MSC.Software: Product Brief - MSC Fatigue. MSC Fatigue PRODUCT BRIEF

Transcription

1 MSC Fatigue PRODUCT BRIEF

2 PRODUCT BRIEF Welcome to MSC Fatigue The Problem: Fatigue Fracture Some estimates put annual costs due to premature fatigue fractures in structural components at well over $100 billion. Yet testing against repeated loading cycles, sometimes millions of times over, is often too expensive and time consuming to be practical. Finite element analysis programs can tell you where stress hot spots exist, but on their own can t tell you whether those hot spots are critical areas for fatigue failure, or when fatigue might become a problem. To avoid contributing further to this statistic many manufacturers simply accept long prototype development cycles, overweight components, unpredictable warranty claims, and loss of customer confidence. The Solution: MSC Fatigue MSC Fatigue enables durability engineers to quickly and accurately predict how long products will last under any combination of timedependent or frequency-dependent loading conditions. Benefits include reduced prototype testing, fewer product recalls, lower warranty costs and increased confidence that your product designs will pass required test schedules. MSC Fatigue Summary MSC Fatigue is a Finite Element (FE) based durability and damage tolerance solver that enables users with minimal knowledge of fatigue to perform comprehensive durability analysis. High-cycle fatigue, low-cycle fatigue and crack growth problems can all be addressed. All MSC Fatigue pre and post-processing is done within the Patran environment. This provides easy access to all analysis options of MSC Fatigue. Job setup and submittal is done through an easy-to-use graphical interface creating a single environment for durability analysis. Results post-processing gives insight into, and identification of, fatigue problem areas allowing for in-depth understanding of model response to changes in fatigue design parameters. Two MSC Fatigue packages are available, each with their own set of functional modules that are described in this document. MSC Fatigue Basic Package: Basic Stress Life and Strain Life Strain Gauge MSC Fatigue Advanced Package: Multiaxial Vibration Fatigue Fracture Spot Weld Wheels Utilities MSC Fatigue Basic Package The MSC Fatigue Basic Package contains foundational functions such as pre and post processing capabilities that include supporting loads and materials databases. It also includes two analysis modules: the Basic Stress Life and Strain Life module and the Strain Gauge module. Pre-Processing All MSC Fatigue pre processing is done within the Patran environment. General capabilities exist for easy viewing and manipulation of models: Groups - break the model up into various sections for application of different material and surface finish/treatment combinations Model manipulation - rotate, pan, and zoom Multiple graphical viewports Various rendering styles (wireframe, hidden line, shaded) and display properties General utilities for coordinate frame creation, node and element attributes Associate time or frequency varying loads to FE load cases Easily set up fatigue analysis parameters All documentation is on-line Loading Multiple FE load cases with associated time variations can be defined and applied simultaneously. A time history database is supplied to facilitate creation and storage of these files. Features include: Up to 500 simultaneously applied load cases Load magnitude definition for normalizing FE results Scale factors (stress concentration definitions) Offsets (constant residual stress definition) Static load cases (variable residual stress definitions across model) Results transformations (global system or surface resolved) 2

