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Nastran Embedded FatigueUsers Guide

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imerftware Corporation reserves the right to make changes in specifications and other information contained ocument without prior notice.cepts, methods, and examples presented in this text are for illustrative and educational purposes only, not intended to be exhaustive or to apply to any particular engineering problem or design. MSC.Software tion assumes no liability or responsibility to any person or company for direct or indirect damages resulting use of any information contained herein.cumentation: Copyright 2013 MSC.Software Corporation. Portions, copyright HBM United Kingdom . Printed in U.S.A. All Rights Reserved.

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ry of ANSYS Inc. ABAQUS is a registered trademark of ABAQUS Inc. All other brand names, product r trademarks belong to their respective owners. PCGLSS 6.0, Copyright 1992-2005, Computational

ions and System Integration Inc. All rights reserved. PCGLSS 6.0 is licensed from Computational ions and System Integration Inc. METIS is copyrighted by the regents of the University of Minnesota. A the METIS product documentation is included with this installation. Please see "A Fast and High Quality el Scheme for Partitioning Irregular Graphs". George Karypis and Vipin Kumar. SIAM Journal on Scientific ing, Vol. 20, No. 1, pp. 359-392, 1999.

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C o n t e n t sMSC NASTRAN Embedded Fatigue Users Guide

1

2

ue PrefaceAbout this Book viii

Acknowledgements ix

List of Nastran Books x

Technical Support xi

Internet Resources xii

Fundamentals of Fatigue AnalysisOverview 2

What is Fatigue? 3

The Fatigue Analysis Five Box Trick 4

Life Prediction Methods 6

Finite Element Analysis Methods 7

Design Philosophies 8

Life Estimation Process 10

When to Use Which Method 11

Introduction to User InterfaceOverview 14

FATIGUE Case Control 16

Fatigue Element Definitions 19

Fatigue Parameters 30

MSC NASTRANEmbedded FatigUsers Guide

MSC NASTRAN Embedded Fatigue Users Guide

iv

Fatigue Loading 35

Analysis Model Units 44

Fatigue Optimization 46

3

4

5

6 Tips for Optimizing Performance 50

A Simple S-N AnalysisProblem Description 52

Fatigue Setup 54

Concluding Remarks 65

Patran Setup 72

Rainflow Cycle CountingProblem Description 80

Fatigue Setup 82


Patran Setup 93

A Simple e-N AnalysisProblem Description 98

Fatigue Setup 100


Patran Setup 120

Multiple LoadingProblem Description 126

Fatigue Setup 128

vCONTENTS

Patran Setup 135

7 A Simple Duty Cycle

8

9

A

B Problem Description 142

Fatigue Setup 146

Patran Setup 154

Modal Transient AnalysisProblem Description 160

Quasi-static Method 162

Modal Transient Method 166

Modal Method 171


Patran Setup 178

Design OptimizationProblem Description 190

Fatigue Setup 193


UtilitiesOverview 2

Descriptions 3

Glossary of TermsGlossary of Terms 10

MSC NASTRAN Embedded Fatigue Users Guide

vi

C References and Further ReadingReferences 84

Further Reading 90

Preface

About this Book Acknowledgements List of Nastran Books Technical Support Internet Resources

MSC Nastran Embedded Fatigue Users GuideAbout this Book

viii

About this BookThe MSC Nastran Embedded Fatigue Users Guide is a guide to the proper use of MSC Nastran for

solving various fatigue analysis problems. This guide serves as both an introduction to fatigue analysis for the new user and a reference for the experienced user. The major emphasis focuses on understanding the physical processes in fatigue and properly applying MSC Nastran to model the fatigue processes while restricting mathematical derivations to a minimum.

The basic types of fatigue analysis capabilities available in MSC Nastran are described in this guide. These common fatigue analysis capabilities include stress-life (S-N), sometimes referred to as total life, and strain-life (-N), more commonly know as crack initiation, and how to apply these using statics, normal modes and, modal transient response analyses. These capabilities are described and illustrative examples are presented. Theory used in fatigue analysis is presented only as it pertains to the proper understanding of the use of each capability.

To effectively use this guide, it is important for you to be familiar with MSC Nastrans static and/or dynamic analysis capabilities and the principles of static and/or dynamic analysis. Basic finite element modeling and analysis techniques are covered only as they pertain to MSC Nastran fatigue analysis. For more information on static and dynamic analysis and modeling, refer to the MSC Nastran Linear Static Analysis Users Guide, the MSC Nastran Dynamic Analysis Users Guide, and to the Getting Started with MSC Nastran Users Guide.

This guide contains many highlighted links (in blue) to other MSC Nastran documents and all the documents were delivered together as a collection. If you keep the collection together the links between documents will work. Two suggestions when working with links are 1) returns you back in the window your mouse is in and 2) you can open the other linked to document in a new window from an Adobe Reader by choosing Open cross-document links in the same window; then you would uncheck the and select OK.

alt Preferences Documents

ixCHAPTER Preface

AcknowledgementsThe 2013 Version of the MSC Nastran Embedded Fatigue Users Guide is part of an ongoing project to

update, consolidate and improve MSC Nastran documentation. The primary editors of this guide include Dr. Neil Bishop, Dr. Marco Veltri, Dr Erwin Johnson, Mr Joe Griffin, Mr. Gopal Nagendra, and Dr Xiaoming Yu.

This guide incorporates all capabilities related to fatigue analysis into one place except the description of each releases capabilities in the Release Guides and quick and direct access to fatigue related case control and bulk data in the MSC Nastran Quick Reference Guide (QRG).

The editor is grateful to Mr. Don Truitt for his patience and dedication in updating this users guide. The editor would also like to thank Dr. Tim Kuhlmann, Dr. Ted Wertheimer, Mr. David Turner, and Ms Martina Coutrier for their technical review of this guide.

This fatigue capability is jointly developed in close cooperation between MSC.Software and its fatigue technology partner, HBM-nCode. Portions of this manual are copyright HBM United Kingdom Ltd 2013.

Alan K. Caserio

MSC Nastran Embedded Fatigue Users GuideList of Nastran Books

x

List of Nastran BooksBelow is a list of some of the Nastran documents. You may find any of these documents from

MSC.Software at www.simcompanion.mscsoftware.com.

Installation and Release Guides Installation and Operations Guide Release Guide

GuidesReference Books

Quick Reference Guide DMAP Programmers Guide Reference Manual

Users Guides Getting Started Linear Static Analysis Dynamic Analysis Embedded Fatigue Thermal Analysis Superelements MSC Demonstration Problems Design Sensitivity and Optimization Implicit Nonlinear (SOL 600) Explicit Nonlinear (SOL 700) Aeroelastic Analysis User Defined Services

xiCHAPTER Preface

Technical SupportFor technical support phone numbers and contact information, please visit:

http://www.mscsoftware.com/Contents/Services/Technical-Support/Contact-Technical-Support.aspx

Support Center (www.simcompanion.mscsoftware.com)

Support Online. The Support Center provides technical articles, frequently asked questions and documentation from a single location.

MSC Nastran Embedded Fatigue Users GuideInternet Resources

xii

Internet ResourcesMSC.Software (www.mscsoftware.com)MSC.Software corporate site with information on the latest events, products and services for the CAD/CAE/CAM marketplace.

MSC Nastran Fatigue Analysis Users Guide Chapter 1: Fundamentals of Fatigue Analysis1 Fundamentals of Fatigue Analysis

Overview The Fatigue Analysis Five Box Trick Life Prediction Methods Finite Element Analysis Methods Design Philosophies Life Estimation Process When to Use Which Method

MSC NASTRAN Embedded Fatigue Users GuideOverview

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OverviewMSC Nastran embedded fatigue life estimation, when used early in a development design cycle has the

potenital to greatly enhance product life as well as reduce testing and prototype costs, thus ensuring greater speed to market.

The purpose of this manual is to provide you with typical example problems to demonstrate proper usage of the program. Each example is designed to show certain aspects and help to convey various principles of fatigue life estimation. The intent is to get you up to speed as quickly as possible without a steep learning curve or hours sifting through a thick manual.

AssumptionsThis guide makes certain assumptions of the reader. The basic assumptions made are, a good knowledge of basic computer skills and terminology, and a working knowledge of finite element analysis using MSC Nastran. This manual does not deal with creation of finite element models or any aspects of actual finite element analyses except where necessary to achieve proper fatigue life estimations.

This manual assumes that the user has little or no experience with fatigue analysis in general and therefore makes every effort to explain principles of fatigue life estimation from example to example. It is not meant to be an exhaustive course on fatigue analysis however. For this we refer you to the many references sited in the Ap. C: References and Further Reading.

Organization of GuideAll chapters starting with Chapter 3, serve as tutorials to learn the basics of fatigue analysis using MSC Nastran.

First read this chapter in its entirety and then familiarize yourself with the Nastran case control and bulk data input in the next chapter, after which it is highly suggested that you start at the first example and work your way sequentially. Each exercise introduces concepts that build on each other from exercise to exercise.

3CHAPTER 1Fundamentals of Fatigue Analysis

What is Fatigue?The first concept to understand before embarking on this tutorial is the definition of the term fatigue within the confines of this guide. Very often the terms Fatigue, Fracture, and Durability are used interchangeably. Each does, however, convey a specific meaning.

Although many definitions can be applied to the word, for the purposes of this manual, fatigue is failure under a repeated or otherwise varying load which never reaches a level sufficient to cause failure in a single application.

It can also be thought of as the initiation and growth of a crack, or growth from a pre-existing defect, until it reaches a critical size, such as separation into two or more parts.

Fatigue analysis itself usually refers to one of two methodologies: either the Stress-Life (S-N) or S-N method, commonly referred to as Total Life since it makes no distinction between initiating or growing a crack, or the Local Strain or Strain-Life (e-N) method, commonly referred to as the Crack Initiation method which concerns itself only with the initiation of a crack.

