MSC.Fatigue User’s Guide
CHAPTER
Preface ■List of MSC.Patran Books, 12
■Technical Support, 13 ■Internet Resources, 15
1
Introduction ■Purpose, 2 ■Overview of MSC.Fatigue, 3 ■Features of MSC.Fatigue, 4 ■Architecture of MSC.Fatigue, 7 ■Organization of Guide, 8■Technology Integration for Durability Management, 10
2
Using MSC.Fatigue
■Introduction, 14
■Stand Alone Usage, 16
■The MSC.Patran Environment, 20
■Job Setup, 21
❑General Setup Parameters, 22
❑Solution Parameters, 25
- Total Life (S-N) Solution Parameters, 26
- Crack Initiation Solution Parameters, 29
- Crack Growth Solution Parameters, 33
❑Materials Information Form, 36
- Materials Form -- Definition of Buttons, 37
- Materials Database Manager, 37
- Select Standard Database, 38
- Select User Database, 38
- S-N Material Parameters, 38
- Crack Initiation Material Parameters, 41
- Crack Growth Material Parameters, 43
❑Loading Information Form, 44
- Time History Database Manager, 44
- General Results Parameters, 46
- Finite Element Results, 47
- Results Types, 52
- Getting and Filtering Database Results, 56
MSC.Fatigue User’s Guide
❑Submit Partial Analysis, 63
❑Translate Only, 64
❑Save Job Only, 64
❑Monitor Job, 65
❑Abort Job, 67
❑Delete Job, 67
❑Read Saved Job, 68
❑Calculate Normals, 69 ❑Interactive, 70 ❑Analysis Manager, 70 ■ Postprocessing Results, 72 ❑Read Results, 73 ❑List Results, 77 ❑Re-Analyze, 77 ❑Design Optimization, 77 ❑Factor of Safety, 78 ❑Sensitivity Plots, 78
❑Extract Time History, 78
❑Extract PSD, 79
❑If the action is set to Extract PSD on the Results form, the following applies when the Apply button is invoked., 79
❑Identify Location, 79
■ Other Modes of Job Setup, 80
3
Material Management
■ Introduction to PFMAT, 86
■ PFMAT Menu Options, 88
❑Full List Option, 89
❑Search and List Option, 90
❑Tabulate Options, 92 ❑Load Option, 96 ❑Unload Option, 98 ❑Edit Option, 99 ❑Create Option, 104 - New Database, 108 - Merged Entries, 109 - Copy Entry, 110 ❑Delete Option, 111 - Selected Entries, 112
❑Weld Classifier Option, 113
❑Graphical Display Option, 116
❑Preferences Option, 119
❑Exit Option, 120
■ Component vs. Material S-N Curves, 121
■ Rules for Changing Young’s Modulus, 123
❑3.7.2 MSC.Enterprise Mvision and MSC.DataMart Access, 148
4
Loading Management
■Introduction to PTIME, 154
■PTIME Menu Options, 160
❑Add an Entry Option, 161
❑Change an Entry Option, 183
❑List All Entries Option, 191
❑Search and List Option, 192
❑Plot an Entry Option, 194
❑Delete Entries Option, 197
❑Validate Database Option, 198
❑Multi-Channel, 200
❑New Directory, 200
❑Exit Option, 200
■Multi-File Display (MMFD), 201
■Peak-Valley Extraction (MPVXMUL), 204
■Auto Spectral Density (MASD), 210
■PTIME Central Database Listing, 223
■DAC File Format Description, 224
■Loading and Units, 233
5
Total Life and Crack Initiation ■Introduction, 238 ❑Terminal Definition, 238 ❑Basic Information, 240 ❑Analysis Route, 241 ❑Necessary Files, 241
❑The Translator (PAT3FAT or FATTRANS), 242
■FE Fatigue Analysis Options (FEFAT), 243
❑Fatigue Preprocessing, 244
❑Fatigue Analysis, 247
❑Factor of Safety Analysis, 250
❑Design Optimization, 256
❑Assess Multiaxiality, 277
❑Output Time Histories, 280
❑Graphical Display of Time Histories, 283
❑Matrix Options, 283
❑Results Processing, 289
❑Utilities, 289
■Reviewing Results (PFPOST), 292
■Fast Analysis (FASTAN), 298
■Description of Files, 299
❑The Analysis Manager Execution Script (FatigueExecute), 321
❑The Fatigue Input File (jobname.fes), 326
❑The Preprocessed File (jobname.fpp), 336
❑The Results Files (jobname.fef/fos), 340
■ FEFAT Batch Operation, 343
6
Multiaxial Fatigue ■ Introduction, 348
■ Global Multiaxial Fatigue Life Analyzer, 351
❑Safety Factor Analysis, 353
- Dang Van Method, 353
❑Crack Initiation Life Analysis, 357
❑FEMLF Batch Operation, 361
■ Local Multiaxial Stress/Strain Fatigue Analyzer (MMLF), 362
❑Summary of Method, 362
❑MMLF Module Operation, 374
❑The Postprocessing Menu, 392
❑MMLF Environment Keywords, 397
❑MMLF Batch Operation, 398
■ Multiaxial Fatigue Theory, 401
❑Multiaxial Stress-Strain State, 401
❑Theories of Multiaxial Fatigue, 405
❑Critical Plane Approaches, 411
❑Multiaxial Low Cycle Fatigue Analysis, 422
❑Multiaxial Safety Factor Analysis, 442
7
Crack Growth ■ Introduction, 450
❑Terminal Definition, 450
❑Analysis Route, 451
❑Necessary Files, 453
■ K Solution Library (PKSOL), 454
❑Background Information, 454
❑Module Operation, 456
❑Post Analysis Options, 472
❑PKSOL K Solution References, 475
■ Crack Growth Prediction (PCRACK), 477
❑Module Operation, 478
❑Post Analysis Menu, 490
■ Reviewing Results (PCPOST), 493
❑PCPOST Module Operation, 494
■ Batch Operations, 500
❑Basic Principles of Fracture Mechanics, 517
❑MSC.Fatigue Crack Growth Models, 520
❑The Service Environment, 521
❑Geometric Description, 522
❑Materials Response, 522
❑Cycle-by-Cycle Approach, 523
❑Applications of Fracture Mechanics, 540
❑Estimation of LEFM Data, 541
❑Multiaxial Stresses and Crack Propagation Methods, 541
8
Vibration Fatigue ■Introduction, 544
❑Terminal Definition, 545
❑Basic Information, 546
❑Analysis Route, 547
❑Necessary Files, 547
❑The Translator (PAT3FAT or FATTRANS) and Submit Script, 548
■Job Setup, 549
❑Solution Parameters, 550
❑Materials Information Form, 552
❑Loading Information Form, 553
❑Job Control, 562
■Postprocessing Results, 567
■FE Vibration Fatigue Analysis (FEVIB), 570
❑Global Vibration Fatigue Analysis, 571
❑Design Optimization, 574
❑Output Power Spectrum, 592
❑Graphically Display a PSD, 594
❑Results Postprocessing, 594
❑Utilities, 594
❑FEVIB Batch Operation, 595
■Frequency Fatigue Life Estimation (MFLF), 598
❑MFLF Module Operation, 598
❑MFLF Postprocessing Menu, 611
❑MFLF Batch Operation, 613
■Vibration Fatigue Theory, 615
❑An Introduction to Random Process Theory, 621
❑What Does the FFT Tell Us?, 635
❑How Do We Use FFTs?, 635
❑Time Domain Characterization of Fatigue Life Estimation, 646
❑Characterization of Structural Response in the Frequency Domain, 652
❑Frequency Domain Approaches of Life Estimation, 655
❑Vibration Analysis using Finite Elements, 661
Weld Analysis ■ Introduction, 676 ❑CWELD Modeling, 677 ■ Job Setup, 678 ❑Solution Parameters, 683 ❑Materials Information, 684 ❑Loading Information, 688 ❑Job Control, 688 ❑Results, 692
■ Spot Weld Analyzer (SPOTW), 695
❑Estimate Fatigue Life, 697
❑Design Optimization, 700
❑List Global Results, 716
❑List .spt File, 716
❑Results Polar Plot, 718
❑Three Sheet Correction, 719
❑Description of Files, 720
❑SPOTW Batch Operation, 722
■ Polar Display (MPOD), 723