3 PRODUCT BRIEF Time History Database The time history database provides the following: Central and local storage of time histories Creation and modification of time histories from: ASCII file import (XY and rainflow matrix data) XY point specification Graphical interaction Wave form definitions (sine, triangular, square) Block definitions Rainflow matrix creation from time series data Graphical plots and hard copies of time history and matrix data including multiple file display, cross plots, and overlays Data transformations Polynomial transforms Lookup tables Unit conversions Sample rate adjustments Peak valley slicing extraction Material Database A materials database manager stores and manipulates a library of cyclic material properties. Features include: Approximately 200 materials (metals) supplied Strain-life curves Cyclic stress-strain curves Add, create, or modify your own or supplied materials data (Imperial & SI units supported) Generate materials data from UTS & E Graphical display of: Cyclic and monotonic stress/strain curves Strain-life curves Material change assessments Reverse searches on material to meet design life Elastic-plastic lines Graphical display, hard copies, and tabular comparison of materials Up to 4000 different material/finish combinations per model Post-Processing All MSC Fatigue post processing is done within the Patran environment. Results Access Fatigue analysis is performed using stress or strain results from FE models. Results access features include FE results data from: Patran database Linear static (stresses and strains) Linear transient (stresses and strains) Includes results from MSC Nastran, Marc, ANSYS, Abaqus, and any other Patran-supported analysis codes MSC Nastran (xdb) database (linear static and transient stresses) External result files Patran nodal and elemental result files Patran FEA result files No limit on number of node or element calculation points Post Processing Options Results from MSC Fatigue analyses, as well as imported FE results (described above), can be post processed in a variety of ways: Scalar icon plots, fringe plots, contour plots, and text reports of: Linear static (stresses and strains) Damage (linear and log scale) Life in repeats or user defined units (linear and log scale) Factor of safety Biaxial assessment parameters Sensitivity (XY) plots of scale factors, residual stresses, certainty of survival Quick graphical identification of most damaged location, worst safety factor, and most biaxiality Access to materials database, time history managers, compliance libraries and single location analyzers. Other comprehensive capabilities for postprocessing FE results include: Postprocessing capabilities of FE results (stresses, strains, displacements, etc.) Deformed plots Contour plots Marker plots (vector, tensor, scalar icon, value) Iso surfaces and streamlines Graphs (XY plots) Results derivations and combinations Text reports Animation Post-Processing Pre-Processing 3

4 PRODUCT BRIEF Basic Stress Life and Strain Life Module This module uses stress or strain results from finite element (FE) models, variations in loading, and cyclic material properties to estimate life-to-failure. Both the traditional total life method, also known as the stress-life (S-N) method, and the crack initiation method, also known as the local strain-life (e-n) method, are available. Features common to both methods include: Temperature corrected analysis Scale factors (stress concentration definitions) Offsets - Static load cases Aerospace load spectrum generation Sensitivity studies of the following can be performed: Multiple scale factors (stress concentrations) Multiple residual stress values Multiple probabilities of failures (design criteria) Surface finish/treatment Mean stress correction methods Change materials or surface finish/treatment Material searches based on design life Stress-Life (S-N) Method The total life method, more commonly known as the stress life or S-N method, typically makes no distinction between crack initiation and growth, but rather, predicts the total life to failure. Features include: Goodman or Gerber mean stress correction Welded Structure Analysis to BS7608 Material and Component S-N Curves Strain Life Method (e-n) Sophisticated crack initiation or strain-life (e-n) modeling provides a method for estimating life to the initiation of a crack. Crack initiation features include: Neuber elastic-plastic correction Advanced elastic-plastic correction - Mertens-Dittman or Seeger-Beste methods Cyclic stress-strain tracking using Masing s hypothesis and material memory modeling Smith-Watson-Topper and Morrow mean stress correction Advanced biaxial corrections (for proportional loading) based on Parameter Modification or Hoffman-Seeger What If Analysis A single location analyzer can be used for what if studies after a global analysis has identified critical locations. Results include: Damage (reported in linear and log form) Life (reported in linear and log form) Life reported in user defined units Multiaxial assessment parameters Biaxiality ratio, standard deviation of biaxiality ratio Most popular angle (maximum principal stress to local x-axis) Mobility of angle (maximum principal stress to local x-axis) Factor of safety Stress history output Cycle and damage histogram plots Back calculations can be made based on design life of: Scale factor (stress concentration) Residual stress Probability of failure (design criterion) Resulting life contours on a component Sensitivity plot: load vs. life Strain Gauge Module This module allows the creation of virtual software strain gauges within an MSC Nastran finite element (FE) model. These gauges can be used to produce analytical response time histories from the FE model under the effect of multiple time varying applied loads. Stress and strain time histories may be extracted at any point on the FE model surface, based on either standard or user-defined strain gauge definitions. The results obtained from the software strain gauge may be based on static, transient, or quasi-static FE loadings. Strain Gauge Definition The software strain gauges are defined as FE groups, each containing from one to three elements. All standard strain gauge definitions are supported in both planar and stacked formulations. User defined gauges may also be created, with definitions stored in a gauge definition file. 4