Fracture specifically concerns itself with the growth or propagation of a crack once it has initiated. MSC Nastran fatigue analysis concerns itself only with the prior two types of fatigue analysis and is not applicable for crack growth or propagation. For this capability you are referred to MSC Nastrans cohesive zone modeling and/or virtual crack closure technique (VCCT) or MSC Fatigue, which uses a LEFM method for crack growth prediction.

Durability is then the conglomeration of all aspects that affect the life of a product and usually involves much more than just fatigue and fracture, but also loading conditions, environmental concerns, material characterizations, and testing simulations, to name a few. A true product durability program in an organization takes all of these aspects (and more) into consideration.

Note: Throughout this manual terms in blue italics mean there is a definition provided in the Glossary of Terms (App. B).

Note: Fatigue cracks initiate and grow as a result of cyclic plastic deformation. Without plasticity there can be no fatigue failure. All attempts are made in this guide to explain how plasticity is taken into account when determining fatigue life from linear elastic finite element analysis.

MSC NASTRAN Embedded Fatigue Users GuideThe Fatigue Analysis Five Box Trick

4

The Fatigue Analysis Five Box TrickThese fatigue analysis example exercises are constructed around the concept of the fatigue five-box

trick. The illustration below depicts this well. For any life analysis whether it be fatigue or fracture there are always three inputs. The first three boxes are the inputs; box four the analysis; and box five the results.

1. Cyclic Material Information: Materials behave differently when they are subject to cyclic as opposed to monotonic loading. Monotonic Properties are the result of material tests where the load is steadily increased until the test coupon breaks. Cyclic Properties are obtained from material tests where the loading is reversed and cycled until failure at various load levels. These parameters differ depending on the fatigue analysis type involved.

2. Service Loading Information: The proper specification of the variation of the loading is extremely important to achieve an accurate fatigue life prediction. The loading can be defined in various manners. Whether it be time based, frequency based, or in the form of some sort of spectra depends on the fatigue analysis type to be used. When working with finite element models the loading can be force, pressure, temperature, displacement, or a number of other types. Loading in the test world usually refers to the acquisition of a response measurement, usually from a strain gauge.

3. Geometry Information: Geometry has different meanings depending on whether you are working from a finite element model or from a test specimen. In the testing world, the geometry input is the Kt (stress concentration factor) since the point of failure is usually away from the actual point of measurement. Therefore a geometry Stress Concentration Factor, Kt, is defined to relate the measured response to that at the failure location. You can think of this as a fudge factor. The corresponding role of finite elements is to produce fields of Kt over the entire model, with the additional complication that these local stress concentration factors are in the form of stress tensors.

4. Analysis: The correctness and accuracy of each of the above inputs is important in that any error in any of these will be magnified through the fatigue analysis procedure, the fourth box, since this process is logarithmic. A ten percent error in loading magnitude could result in a 100% error in the predicted fatigue life. In a conventional finite element based fatigue analysis, the 4th box often contains both the stress prediction and fatigue life calculation.


5. Results: The fifth box is the postprocessing or results evaluation. This can take on the form of color contours on a finite element model or a tabular listing but also quite often leads back into the three inputs to see what effect variations of these inputs will have on the life prediction. This

is referred to as a sensitivity or a what if study. This is extremely useful at times when you are not quite sure about the accuracy of one of the inputs. This then leads to design optimization using fatigue life as a design constraint or possibly even as a design objective.

MSC NASTRAN Embedded Fatigue Users GuideLife Prediction Methods

6

Life Prediction MethodsThere are three main life prediction methods as already mentioned earlier. These are Total Life, Crack

Initiation, and Crack Growth (Propagation). Total life is aptly named in that only the total life of the component is of concern and not when a crack will initiate or how quickly it will grow.

The three methods are related to each other by the fact that the total number of cycles to failure, Nf, equals the number of cycles to initiate a crack, Ni, plus the number of cycles to propagate that crack, Np. The three methods have grown out of different needs over the decades using different techniques and having different degrees of accuracy. So in theory this equation is true, but in practice when applying the three methods to the same problem, rarely, if ever does it add up.

In reality however, rarely are all three methods used on the same problem, mainly because different industries adopt different analysis methods depending on the driving design philosophy. See Design Philosophies, 8.


Finite Element Analysis MethodsIn order to do life predictions, MSC Nastran embedded fatigue analysis supports use of stress-life and

strain-life methods using the stress/strain response results from different finite element (FE) analysis techniques. The table below summarizes which FE analysis types are applicable to which life prediction methods in this release of the software.

Table 1-1 Life Prediction Methods vs. FE Analysis Results

Total Life (S-N) Crack Initiation (-N)Linear Static SOL 101

Supported Supported

Normal Modes SOL 103

Supported Supported

Modal Transient Response SOL 112

Supported Supported

Design OptimizationSOL 200

ANALYSIS=STATICS only ANALYSIS=STATICS only

MSC NASTRAN Embedded Fatigue Users GuideDesign Philosophies

8

Design PhilosophiesThere are three main fatigue design philosophies. Each centers around one of the fatigue life estimation

methodologies. To illustrate the three consider the design of a stool.

Safe Life

The Safe Life philosophy is a philosophy adopted by many, but especially the ground vehicle industry. Products are designed to survive a specific design life. Full scale tests are usually carried out with margins of safety applied. In general, this philosophy results in fairly optimized structures such as a stool with three legs. Any less than three legs and it would fall over. This philosophy adopts the crack initiation method and is used on parts and components that are relatively easy and inexpensive to replace and not life threatening if failure were to occur. Most of the life is taken up in the initiation of a crack. The propagation of that crack is very rapid and short in comparison.

Fail Safe

On the other end of the spectrum of design philosophies is that of Fail Safe. This is where a failure must be avoided at all costs. And if the structure were to fail it must fall into a state such that it would survive until repairs could be made. This is illustrated with our stool now having six legs. If one leg were to fail, the stool would remain standing until repairs could be made. This philosophy is heavily used in safety critical items such as in the aerospace or offshore industries.


Damage Tolerant

The middle ground philosophy is that of Damage Tolerant. This philosophy, adopted heavily in the

aerospace community and nuclear power generation, relies on the assumption that a flaw already exists and that a periodic inspection schedule will be set up to ensure that the crack does not propagate to a critical state between inspection periods. As implied, this philosophy adopts the crack growth method. This is illustrated using our stool (now with four legs) and with someone inspecting it occasionally.

This particular design philosophy is generally used in conjunction with the fail safe philosophy, first to design for no failure. and then to assume that, for whatever reason, a flaw exists and must be monitored. MSC Nastrans cohesive zone and virtual crack closure technique (VCCT) modeling capabilities or some other fracture mechanics technique such as MSC Fatigue (LEFM based) are best suited for this damage tolerant design philosophy and are not covered topics of this manual. Fail safe and safe life philosophies using the S-N and -N methods are the topics covered by this manual.

MSC NASTRAN Embedded Fatigue Users GuideLife Estimation Process

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Life Estimation ProcessThe life estimation process really centers around two major relationships.1. The first relation is that of the loading environment to the stresses and strains in the component or model. This load-strain or load-stress relation is determined using finite element modeling and running linear elastic FE analysis. It is dependent on the characterization of the material properties and in some instances requires that a Notch Correction procedure take place. For the purposes of this discussion a notch correction is simply a way to compensate for plasticity from a linear FE analysis.

2. The second relation is that of the stresses or stains to the life of the component or model. This is accomplished by using damage modeling. Each fatigue life method has its own techniques to determine and sum damage which shall be explained as you progress through the example problems.


When to Use Which MethodOf the three fatigue methods used to predict life, it is important to understand when to use which. This

will become more evident as you proceed through this manual and work each exercise. As a quick answer to this question, the following guidelines are presented.

Stress-Life (S-N or Total Life) Long life or High Cycle Fatigue (HCF) problems, where there is little Plasticity since the S-N

method is based on nominal stress Components where crack initiation or crack growth modeling is not appropriate, e.g.,

composites, welds, plastics, and other non-ferrous materials Situations where large amounts of pre-existing S-N data exist Components which are required by a control body to be designed for fatigue using standard data

such as MIL handbook data. Spot weld analysis and random vibration induced fatigue problems

Strain-Life (Crack Initiation or Local Strain or -N) Mostly defect free, metallic structures or components Components where crack initiation is the important Failure Criterion - safety critical

components Locating the point(s) where cracks may initiate, and hence the growth of a crack should be

considered Evaluating the effect of alternative materials and different surface conditions Components which are made from metallic, isotropic ductile materials which have symmetric

cyclic stress-strain behavior Components that experience short lives - Low Cycle Fatigue (LCF) - where plasticity is

dominant

Crack Growth (Damage Tolerant Design) Pre-cracked structures or structures which must be presumed to be already cracked when

manufactured such as welds Prediction of test programs to avoid testing components where cracks will not grow Planning inspection programs to ensure checks are carried out with the correct frequency To simply determine the amount of life left after crack initiation Components which are made from metallic, isotropic ductile materials which have symmetric

cyclic stress-strain behavior

MSC NASTRAN Embedded Fatigue Users GuideWhen to Use Which Method

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MSC Nastran Fatigue Analysis Users Guide Chapter 2: Introduction to User Interface2 Introduction to User Interface

Overview FATIGUE Case Control Fatigue Element Definitions Fatigue Parameters Fatigue Loading Analysis Model Units Fatigue Optimization

MSC NASTRAN Embedded Fatigue Users GuideOverview

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OverviewFatigue analysis using MSC Nastran consists of a FATIGUE case control output request and various bulk

data to define cyclic material properties, loading definitions and various other parameters, each of which is described in this Chapter. A brief description of each entry is given below. Details of each entry are given in subsequent sections of this Chapter.

Case Control

Bulk Data

The relationship between each entry and other material and/or element property entries is illustrated below for various cases.

FATIGUE Request a fatigue analysis and resultant life and damage output. See FATIGUE Case Control, 16.

DRESP1 Define fatigue responses in optimization (SOL200) runs. See Fatigue Optimization, 46.