❑MPOD Module Operation, 723
❑MPOD Extra Details Keywords, 730
❑MPOD Batch Operation, 730
■ Spot Weld Analysis Theory, 731
■ Seam Weld Analysis, 738
❑Introduction, 738
- General Procedure, 738
❑Mean Stress Correction, 742
❑Job Setup, 743 - Basic Information, 745 - Analysis Route, 745 - Necessary files, 746 - Solution Parameters, 747 - Material Information, 747 - Loading Information, 750 - Job Control, 750
- Job Execution Status Messages, 751
- What To Do When a Job Stops, 752
- Results, 752
- Marker Plots in Insight, 752
- Damage, 753
10
Rotating Structures Analysis ■ Introduction, 756 ■ Job Setup, 757 ❑Solution Parameters, 761 ❑Materials Information, 762 ❑Loading Information, 763❑Results Postprocess, 771
❑Extract Time Histories, 772
❑FEROT Batch Operation, 773
11
Software Strain Gauges
■Introduction, 776
■The Gauge Tool, 779
❑The Gauge Definition File, 780
❑Creating and Modifying Gauges, 783
❑Extracting the FE Results, 787
❑Creating a Fatigue Input File, 789
■Software Strain Gauge Module (SSG), 792
❑Technical Details, 794
❑Correlation with Test, 795
❑SSG Batch Operation, 796
■Stress-Strain Analysis (MSSA), 797
❑Strain Gauge Rosettes, 797
❑Calculation of Principal Strains & Stresses, 799
❑MSSA Module Operation, 804
❑MSSA Batch Operation, 818
12
Fatigue Utilities ■Introduction, 822
■Advanced Loading Utilities, 827
❑Arithmetic Manipulation - (MART), 827
❑Multi-Channel Editor - (MCOE), 834
❑Rainflow Cycle Counter - (MCYC), 844
- Histogram Limits, 845
❑Formula Processor (MFRM), 848
❑File Cut and Paste - (MLEN), 881
❑Multi-File Manipulation - (MMFM), 889
❑Peak-Valley Extraction - (MPVXMUL), 894
❑Simultaneous Values Analysis DAC/RPC - (MSIMMAX), 895
❑Amplitude Distribution - (MADA), 896
❑Auto Spectral Density - (MASD), 897
❑Fast Fourier Filter - (MFFF), 898
❑Butterworth Filtration - (MBFL), 905
❑Frequency Response Analysis - (MFRA), 910
❑Statistical Analysis - (MRSTAT), 922
❑Header/Footer Manipulation - (MFILMNP), 930
■Advanced Fatigue Utilities, 943
❑Single Location S-N Analysis - (MSLF), 943
❑Single Location e-N Analysis - (MCLF), 953
❑Cycle and Damage Analysis - (MCDA), 969
❑Cycles File Lister - (MCYL), 974
❑Time Correlated Damage - (MTCD), 979
❑Multi-Axial Life Analysis - (MMLF), 987
❑Crack Growth Data Analysis - (MFCG), 988
❑Kt/Kf Evaluation - (MKTAN), 988
■ Graphics Display Utilities, 1000
❑Graphical Editing - (MGED), 1000
❑Multi-File Display - (MMFD), 1001
❑Quick Look Display - (MQLD), 1001
❑Two Parameter Display - (MTPD), 1002
❑Polar Display - (MPOD), 1002
❑Three Dimensional Display - (MP3D), 1003
❑UNIX Based Plotting Utility - (MQPLOT), 1003
❑Windows-Based Plotting Utility - (MWNPLOT), 1007
❑Printer/Plotter Definition Module - (MPLTSYS), 1014
❑Plot/Pen Colors Utility - (MNCPENS), 1030
■ File Conversion Utilities, 1032
❑Binary/ASCII Convertor - (MDTA/MATD), 1032
- MDTA - Binary to ASCII, 1032
- MATD - ASCII to Binary, 1033
❑Signal Regeneration - (MREGEN), 1047
❑RPC to DAC - DAC to RPC - (MREMDAC/MDACREM), 1054
❑Cross-Platform Conversion - (MCONFIL), 1061
❑Waterfall File Create - (MWFLCRE), 1065
- Option 1. - Create .WFL from individual files, 1066
- Option 2. - Split .WFL to .ASD files, 1066
- Option 3. - Convert .WFL file to .SAN file, 1067
- Option 4. - Convert .SAN to .WFL file, 1067
13
Validation Problems
■ Introduction, 1070
■ Problem 1: Analysis of a Keyhole Specimen, 1071
❑S-N Analysis of Keyhole, 1073
❑Crack Initiation of Keyhole, 1084
❑Crack Growth of Keyhole, 1091
❑Keyhole Results, 1099
■ Problem 2: Analysis of an Underwater Pressure Vessel, 1112
❑Crack Initiation of Weld, 1113
❑Crack Growth of Weld, 1121
■ Problem 3: Comparison to Another Code, 1127
■ Problem 4: Ten Simple Notched Geometries, 1137
■ Problem 5: Transient Results, 1148
❑Simple Transient Comparison, 1148
❑MSC.Nastran Transient Results, 1153
■ Problem 6: Spot Weld Analysis, 1158
❑H-Profile Spot Weld, 1158
❑Measured Responses, 1172
❑Finite Element Model Responses, 1182
14
Fatigue Theory ■Introduction, 1190
❑Background, 1190
❑The History of Fatigue, 1191
❑High Cycle versus Low Cycle Fatigue, 1192
❑Summary, 1192
❑Inputs to Fatigue Life Estimation Models, 1193
■Total Life (S-N) Analysis, 1202
❑Stress Cycles, 1202
❑The S-N Curve, 1204
❑Procedure for Determining the S-N Curve, 1205
❑Limits of the S-N Curve, 1208
❑Tensile Properties and the S-N Curve, 1209
❑The Influence of Mean Stress, 1210
❑Factors Influencing Fatigue Life, 1215
❑Application in MSC.Fatigue, 1224
■Crack Initiation/Strain-Life (e-N) Analysis, 1233
❑The Microscopic Aspects of Fatigue Failure, 1233
❑The Strain-Life Methodology, 1235
❑Monotonic Stress-Strain Behavior, 1236
❑Cyclic Stress-Strain Behavior, 1244
❑The Strain-Life Curve, 1253
❑Strain-Life vs. Stress-Life, 1255
❑Transition Life, 1256
❑The Effect of Mean Stress, 1258
❑Factors Influencing Fatigue Life, 1260
❑Application in MSC.Fatigue, 1261
■The Statistical Nature of Fatigue, 1269
❑Representation of Fatigue Data on a Statistical Basis, 1270
❑The Statistical Distribution Function, 1270
❑Probability of Failure at a Finite Life, 1271
❑Probability of Failure for Infinite Life, 1272
❑Handling Statistics Under Random Loading Conditions, 1273
❑The Absolute Accuracy of Fatigue Life Estimation, 1277
■Estimating Material Cyclic Properties From UTS & E, 1278
A
References ■References, 1282
■Further Reading, 1288
Module Operations ■ Terminal Definition, 1290
■ MASK (X) Mode, 1291
❑Description of the Text Screen, 1291
❑Using the Keypad, 1292
❑Special Commands, 1293
❑Correcting Input Errors on the Text Screen, 1294
❑Inputting a Range of Numbers, 1294
❑List Function Operation, 1294
❑Graphical Screen Manipulation, 1296
❑Graphical Mouse Operations, 1298
❑Graphical Command Line, 1298
❑Font Selection (PFSETFONT), 1299
■ MOTIF (and Windows NT) Mode, 1300
❑Graphical Options, 1301
❑Graphical Command Line, 1303
■ Modifying the MSC.Fatigue Environment (MENM), 1310
C
Limitations and Error Messages ■ Program Limitations, 1316 ■ Error Messages, 1317 ❑PCL Form Messages, 1317❑Translator (PAT3FAT) Messages, 1321
❑Analyzers (FEFAT, PCRACK), 1327
❑Analyzer FEVIB, 1334
D
MSC.Fatigue Information ■ About MSC.Fatigue, 1338 ■ Using MSC.Fatigue, 1339■ Common MSC.Fatigue Issues, 1340
■ MSC.Fatigue and a Corporate Durability Management System, 1341
■ More Information about nCode International, 1342
■ List of MSC.Patran Books ■ Technical Support
■ Internet Resources
List of MSC.Patran Books
Below is a list of some of the MSC.Patran documents. You may order any of these documents from the MSC.Software BooksMart site at www.engineering-e.com.
