VTL Tutorial. MAHLE Virtual Tribology Laboratory VTL 3.8

Transcription

1 VTL Tutorial MAHLE Virtual Tribology Laboratory VTL 3.8 Francisco Profito Eduardo Tomanik August/ VTL (Virtual Tribology Laboratory) is a computational program developed by MAHLE in order to simulate friction and wear behaviours of reciprocating bench tests. Mixed lubrication conditions are evaluated by taking into account both hydrodynamic and asperity contact phenomena. The former is mathematically described by means of the one-dimensional Reynolds equation whereas the latter by the Greenwood & Williamson and Greenwood & Tripp formulations. - The current version includes several optional sub-models, e.g. viscosity-pressure and viscosity shear-thinning effects, different cavitation models, prediction of the worn profile (Archard s law) etc. - Several calculated results are graphically displayed in plots which may be handled by the included MATLAB tools. - This computational program was developed during the MSc. research of the first author in order to support mathematical modelling for textured surfaces [1,2,6]. The open-source version of VTL is intended to maximize interactions with academic partners, inclusions of additional models and for didactic purposes. The current VTL code version simulates 3 kinds of tests: - Instantaneous Test - Reciprocating Test - Wear Test A brief description, as well as examples of such simulation modules are shown in the next slides. The installation guide of the program is also available at the end of this tutorial. 1

2 Contents 1. Introduction

3 1. Introduction The following figure illustrates a general situation of the idealized tribo-system from which the mathematical models that compose the VTL program have been developed. Although the model assumes only the upper surface as mobile and the bottom fixed, different kinematics can be reproduced, the user using the relative speed as input. It is recommended to save all the input and output files (*.txt) created by the user on the subfolders located within the main folder \DATA_BASE. This main folder is automatically generated after VTL installation (see Installation Guide, item 6). Some demo examples concerning each simulation modules are available and stored in these subfolders. 3

4 Contents 2. VTL MainScreen 4

5 2. VTL MainScreen Create new test simulation Save input data of the test simulation Change advanced options About VTL Choose the desired test Open input data of an existing test simulation General info about the simulation progress Click to run 5

6 Contents 3. Module Instantaneous Test 6

7 3. Module Instantaneous Test (MainScreen) Simulation of a general steady-state conditions (squeeze effect neglected). General test conditions: - velocity - inlet and outlet pressures - relative position of the mobile surface - tilt of the mobile surface - width of the surfaces - boundary friction coefficient Lubricant Geometry and parameters of the surfaces. Material properties Roughness Greenwood Asperity contact parameters Representation of the surfaces geometry Feature under construction 7

8 3. Module Instantaneous Test (Included Examples) Instantaneous Test examples available in this current release version (see subfolder \DATA_BASE\INSTANTANEOUS_TEST): \validation_cases\ \hydro_lubrication_model Name Profile Visco- Asperity Cavitation Correction Model Model Validation Obs. wedge1 wedge NO analytical - Analysis of the visco-pressure wedge2 wedge YES HALF- - effects SOMMERFELD parabolic parabolic NO - raylegh_step raylegh step NO analytical - SWIFTsecant secant - STEIBER \mixed_lubrication_model Name wedge_mixed_g W(0.2) wedge_mixed_g W(1.0) ring_mixed_gw- GT(1.0+Zs) Profile wedge wedge Asymmetric 3mm piston ring Visco- Correction NO Asperity Model GW GW and GT Cavitation Model Validation Obs. HALF- SOMMERFELD Code from ref. [6] - low speed (0.2m/s) - asperity model without Zs - high speed (1.0m/s) - asperity model without Zs - high speed (1.0m/s) - asperity model with Zs \textured_profiles\ Name full_textured_p150_slide full_textured_p250_slide full_textured_p450_slide partial_textured_ p150_slide partial_textured_ p250_slide partial_textured_ p450_slide Profile flat 3 mm piston ring full textured flat 3 mm piston ring partial textured Visco- Correctio n NO Asperity Model GT Cavitation Model SWIFT- STEIBER Validation - Obs. - Asperity parameters from a slide honed topography - Texture dimensions: diameter = 100 µm depth = 10 µm pitch = 150, 250, 450 µm 8