DTI, UNITS Specify the model analysis stress units. See Analysis Model Units, 44.

FTGDEF Define areas (elements) of the model on which to perform fatigue analysis. See Fatigue Element Definitions, 19.

FTGPARM Define various fatigue parameters such as the type of fatigue analysis. See Fatigue Parameters, 30.

FTGEVNT Define loading events consisting of one or more simultaneously occurring cyclic loading definition. Fatigue Loading, 35.

FTGLOAD Associate loading from a particular subcase or mode to its time (cyclic) variation. Fatigue Loading, 35.

FTGSEQ Define a sequence of load events, sometimes referred to as a duty cycle. Fatigue Loading, 35.

MATFTG Define cyclic material properties in the form of S-N or -N data. See Fatigue Element Definitions, 19.

PFTG Define various physical fatigue properties to the elements of interest. See Fatigue Element Definitions, 19.

TABLFTG Define the cyclic variation of a particular load. Fatigue Loading, 35.

UDNAME Alternate method to associate the cyclic variation of a particular load to an external file. Fatigue Loading, 35.

15CHAPTER 2Introduction to User Interface

Relationship Between InputsCase Control (defines fatigue life output request):

FATIGUE[([PRINT,PLOT],[FORMAT=CODE],[BULK/SET]) ] = n

Bulk Data:

1 2 3 4 5 6 7 8 9 10FTGPARM ID TYPE FACTOR NTHRD LOGLVL

"STRESS" orSTRAIN

COMB CORR PLAST LOC INTERP

"RAINFLOW" RTYPE GATE PCTRED

"CERTNTY" SURV

"FOS" OPTION LIFE BACKACC MAXFAC

1 2 3 4 5 6 7 8 9 10FTGDEF ID TOPSTR PFTGID

"ELSET" ELSID1 PFTGID1 ELSID2 PFTGID2 ELSID3 PFTGID3

ELSID4 PFTGID4 ... ... ... ...

"XELSET" XELSID1 XELSID2 XELSID3 XELSID4 XELSID5 XELSID6 -etc-

1 2 3 4 5 6 7 8 9 10FTGSEQ ID EVNTOUT METHOD

FID1 N1 FID2 N2 FID3 N3 -etc-

"UNITS" EQUIV EQNAME

1 2 3 4 5 6 7 8 9 10FTGEVNT ID FLOAD1 FLOAD2 FLOAD3 FLOAD4 FLOAD5 FLOAD6 -etc-

1 2 3 4 5 6 7 8 9 10FTGLOAD ID TID LCID LDM SCALE OFFSET TYPE

1 2 3 4 5 6 7 8 9 10 MATFTG MID CNVRT

"STATIC" YS UTS CODE TYPE RR SE

SN SRI1 b1 Nc1 b2 Nfc

M1 M2 M3 M4

"TABLE" VALUE1 TID1 VALUE2 TID2 VALUE3 TID3

VALUE4 TID4 ... ... -etc.-

"BASTEN" A B c Eb Sd

"EN" Sf b c Ef n K Nc

SEe SEp SEc Ne FSN S

1 2 3 4 5 6 7 8 9 10PFTG ID LAYER FINISH KFINISH KF SCALE OFFSET

SHAPE KTREAT

What to Calculate

Where to Calculate

Cyclic Loading}Materials

Properties

Points to SET1, SET3, SET4 entries to define elements

Points to SUBCASE for stress/strain extraction

Points to TABLFTG or TABLED1 or UDNAME to define cyclic loading

Associated to PSHELL, PSOLID, or PSHEAR and corresponding MAT1 entries.

Points to TABLEM1 for defining discrete S-N or e-N curves.

MSC NASTRAN Embedded Fatigue Users GuideFATIGUE Case Control

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FATIGUE Case ControlAll fatigue analyses must be initiated with a FATIGUE case control output request as described below.Requests one or more fatigue analyses for use in pseudo-static (SOL 101), modal (SOL 103) and modal transient (SOL 112) runs.

Format:

Examples:Three examples are shown here. The first and second are identical and use the default BULK option where bulk data entries FTGDEF, FTGPARM, and FTGSEQ of ID 100 are called out for the fatigue analysis. The third example shows the SET option where case control SET ID 99 is called out. The case control SET of ID 99 contains two IDs, 100 and 200. Thus two fatigue analyses are called out where bulk data entries FTGDEF, FTGPARM, and FTGSEQ of IDs 100 and 200 are called out.

FATIGUE=100FATIGUE(BULK)=100SET 99 = 100, 200FATIGUE(SET)=99

Remarks:1. Both PRINT and PUNCH may be requested.

FATIGUE Fatigue Output Request

Describer Meaning PRINT The printer will be the output medium (default).PUNCH The punch file will be the output medium.PLOT Results will be generated but no printer output.FORMAT Request that fatigue be output in specific file formats. CODE Codes for specific file format output. See Remark 7.BULK Specifies that the n refers directly to bulk data IDs of FTGSEQ/ FTGLOAD,

FTGPARM and FTGDEF entries of the same ID (default). SET Specifies that the n refers to a previously appearing SET ID. n ID of a SET case control entry (SET option) or ID of FTGSEQ/FTGLOAD,

FTGPARM, FTGDEF bulk data entries of the same ID (BULK option).

FATIGUE[ ([PRINT,PUNCH,PLOT], FORMAT=[CODE], [BULK/SET ] )] =n


2. A single FATIGUE case control is required to perform one or more fatigue analyses and must be present above the SUBCASE level. If not present, no fatigue analysis will occur regardless of the presence of other bulk data related to fatigue analysis.3. A STRESS and/or STRAIN case control output request is also required in order for the FATIGUE output request to obtain the necessary stresses or strains for the fatigue calculation.

4. For a single fatigue analysis, BULK=n points to a FTGDEF, a FTGPARM, and a FTGSEQ (or FTGLOAD) entry, each with ID=n.

5. For multiple fatigue analyses, SET=n points to a previously appearing SET case control and each member of the SET is the ID of a FTGDEF, a FTGPARM, and a FTGSEQ (or FTGLOAD) bulk data entry with that ID.

6. A fatigue analysis must have, at a minimum, loading and material data defined on either FTGSEQ or FTGLOAD and MATFTG bulk data entries, respectively, for a fatigue analysis to be valid. FTGPARM and FTGDEF entries can be absent, in which case, defaults will be used.

7. The following additional, optional, fatigue output file formats may be requested. The given codes must be summed if multiple files are requested. Example: CSV file and FEF file CODE would be 64+128=192

8. Standard fatigue output is:

File Format CODENo additional output 0FER (Design Life Output File) 4UNV (Universal File) 32CSV File (Comma Separated - Excel File) 64FEF (Patran Results File) 128

Stress-Life (SN) Analysis Strain-Life (eN) AnalysisLIFE (Repeats) LIFE (Repeats) LOG of LIFE (Repeats) LOG of LIFE (Repeats) LIFE (user units*) LIFE (user units) LOG of LIFE (user units) LOG of LIFE (user units) DAMAGE DAMAGELOG of DAMAGE LOG of DAMAGE MAX STRESS MAX STRESS or STRAIN MIN STRESS MIN STRESS or STRAIN

MSC NASTRAN Embedded Fatigue Users GuideFATIGUE Case Control

18

* User units are fatigue equivalent units as defined on the FTGSEQ or FTGLOAD en-try and other output is available depending on the settings of the FTGPARM entry.

Dependent on STRESS or STRAIN flag set on FTGPARM entry.


Fatigue Element DefinitionsTo perform fatigue analysis, locations on the model (elements) and specific material and physical

properties must be specified. This is done with three main bulk data entries described here. The MATFTG entry is required and for each MATFTG entry there must be a corresponding MAT1 entry of the same ID, otherwise an error will occur as no cyclic material definitions would be available for the fatigue analysis. The other two are the FTGDEF and PFTG entries used to limit the number of entities and define physical fatigue properties, respectively. If there are no FTGDEF and PFTG entries, then every element in the model associated to a MAT1 / MATFTG entry will be used with default properties.

Defines elements and their associated fatigue properties to be considered for fatigue analysis.

Format:

Examples:Two examples are shown here. The first simply defines all elements of the model (that have fatigue material properties) to use the physical fatigue properties defined by PFTG ID 3. The second example defines actual element sets where IDs 14 and 15 refer to either SET1, SET3, or SET4 entries that define a set of elements and each of these is assigned different physical fatigue properties defined by PFTG IDs 3 and 4.

FTGDEF Fatigue Element Definitions

1 2 3 4 5 6 7 8 9 10FTGDEF ID TOPSTR PFTGID

"ELSET" ELSID1 PFTGID1 ELSID2 PFTGID2 ELSID3 PFTGID3 ELSID4 PFTGID4 ... ... ... ...

"XELSET" XELSID1 XELSID2 XELSID3 XELSID4 XELSID5 XELSID6 XELSID7 XELSID8 ... ... ... ... ... ...

FTGDEF 22 100.0 3

FTGDEF 22ELSET 14 3 15 4

Field ContentsID Unique identification number. (Integer > 0). TOPSTR Top stress percentage. Only elements with combined stress in this top percentage

will be retained and report results. (0.0 < Real 100.0; Default = blank - 100% will be used). Should not be used with SOL 200 and should be left blank.

MSC NASTRAN Embedded Fatigue Users GuideFatigue Element Definitions

20

PFTGID ID of a PFTG entry for associating fatigue properties to all elements of the model. Field ContentsRemarks:1. FTGDEF bulk data entries are ignored if not selected by a FATIGUE case control. If no FTGDEF

is present for a given fatigue analysis, all elements of the model that have fatigue material properties defined will be used with default properties.

2. If no PFTGID or PTFGIDi is specified, default properties will be assigned to the entities.3. If a SET3 is specified, field 3 of the SET3 entry must be set to "ELEM". The SET4 entry must be

specified to select elements by property ID. Currently only elements that can be referenced by PSHELL, PSHEAR, and PSOLID properties are supported - viz. CQUAD4, CQUADR, CQUAD8, CSHEAR, CTRIA3,CTRIAR, CTRIA6, CHEXA, CPENTA, and CTETRA.