Installation and Release Guides
❏ Installation and Operations Guide
❏ Release Guide
User’s Guides and Reference Manuals
❏ MSC.Patran User’s Guide
❏ MSC.Patran Reference Manual
❏ MSC.Patran Analysis Manager
❏ MSC.Patran FEA ❏ MSC.Patran Materials ❏ MSC.Patran Thermal Preference Guides ❏ ABAQUS ❏ ANSYS ❏ LS-DYNA ❏ MSC.Marc ❏ MSC.Dytran ❏ MSC.Nastran ❏ PAMCRASH ❏ SAMCEF
Technical Support
For help with installing or using an MSC.Software product, contact your local technical support services. Our technical support provides the following services:
•
Resolution of installation problems•
Advice on specific analysis capabilities•
Advice on modeling techniques•
Resolution of specific analysis problems (e.g., fatal messages)•
Verification of code error.If you have concerns about an analysis, we suggest that you contact us at an early stage. You can reach technical support services on the web, by telephone, or e-mail:
Web Go to the MSC.Software website at www.mscsoftware.com, and click on Support. Here, you can find a wide variety of support resources including application examples, technical application notes, available training courses, and documentation updates at the MSC.Software Training, Technical Support, and Documentation web page.
Phone and Fax United States Telephone: (800) 732-7284 Fax: (714) 784-4343 Frimley, Camberley Surrey, United Kingdom Telephone: (44) (1276) 67 10 00 Fax: (44) (1276) 69 11 11 Munich, Germany Telephone: (49) (89) 43 19 87 0 Fax: (49) (89) 43 61 71 6 Tokyo, Japan Telephone: (81) (3) 3505 02 66 Fax: (81) (3) 3505 09 14 Rome, Italy Telephone: (390) (6) 5 91 64 50 Fax: (390) (6) 5 91 25 05 Paris, France Telephone: (33) (1) 69 36 69 36 Fax: (33) (1) 69 36 45 17 Moscow, Russia Telephone: (7) (095) 236 6177 Fax: (7) (095) 236 9762
Gouda, The Netherlands Telephone: (31) (18) 2543700 Fax: (31) (18) 2543707 Madrid, Spain Telephone: (34) (91) 5560919 Fax: (34) (91) 5567280 Main Index
Email Send a detailed description of the problem to the email address below that corresponds to the product you are using. You should receive an acknowledgement that your message was received, followed by an email from one of our Technical Support Engineers.
Training
The MSC Institute of Technology is the world's largest global supplier of
CAD/CAM/CAE/PDM training products and services for the product design, analysis and manufacturing market. We offer over 100 courses through a global network of education centers. The Institute is uniquely positioned to optimize your investment in design and simulation software tools.
Our industry experienced expert staff is available to customize our course offerings to meet your unique training requirements. For the most effective training, The Institute also offers many of our courses at our customer's facilities.
The MSC Institute of Technology is located at: 2 MacArthur Place
Santa Ana, CA 92707 Phone: (800) 732-7211 Fax: (714) 784-4028
The Institute maintains state-of-the-art classroom facilities and individual computer graphics laboratories at training centers throughout the world. All of our courses emphasize hands-on computer laboratory work to facility skills development.
We specialize in customized training based on our evaluation of your design and simulation processes, which yields courses that are geared to your business.
In addition to traditional instructor-led classes, we also offer video and DVD courses, interactive multimedia training, web-based training, and a specialized instructor's program.
Course Information and Registration. For detailed course descriptions, schedule information, and registration call the Training Specialist at (800) 732-7211 or visit www.mscsoftware.com.
MSC.Patran Support MSC.Nastran Support
MSC.Nastran for Windows Support MSC.visualNastran Desktop 2D Support MSC.visualNastran Desktop 4D Support MSC.Abaqus Support
MSC.Dytran Support MSC.Fatigue Support
MSC.Interactive Physics Support MSC.Marc Support
MSC.Mvision Support MSC.SuperForge Support
MSC Institute Course Information
[email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected]
Internet Resources
MSC.Software (www.mscsoftware.com)
MSC.Software corporate site with information on the latest events, products and services for the CAD/CAE/CAM marketplace.
Simulation Center (simulate.engineering-e.com)
Simulate Online. The Simulation Center provides all your simulation, FEA, and other engineering tools over the Internet.
Engineering-e.com (www.engineering-e.com)
Engineering-e.com is the first virtual marketplace where clients can find engineering expertise, and engineers can find the goods and services they need to do their job
MSC.Linux (www.mscsoftware.com/hpc)
Now with almost 40-years of unparalleled experience in scientific and technical computing, MSC.Software is leveraging this knowledge to deliver its customers state-of-the-art, high performance computing solutions based on clustered computing for running engineering and life sciences applications.
CATIASOURCE (plm.mscsoftware.com)
Your SOURCE for Total Product Lifecycle Management Solutions.
Process Architecture Lab (PAL) (pal.mscsoftware.com/services/pal)
PAL is a virtual product development environment that enables PAL participants and customers to define, validate, and demonstrate advanced tools, processes, and e-business solutions.
CHAPTER
1
Introduction
■ Purpose ■ Overview of MSC.Fatigue ■ Features of MSC.Fatigue ■ Architecture of MSC.Fatigue ■ Organization of Guide■ Technology Integration for Durability Management
1.1
Purpose
MSC.Fatigue is an advanced fatigue life estimation software package for use with finite element analysis results. It provides state-of-the-art fatigue analysis tools which can be used to optimize the life of a product early in the design process. MSC.Fatigue has been developed jointly by nCode International Ltd. and MSC.Software Corporation (MSC). nCode is a recognized leader worldwide in durability management solutions with specialties in fatigue life estimation software systems and consultancy services. MSC in the world market leader in finite element analysis solutions.
