16mm) Joint D: Joint-Cb(Pook)(38mm) Mantaghi, F (t=12.7mm), S. and Maddox, S.J., 1993, The Joint Application E (t=12.7 mm) for Offshore Structures under Various Amplitude Loading, t of Fatigue Design Rules to Large Joint E (t=12.7mm) Welded Joint F(Rorup)(12.5mm) Structures, t Bell (t=16mm) Journal of Offshore Mechanics and Arctic Engineering, Vol.115, pp CP1 (t=1.5mm) Joint F CP1 (t=12.7mm), (t=1.5mm) J o in t E : M a ag hi, S. an d M ad do x, S.J., , T h e Ap p lica tio n o f F a tig u e D esig n R u les to L a rg e Joint E (t=12.7mm) t Joint t Welded F(Rorup)(12.5mm) Stru ctures, t t Bell (t=16mm) t t t Bell (t=16mm) Joint E (t=12.7mm) t t Joint F: Mantaghi, S. and Maddox, S.J., 1993, The Application Bell: of Bell, Fatigue R., and Design Vosikovsky, Rules to Large O., 1993, Fatigue Joint E: Mantaghi, S. and Maddox, S.J., 1993, The Application t Double Life Edge Prediction Gusset (90mm) of Welded Joints Bell: Welded Bell, R., Structures, and Vosikovsky, LS1 of (t=1.5mm) Fatigue O., 1993, Design Fatigue Rules Life to Prediction Large of Welded Joints for Offshore Structures under Various CP 1: Zhang, Amplitude J., Dong, P.and Loading, Gao, Y., 2001, Evaluation of Stress Intensity Factor-Based Predictive Welded Structures, for Offshore Structures under Various Amplitude Loading, Joint J o int F (t= m m ), Joint F(Rorup): E: Mantaghi, Rorup, S. J., and and Maddox, Petershagen, S.J., 1993, H., The 2000, Application The Effect of Fatigue CP of 1: Compression Zhang, Design J., Rules Dong, P.and t to Mean Large Gao, Stress Y., 2001, Evaluation of Stress Bell: Intensity CP1 (t=1.5mm) Journal of Offshore Mechanics Joint F (Rorup and )(12.5 Arctic Double Bell, Technique Factor-Based m m ) Engineering, Edge R., and for Gusset Fatigue Predictive Vosikovsky, Life (90mm) of Resistance O., 1993, Spot Fatigue Welds, SAE Life paper Prediction , o f SAE Vol.115, pp Welded Joints t Journal LS1 (t=1.5mm) of Offshore Mechanics and Arctic Engineering, Vol.115, pp Technique for Fatigue Life of Resistance Spot Welds, SAE paper , SAE on the Welded fatigue Structures, Strength of Welded Structures, Welding in the World, Vol., 44(5), pp for Offshore Structures t under Various Amplitude Loading, J o in t F : M a nta g hi, S. a n d M a d do x, S.J., , T h e Ap p lica tio n o f F a tig u e D e sig n R u les to L ajournal rg e of Offshore Mechanics and Arctic Engineering, Vol.115, pp CP1 (t=1.5mm) W eld ed S tru ctu res, J o in t F (R o r u p ): R o ru p, J., a n d P et ers h ag en, H., , T he E ff ect o f C o m pre ssio n M e an Stre ss t Double Gussets (t=90mm, crack=2mm) t on the fatigu e Strength of W elded Structures, t Welding in the World, V o l., 4 4 (5 ), pp t Double Gussets (t=90mm, crack=2mm) LS 1: Zhang, J., Dong, P. and Gao, Y., 2001, Evaluation of Stress Intensity Factor-Based Predictive Technique for Fatigue Life of Resistance Spot Welds, SAE paper , SAE t LS1 (t=1.5mm) t Double Gussets(Niemi): Wagner, M., 1998, Fatigue Strength of Structural Members Double Gussets(Niemi): Wagner, M., 1998, Fatigue Strength of Structural with In-Plane Members Notches, IIW Doc. XIII , IIW. with In-Plane Notches, IIW Doc. XIII , t IIW. Fig. 2: Type b) Crack Scenarios at Welds LS1 on Plate (t=1.5mm) Edges Joint F (t=12.7mm), CP 1: Joint Zhang, F J., (t=12.7mm), Dong, P.and Gao, Y., 2001, Evaluation of Stress Intensity Factor-Based Predictive t LS1 (t=1.5mm) t LS 1: Zhang, J., Dong, P. and Gao, Y., 2001, Joint F(Rorup)(12.5mm) t Evaluation of Stress Intensity Factor-Based Predictive Joint F(Rorup)(12.5mm) Technique for Fatigue Life of Resistance Spot Welds, SAE paper Technique , for Fatigue SAE Life of Resistance Spot Welds, SAE paper , SAE Figure 4-9 Joint F: Mantaghi, S. and Maddox, S.J., 1993, The Application of Fatigue Design Rules to Large Joint F: Mantaghi, S. and Maddox, S.J., 1993, The Application of Fatigue Design Rules to Large LS 1: Zhang, J., Dong, P. and Gao, Y., 2001, Evaluation LS 1: Zhang, of J., Stress Dong, P. Intensity and Gao, Factor-Based Y., 2001, Evaluation Predictive of Stress Intensity Factor-Based Predictive Welded Structures, Welded Structures, Technique for Fatigue t Life Double of Resistance Gussets (t=90mm, Spot Technique crack=2mm) Welds, SAE for Fatigue paper Life , of Resistance Spot SAEWelds, SAE paper , SAE Joint F(Rorup): Rorup, J., and Petershagen, H., 2000, The Effect of Compression Mean Stress Joint F(Rorup): Rorup, J., and Petershagen, H., 2000, The on the fatigue Effect Strength of Compression of Welded Structures, Mean Stress Welding in the World, Vol., 44(5), pp on the fatigue Strength of Welded Structures, Welding in the World, Vol., 44(5), pp Double Gussets(Niemi): Wagner, M., 1998, Fatigue Strength of Structural Members with In-Plane Notches, IIW Doc. XIII , IIW. For each set of specimens and fatigue tests, the structural stress calculations were performed under Fig. 3: Corner Joints Tested by Yagi (1992) given loading conditions and failure criteria. The results are summarised in Figure 4-10 in terms of both nominal stress range and equivalent structural stress range as given in Eq. (9). A wide scatter can be seen in (a), which is expected. Once the equivalent structural stress range is used according to Eq. (9), the all the S-N data are collapsed into a narrower band, regardless of the diverse joint types, plate thicknesses, and load modes under which the fatigue tests were conducted over about 40 years. The same methodology has been proven with the same effectiveness in correlating tubular and pipe/vessel joints. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 63

66 Preparing FE Models for use with Verity Figure 4-10 By regression analysis, the mean line of (b) can be represented in the form of: t 1 s m' CN m 1 2m m I( r) N (11) with the stress unit in MPa and thickness in mm and m = 3.6. In Eq. (11), 1/m' represents the negative slope of the master S-N curve in (b). Note that although in various publications, m = m' (=3 for steel welds) is often assumed. In this investigation, it is found that they are close, but not necessarily the same. For simple fatigue test specimens, nominal stresses are often well-defined, then, SCF s ss S n in which SCF ss signifies the structural stress based SCF and S n the typical nominal stress range definition. 64 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

67 Preparing FE Models for use with Verity For a given simple joint specimen of interest, the structural stress based SCF can be calculated using the present structural stress procedure. Then the nominal stress based S-N behaviour can be predicted by using the master S-N curve from Eq. (11) as: 2m m m t I( r) m' Sn C N (12) SCFss Both C and m' are given in Eq. (11) based on the master S-N database generated in this investigation. Two examples are given: Figure 4-11 The mean nominal stress S-N curves for various plate thicknesses are predicted using Eq. (12) for the cruciform joint tests (under remote tension loading) by Maddox. A good correlation between the test data and those predicted by the master S-N (Eq. 11) curve is evident. Hong and Forte [2] showed that a similar master S-N curve can be derived for shear dominated loadings using Eq. (10) for the shear equivalent structural stress, but the slope is modified to. Further details are given in [2]. The mean shear-dominant S-N curve is: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 65

68 Preparing FE Models for use with Verity 4.5 A Simple Example of the Structural Stress Method As widely documented in many text books on basic Finite Element theory, displacement based Finite Element methods (commonly used in industrial day to day applications) tend to over-estimate the stiffness of a structure. An adequate mesh refinement is always required in order to achieve a converged solution of the displacement field predicted by the structural mechanics theory. This becomes particularly important when dealing with bending due to the potential presence of shear locking, for example discussed by Cook et al. To demonstrate how the equilibrium-based structural stress procedure discussed above can be applied to a simple problem on which a hand calculation using the above equation can be carried out, a cantilever bending example was directly taken out from an elementary Finite Element text book by Cook et al, as shown: Figure 4-12 Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

69 Preparing FE Models for use with Verity Two linear plane stress elements were used to model the simple beam, as shown. Such a model is deemed too coarse to provide any meaningful stress results in the Finite Element calculations. Indeed, as shown in Figure 4-15, the stresses calculated at the mid-length of the beam (Section A-A) are ±117.6MPa from the element on the right, in contrast to the beam theory solution of 750MPa. If averaged stresses between the two elements (from both right and left sides of A-A section) at the nodal positions were used, the calculated stresses become 235.3MPa. Due to its equilibrium considerations, the structural stress procedure using nodal forces should provide improved estimate of the stresses. The nodal forces from the Finite Element calculations are also shown. By applying Eq. (2), after substituting the nodal forces in x-direction, the line forces at Node 2 (at beam bottom) and Node 5 (at beam top) becomes, respectively: f f (2Fx2 Fx5 ) l 2 [2 250 ( 250)] 750N/mm 2 2 (2Fx5 Fx2 ) l 2 [2 ( 250) 250] 750N/mm 2 (12) Note that the beam thickness (t) is 1mm, the structural stresses are solely determined by the membrane component, for example, at Node 2 (bottom): 750N/mm s m 750MPa (13) 1mm The structural stress procedure for this case provides exactly the same solution as the beam theory. This is expected since the beam is under statically determined loading conditions. The equilibrium arguments underlying the structural stress procedure require that the structural stress so calculated should satisfy the equilibrium conditions. It should be cautioned that this example is only intended to illustrate the basic concept of the structural stress method and does not imply that the method can be used without limitation. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 67

70 Preparing FE Models for use with Verity 68 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

71 Preparing FE Models for use with Verity 5 Preparing FE Models for use with Verity 5.1 Supported FE Programs For line weld assessment the following Finite Element programs are supported by Verity in fe-safe: Abaqus Nastran I-DEAS Ansys For spot weld assessment only Abaqus and Nastran packages are supported. Irrespective of the type of weld under consideration Verity in fe-safe requires element nodal forces and the model geometry. The FE results must include the element nodal forces for each element that contributes to the nodal forces acting along each defined weld, saved in the global coordinate system. The elements comprising a weld definition can be 3D shells or 3D solids. 3D beam and 1D solid elements are also recognised, to allow their use in the FE model without generating error messages when the weld connectivity is processed. Supported Finite Elements types are listed for each FE program below, with the appropriate element identifier and a brief description of the formulation. Unsupported element types will be ignored a warning message will be issued stating that for correct results the element must not be used in any weld line definition. Where element thickness has been read, the Current FE Models Assembly item will have a sub-item labelled Element Thickness. If this is not present for a shell model the Plate Thickness parameter must be set, see Numbering Schemes Node numbering around each of the supported elements can be found in the relevant FE program documentation. Based on this node numbering, an edge, face, and face edge numbering scheme is established that is used in the algorithms to identify the weld line connectivity. Numbering scheme tables are included below for each FE program. In each table the node positions are the positions in the node numbering array, also known as the element incidences. Each table is arranged in terms of the element shape. The element shape encompasses both linear and quadratic element orders, so that the specified midside nodal positions are only relevant for quadratic elements. For the face numbering schemes, the nodal positions are arranged such that the normal to the face is outward from the element. The first midside node position occurs between the first and second corner node positions, the second midside node between the second and third corner nodes, etc., until the last midside node occurs between the last and first corner nodes. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 69

72 Preparing FE Models for use with Verity For the edge connectivity and face edge connectivity, the positive edge direction points in the direction from the first corner node to the second corner node. In the debug output concerning the weld line node connectivity, edges or face edges and faces are identified by numbers that correspond to the tables. If the edge has a negative number, it means that the direction pointing from a weld line node to the next weld line node is in the negative edge direction. The element face on the weld toe surface for 3D shell elements is always 1 by default since there is only one face Abaqus Supported versions: File type: 6.10 and above. Sequential access FIL file (extension.fil). Output database ODB file (extension.odb) Output method: Element nodal forces are output using the NFORC option in the *EL FILE or *ELEMENT OUTPUT commands Reading of element thickness in ODB models is supported. More fe-safe details: fe-safe Documentation, Appendix G. 3D shell connectivity: Element Shape quadrilateral triangle Edge Node Positions Edge 1 st corner 2 nd corner midside Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

73 Preparing FE Models for use with Verity 3D solid face connectivity: Element Shape brick wedge tetrahedron Face Node Positions Face corner midside 1 st 2 nd 3 rd 4 th 1 st 2 nd 3 rd 4 th Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 71

74 Preparing FE Models for use with Verity 3D solid face edge connectivity: Face Edge Node Positions Element Shape Face Face Edge 1 st corner 2 nd corner midside brick wedge Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

75 Preparing FE Models for use with Verity Face Edge Node Positions Element Shape Face Face Edge 1 st corner 2 nd corner midside Element Shape Face Face Edge Face Edge Node Positions tetrahedron Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 73

76 Preparing FE Models for use with Verity Supported elements: Element Type Element Name 1 Brief Description 2 3D Shells 3D Solids 3D Beams S4 S4R S8R S3 = S3R C3D4(H) C3D6(H) C3D8(H,I,IH) C3D8R(H) C3D10(H,M,MH) C3D15(H) C3D20(H) C3D20R(H) B31(H) B31OS(H) B32(H) B32OS(H) B33(H),B34 PIPE31(H) PIPE32(H) 4-node linear general-purpose full quadrilateral 4-node linear general-purpose reduced quadrilateral 8-node quadratic thick reduced quadrilateral 3-node linear general-purpose reduced triangle 4-node linear reduced tetrahedron 6-node linear reduced wedge 8-node linear full brick 8-node linear reduced brick 10-node quadratic reduced tetrahedron 15-node quadratic reduced wedge 20-node quadratic full brick 20-node quadratic reduced brick 2-node linear reduced 2-node linear reduced warped 3-node quadratic reduced 3-node quadratic reduced warped 2-node cubic full 2-node linear reduced pipe 3-node quadratic reduced pipe 1 ( ) denotes optional extensions: (I)=incompatible modes, (H)=hybrid w/ pressure, (M)=modified 2 See Abaqus documentation for a more complete element description. Note: Elements using five degrees of freedom (S4R5, STRI65, S8R5, S9R5) are not supported as for those elements moments corresponding to the in-surface rotations are not available for output. 74 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

