Introduction to FE Based Fatigue Analysis Fatigue
Contents
1. MSC Fatigue Set Up the Fatigue Analysis 3 of 8 A MSC Patran Property s t es ElementTopology Property Type an m Create Single Group Y Ci Material Information Material ae Post You now need to associate fatigue property is l Bandis data for the various element groups used in the FE Element ID analysis Each group of elements can be assigned its MPC Type own fatigue properties so welds could be associated with a different property to that of the parent metal for example This stage is necessary because the FE solver knows nothing about the fatigue properties of a material Existing default group The first step is to create a group which contains all the comprising of all entities shels zt New group name shell elements of the finite element model There are a V Make Current Unpost All Other Groups number of ways to substructure your model in groups For example select Group Create from the main menu bar of MSC Pairan change the Method to Element Topologies Element Topology call the new group shells and select Quad4 and Tria3 Press the Apply button to select the multiple items Note MSC Fatigue can only process locations connected to shell or solid elements with available stress results This means the bar elements have to be excluded from our fatigue analysis group lg to select multiple items Groups This is an important feature in MSC Fatigu2. Max Y 67 36 Min Y 100 1 100 1 45 46 47 48 49 Screen 1 nCode K MSC SOFTWARE SIMULATING REALITY Managing Durability Copyright 2005 nCode International Ltd nCode K MSC Managing Durability MSC Fatigue Set Up the Fatigue Analysis 7 of 8 E Loading Information MSC Fatigue Equiv Units trepeats of the loading 200 r Results Parameters Results Type Results Transformations No Transformation x Use Load Spectrum Results From Surface Current Time Directory Number of Static Load Cases Selected Static Load Cases Load Case ID Time History Load Magnitude ES 21 2 1 6 LOADO1 DAC i EJ 3 2 2 1 6 LOAD02 DAC 100 3 4 3 2 1 6 LOAD03 DAC 100 lt gt Results Parameters Select a Results Load Case 2 1 Load Case 1 Static Subcase 3 2 Load Case 2 Static Subcase 4 3 Load Case 3 Static Subcase If shell elements are used in the FE model you can choose whether to use the top or bottom surfaces In this example select Z1 layer for all load cases this is the bottom shell surface results SOFTWARE SIMULATING REALITY Fatigue life is usually expressed as the number of repeats of a time history required to fail the compo nent It is often desirable to express this in more mean ingful units such as miles Therefore the user can specify that 1 repeat is equivalent to x m
3. To begin setup for a fatigue analysis from the Fatigue Pre Processing gt linear static analysis the options Results Templates Tools pulldown menu in MSC Patran select include EN and SN along with General arameters S MSC Fatigue and then Main Interface This will bring ae Analysis a Rebar Definitions Load Management various multiaxial methods i Laminate Modeler gt Material Management gt up the MSC Fatigue main form from which all Random Vibration Fatigue is Fi ise UR CATATAN Compliance Generator parameters loading and materials information and available if PSD results are used alki Advanced Loading Utilities analysis control are accessed n m wel n wel Nodal Ave Experimental Data Fitting Solv gt fg a sd a i Soe R Once the form is open set the General Setup a atigue Utilities p F E Results stress 7 Graphic Olsploy Widen gt Parameters as shown For general analysis we recom File Conversion Utilities gt mend an EN approach first and Sg Environment Settings then decide whether a multiaxial approach is required following an inspection of the biaxiality plots We will discuss this later SN is not preferred for most FE analysis because it is invalid in regions of elastic plastic stress such as those adjacent to notches and holes Jobname 2 chrs max Specific Setup Forms Solution Params Most FE solvers pay no heed to nan the un
4. MSC Fatigue Action Read Results M Select Read Results to read the fatigue analysis Method Single Analysis ki results into the MSC Patran database for post Apply Cancel processing nCode K MSC SOFTWARE SIMULATING REALITY Managing Durability Copyright 2005 nCode International Ltd MSC Patran 2004 r2 24 Mar 05 16 59 40 Fringe Crack Initiation shackfef Log of Life Miles NON LAYERED MSC A SOFTWARE SIMULATING REALITY 2 23 001 17 001 Object Quick Plot Select Result Cases Load Case 1 Static Subcase Load Case 2 Static Subcase Subcase 5 62 000 default_Fringe Max 2 23 001 Nd 18150 Min 5 62 000 Nd 31114 fees 2 Gtatin Load Case 3 Static Factor of Safety shockfos Click this button Fringe Attributes to change the contour Select Fringe Result plot settings such as Life miles style and shading Life in Repeats Log of Damage Log of Life in Repeats Ps Just as you viewed the stresses earlier you can view the damage and life plots Select the Results application switch on the MSC Patran toolbar The Create Quick Plot form will appear On this form select the Crack Initiation shockfef item in the Select Result Cases listbox and the Log of Life Cycles item in the Select Fringe Result listbox and then press Apply Note that the smallest life reported is approximately 5