5 PRODUCT BRIEF Strain Gauge Implementation The virtual strain gauges are positioned on the FE model surface, with the gauge aligned in any orientation and the gauge positioned independently of existing finite elements. The results obtained from the software strain gauge are averaged results from the underlying finite elements, modeling the same geometric averaging obtained with actual instrumentation from a physical prototype. Results are transformed to the coordinate system, and alignment of the software strain gauge and results must be surface resolved. Capabilities of the Software Gauge The software strain gauge has the following capabilities: Extracts FE results and combines with loading time variations to create response time history for each leg of strain gauge Multiple gauge geometries Uniaxial gauges T gauges Delta and rectangular gauges Stacked and planar gauges User-specified gauge definitions Gauge definition file of up to 200 simultaneous software strain gauges of stress or strain output types Hoffmann-Seeger proportional loading correction Neuber, Mertens-Dittmann, or Seeger Beste elastic-plastic correction methods Other Applications The software strain gauge is also of benefit to the analyst performing MSC Fatigue weld durability calculations in accordance with British Standard The gauge tool allows ready access to strain time histories at the weld toe, providing important information for weld durability calculations. MSC Fatigue Advanced Package The MSC Fatigue Advanced package provides a set of modules which can be used in addition to the Basic package, which is a prerequisite. These modules provide advanced analysis and data processing capabilities. Multiaxial Module In this module, a nonproportional, multiaxial stress state is assumed as opposed to the usual uniaxial or proportional loading states. The strain life (e-n) and stress life (S-N) methods are used in the life prediction and safety factor analyses, respectively. Safety Factor Analysis Safety factor analysis can be performed over the entire FE model or on a portion thereof. Analysis methods for multiaxial stress states include: Dang Van method McDiarmid method Crack Initiation Modeling Sophisticated crack initiation or strain-life (e-n) modelling provides a method for estimating life to the initiation of an engineering crack from a multiaxial stress state. Six local strain critical plane methods of calculation are available: Normal Strain Shear Strain SWT-Bannantine Fatemi-Socie Wang-Brown (with and without mean stress correction) All methods at once These methods include a multiaxial non-proportional notch correction procedure, incorporating an energy-based notch rule based on Neuber s rule and a Mroz-Garud cyclic plasticity model. Physical strain gauge Single Shot Analyzer A single shot multiaxial analyzer accepts elastic-plastic rosette stress or strain time histories directly. This input data can be from FE-derived histories or measured data. Methods of calculation include: Normal Strain Shear Strain SWT-Bannantine Fatemi-Socie Wang-Brown (with and without mean stress correction) All methods at once Multiple loading conditions Software strain gauge 5

6 PRODUCT BRIEF Vibration Fatigue Module This module predicts the fatigue life of structures subjected to random vibration loads. Durability analysis is performed in the frequency domain rather than the traditional time-based approach. Both the input loads characterization and the damage analysis are performed in the frequency domain. It is important for designers to estimate response at resonance for structures subjected to random input loads and this analysis is best performed in the frequency domain using Power Spectral Densities (PSDs) of input loading and stress response. The uniqueness of the Vibration Fatigue module is that it provides the analyst with the capability to perform fatigue analysis using either direct external response PSDs or computed PSDs from within the MSC Fatigue Vibration module using the input loading PSDs and system transfer functions. Analysis Features The Vibration Fatigue module uses using the S-N method to predict life and a single shot analyzer that accepts a measured or analytically determined stress response PSD. Specific features include: Welded structure analysis to BS7608 Goodman and Gerber Mean stress corrections Probability density functions of rainflow cycles supporting various matrix (bin) sizes (32, 64, 128) Stress/Strain tensor combination/resolution (Individual Components, Max Abs Principal, Signed Von Mises, Signed Tresca/Shear) FE results transformations Computation of response PSDs on any location from transfer functions and input loading PSDs. Palmgren-Miner linear damage summation including flexible Miner s sum (>0, default=1.0) Multiple analysis methods: Dirlik Narrow Band Steinberg Tunna Wirsching Hancock Kam & Dover Multiaxial stress state assessments Loading There are some noteworthy loading features specific to the Vibration Fatigue module. Twenty FE load cases with associated input load PSDs can be applied simultaneously. A loading database is also supplied to facilitate creation and storage of these PSDs. Other loading features include: PSD creation from time series data, ASCII file import, graphical or XY point specification, wave form definitions (sine, triangular, square) Data transformations Plots of PSDs and rainflow data Fatigue life due to multi-input vibration load Fracture Module This module uses stress results from finite element (FE) models, variations in loading, and cyclic material properties to estimate crack propagation rates and times. Stress results can be nominal or far field stress, and can be defined as a single location or averaged from an area on the model. Manual input is also possible with no reliance on an FE model. Traditional linear elastic fracture mechanics (LEFM) are used to determine crack growth. Analysis Features Sophisticated crack growth modeling provides a method for estimating life to grow a crack through a structure. Crack growth specific features include: Kitagawa minimum crack sizing Fracture toughness failure criterion Mean stress correction Rain flow cycle counting with cycle re-ordering Initial and final crack length specifications Plane stress correction Notch effects modeling Retardation and closure effects modeling Modified Paris law modeling based on effective stress intensity range User-defined life units Fracture mechanics triangle solutions (stress stress intensity crack length) Graphical interface to NASA/FLAGRO 2.03 (via Patran) Stress tensor combination/resolution Any individual component Maximum absolute maximum Signed von Mises Signed Tresca/Shear 6