77 Preparing FE Models for use with Verity Nastran Supported versions: File type: Output method: 70.7 and above. Sequential access OP2 (OUTPUT2) file (extension.op2). Element nodal forces are output using the GPFORCE command. The OP2 file is requested by issuing the bulk data commands PARAM,POST,-1 or PARAM,POST,-2. No other values of POST are supported. For POST equal to 1 or 2, the bulk data command PARAM,POSTEXT,YES must be issued as well in order for datablocks required to be written to the database. Note that the geometry must be included in the file, that is PARAM,OGEOM,NO command must not be used. If the NASTRAN bulk data parameter POST is assigned the value 1, then a labelled results database with an.op2 extension will be written. If POST is assigned the value 2 then an unlabeled results database with a.op2 extension will be written. If the NASTRAN-level parameter OP2NEW is set to YES and POST is set to 1 or 2, then the datablocks will be written in post-2001 format. If OP2NEW is instead set to NO with POST equal to 1 or 2, then the datablocks will be written in pre-2001 format. The NASTRAN default for OP2NEW is NO. Reading of element thickness in OP2 models is supported. More fe-safe details: fe-safe Documentation, Appendix G. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 75

78 Preparing FE Models for use with Verity 3D shell and See Abaqus table. connectivity: 3D solid face connectivity: Element Shape brick wedge tetrahedron Face Node Positions Face corner midside 1 st 2 nd 3 rd 4 th 1 st 2 nd 3 rd 4 th Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

79 Preparing FE Models for use with Verity 3D solid face edge connectivity: Face Edge Node Positions Element Shape Face Face Edge 1 st corner 2 nd corner midside brick wedge Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 77

80 Preparing FE Models for use with Verity Face Edge Node Positions Element Shape Face Face Edge 1 st corner 2 nd corner midside tetrahedron Supported elements: Element Type Element Name Brief Description 3D Shells 3D Solids 3D Beams 1D Solids CQUAD4, CQUADR CQUAD8, CQUAD4, CQUAD4FD, CQUAD9FD, CQUADX, CQDX4FD, CQDX9FD CTRIAR, CTRIX3FD CTRIA6, CTRIA6FD, CTRIA3FD, CTRIAX, CTRIAX6, CTRIAX6FD CHEXP CHEXA, CHEXA20F, CHEXAFD, CHEXAL, CHEXPR CPENP CPENTA, CPENPR, CPENT15F, CPENT6FD CTETP CTETRA, CTETPR, CTETR10F, CTETR4FD CBAR CBEAM CROD 4-node linear quadrilateral (3D shell) 8-node quadratic quadrilateral (3D shell) 3-node linear triangle (3D shell) 6-node quadratic triangle (3D shell) 8-node linear brick 20-node quadratic brick 6-node linear wedge 15-node quadratic wedge 4-node linear tetrahedron 10-node quadratic tetrahedron 2-node linear beam or solid 2-node linear warped beam 3-node quadratic beam or solid 78 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

81 Preparing FE Models for use with Verity Note: CTRIA3 elements do not support stress output to element-nodes, only to centroids, which causes a data mismatch if such elements were to be used for Verity analysis nodal force data is stored at nodes and stress data is stored at the centroid. As this may cause the results of fatigue analysis to be incorrect and dependant on the element orientation along the weld line the CTRIA3 element type is not supported for Verity analysis; it is recommended to use the CTRIAR elements instead. Note: It is not recommended to use a mix of element types (e.g. CQUADR and CQUAD4) along the weld line I-DEAS Supported versions: Tested with NX series version 11. File type: Output method: Sequential access UNV (universal) file (extension.unv). Element nodal forces are output using the ELEMENT FORCE option. More fe-safe details: fe-safe Documentation, Appendix G. 3D shell and connectivity: 3D solid face connectivity: 3D solid face edge connectivity: See Abaqus table and the note on node numbering below. See Abaqus table and the note on node numbering below. See Abaqus table and the note on node numbering below. Node numbering in the UNV file is in an inconvenient form for processing since the corner nodes are not given first for higher order elements. As a consequence, the program modifies the I-DEAS node numbering to match that of Abaqus: Element Type I-DEAS Element Incidence in Abaqus order 6-node triangle node quad node tet node wedge node brick Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 79

82 Preparing FE Models for use with Verity Supported elements: Element Type Descriptor ID Brief Description 3D Shells 3D Solids 94 4-node linear quadrilateral 95 8-node quadratic quadrilateral 91 3-node linear triangle 92 6-node quadratic triangle node linear brick node quadratic brick node linear wedge node quadratic wedge node linear tetrahedron node quadratic tetrahedron 80 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

83 Preparing FE Models for use with Verity Ansys Supported versions: File type: Output method: 5.7 through 13.x. Direct access RST file (extension.rst). Element nodal forces are output using the command OUTRES,NLOAD. Reading of element thickness in RST models is supported. More fe-safe details: fe-safe Documentation, Appendix G. 3D shell See Abaqus table. connectivity: 3D solid face connectivity: 3D solid face edge connectivity: See Abaqus table. See Abaqus table. Supported elements: Element Type Element Number Brief Description 3D Shells 3D Solids 28, 41, 43, 57, 63, 143, node linear quadrilateral 91, 93, 99, node quadratic quadrilateral 5, 45, 46, 62, 64, 65, 69, 70, 73, 96, 97, 122, 164, node linear brick 90, 95, 117, 128, 147, 186, 191, 226, node quadratic brick 87, 92, 98, 123, 127, 148, 168, 187, 227, node quadratic tetrahedron 1 triangle if linear element degenerated to 3 nodes or quadratic degenerated to 6 nodes 2 tetrahedron if linear element degenerated to 4 nodes or quadratic element degenerated to 10 nodes, wedge if linear element degenerated to 6 nodes or quadratic element degenerated to 15 nodes 3 See Ansys manual for a more complete element description Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 81

84 Preparing FE Models for use with Verity 5.2 Modelling Considerations And Applications The structural stress calculation procedure is based on equilibrium considerations, using nodal forces and moments in shell and plate element models. Therefore, a reasonable representation of the overall load path to a joint and joint stiffness is all that is required in modelling a structure. As a result, the modelling requirements for the presence of welds can be significantly relaxed from those in typical stress-based Finite Element computations. Some detailed parametric analyses are presented below to illustrate how typical joint types can be effectively modelled, and where special care is required when using Verity Full Penetration Welds A full penetration fillet weld in a plate T-fillet joint can be modelled using an inclined weld element forming a triangle with the two base plates: Figure 5-1 In this type of joint configuration with full penetration, weld toe failure into the base plate is often the dominant fatigue failure mode (as shown). The weld element thickness t w = l/ 2 has been used for all reported results cited here, where l is the fillet weld leg length. Due to the rigidity of the triangle formation, the structural stresses calculated for weld toe cracking are not sensitive to variations in assumed weld element thickness. 82 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

85 Preparing FE Models for use with Verity A 3D T-joint example was employed: Figure 5-2 A solid element model (a) was used to establish the reference structural stress. A series of plate element models (b) with various weld element thickness assumptions were used to compare the structural stress calculations at the same weld toe location as that in the solid model. The results are summarised in (c). The structural stress for the case with t w = l 2 (overall weld throat depth) was slightly over-estimated, comparing the results from the solid model in which the weld size and shape was accurately represented. The over-estimation is primarily due to the asymmetrically increased stiffness as the weld element thickness was increased. If the vertical element in the triangle formation is proportionally increased, the increase in the structural stress results becomes much less noticeable Partial Penetration Weld and Root Failures The same fillet-welded T-joint can be used to illustrate the applications of the structural stress procedures in partial penetration welds: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 83

86 Preparing FE Models for use with Verity Figure 5-3 Weld representation in a plate element model and various possible failure modes in T-fillet weld with partial penetration In addition to the weld toe failure modes (Toe 1 and Toe 2) in (a), a weld failure originating from the weld root can be approximately modelled using a plate element model as shown in (b). In reality, three weld throat failure modes through the weld metal are possible, indicated by (1)-(3) in (b). In addition, failure path (4) corresponds to a crack originating from the weld root and propagating through the base plate. The structural stresses relevant to the four weld root failure paths can be approximated as normal stresses to the respective arrow lines (1) through (4), as shown in (c) with respect to the plate element representation of the partial penetration weld. For failure mode (2), two weld elements are needed so that the nodal forces from the middle node can be used as weld line nodes (c). This was not considered in the current investigation, since the corresponding structural stresses can be approximated by taking the algebraic sum of those corresponding to failure paths (1) and (3). 84 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

87 Preparing FE Models for use with Verity A parametric analysis on the effects of fillet weld leg size on structural stress behaviour for the same fillet-welded T-joint discussed earlier, but with partial penetration this time, is shown below: Figure 5-4 Parametric analysis of structural stress as a function of weld size and failure mode (reference SS values are calculated using solid model at l =1t) The structural stresses with respect to various potential failure modes are summarised in (b) as a function of the fillet weld throat size t w in terms of the fillet weld leg length l. In this parametric investigation, the structural stress corresponding to weld throat failure mode (2) was also calculated using a solid element model for verification purposes at l=t, represented as Throat (2) Ref in (b). With the same solid model, the reference structural stress values for failure modes Toe 2 Ref and Throat (4) Ref were calculated for comparison with the plate element model results for l=t. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 85

88 Preparing FE Models for use with Verity As shown in (b), if the fillet weld leg length is small, the structural stresses corresponding to the two weld throat failure modes (1) and (3) dominate the fatigue behaviour, since the structural stresses corresponding to the two weld toe failure modes ( Toe 1 and Toe 2 ) are relatively low. As the weld leg length increases up to about l=t, there is a rapid reduction in the magnitude of the structural stresses characterising weld throat failures through the weld metal. Both weld root failure mode (4) into the plate and weld toe failure modes become dominant. Note that for weld root failure mode (4), as the weld leg length increases, the failure position with respect to the horizontal plate also changes due to the limitations of this particular Finite Element model. Therefore, the failure mode modelled in the plate element model no long represents failure mode (4) in (b). With l=t, a good agreement between the structural stress results from both plate element model and solid element models can be seen for failure mode Toe 2 and Throat (4) in (b). For failure mode Throat (2), the structural stress calculated from the solid element model takes an average of those corresponding to Throat (1) and Throat (3) calculated from plate element models. Consequently, the results suggest that the simple weld representation scheme shown in (c) for partial penetration welds is adequate to capture some of the major weld throat failure modes. The procedures discussed above for partial penetration welds can be used to determine a minimum weld leg size beyond which weld throat failure modes can be effectively suppressed. From Figure 5-4, it can be inferred that the minimum leg size should be at least l=t for this T-joint. Such an observation can be related to practical experiences with weld toe failures in partial penetration welds. This also highlights the potential variability in predicting weld throat failures in partial penetration welds, since any stress analysis procedure requires a precise weld throat depth (i.e., weld element thickness t w ) known before hand. In practice, the weld throat depth can vary significantly even within the same weld. 86 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

89 Preparing FE Models for use with Verity A more complex example is shown below for a tube-to-tube joint with partial penetration fillet welds with a leg size of about 2t: Figure 5-5 The dominant failure mode is weld toe failure into the horizontal tube (or chord) wall under the given inplane bending conditions. Two possible weld representation schemes were examined (b). Under a fixed t w = 3mm, Figure 5-6a shows the structural stress results as a function of the vertical element thickness in the triangle representation of the fillet weld. For t r =0, a gap is assumed as shown in Figure 5-5b. By varying both t w and t r (see Figure 5-6b for details), the difference in the structural stress calculations is not noticeable. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 87

90 Preparing FE Models for use with Verity In view of these parametric investigations, for weld toe failure the weld representation for partial penetration welds can use either a triangle formation or single inclined weld element shown in Figure 5-5b. The weld element thickness t w can be simply calculated based on nominal weld leg size. Any additional variations have no significant effects on the structural stress calculations. However, it must be noted that when using the triangle formation in Figure 5-5b, the ability to calculate the structural stresses with respect to the weld element (t r ) for characterising weld throat failures is lost, unless t r is made negligible (such as t r 0.1t). If weld throat cracking is of interest, the weld should be represented as a row of inclined weld elements with element thickness t w being a nominal or a minimum weld throat depth specified as a weld, which can vary significantly in practice. For this reason, the S-N data representing weld throat failures typically exhibit a much wider scatter than those representing weld toe failures. Figure 5-6 structural stress results using two weld presentation schemes for partial penetration weld and various weld element thickness definition (see Figure 5-5b), assuming weld toe cracking into the chord tube wall. 88 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

91 Preparing FE Models for use with Verity Lap Fillet Weld and Failure Modes Non-Load Carrying Lap Fillet Weld A cover plate fillet weld specimen is shown below with two weld presentation schemes. For weld toe failure into the base plate, the two schemes yield the same structural stress based SCF, supporting the findings discussed earlier. In such non-load carrying lap fillet weld, weld throat cracking is unlikely. Figure 5-7 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 89

92 Preparing FE Models for use with Verity Load Carrying Lap Fillet Weld Load-carrying lap fillets are used frequently in many automotive applications. One simple joint configuration in this category is shown below, with the potential failure modes: Figure 5-8 As discussed in section 5.2.2, the weld leg size is critically important in determining which failure mode is dominant for this type of joint. For convenience, the weld throat depth is again measured in terms of the weld leg size on the bottom plate in (b). In the shell element representation (b), failure Mode (A) can be directly modelled as shown. Mode (B) and Mode (C) are approximate representations of the weld failures at the top and bottom edges (or fusion lines) of the weld. As discussed earlier, it can be shown that the stress states from Mode (B) and Mode (C) in (b) can be used to represent mode (D) in (a) by taking the algebraic sum of the two. 90 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

93 Preparing FE Models for use with Verity (c) summarises a parametric study on the weld size effects on structural stress based SCF for each of the potential failure modes in (b). A solid model with a precise representation of the partial penetration weld geometry (leg length l=t) and the two well-defined failure orientations ( Weld Toe Ref and A Ref ) was used to calculate their respective structural stresses as the reference values for comparison purposes with the simplified weld presentation in the shell model. The structural stress based SCFs are shown in (c) as the symbols and for the two failure modes, which are essentially the same as the shell model results at l/t=1, validating the adequacy of the shell element representation of the fillet weld in the shell model. When the weld leg size (l/t) is smaller than unity, the weld throat failures (A) and (C) in (b) dominate the failure mode in this specimen. The algebraic summation of the structural stresses from (A) and (C) is near zero for all weld leg sizes investigated, implying that the weld throat failure through the middle of the weld metal (D) in (a) is unlikely. Furthermore, failures corresponding to (A) and the weld toe on the horizontal plate become more dominant. Again, the structural stress based SCFs for both mode (A) and the weld toe in the bottom plate are not sensitive to the variation in weld size investigated Fillet Weld between Two Plates with Dissimilar Thicknesses The earlier fillet weld examples were analysed by assuming that two plates joined by a fillet weld are of similar thicknesses, and that the fillet weld size is of the order of the plate thickness. In such situations, the weld element can be easily defined by connecting the mid-thickness planes between the two plates, such as that shown in Figure 5-7a. If the thicknesses of the two plates are significantly different, or if the fillet weld is significantly smaller than one of the plate thickness, the resulting additional local bending effects not captured using the previous weld presentation can be significant. The previous weld representation discussed in the earlier sections is shown as a direction connection between the inclined weld elements with the mid-thickness nodes in the two adjacent plates: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 91 Figure 5-9

94 Preparing FE Models for use with Verity Without losing generality, (b) illustrates a typical situation in which the local bending effects can be approximated by placing the weld element nodes through the mid-positions of the two fillet weld leg lengths. This issue was first identified when comparing the structural stress results between 3D solid element models and shell element models for a padding plate joint, see Figure As shown in Figure 5-10a, the difference in the two plate thicknesses is 5mm. In addition, the fillet weld has a leg length of 5mm. The simplest weld representation ( Scenario 1 in Figure 5-10b) does not consider the localised load transfer through the weld. According to the discussions with respect to Figure 5-9b, an improved modelling scheme ( Scenario 2 in Figure 5-10c) is applicable to such problems. The overall structural stress distributions along the weld toe in the base plate are compared in Figure 5-11a. The increase in structural stress based SCF using Scenario 2 is due to the additional bending effects captured by using the weld representation scheme shown in Figure 5-10c. The actual structural stress based SCF can be accurately calculated by using 3D solid element models in which the small fillet weld can be correctly modelled. As shown in Figure 5-11b, the results from the shell element models with scenario 2 are very close to those from the 3D solid element models. The shell element models with the weld representation described as Scenario 1 (Figure 5-10b) under-estimate the structural stress based SCF. Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