5. MSC Patran 2004 r2 14 Mar 05 11 51 55 Object Quick Plot Fringe Crack Initiation shocktet Log of Damage NON LAYERED 3994 2 a amp S 8 Select Result Cases But are you sure In the next few frames we will conduct a sensitivity analysis on the component to determine whether a non proportional multiaxial analysis is required we will investigate the effect of residual stresses caused by cold forming and we will look at the quality of the FE mesh Loa of Life in Repeats Select Deformation Result I Animate 2 00 001 default Fringe Max 3 32 000 Nd 31112 Min 2 01 BNA 1R15N xj tes_display_tool_unpost Deformation default Deformation a o res data load dbresult 0 Nodal Scalar Crack Initiation shockfef Log of Damage NON LAYERED Default DeriveAverage AI ShapeFunc res data title 0 Nodal Scalar 1 Fringe Crack Initiation shockfef Log of Damage NON LAYERED res display fringe create FreeFaces 0 12 Range Fri_default_Fringe RangeOverwrite ON FringeStyle Discrete Smooth Shade None ElemE dge FreeEdge Blue Solid 1 Shrink 0 TitleDisplay ON MinMaxDisplay ON ValueDisplay OFF Fi tes display fringe post 0 Nodal TRUE TRUE v MSC Fatigue Results Job Control Results For Help press F1 How would residual stresses caused by cold fo
6. 62 This is a log base 10 value So the actual life value is 10 which is about 400 000 miles Look at the Damage and Facior of Safety plots in the same way use Factor of Safety shockfos in the Select Result Cases listbox for factor of safety Reporting life values in log units tends to spread the contour bands out for better results interpretation Since such a large spread of results values can occur from finite to infinite at locations where no damage occurs it is not really practical to plot pure life values PBL FPF PPPOPL LP LOL OL OL ODF OL TS IF Life 400 000 Miles Min Factor of Safety 1 28 Copyright 2005 nCode International Ltd Introduction to Sensitivity Analysis Does the multiaxial load cause a multiaxial Is the FE analysis adequate stress state at the critical region You have now carried out your first MSC Fatigue analysis You have a nice contour plot showing where the component is likely to fail and have determined an estimated fatigue life of 400 000 miles with a Factor of Safety on overload of 1 2 At the moment everything is looking fine MSC Patran DER File Group Viewport Viewing Display Preferences Tools Insight Control Help DOSES BAR SCSSS RHF SSAA gs i 4 a H Eg Q Geometry Elements Loads BCs Materials Properties Load Ca Fields Analysis Results Insight XY Plot ib IM shock db default_viewport shells Entity DE Bj x Action Create Y
7. Dor E Loading Information MSC Fatigue N i amplitude or variable amplitude Constant amplitude loads are entered directly using Wave creation Variable loads are represented by a time signal file in either nCode DAC or MTS RPCIII format ASCII files can be translated if C white Noise C Psd matrix C exit C copy from Remote C Enter points C enter x psd C Graphical create C Wave creation Block program tainflow Matrix C creaTe psd from time New directory m Results Parameters oad tiles Results Type Static Y C ASCII convert load Copy from central Results From required Variable loads are loaded to the database using Load files Add a description to the Loading Database manager of each time history file here and then set Load type and Units to Force and Newtons respectively In order to report fatigue life in units which are more appropriate for the component or structure being analysed it is required to enter both the number of units and unit type here which de scribes the duration of the loading nCode K MSC Managing Durability SOFTWARE SIMULATING REALITY ea PTIME Load Time History Source Filename Le Loano DAC fleadoi load direction 1 Force z Target Filename Description 1 Description 2 Load type Units Newtons v fi fF epeats Number of fatigue equivalent units Fatigue
8. Durability Copyright 2005 nCode International Ltd MSC Fatique Running the Fatigue Solver MSC Fatigue i Action Monitor Job MSC Fatigue Montor Job _ Action Full Analysi v Partial Analysis oe cometh Method Single Analysis V You are now ready to run the fatigue analysis Save Job On 3 Method Single Analysis Y aa Open the Job Control form Set the Action to poring Status of job Full Analysis and press the Apply button The database yds Delete Job will close momentarily as the results information is inn eee a SS extracted When the database reopens the job will Bill ig 5 a have been submitted You can then set the Action to Analysis Manager Monitor Job and press the Apply button from time to ind time to view the progress The solution should only lt lt take a minute or so to complete When the message Ee pun Safety factor analysis completed successfully elect Monitor Job to appears the analysis is complete Close down the Job view the progress of the EN aan ae Control form when done and then open the analysis run Scone Results form on the main MSC Fatigue setup form a sae not to be confused with the Results application switch on the MSC Patran main toolbar With the Action set to Read Results press Apply The fatigue analysis Cancel results will now be read into the MSC Patran database and then be accessed as any other FE result