4. If only the XELSET flag is present, then the entire model is included in the fatigue analysis less the excluded entities.

Ignored if ELSET flag is present and should be left blank in this case. (Optional, Integer > 0). See Remark 2.

ELSET Flag indicating that a list of element set and property pairs will follow, defining the elements and their associated properties for consideration in the fatigue analysis. (Optional, Character = ELSET)

ELSIDi ID of a SET1, SET3, or SET4 entry listing entities of the model (elements) to be included in the fatigue analysis. (Integer > 0). See Remark 3.

PFTGIDi ID of a PFTG entry, which indicates the fatigue property associated to the preceding entities defined by ELSIDi. (Optional, Integer > 0). See Remark 2.

XELSET Flag indicating that sets of elements to be excluded from the fatigue analysis will follow. (Optional, Character). See Remark 4.

XELSIDi ID of a SET1 or SET3 entry listing elements of the model to be excluded from the fatigue analysis. (Integer>0). See Remark 3. about SET3 specification.


MATFTG Fatigue Material PropertiesDefines fatigue material properties.

Format:

Examples:Two examples are shown here. The first defines only the STATIC line, which define an ultimate tensile stress (UTS) and a material code (CODE). In this case, with no other lines of data, the cyclic material properties for either an S-N or -N analysis will be derived. The second example contains a line specifically defining the parameters for an S-N curve. The STATIC line is required in either case as UTS must be defined.

1 2 3 4 5 6 7 8 9 10 MATFTG MID CNVRT

"STATIC" YS UTS CODE TYPE RR SESN SRI1 b1 Nc1 b2 Nfc

M1 M2 M3 M4"TABLE" VALUE1 TID1 VALUE2 TID2 VALUE3 TID3

VALUE4 TID4 ... ... -etc.- "BASTEN" A B c Eb Sd

"EN" Sf b c Ef n K Nc SEe SEp SEc Ne FSN S

MATFTG 9STATIC 430 682 99

MATFTG 9STATIC 430 682 0.1

SN 3095 -0.1339 1.e8 0.0 1.e8

Field ContentsMID Unique material ID that matches the identification of a MAT1 entry

(Integer>0). See Remark 1.CNVRT Conversion factor. See Remark 2. regarding units. STATIC Required flag indicating that yield and/or ultimate tensile strengths and other

common parameters are supplied (Character=STATIC). See Remark 3. and 4.


22

YS Yield strength (Valid range equivalent in MPa: 50.0 Real 3000). See Field ContentsRemark 2. regarding units. UTS Ultimate tensile strength (Valid range equivalent in MPa: 100.0 Real

4000). See Remark 2. regarding units. CODE Material code used in automatically generating S-N or -N data curves and

for surface finish corrections. See Remark 3.TYPE Specification of the type of S-N curves defined using the TABLE or

BASTEN flag (no Default). See Remark 4. RR R-ratio of test. (-1.0e30 Real 1.0, Default=-1.0).SE Standard Error of Log(N). (0.0 Real 10.0, Default=0.1).

SN Flag indicating the definition of an S-N curve follows (Character=SN, optional). See Remark 5..

SRI1 Stress range intercept. (Valid range equivalent in MPa: 1.0 Real 2.5e4, no Default). See Remark 2 regarding units.

b1 First fatigue strength exponent. (-1.0 < Real< -0.02, no Default) Nc1 In 1-segment S-N curve, the cycles limit of endurance. In 2-segment S-N

curve, this is the fatigue transition point. Both are defined in cycles. (1.0 Real 1.0E25; no Default).

b2 Second fatigue strength exponent. It is zero when defining 1-segment S-N curve; (-0.5 < Real 0.0, Default=0.0).

Nfc Fatigue cutoff. (1.e-9 Real 0.0; Default=1.0e30). M1 - M4 Mean stress slope parameters M1 through M4 representing sensitivity to

mean stress in four (4) regimes of R-ratio as plotted on a constant life Haigh diagram and used in FKM mean stress correction. (-0.99 Real 0.0; Default = blank). See Remark 6.

TABLE Flag indicating the definition of S-N curves as a number of tables follows (Character=TABLE; optional). See Remark 5.

VALUEi The constant mean stress, R-ratio, or life (in cycles) of this particular S-N curve. (Real; no Default). See Remark 2 regarding units.

TIDi A TABLEM1 ID defining the S-N curve of stress range (y) vs. life (x) in cycles for this particular S-N curve, or mean stress (x) vs. stress amplitude (y) for constant life (Haigh diagram) curves (Integer>0). See Remark 2. regarding units.

BASTEN Flag indicating the definition of an S-N curve based on the Bastenaire S-N approach (Character-BASTEN; optional). See Remark 5.

A Bastenaire coefficient - a parameter positioning the curve along the life axis. (Valid range equivalent in MPa: 1.0e4 Real 1.0e10). See Remark 2. regarding units.


B Scale Factor parameter. (Valid range equivalent in MPa: 1.0 Real Field ContentsRemarks:1. The material ID must match that called out by the property entry. Element properties must

reference MAT1 entries in order to also reference MATFTG entries as only metal fatigue analysis of isotropic materials is supported.

2. The CNVRT field is only used if fatigue material stress based parameters are directly input using the "STATIC," "SN," "EN," "TABLE," or "BASTEN" methods. It is used to allow the user to input the fatigue material stress related parameters, (YS, UTS, SRI1, VALUEi, TIDi, A, B, Eb, K) in different units other than the model's consistent units. Example: model is producing stresses in PSI units, fatigue material parameters input in MPa, the CNVRT factor should be

1.0e10). See Remark 2. regarding units. c Bastenaire exponent. (0.01 Real 1.1e10) Eb Bastenaire fatigue limit (Valid range equivalent in MPa: 1.0 Real

1.0e10). See Remark 2 regarding units. Sd Bastenaire scatter factor. (Valid range equivalent in MPa: 0.0 Real

1.0e25). See Remark 2 regarding units. EN Flag indicating the definition of an -N curve is to follow. (Character=EN;

optional). See Remark 5..Sf Fatigue strength coefficient (Valid range equivalent in MPa: 50.0 Real

4000.0; no Default). See Remark 2. regarding units. b Fatigue strength exponent (-0.5 Real -2.0e-3; no Default). c Fatigue ductility exponent. (-1.2 Real -0.15; no Default). Ef Fatigue ductility coefficient, (0.001 Real 10.0; no Default).n Cyclic strain-hardening exponent, (5.0e-3 Real 0.5; no Default).K Cyclic strength coefficient, (Valid range equivalent in MPa: 50 Real

1.2e4; no Default). See Remark 5. regarding units. Nc Cut-off (reversals), (1.0e5 Real 1.0e25; Default=2.0e8). SEe Standard Error of Log(e) (elastic), (0.0 Real 10.0; Default=0.0). SEp Standard Error of Log(e) (plastic), (0.0 Real 10.0; Default=0.0). SEc Standard Error of Log(e) (cyclic), (0.0 Real 10.0; Default=0.0). Ne Endurance Limit (Reversals), (1.0e-9 Real 1.0e25; Default=2.0e8).FSN Fatemi-Socie Parameter, (0.0 Real 10; Default=0.6)S Wang Brown Parameter, (-10.0 Real 10; Default=1.0)


24

145.0377 to convert MPa to PSI. Note that the y-values of any referenced TABLEM1 entries are also converted for the S-N method or both the x- and y-values when TYPE=LIFE (Haigh curves). It is also necessary to use the DTI,UNITS for defining the model's stress units. See DTI,UNITS.

(Real; Default=1.0)

3. If only STATIC is supplied, then the S-N or -N curve is derived using the UTS and a material CODE. Valid codes are listed in the table below. At a minimum UTS must be supplied along with the material CODE and E on MAT1, or an error will be issued. If either flag SN or EN flag is present, then the automatic generation is suppressed and all the data necessary to define S-N or -N curves are required. The determination as to whether S-N or -N curves are generated is determined by the TYPE field set on the FTGPARM entry. If surface finish corrections are to be applied, CODE is also required (see PFTG entry). When curves are derived, the specified CODE gets internally converted to generic code ferrous=99 for CODE 1; M2 for - < R < 0; M3 for 0 < R < 0.5; M4 for 0.5 < R < 1. If M1-4 are undefined, and the material type (CODE) is given , all the parameters will be estimated using emprically defined rules for the FKM mean stress correction method. If only M2 is defined, then M1 and M4 will be set to zero and M3 to M2/3

Table 2-1 Table of Material CODEs

CODE Description1 Flake cast iron (FCI)2 Ferritic cast iron with compacted graphite (FCICG)3 Pearlitic cast iron with compacted graphite (PCICG)4 Bainitic cast iron with compacted graphite (BCICG)


5 Ferritic cast iron with spheroidal graphite (FCISG)CODE Description6 Ferrite/pearlite cast iron with spheroidal graphite (FPCISG)7 Pearlitic cast iron with spheroidal graphite (PCISG)8 Bainitic cast iron with spheroidal graphite (BCISG)9 Cast steel with less than 0.2% carbon (CSL2C)10 Normalized cast steel with 0.2-0.4% carbon (NCS24C)11 Quenched & tempered cast steel with 0.2-0.4% carbon (QTCS24)12 Normalized cast steel with 0.4-0.7% carbon (NCS47)13 Plain carbon wrought steel with < 0.2% carbon (PCWS)14 Hot rolled/normalized plain carbon wrought steel, 0.2-0.4% carbon (HNPCWS24)15 Quenched & tempered cast steel with 0.4-0.7% carbon (QTCS47)16 Quenched & tempered plain carbon wrought steel, 0.2-0.4% carbon (QTPCWS24)17 Hot rolled/normalized plain carbon wrought steel, 0.4-0.7% carbon (HNPCWS47)18 Quenched & tempered plain carbon wrought steel, 0.4-0.7% carbon (QTPCWS47)19 Normalized low alloy wrought steel (NLAWS)20 Quenched & tempered low alloy wrought steel (QTHSLAWS)21 Normalized Ni/Cr/Mo wrought steel (NNCMWS)22 Quenched & tempered Ni/Cr/Mo wrought steel (QTNCMWS)23 Austenitic stainless steel (ASS)24 Ferritic stainless steel (FSS)25 Martensitic stainless steel (MSS)26 Annealed plain carbon wrought steel, 0.2-0.4% carbon (APCWS24)27 Annealed plain carbon wrought steel, 0.4-0.7% carbon (APCWS47)28 Normalized carbon/manganese steel (MCMS)29 Quenched and tempered carbon/manganese steel (QTCMS)30 Hardened chromium steel (HCS)31 Quenched and tempered chromium steel (QTCS)99 Steel of unknown heat treatment (STEEL)100 Wrought aluminium (WA)101 Wrought aluminium-copper alloy (WACA)102 Wrought aluminium-manganese alloy (WAMNA)103 Wrought aluminium-magnesium alloy (WAMGA)