9 3. Module Instantaneous Test (Plots) After simulation completion, 3 graphs are generated summarizing the calculated results. Follows a quickly description of these graphs (from the included example named ring_mixed_gw-gt(1.0+zs)): Plot 1: Illustrations of the relative position of the surfaces and the Zoom In on the contact region (units: m) Relative position of the surfaces - Black: mobile surface - Red: fixed surface V (positive direction) Zoom In on the Contact Region V (positive direction) 9

10 3. Module Instantaneous Test (Plots) Plot 2: Pressure fields over the mobile surface (units: Pa) Pressure fields over the mobile surface - Blue: hydrodynamic pressure - Red: asperity contact pressure Zoom In on the Contact Region Plot 4 is identical, but for the fixed surface. once the numerical meshes of the mobile and fixed surfaces are different, the pressure fields over the latter are obtained by interpolation of the pressures calculated with respect to the mesh of the mobile surface (plot 2 above). 10

11 3. Module Instantaneous Test (Plots) Plot 3: Viscosity correction field. This plot appears only when the visco-pressure and/or the visco-shear-thinning effects were taken in account. (units: %) Viscosity correction over the mobile surface Zoom In on the Contact Region 11

12 Contents 4. Module Reciprocating Test 12

13 4. Module Reciprocating Test (MainScreen) Simulation of reciprocating bench tests. The squeeze film effect is considered. The fixed surface is always assumed flat for less computational cost. For more general conditions see Wear simulation. General test conditions: - crank-rod mechanism - inlet and outlet pressures (constant) - tilt of the mobile surface (constant) - surfaces width - boundary friction coefficient Simulated regimes: - speeds - external loads Feature under construction 13

14 4. Module Reciprocating Test (Plots) Reciprocating Test examples available in this current release version (see subfolder \DATA_BASE\RECIPROCATING_TEST): \validation_cases\ Name reciprocating_test_plateau reciprocating_test_slide Profile Asymmetric 3mm piston ring Visco- Correction YES Asperity Model GT Cavitation Model SWIFT- STEIBER Validation Experimental results from ref. [3] Obs. - Asymmetric piston ring sliding against liner specimens with plateau and slide honing finishing \textured_profiles\textured_profiles_slide Name full_textured_p150_slide full_textured_250_slide full_textured_450_slide partial_textured_ 150_slide partial_textured_ 250_slide partial_textured_450_slide Profile flat 3 mm piston ring full textured flat 3 mm piston ring partial textured Visco- Correction Asperity Model NO GT SWIFT-STEIBER - Cavitation Model Validation Obs. - Same conditions considered on the validation case for liners specimens with slide honing finishing (table above) - Texture dimensions: diameter = 100 µm depth = 10 µm pitch = 150, 250, 450 µm \textured_profiles\textured_profiles_slide(engine_speed) Name barrel_shape_ring_slide partial_textured_ 150_slide Profile Asymmetric 3 mm piston ring un-textured flat 3 mm piston ring partial textured Visco- Correction Asperity Model NO GT SWIFT-STEIBER - Cavitation Model Validation Obs. - simulation with textured profile at high speed conditions - in this case it was considered dimensions of an actual engine crank rod mechanism. \stribeck_viscosity\ Name stribeck_viscosity_slide Profile Asymmetric 3mm piston ring Visco- Correction NO Asperity Model GT Cavitation Model HALF- SOMMERFELD Validation - Obs. -reciprocating test with large speed range ( rpm) -- create a complete Stribeck-like curve 14

15 4. Module Reciprocating Test (Plots) After simulation completion, several graphs are generated summarizing the calculated results. Follows a quickly description of these graphs (for that, it was considered the included example named reciprocating_test_slide): Plot 1: Illustrations of the surfaces geometry considered in the simulation. (units: m) V (positive direction) Surfaces geometry - Black: mobile surface - Red: fixed surface (always assumed flat in this module) 15