9. Tensor as your tensor option and then press the Fill Cel button Fill in the remaining columns as shown Copyright 2005 nCode International Ltd MSC Fatigue Set Up the Fatigue Analysis 8 of 8 MSC Fatigue Action Calculate Normals Method Single Analysis gt Calculate Normals Within the MSC Fatigue main interface open the Job Control form The Calculate Normals option is an essential precursor to running the biaxiality analysis if you know your results are not surface resolved z normal is not zero This routine determines surface normals at each surface node and writes them to the file jobname vec MSC Fatigue detects the presence of this file and uses it to define a local coordinate system at each surface node that has its z axis normal to the surface The stress results in the fatigue analysis input file are then written in this coordinate system permit ting the software to carry out a biaxiality analysis in the x y plane only Remove Vectors These averaged nodal outward normals are also graphically plotted for visualisation and verification purposes Press the Remove Vectors button to re You can read about calculating normals in the move them Once they MSC Fatigue Quickstart Guide Chapter 11 A have been removed Multiaxial Assessment they can only be replot ted if the whole proce dure is repeated nCode K MSC SOFTWARE SIMULATING REALITY Managing
10. conversion Duplicate file C List all entries three load Cases use the Multi channel Display Search and list Sample rete adjust look program C Search and list Histories option This will run the multi file display noise Rainflow matrix 3 pome module MMFD When MMFD appears use the list w Plot an entry Psd matrix elete entries ye i reese m os rhe FR pecan facility to select the four files above use the Shift key amp Multi channel to make multiple selection from the file browser Note Delete entries A New directory Peak Valley Extract that the files will not appear in the databox but the exit Validate database Quick validation Full validation number of files selected will appear below it Accept all the other defaults on the form and press OK The files Display Hi i t Multi channel pi Extract Tagluntag will be displayed New directory Untag all eXit A Force Newtons load01 F Sample 1000 pve i A pa i a yo Npts 6001 F f A na a a aa The Multi file Display provides summary eal AE Doers data for each time history such as l ae 36 a as sample rate number of points and maximum and minimum values Force Newtons load02 r Sample 1000 Npts 6001 me mill ihr gegen yl b w PA vy Wy 1 y y Max Y 2 956 Min Y 2 648 a caai f f 45 46 47 48 49 Force Newtons load03 6 6 Sample 1000 La wil Npts 6001
11. the Analysis toggle switch on the MSC Patran main toolbar When the Analysis form appears set the Action to Access Results the Object to Read Output2 and the Method to Both model and results Press the Select Results File button and select the file shock op2 Press the Apply button The model will then appear and you are ready to set up a fatigue analysis Before moving on to the fatigue analysis first press the Results application switch on the main form to view the stress results from the MSC Nastran analysis The Create Quick Plot form is displayed Go to the Select Results Case listbox and select Load Case 1 Then from Select Fringe Result listbox and select Stress Tensor Set the Quantity option menu to Maximum Creating 6080 Elements nCode K MSC Managing Durability a i Middle mouse button to SOFTWARE SIMULATING REALITY Rotate model Principal 2D Press the Apply button and note the areas of high stress The maximum principal stress appears to be about 62 MPa Copyright 2005 nCode International Ltd MSC Fatigue Set Up the Fatigue Analysis 1 of 8 splay Preferences Fees RF ust ie The analysis type offered depends ials Properties Load on the FE results available For Pfault_group Enti Insight Control Help Mass Properties Beam Library Model Variables Design Study gt BS MS E ae Ge Rx Ee ch 2k BE XY Plot is Insight