95 Preparing FE Models for use with Verity Figure Weld Line Curvature Modelling Weld line curvature requires some additional considerations when using Verity. A weld line is defined as a continuous curve in space, described by a series of inter-connected nodes with unique nodal numbers in a Finite Element model. For example, consider a curved weld line in a linear shell element model: Figure 5-12 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 93

96 Preparing FE Models for use with Verity The normal vector direction (y ) at Node 3 (N3) between the Elements 2 and 3 (E2 and E3) is determined by the vector summation of y E2 and y E3. If the intersection angle () is too large, mesh-size sensitivity can develop, and the structural stress calculated at this node may not correctly represent the actual structural stress state for fatigue evaluation purposes. Analyses performed for various curved welds suggest that in general if the intersecting angle is smaller than ~30, the structural stress results are not noticeably affected. This criterion can often be relaxed for a particular application, either through an analyst s experience or by performing a series of parametric analyses. For example, consider a longitudinal stiffener joint modelled by a shell element model with half symmetry assumed: Figure 5-13 A longitudinal stiffener and a curved weld line definition for structural stress calculation for weld toe crack with respect to the base plate (note: the weld end on the base plate in txt mesh is simulated with 4 linear elements over the 180 angular span) The weld line definition for weld toe cracking into the base plate is shown by the arrow line encircling the entire weld toe, along which Verity calculates structural stresses in a simultaneous manner. In the mesh shown, four linear elements were used to model the half circle around weld end (=45 in this case). If more elements are used in the.5t mesh, the change in the structural stresses is still not significant, but this cannot be generalised for broad applications. It is always desirable to perform a few parametric analyses to establish a criterion for representing weld line curvature, if a coarse mesh is to be used. 94 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

97 Preparing FE Models for use with Verity The above discussions also imply that a 90 sharp turn along a weld line in a Finite Element model should be avoided. For the same longitudinal stiffener joint: Figure 5-14 Representation producing a sharp corner at weld end on base plate (not recommended) One single weld line definition encircling the weld toe contour can no longer be correctly presented as a continuous curve. As a result, structural stresses calculated at the weld end and corner are meshsensitive and lacking physical meaning. If there are no other choices, the weld toe cracking (into the base plate thickness) at the weld end may be analysed by considering an alternate weld definition (straight line). Obviously, the SCF at the weld end is much higher than that shown in Figure Weld toe cracking along the two straight sides of the weld can be simulated by using a straight weld line definition on each side of the weld toe (dashed lines in Figure 5-14). At the weld end, the structural stresses normal to the weld line (x direction) will be calculated in Verity with the virtual node method automatically. However, the structural stress information for failure locations situated within the curved weld end in Figure 5-13 will not be available from the straight weld line definition. It should be noted that the weld line definition along the weld toe on attachment plate side is not affected in Figure The resulting structural stresses are reasonably accurate, comparing with those with the weld being properly modelled in Figure Further discussions on this (using a different example) follow. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 95

98 Preparing FE Models for use with Verity Calculations without Modelling Weld An extreme case in simplified weld representations is shown in Figure 5-15a for the same joint type as Figure 5-13 and Figure 5-14, in which the fillet weld is only represented as a line of nodes connecting the two plates: Figure 5-15 An extreme case in which the fillet weld is not modelled an alternative weld line definition for calculating the structural stress SCF at the weld end in the direction of loading (SS calculated using nodal forces at N1 and N2 from the one element shown) 96 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

99 Preparing FE Models for use with Verity Special caution must be taken in interpreting the analysis results since some of the load transfer mechanisms may not be correctly represented when using the oversimplified weld representation procedure. Under the loading direction given in (a), the structural stress normal to the weld end (in the direction of loading or negative y direction) can be calculated with a weld line definition as shown (solid blue line). However, the virtual node position in this instance should be determined as the actual weld toe position measured from the mid-plane of the attachment plate (l 1 =t in this example). Once Verity is used with respect to the weld line, the corresponding structural stresses at the weld (in the negative y direction) should be very close to those shown in (b). The structural stress based SCFs were calculated manually before the virtual node method was implemented in Verity. The required nodal forces in the negative y direction were retrieved for each of the highlighted elements in each of the four models with different element sizes. The line force f 1 at the weld end was then calculated using l 1 =t. The line moment m1 was calculated in the same way by retrieving the nodal moments with respect to x from the same elements. Given the over-simplified weld representation scheme used in Figure 5-15, it is surprising to see that the structural stress based SCFs are close to those calculated using the curved weld line definition in Figure Furthermore, as the element size increases, the SCF remains essentially the same up to 10t10t. This proves the effectiveness of the virtual node method. However, the surprising consistency of the structural stress results from the four meshes is attributed to the fact that in the plate element model in Figure 5-15, the overall geometry remains the same as the element size increases, while the 180 arc at the weld end in Figure 5-13 deviates increasingly from the smoothness requirements (Section 5.2.5) in the linear element models. For this particularly example the structural stresses at the weld end can be calculated with reasonable accuracy using the specific calculation procedures as described, but if the loading is applied in the x direction on one of the two longer edges of the base plate, the structural stress based SCFs in the x direction become unity since there are no interactions between the base and longitudinal attachment plates without modelling the presence of the weld. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 97

100 Preparing FE Models for use with Verity With the same considerations, if FPSO Detail 5 is analysed without modelling the weld it does not introduce any significant error in the structural stress calculations for the weld toe on the base plate: Figure 5-16 Comparison of the structural stress results with element sizes without modelling the presence of the weld 98 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

101 Preparing FE Models for use with Verity Figure 5-17 Comparison of the structural stress results with element sizes with a proper weld representation The structural stress based SCF is at about 1.6 (Figure 5-16) without modelling the weld, versus about 1.5 with modelling the weld (Figure 5-17). Note that at the time of these calculations, the virtual node position was placed at 10mm (or l 1 = 10mm). In the earlier discussions regarding S-N data interpretation for the same detail, l 1 = 20mm was used to be consistent with the actual failure criterion reported Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 99

102 Tutorial A: Single Weld Line 100 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

103 Tutorial A: Single Weld Line 6 Tutorial A: Single Weld Line (Using Abaqus) 6.1 Introduction This tutorial outlines how to analyse welded structures using Verity. This analysis is based upon a solid hexahedral model with one row of elements through the thickness. The model was created for the SAE Fatigue Challenge in 2003 and Figure 6-1 shows the model; the plot was created using an FEA pre-processor: Figure 6-1 The brown area shows the weld itself. For this analysis the weld line to be analysed is the one between the weld (brown) and the marked weld toe (dark blue). In practice most likely two weld lines, one at each side of the weld, would be analysed. The remainder of the model will be analysed using a local strain approach and the material Manten steel. The model is provided in all the supported formats. This tutorial will use an Abaqus model; you can use one of the other FEA results format if you prefer, but if so the element and node numbers in the weld line and weld toe will need to be modified. A full weld definition configuration file is supplied for each format. 6.2 Preparation Start the program by selecting fe-safe from the Windows Start menu (Windows) or by running the script fe-safe (Linux) (see section 5.2 in the fe-safe User Guide). When starting fe-safe, the Configure fe-safe Project Directory dialog appears. The path shown in the Project Directory field is where the fe-safe project directory will reside. The user can either accept the default name and location or enter a more convenient name and location. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 101

104 Tutorial A: Single Weld Line If an existing project directory is chosen, existing data in that project will be retained. This includes model data, load history files, analysis settings, and more. Reset any existing analysis options to their defaults in the Clear Data and Settings dialog box [Tools >> Clear Data and Settings...] by selecting the Check all option and clicking OK. 6.3 Open the Model Select the Datasets To open the model, select File >> FEA Solutions >> Open Finite Element Model... On the file selection dialog box select the file <DataDir>\weld_fatigue\solid-tubess3_xx.odb and click Open. This will display the Select Datasets to Read pre-scan dialog box: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

105 Tutorial A: Single Weld Line The dialog box shows that there is a dataset containing Stresses (used by fe-safe) and Nodal Forces (used by Verity ). Ensure that both are selected so that the weld can be analysed using Verity and the rest of the model can be analysed using fe-safe, then click OK. The stresses will be extracted from the model and information similar to that shown below will be displayed in the Message Log window. This information is also written to the file <ProjectDir>\Model\reader.log. odb_io version :9994 Reads Abaqus 6 ODB databases Copyright Dassault Systemes UK Limited Reading : C:\data\verity\solid-tubess3_610.odb Writing : Pre-scan Strains : Read all (Pre-scanning) ODB interface exe exited with code Pre-scan complete. odb_io completed NOTE : Storing current session macro commands to D:\Data\Users\fe-safe.version.6.3\output\current.macro odb_io version :9994 Reads Abaqus 6 ODB databases Copyright Dassault Systemes UK Limited Reading : C:\Program Files (x86)\safe_technology\fesafe\version.6.3\data\verity\solid-tubess3_610.odb pre-scan Writing : D:\Data\Users\fe-safe.version.6.3\projects\project_01\model\FESAFE.FED Selected position is Element Nodal Strains : Selected datasets Dataset : S From Step : 1 Iteration : 1 Time : 2.22e-16 Title : Direct Min/Max : Shear Min/Max : No. Elements : 4412 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 103

106 Tutorial A: Single Weld Line When the model has finished loading, the Loaded FEA Models Properties dialog box dialog box appears, as shown in Figure 6-3. Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

107 Tutorial A: Single Weld Line If the dialog box dialog box does not appear automatically, then it can be displayed by right-clicking on the icon in the Current FE Models window and selecting Properties: Figure 6-4 Ensure that the units are as shown in Figure 6-3, then click OK. A dialog box will show prompting to edit element groups loaded from the model, click No. A summary of the open model appears in the Current FE Models window, showing the loaded datasets and element group information see Figure 6-5. Figure 6-5 Note: If the window does not appear exactly as shown in Figure 6-5, then expand the tree view to show more details. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 105

108 Tutorial A: Single Weld Line When a new model is loaded, the output filename automatically defaults to: <ResultsDir>\{source_file_name}Results.{source_file_extension} which in this example is: <ResultsDir>\solid-tubess3_xxResults.odb The output filename can be modified either by manually editing the Output File field in the Fatigue from FEA dialog box, or by clicking the adjacent browse button: Define the Weld After the model has been opened the weld locations should be defined prior to evaluation of the structural stresses. This can be done using the Weld Preparation>> Define and Analyse Weld Geometry menu. A new dialog box will be displayed: Figure 6-6 If this is the first time Verity has been used, the weld tree area will most likely be blank. If it is not then use the Delete All button to clear the tree. 106 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

109 Tutorial A: Single Weld Line To create a weld, click the Add button and select Legacy Line Definition as the type of the weld to be defined. This will add a new weld definition to the tree with the name New Line Weld: Figure 6-7 Note: If the New Weld Line does not appear as shown above, then expand the tree view to show more details. To edit parameters in the weld tree, select each parameter and click on the Edit button, or double-click the parameter or value. Define each required weld parameter as discussed below: Name Rename the weld line by or double-clicking on the New Line Weld value. This will allow the item to be edited in the tree. Change the weld name to TV_to_LG_tube in_tv_tube and press the enter key () to accept it. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 107

110 Tutorial A: Single Weld Line Element Type To indicate that this weld domain contains Solid hexahedral elements (as opposed to Tetrahedrons or Shells), edit the Element Type=Shells parameter: Figure 6-8 Use the drop-down box to select Solids. The weld tree will be rebuilt to include the parameters required for a weld in a solid model. Plate Thickness Edit the plate thickness value and specify a thickness as inches. All measurement defined in the Weld Definition dialog box match those of the consistent units system specified in the Current FE Models window. The FE model contains distances in inches and loads in lbf, so the definition must match these. The plate thickness needs to be constant for the length of the weld. 108 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

111 Tutorial A: Single Weld Line Reference Normal Next, specify the Reference Normal. This is only required for Solid (hexahedral) or Tetrahedral elements. This parameter is the normal to the free surface of the start element. Edit this parameter and set the normal to (0,0, 1) in the displayed dialog box: Figure 6-9 Click OK. Start Element & Start Node The start node and element are required to tell fe-safe where one end of the weld starts. From Figure 6-10 and Figure 6-12 it can be seen that they are element 76 and node 354. Define the two parameters: Start Element =76 Start Node =354 in the tree for the weld definition. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 109

112 Tutorial A: Single Weld Line Weld Line Nodes The position of the weld is defined using a line of nodes along the weld and in the weld toe surface. The top left section of the weld (including node numbers) is shown below. Following the weld line (between brown and dark blue sections) the sequence of nodes beginning 354, 353, 352 can be seen to define the weld line. Figure 6-10 Edit the parameter Weld line nodes. This will pop up the weld line nodes group selector dialog box. In this example a nodal set with all weld line nodes has been already defined in the FE model with a name of NTT, so select NTT_nodal (or PART-1-1_NTT_nodal in the case that instance support is turned on in fe-safe) from the list and click OK to confirm: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

113 Tutorial A: Single Weld Line Note: If the finite element model does not include a node group containing the weld line nodes, a user defined group can be configured as discussed in section 5 of the fe-safe User Guide. Groups defined for Verity need not contain node numbers defined in order. Weld Reference Elements The weld reference elements define a theoretical crack path along the weld toe through the base material for this example. Elements in the base material along the weld toe are used for weld toe failure analyses and elements in the weld fillet material is used for weld throat failure analyses. The toe defines the section where the base metal joins the weld. The requirement for weld toe element preparation on solid mesh topology is that only rectangular element faces may lie upon the throughthickness cut from the weld line and that the mesh is regular on the through-thickness cut. By regular it is meant that corner nodes line up with corner nodes, midside nodes line up with midside nodes, and all nodes lie upon the line normal to the weld toe surface. The top half of the weld including element numbers is shown below: Figure 6-12 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 111

114 Tutorial A: Single Weld Line Edit the parameter Weld reference elements, which will pop up the weld reference elements group selector dialog box. Again for this example an elements set with all weld toe elements has been defined in the FE model with a name of TTOE. Select TTOE (or PART-1-1_TTOE in the case that instance support is turned on in fe-safe) from the list and click OK to confirm: Figure 6-13 Click OK. Note: As with nodes, a user defined group can be configured for elements. Groups defined for Verity need not contain element numbers defined in order. Final Configuration This tutorial analyses a single weld only, additional welds can be defined in the same manner. The Just Save button can save this definition to disk for later use. The configuration you have just defined has been included in your installation directory in the file <DataDir>\weld_fatigue\solid-tubess3.def. You can load this definition using the Open button if you have had problems defining the analysis. Now the configuration is complete it should look similar to: 112 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

115 Tutorial A: Single Weld Line Figure 6-14 Note: If support for instances was turned on (FEA Fatigue>>Abaqus ODB Interface Options with a checkbox engaged next to Allow ODB files with multiple parts and instances) at the time of ODB reading, the groups will appear as shown above with the instance (PART-1-1) Evaluate the structural stresses Now click Save and analyse and Verity will evaluate the structural stresses. After the structural stresses are calculated Information similar to that shown below will be displayed in the Message Log window. This information is also written to the file <ProjectDir>\Model\verity-diagnostics.log. Running Verity module on 1 line welds... Verity structural stress file backed up to C:\temp\model\verity-ss.arc. Processing weld New_Line_Weld. Processing forces dataset 1.1 at time 2.22e-016. Processing forces for weld New_Line_Weld. Saving structural stresses to FED file... Verity stress generation and import completed. Analysis of welds took seconds. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 113