16 4. Module Reciprocating Test (Plots) Plot 2: Stribeck-like curve summarizing the cycle average friction coefficients calculated for each simulated regime (speed/load conditions). As the profile can be non-symmetrical, plots for the positive and the negative directions are generated. 16

17 4. Module Reciprocating Test (Plots) Plot 3: General boundary conditions considered over the complete reciprocating cycle. A set of plots (one screen) is generated for each simulated regime. Tilt of the mobile surface* [deg] Relative position of the mobile surface for each crank angle [m] Inlet boundary pressure* [Pa] Velocity of the mobile surface for each crank angle [m/s] External force load* [N] Outlet boundary pressure* [Pa] *Assumed constant in this module over the complete reciprocating cycle. For more general cases see the wear module. External pressure load* [Pa] Average lubricant temperature* [oc] 17

18 4. Module Reciprocating Test (Plots) Plot 4: General mixed lubrication results calculated over the complete reciprocating cycle (results for each crank angle). These set of results are generated for each simulated regime (speed/load condition). Minimum oil film thickness for each crank angle[m] Hydrodynamic pressure field over the mobile surface for each crank angle [Pa] Mixed friction coefficient for each crank angle [-] Asperity pressure field over the mobile surface for each crank angle [Pa] Average viscosity correction for each crank angle [%] Wear load over the mobile surface for each crank angle [Pa] Obs.: Except for the squeeze effect, the results calculated for each crank angle are equivalent to those obtained with the module Instantaneous Test considering the same conditions of velocity, external loads, boundary pressures and tilt. 18

19 4. Module Reciprocating Test (Plots) Plot 4: Details of the right hand graphs (field graphs) illustrated in the previous slide. Example of MATLAB manipulation Pressure field over the mobile surface for each crank angle 19

20 Contents 5. Module Wear Test 20

21 5. Module Wear Test (MainScreen) Generalization of the reciprocating test module (in this case, the boundary conditions may changes over the reciprocating cycle). Prediction of the worn geometry of the surfaces. Crank-rod mechanism Boundary condition over the reciprocating cycle: - loads - tilt angle - boundary pressures (inlet and outlet pressures) Number of wear cycles Feature under construction 21

22 5. Module Wear Test (Examples Included) Wear Test examples available in this current release version (see subfolder \DATA_BASE\WEAR_TEST): \reciprocating_wear_example\ Name wear_test_plateau wear_test_slide Profile Parabolic 3mm piston ring Visco- Correction YES Asperity Model GT Cavitation Model HALF- SOMMERFEL D Validation - Obs. - Evaluation of the wear model implemented in VTL considering typical speed/load conditions of the Wear Test usually carried using UMT devices. \engine_example\ Name engine_example_slide Profile Parabolic 1mm piston ring Visco- Correction YES Asperity Model GT Cavitation Model HALF- SOMMERFEL D Validation - Obs. - Example considering variable boundary conditions of a top piston ring 22

23 5. Module Wear Test (Plots) After simulation completion, several graphs are generated summarizing the calculated results. Figure below reproduces the included example named engine_example: Plot 1: Illustrations of the initial surfaces geometry considered in the simulation. (units: m) V Initial mobile surface geometry (positive direction) Initial fixed surface geometry 23

24 5. Module Wear Test (Plots) Plot 2: Wear prediction of the mobile surface Blue: initial geometry Red: after the wear cycles Wear evolution of the mobile surface 24

25 5. Module Wear Test (Plots) Plot 3: Wear prediction of the fixed surface Blue: initial geometry Red: after the wear cycles Wear evolution of the fixed surface 25

26 5. Module Wear Test (Plots) Plot 4: Stribeck-like curve summarizing the evolution of the cycle average friction coefficients for each wear cycle. Notice that in the given example, friction is initially equal for both directions, The ring profile is symmetric. With wear, friction increases in one direction, reduces in the other, due to the taper worn profile. Friction change due to wear evolution 26