12. Average All ShapeFunc Discrete Smooth Shade None ElemE dgeiElemE dge Black Sold Shrink 0 TieDisplay ON Mi If element stresses are chosen for the Results Loc on the General Setup Parameters form the contour plots are all displayed as colour patch plots These are less attractive than the fringe plots but show poor meshing in a much more apparent fashion You may wish to re run this tutorial from Frame 4 using Element results instead of Node if you have time when you ve finished nCode k MSC SOFTWARE Managing Durability age Copyright 2005 nCode International Ltd Mesh Quality 8 Stress State Analysis Multiaxial Check Back on the main MSC Fatique toolbar press We commonly talk of three types of stress state the Results toggle change the Action to List 1 Uniaxial has only 1 principal stress which changes in magnitude but not direction Results and hit Apply This will start the module 2 Proportional biaxial has 2 principal stresses which change proportionally in magnitude but do not change PFPOST which lists the fatigue analysis results in in direction tabular form Accepting the jobname and the default filtering values by pressing OK a couple of times will 3 Non proportional biaxial has 2 principal stresses that can vary non proportionally in magnitude or direction get you to the main menu Press or double click the Measured Fatigue curves SN am
13. Japan MSC Software Japan Ltd 81 3 3505 0266 Copyright 2005 nCode International Ltd nCode K MSC SOFTWARE SIMULATING REALITY Managing Durability Copyright 2005 nCode International Ltd
14. MSC gt SOFTWARE SIMULATING REALITY nCode hy Managing Durability DEK File Group Viewport Display Preferences Tools Insight Control Help g A DAGAR Fests MeeoSQQ M we ee a 14 m iS PS i ia e E ME Z ee E Geometry Elements Loads BCs Materials Properties Load Ca Fields BI x a IM shock db default viewport default group Entity Action Create Y Object QuickPlot Y Select Result Cases Load Case 1 Static Subcase Load Case 2 Static Subcase Load Case 3 Static Subcase Crack Initiation shockfef Factor of Safety shockfos Gate in Stress Units Life Miles Life in Repeats q Select Deformation Result I Animate Oa m et Copyright 2005 nCode International Ltd Introduction to the Problem Ch2 Input Forces Ch3 Input Forces load Ch 1 Force load Ch 3 Force Newtons B 8 o o o o 44 44 5 45 45 5 46 46 5 47 47 5 48 48 5 49 49 5 50 Time Secs Legend Line load Ch 1 Force 1852 4158 5 332E 5 3 2 load Ch 2 Force 14 78 13 24 2 628 load Ch 3 Force 336 8 5005 5128 nCode K MSC SOFTWARE SIMULATING REALITY Managing Durability Introduction This guide takes a new user through a typical FE based fatigue analysis It describes each stage of the process from viewing the FE model and stresses to post processing th
15. aterials r Selected Materials Information Material Finish Treatment Region No Treatment worst 1 SAE1008 91 HR No Finish Action Create V Method Select Entity Existing Group Names default group shells shock critlocs Defaults Filter Defaults New Group Name worst V Make Current Unpost All Other Groups Subsequent sensitivity studies need only be conducted on the top Offset can be used to model the residual stresses arising from cold forming Determin ing the actual residual stresses is a fairly costly undertaking involving prototype testing or non linear FE analysis In this analysis we apply the most pessimistic residual stress that of yield in tension and determine whether this would unduly compromise the component 4 Listing of FE fatigue results file shock Lite Mies gT ean Ratio Ps Firstly create a new group of the top 3 nodes Use the Group Create Select Entity New Group Name worst and enter Node 31114 26994 27386 Return to the MSC Fatigue main interface Open the Material Info form and click on the Region box for material 1 Select the new worst group Then move the slider to the right to show the Offset box Click this box and enter Offset Value 253 this is the yield stress of the material Press Enter to apply this offset and t
16. e It is necessary to specify a group which contains the nodes and or elements for which you wish to perform a fatigue analysis Select All Select None In MSC Patran by default all elements and nodes are contained in the default group However groups can be created to handle a reduced set of nodes elements when the model needs to be broken into more than one group for defining multiple combinations Apply Cancel of materials and surface finishes treatments Creating a group is relatively straight forward and can be done in many automated ways Alternatively you can supply a name and graphically select entities from the graphics screen or type them in the appropriate databox manually using the conven nCode K MSC A SOFTWARE tion Node or Elem in front of any list of nodes or elements SIMULATING REALITY Managing Durability Copyright 2005 nCode International Ltd MSC Fatigue Set Up the Fatigue Analysis 4 of 8 Surface Finish and Treatments are modelled using the Kf approach Kf values are published for various finishes and are represented as a function of material strength These values only apply to Steels and should only be used for quali tative comparisons The strength reduction factor Kf is used by fatigue engineers for model ling many effects such as notches surface finish and treatment etc It acts by either scaling the stresses prior to Neuber correction or rotating the SN curve dow