116 Tutorial A: Single Weld Line The structural stresses evaluated by Verity have been merged in with the stresses read by fe-safe and a new group named WELD has been created. A summary of the Verity analysis run can be found in the verity-diagnostics.log file (Weld Preparation>> View Structural Stress Diagnostics Log menu) and a table of the structural stresses calculated can be found in the verity-ss.txt file (Weld Preparation >> View Structural Stress File menu). Note: a warning containing the information that an item in the definition that has no instance defined, may be displayed. fe-safe will try to accommodate for the lack of instance, which should allow the tutorial to continue without issue. 6.4 Analyse the Model After evaluating the structural stresses using Verity we should have a group named WELD in the Fatigue from FEA window. The material will have defaulted to the Steel Weld 50% S-N curve, and the algorithm will have defaulted to SSM-Normal. In this tutorial the mean life curve will be used for the weld. The remainder of the model will be analysed using a local strain approach and the material Manten steel Define the Loading The loading will be constant amplitude zero mean loading (this is sometimes referred to as R=-1). We will cycle between the stresses in the dataset multiplied by 1 and multiplied by 1. On the Fatigue from FEA dialog box select the Loading Settings tab to switch to the loading tree. Right mouse click on the loadings tree and select Clear all loadings to remove any existing loading. Select the dataset named Dataset 1: (1.1) S : Stress from the Current FE Models window. Click the Add... button and then select the A user-defined LOAD * dataset. Specify 1 and 1 in the Loading Scale box: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

117 Tutorial A: Single Weld Line Click OK. This will add an item to the loading as shown: Figure 6-16 Select the Analysis Settings tab from the Fatigue from FEA dialog box to switch to the main settings Define the Materials In the Group Parameters table double-click the Algorithm column and in the displayed dialog box select Analyse with Material s default Algorithm and click OK. This will configure all applicable groups to use the algorithm best suited to the selected material. Select the material SAE_950C-Manten in the local.dbase file in your Material Databases window and double-click the column titled Material. You will be asked if you wish to set the material, click Yes. The material for the WELD group should then be reverted to a material from the verity.dbase. The default life curve can easily be changed from the mean curve to a 2 or 3 standard deviations life curve. To do this select the required life curve in the verity.dbase file in the Material Databases window and then click on the cell defining the WELD group material in the Group Parameters table on the Fatigue from FEA dialog box. Figure 6-17 shows the current list of S-N curves in the Verity database. Figure 6-17 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 115

118 Tutorial A: Single Weld Line Perform the Analysis The Fatigue from FEA dialog box should now look similar to: Figure 6-18 The results filename will have defaulted to a new.odb file. To start the analysis, click the Analyse button. A summary of what you have defined is displayed. Click Continue and the analysis will start. As the analysis is being performed the worst life so far is displayed in the Message Log window. Summary ======= Worst Life-Repeats : at Element [0] Analysis time : 0:00: Fatigue Analysis Completed. The analysis log shows that the worst-case life for the whole model is: repeats of the loading, at element 1398, node Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

119 Tutorial A: Single Weld Line A copy of the original.odb file was created, onto which a new step containing the fatigue results was appended. The exported fatigue results in the file contain the log10(life) contour of fatigue lives, which should look similar to: Figure 6-19 Note that element 1398 is not at the weld, and comes from analysis on the base materials using SAE Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 117

120 Tutorial B: Multiple Weld Lines 118 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

121 Tutorial B: Multiple Weld Lines 7 Tutorial B: Multiple Weld Lines (Using Ansys) 7.1 Introduction This tutorial outlines how to analyse welded structures in an Ansys.rst file using Verity. Figure 7-1 shows the solid hexahedral model with one row of elements through the thickness. The model was created for the SAE Fatigue Challenge in 2003 and Figure 7-1 All of the weld definitions are merged to one group for configurations with the nominal master S-N curve for weld fatigue at toes. The remainder of the model will be configured for no analysis. The tutorial uses an Ansys RST model. However, the same techniques can be applied to all FE formats supported for Verity-in-fe-safe, which currently include: Ansys results (*.rst) files Abaqus ODB files Nastran OP2 files 7.2 Preparation Start the program by selecting fe-safe from the Windows Start menu (Windows) or by running the script fe-safe (Linux) (see section 5.2 in the fe-safe User Guide). Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 119

122 Tutorial B: Multiple Weld Lines When starting fe-safe, the Configure fe-safe Project Directory dialog appears. The path shown in the Project Directory field is where the fe-safe project directory will reside. The user can either accept the default name and location or enter a more convenient name and location. If an existing project directory is chosen, existing data in that project will be retained. This includes model data, load history files, analysis settings, and more. Ensure that the following basic settings are correctly configured. If fe-safe is being run for the first time then it is possible to skip this preparatory section. Reset any existing analysis options to their defaults in the Clear Data and Settings dialog box [Tools >> Clear Data and Settings...] by selecting the Check all option and clicking OK. 7.3 Open the Model Select the Datasets To open the model, use the File >> FEA Solutions >> Open Finite Element Model... menu, select the file <DataDir>\weld_fatigue\t-tube_sld_xx.rst and click Open. This will display the Select Datasets to Read pre-scan dialog box: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

123 Tutorial B: Multiple Weld Lines The dialog box shows that there is a dataset containing stresses, strains, temperatures and forces. For this tutorial make sure that Forces and Stress datasets are selected so that the weld can be analysed using Verity and the rest of the model can be analysed using fe-safe, then click OK. The selected datasets will be extracted from the model. Once this process is complete, the Loaded FEA Models Properties dialog box dialog box appears, as shown in Figure 7-3. Figure 7-3 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 121

124 Tutorial B: Multiple Weld Lines If the dialog box dialog box does not appear automatically, then it can be displayed by right-clicking on the icon in the Current FE Models window and selecting Properties: Figure 7-4 Ensure that the units are as shown in Figure 7-3, then click OK. A dialog box dialog box will appear prompting to edit element groups loaded from the model, click No. 7.4 Define the Welds After the model has been opened the weld locations should be defined prior to evaluation of the structural stresses. This can be done using the Weld Preparation >> Define and Analyse Weld Geometry menu. A new dialog box dialog box will be displayed. Initially this may contain the weld definitions that were used in the previous Verity run (Tutorial A): Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

125 Tutorial B: Multiple Weld Lines These welds will not be needed, unless you are re-running the same job. Use the Delete All button to clear the tree, and click OK when prompted. Tutorial A covers the details of defining a weld. For this tutorial, click the Open button. The Open Verity Weld Definition dialog box dialog box will appear: Figure 7-6 Use the drop-down list to sort the directory by the weld definition of type Weld Definition *.def. select the file <DataDir>\weld_fatigue\t-tube_sld1.def, and click OK. This will load the correct set of welds into the weld definition tree. In this case there will be four defined welds: Figure 7-7 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 123

126 Tutorial B: Multiple Weld Lines The weld definition and configuration should be complete and look similar to this: Figure 7-8 Expand the defined welds to view configuration details. The lists of nodes and elements are defined in the weld definition file as opposed to the finite element nodel. These can be accessed by editing Weld line nodes or Weld reference elements (as discussed in Tutorial A). 124 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

127 Tutorial B: Multiple Weld Lines Evaluate the structural stresses Now click Save and analyse and Verity will evaluate the structural stresses. An information similar to that shown will be displayed in the Message Log window after the structural stresses have been calculated. This information is also written to the file <ProjectDir>\Model\veritydiagnostics.log: Running Verity module on 4 line welds... Verity structural stress file backed up to C:\temp\model\verity-ss.arc. Processing weld tvtb_to_lgtb_in_tvtb_neg_z. Processing weld tvtb_to_lgtb_in_tvtb_pos_z. Processing weld tvtb_to_lgtb_in_lgtb_neg_z. Processing weld tvtb_to_lgtb_in_lgtb_pos_z. Processing forces dataset 1.1 at time 1. Processing forces for weld tvtb_to_lgtb_in_tvtb_neg_z. Processing forces for weld tvtb_to_lgtb_in_tvtb_pos_z. Processing forces for weld tvtb_to_lgtb_in_lgtb_neg_z. Processing forces for weld tvtb_to_lgtb_in_lgtb_pos_z. Saving structural stresses to FED file... Verity stress generation and import completed. Analysis of welds took seconds. The structural stresses evaluated by Verity have been merged in with the stresses read by fe-safe and a new group named WELD has been created. A summary of the Verity analysis run can be found in the verity-diagnostics.log file (Weld Preparation >> View Structural Stress Diagnostic Log menu) and a table of the structural stresses calculated can be found in the verity-ss.txt file (Weld Preparation >> View Structural Stress file menu). 7.5 Analyse the Model After evaluating the structural stresses using Verity we should have a group named WELD in the Fatigue from FEA window. The material will have defaulted to the Steel Weld 50% S-N curve. In this tutorial the mean life curve will be used for the weld. The remainder of the model will be configured for no analysis Define the Loading The loading will be constant amplitude zero mean loading (this is sometimes referred to as R=-1). We will cycle between the stresses in the dataset multiplied by 1 and multiplied by 1. On the Fatigue from FEA dialog box dialog box select the Loading Settings tab to switch to the loading tree. Right mouse click on the loadings tree and select Clear all loadings to remove any existing loading. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 125

128 Tutorial B: Multiple Weld Lines Select the dataset named Dataset 1: (1.1) S : Stress from the Current FE Models window. Click the Add... button and then select the A user-defined LOAD * dataset. Specify 1 and 1 in the Loading Scale box: Figure 7-9 Click OK. This will add an item to the loading as shown: Figure 7-10 Select the Analysis Settings tab from the Fatigue from FEA dialog box dialog box to switch to the main settings. 126 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

129 Tutorial B: Multiple Weld Lines Define the Materials For this analysis, we will turn off the analysis for the entire model, then turn on just the analysis of the WELD group of elements. In the Group Parameters table double-click on the cell in the Algorithm column and WELD row and select Normal Structral Stress: Click OK. Figure 7-11 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 127

130 Tutorial B: Multiple Weld Lines This tutorial uses the default material, Steel Weld (50%) for the WELD group. Select the algorithm cells of the other groups (Material1,Material2 and Default), then right click and Select Edit, then change the algorithm selection in the resulting dialog to Do Not Analyse. The Fatigue from FEA dialog box dialog box should now look similar to the following: Figure 7-12 If you have some options configured in Exports from a previous analysis, click Exports, select the List of Items tab, click None, and then click OK. The results filename will have defaulted to a new.rst file. 128 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

131 Tutorial B: Multiple Weld Lines Perform the Analysis To start the analysis, click the Analyse button. A summary of what you have defined is displayed: Figure 7-13 Click Continue and the analysis will start. As the analysis is being performed the worst life so far is displayed in the Message Log window. Summary ======= Worst Life-Repeats : at Element Analysis time : 0:00: Fatigue Analysis Completed. The analysis log shows that the worst-case life for the whole model is: repeats of the loading, at element 2809, node 3. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 129

132 Tutorial B: Multiple Weld Lines A copy of the original.rst file excluding the original steps was created, onto which a new step containing the fatigue results was written. The exported fatigue results are written to the Ansys variable SX and contain the log10(life) contour of fatigue lives, which should look similar to: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

133 Tutorial C: Shell Weld Line 8 Tutorial C: Shell Weld Lines (Using Nastran) 8.1 Introduction This tutorial outlines how to analyse welded structures in a Nastran.op2 file using Verity. Figure 8-1 shows a linear shell model which is based on models created for the SAE Fatigue Challenge in 2003 and Figure 8-1 The weld definitions will be generated as separate groups for configurations with different master S-N curves for weld fatigue at toes. The remainder of the model (except the weld material shown in yellow) will be analysed using a local strain approach and the material Manten steel. The tutorial uses a Nastran OP2 model. However, the same techniques can be applied to all FE formats supported for Verity-in-fe-safe, which currently include: Ansys results (*.rst) files Abaqus ODB files Nastran OP2 files 8.2 Preparation Start the program by selecting fe-safe from the Windows Start menu (Windows) or by running the script fe-safe (Linux) (see section 5.2 in the fe-safe User Guide). Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 131

134 Tutorial C: Shell Weld Line When starting fe-safe, the Configure fe-safe Project Directory dialog appears. The path shown in the Project Directory field is where the fe-safe project directory will reside. The user can either accept the default name and location or enter a more convenient name and location. If an existing project directory is chosen, existing data in that project will be retained. This includes model data, load history files, analysis settings, and more. Ensure that the following basic settings are correctly configured. If fe-safe is being run for the first time then it is possible to skip this preparatory section. Reset any existing analysis options to their defaults in the Clear Data and Settings dialog box dialog box [Tools >> Clear Data and Settings...] by selecting the Check all option and clicking OK. 8.3 Open the Model Select the datasets To open the model, use the File >> FEA Solutions >> Open Finite Element Model... menu, select the file <DataDir>\weld_fatigue\t-tube_2k4_pn2.op2 and click Open. This will display the Select Datasets to Read pre-scan dialogue: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

135 Tutorial C: Shell Weld Line The dialog box shows that there is a dataset containing stresses, strains, temperatures and forces. For this tutorial make sure that Forces and Stress datasets are selected so that the weld can be analysed using Verity and the rest of the model can be analysed using fe-safe, then click OK. The selected datasets will be extracted from the model. Once this process is complete, the Loaded FEA Models Properties dialog box dialog box appears, as shown in Figure 8-3. Figure 8-3 Ensure that the units are as shown in Figure 8-3, then click OK. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 133

136 Tutorial C: Shell Weld Line A dialog box will appear prompting to edit element groups loaded from the model, click Yes. Figure 8-4 Use the button to move the group associated with Property 3 (property definition 3 in the Nastran input file) which represents the elements in the weld fillet, and the group associated with Matierial 1 which represents all elements in the whole model with material definition 1. The Default group will be used to limit analysis in the weld elements which are not part of the remaining Property 1 and Property 2 groups. Click OK. If the Current FE Models Properties dialog box dialog box does not appear automatically, then it can be displayed by right-clicking on the icon in the Current FE Models window and selecting Properties. If the Edit Group List prompt does not appear, the Select Groups to Analyse dialog box can be opened using FEA Fatigue >> Manage Groups menu selection. 134 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

137 Tutorial C: Shell Weld Line Define the materials From the Material Databases window in the local.dbase file select the material SAE_950C-Manten material and in the Group Parameters table double-click the column titled Material. You will be asked if you wish to set the material, click Yes Define the welds After the model has been opened the weld locations should be defined prior to evaluation of the structural stresses. This can be done using the Weld Preparation >> Define and Analyse Weld Geometry menu. A new dialog box will be displayed. Initially this may contain the weld definitions that were used in a previous Verity run (e.g. a previous Tutorial): Figure 8-5 These welds will not be needed, unless you are re-running the same job. Use the Delete All button to clear the tree, and click OK when prompted. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 135

138 Tutorial C: Shell Weld Line Tutorial A covers the details of defining a weld. For this tutorial, click the Open button. The Open Verity Weld Definition dialog box will appear: Figure 8-6 Use the drop-down list to sort the directory by the weld definition of type Weld Definition *.def. select the file <DataDir>\weld_fatigue\t-tube_2k4_pn2.def, and click OK. This will load the correct set of welds into the weld definition tree. In this case there will be two defined welds: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