27 5. Module Wear Test (Plots) Plot 5: General boundary conditions considered for all wear cycles. These boundary conditions may change over the reciprocating motion. Tilt of the mobile surface for each crank angle* [deg] Relative position of the mobile surface for each crank angle [m] Inlet boundary pressure* Pa] Velocity of the mobile surface for each crank angle [m/s] Outlet boundary pressure* [Pa] External force load* [N] *These boundary conditions may change over the reciprocating motion. External pressure load* [Pa] Lubricant temperature (always const.) [oc] 27

28 5. Module Wear Test (Plots) Plot 6: General mixed lubrication results calculated over the complete wear cycle (results for each crank angle). These set of results are generated for each wear cycles simulated and will be different according to the wear evolution of the contacting surfaces. Minimum oil film thickness for each crank angle [m] Hydrodynamic pressure field over the mobile surface for each crank angle [Pa] Mixed friction coefficient for each crank angle [-] Asperity pressure field over the mobile surface for each crank angle [Pa] Average viscosity correction for each crank angle [%] Wear load over the mobile surface for each crank angle [Pa] Obs.: These plots have the same means that those generated on the Reciprocating Test. 28

29 Contents 6. Installation Guide 29

30 6. VTL Installation Guide VTL is written in Matlab language. Users that do not have the Matlab Compiler Runtime 2009 (MCR_2009) must install it executing the complete VTL package (matgui_pkg_complete.exe file). Once installed the MCR_2009, only the installation of the VTL eventual updates is needed. The next steps will help you to perform the complete installation of MCR_2009 and VTL. Alternately, MCR may be also downloaded from the MathWorks website: 1) Run the provided file matgui_pkg_complete.exe within a given folder. A MSDOS window control will appear showing all files unzipped. Automatically, the file MCRInstaller.exe will run: 1.1) MSDOS window control with unzipped files 1.3) All unzipped files are stored on the initial user defined folder. 1.2) Automatically run MCR_2009 installation (MCRInstaller.exe). 2) Press next to continue installing the Matlab Compiler Runtime 2009 (MCR_2009): 30

31 6. VTL Installation Guide 3) After the MCR_2009 installation, you can delete the file MCRInstaller.exe, leaving in the main folder only the following files and subfolder: the original installation matgui_pkg_complete.exe (to futures installations); the executable file VTL_3.8.exe; the file matgui.exe; the file matgui.exe.manifest the image logo_mahle_usp.bmp; the image matgui.bmp; the folder DATA_BASE with several examples cases already simulated with VTL. 4) Finally, VTL is ready to run (execute VTL_3.8.exe) 31

32 Contents 7. VTL Advanced Options 32

33 7. VTL Advanced Options In this window, the user can select different models and numerical methods. 33

34 Contents 8. References 34

35 8. References [1] PROFITO, F.. Modelagem Unidimensional do Regime Misto de Lubrificação Aplicada a Superfícies Texturizadas. Dissertação de Mestrado Escola Politécnica da Universidade de São Paulo, (will be submitted in 22-Sep-2010) [2] PROFITO, F., TOMANIK, E., ZACHARIADIS, D.C., An improved surface characterization of textured surfaces on mixed lubrication regimes. SAE paper [3] TOMANIK, E., Friction and Wear Bench Tests of Different Engine Liner Surface Finishes. Tribology International, vol. 41, p , [4] TOMANIK, E., CHACON, H., TEIXEIRA, G., A Simple Numerical Procedure to Calculate the Input Data of Greenwood-Williamson Model of Asperity Contact for Actual Engineering Surfaces. 29th Leeds-Lyon Symposium on Tribology. Tribological Research and Design for Engineering Systems. [5] TOMANIK, E., Modelling of the Asperity Contact Area on Actual 3D Surfaces. SAE paper [6] PROFITO, F.J., ZACHARIADIS, D.C., TOMANIK, E., One Dimensional Mixed Lubrication Regime Model for Textured Piston Rings. 21st Brazilian Congress of Mechanical Engineering,