17. e fatigue results The reader is encouraged to undertake various sensitivity studies to establish the adequacy of the component in fatigue The guide introduces two MSC programs MSC Patran MSC s FE pre and post processor MSC Fatigue MSC s FE based fatigue solver The Problem You have to carry out a fatigue analysis on the front shock tower of a new car The FE department have prepared the FE model and have obtained static stress solutions for 3 loading directions as indicated in the drawing The road load data department have provided characteristic loading for some of the worst events The time signals have the equivalent damage of approximately 200 miles 820 km of normal driving The component should last at least 200 000 miles 320 000 km based on this harsh loading environment The component will behave quasi statically Copyright 2005 nCode International Ltd Some Program Basics Before We Start FIN stands for o Fatigue INformation file Es pt nla x Be Gap Vewgort Meng Deploy Preferences Jools 7 bep Unites TA ey was takes ts rte AS POPU RENN NS A MSC Fatigue accesses MSC Patran groups sh NN i ER ie and stress strain information selects the relative fatigue material from its own material database and handles the time variation for all target locations at 3 once MSC Fatigue MSC Fatique in Access create defi vei 9 The analysis is submitted to the fatigue solver and t
18. ents Principal stresses or stress invariants like Von Mises can be obtained from the components This selection allows the user to pick which stress property to use for the fatigue analysis In general the Abs Max Principal stress should be used as this yields the best fatigue results Standard EN material properties are applicable only for uniaxial stress states Where stresses are proportional biaxial e g plane strain torsion etc a correction is required would always recommend using the Hoffmann Seeger method for all analyses If the stress state is non proportional we must use a more complex fatigue analysis We investigate the stress state in more detail later in the book nCode K MSC Managing Durability MSC Fatique Crack Initiation Analysis Method S W T Plasticity Correction Neuber Y V Run Biaxiality Analysis Biaxiality Correction Stress Strain Combinatig Max Abs Principf Max Principa Min PrinciyAl C Signed on Mises Critical Plane X Normal Y Normal Z Normal C X Y Shear Y Z Shear C ZX Shear C Voises C igned Max Shear Signed Tresca A Certainty of Survival Factor of Safety Analysis V Run Factor of Safety Analysis Enter a Design Life 200000 Enter Maximum Factor for Calculation Defaults Cancel SOFTWARE SIMULATING REALITY the residual stress field in the component and the
19. equivalent units Loading Information Now in order to do a fatigue analysis using linear static FE results we must define how the loads vary with time This is easily done in MSC Fatigue using the Loading Database Manager PTIME Open the Loading Info form on the MSC Fatigue main interface Then press the Time History Manager button This will launch PTIME PTIME is a loading time series histogram PSD database manager which has been designed to enable the MSC Fatigue user to manipulate and manage time history and other data file types The time history and other loading type files are not loaded into the database but are resident in the local working directory together with the ptime adb file which contains the associated database data for each loading file In this case Load files browse for the first time histories load01 dac and complete the options as shown Repeat this for load02 dac and load03 dac Copyright 2005 nCode International Ltd MSC Fatigue Set Up the Fatigue Analysis 6 of 8 a PTIME Database Options Load files Number of entries 3 i ragga Current directory C ncode_projects Change an entry Graphical edit iawn Loading Information continued I is oat Edit X Y point x Y psd entry C Add an entry i fi i z i iati r AE Polynomial transform Graphical create pe oe si Multi file Display to look at the time variations of the Units
20. he FEM efine analysis Fattrans display fati damage results are recovered while leveraging on the FE model amp results type fatigue translator state of the art pre amp post capabilities of MSC Patran material loading As a key component in your Virtual Product Develop ment VPD process MSC Fatigue enables you to quickly and accurately predict how long your products will last under any combinations of time dependent or fes frequency dependent loading conditions and to file optimize your products for weight all within the familiar MSC Patran environment optimize fatigue results MSC Fatigue solver E a venpon noe te diaa vengon 9 BOE 3 665231 1 Ek vinot sioe seti delak veengort 11 511811 6 015740 1 For Help press Pi a aad Note The example case study is based on a real CAD model donated by one of our valued customers The MSC Fatigue supports all formats and codes accessible by MSC Patran including o MSC NASTRAN op2 and xdb FE mesh material property data and road load data are however all fictitious and have been prepared e MSC Marc t16 FES stands for Finite Element Stress results especially for this example o ABAQUS fil and odb e ANSYS rst e LS Dyna D3plot nCode iy MSC SOFTWARE SIMULATING REALITY Managing Durability Copyright 2005 nCode International Ltd Analysis Access Results to import the FE MSC Patran Viewing