26

104 Wrought aluminium-magnesium-silicon alloy (WAMGSA)CODE Description105 Wrought aluminium-zinc alloy (WAZA)106 Cast aluminium alloy (CAA)107 Wrought complex special purpose aluminum alloys (WCSPAA)200 Wrought copper (WCU)201 Wrought brass (WBR)202 Wrought aluminium bronze (WABR)203 Cupronickel (CUPNI)204 Nickel silver (NIAG)205 Wrought phosphor bronze (WPHBR)206 Wrought copper beryllium (WCUBE)207 Cast copper alloys (CCUA)300 Titanium alloy (TA)400 Wrought magnesium alloys (WMGA)401 Cast magnesium alloys (CMGA)500 Fusible alloys, solders (FUSSOL)600 Cast zinc alloys (CZINCA)700 Wrought nickel alloys (WNIA)701 Cast nickel alloys (CNIA)800 Precious metals (PRECMET)900 Clad materials (CLADMAT)1000 Thermoplastics (THERPLAS)1001 Thermosetting plastics (TSETPLAS)


PFTG Fatigue PropertiesDefines fatigue properties.

Format:

Examples:This example shows that PFTG ID defines the elements associated with it (called out by the FTGDEF entry) to have a polished surface finish and for the associated stresses to be scaled by a factor of 1.2.

Remarks:1. For shell elements, it is necessary to specify the top or bottom or the worst (larger damage

between top and bottom at the same location).

1 2 3 4 5 6 7 8 9 10PFTG ID LAYER FINISH KFINISH KF SCALE OFFSET

SHAPE KTREAT

PTFG 3.0 POLISH 1.2

Field ContentsID Unique ID referenced by a FTGDEF bulk data entry. (Integer>0) LAYER Region layer for shell elements. Values can be 0=Worst, 1=Top (Z2), 2=Bottom

(Z1). (Integer; Default=0). See Remark 1.FINISH Material Surface Finish. This is a result of manufacturing process. Value can be

NONE, POLISH, GROUND, MACHINE, POOR, ROLLED, CAST, KROUGH, KSURFC (Character; Default=NONE). See Remark 2.

KFINISH Roughness factor for FINISH = KROUGH (0.0 < Real < 1.0, no Default). Surface roughness in microns for FINISH = KSURFC (Real > 0.0; no Default; 0.0 Real for materials not listed in Remark 3.).

KF Fatigue strength reduction factor. (Real 0.0, Default=1.0). See Remark 4.SCALE Factor used to scale the resulting FE stresses of entities associated to this property set

(Real; Default=1.0). OFFSET Offset used to offset the resulting FE stresses of entities associated to this property set

(Real; Default=0.0).SHAPE Shape factor (Real 1.0; no Default). See Remark 5. KTREAT Treatment factor (Real 0.0; Default = 1.0).


28

2. The KF field can be used in lieu of or in addition to the FINISH & KTREAT field to modify the fatigue limit by multiplying the original fatigue limit by this value. POOR = Poor Machined. ROLLED = As Rolled. CAST = As Cast. KROUGH and KSURFC require that a KFINISH be

entered. A material CODE on the MATFTG entry must be supplied to use anything other than NONE or POLISH, otherwise an error is issued.

3. If KFINISH = KSURFC, the user should enter a value for surface roughness Rz in m. This is the average surface roughness according to the German standard DIN 4768. The Surface Roughness Factor Kr will then be calculated based on the strength and type of material (for example stronger materials are in general more sensitive to surface finish, and cast materials less so). The method for calculating Kr is taken from the FKM guideline Analytical Strength Assessment of Components in Mechanical Engineering.If Rz


Table 2-3 Availability of Settings for Different Analysis TypesAvailable* Available for Multi-temperature curve Not available for Multi-mean or Multi R-ratio curves

Fatigue Property

Analysis / Material Type Category

SN ENDang Van

SpotWeld

SeamWeld

Multiaxial -N AdhesiveBond CompositeScale Factor Offset KTreatment KUser KRoughness Weld diameter

Default temperature

* *

ShapeFactor Adhesive Thickness

Bond Line Offset

Initial Crack Size

MSC NASTRAN Embedded Fatigue Users GuideFatigue Parameters

30

Fatigue ParametersFatigue parameters are defined with the entry described below. The main use of this entry is to specify

the type of fatigue analysis (S-N or -N), but many other parameters may be set using this entry. Most of these are explained in the tutorials that follow in subsequent chapters.

Defines parameters for a fatigue analysis.

Format:

Examples:The first example defines an S-N analysis with all other parameters defaulted. The second example specifies STRESSes to be passed to the fatigue analysis and to convert the stress tensor to a signed von Mises (SGVON) scalar value and to perform no mean stress correction (NONE).

FTGPARM Fatigue Parameters

1 2 3 4 5 6 7 8 9 10FTGPARM ID TYPE FACTOR NTHRD LOGLVL

"STRESS" or

STRAIN

COMB CORR PLAST LOC INTERP

"RAINFLOW" RTYPE GATE PCTRED "CERTNTY" SURV

"FOS" OPTION LIFE BACKACC MAXFAC

FTGPARM 22 SN

FTGPARM 22 SNSTRESS SGVON NONE

Field ContentsID Unique ID of the FTGPARM entry (Integer > 0). See Remark 1.TYPE Type of fatigue analysis: "SN" or "EN" (Character, Default=SN). FACTOR Global scale factor to be applied to combined resultant stress output (Real > 0.0,

Default=1.0). NTHRD Number of treads to use for parallel processing for this fatigue analysis Integer

0; Default = 1). Zero (0) is used as a flag to tell the code to automatically determine the number of threads to use.


LOGLVL Level of messaging sent to the log file (Integer 0, Default = 0; 0=None, 1=Error, Field Contents2=Info, 3=Low, 4=Medium, 5=High). Note that LOGLVL > 3 can result in a significant performance penalty and should be used for debugging purposes only.

"STRESS" Flag indicating that stress is used in the fatigue calculation. See Remark 2.STRAIN Flag indicating that strain is used in the fatigue calculation. Not valid for TYPE =

SN. See Remark 2. COMB Stress/strain combination to use in the fatigue analysis. Acceptable values are

listed in Table 2-4 after the Remarks below (Character; Default=ABSMAXPR). CORR Mean stress correction to use in the fatigue analysis. Acceptable values are listed

in Table 2-5 and Table 2-6 after the Remarks below (Character; Default=None).PLAST Plasticity correction for TYPE = EN. Value can be "NEUBER," or "SEEGER" for

Neuber or Hoffmann-Seeger methods, respectively (Character; Default=NEUBER). See Remark 3.

LOC Location to report fatigue lives. Values are "NODE" or "ELEMENT" (Default=NODE). See Remark 4.

INTERP Interpolation limit for multi-curve mean stress correction method (Integer0; 0=Use Max Curve, 1=Extrapolate; Default = 0).

"RAINFLOW" Flag indicating that parameters that follow define rainflow cycle counting parameters for rainflow data reduction. See Remark 5.

RTYPE Method of rainflow data reduction (Time History Compression). Value can be "LOAD" for load time history data reduction on each load time history or "FAST" for performing a less accurate, but computationally faster method (Character; no default).

GATE Load value used as gate range. This load is used for gating out small disturbances of "noise" in the time history using a peak-valley extraction method to speed up the analysis. Only used if RTYPE=LOAD. GATE and PCTRED are mutually exclusive. PCTRED ignored if GATE is supplied. (Rea l 0.0, Default=0.0)

PCTRED Percent reduction value based on the maximum load range to used to reduce the load time history using a peak-valley extraction method to speed up the analysis. Only used if RTYPE=LOAD. Ignored if GATE is supplied. GATE and PCTRED are mutually exclusive. (0.0 Real 100.0, Default = 50.0)

"CERTNTY" Flag indicating that the parameter that follows defines the certainty of survival in fatigue analysis.

SURV Certainty of survival based on the scatter in the S-N or -N curves. (0.1 Real 99.9; Default = 50.0). See Remark 6.

"FOS" Flag indicating that parameters that follow are used in a factor of safety analysis. The presence of this flag triggers a factor of safety analysis. See Remark 7.


32

OPTION Supported option is LIFE, requesting a life-based factor of safety analysis Field ContentsRemarks:1. FTGPARM bulk data will be ignored if not selected by a FATIGUE case control entry. If a

FTGPARM entry is not defined, default properties are used for the requested fatigue analysis.2. For total life or stress-life (TYPE=SN), only STRESS results can be used. For crack initiation or

strain-life (TYPE=EN), the fatigue analyzer may use either STRESS or STRAIN results from the finite element analysis. This selection should make no difference to the final results of a crack initiation calculation, as strains will always be calculated. 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. It is an error to have both STRESS and STRAIN lines. If both are missing, then STRESS will be assumed with its default values.