MSC.Fatigue can run stand alone with its own graphical pre- and postprocessor but is also tightly integrated into the MSC.Patran environment. All of MSC.Fatigue’s analysis capabilities and generated results are available from within the MSC.Patran environment; however, it is flexible enough to be run outside of the MSC.Patran or its own graphical environment also. With the tight integration within MSC.Patran the casual user will never need to be aware that separate programs are actually used.
For the expert user, there are various components that make up MSC.Fatigue: a PCL (PATRAN Command Language) library to provide the customization of MSC.Patran for MSC.Fatigue, a translator to convert model data from MSC.Patran into the fatigue analysis code and to bring results from the fatigue analysis code back into the MSC.Patran database, as well as the various fatigue analysis modules that make up MSC.Fatigue itself.
MSC.Fatigue is used most effectively within its own pre- and postprocessor or within the MSC.Patran environment and not in isolation. It requires loading data and material properties which will often be supplied by measurement and materials test laboratories respectively and also requires preprocessing of finite element stress data. The fatigue life estimation process embodied in a MSC.Fatigue analysis can also be correlated with test results. The integration of the measurement, test, and design analysis functions, to develop optimized products, is known as Integrated Durability Management (IDM). IDM is the key to the effective use of MSC.Fatigue. SeeTechnology Integration for Durability Management(p. 10).
1.2
Overview of MSC.Fatigue
In today’s competitive marketplace, companies are seeking to improve product quality, performance, and durability, as well as shorten time-to-market. The complexity of modern products demands the use of computerized engineering analysis to optimize the product design and to increase competitiveness.
Analysis reduces development costs by allowing the effects of varying design parameters to be explored quickly and efficiently in the computer, without building prototypes. For the structural analyst whose goal is to predict stresses and displacements, these parameters typically include geometry changes, loading, and choice of materials. However, the prediction of stresses is only part of product design optimization. An additional critical requirement of computerized engineering analysis in the product’s design process is to estimate the product’s serviceable life. Analytically predicting fatigue life is, therefore, an important tool.
Designers and engineers often use simple handbook calculations to address product durability during the conceptual design phase. Frequently however, product durability is not examined in detail until the prototype and testing phases of the development cycle. Furthermore,
considerable expense can be incurred in reaching the prototype and testing phase.
The use of testing alone cannot evaluate all design parameters and often fatigue related failures are not discovered until the product has been in service for a length of time. At this stage, fatigue problems can have disastrous effects, including costly recalls and damaged product reputations, not to mention possible loss of life.
The ability to assess fatigue related problems and to perform durability analysis to estimate product life early in the design phase offers great benefits to a company in reducing
development and testing costs, shortening time-to-market, and improving product life. MSC.Fatigue should be a part of any engineering organization interested in these benefits.
1.3
Features of MSC.Fatigue
MSC.Fatigue allows the designer or analyst to carry out fatigue calculations early in the design process. It takes the detailed stress distributions produced by a finite element analysis and a description of the variation of the loading with time, carries out fatigue calculations using state-of-the-art fatigue life estimation methods, and produces fatigue life results in the form of contour plots. These life plots can be displayed using standard MSC.Patran imaging tools as well as imaging tools from other popular pre- and postprocessing systems.
MSC.Fatigue offers a unique integration between finite element analysis (FEA) and fatigue life estimation by enabling the user to select areas of the finite element (FE) model for fatigue life analysis with specific tools provided in the display postprocessor. All three commonly used fatigue life estimation techniques are supported: total life or nominal stress-life (including analysis of welded structures), crack initiation (otherwise known as strain-life), and crack growth or Linear Elastic Fracture Mechanics (LEFM) life estimation techniques.
Both the crack initiation and total life approaches provide the capability to investigate the effect of local changes in surface finish and treatment. A comprehensive materials database is
provided that has sophisticated search facilities. Full elastic-plastic transformations are carried out in the crack initiation modeling. Multiple or single static and/or offset load cases may be defined. Fatigue results may be presented in a number of different ways including scaling the results in terms of user-defined units such as hours, miles, flights, etc. Full-color life contour plots may be produced providing a rapid assessment of fatigue critical areas.
Detailed analysis may be carried out to establish sensitivities to variation in material,
manufacturing process or loading, using the Design Optimization analyzer. Crack growth may be investigated using the cycle-by-cycle linear elastic growth analysis facilities.
The link between finite elements and fatigue introduces a control on fatigue life performance at an early stage in the design cycle. This integrated approach promotes a total quality policy enhancing the design/development process within a company.
Key Features of MSC.Fatigue
1. Total Lifeanalysis (S-N) based on the nominal stress-life method using rainflow cycle counting and Palmgren-Miner linear damage summation. Various analysis parameters may be chosen such as mean stress correction methods and confidence parameters. Both component and material S-N curves may be accessed. Material S-N curves allow for specification of material surface finish and treatment.
2. Crack Initiationanalysis (ε-N) or the local strain method using cyclic stress-strain
modeling and Neuber elastic-plastic correction. The mean stress correction method, surface finish and treatment factors may be adjusted to investigate the effect of these fatigue dependent parameters.
3. Crack Growthanalysis using linear elastic fracture mechanics (LEFM) and cycle-by-cycle modeling of crack closure due to overloads, the effect of chemical environment, the loading rate and history effects. On-line displays of crack progress report the rate of crack growth, and postprocessing menus enable interpolation of results.
4. Factor of Safetyanalysis for structures designed for infinite life (such as powertrain and engine components) is available also for the crack initiation and the total life methods.
5. Fatigue analysis of steel or aluminum welded structures using the total life approach as defined in the British Standard, BS7608, design code including aWeld Classifier.
6. A state-of-the-artSpot Weldanalyzer is also available as a separate module where spot welds are modeled in MSC.Nastran as stiff bars between two sheets. The forces in the bars are then converted to stress and used in a S-N analysis using the Rupp-Stoerzel-Grubisic method. The method calculates fatigue life on the basis of structural stresses around each spot weld which are in turn calculated on the basis of the cross-sectional forces and moments in the CBAR elements. A relatively coarse mesh is required, and results can be visualised to good effect using INSIGHT.
7. Vibration Fatigueanalysis calculates fatigue lives directly from Power Spectral Density Functions (PSDF or PSD) using the S-N method. This is a very powerful capability when in is not convenient to analyze a structure in the time domain making it necessary to do a random vibration analysis.
8. Global life estimates presented as color fringe contour plots enable the rapid assimilation of theResultsand easy identification of the fatigue critical areas.
9. InteractiveDesign Optimizationallowing the rapid assessment of analysis parameters and design options including alternative geometries, surface finishes, surface
treatments, weld details, or materials.
10. Materials Databaseloaded with standard fatigue data sets. Access to the database is provided by a sophisticated materials database which offers loading, editing, creating, searching, and data visualization.
11. LoadingTime History Databasemanager provides a method of archiving loading time histories together with their details. In addition, full graphical editing and signal creation facilities offer the ability to prepare time histories, spectrums and PSDs from measured field data or artificially synthesized data.
12. The combined effect ofMultiple Loadinghistories may be explored together with
Multiple Materialsdatasets on one structure. Substructures may be analyzed by selecting specific geometric entities within MSC.Patran.