21. hen OK to close the form Open the Job Control form Set the Action to Full Analysis and press the Apply button Fatigue life is not reduced signifi cantly 10 with residual stress therefore a costly residual stress 3 845E5 calculation is not required 4 417E5 8 969E5 0 8962 0 0296 0 5362 31114 26994 27386 5 201E 4 4 528E 4 2 23E 4 few nodes In this case we have chosen the top 3 Group Contents Add Entity Selection pi Entity Selection Node 31114 26994 27386 Apply Cancel SOFTWARE SIMULATING REALITY nCode K MSC Managing Durability Copyright 2005 nCode International Ltd Conclusions Congratulations you have run your first MSC Fatigue analysis Analysis Conclusions This is just one type of analysis that can be done Design Life 200 000 Miles Estimated Fatigue life 400 000 Miles OK Factor of 2 on life Supported FE Results General Fatigue Models Permissible overload safety factor 1 2 OK Shells Solids Bars Spot weld Local Strain Life EN Sensitivity to residuals 10 380 000 Miles ok Stress or Strain Multiaxial EN numerous methods including Wang Brown and Fatemi Socie Transient Dynamic Nominal Stress Life SN Convergence on stress 112 60 60 87 error VERY POOR Linear Static and Quasi static Modal Transient Multiaxial SN including Dang Van Convergence
22. iles for example Set to 1 repeat 200 miles or 320 km A single linear FE analysis could be used to perform fatigue analyses at different stress levels MSC Fatigue will use the load magnitude to divide all the stress results before scaling them according to the time signal file Loading Information continued Fill out the spreadsheet on the Loading Info form the spreadsheet is used to establish the association between the load histories the time variation of the load and the FE load cases MSC Fatigue scales and combines the stress distribu tions according to the time histories to obtain the stress history for each node Set the Number of Static Load Case to 3 and press the Return or Enter key to effect the change Place the cursor in the cell in the first column and click the mouse button This selects the cell A number of listboxes buttons and pulldown menus appear below the spreadsheet This is where you specify the FE analysis results that you will use in the fatigue analysis They appear empty at first To fill them press the Get Filter Results button On this form turn the Select All Results Cases toggle ON and press the Apply button This will fill the listbox on the left with all available result load cases in our MSC Patran database Make sure that the Fill Down toggle in the middle of the form is set to ON and select the first available loadcase In the now populated second listbox select Stress
23. its used provided they are consistent It is necessary however for the fatigue solver to know the original stress units used in the FE analysis so it can translate the appropriate material data Loading Info Job Control Results Forms Job Control Results no SOFTWARE SIMULATING REALITY nCode K MSC Managing Durability Post Processing Hex8 Spotwelds Read op2 files for CWELDs HEX to BAR Results Here we have a choice of Element or Nodal results We would usually recommend the Element result option for shell elements as this yields the most accurate stresses however we will choose the Node option in this example In this case we will use the stress results however the user can opt to use strain if these are present For linear analyses or non linear where material hardening is not considered there s no difference between taking stress or strain However if you wish to include non linear material behaviour in the FE analysis you should use the Strain results here and select E P Input elastic plastic Enter a Jobname and Title for this analysis here Copyright 2005 nCode International Ltd MSC Fatigue Set Up the Fatigue Analysis 2 of 8 EM Solution Parameters Fatigue is influenced by The FE results file contains 6 component stresses or strains for each element These pertain to the three axial and three shear compon
24. mean stress of the cyclic hysteresis loop Several methods are available to account for this the default is taken as the most popular method Solution Parameters Within the MSC Fatigue main interface open the Solution Params form On this form set the parameters as shown Elastic plastic correction can be over ridden if a non linear analysis of material hardening is carried out in the FE analysis A degree of statistical scatter is usually observed in the fatigue properties of materials Many test labs provide the standard error coefficient to express this scatter lf these data are available the program allows the user to vary the certainty of survival A 50 COS describes the least square fit through the data a 97 7 COS would represent the mean minus 2 standard deviations The higher the COS the greater the confidence It is recommended that 50 be chosen for the first analysis run followed by a sensitivity study on the influence of material quality Many data sources omit this value and usually give properties for the mean minus 2 Standard Deviations In this case varying the COS will have no effect on the results A factor of safety on stress overload can be computed The user enters the required life of the component and MSC Fatigue will back calculate to determine the allowable stress overload Scale factor that can be withstood without compromising the fatigue life Copyright 2005 nCode International Ltd