3. PLAST can be set to NEUBER or SEEGER. Please note that NEUBER can be used universally for uniaxial stress states. SEEGER requires a 2D stress state and is generally used when the stress state in not purely uniaxial. PLAST is only valid for TYPE=EN.

4. If LOC=ELEMENT is selected, fatigue lives are calculated based on stresses/strains at element centroids (not recommended for anything but shell or 2D solid elements (plane stress/strain and axisymmetric). If LOC=NODE is selected, the fatigue lives are calculated from the stresses/strains at the element nodes.

5. This RAINFLOW flag is only necessary to use if it desired to speed up the analysis for purposes of quick critical location identification or for sanity checks. RTYPE determines how to compress the input time history data for the purposes of speeding up the calculation, possibly at the loss of accuracy of the results. RTYPE=FAST simply reduces the load time histories to a single cycle using only the minimum and maximum from the input time series data, without losing phase information across multiple load cases. RTYPE=LOAD using PCTRED performs a multi-channel peak-valley extraction on the time series data prior to processing with PCTRED value set as a percentage of the range of the input data. RTYPE=LOAD using GATE performs a multi-channel peak-valley extraction on the time series data prior to processing with GATE value applied directly in the units of the time series data.

(Character; default=LIFE). LIFE The targeted design life given in user defined life units (such as laps, miles, etc.)

as defined by UNITS line on FTGSEQ or FTGLOAD entry, or Repeats of the cyclic loading if no UNITS line exists (Real > 0, no default).

MAXFAC The maximum safety factor to calculate. When this factor is exceeded, the analysis will go on to the next element and report the maximum for the exceeded element (20.0 Real 5.e6; no Default).

BACKACC The back calculation accuracy used to control back calculation iterations to determine the scale factor on the applied stress level to achieve the target design life. (0.01 Real 100.0, Default = 1.0).


6. Certainty of survival is based on scatter in the S-N or -N curves. It is used to modify the curves according to the standard error parameters ( ) defined in the MATFTG material entry. A higher reliability level requires a larger certainty of survival.

SEn7. This FOS option will calculate a type of safety factor for over design analysis to be performed. This analysis is in addition to the normal fatigue life/damage output and must be requested by the presence of this FOS flag and its parameters. This analysis method can be very useful for those components which predict infinite life, providing a measure of the risk of fatigue failure. The results of this analysis are factors by which the stress would have to be scaled to attain the specified design life. A value of one suggests that the specified life will be exactly attained whereas a factor less than one means the desired life will not be attained. Factors greater than one are, therefore, most desirable. By definition the resulting life values will be the target life, thus only the scale factor and maximum/minimum stress results are of interest when FOS is defined.

Table 2-4 Allowable Values for the COMB Field *

* The six multiaxial components defined by the stress tensor (or strain tensor) are resolved intoone uniaxial or combined value for fatigue calculations for each node or element for each timestep. This is necessary since the fatigue damage models used are based on theories which dealwith uniaxial stress. These stress scalar combinations can be any of the above. For S-N anal-ysis, the signed von Mises (SGVON) will be smaller than the Absolute Maximum Principal(ABSMAXPR) when there is positive biaxiality and hence this selection would be less conser-vative. (Note also that some BS weld classes require shear stress to be used.) The sign on thesigned parameters is taken from the sign of the absolute maximum principal value. It is neces-sary to sign these stress parameters, otherwise non-conservative fatigue life estimates will re-sult. It is therefore not recommended to use non-signed values (MAXPRINC, VONMIS,MAXSHR), but the options are available.

Stress/Strain Combination

Valid for TYPE Meaning

ABSMAXPR SN, EN Absolute Maximum Principal (default) MAXPRINC SN Maximum Principal Stress SGVON SN, EN Signed von Mises Stress VONMIS SN von Mises StressSGMAXSHR SN, EN Signed Maximum ShearMAXSHR SN Maximum ShearCRITICAL SN, EN Critical Plane Analysis - every 10 degrees - Not valid for 3D solid

elements


34

Table 2-5 Allowable Values for the CORR Field Mean Stress Correction

Valid for TYPE Meaning

NONE SN, EN No mean stress correction (default)GOODMAN SN Goodman mean stress correctionGERBER SN Gerber mean stress correctionGDMANT SN Tension only Goodman mean stress correctionGRBERT SN Tension only Gerber mean stress correctionFKM SN FKM mean stress correction method. Uses M1, M2, M3, M4 slopes as

defined in MATFTG entry. See remarks in MATFTG entry.INTERP SN Interpolation method used with multiple SN curves only. TYPE field of

MATFTG entry must be set to MEAN, RRATIO, or LIFE. Requires that there be multiple curves defined, one at R=-1 for TYPE=RRATIO, or one at zero (0) mean stress for TYPE=MEAN.

SWT EN Smith-Watson-Topper mean stress correctionMORROW EN Morrow mean stress correction

Table 2-6 Allowable S-N vs. Mean Stress Correction Methods

Mean Stress Correction

S-N Method

StandardMulti Mean

CurveMulti R-

Ratio Curve Haigh BastenaireNONE YES YES*

* Allowed but a curve at zero mean stress must be present.

YES

Allowed but a curve at R = -1 must be present.

NO YESGOODMAN YES YES* YES NO YESGERBER YES YES* YES NO YESGDMANT YES YES* YES NO YESGRBERT YES YES* YES NO YESFKM YES YES* YES NO YESINTERP NO YES YES YES NO


Fatigue LoadingFatigue analysis must have a definition of the cyclic nature of the loading. This is accomplished using a

number of bulk data entries and can be as simple as a single load oscillating between one (1) and minus one (-1) to a complicated duty cycle consisting of multiple load events each containing multiple, simultaneously acting loads. These entries are described here and more specific examples given in each of the examples in this manual to clarify the proper usage of these entries. For a valid fatigue analysis, a FTGSEQ entry must be defined or at a minimum, a FTGLOAD entry must be defined, in the case of only a single loading.

Defines the loading sequence for pseudo-static fatigue analysis using SOL 101 or modal transient fatigue analysis using SOL 103 or SOL 112.

Format:

Example:This example simply shows that the load sequence defined by FTGSEQ ID 1 is made up of a single loading event defined by FTGEVNT entry of ID 6 (in the case of SOL 101 or 103) or SUBCASE 6 (in the case of SOL 112) and that event is repeated or occurs 1.5 times.

FTGSEQ Fatigue Load Sequence

1 2 3 4 5 6 7 8 9 10FTGSEQ ID EVNTOUT METHOD

FID1 N1 FID2 N2 FID3 N3 FID4 N4 FID5 N5 ... ... ... ... ... ... -etc.-


FTGSEQ 1 6 1.5

Field ContentsID Unique ID with respect to all other FTGSEQ and FTGEVNT entries. (Integer>0) See

Remark 1.EVNTOUT Flag for requesting fatigue output for each event individually. (Integer; 0=no or 1=yes;

Default = 0). See Remark 7.METHOD Event processing method. 0=independent, 1=Combined Full, 2= Combined Fast

(Integer; Default = 0). See Remark 2.

MSC NASTRAN Embedded Fatigue Users GuideFatigue Loading

36

FIDi ID of a FTGEVNT or another FTGSEQ entry for pseudo-static fatigue analysis using Field ContentsRemarks:1. FTGSEQ bulk data are called out by FATIGUE case control.2. Processing of events can be done by determining the damage due to each event independently

(default) and then summing the damage due to all events. Or the events can be concatenated and damage determined after rainflow cycle counting over all events. The advantage of the independent method over the combined methods is computational expense versus accuracy. The combined method will close all cycles, whereas the individual method may miss a large damaging cycle if the cycle begins in one event and ends or closes in a subsequent event. The combined fast method performs a rainflow count data reduction to speed up the analysis and determine the most critical locations first and then redoes a full analysis on the critical locations.

3. Once a FTGSEQ bulk data entry is referenced in an FIDi field, it can't be referenced again in any other FTGSEQ entries (within its own associations - the same fatigue analysis) to avoid infinite loops. And if it is referenced by the FATIGUE case control, it cannot appear in any FIDi field of the FTGSEQ bulk data.

4. Different FTGEVNTs can be set up and the user can construct each sequence by specifying how many times to repeat each event in a sequence. One sequence could then be referenced in another sequence to tell the new sequence how many times to repeat that sequence. As an example, assume there are three events an automobile is subjected to: cobble stones, pot holes, speed bumps. One sequence might be five (5) "cobble stones," six (6) "potholes" and three (3) "speed bumps." This sequence may be called "torture track." Also define two more events called "cornering left" and "cornering right." A load sequence of ten (10) "cornering left" and ten (10) "cornering right" might be called "country road." Now with a nested FTGSEQ you can put these together any way you want. So one fatigue analysis might use a sequence of only "country road," another of only "torture track" and another of a combined six (6) "torture tracks," five (5) "country roads," followed by one (1) more "torture track" and one (1) more "country road" This would result in 3 fatigue analyses.

SOL 101 or a modal analysis using SOL 103, or a subcase ID that represents the loading event or another FTGSEQ entry for modal transient fatigue analysis using SOL 112. (Integer > 0). See Remark 3. and 4.

Ni Number of repeats of this loading sequence or event (Real>0.0, Default=1.0). For METHOD=1 and 2, Ni must be a whole number, i.e., 1.0, 2.0, 3.0, etc. In other words, fractions of events are not allowed. See Remark 3. and 4.

"UNITS" Flag indicating that a fatigue equivalent unit name is applied to this loading. See Remark 5. and 6.

EQUIV Number of equivalent units. (Real>0.0; Default=1.0). See Remark 5. and 6.EQNAME Equivalent name of this loading event. EQNAME can span across fields 4 through 9.

If not defined it will be called Repeats. (Character) See Remark 5. and 6. Spaces are not allowed in the name.