13. ABiaxiality Analysisfeature helps in determination of necessary fatigue analysis methods when complex multi-axial loadings are involved and the validity of an associated fatigue analysis. Corrections can be made for proportional loading and if non-proportional loading is determined a separate module allows forMultiaxial Fatiguelife calculations.
14. Finite element stress/strain results may be used from eitherLinear Static/Transient Dynamic/Forced VibrationorFrequency Response/Random Vibrationanalyses. Results are read directly from the MSC.Patran database or from either a MSC.Patran FEA results file or external MSC.Patran results files. This architecture supports results from virtually any analysis code that is supported by PATRAN 2.5 or MSC.Patran. In addition results may be read from other external results files from analysis codes such as MSC.Nastran and I-deas.
15. An interface toNASA/FLAGROis also featured within MSC.Fatigue via the MSC.Patran PCL forms. NASA/FLAGRO is a two dimensional crack growth code developed by NASA which is complimentary to the crack growth module featured in MSC.Fatigue.
16. ASoftware Strain Gaugemodule allows the MSC.Fatigue user within the
MSC.Patran environment to simulate an actual strain gauge. This allows for extraction of time varying strain results from a fatigue analysis in the coordinate system(s) of the strain gauge for test/analysis comparison and correlation.
17. A number of usefulUtilitiesare include as a separate module of MSC.Fatigue. These include many time history manipulation and display utilities and additional fatigue life analysis features such as calculations from measured stress or strain data and time correlated damage.
Note: MSC.Fatigue has used the Pat3fat translator to generate input data for the solvers. While this translator has been effective for handling small to medium size models, inadvertent failures were being experienced for large models. To mitigate this
problem, MSC.Fatigue incorporated a new translator called FATTRANS in V2004. This will be the default translator for V2005r2 and subsequent versions. Any references to Pat3fat in this and in any other documents apply to FATTRANS as well.
1.4
Architecture of MSC.Fatigue
MSC.Fatigue is organized into three distinct analysis modes.
The first mode is theGlobalmulti-location analysis which allows selection of a region or regions containing nodes and/or elements of the FE model in which to carry out a fatigue life analysis. The life estimates may be contoured to provide a visual indication of the fatigue critical areas. This mode of operation relies on a tight integration between MSC.Patran and the MSC.Fatigue system or use of MSC.Fatigue’s own graphical display. Retrieval of the FE results is generally achieved by direct access to the MSC.Patran database. The definition of MSC.Fatigue job parameters is achieved through the use of forms and menus accessible directly within
MSC.Patran or MSC.Fatigue’s own graphical display. The fatigue analysis may be submitted, monitored, and aborted, directly from these forms and menus. All fatigue analysis methods may be accessed through this Global method.
Another mode of operation provides aDesign Optimizationcapability based on calculations at a localized node or element. This mode of operation provides the engineer with a fast and efficient method of assessing alternative materials, surface finishes/treatments, weld
procedures, etc. In general terms, when the engineer has located the fatigue problem areas using the Global multi-node/element analysis, the design may then be optimized in terms of fatigue performance using the Design Optimization facilities. These analysis modules use information from the Global analysis to provide the ability to carry out fatigue life estimation rapidly in a localized region, assessing various design optimization options until a solution has been found which meets the fatigue life criteria. A back calculation facility allows the definition of a desired life and the analysis code will find the optimum value of a chosen parameter to meet that life requirement.
Having located the region where a crack will initiate the progress of the crack as it grows can be modeled using theCrack Growthanalysis capabilities. This is the third mode of operation. In addition to these three modes there are additional modules for more specialized analyses such as mentioned in the previous section. These include things such as spot welds, software strain gauges, factors of safety, multi-axial assessments, and much more.
1.5
Organization of Guide
This document describes the use of MSC.Fatigue to solve fatigue problems using finite element analysis results. The guide includes the following chapter topics:
Introduction(Ch. 1) provides an overview of the features of MSC.Fatigue.
Using MSC.Fatigue(Ch. 2) describes the details involved in setting up, submitting, monitoring, and aborting a MSC.Fatigue job both within the MSC.Patran environment and in its own stand alone mode. Also the graphical postprocessing of results is described including two modules, PFPOST and PCPOST, used for tabular viewing of fatigue results.
Material Management(Ch. 3) describes in detail the creation and manipulation of cyclic material properties using the materials database manager, PFMAT, which can be accessed directly from the MSC.Fatigue setup forms or from the computer’s operating system.
Loading Management(Ch. 4) describes in detail the creation and manipulation of loading time histories, power spectral density functions (PSDs), and rainflow matrices (spectrums) using the database manager, PTIME, which can be accessed directly from the MSC.Fatigue setup forms or from the computer’s operating system. Other modules for multiple graphical displays, MMFD, and peak-valley-extraction, MPVXMUL, are also described.
Total Life and Crack Initiation(Ch. 5) describes the operation of the fatigue solver, FEFAT, including the fatigue preprocessing (rainflow cycle counting), fatigue analysis, sensitivity studies, and factor-of-safety calculations. The details of this module as both an interactive and batch operation, which offers a fast route for processing multiple MSC.Fatigue jobs, is explained also.
Multiaxial Fatigue(Ch. 6) addresses multiaxial consideration when loading conditions are nonproportional. Standard accepted uniaxial methods break down when these conditions exist.
Crack Growth(Ch. 7) describes the crack growth module, PCRACK, both its interactive and batch operations. The K solution or compliance function preparation module, PKSOL, for defining crack geometries is also described in this chapter as well as postprocessing options. The interface to NASA/FLAGRO is also explained in this chapter.
Vibration Fatigue(Ch. 8) describes the operation of the fatigue analyzer, FEVIB, where loading is in the form of PSDFs and the finite element results are from frequency response or random vibration analyses.
Weld Analysis(Ch. 9) describes the fatigue spot weld analyzer, SPOTW, where spot welds are modelled as rigid bars between two sheets using MSC.Nastran. Polar display of results is also explained in this chapter.
Software Strain Gauges(Ch. 11) describes the creation of software strain gauges, directly on to locations of the FE model, the extraction of FE results from these gauges, and the subsequent fatigue analysis, SSG, of these results with possible correlation to actual data from hardware strain gauges.
Fatigue Utilities(Ch. 12) describes the collection of utility modules for advanced loading and cycle/damage display and manipulation as well as other useful utilities such as cross-platform file transfers, hardcopy plotting, and fatigue calculations from measured stress and/or strain data.
Validation Problems(Ch. 13) shows detailed examples of each of the fatigue analyzers available in MSC.Fatigue including how to set up jobs, submit and monitor them and evaluate the results. Some of these problems are used for benchmarking and validation of the
MSC.Fatigue application.
Fatigue Theory(Ch. 14) covers the basic fatigue theories for S-N and crack initiation analysis used in MSC.Fatigue. Theory for other analysis types are covered in their respective chapters. This chapter in not intended to be complete technical text on fatigue analysis, but rather a fairly comprehensive overview of the techniques adopted by MSC.Fatigue.
Various appendices cover technicalReferences(App. A), different aspects ofModule Operations(App. B), andLimitations and Error Messages(App. C).
A comprehensive Quick Start Guide is also available separately from this guide to quickly get you started as a productive MSC.Fatigue user including several useful example problems.
