High Cycle Fatigue (eBook)

Front cover 1
Title page 4
Copyright page 5
Table of contents 6
Preface 11
Part One Introduction and Background 16
1 Introduction 18
Historical background 18
What is High Cycle Fatigue? 19
HCF design considerations 20
HCF design requirements 24
Root causes of HCF 26
Field failures 28
Damage tolerance 31
Application to HCF 35
Current status 38
Field experience 40
2 Characterizing Fatigue Limits 42
Constant life diagrams 42
Gigacycle fatigue 42
Characterizing fatigue cycles 49
Fatigue limit stresses 50
Equations for constant life diagrams 56
Haigh diagram at elevated temperature 62
Role of mean stress in constant life diagrams 66
Jasper equation 71
Observations on step tests at negative R 80
3 Accelerated Test Techniques 85
Historical background 85
Coaxing 85
Early test methods 87
Step test procedures 90
Statistical considerations 91
Influence of number of steps 93
Validation of the step-test procedure 95
Observations from the last loading block 100
Comments on step testing 104
Staircase testing 105
Probability plots 106
Statistical analysis 110
Dixon and Mood method 110
Numerical simulations 114
Sample size considerations 119
Construction of an “artificial” staircase 120
Other methods 121
Random fatigue limit (RFL) model 124
Data analysis 128
Summary comments on FLS statistics 135
Constant stress tests 138
Run-outs and maximum likelihood (ML) methods 141
Resonance testing techniques 144
Frequency effects 149
Part Two Effects of Damage on HCF Properties 158
4 LCF–HCF Interactions 160
Small cracks and the Kitagawa diagram 160
Behavior of notched specimens 164
Effects of LCF loading on HCF limit stress 168
Studies of naturally initiated LCF cracks 185
Crack-propagation thresholds 185
Overloads and load-history effects 187
An overload model 195
Analysis using an overload model 197
Examples of LCF–HCF interactions 198
Design considerations 208
LCF–HCF nomenclature 211
Example of anomalous behavior 212
Another example of anomalous behavior 215
Combined cycle fatigue case studies 219
5 Notch Fatigue 228
Introduction 228
Stress concentration factor 228
What is kt? 230
Fatigue notch factor 231
kf versus kt relations 232
Equations for kf 233
Fracture mechanics approaches for sharp notches 237
Cracks versus notches 240
Mean stress considerations 243
Plasticity considerations 247
Negative mean stresses 253
Fatigue limit strength of notched components 254
Non-damaging notches 256
Size effects and stress gradients 257
Critical distance approaches 257
Analysis methods 261
Effects of defects on fatigue strength 266
Notch fatigue at elevated temperature 269
6 Fretting Fatigue 276
Introduction 276
Observations of fretting fatigue 278
Representing total contact loads, Q and P 282
Load and stress distributions 286
Effects of local and bulk stresses on stress intensity 287
Mechanisms of fretting fatigue 292
Mechanics of fretting fatigue 294
Stress analysis of contact regions 296
Multiple crack considerations 298
Analytical solutions 299
Role of slip amplitude 307
Stress-at-a-point approaches 310
Fracture mechanics approaches 315
A combined stress and K approach 321
Comparison of fretting-fatigue fixtures 324
Role of coefficient of friction 327
Average versus local coefficient of friction 332
Summary comments 332
7 Foreign Object Damage 337
Introduction 337
Field experience and observations 339
Repair by blending 340
Background 341
FOD data mining and investigation 341
Definition of FOD 343
Types of damage 344
Scope of the FOD problem 351
Laboratory simulation methods 353
Solenoid gun 353
Pendulum 353
Quasi-static 354
Simulations using a leading edge geometry 354
Role of residual stresses 359
Energy considerations 360
Fatigue limit strength 362
Simulations using a flat plate 367
Other laboratory FOD simulations 374
Analytical modeling of FOD 382
Perturbation study 386
Summary comments 389
Part Three Applications 392
8 HCF Design Considerations 394
Factors of safety 394
Modeling errors 396
Material variability 399
Fracture mechanics considerations 401
Effects of defects 405
Application to LCF–HCF 411
Damage tolerance for HCF 413
Material allowables 415
Threshold concept for HCF 418
Representing fatigue limit data 420
Threshold considerations 423
Experimental threshold measurements 424
“Jump-in” method 424
Mechanisms in threshold testing 427
Load-history effects 429
Compression precracking 431
Load-shed rates 431
Crack closure 433
Kmax DeltaK concept 434
Crack propagation stress intensity factor 437
An engineering approach to thresholds 438
Observations from field failures 439
Probabilistic approach to HCF/FOD design 440
Residual stresses in HCF design 445
Application to notches 451
Shot peening 456
Deep residual stresses 462
Application to an airfoil geometry 464
Crack arrest 473
Crack growth retardation 476
A numerical example 477
Autofrettage 479
Appendices 487
Appendix A Early Railroad Accidents and the Origins of Research on Fatigue of Metals 487
Appendix B Final Report for the USAF High Cycle Fatigue Program 508
Appendix C HCF in ENSIP 514
Appendix D Evaluation of the Staircase Test Method using Numerical Simulation 532
Appendix E Estimation of HCF Threshold Stress Levels in Notched Components 546
Appendix F Analytical Modeling of Contact Stresses 557
Appendix G Experimental and Analytical Simulation of FOD 573
Appendix H FOD in JSSG 615
Appendix I Computation of High Cycle Fatigue Design Limits under Combined High and Low Cycle Fatigue 632
Index 654