5. If the "UNITS" flag is absent, the default fatigue equivalent unit is 1.0 Repeats of the resulting stress time history sequence. Equivalent units specified on FTGLOAD entries are ignored when FTGSEQ entries are used6. Example of using equivalent units: If one repeat of the sequence is equivalent to 5 times around a test track, the equivalent unit name, EQNAM, might be "laps," and the equivalent unit, EQUIV, would be 5. Fatigue life will be reported in these units if defined, otherwise they are reported as repeats of the loading sequence. Life output is reported in both Repeats and the fatigue equivalent units, if defined.

7. For duty cycle jobs, temporary DAC files are created. Use EVNTOUT=1 if you wish to keep the files, otherwise they are deleted after job terminates. For SOL 200 only EVNTOUT=0 is supported.


38

FTGEVNT Fatigue Loading EventsGroups simultaneously applied loads into loading events for pseudo-static fatigue analysis using SOL 101 or modal analysis using SOL 103 by referencing FTGLOAD entries.

Format:

Example:This example shows that this fatigue load event consists of two separate, but simultaneously applied, loading defined by FTGLOAD entries of IDs 4 & 11.

Remarks:1. Each FTGEVNT ID must be unique relative to all other FTGEVNT and FTGSEQ IDs

1 2 3 4 5 6 7 8 9 10FTGEVNT ID FLOAD1 FLOAD2 FLOAD3 FLOAD4 FLOAD5 FLOAD6 FLOAD7

FLOAD8 ... ... ... ... ... ... -etc-

FTGEVNT 22 4 11

Field ContentsID Unique ID. See Remark 1.FLOADi ID of a FTGLOAD entry (Integer > 0, no default).


FTGLOAD Fatigue Loading Time VariationDefines loading time variation for pseudo-static fatigue analysis using SOL 101 or modal analysis using SOL 103.

Format:

Examples:Two examples are shown here where the first associates SOL 101 subcase ID 2 to its cyclic variation defined by TABLFTG ID 4. This could also be a SOL 103 mode number associated to its modal participation factor (modal loading). The second shows the same thing except that now it is subcase ID 5 associated to UDNAME entry 4 (flagged by the DB). The UDNAME entry defines an external file containing the cyclic variation of the loading.

1 2 3 4 5 6 7 8 9 10FTGLOAD ID TID LCID LDM SCALE OFFSET TYPE


FTGLOAD 55 4 2 1.0 1.0 0.0

FTGLOAD 23 4 5 1.0 1.0 0.0 DBUNITS 5.5 Flights

Field ContentsID Unique ID which is referenced by an FTGEVNT entry or directly by a FATIGUE case

control (Integer > 0). See Remark 1. TID Table ID of a TABLFTG (or TABLED1) entry that defines the time variation of the

loading or the ID of a UDNAME entry for external definition of the loading time variation (Integer > 0). See Remarks 2. through 5.

LCID Subcase ID of a linear static solution SUBCASE for SOL 101 or a mode number for SOL 103 (Integer > 0, no default) .

LDM Largest magnitude of the applied load (in the same units used to define the load time variation in field TID) used to normalize the load (Real, default=1.0). This effectively scales the stress to simulate a stress state due to a unit load. See Remark 6.

SCALE Scale factor applied to the load time history (Real, default=1.0). See Remark 6.OFFSET Offset applied to the load time history (Real, default=0.0). See Remark 6.TYPE Flag indicating the type of load being defined. Values can be blank, "DB", or "STATIC".

Default is blank. See Remarks 2. through 5.


40

"UNITS" Flag indicating that a fatigue equivalent unit name is defined for this loading. See Field ContentsRemarks:1. If referenced directly by a FATIGUE case control, there cannot be a FTGSEQ bulk data entry by

the same ID.2. If the TYPE field is blank then TID references a TABLFTG or TABLED1 entry. 3. If TYPE=DB, then TID references a UDNAME ID. A UDNAME entry must be supplied in this

case to specify the file and path of the externally defined load time variation. This file is expected to be in standard DAC format.

4. If TYPE is STATIC, the TID field should be left blank as it will be ignored. STATIC indicates that the stress state from the specified LCID is to act as a static offset with no load time variation when performing the linear superposition, which will give every element a different offset defined by the stress state at each element of the specified subcase, as opposed to simply specifying the OFFSET field, which gives every element the same offset. If the "STATIC" flag is specified, there must be at least two FTGLOAD entries defined and called out by a FTGEVNT entry, one of which must be time varying (see Remark 6.).

5. For modal analysis using SOL 103, the referenced load variation defines the modal participation factors for the referenced mode.

6. The LDM, SCALE, and OFFSET are used together in the following manner to scale/modify the stress state in order to determine the resulting stress time variation:

where is the resulting stress tensor at time t, is the stress tensor from the subcase or mode defined by the LCID field, and P(t) is the y value of the load-time history at time t as defined by the TID field. For multiple loads, the principle of linear superposition is used to combine all loads for a single event.

7. If the "UNITS" flag is absent, the default fatigue equivalent unit is 1.0 Repeats of the stress time history. If this FTGLOAD is referenced by a FTGEVNT, then the equivalent units on this entry are ignored and those on the FTGSEQ entry take precedent. Only if a FTGLOAD is directly referenced by a FATIGUE case control are the fatigue equivalent units used as defined on the FTGLOAD entry.

Remarks 7. and 8.EQUIV Number of equivalent units (Real>0.0, default=1.0). See Remarks 7. and 8.EQNAME Equivalent name of this loading history. EQNAME can span across fields 4 through 9.

If not defined it will be called Repeats (Character). See Remarks 7. and 8.

i j t P t i j , l

LDM------------- SCALE OFFSET+=

i j t i j l


8. Example of using equivalent units: If one repeat of the defined time history is equivalent to 5 times around a test track, the equivalent unit name, EQNAM, might be "laps," and the equivalent unit, EQUIV, would be 5.0. Fatigue life will be reported in these units if defined, otherwise they

are reported as Repeats of the loading. Life output is reported in both Repeats and the fatigue equivalent units, if defined.

9. All FTGLOAD entries referenced by a FTGEVNT should reference different SUBCASEs for SOL 101 (or modes for SOL 103) and must have time variations consisting of the same number of points.


42

TABLFTG Fatigue Loading Tabular DataDefines tabular data for defining fatigue cyclic loading with respect to time (time history).

Format:

Example:

Remarks:1. The TABLFTG is referenced by a FTGLOAD entry.2. The x-values are assumed to be in ascending order. For rainflow cycle counting purposes the

actual x values are inconsequential.3. For modal analysis using SOL 103, this would define the modal participation factors for a

particular mode.

1 2 3 4 5 6 7 8 9 10TABLFTG TID

y1 y2 y3 y4 y5 y6 y7 "ENDT"

TABLFTG 1 0.000 -1.0 1.0 0.0 ENDT

Field ContentsTID Table identification number. (Integer > 0)yi Y value of each point in the time history curve. (Real). "ENDT" Flag indicating the end of the table.


UDNAME User Defined File NameProvides the name of a file that can be referenced from other bulk data entries such as FTGLOAD.

Format:

Example:

Remarks:1. The UDID is referenced by a FTGLOAD entry.2. The NAME can be of any length, but the Nastran Fatigue capability only supports up to 64 words

which corresponds to four lines of data in fields 2 through 9. 3. If only a NAME with no path (e.g., sine01.dac) is supplied, the file is assumed to be located in

the same directory as the Nastran input file. If an absolute or relative path is supplied (e.g, /local/user/fatigue/sine01.dac), it will be used.

1 2 3 4 5 6 7 8 9 10UDNAME UDID

NAME

Field ContentsUDID Unique UDID (Integer>0). See Remark 1.NAME Name of a file (with or without path) such as the external loading time history in DAC format

(Character).

MSC NASTRAN Embedded Fatigue Users GuideAnalysis Model Units

44

Analysis Model UnitsWhen performing fatigue analysis, it is important to understand the relationship between the

models units and those necessary for a fatigue analysis. Please see Remark 2 in the description of DTI, UNITS below.

Defines units necessary for conversion during the analysis for the Nastran/ADAMS interface or a Nastran fatigue analysis.

Format:

Example:For fatigue analysis, only the stress units are necessary.

Remarks:1. The DTI,UNITS Bulk Data entry is required for a ADAMSMNF FLEXBODY=YES run. See the

ADAMSMNF*, 218 case control entry. ADAMS is not a unitless code (as is Nastran). Units must be specified. A DTI Bulk Data entry provides UNITS (a unique identifier) input as the above example illustrates. Once identified, the units will apply to all superelements in the model. Acceptable character input strings are listed in the table below. MASS, FORCE, LENGTH, and TIME are required for ADAMS interface.

2. Fatigue analysis as performed by MSC Nastran requires the identification of the stress units used in the analysis. MSC Nastran is a unitless code and it is therefore up to the user to ensure compatible units between all interactions. However, during the fatigue analysis, the stresses must be converted to SI units of MPa. This is because the fatigue material property stress parameters as defined on the MATFTG entry are internally converted to standard SI units of MPa and the stresses from the analysis must match. Thus it is necessary for the user to use DTI,UNITS to define the stress units to ensure proper conversion. If the model units system produces stresses in MPa, then DTI,UNITS is not necessary or DTI,UNITS should be set to MPa (the default).

DTI,UNITS Unit Definitions

1 2 3 4 5 6 7 8 9 10DTI UNITS 1 MASS FORCE LENGTH TIME STRESS

DTI UNITS 1 MPA


Mass Force Length Time Stress

KG - kilogram N - newton KM - kilometer H - hour MPA -

megapascalLBM - pound-mass

LBF - pounds-force M - meter MIN - minute PA - pascal

SLUG - slug KGF - kilograms-force

CM - centimeter S - second PSI - pound per square inch

GRAM - gram OZF - ounce-force MM - millimeter MS - millisecond KSI - kilo pound per square inch

OZM - ounce-mass

DYNE - dyne MI - mile US - microsecond PSF - pound per square foot

KLBM - kilo pound-mass (1000 lbm)

KN - kilonewton FT - foot NANOSEC - nanosecond

KSF - kilo pound per square foot

MGG - megagram KLBF - kilo pound-force (1000 lbf)

IN- inch D - day DYNECM2 - dyne per square centimeter

SLINCH - 12 slugs

MN - millinewton UM - micrometer BAR - bar

UG - microgram UN - micronewton NM - nanometer ATM - physical atmosphere

NG - nanogram NN - nanonewton ANG - angstromUSTON - US ton YD - yard

MIL - milli-inchUIN - micro-inch

MSC NASTRAN Embedded Fatigue Users GuideFatigue Optimization

46

Fatigue OptimizationDesign optimization usinig SOL 200 allows for the definition of fatigue life or damage responses. These

responses can be used as design objectives, such as maximizing life or minimizing damage, or for defining constraints on fatigue life or damage at particular locations on the model. Below is a partial listing of the DRESP1 entry explaining how it is used for fatigue responses only. The fatigue item codes are also listed.