25. nwards for more information please refer to the Fatigue Theory Training course This option allows the user to enter an additional Kf factor that will apply to all elements in a group This function is useful in de featured FE analyses and for sensitivity studies into quality of finish E Materials Information ua MSC Fatigue Crack Initiation Materials Database Manager Select Standard Database Select User Database Temp Type None Temp Unit Celsius VY Fill Down OFF r Selected Materials Informations Material Finish Treatment Region 1 SAE1008 91 HR No Finish No Treatment shells Selected Materials Information Kf Shape Factor Multiplier Offset 1 0 0 0 1 0 0 0 Cancel The default for this parameter is infinity which implies a Neuber elastic plastic cor rection When selecting the Mertens Dittmann or Seeger Beste methods any value greater than 1 0 may be defined Only these methods use this parameter and setting the parameter to infinity reverts this method back to the traditional Neuber elastic plastic correction The shape factor or elastic strain concentration is a function of the shape of the cross section of the component and the type of load ing see Elastic Plastic Correction chapter in the User Manual nCode K MSC Managing Durability by the Muliplier and then summed with the offset SOFTWARE SIMULATING REALITY These op
26. on Life VERY POOR e Random Vibration PSD and McDiarmid Certainty of Survival insufficient material data No Dirlik Vibration Fatigue e Non linear std error given in material data Weld Fatigue Models Multiaxiality study Critical nodes are proportional but some nodes have biaxiality gt 0 3 a multiaxial assessment will be required when better FE results are e BS7608 SN approach available LBF Spot Weld approach e Volvo LBF Seam Weld approach COMPONENT NOT PROVEN Requires better FE model nCode K MSC SOFTWARE SIMULATING REALITY Managing Durability Copyright 2005 nCode International Ltd For further details To find your local nCode or MSC Software office or to learn more about the companies and products please contact nCode K Managing Durability Europe Sheffield UK nCode International 44 114 275 5292 info uk ncode com Worldwide Web www ncode com USA Southfield Ml nCode International Inc 1 248 350 8300 info americas ncode com nCode K MSC gt SOFTWARE 2 SIMULATING REALITY Managing Durability MSC gt SOFTWARE SIMULATING REALITY USA Santa Ana California MSC Software Corporation 1 714 540 8900 Information Centre 1 800 642 7437 ext 2500 U S only 1 978 453 5310 ext 2500 International Worldwide Web www mscsoftware com Europe Munich Germany MSC Software GmbH 49 89 43 19 870 Asia Pacific Tokyo
27. p EN pertain to Uniaxial stresses only Biaxiality corrections like Hoffmann Most damaged nodes switch to view a tabular listing Seeger extend these results so they can be applied to most Proportional biaxial stresses Non proportional biaxial stresses are very rarely located in regions of high fatigue damage however if you are unfortunate See discussion of results on this page enough to encounter them you will have to switch to a multiaxial fatigue model like Wang Brown for these elements Multiaxial fatigue models require longer computation time that the others so most users start by assuming uniaxial or proportional biaxial conditions and then check the stress states in the critical regions to see if the assumption is valid If a non proportional state is encountered then a multiaxial analysis is conducted on a small subset of elements In this frame we will investigate the stress state of the critical nodes and determine whether a multiaxial analysis is required q Listing of FE fatigue results file shock fef DER Multiaxial Rules of Thumb Mes Dsnage Liemies Menaio SDan Manat ang Spare FE Mesh Quality and Convergence 4 046E 4 4 943E5 0 0296 0 01102 845 8 1 913E 4 1 045E6 0 5362 3 221E 3 806 8 j 1 711E 4 1 169E6 0 3535 1 584E 3 609 9 j i i Hoffmann Seeger method is pee eee ieee ote A aa Fatigue damage is exponentially related to the stress range adequate where ee ieee ma a ee and so we would expect to see lo