7 PRODUCT BRIEF Compliance Function Library Various crack geometries are supported for determining the K-solution which include: Standard specimens: Single edge crack in tension or pure bending Double edge crack in tension Center cracked plate in tension Center cracked square plate in tension Three-point bend specimen Compact tension specimen Round compact tension specimen Wedge opening load specimen Quarter circular corner crack tension specimen Cracks at holes: Single crack at a hole in tension Double crack at a hole in tension Surface crack at a hole in tension Elliptical, semi-elliptical cracks in plates: Surface cracks in tension or bending Embedded cracks in tension or bending Surface and embedded cracks in combined loading Cracks at corners: Quarter elliptical corner crack in tension Quarter elliptical corner crack at a hole in tension Cracks in solid cylinders Circumferential crack in tension Straight crack in tension Semi-circular crack in tension Crack at thread in tension Straight crack in bending Semi-circular crack in bending Cracks in hollow cylinders Internal surface crack under a hoop stress Circumferential crack in thin-walled tube in tension Cracks in welded plate joints Weld toe surface cracks in tension or bending Weld toe embedded cracks in tension or bending Surface cracks in combined tension and bending Cracks in welded tubular joints Cracks at spot welds in tension User parametric definitions Results A variety of fracture-specific results data is reported both in tabular form and in result files for graphical display. Results data include: Interactive XY plot of crack growth during the analysis Final crack length versus life curve Final crack growth rate curve Life reported in user defined units Life interpolation due to different initial and final crack sizes Tabular listing of: Life (user unit or cycles) Crack size Growth rate Stress range Apparent or effective DK Current overload K Residual K K at crack closure K from static fracture Effective stress ratio Notch correction factor Growth corrosion enhancement Sensitivity studies of: Multiple initial and final crack sizes Materials Cyclic material parameters Mean stress Crack type Environment Loading Graphical display and hardcopy of plots Stress history output Consider notch effects da/dn curves 7