Defines a set of structural responses that is used in the design either as constraints or as an objective.

Format:

Example:This example defines a fatigue life response (ATTA=4) on element 321 (ATT1=321) defined by the fatigue analysis called out by FATIGUE case control of ID 44 (ATTB=44). A label called FLIGHTS is used to name the response.

DRESP1 Design Sensitivity Response Quantities

1 2 3 4 5 6 7 8 9 10DRESP1 ID LABEL RTYPE PTYPE REGION ATTA ATTB ATT1

ATT2 -etc.-

DRESP1 55 FLIGHTS FATIGUE ELEM 4 44 321

Field ContentsID Unique entry identifier. (Integer > 0)LABEL User-defined label. (Character)RTYPE Response type. See Table 2-7. (Character)PTYPE Element flag (PTYPE = ELEM) or property entry name. Used with element

type responses (stress, strain, force, etc.) to identify the property type, since property entry IDs are not unique across property types. (Character: ELEM, PBAR, PSHELL, etc.)

REGION Region identifier for constraint screening. (Integer > 0)ATTA, ATTB, ATTi

Response attributes. See Table 2-7. (Integer > 0 or Real or blank)


Table 2-7 Design Sensitivity Response AttributesRemarks:1. Fatigue item codes can be found in Table 2-8. 2. For RTYPE = FATIGUE, PTYPE must be set to ELEM or PSOLID or PSHELL. ATTB is the

ID of a FATIGUE case control. If a FATIGUE case control references a SET ID, then ATTB must reference one of the IDs referenced by the SET.

3. Design optimization using fatigue responses is currently limited to one fatigue analysis, that is, one loading sequence. Multiple fatigue responses referencing different loading sequences, i.e., FATIGUE case control IDs, will result in an error.

Remarks:1. Element Group A consists of CHEXA, CPENTA, CTETRA, CQUAD4, CQUAD8, CQUADR,

CTRIA3, CTRIA6, CTRIAR, CSHEAR. 2. Also used for CTRIA3 and CSHEAR elements with LOC=ELEMENT option on FTGPARM.

Response Type

(RTYPE)

Response Attributes

ATTA (Integer > 0)ATTB (Integer > 0 or

Real > 0.0) ATTI (Integer > 0)FATIGUE Fatigue Item Code. See

Remark 1.ID of a FATIGUE case control. See Remark 2. and 3.

Property ID (PID) or Element ID (EID)

Table 2-8 Fatigue Item Codes for LOC=ELEMENT on FTGPARM

Element NameReal Element Data

Item Code ItemElement Group A 4 Fatigue life in Repeats of the loading sequence

5 Log of fatigue life in Repeats of the loading sequence

6 Fatigue life in user defined fatigue equivalent units7 Log of fatigue life in user defined fatigue

equivalent units8 Fatigue damage9 Log of fatigue damage

12 Scale factor from Factor of Safety analysis

MSC NASTRAN Embedded Fatigue Users GuideFatigue Optimization

48

Table 2-9 Fatigue Item Codes for LOC=NODE on FTGPARMElement Name Item CodesReal Element Data

ItemElement Group B 4,15,26,37 Life in Repeats of the loading sequence

5,16,27,38 Log of life in Repeats of the loading sequence6,17,28,39 Life in user defined fatigue equivalent units7,18,29,40 Log of life in user defined equivalent units8,19,30,41 Fatigue damage9,20,31,42 Log of fatigue damage12,23,34,45 Scale factor from Factor of Safety analysis

Element Group C 4,15,26 Fatigue life in Repeats of the loading sequence5,16,27 Life in Repeats of the loading sequence6,17,28 Log of life in Repeats of the loading sequence7,18,29 Life in user defined fatigue equivalent units8,19,30 Log of life in user defined equivalent units9,20,31 Fatigue damage12,23,34 Log of fatigue damage

Element Group D 4,15,26,37,48,59 Life in Repeats of the loading sequence5,16,27,38,49,60 Log of life in Repeats of the loading sequence6,17,28,39,50,61 Life in user defined fatigue equivalent units7,18,29,40,51,62 Log of life in user defined equivalent units8,19,30,41,52,63 Fatigue damage9,20,31,42,53,64 Log of fatigue damage12,23,34,45,56,67 Scale factor from Factor of Safety analysis

Element Group E 4,15,26,37,48,59,70,81 Life in Repeats of the loading sequence5,16,27,38,49,60,71,82 Log of life in Repeats of the loading sequence6,17,28,39,50,61,72,83 Life in user defined fatigue equivalent units7,18,29,40,51,62,73,84 Log of life in user defined equivalent units8,19,30,41,52,63,74,85 Fatigue damage9,20,31,42,53,64,75,86 Log of fatigue damage12,23,34,45,56,67,78,89 Scale factor from Factor of Safety analysis


Remarks:1. Element Group A consists of CHEXA, CPENTA, CTETRA, CQUAD4, CQUAD8, CQUADR,

CTRIA3, CTRIA6, CTRIAR, CSHEAR.

2. Element Group B consists of elements with 4 corner nodes (CQUAD4, CQUAD8, CQUAD4,

CTETRA) and item codes are listed for Grids 1 through 4, respectively.1. Element Group C consists of elements with 3 corner nodes: CTRIA6, CTRIAR, and item codes

are listed for Grids 1 through 3, respectively.2. Element Group D consists of elements with 6 corner nodes: CPENTA, and item codes are listed

for Grids 1 through 6, respectively.3. Element Group E consists of elements with 8 corner nodes: CHEXA, and item codes are listed

for Grids 1 through 8, respectively.4. For CTRIA3 and CSHEAR elements, LOC=ELEMENT and LOC=NODE options on

FTGPARM use the same item codes in Table 2-8.5. If it is desired to use a life response (or other item) for all nodes (using LOC=NODE on

FTGPARM), all item codes for the particular item are required, e.g., 4, 15, 26, and 37 for Element Group B (one DRESP1 entry for each item code).

MSC NASTRAN Embedded Fatigue Users GuideTips for Optimizing Performance

50

Tips for Optimizing PerformanceFollow these tips to ensure your fatigue analysis runs as quickly as possible.1. Set LOGLVL field on FTGPARM to something less than three (3). Ideally just leave it blank. Set it to three (3) or higher for debugging purposes only.

2. Use as many threads as possible. This is set in the NTHRD field on FTGPARM bulk data entry. Setting it to zero (0) will allow the progam to automatically select the number of threads available.

3. Use TOPSTR on FTGDEF entry to process only critically stressed locations.4. Consider using RAINFLOW with GATE option on the FTGPARM entry.5. Very large duty cycle jobs can result in many open files during the analysis proceedure. Make sure

your resource limits on your machine allow for this. The number of open files is typically set to 1024 by default. The installation manual explains how to change these limits.

6. Estimate the amount of memory that is needed. The amount of RAM (in words) needed is approximately:49 times the Number of Materials plus(6+12) times the Number of Entities (nodes or elements) plus Number of Time Steps in each Time History plus6 times the Number of Entities times the Number of Load Cases (or Modes) plusSmall amounts for Events, tables, etc.Using I8 doubles the requirement.

7. Therefore, the use of FTGDEF to limit the results on large models is very beneficial.

MSC Nastran Fatigue Analysis Users GuideChapter 3: A Simple S-N Analysis3 A Simple S-N Analysis

Problem Description Fatigue Setup Concluding Remarks Patran Setup

MSC NASTRAN Embedded Fatigue Users GuideProblem Description

52

Problem DescriptionIn this first example problem we start with a very simple model to introduce some fatigue analysis

concepts by investigating the Total Life, of the component shown below. For the purpose of this exercise we will refer to it as the keyhole model as it is a keyhole shape notched component. A fully reversed loading (p) of +/- 10,000 N is applied on the sample to open and close the notch. Clearly, the notch root will see the highest stress. Because the model is symmetric about the notch, a half- model with a symmetric boundary condition is all that is required.

Figure 3-1 The S-N Analysis of the Keyhole Model

Objective To introduce the S-N fatigue life prediction method, commonly referred to as the

Stress-Life (S-N) or Total Life method.

Files RequiredAll files necessary to run this and subsequent examples are found in the test problem library (nast/tpl/fatigue) directory in a complete MSC Nastran installation.

Table 3-1 Files Required

Files Required DescriptionsimpleSN_v1.dat Simple S-N curve - fully reversed constant amplitude loadingsimpleSN_v2.dat Simplified form of input file - equivalent to simpleSN_v1.datsimpleSN_v3.dat Derived material S-N properties

53CHAPTER 3A Simple S-N Analysis

Table 3-1 Files Required

Files Required Description

simpleSN_v4a.dat Multiple constant mean S-N curves - 0.0 MPa meansimpleSN_v4b.dat Multiple constant mean S-N curves - 100 MPa meansimpleSN_v5.dat Multiple constant R-Ratio S-N curvessimpleSN_v6.dat Multiple constant life (Haigh) curvessimpeSN_v7.dat Bastanaire S-N curve

MSC NASTRAN Embedded Fatigue Users GuideFatigue Setup

54

Fatigue SetupThis fatigue analysis is done using a linear static solution (SOL 101) with a load magnitude of 10,000

Newtons. The partial input deck