139 Tutorial C: Shell Weld Line Expand the defined welds to view configuration details. The lists of nodes and elements are defined in the weld definition file as opposed to the finite element nodel. These can be accessed by editing Weld line nodes or Weld reference elements (as discussed in Tutorial A). Figure 8-8 Deselect the checkbox to Merge all groups into WELD group. This allows the two weld lines to be configured differently in the Groups Parameters settings (e.g. materials and algorithms) Evaluate the structural stresses Now click Save and analyse and Verity will evaluate the structural stresses. Information similar to that shown below will be displayed in the Message Log window after the structural stresses have been calculated. This information is also written to the file <ProjectDir>\Model\veritydiagnostics.log: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 137

140 Tutorial C: Shell Weld Line Running Verity module on 2 line welds... Verity structural stress file backed up to C:\Users\E5Q\Documents\fesafe.version.6.5\projects\project_01\model\verity-ss.arc. Processing weld TV_to_LG_tube_in_TV_tube. Processing weld TV_to_LG_tube_in_LG_tube_open. Processing forces dataset 1.1. Processing forces for weld TV_to_LG_tube_in_TV_tube. Processing forces for weld TV_to_LG_tube_in_LG_tube_open. Saving structural stresses to FED file... Verity stress generation and import completed. Analysis of welds took seconds. The structural stresses evaluated by Verity have been merged in with the stresses read by fe-safe and two groups starting with WELD have been created, representing each of the weld definitions. A summary of the Verity analysis run can be found in the verity-diagnostics.log file (Weld Preparation >> View Structural Stress Diagnostic Log menu) and a table of the structural stresses calculated can be found in the verity-ss.txt file (Weld Preparation >> View Structural Stress File menu). 8.4 Analyse the Model After evaluating the structural stresses using Verity we should have two groups starting with WELD in the Fatigue from FEA window. The algorithm will have defaulted to SSM-Normal, and the material will have defaulted to the 50% failure equivalent structural stress S-N curve for both groups. This will suffice for the toe of the TV tube, whilst the toe on the LG tube will need to be represented by the 2.2% failure equivalent structural stress S-N curve. The remainder of the base materials will be configured for analysis with Manten steel Define the loading The loading will be constant amplitude zero mean loading (this is sometimes referred to as R=-1). We will cycle between the stresses in the dataset multiplied by 1 and multiplied by 1. On the Fatigue from FEA dialog box select the Loading Settings tab to switch to the loading tree. Right mouse click on the loadings tree and select Clear all loadings to remove any existing loading. 138 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

141 Tutorial C: Shell Weld Line Select the dataset named Dataset 1: (1.1) S : Stress from the Current FE Models window. Click the Add... button and then select the A user-defined LOAD * dataset. Specify 1 and 1 in the Loading Scale box: Figure 8-9 Click OK. This will add an item to the loading as shown: Figure 8-10 Select the Analysis Settings tab from the Fatigue from FEA dialog box to switch to the main settings Define the algorithm In the Group Parameters table double-click the Algorithm column and in the displayed dialog box select Analyse with Material s default Algorithm and click OK. This will configure all applicable groups to use the algorithm best suited to the selected material. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 139

142 Tutorial C: Shell Weld Line Double-click the cell defining the Default group in the Algorithm column and select Do not analyse and click OK. Figure 8-11 Check the Algorithm column to make sure that each Algorithm-related cell is configured as above Define the Weld material Figure 8-12 shows the current list of S-N curves in the Verity database. This tutorial uses the default material, Steel Weld (50%) for the WELD_TV_to_LG_tube_in_TV_tube group and Steel Weld -2SD (2.2%) for the WELD_TV_to_LG_tube_in_LG_tube_open group. Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

143 Tutorial C: Shell Weld Line From the Material Databases window in the verity.dbase file select the Steel Weld -2SD (2.2%) material and in the Group Parameters table double-click on the cell defining the WELD_TV_to_LG_tube_in_LG_tube_open group in the column titled Material. Click Yes. Check the other options to make sure no more adjustments are required; the Fatigue from FEA dialog box should now look similar to the following: Figure 8-13 If you have some options configured in Exports from a previous analysis, click Exports, select the List of Items tab, click None, and then click OK. The results filename will have defaulted to a new.op2 file. Change the Output File name and extension for a third-party post-processing format if needed Perform the analysis To start the analysis, click the Analyse button. A summary of what you have defined is displayed. Click Continue and the analysis will start. As the analysis is being performed the worst life so far is displayed in the Message Log window. Summary ======= Worst Life-Repeats : at Element :1 Analysis time : 0:00: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 141

144 Tutorial C: Shell Weld Line Fatigue Analysis Completed. The analysis log shows that the worst-case life for the whole model is: repeats of the loading, at element 1262, node 1, bottom layer. A copy of the original.op2 file excluding the original steps was created, onto which a new step containing the fatigue results was written. 142 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

145 Tutorial D: Spot Welds by Detect All 9 Tutorial D: Spot Welds (Detect all connecting elements) 9.1 Introduction This tutorial outlines how to analyse spot welds in an Abaqus.odb file by using Verity. Figure 9-1 shows the model which consists of two sheet metal strips joined by four spot welds. Each spot is modelled using a beam (B31) element. The FEA loading applied is lap shearing. Figure 9-1 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 143

146 Tutorial D: Spot Welds by Detect All 9.2 Preparation Start the program by selecting fe-safe from the Windows Start menu (Windows) or by running the script fe-safe (Linux) (see section 5.2 in the fe-safe User Guide). When starting fe-safe, the Configure fe-safe Project Directory dialog appears. The path shown in the Project Directory field is where the fe-safe project directory will reside. The user can either accept the default name and location or enter a more convenient name and location. If an existing project directory is chosen, existing data in that project will be retained. This includes model data, load history files, analysis settings, and more. Ensure that the following basic settings are correctly configured. If fe-safe is being run for the first time then it is possible to skip this preparatory section. Reset any existing analysis options to their defaults in the Clear Data and Settings dialog box [Tools >> Clear Data and Settings...] by selecting the Check all option and clicking OK. 9.3 Open the Model Select the Datasets To open the model, use the File >> FEA Solutions >> Open Finite Element Model... menu, select the file <DataDir>\weld_fatigue\four_beams_lap_shear_2017.odb and click Open. This will display the Select Datasets to Read pre-scan dialogue: 144 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

147 Tutorial D: Spot Welds by Detect All Figure 9-2 The dialog box shows that there are 5 increments containing Stresses and Nodal Forces. Use the Quick-select options to select the Stress and Force datasets for the Last increment only, and click on Apply to Dataset List. This will result in the selections shown in Figure 9-2. Once this is done click OK. When the model has finished loading, the Loaded FEA Models Properties dialog box dialog box appears. Ensure that the units are as shown in Figure 9-3, then click OK. A dialog box will appear prompting to edit element groups loaded from the model, click No. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 145

148 Tutorial D: Spot Welds by Detect All Figure 9-3 If the dialog box dialog box shown in Figure 9-3 does not appear automatically, then it can be displayed by double-clicking on the icon in the Current FE Models window and selecting Properties (see Figure 9-4). 146 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

149 Tutorial D: Spot Welds by Detect All A summary of the open model appears in the Current FE Models window, showing Stress and Force datasets and element groups - see Figure 9-4. Figure 9-4 Note: If the window does not appear exactly as shown in Figure 9-4, then expand the tree view to show more details. When a new model is loaded, the output filename automatically defaults to: <ResultsDir>\{source_file_name}Results.{source_file_extension} which in this example is: <ResultsDir>\four_beams_lap_shear_613Results.odb The output filename can be modified either by manually editing the Output File field in the Fatigue from FEA dialogue, or by clicking the adjacent browse button:. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 147

150 Tutorial D: Spot Welds by Detect All Define the Welds After the stresses and forces have been read-in the user needs to define the spot welds that are to be evaluated. This can be done by using the Weld Preparation >> Define and Analyse Weld Geometry menu. A new dialog box will appear. If there are weld definitions on display use the Delete All button to create a blank screen. Figure 9-5 To create a weld definition click the Add button. A pop-up menu is then displayed (see Figure 9-5). Here, the user has two spot weld evaluation options. By selecting Spot (Detect All Connecting Elements) the resultant definition will ensure that every spot weld in the model will be detected and then evaluated by Verity. This is based on the assumption that every connecting element represents a spot weld (as stipulated in Section 3.1.3). The alternative option, Spot (Detect Connecting Element Group), allows the user to select a group of spot welds for evaluation purposes. 148 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

151 Tutorial D: Spot Welds by Detect All In this example there are four beam elements in the entire model with each representing a spot weld. The intention is to evaluate these four welds. The Spot (Detect All Connecting Elements) option should therefore be selected. The resultant weld definition is displayed in Figure 9-6: Figure 9-6 Note: If the New Spot Welds item does not appear as shown above, then expand the tree view to show more details. Connecting Elements Whenever the Spot (Detect All Connecting Elements) option is selected the Connecting Elements parameter is set to All (which is non-editable). Nugget Diameter The four spot weld nuggets under investigation have a diameter of 5mm. The default value will therefore suffice. Note that the two optional parameters (that can be viewed by selecting the Show all configuration options checkbox) do not need to be modified, i.e. there is no need to calculate an estimate for the nugget diameter values and the Structural Joints / Displacement Control I(r) function will be sufficient for the problem at hand. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 149

152 Tutorial D: Spot Welds by Detect All Evaluate the structural stresses Click Save and analyse and Verity will evaluate the structural stresses. During this calculation phase a series of calculation-related messages will be displayed in the Message Log. This information is also written to the Verity diagnostics file in the Project Directory, such as: <ProjectDir>\Model\verity-diagnostics.log. The log will show the detection of each beam, and the processing of each spot weld, for the one Force dataset: Running Verity module on all detected spot welds... Processing forces dataset 1.4 at time 1. 4 beam elements detected. 4 spot welds have been prepared for assessment. 4 spot welds have been processed. Saving structural stresses to FED file... Verity stress generation and import completed. The structural stresses evaluated by Verity have been merged in with the stresses read by fe-safe and a new group named WELD has been created. A summary of the Verity analysis can be found in the verity-diagnostics.log file (select the menu option Weld Preparation >> View Structural Stress Diagnostics Log) and a table of the structural stresses calculated can be found in the verity-ss.txt file (select the menu option Weld Preparation >> View Structural Stress File menu). 9.4 Analyse the Model After evaluating the structural stresses we should have a group named WELD in the Fatigue from FEA window. The material will have defaulted to the 50% failure equivalent structural stress S-N curve. In this tutorial the mean life curve will be used for the weld Define the Loading The loading will be constant amplitude loading with a minimum load of zero (this is sometimes referred to as R=0). We will cycle between the stresses in the dataset multiplied by 10 and multiplied by 0. On the Fatigue from FEA dialog box select the Loading Settings tab to switch to the loading tree. Right mouse click on the loadings tree and select Clear all loadings to remove any existing loading. 150 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

153 Tutorial D: Spot Welds by Detect All Select the dataset named Dataset 1: (1.4) S : Stress from the Current FE Models window. Click the Add... button and then select the A user-defined LOAD * dataset. Specify 10 and 0 in the Loading Scale box: Figure 9-7 Click OK. This will add an item to the loading as shown: Figure 9-8 Select the Analysis Settings tab from the Fatigue from FEA dialog box to switch to the main settings. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 151

154 Tutorial D: Spot Welds by Detect All Define the Materials For this analysis, we will turn off the analysis for the entire model, then turn on just the analysis of the WELD group of elements. In the Group Parameters table double-click the Algorithm column and in the displayed dialog box select Do not analyse and click OK. This will stop analysis for elements in all groups. Next, double-click on the cell in the Algorithm column and WELD row and select Normal Structural Stress: Click OK. Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

155 Tutorial D: Spot Welds by Detect All This tutorial uses the default material, Steel Weld (50%). Check the other options to make sure no more adjustments are required; the Fatigue from FEA dialog box should now look similar to the following: Figure Perform the Analysis The results filename will have defaulted to a new.odb file. To start the analysis, click the Analyse button. A summary of what you have defined is displayed: Figure 9-11 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 153

156 Tutorial D: Spot Welds by Detect All Click Continue and the analysis will start. As the analysis is being performed the worst life so far is displayed in the Message Log window. Summary ======= Worst Life-Repeats : at Element [0]187.3:1 Analysis time : 0:00: Fatigue Analysis Completed. The analysis log shows that the worst-case life for the whole model is: repeats of the loading, at element 187, node 3. A copy of the original.odb file excluding the original steps was created, onto which a new step containing the fatigue results was written. The exported fatigue results in the file contain the log10(life) contour of fatigue lives, which should look similar to: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

157 Tutorial E: Spot Welds by Group 10 Tutorial E: Spot Welds (Detect connecting element group) 10.1 Introduction This tutorial outlines how to analyse spot welds in an Abaqus.odb file by using Verity. Figure 10-1 shows the model which consists of two sheet metal strips joined by four spot welds. Each spot is modelled using a beam (B31) element. The FEA loading applied is lap shearing. Figure 10-1 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 155

158 Tutorial E: Spot Welds by Group 10.2 Preparation Start the program by selecting fe-safe from the Windows Start menu (Windows) or by running the script fe-safe (Linux) (see section 5.2 in the fe-safe User Guide). When starting fe-safe, the Configure fe-safe Project Directory dialog appears. The path shown in the Project Directory field is where the fe-safe project directory will reside. The user can either accept the default name and location or enter a more convenient name and location. If an existing project directory is chosen, existing data in that project will be retained. This includes model data, load history files, analysis settings, and more. Ensure that the following basic settings are correctly configured. If fe-safe is being run for the first time then it is possible to skip this preparatory section. Reset any existing analysis options to their defaults in the Clear Data and Settings dialog box [Tools >> Clear Data and Settings...] by selecting the Check all option and clicking OK. 156 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

159 Tutorial E: Spot Welds by Group 10.3 Open the Model Select the Datasets To open the model, use the File >> FEA Solutions >> Open Finite Element Model... menu, select the file <DataDir>\weld_fatigue\four_beams_lap_shear_613.odb and click Open. This will display the Select Datasets to Read pre-scan dialogue: Figure 10-2 The dialog box shows that there are 5 increments containing Stresses and Nodal Forces. Use the Quick-select options to select the Stress and Force datasets for the Last increment only, and click on Apply to Dataset List. This will result in the selections shown in Figure Once this is done click OK. When the model has finished loading, the Loaded FEA Models Properties dialog box dialog box appears. Ensure that the units are as shown in Figure 10-3, then click OK. A dialog box will appear prompting to edit element groups loaded from the model, click No. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 157

160 Tutorial E: Spot Welds by Group Figure 10-3 If the dialog box dialog box shown in Figure 10-3 does not appear automatically, then it can be displayed by double-clicking on the icon in the Current FE Models window and selecting Properties (see Figure 10-4). 158 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

161 Tutorial E: Spot Welds by Group A summary of the open model appears in the Current FE Models window, showing Stress and Force datasets and element groups see Figure Figure 10-4 Note: If the window does not appear exactly as shown in Figure 10-4, then expand the tree view to show more details. When a new model is loaded, the output filename automatically defaults to: <ResultsDir>\{source_file_name}Results.{source_file_extension} which in this example is: <ResultsDir>\four_beams_lap_shear_613Results.odb The output filename can be modified either by manually editing the Output File field in the Fatigue from FEA dialogue, or by clicking the adjacent browse button:. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 159