1.6
Technology Integration for Durability Management
Durability Management is the control and organization of design, test, and production, to ensure products are developed to meet the required life within cost and on time. The process has evolved over the last 150 years since fatigue failures were first recognized. While there are many technologies that have contributed to the understanding of fatigue and to the solution of fatigue problems, two major procedures are used in durability management: fatigue testing and fatigue modelling.
Fatigue Testing. The first fatigue tests were carried out on full scale components to establish their safe working stress. Later, the more complete relationship between cyclic stress or strain and fatigue life was established. Small scale specimens were tested to study component life and also fatigue mechanisms. In more recent times, as tests had to become increasingly realistic, special test techniques were developed such as Remote Parameter Control. Today, testing is still the most common way of confirming the fatigue life of a product prior to releasing it onto the market. However, testing often reveals weaknesses which necessitate re-design. Assessing the suitability of particular design modifications using fatigue testing alone can be time consuming and cost far more than just a delayed product.
Fatigue Modelling. The estimation of fatigue life using mathematical modelling techniques was developed to assist the engineer in solving fatigue problems without always having to physically test all the options. For this reason, techniques such as local strain or crack initiation modelling have become widely used. Improvements in the power of computers have enabled the effective use of these techniques. Today, most major companies designing mechanical structures will use a fatigue life estimation tool such as MSC.Fatigue in conjunction with testing. By the late 1980s the use of finite element analysis (FEA) had become established as a tool for stress analysis. At the same time the integration of FEA and fatigue life estimation through the MSC.Fatigue product began to provide new benefits by assessing fatigue earlier in the
development process.
Integrated Durability Management. Understanding and effective implementation of
durability management strategies require a partnership between test and design analysis. It can reduce product lead time by focussing the use of fatigue testing to the essential correlation and sign-off tests. The use of fatigue modeling, at the design analysis stage, allows more options to be assessed for little incremental cost. Integrated durability management can produce better products more quickly and cheaply.
Figure 1-1illustrates some of the links and benefits from this integration. In summary they are:
•
Correlation of test and analysis to improve the accuracy of analytical designoptimization
•
Early fatigue life estimates in the design process leading to better products earlier•
Analytical fatigue design optimization based on realistic descriptions of serviceenvironments.
With reference toFigure 1-1, service environment descriptions can be edited to produce drive files for fatigue test or nominal loading data for use in FE based fatigue analysis. Fatigue optimization analysis may be carried out on local structural response histories extracted from the FEA based fatigue simulation or from measurements made on structures under test. Early estimates of life at the design stage can be made using nominal stress data and calibration. Correlation between component test lives and calculated lives form an important step in developing appropriate analytical procedures for specific components.
Figure 1-1 Schematic for Integrated Durability Analysis Service Environment Component Tests Finite Element Based Fatigue Analysis Fatigue Optimization Analysis Finite Element Analysis Calculated Life Material Parameter Database Nominal Loading Files Sign-off Life Component Life Curves Local Strain Files Drive Files Correlation K t Nominal Stress and Calibration Main Index
CHAPTER
2
Using MSC.Fatigue
■ Introduction ■ Stand Alone Usage
■ The MSC.Patran Environment ■ Job Setup
■ Job Control
■ Postprocessing Results ■ Other Modes of Job Setup
2.1
Introduction
A MSC.Fatigue analysis is initiated in one of three ways. The most useful and practical way is either through its own graphical interface or directly through the MSC.Patran environment. The stand alone operation is described inStand Alone Usage(p. 16) and the MSC.Patran
environment is described inThe MSC.Patran Environment(p. 20).
A MSC.Fatigue job can also be setup outside of any type of graphical environment directly through the MSC.Fatigue modules themselves, although this is limiting. SeeOther Modes of Job Setup(p. 80).
Regardless of how a fatigue analysis is set up there are always three basic inputs that must be specified before an analysis can proceed. Only setup for the basic analysis types (Total Life and Crack Initiation(Ch. 5) andCrack Growth(Ch. 7)) are explained in this chapter. For other more advanced fatigue analysis setup (Vibration Fatigue(Ch. 8),Weld Analysis(Ch. 9),Software Strain Gauges(Ch. 11),Multiaxial Fatigue(Ch. 6)), see the appropriate chapter.
Preparing for a MSC.Fatigue Analysis. The three basic pieces of information needed to compute a fatigue life estimation using MSC.Fatigue are:
•
Materials Information:This is information describing the cyclic fatigue properties of the component or material. This can be accomplished using MSC.Fatigue’s materials database manager, PFMAT. The materials data may already be found in the materials database, or it may be generated from the UTS of the material based on empirical formulations, or it may be obtained from materials tests or other references and input manually into the materials database. SeeMaterial Management(Ch. 3).•
Loading Information:Loads can be in the form of time histories, power spectral density functions (PSDFs) or cycle definitions (rainflow matrices). The loading is defined externally to the FE model in the case of static and frequency response FE analysis or else must be an integral part of the FE analysis for transient and random vibration analyses. External loading is defined using MSC.Fatigue’s time history database manager, PTIME. SeeLoading Management(Ch. 4).•
Geometry Information:For most fatigue analyses, this entails the finite element model and the stress or strain results. In the case of a crack growth analysis, a comprehensive library of compliance functions is provided in the module, PKSOL, to define the crack geometry. To obtain the stress/strain information, an appropriate finite element (FE) analysis must have been performed. Any fatigue analysis begins where a finite element analysis ends. Therefore, this guide does not go into any detail concerning model creation or finite element analysis itself.The fatigue analysis can be thought of as a “five box trick” as shown inFigure 2-1where the first three are the inputs as described above, the fourth is the actual fatigue analysis, and the fifth is the interpretation and/or postprocessing of the results which could lead to a loop back to the first three inputs for sensitivity studies.
This is an important concept in MSC.Fatigue in that it allows you to build a “fatigue model.” Fatigue analysis is a logarithmic process, thus amplifying any errors or discrepancies of the three inputs through the analysis process. Sensitivity studies allow for easy and quick interpretation of resulting life predictions to see how sensitive your model is to variations in any of the inputs.
Figure 2-1 The MSC.Fatigue “five-box trick”
Cyclic Material
Properties
Service Loading
Geometry and
Stress Information
FATIGUE Analysis
Results Evaluation
and Postprocessing
2.2
Stand Alone Usage
To run MSC.Fatigue using its own graphical pre- and postprocessor you invoke it from the command prompt by typing, fatxx or fxx or simply fatigue where xx is the version number. This will bring up the following interface.
The following operations need to be performed to successfully set up and run a MSC.Fatigue job. All of these are described in detail in this section.
1. Open a new database (under File/New) and import the FE model along with its results. This needs to be done only once for any particular model. Various methods of import are supported as described below.
2. Perform any model manipulations necessary such as creating groups, changing display styles or even viewing and manipulating the FE stress/strain results.
3. Set up the MSC.Fatigue job and submit the job for analysis. This consists of defining the three inputs to the fatigue analysis (material, loading, and geometry information). 4. Import the fatigue analysis results and postprocess them for in-depth understanding. Import FE Model/Results. When a new database is opened you will be presented with a form asking you to set the Analysis Preference. The default is MSC.Nastran. Set the Analysis
Preference to the FE code from which you will be importing the model and results. If the FE code that you used is not in the selection, then accept the default. The Analysis Preference can be changed later under Preferences/Analysis if necessary.
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The following table describes the different methods of importing a FE model and its
stress/strain results into a database. Additional help can be obtained on any of these topics by pressing the F1 key with the cursor in the appropriate form.