8 PRODUCT BRIEF Spot Weld Module This module predicts the fatigue life of spot welded sheet connections using static or dynamic FE results with the total life (S-N) method. Both spot weld and seam weld modeling techniques are supported. Spot Weld Modeling Modern automotive structures can have spot welds and approximately 80% of automotive body durability problems are associated with spot welds. Tooling costs for spot welds are high and the need for rapid and accurate predictions of fatigue life on spot welds early in the design stage is very important. Besides the structural importance, durability of spot welds can have an important effect of perceived quality of a part or component. MSC Fatigue Spot Weld supports results from three commonly used modelling methods and uses the Rupp, Storzel and Grubisic algorithm for computing stresses in each spot weld nugget and adjacent sheets: Spot welds modelled as stiff beams. The method requires attention to align the spot weld nodes on each flange but is suitable for application to large models as local mesh refinement around the spot weld is not required MSC Nastran CWELD elements. The power and modelling flexibility afforded by CWELD element is utilized. The CWELD allows users to model spot welds between dissimilar meshes of any refinements. CWELD results are used directly by MSC Fatigue spot weld. Spot welds modelled using CHEX/MPC. This method also allows users to model spot welds between dissimilar meshes. MSC Fatigue computes equivalent bar forces automatically and posts fatigue results on the faces of the CHEX elements. Seam Weld Modeling Fatigue failure prediction in welded joints is difficult due to geometric complexities and inaccuracies in the stress and strain results. Often the approach most relied upon is the component SN method which involves the construction of several prototypes followed by fatigue testing to produce a component SN curve. However, component testing is not a viable approach during the product design phase as it is time consuming and expensive. MSC Fatigue Spot Weld provides an attractive alternative method for estimating fatigue life of welds in thin sheets. The method is based on modelling the weld with relatively stiff plate elements that are used as load transducers and extracting bending and axial nodal stresses at the weld line nodes from elements adjacent to the weld. The shell toe groups are automatically extracted in MSC Fatigue with the addition of a simple GUI to the material form. Common nodes on the toe side of the weld are determined and stress extracted. These stresses are then used to estimate fatigue life using one of two S-N curves depending of the ratio of the bending to axial stresses. The ratio identifies the seam node as stiff or flexible and the corresponding stiff or flexible S-N curve is used to estimate damage. Critical seam weld nodes are easily identified with the aid of marker plots and optimization studies may be carried out. Analysis Important analysis functionality in the MSC Fatigue Spot Weld module include: Spot weld S-N curves (including generic spot weld S-N curves for nugget and sheet) added to the materials database Analysis of welds joining two metal sheets Three sheet correction Weld nugget and sheet fatigue life 108 fatigue calculations performed per spot weld (>0, default=1.0) Rainflow cycle counting Various matrix (bin) sizes (32,64,128) Statistical confidence parameters Palmgren-Miner linear damage summation Flexible Miner s sum FE model of automobile body component Location and fatigue life of spot welds Seam weld modeling showing plate elements 8

9 PRODUCT BRIEF Wheels Module This module allows users to conduct fatigue analyses on wheels for a sequence of loading conditions. This capability can be used for any rotating body where the applied loads travel around the periphery of the body. The simulation is achieved by applying loads to consecutive segments of the wheel. A single distributed load represents one of the loading conditions out of a set that describes the load travel. MSC Fatigue allows users to specify additional loading conditions to simulate events that specify a complete loading environment. A stress history plot of a node on the wheel will show variance in time as loads are applied to consecutive segments of the wheel. By using the stress results from the loading conditions, a complete stress-time history and fatigue damage in angular increments about each node is determined. Fatigue results are displayed, as shown below, as contour plots of fatigue life and fatigue damage for all nodes at the worst (most damaging) surface angle. Distributed load on FE wheel model Utilities Module This module contains advanced and practical applications to help the MSC Fatigue user who has a need to collect, analyze, and postprocess measured data, such as stress or strain time histories, or to process such data to prepare for a subsequent MSC Fatigue analysis. The utility modules are broken into three basic categories: Advanced loading manipulation Advanced fatigue analysis and display File translation Advanced Loading Manipulation A loading database and database manager is delivered with the MSC Fatigue Basic Package. It contains standard functions necessary for the FE analyst to conveniently set up fatigue analyses. The following functions are included in this Utilities module for advanced loading manipulation purposes: Arithmetic manipulation allows application of arithmetic operations such as adding, subtracting, multiplying, and dividing by a constant to any time signal or histogram. Additional functions which can be applied to the full signal or portions thereof are: Normalization of signal to new mean Raise to a power Application of trigonometric and logarithmic functions Absolute value determination Application of linear equation Y=mX+c Stress due to travel of distributed load Multiple channel creator/editor allows for tabular viewing, editing, and creation of multiple time signals (files/channels) simultaneously. Features include: Inserting sections of signals Appending sections of signals Joining sections of signals Plotting channels simultaneously Outputting data to ASCII file in various formats Rescaling and offsetting Other editing options such as copying, pasting, cycling, deleting, and inserting gaps Multiple file cut and paste allows for adjustment in length of time signals by extracting or deleting sections, concatenating files, reversing and smoothing data. This operation works on single or multiple files simultaneously Multiple file manipulation allows for addition, subtraction, multiplication, division, and vector addition of multiple time signals to create new signals Formula processor a powerful formula processor for time series data or histogram files, which includes its own programming language. Virtually any formula can be applied to any number of files which is defined manually by a text editor Header and footer manipulation allows for viewing and modification of header and footer information of loading signals Statistical analysis of signal segments analyzes time signals and produces running statistics about the signal which can be plotted. Statistics are determined by breaking the signal into segments (user has control over segment length and overlap). Supported output: Root mean square (rms) Standard deviation Maximum value Minimum value Absolute maximum value Area under data Amplitude distribution analysis calculates probability density distribution (which defines the probability of finding a value of a particular magnitude within the population of measured values) and other functions of a time signal Auto spectral density performs frequency analysis of a time signal to determine frequency content. Various output is available such as: Waterfall analysis Power spectral density Amplitude spectrum Magnitude of FFT Energy spectral density Real and imaginary components Fast Fourier filtering uses filtering techniques to remove frequency content from a time signal. Low pass, high pass, band pass, and stop pass filters available Butterworth filtering additional filtering technique to remove frequency content from a time signal. Low pass, high pass, band pass, and stop pass filters available 9