162 Tutorial E: Spot Welds by Group Define the Welds After the stresses and forces have been read-in the user needs to define the spot welds that are to be evaluated. This can be done by using the Weld Preparation >> Define and Analyse Weld Geometry menu. A new dialog box will appear. If there are weld definitions on display use the Delete All button to create a blank screen. Figure 10-5 To create a weld definition click the Add button. A pop-up menu is then displayed (see Figure 10-5). Here, the user has two spot weld evaluation options. By selecting Spot (Detect All Connecting Elements) the resultant definition will ensure that every spot weld in the model will be detected and then evaluated by Verity. This is based on the assumption that every connecting element represents a spot weld (as stipulated in Section 3.1.3). The alternative option, Spot (Detect Connecting Element Group), allows the user to select a group of spot welds for evaluation purposes. In this example there are four beam elements in the entire model with each representing a spot weld. The intention is to evaluate one of the four weld groups. The Spot (Detect Connecting Element Group) option should therefore be selected. The two required parameters will be shown. 160 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

163 Tutorial E: Spot Welds by Group Connecting Elements Whenever the Spot (Detect Connecting Element Group) option is selected the Connecting Elements parameter is used to select the group containing the connecting elements of interest. Edit the Connecting Elements parameter. Select the group SPOTWELD-BEAM4. Nugget Diameter The spot weld nugget under investigation has a diameter of 5mm. The default value will therefore suffice. Note that the two optional parameters (that can be viewed by selecting the Show all configuration options checkbox) do not need to be modified, i.e. there is no need to calculate an estimate for the nugget diameter values and the Structural Joints / Displacement Control I(r) function will be sufficient for the problem at hand. The resultant weld definition is displayed in Figure 10-6: Figure 10-6 Note: If the New Spot Welds item does not appear as shown above, then expand the tree view to show more details. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 161

164 Tutorial E: Spot Welds by Group Evaluate the structural stresses Click Save and analyse and Verity will evaluate the structural stresses. During this calculation phase a series of calculation-related messages will be displayed in the Message Log. This information is also written to the Verity diagnostics file in the Project Directory, such as: <ProjectDir>\Model\verity-diagnostics.log. The log will show the detection of the beam, and the processing of the spot weld, for the one Force dataset: Running Verity module on all detected spot welds... Processing forces dataset 1.4 at time 1. 1 connecting element detected. 1 spot weld has been prepared for assessment. 1 spot weld has been processed. Saving structural stresses to FED file... Verity stress generation and import completed. The structural stresses evaluated by Verity have been merged in with the stresses read by fe-safe and a new group named WELD has been created. A summary of the Verity analysis can be found in the verity-diagnostics.log file (select the menu option Weld Preparation >> View Structural Stress Diagnostics Log) and a table of the structural stresses calculated can be found in the verity-ss.txt file (select the menu option Weld Preparation>> View Structural Stress File menu) Analyse the Model After evaluating the structural stresses we should have a group named WELD in the Fatigue from FEA window. The material will have defaulted to the 50% failure equivalent structural stress S-N curve. In this tutorial the mean life curve will be used for the weld Define the Loading The loading will be constant amplitude loading with a minimum load of zero (this is sometimes referred to as R=0). We will cycle between the stresses in the dataset multiplied by 10 and multiplied by 0. On the Fatigue from FEA dialog box select the Loading Settings tab to switch to the loading tree. Right mouse click on the loadings tree and select Clear all loadings to remove any existing loading. 162 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

165 Tutorial E: Spot Welds by Group Select the dataset named Dataset 1: (1.4) S : Stress from the Current FE Models window. Click the Add... button and then select the A user-defined LOAD * dataset. Specify 10 and 0 in the Loading Scale box: Figure 10-7 Click OK. This will add an item to the loading as shown: Figure 10-8 Select the Analysis Settings tab from the Fatigue from FEA dialog box to switch to the main settings. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 163

166 Tutorial E: Spot Welds by Group Define the Materials For this analysis, we will turn off the analysis for the entire model, then turn on just the analysis of the WELD group of elements. In the Group Parameters table double-click the Algorithm column and in the displayed dialog box select Do not analyse and click OK. This will stop analysis for elements in all groups. Next, double-click on the cell in the Algorithm column and WELD row and select Normal Structural Stress: Click OK. Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

167 Tutorial E: Spot Welds by Group This tutorial uses the default material, Steel Weld (50%). Check the other options to make sure no more adjustments are required; the Fatigue from FEA dialog box should now look similar to the following: Figure Perform the Analysis The results filename will have defaulted to a new.odb file. To start the analysis, click the Analyse button. A summary of what you have defined is displayed: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 165 Figure 10-11

168 Tutorial E: Spot Welds by Group Click Continue and the analysis will start. As the analysis is being performed the worst life so far is displayed in the Message Log window. Summary ======= Worst Life-Repeats : at Element 172.3:1 Analysis time : 0:00: Fatigue Analysis Completed. The analysis log shows that the worst-case life for the whole model is: repeats of the loading, at element 172, node 3. A copy of the original.odb file excluding the original steps was created, onto which a new step containing the fatigue results was written. The exported fatigue results in the file contain the log10(life) contour of fatigue lives, which should look similar to: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

169 Tutorial F: Multiple Solid Weld Lines using Abaqus 11 Tutorial F: Automatic weld finder for Solid Welds (using Abaqus) 11.1 Introduction This tutorial outlines an alternative way of analysing solid weld lines in an Abaqus.odb file using Verity. The intention is to provide a simpler way of defining the weld domain and weld lines, especially when multiple weld lines are to be analysed, or several different failure modes (Toe, Fusion, Throat, Root). Figure 11-1 shows the solid hexahedral model with one row of elements through the thickness.. Note that this is the same model as was used in Tutorial A (See section 7 above). The difference here is that instead of inputting the weld domain and detailed information on the weld line nodes for each line and failure mode, the weld fillet material is defined as a group is defined instead. The various weld lines and weld domains are then automatically computed by fe-safe, although it is still necessary to provide a domain group for root failures. Note that as well as the fillet displayed on the underside of the intersecting tubes, there is a similar fillet on the upper side (occluded in Figure 11-1). Both weld fillets can be supplied as a single fillet group and the software will automatically locate the separate lines in the two fillets. fe-safe locates potential weld lines by connecting up nodes with edges lying along the interface between fillet and non-fillet elements. Note that this will typically produce some spurious short potential weld lines on the edges of the weldends. However these are rejected, because they form closed loops including a fillet edge, and will be labelled as Weld_End lines in the fe-safe message logs. The root lines are also located, either because these are formed from internal surface nodes in fully penetrative welds, or lie on a fillet-parent material interface where there are two faces with significant change in normal direction. This analysis is based upon a solid hexahedral model with one row of elements through the thickness. Figure 6-1 shows the model: Figure 11-1 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 167

170 Tutorial F: Multiple Solid Weld Lines using Abaqus The brown area shows the weld fillet. The dark blue elements are the one used in the weld line previously analysed in Tutorial A, but the automatic solid weld finder software used in this tutorial locates three other toe domains: one on the other side of the displayed fillet, and a similar pair of toe domains on the other side (occluded in Figure 11-1). The tutorial uses an Abaqus ODB model. However, the same techniques can be applied to all FE formats supported for Verity-in-fe-safe, which currently include: Ansys results (*.rst) files Abaqus ODB files Nastran OP2 files Only the definition of the lines (and the number of lines) differs from the classic Verity method of Tutorial A; once the software has located the weld lines and extracted the Verity local coordinate system, the Verity method proceeds as before (although there can be some differences in exactly how the though thickness domain has been assigned, and also the assumed plate thickness will default to being determined by the extracted geometry, not the specified nominal thickness). Note that minor differences may also be observed in Verity results due to slight differences in the way that surface normals, and hence the Verity local coordinate system have been extracted. These differences would probably appear on curved sections when using quadratic elements Preparation Start the program by selecting fe-safe from the Windows Start menu (Windows) or by running the script fe-safe (Linux) (see section 5.2 in the fe-safe User Guide). When starting fe-safe, the Configure fe-safe Project Directory dialog appears. The path shown in the Project Directory field is where the fe-safe project directory will reside. The user can either accept the default name and location or enter a more convenient name and location. If an existing project directory is chosen, existing data in that project will be retained. This includes model data, load history files, analysis settings, and more. Reset any existing analysis options to their defaults in the Clear Data and Settings dialog box [Tools >> Clear Data and Settings...] by selecting the Check all option and clicking OK. 168 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

171 Tutorial F: Multiple Solid Weld Lines using Abaqus 11.3 Open the Model Select the Datasets To open the model, select File >> FEA Solutions >> Open Finite Element Model... On the file selection dialog box select the file <DataDir>\weld_fatigue\solid-tubess3_xx.odb and click Open. When prompted Do you want to pre-scan solid-tubes3*.odb click Yes and the Select Datasets to Read pre-scan dialog box will appear: Figure 11-2 The dialog box shows that the last increment in the step contains a dataset containing Stresses (used to generate loading for Verity in fe-safe) and Nodal Forces (used by Verity ). Ensure that both are selected and click OK. The stresses will be extracted from the model and information similar to that shown below will be displayed in the Message Log window. This information is also written to the file <ProjectDir>\Model\reader.log. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 169

172 Tutorial F: Multiple Solid Weld Lines using Abaqus odb_io version :9994 Reads Abaqus 6 ODB databases Copyright Dassault Systemes UK Limited Reading : C:\data\verity\solid-tubess3_610.odb Writing : Pre-scan Strains : Read all (Pre-scanning) ODB interface exe exited with code Pre-scan complete. odb_io completed NOTE : Storing current session macro commands to D:\Data\Users\fe-safe.version.6.3\output\current.macro odb_io version :9994 Reads Abaqus 6 ODB databases Copyright Dassault Systemes UK Limited Reading : C:\Program Files (x86)\safe_technology\fesafe\version.6.3\data\verity\solid-tubess3_610.odb pre-scan Writing : D:\Data\Users\fe-safe.version.6.3\projects\project_01\model\FESAFE.FED Selected position is Element Nodal Strains : Selected datasets Dataset : S From Step : 1 Iteration : 1 Time : 2.22e-16 Title : Direct Min/Max : Shear Min/Max : No. Elements : Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

173 Tutorial F: Multiple Solid Weld Lines using Abaqus When the model has finished loading, the Loaded FEA Models Properties dialog box dialog box appears, as shown in Figure Figure 11-3 Set the Loaded FEA Models Properties to Stress Units of psi and Force Units of lbf and Distance Units of in as shown. Ensure that the units are as shown in Figure 11-3, then click OK. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 171

174 Tutorial F: Multiple Solid Weld Lines using Abaqus If the dialog box dialog box does not appear automatically, then it can be displayed by right-clicking on the icon in the Current FE Models window and selecting Properties: Figure 11-4 A dialog box will show prompting to edit element groups loaded from the model, click No. 172 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

175 Tutorial F: Multiple Solid Weld Lines using Abaqus A summary of the open model appears in the Current FE Models window, showing the loaded datasets and element group information see Figure Figure 11-5 Note: If the window does not appear exactly as shown in Figure 11-5, then expand the tree view to show more details. When a new model is loaded, the output filename automatically defaults to: <ResultsDir>\{source_file_name}Results.{source_file_extension} which in this example is: <ResultsDir>\solid-tubess3_xxResults.odb The output filename can be modified either by manually editing the Output File field in the Fatigue from FEA dialog box, or by clicking the adjacent browse button:. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 173

176 Tutorial F: Multiple Solid Weld Lines using Abaqus 11.4 Fillet Group The only compulsory input to this style of solid weld definition, is that a group must be defined in fe-safe for the weld fillet material (which may comprise in fact several fillets). Sometimes this group may have been loaded automatically with the Finite Element model, for example as one of the existing element set, material or property groups. If so then this group can be selected, but here we assume that the required group has not been identified in the pre-processor and needs to be defined as an elemental group in the fe-safe Group Manager. Using the Group Manager this list of numbers can be used to define the group in order that it be available to the automatic weld line extraction. In this case the weld fillet elements are in the range and (inclusively). This group will not be configured for analysis in the list of Group Parameters, but it will be used below to define the weld. Select FEA Fatigue >> Manage Groups to display the Select Groups to Analyse dialog box. Define a new (elemental) group in the in the Advanced Group Creation area of the dialog box with a Name: Weld_Fillet. Set the value of the group to the series of IDs: , then click the Create Button. The Weld_Fillet (56 elements) group will appear in the list of Unused Groups. Click OK to dismiss the dialog box. Alternatively, a file definition of this group has been provided, in a text file according to the format for User-Defined ASCII group files in fe-safe (see Appendix E of the fe-safe documentation for details). This file is in the data directory of your installation along with the model file for this exercise. To load the group file, select the Load button from the Group Manager dialog box, and select the file <DataDir>\weld_fatigue\solid_tubes3_weld_fillet_group.txt. You may need to change the file type to Text files (*.txt) to locate your required group definition file. Click Open. After selecting the fillet group definition, select Load As Elemental and click OK when prompted, and then click OK to dismiss the Group Manager dialog box when the Weld_Fillet (56 elements) group appears in the list of Unused Groups. Note that if the fillet was already defined in the FEA model file by an existing group, then there would be no need to create a new one 174 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

177 Tutorial F: Multiple Solid Weld Lines using Abaqus 11.5 Define the Weld After the model has been opened the weld locations should be defined prior to evaluation of the structural stresses. This can be done using the Weld Preparation >> Define and Analyse Weld Geometry menu. A new dialog box will be displayed: Figure 11-6 If this is the first time Verity has been used, the weld tree area will most likely be blank. If it is not then use the Delete All button to clear the tree. Click Yes when prompted to delete. To create a weld, click the Add button and select Line Welds (From Weld Fillet Elements) as the type of the weld to be defined. This will add a new weld definition to the tree with the name New Solid Weld: Note: If the New Weld Line does not appear as shown in Figure 11-7, then expand the tree view to show more details, and click the checkbox to show all configuration options. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 175

178 Tutorial F: Multiple Solid Weld Lines using Abaqus Figure 11-7 To edit parameters in the weld tree, select each parameter and click on the Edit button, or double-click the parameter or value. Define each required weld parameter as discussed below: Name Rename the weld line by or double-clicking on the New Line Weld value. This will allow the item to be edited in the tree. Change the weld name to Toes_LG_tube in_tv_tube and press the enter key () to accept it. 176 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

179 Tutorial F: Multiple Solid Weld Lines using Abaqus Fillet Group Double click on the blank Fillet Group value and then select the previously created Weld_Fillet group in the resulting list. Click OK. Figure 11-8 Failure Modes In this analysis we only consider toe failures, so double click on the Auto-detect Fusion Failures and change the setting to Off. The analysis definition is now complete. The analysis definition can also be obtained by using the Open button in the Weld Definition dialog and loading <DataDir>\weld_fatigue\solid_tubes3_solid_weld_toe.wdf (you may need to change the file type filter from.def to.wdf). Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 177

180 Tutorial F: Multiple Solid Weld Lines using Abaqus The updated weld definition dialog box should now look like Figure 11-9 below. Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

181 Tutorial F: Multiple Solid Weld Lines using Abaqus Evaluate the structural stresses Now click Save and analyse and the automatic weld finder for solid welds will identify 4 weld lines along the interface edges between the fillet and the parent tube material. The weld toe element and node domains will be automatically defined along with the associated through thickness nodes (when necessary) for each weld line node. Based on the extracted domains and line geometry, Verity will evaluate the structural stresses. After the structural stresses are calculated, information similar to that shown below will be displayed in the Message Log window. This information is also written to the file <ProjectDir>\Model\verity-diagnostics.log. Number of nodes found on line 0 is 57 Start and end nodes are: n2062, n354 Classification of line 0 is Weld_Line_Surface Number of nodes found on line 1 is 3 Start and end nodes are: n302, n354 Classification of line 1 is Weld_End Number of nodes found on line 2 is 3 Start and end nodes are: n1714, n2062 Classification of line 2 is Weld_End Number of nodes found on line 3 is 57 Start and end nodes are: n267, n1709 Classification of line 3 is Weld_Line_Surface Number of nodes found on line 17 is 2 Start and end nodes are: n17346, n17649 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 179 Classification of line 17 is Fillet_Edge Processing weld Toe_Welds_Tube_Toe_1. Processing weld Toe_Welds_Tube_Toe_2. Processing weld Toe_Welds_Tube_Toe_3. Processing weld Toe_Welds_Tube_Toe_4. Processing forces dataset 1.1 at time 2.22e-016. Processing forces for weld Toe_Welds_Tube_Toe_1. Processing forces for weld Toe_Welds_Tube_Toe_2. Processing forces for weld Toe_Welds_Tube_Toe_3. Processing forces for weld Toe_Welds_Tube_Toe_4.