Parameter Description
MSC.Patran Neutral File
Under File | Import you can set the Object to Model and the Source to Neutral. This will allow import of the FE model from the selected MSC.Patran neutral file after pressing the Apply button.
MSC.Patran Results File
Under File | Import you can set the Object to Results and the Format to any of the valid MSC.Patran result file types. This will allow import of the FE results for a model. You must be sure that the model already exists in the database and the result file is compatible with the existing model and you must know whether the result files contain nodal or elemental data.
MSC.Nastran Input File
You can read the MSC.Nastran input file one of two ways. Under File | Importwith the Object set to Model and the Source set to
MSC.Nastran Input. Or you may do the same operation under the Import switch on the main form when the Analysis Preference is set to MSC.Nastran. Set the Action to Read Input File.
MSC.Nastran Output2 File
You can read both model and results data from a MSC.Nastran Output2 file with the Analysis Preference set to MSC.Nastran. Press the Import switch on the main form and set the Action to Access Resultsand set the Object to Read Output2 and the Method to the appropriate selection.
MSC.Nastran XDB File
You can attach to an external MSC.Nastran XDB results database with the Analysis Preference set to MSC.Nastran. Press the Import switch on the main form and set the Action to Access Results, set the Object to Attach XDB, and set the Method to the appropriate selection. No results are actually imported into the database but remain in the XDB file and are directly accessed when needed.
ABAQUS ANSYS MSC.Marc Advanced FEA
Both model and results data can be imported from any of these codes when the Analysis Preference is set appropriately under Preferences | Analysis. Press the Import switch on the main form and set the Action to Read Results.
Universal File Both model and results data can be imported from a Universal file under File | Import. Set the Object to Model and the Source to Universal File. Select the appropriate file and press Apply. Although the Object is set to Model both model and results information will be imported if they exist in the file.
Fatigue results can also be output in Universal File format; set the keyword FEFTYPE to the value UNIVERSAL using the MENM module. SeeModifying the MSC.Fatigue Environment (MENM)
(p. 1310).
MSC.Patran Database
You can share information from an existing MSC.Patran database and merge the model into your database. Under File | Import set the Object to Model and the Source to MSC.Patran DB. Select the appropriate database and press Apply.
Model Manipulations. The following table described the various options available to you to manipulate your FE model and view the stress/strain results once they have been imported. Additional help on any of these topics can be obtained online by pressing the F1 key with the cursor in the appropriate form.
Parameter Description
Group This is an important tool in MSC.Fatigue. It is necessary to specify a group which contains the nodes and/or elements for which you wish to perform a fatigue analysis. By default all elements and nodes are contained in the default_group. But if a reduced set of nodes/elements is needed or the model needs to be broken into more than one group for defining multiple combinations of materials and surface
finishes/treatments, then it will be necessary for you to create groups. Creating a group is relatively straight forward. Supply a name and graphically select entities from the graphics screen or type them in the appropriate databox manually using the convention Node or Elem in front of any list of nodes or elements.
Vieiwport This pulldown menu allows you to create and manipulate multiple graphical viewports for advanced visualization. This is useful for looking at multiple views simultaneously or posting different groups into separate viewports.
Viewing This pulldown menu gives access to view manipulation tools such as zooming, panning, rotating, and translating the model. Most of this functionality is available from icon buttons on the main form which change the way the mouse is used in graphically manipulating the model. Pressing the middle mouse button and rolling the mouse in the graphics viewport will move the model.
Display This pulldown menu gives access to allow changes in the display attributes of the model. Again, many of these features are available from the button icons on the main form. Shading, hidden line mode, entity coloring, plotting and erasing are all accessed from this menu.
Preferences This pulldown menu allows you to set preferences. Everything from the FE analysis preference to how graphical picking works is set from this menu.
Tools: List This pulldown menu allows you to create and process lists of FEM or Geometry data.
Tools: Fatigue Utilities
Many of the MSC.Fatigue utility modules may be spawned from this pulldown menu including the loading, materials, and compliance function managers. Usage of these modules is explained in:
Material Management(Ch. 3),Loading Management(Ch. 4),Crack Growth(Ch. 7), andFatigue Utilities(Ch. 12).
Insight Control This pulldown is discussed in more detail as it pertains to postprocessing and the Insight Utility.
Finite Elements This is a utility to allow you to node and element attributes such as location, distance, coordinate systems, and associations.
Job Setup. Once the FE model and results have been imported, you are then ready to set up a fatigue analysis. With the MSC.Fatigue Pre&Post module you do this by pressing the Analysis switch on the main menu bar. This procedure it explained in detail inJob Setup(p. 21) andJob Control(p. 59).
Postprocessing. After the fatigue analysis is completed, you may import the results for graphical postprocessing or you may run one of MSC.Fatigue’s postprocessing modules for further interpretation of results and “what-if” studies. This is explained in detail in
Postprocessing Results(p. 72).
Coordinate Frames
This is a utility to allow you to create coordinate frames and modify, transform, and show attributes of coordinate frames. This utility is mainly for use if it becomes necessary to transform FE results to alternate coordinate systems.
Results / Insight These two utilities are described in more detail as they pertain to postprocessing fatigue results but are available for postprocessing the imported FE stress and strain results also.
XY Plot This utility allows you to create XY plots of data. The Results application and certain aspects of postprocessing fatigue results automatically create XY plots. This application allows you to manipulate those XY plots.
Parameter Description
2.3
The MSC.Patran Environment
MSC.Fatigue is fully integrated into the MSC.Patran environment. It is assumed that the user has a working knowledge of MSC.Patran. The setup for a MSC.Fatigue job is accessed through the Tools pulldown menu by selecting MSC.Fatigue and then Main Interface from the Submenu. Other items are available from the MSC.Fatigue pulldown but are described elsewhere in this guide.
The following operations are need to perform a successfully MSC.Fatigue job from within MSC.Patran once a model has been created and the FE analysis completed:
1. Open a database (under File menu). Import the FE model along with its results if necessary when starting from a new database. It is generally necessary that all model geometry and FE results be stored in the database.
2. Perform any model manipulations necessary such as creating groups, changing display styles or even viewing and manipulating the FE stress/strain results.
3. Set up the MSC.Fatigue job and submit the job for analysis. This consists of defining the three inputs to the fatigue analysis (material, loading, and geometry information). 4. Import the fatigue analysis results and postprocess them for in-depth understanding. It is assumed that the user has a working knowledge of how to perform the first two operations. The last two are described inJob Setup(p. 21),Job Control(p. 59), andPostprocessing Results(p. 72).
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2.4
Job Setup
When the Analysis switch is selected from MSC.Fatigue Pre&Post or MSC.Fatigue is selected from the Tools pull-down menu from MSC.Patran, the following form appears.
MSC.Fatigue Initiation Analysis: Node Results Loc.: Global Nodal Ave.: MPa F.E. Results:
General Setup Parameters:
Jobname (32 chrs max) =
Title (80 chrs max) =
Solution Params...
Material Info...
Loading Info...
Specific Setup Forms:
Job Control...
Results...
Job Control/Results Forms:
Motif Mask Module Drivers:
Cancel
Job Control: These two buttons allow for job submission, monitoring, and aborting in addition to reading results into the database and inputting old, saved job parameters. SeeJob Control(p. 59), and
Postprocessing Results(p. 72).
General Setup: This section allows the user to define the fatigue analysis type and specifics about the type of finite element results to use including choice of stress or strain, and stress units. SeeGeneral Setup Parameters(p. 22).