10 PRODUCT BRIEF Frequency response analysis performs frequency response analysis and calculates transfer function of a single input, single response system. Calculates cross correlation function between the two supplied response signals. Advanced Fatigue Analysis and Display The following functions are included in the Utilities module for advanced fatigue analysis and display purposes. All input to these modules are in the form of response signals which can be measured or analytically determined from FE-based fatigue analysis. These are single shot, single location analyzers as opposed to FE analysis-based, global multi-location analyses. All analyzers use materials and loading information as available from all other MSC Fatigue modules, and results display is similar to all other MSC Fatigue modules. Crack initiation analysis critical location fatigue analysis based on local strain method from stress or strain responses Cycles and damage analysis display of two-dimensional cycle and damage histogram results for comparison purposes S-N fatigue analysis total life (S-N) fatigue analysis of stress responses Cycle file lister convenient utility to list rain flow cycles to a file or screen Kt evaluation a database library for calculating and storing stress concentration values for various geometries Time correlated damage strain-based damage calculation. Damage is summed over time and in the sequence in which cycles are seen to assess cumulative effects of response signals Stress-strain analysis performs elastic to elastic-plastic analysis of time signals, multiaxial assessments, rosette analysis, and critical plane analysis stress/strain responses. Also available in the MSC Fatigue Basic Package s Strain Gauge module Crack growth data analysis calculates Paris Law coefficient, C, and exponent, m, in the expression da/dn=c(δk)m from actual raw test data obtained under constant amplitude loading conditions File Translation The following capabilities are included for file translation purposes: RPC to DAC and DAC to RPC converts MTS RPC (remote parameters files) into and from MSC Fatigue formatted loading and response signals Binary/ASCII converter converts binary MSC Fatigue formatted loading and response signals to ASCII format. The reverse operation is performed by the MSC Fatigue loading database manager Signal reconstruction recreates statistically equivalent time signals from histogram representations Cross platform file conversion converts binary platform dependent MSC Fatigue loading and response signals, load and material database files, compliance functions, and surface finish/ treatment definitions files to other supported platform types Signal for processing Data cleaning (early spikes removed below) Corporate MSC Software Corporation 2 MacArthur Place Santa Ana, California Telephone Europe, Middle East, Africa MSC Software GmbH Am Moosfeld Munich, Germany Telephone Asia-Pacific MSC Software Japan LTD. Shinjuku First West 8F 23-7 Nishi Shinjuku 1-Chome, Shinjuku-Ku Tokyo, Japan Telephone Asia-Pacific MSC Software (S) Pte. Ltd. 100 Beach Road #16-05 Shaw Tower Singapore Telephone The MSC.Software corporate logo, MSC, and the names of the MSC. Software products and services referenced herein are trademarks or registered trademarks of the MSC.Software Corporation in the United States and/or other countries. All other trademarks belong to their respective owners MSC.Software Corporation. All rights reserved. FWN*2010APR*PB