182 Tutorial F: Multiple Solid Weld Lines using Abaqus Saving structural stresses to FED file... Verity stress generation and import completed. Analysis of welds took seconds. The structural stresses evaluated by Verity have been merged in with the stresses read by fe-safe and a new group named WELD[Toe] has been created, which appears in the Group Parameters area of the Analysis Settings tab. A summary of the Verity analysis run can be found in the verity-diagnostics.log file (Weld Preparation>> ViewStructural Stress Diagnostics Log menu) and a table of the structural stresses calculated can be found in the verity-ss.txt file (Weld Preparation>> View Structural Stress File menu). The automatically located toe weld domains are displayed in red in Figure Note that the Wrap Around Angle parameter offers further control of exactly which elements are included around the ends of the weld line (see 3.1.2). Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

183 Tutorial F: Multiple Solid Weld Lines using Abaqus Set the Wrap Around Angle parameter to 90 to achieve the correct weld domain for the topmost and bottommost weld lines shown. Note: a warning containing the information that an item in the definition that has no instance defined, may be displayed. fe-safe will try to accommodate for the lack of instance, which should allow the tutorial to continue without issue Analyse the Model After evaluating the structural stresses using Verity we should have a group named WELD[Toe] in the Group Parameters area of the Fatigue from FEA window. The material will have defaulted to the mean weld master S-N curve called Steel Weld 50% The Algorithm will have defaulted to SSM-Normal:- None. In this tutorial the mean life curve will be used for the weld. The remainder of the model will not be analysed as we are only interested in the weld in this context (see Tutorial A if the entire model is to be analysed) Define the Loading The loading will be a fully reversed load with R=-1. We will cycle between the stresses in the dataset multiplied by 1 and multiplied by 1. This is the normal default loading in fe-safe, so some of the following steps may not be necessary. dialog box In the Current FE Models window, select the stress dataset corresponding to step 1 increment 1 of the loaded FE model: Dataset 1: (1.1) S : Stress. On the Fatigue from FEA dialog box select the Loading Settings tab to switch to the loading tree. Right mouse click on the loadings tree and select Clear all loadings to remove any existing loading. Click Yes when prompted to Delete Loadings. Click the Add... button and then select the A user-defined LOAD * dataset. Click OK when prompted with the Automatic Block Creation dialog box. In the Dataset Embedded Load History dialog box, specify 1 and 1 in the Loading Scale box: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 181 Figure 11-11

184 Tutorial F: Multiple Solid Weld Lines using Abaqus Click OK. This will add an item to the newly created Elastic Block as shown: Figure Select the Analysis Settings tab from the Fatigue from FEA dialog box to switch to the main settings Limit analysis to the weld toe groups In the Group Parameters table, select all of the groups except the WELD[Toe] group and right-click the Algorithm column and select Edit. In the displayed dialog box select Do Not Analyse and click OK Figure This tutorial uses the default material, Steel Weld (50%). Check the other options to make sure no more adjustments are required. 182 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

185 Tutorial F: Multiple Solid Weld Lines using Abaqus Perform the Analysis The Fatigue from FEA dialog box should now look similar to Figure 11-14: Figure The Output File field will have defaulted to a new.odb file. To start the analysis, click the Analyse button. A summary of what you have defined is displayed. Click Continue and the analysis will start. As the analysis is being performed the worst life so far is displayed in the Message Log window. Summary ======= Worst Life-Repeats : at Element 15.5 Analysis time : 0:00: Fatigue Analysis Completed. The analysis log shows that the worst-case life for the four toe domains is: repeats of the loading, at element 15, node 5. A copy of the original.odb file was created, onto which a new step containing the fatigue results was appended. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 183

186 Tutorial F: Multiple Solid Weld Lines using Abaqus The exported fatigue results in the file contain the log10(life) contour of fatigue lives, which should look similar to: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

187 Tutorial H: Multiple Solid Weld Lines using Ansys 12 Tutorial G: Automatic weld finder for Solid Welds (Using Ansys) 12.1 Introduction This tutorial outlines an alternative way of analysing solid weld lines in an Ansys.rst file using Verity. The intention is to provide a simpler way of defining the weld domain and weld lines, especially when multiple weld lines are to be analysed, or several different failure modes (Toe, Fusion, Throat, Root). Figure 12-1 shows the solid hexahedral model with two rows of elements through the thickness. Note that this is the same model as was used in Tutorial B (See section 8 above). The difference here is that instead of inputting the weld domain and detailed information on the weld line nodes for each line and failure mode, the weld fillet material is defined as a group instead. The various weld lines and weld domains are then automatically computed by fe-safe, although it is still necessary to provide a domain group for root failures. Note that as well as the fillet displayed on the underside of the intersecting tubes, there is a similar fillet on the upper side (occluded in Figure 12-1). Both weld fillets can be supplied as a single fillet group and the software will automatically locate the separate lines in the two fillets. fe-safe locates potential weld lines by connecting up nodes with edges lying along the interface between fillet and non-fillet elements. Note that this will typically produce some spurious short potential weld lines on the edges of the weldends. However these are rejected, because they form closed loops including a fillet edge, and will be labelled as Weld_End lines in the fe-safe message logs. The root lines are also located, either because these are formed from internal surface nodes in fully penetrative welds, or lie on a fillet-parent material interface where there are two faces with significant change in normal direction. This analysis is based upon a solid hexahedral model with two rows of elements through the thickness. Figure 6-1 shows the model: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 185

188 Tutorial H: Multiple Solid Weld Lines using Ansys Figure 12-1 The tutorial uses an Ansys RST model. However, the same techniques can be applied to all FE formats supported for Verity-in-fe-safe, which currently include: Ansys results (*.rst) files Abaqus ODB files Nastran OP2 files Only the definition of the lines differs from the classic Verity method of Tutorial B; once the software has located the weld lines and extracted the Verity local coordinate system, the Verity method proceeds as before (although there can be some differences in exactly how the though thickness domain has been assigned, and also the assumed plate thickness will default to being determined by the extracted geometry, not the specified nominal thickness). Note that minor differences may also be observed in Verity results due to slight differences in the way that surface normals, and hence the Verity local coordinate system have been extracted. These differences would probably appear on curved sections when using quadratic elements Preparation Start the program by selecting fe-safe from the Windows Start menu (Windows) or by running the script fe-safe (Linux) (see section 5.2 in the fe-safe User Guide). When starting fe-safe, the Configure fe-safe Project Directory dialog appears. The path shown in the Project Directory field is where the fe-safe project directory will reside. The user can either accept the default name and location or enter a more convenient name and location. 186 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

189 Tutorial H: Multiple Solid Weld Lines using Ansys If an existing project directory is chosen, existing data in that project will be retained. This includes model data, load history files, analysis settings, and more. Reset any existing analysis options to their defaults in the Clear Data and Settings dialog box [Tools >> Clear Data and Settings...] by selecting the Check all option and clicking OK Open the Model Select the Datasets To open the model, use the File >> FEA Solutions >> Open Finite Element Model... menu, select the file <DataDir>\weld_fatigue\t-tube_sld_v12.rst and click Open. When prompted Do you want to pre-scan t-tube_sld_v12.rst click Yes and the Select Datasets to Read pre-scan dialog box will appear: Figure 12-2 The dialog box shows that there is a dataset containing stresses, strains, temperatures and forces. Ensure that Forces and Stress datasets are selected and click OK. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 187

190 Tutorial H: Multiple Solid Weld Lines using Ansys The selected datasets will be extracted from the model. Once this process is complete, the Loaded FEA Models Properties dialog box dialog box appears, as shown in Figure Figure 12-3 Set the Loaded FEA Models Properties to Stress Units of psi and Force Units of lbf and Distance Units of in as shown. Ensure that the units are as shown in Figure 12-3, then click OK. 188 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

191 Tutorial H: Multiple Solid Weld Lines using Ansys If the dialog box dialog box does not appear automatically, then it can be displayed by right-clicking on the icon in the Current FE Models window and selecting Properties: Figure 12-4 Ensure that the units are as shown in Figure 12-3, then click OK. A dialog box will appear prompting to edit element groups loaded from the model, click No Fillet Group The only compulsory input to this style of solid weld definition, is that a group must be defined in fe-safe for the weld fillet material (which may comprise in fact several fillets). Sometimes this group may have been loaded automatically with the Finite Element model, for example as one of the existing material groups. If so then this group can be selected, but here we assume that the required group has been defined in a text editor but needs to be loaded into the fe-safe Group Manager, in order that it be available to the automatic weld line extraction. The file should contain a list of element identifiers for the fillet material (NOT the weld domain!), in a text file according to the format for User-Defined ASCII group files in fe-safe (see Appendix E of the fe-safe documentation for details). A file is provided in the data directory of your installation along with the model file for this exercise. The group contains the following elements representing the weld fillet material: GROUP both_fillets , , END Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 189

192 Tutorial H: Multiple Solid Weld Lines using Ansys Select FEA Fatigue >> Manage Groups to display the Select Groups to Analyse dialog box. To load the User-Defined ASCII group file, select the Load button from the Group Manager dialog box, and select the file <DataDir>\weld_fatigue\t-tube_sld_both_fillets_group.txt. You may need to change the file type to Text files (*.txt) to locate your required group definition file. click Open. After selecting the fillet group definition, select Load As Elemental and click OK when prompted. The group both_fillets (180 elements) will appear in the list of Unused Groups. Click OK to dismiss the dialog box. Note that if the fillet was already defined in the FEA model file by an existing group, then there would be no need to create a new one 12.5 Define the Welds After the model has been opened the weld locations should be defined prior to evaluation of the structural stresses. This can be done using the Weld Preparation >> Define and Analyse Weld Geometry menu. A new dialog box will be displayed: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

193 Tutorial H: Multiple Solid Weld Lines using Ansys If this is the first time Verity has been used, the weld tree area will most likely be blank. If it is not then use the Delete All button to clear the tree. Click Yes when prompted to delete. To create a weld, click the Add button and select Line Welds (From Weld Fillet Elements) as the type of the weld to be defined. This will add a new weld definition to the tree with the name New Line Welds: Note: If the New Line Welds options do not appear as shown in Figure 12-6, then expand the tree view to show more details, and click the checkbox to show all configuration options. Figure 12-6 To edit parameters in the weld tree, select each parameter and click on the Edit button, or double-click the parameter or value. Define each required weld parameter as discussed below: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 191

194 Tutorial H: Multiple Solid Weld Lines using Ansys Fillet Group Double click on the blank Fillet Group value and then select the previously loaded both_fillets group. Click OK. Figure 12-7 Failure Modes By default Toe failures are automatically enabled, but for this tutorial we will analyse both Toe and Fusion failure modes, so double click the Auto-Detect Fusion Failures value fields, and select On from the drop-down menu box which then appears. Ensure that the Shell Root Failures and Throat failures are set to off. If not, double click the fields and change the value. The analysis definition can also be obtained by using the Open button in the Verity definition dialog and loading <DataDir>\weld_fatigue\t-tube_sld_solid_weld_toe-fusion.wdf (you may need to change the file type filter from.def to.wdf). 192 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

195 Tutorial H: Multiple Solid Weld Lines using Ansys The updated weld definition dialog box should look like Figure 12-8 below. Figure 12-8 Evaluate the structural stresses The weld definition for both fillets is now complete fe-safe will extract the weld lines and domains automatically. Note that nodes will be added to the weld domain either until a specified plate thickness is reached, or a surface is reached, or any optionally specified domain is exhausted. In this case we simply want to go all the way through the (hollow) tubes, so it is not necessary to specify any plate thickness. Click Save and Analyse. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 193

196 Tutorial H: Multiple Solid Weld Lines using Ansys The weld toe element and node domains will be automatically defined along with the associated through thickness nodes (when necessary) for each weld line node. Based on the extracted domains and line geometry, Verity will evaluate the structural stresses. After the structural stresses are calculated, information similar to that shown below will be displayed in the Message Log window. This information is also written to the file <ProjectDir>\Model\verity-diagnostics.log. Number of nodes found on line 0 is 5 Start and end nodes are: n5, n6245 Classification of line 0 is Weld_End Number of nodes found on line 1 is 61 Start and end nodes are: n25181, n6245 Classification of line 1 is Weld_Line_Surface Number of nodes found on line 2 is 5 Start and end nodes are: n7, n5 Classification of line 2 is Weld_End Number of nodes found on line 17 is 3 Start and end nodes are: n28653, n34263 Classification of line 17 is Fillet_Edge Weld Element Domains: Domain: 1 Name: both_fillets Elements: , , , Output Parameters: Output Directory: C:\installations\user_directories\fesafe.version.2016_15943\projects\project_07\jobs\job_01\fe-results Output Printed Structural Stresses to file verity-ss.txt Processing weld New Line Welds_Toe_1. Processing weld New Line Welds_Toe_2. Processing weld New Line Welds_Toe_3. Processing weld New Line Welds_Toe_4. Processing weld New Line Welds_Fusion_1. Processing weld New Line Welds_Fusion_2. Processing weld New Line Welds_Fusion_3. Processing weld New Line Welds_Fusion_4. Processing forces dataset 1.1 at time 1. Processing forces for weld New Line Welds_Toe_1. Processing forces for weld New Line Welds_Toe_2. Processing forces for weld New Line Welds_Toe_3. Processing forces for weld New Line Welds_Toe_ Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

197 Tutorial H: Multiple Solid Weld Lines using Ansys Processing forces for weld New Line Welds_Fusion_1. Processing forces for weld New Line Welds_Fusion_2. Processing forces for weld New Line Welds_Fusion_3. Processing forces for weld New Line Welds_Fusion_4. Saving structural stresses to FED file... Verity stress generation and import completed. Analysis of welds took 0.18 seconds. In total, 8 weld lines have been analysed by Verity consisting of two Toe and two Fusion failure modes on both fillets. The structural stresses evaluated by Verity have been merged in with the stresses read by fe-safe and two new groups named WELD[Fusion] and WELD[Toe] have been created. A summary of the Verity analysis run can be found in the verity-diagnostics.log file (Weld Preparation >> ViewStructural Stress Diagnostics Log menu) and a table of the structural stresses calculated can be found in the verity-ss.txt file (Weld Preparation>> View Structural Stress File menu). The automatically determined Toe domains are illustrated in Figures and Two Weld groups have been added to the analysis panel (for Toe and Fusion failures). The analysis panel will look as follows: Figure 12-9 Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 195