Module Drivers: On UNIX the external MSC.Fatigue modules can be driven in either a Motif interface (default) or in the original Mask form. The Motif interface is described throughout the document. For a description of the Motif and Mask interfaces, please refer toModule Operations(App. B). Windows machines use the native environment and this option is not available.
Info Res. Units:
Stress
Job description: Really part of the general setup parameters, these two widgets simply allow you to define a job name and give it a textual description.
Specific Setup: This section allows the user to define the specific fatigue parameters associated with each analysis type. These buttons display additional forms which may be different for the different analysis types. SeeSolution Parameters(p. 25),Materials Information Form(p. 36), andLoading Information Form(p. 44).
◆◆ ◆
General Setup Parameters
The following table explains each of the options for the general setup parameters:
Parameter Description
Analysis Three basic fatigue analysis types are possible: Crack Initiation, Crack
Growth, and Total Life (S-N). Other types of analysis are available also
and explained in their respective chapters. SeeVibration Fatigue
(Ch. 8),Multiaxial Fatigue(Ch. 6),Rotating Structures Analysis
(Ch. 10),Software Strain Gauges(Ch. 11), andWeld Analysis
(Ch. 9).
Results Location This parameter tells MSC.Fatigue whether to expect Nodal stress/strain results or Elemental centroid stress/strain results. This dictates whether the user is setting up a global multi-node or global multi-element fatigue analysis. Subsequent parameters, results file types, and results displays are dependent on whether nodal or elemental data is being considered. If nodal data is being considered, the resulting fatigue lives are reported at the nodes. Conversely, if elemental data is being considered, the fatigue lives are reported at the element centroids. Fatigue cracks invariably occur at free surfaces, and hence when a crack initiation method is used, node points results are usually
required. The exception is when a shell model is used, element centroid results may be extrapolated to the top or bottom surface. This is useful when there may be some doubt as to the accuracy of the node point results due to extrapolation and/or nodal averaging practices. The spot weld analyzer uses forces and moments from both nodes and elements. The SEAM-weld analyzer takes stresses from both the top and bottom surface and needs both nodes and elements for this.
Nodal Averaging Depending on how the finite element results are defined, nodal averaging of the stresses or strains may take place. If grid point stresses exist and are selected, no averaging will occur. However if the stresses or strains selected for the fatigue analysis are elemental based, such as results at integration points or elemental nodal values such that each element has a different value at the shared grid points, then nodal averaging will occur. This averaging is done on a global basis such that every contributing element surrounding a particular node will be used in the averaging. The exception to this is if Group is selected in which case only elements in the Current Group will be used in the averaging. For the SEAM-weld analyzer only the current group can be used and no choice will be given.
F.E. Results For crack initiation, the fatigue analyzer may use either Stress, Strain, or
E-P Input results from the finite element analysis. For crack growth and
total life, only stress results can be used and no choice will be given. If Stress is selected, the intermediatejobname.fesfile will contain nodal
or element stresses for each load case or time step as opposed to strains. This selection should make no difference to the final results of a crack initiation calculation, as MSC.Fatigue will always calculate the strains. The exception is when shell results are used. In this case, Stress should be selected because only 2D results are available and the absence of the out-of-plane strains will cause incorrect calculation of combined parameters. Another exception: when Strain results are selected, the analyzer requires finite element results in the form of six (6) components of strain, three (3) direct strains and three (3)
engineering shear strains (i.e. two times the tensor shear strains). If FE
strains are not available in this form, Stress results should be selected. Selecting E-P Input allows for elastic-plastic input when doing a crack imitation or a multiaxial CI analysis. The spotweld analyzer uses only forces and no choice will be given.
Results Units This option menu is active for all analysis types utilizing stress results. The stress unit type must be identified for proper conversions within the fatigue analyzer. Available units are MPa, Pascals, PSI, KSI,
KG/M**2. This parameter is set to None if the Tensor parameter is set to
strain. The spot weld analyzer requires both cross sectional forces and moments from the CBAR elements representing the spot welds. For this reason, both the force and dimension units are required.
Allowable options for forces & dimensions are: N and m, N and mm, lbf and in, and kip and in.
Jobname In this databox, the user supplies a unique name by which to distinguish the fatigue job. All subsequent forms will key off of this jobname when performing certain tasks. If the jobname already exists when submitting the job, permission for overwrite will be requested. This jobname is limited to thirty-two (32) characters. Also, if a jobname is typed into this databox and the user presses the
<RETURN>
key the program will check for its existence and ask the user if he wishes to read in the old job parameters.Title A descriptive textual title can be supplied in this databox. The length is limited to eighty (80) characters.
Parameter Description
The MSC.Fatigue Jobname. The MSC.Fatigue jobname is used in all unique file names created during a MSC.Fatigue run, and is used for retrieving previously executed MSC.Fatigue jobs for editing, re-running and results display. The jobname is a character string containing a maximum of 32 characters with no spaces. On some systems, characters such as [, *, /, or : , are not allowed, and in fact only alphanumeric characters are recommended. The jobname related files generated during a MSC.Fatigue run are shown in the table below.
Important: The same answers should result whether stress or strain FE results are used in a crack initiation analysis. However, if the Young’s modulus is different between the finite element analysis and the MSC.Fatigue material being used, significant differences in fatigue results can occur when comparing between stresses and strains. For strain results, no conversion is necessary. Total life and crack growth jobs use stress tensors, so no conversion is required or allowed. Also there could be a problem using strains with 2-D elements if any combined strain component is used which includes the Z-component strain. This is because the Z-component strain appears as zero from 2D elements in the .fesfile which is not generally
true. Absolute maximum principal, x and y component strain should be unaffected.
Filename Description
jobname.fin Job parameter file (ASCII).
jobname.fes MSC.Fatigue Input file (Binary).
jobname.asc ASCII version of thejobname.fesfile.
jobname.fpp MSC.Fatigue intermediate results file (Binary).
jobname.msg/log MSC.Fatigue message and log files (ASCII).
jobname.sta Job status file (ASCII).
jobname.fef Global multi-node/element results file (ASCII).
jobname.fos Factor of Safety results file(ASCII).
jobname.abo Job abort file (ASCII).
jobname.tcy Time ordered stress cycles file (Binary).
jobname.crg Crack growth results file (Binary).
jobname.vec Surface normals file (ASCII).
jobname.fpr Job currently active alert file (ASCII).
jobnamenn.kfl/.kfm Stress concentration-Life XY data for specific node/element, nn (ASCII/Binary).
jobnamenn.dcl/.dcm Design criterion-Life XY data (ASCII/Binary).
jobnamenn.fal/.fam Scale factor-Life XY data (ASCII/Binary).
Solution Parameters
Each analysis type has its own unique set of solution parameters. These are described inTotal Life (S-N) Solution Parameters(p. 26),Crack Initiation Solution Parameters(p. 29), and
Crack Growth Solution Parameters(p. 33).
jobnamenn.dhh Damage distribution at node/element (ASCII).
*.ksn K solution files (Binary).
*.dac, *.cyh Loading time history/rainflow matrix files (Binary).
*.xyd K solution XY data (ASCII).
*.tem Plotting format data (ASCII PCL file).
*_tmpl Results template files (ASCII).
jobname_ts*/ls*.nod Nodal results files from coordinate transforms (ASCII). *.adb/.tdb/.mdb Time history and Materials database description files
(ASCII/Binary/Binary).
Filename Description