28. rming affect the fatigue life nCodeVay4 MSC SOFTWARE SIMULATING REALITY Managing Durability Copyright 2005 nCode International Ltd Mesh Quality MSC Patran Viewport Viewing Display Preferences Tools Insight Covirol Help B SS5O4KR SOS Re SSAA GSSSY HERA Pee sus a e Results Insight XY Plot Select the Results application switch on MSC Patran toolbar On the Create Quick Plot form select the Total Life shockfef item in the Select Result Cases listbox and the Damage item in the Select Fringe Result listbox and then press Apply oe M Sements Loads BCs Select Fringe Attributes button and set Fringe Edges Display to Element Edges You can also change the legend colours using Spectrum the one used in these plots is hotcold1 2 Zoom in to the critical area and notice how coarse the mesh is relative to damage gradient Viewing Display Preferences Tools Insight Contro Help KSSHe Re So SQa GG wes wee wee Me oes i Ba Results Look at the stress results by selecting each load case and changing the display to view the Von Mises plot Notice Von Mises stress gradient over the critical element 112MPa to 60MPa pe LA A 8 29 0021 j ONG 31114 I BD na 33255 Smooth contoured Fringe plots can hide many sins if you don t know how to look for them Default Derive
29. the FE Model and Stresses Results Create Quick Plot to Plot stress results and results model file File Group Yiewport Viewing Display Preferences Tools Insight Control Help Utilities D a 4 H i ge n Elements Loads BCs Materials Properties Load Ca Fields Analysis Results Insight XY Plot Ei ol Te Be Me all ok NY MY al S PECEL axi Action Create Y Object Quick Plot z a PSK Select Result Cases Load Case 1 Static Subcase Load Case 2 Static Sul e Load Case 3 Static Subcase 4 2 Position At Z1 ity v von Mises X Component Y Component Z Component XY Component YZ Component 2 Component XY Engr Component Max Shear 2D isplay_fringe_post 0 Nodal TRUE TRUE Named View Options Results Linear static finite element analyses have been performed already with three load cases each of magnitude of 1000 Newtons and the model and results are contained in the results file shock op2 To begin access this model and results information into a new database using MSC Paitran Note that all instructions using MSC Pairan apply for MSC Fatigue Pre amp Post users too Start the graphical interface and open a new database from File New and call it shock The model was run through an MSC Nasiran analysis so keep the Analysis Preference set to MSC Nastran when asked Click on
30. tions allow you to apply an additional Multiplier or Offset value to all elements in the group The stress is first of all multiplied Material Information From the MSC Fatigue main interface open the Material Info form We now have to associate the element group proper ties with appropriate material fatigue properties i e a suitable EN curve e Click on the first cell in the Selected Materials Information spreadsheet 1 Material and pick material SAE1008 91 HR from the list of available materials in the standard materials database e Click on Region column and select the shells group e Leave all other options Finish Treatment Kf Shape Factor and Multiplier to their default settings In order to manipulate and view all the available material properties in the database press the Materials Database Manager button to launch PFMAT Let us take a look at materials we have used Load the material by pressing the Load data set switch and selecting SAE1008 91 HR from the list Press or double click Graphical Display Strain life plot to view the strain life curve for this material Strain Amplitude twm a Copyright 2005 nCode International Ltd MSC Fatigue Set Up the Fatigue Analysis 5 of 8 ea PTIME Database Options Number of entries 0 Loading can be in the form of constant Current directory C ncode_projects
31. wer convergence between 1 417E 4 1 411E6 0 04246 3 732E 3 618 4 neighbouring nodes than would be observed with stress re 1 368E 4 1 462E6 0 2516 8 758E 3 636 j SD Ratio lt 0 1 eee g ANE h SE En sults However we would still usually expect much less than a 1234 1 S24E8 rie Rs oe factor of 2 in life between neighbouring nodes Isolated hot 2 Mean Ratio lt 0 3 1139E 4 1 756E6 04761 2991E 3 7079 spots of damage like those observed here are indicative of a o 1 104E 4 1 812E6 0 2247 7 585E 3 487 8 2 i iti i i j i 3 Ang Spd lt 10 fee een TA Er o EA singularities or poor stress meshing like that seen in the previ 7 675E 5 2 606E6 0 8033 1 437E 3 594 2 ous frame 7 576E 5 2 64E6 0 4392 1 567E 4 646 9 7 275E 5 2 749E6 0 4739 1 962E 3 482 5 Node 27386 may be 7 27465 2 75E6 0 4549 4 663E 3 595 9 l l P l l questionable in this case 7 046E 5 2 839E6 0 9278 3 396E 4 627 6 For more information on Multiaxial Fatigue Analysis please refer to the Users Manual or the Fatigue Theory training course nCode K MSC SOFTWARE SIMULATING REALITY Managing Durability Copyright 2005 nCode International Ltd The Effect of Residual Stresses EM Materials Information MSC Fatigue r Crack Initiation Materials Database Manager Select Standard Database Select User Database Temp Unit Celsius V Temp Type None Current Mat Database SC Softwara MS fi Fill Down OFF Number of M
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