198 Tutorial H: Multiple Solid Weld Lines using Ansys Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

199 Tutorial H: Multiple Solid Weld Lines using Ansys Figure Analyse the Model After evaluating the structural stresses using Verity we should have the two groups named WELD[Fusion] and WELD[Toe] in the groups parameters area of the Fatigue from FEA window. The material will have defaulted to the 50% failure equivalent structural stress S-N curve, and the algorithm to SSM-Normal. In this tutorial the mean life curve will be used for the weld. The remainder of the model will be configured for no analysis Define the Loading The loading will be a fully reversed load with R=-1. We will cycle between the stresses in the dataset multiplied by 1 and multiplied by 1. This is the normal default loading in fe-safe, so some of the following steps may not be necessary. In the Current FE Models window, select the stress dataset corresponding to step 1 increment 1 of the loaded FE model: Dataset 1: (1.1) S : Stress. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 197

200 Tutorial H: Multiple Solid Weld Lines using Ansys On the Fatigue from FEA dialog box select the Loading Settings tab to switch to the loading tree. Right mouse click on the loadings tree and select Clear all loadings to remove any existing loading. Click Yes when prompted to Delete Loadings. Click the Add... button and then select the A user-defined LOAD * dataset. Click OK when prompted with the Automatic Block Creation dialog box. In the Dataset Embedded Load History dialog box, specify 1 and 1 in the Loading Scale box: dialog box Figure Click OK. This will add an item to the newly created Elastic Block as shown: Figure Select the Analysis Settings tab from the Fatigue from FEA dialog box to switch to the main settings. 198 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

201 Tutorial H: Multiple Solid Weld Lines using Ansys Limit analysis to the Weld groups Select the non-weld groups in the Algorithm column,right-click the Algorithm column and select Edit. In the displayed dialog box select Do Not Analyse and click OK. Figure Click OK. This tutorial uses the default material, Steel Weld (50%). Check the other options to make sure no more adjustments are required; Perform the Analysis the Fatigue from FEA dialog box should now look similar to the following: Figure Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 199

202 Tutorial H: Multiple Solid Weld Lines using Ansys The results filename will have defaulted to a new.rst file. To start the analysis, click the Analyse button. A summary of what you have defined is displayed. Click Continue and the analysis will start. As the analysis is being performed the worst life so far is displayed in the Message Log window. Summary ======= Worst Life-Repeats : at Element Analysis time : 0:00: The analysis log shows that the worst-case life for the eight weld domains is: repeats of the loading, at element 2809, node 3. A copy of the original.rst file excluding the original steps was created, onto which a new step containing the fatigue results was written. The exported fatigue results are written to the Ansys variable SX and contain the log10(life) contour of fatigue lives, which should look similar to Figure and Figure Both sides of the welding are visible in Figure 12-17, but the model loading was applied from the left end, so the left side (seen in Figure 12-16) has the lowest life elements (seen in red). Note that the values appearing on the surface of the fillet are from the Fusion failure analysis. 200 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

203 Tutorial H: Multiple Solid Weld Lines using Ansys Figure Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 201

204 Tutorial H: Multiple Solid Weld Lines using Ansys Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

205 Tutorial H: Multiple Solid Weld Lines using Ansys 13 Tutorial H: Automatic Weld Finder for Shell Welds (Using Nastran) 13.1 Introduction This tutorial outlines how to analyse welded structures in a Nastran.op2 file using the fe-safe shell weld finder and Verity. See also Tutorial C, in which the legacy manual line definitions are used to perform a similar analysis.. Figure 13-1 shows a linear shell model which is based on models created for the SAE Fatigue Challenge in 2003 and Figure 13-1 The weld line definitions will be generated from a group of weld fillet elements (yellow material above). Whereas the legacy line definition required a separate complex line definition for each weld line and failure mode, the weld finder only needs a group of all fillet elements. The weld finder then locates weld lines and determines all other information needed. The located domains in this example will be analysed for weld fatigue at toes. The remainder of the model (except the weld material shown in yellow) will be analysed using a local strain approach and the material Manten steel. The tutorial uses a Nastran OP2 model. However, the same techniques can be applied to all FE formats supported for Verity-in-fe-safe, which currently include: Ansys results (*.rst) files Abaqus ODB files Nastran OP2 files Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 203

206 Tutorial H: Multiple Solid Weld Lines using Ansys 13.2 Preparation Start the program by selecting fe-safe from the Windows Start menu (Windows) or by running the script fe-safe (Linux) (see section 5.2 in the fe-safe User Guide). When starting fe-safe, the Configure fe-safe Project Directory dialog appears. The path shown in the Project Directory field is where the fe-safe project directory will reside. The user can either accept the default name and location or enter a more convenient name and location. If an existing project directory is chosen, existing data in that project will be retained. This includes model data, load history files, analysis settings, and more. Ensure that the following basic settings are correctly configured. If fe-safe is being run for the first time then it is possible to skip this preparatory section. Start a new project, if an existing project is loaded select [File >> Project >> New Project ] and choose a new location for a project Open the Model Select the datasets To open the model, use the File >> FEA Solutions >> Open Finite Element Model... menu, select the file <DataDir>\weld_fatigue\t-tube_2k4_pn2.op2 and click Open. This will display the Select Datasets to Read pre-scan dialogue: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

207 Tutorial H: Multiple Solid Weld Lines using Ansys The dialog box shows that there is a dataset containing stresses, strains, temperatures and forces. For this tutorial make sure that Forces and Stress datasets are selected so that the weld can be analysed using Verity and the rest of the model can be analysed using fe-safe, then click OK. The selected datasets will be extracted from the model. Once this process is complete, the Loaded FEA Models Properties dialog box dialog box appears, as shown in Figure 8-3. Figure 13-3 Ensure that the units are as shown in Figure 8-3, then click OK. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 205

208 Tutorial H: Multiple Solid Weld Lines using Ansys A dialog box will appear prompting to edit element groups loaded from the model, click Yes. Figure 13-4 Use the button to move the group associated with Property 3 (property definition 3 in the Nastran input file) which represents the elements in the weld fillet, and the group associated with Matierial 1 which represents all elements in the whole model with material definition 1. The Default group will be used to limit analysis in the weld elements which are not part of the remaining Property 1 and Property 2 groups. Click OK. If the Current FE Models Properties dialog box dialog box does not appear automatically, then it can be displayed by right-clicking on the icon in the Current FE Models window and selecting Properties. If the Edit Group List prompt does not appear, the Select Groups to Analyse dialog box can be opened using FEA Fatigue >> Manage Groups menu selection. 206 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

209 Tutorial H: Multiple Solid Weld Lines using Ansys Define the welds After the model has been opened the weld locations should be defined prior to evaluation of the structural stresses. This can be done using the Weld Preparation>> Define and Analyse Weld Geometry menu. A new dialog box will be displayed. Initially this may contain the weld definitions that were used in a previous Verity run (e.g. a previous Tutorial): Figure 13-5 These welds will not be needed, unless you are re-running the same job. Use the Delete All button to clear the tree, and click OK when prompted. For this tutorial, click the Add button, and then select the Line Welds (From Weld Fillet Elements) option A new weld finder definition will appear called New Line Welds. Double click on the name and change it to TV_to_LG_tube. Click on the arrow icon to expand the property tree so that you can set the fillet group. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 207

210 Tutorial H: Multiple Solid Weld Lines using Ansys Figure 13-6 Double-click on the Fillet Group field to obtain the group selection dialog, and then select Property 3 as the group (see Figure 13-1 for groups). Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

211 Tutorial H: Multiple Solid Weld Lines using Ansys This completes the weld definition, as shown below in Figure Select the Merge all groups into WELD group checkbox, deselect the Output Extensive Diagnostics checkbox, then click Save and Analyse, which will generate the weld line definitions and associated element domains, and then invoke Verity to calculate their associated structural stresses. A group will be created called WELD[Toe]. Information similar to that shown below will appear in the Message Log, and in the structural stress diagnostics log (file <ProjectDir>\Model\verity-diagnostics.log). Verity Diagnostic Log Deleting Verity warning groups: Weld Element Domains: Domain: 1 Name: Property 3 Elements: , Output Parameters: Output Directory: E:\testprojects\Verity\shelltut\jobs\job_01\fe-results Output Printed Structural Stresses to file verity-ss.txt Verity structural stress file backed up to E:\testprojects\Verity\shelltut\model\verity-ss.arc. Processing weld TV_to_LG_tube_1[Toe]. Processing weld TV_to_LG_tube_2[Toe]. Processing weld TV_to_LG_tube_3[Toe]. Processing weld TV_to_LG_tube_4[Toe]. Processing forces dataset 1.1. Processing forces for weld TV_to_LG_tube_1[Toe]. Processing forces for weld TV_to_LG_tube_2[Toe]. Processing forces for weld TV_to_LG_tube_3[Toe]. Processing forces for weld TV_to_LG_tube_4[Toe]. Saving structural stresses to FED file... Verity stress generation and import completed. Analysis of welds took seconds Analyse the Model After evaluating the structural stresses using Verity there should be a group called WELD[Toe] in the Fatigue from FEA window. The algorithm will have defaulted to SSM-Normal (SSM means Structural Stress Method), and the material will have defaulted to the 50% failure equivalent structural stress S-N curve. The remainder of the base materials will be configured for analysis with Manten steel. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 209

212 Tutorial H: Multiple Solid Weld Lines using Ansys Define the loading The loading will be constant amplitude zero mean loading (this is sometimes referred to as R=-1). We will cycle between the stresses in the dataset multiplied by 1 and multiplied by 1. On the Fatigue from FEA dialog box select the Loading Settings tab to switch to the loading tree. Right mouse click on the loadings tree and select Clear all loadings to remove any existing loading. Select the dataset named Dataset 1: (1.1) S : Stress from the Current FE Models window. Click the Add... button and then select the A user-defined LOAD * dataset. Specify 1 and 1 in the Loading Scale box: Figure 13-6 Click OK. This will add an item to the loading as shown: Figure 13-7 Select the Analysis Settings tab from the Fatigue from FEA dialog box to switch to the main settings. 210 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

213 Tutorial H: Multiple Solid Weld Lines using Ansys Define the algorithm In the Group Parameters table double-click the Algorithm column and in the displayed dialog box select Analyse with Material s default Algorithm and click OK. This will configure all applicable groups to use the algorithm best suited to the selected material. Double-click the cell defining the Default group in the Algorithm column and select Do not analyse and click OK Define the materials From the Material Databases window in the local.dbase file select the material SAE_950C-Manten material and in the Group Parameters table select the Property 1 and Property 2 groups, then right click and select Edit. You will be asked if you wish to set the material, click Yes. Check the other options to make sure no more adjustments are required; the Fatigue from FEA dialog box should now look similar to the following: Figure Perform the analysis To start the analysis, click the Analyse button. A summary of what you have defined is displayed. Click Continue and the analysis will start. As the analysis is being performed the worst life so far is displayed in the Message Log window, ended with the followng summary. Summary ======= Worst Life-Repeats : at Element :1 Analysis time : 0:00: Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 211

214 Tutorial H: Multiple Solid Weld Lines using Ansys This shows the worst model life or repeats occurred at element 1262 node 4, bottom layer. A copy of the original.op2 file excluding the original steps was created, onto which a new step containing the fatigue results was written Specific line analysis The next section shows how the weld finder can be configured to create more specific line groups, so that different master S-N curves can be assigned. Suppose that it is desired to analyse the weld toes on the TV tube with the 50% Steel-Weld mean material, whilst the toes on the LG tube require the more conservative 2.2% failure equivalent structural stress S-N curve. This requires us to generate individual line groups that allow this distinction. Unchecking the Merge all groups into WELD group checkbox on the Weld Definition dialog would generate four separate line groups, but the group naming in terms of line index counts does not make it immediately apparent which lines are from the TV tube, and which from the LG. For this it is necessary to provide two separate weld finder definitions. Each definition uses the same fillet material group, but the toe domains are specifically defined as coming from the TV tube or LG Tube respectively. Note that the domain groups provided to the weld finder will be the complete set of all elements in the TV or LG tube (Property 2 or Property 1 groups respectively). It is not necessary to restrict the domain group to only the actual weld domain, as this will still be determined by the weld finder; but the domain definition restricts the weld finder selection to those elements contained in the defined domain. This contrasts with the Legacy Line Definition, which would require the specific weld domain. 212 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

215 Tutorial H: Multiple Solid Weld Lines using Ansys Define the line welds Reopen the Weld Definition dialog (Weld Preparation > Define and Analyse Weld Geometry ), and press the Delete All button to remove the previous definition. Click Add.. then select Line Welds (From Weld Fillet Elements) to create a new weld definition. Double click on the default name of New Line Welds and change it to TV_to_LG_tube_in_TV_tube to create a definition for the TV tube. Repeat the process to create a definition for the LG tube, modifying the weld definition name to TV_to_LG_tube_in_LG_tube_open. Expand the tree for each definition in turn and select the Fillet Group to be group Property 3 as before to obtain the definitions below. Figure 13-1 Next deselect the Merge all groups into WELD group checkbox so that individual line groups will be created. In order to associate each definition with its respective tube, it is necessary to set the Toe Domain for each. Click the Show all configuration options checkbox which will extend the options displayed. In the first TV_to_LG_tube_in_TV_tube, double click on the Toe Domain value field, and select Property 2 (the TV tube) from the disaplyed list of element groups. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 213

216 Tutorial H: Multiple Solid Weld Lines using Ansys This results in the definition below: Figure Similarly set the Toe Domain Group for the LG Tube in TV_to_LG_tube_in_LG_tube_open to be Property 1. This weld definition configuration may also be obtained by opening (click Open ) weld definition file <DataDir>\weld_fatigue\t-tube_2k4_pn2_auto.wdf. Click Save and analyse to invoke the weld finder s generation of the line definitions, and their consequent processing by Verity to generate structural stresses and associated fe-safe analysis groups. 214 Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

217 Tutorial H: Multiple Solid Weld Lines using Ansys Analyse the Model After running the weld finder and evaluating the structural stresses using Verity we should have four groups starting with WELD in the Fatigue from FEA window, one for each individual line. The algorithm will have defaulted to SSM-Normal, and the material will have defaulted to the 50% failure equivalent structural stress S-N curve for both groups. The analysis panel should look as below. Figure This default weld material will suffice for the toe of the TV tube, whilst the toe on the LG tube will need to be represented by the 2.2% failure equivalent structural stress S-N curve. The remainder of the base materials will be configured for analysis with Manten steel. Figure Define the materials From the Material Databases window in the local.dbase file select the material SAE_950C-Manten material and in the Group Parameters table double-click the column titled Material. You will be asked if you wish to set the material, click Yes. Figure 8-12 shows the current list of S-N curves in the Verity database. This tutorial uses the default material, Steel Weld (50%) for the two_tv_to_lg_tube_in_tv_tube derived line element groups and Steel Weld -2SD (2.2%) for the two_tv_to_lg_tube_in_lg_tube_open line element groups. Copyright 2016 Dassault Systemes Simulia Corp. Verity in fe-safe V2 User Manual 215

218 Tutorial H: Multiple Solid Weld Lines using Ansys Figure From the Material Databases window in the verity.dbase file select the Steel Weld -2SD (2.2%) material and in the Group Parameters table double-click on the cell defining the WELD_TV_to_LG_tube_in_LG_tube_open _3[Toe] group in the column titled Material. Click Yes. Then repeat similarly for the other TV_to_LG_tube_in_LG_tube_open derived weld group. Check the other options to make sure no more adjustments are required; the Fatigue from FEA dialog box should now look similar to the following: Figure Verity in fe-safe V2 User Manual Copyright 2016 Dassault Systemes Simulia Corp.

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