Fatigue Limit in Metals

Claude Bathias is Emeritus Professor at the University of Paris 10-La Defense in France. He started his career as a research engineer in the aerospace and military industry where he remained for 20 years before becoming director of the CNRS laboratory ERA 914 at the University of Compiègne in France. He has launched two international conferences about fatigue: International Conference on the Fatigue of Composite Materials (ICFC) and Very High Cycle Fatigue (VHCF).

• ACKNOWLEDGEMENTS viiCHAPTER 1. INTRODUCTION ON VERY HIGH CYCLE FATIGUE 11.1. Fatigue limit, endurance limit and fatigue strength 11.2. Absence of an asymptote on the SN curve 51.3. Initiation and propagation 61.4. Fatigue limit or fatigue strength 71.5. SN curves up to 109 cycles 81.6. Deterministic prediction of the gigacycle fatigue strength 101.7. Gigacycle fatigue of alloys without flaws 121.8. Initiation mechanisms at 109 cycles 131.9. Conclusion 131.10. Bibliography 14CHAPTER 2. PLASTICITY AND INITIATION IN GIGACYCLE FATIGUE 172.1. Evolution of the initiation site from LCF to GCF 172.2. Fish-eye growth 202.2.1. Fracture surface analysis 202.2.2. Plasticity in the GCF regime 232.3. Stresses and crack tip intensity factors around spherical and cylindrical voids and inclusions 292.3.1. Spherical cavities and inclusions 292.3.2. Spherical inclusion 312.3.3. Mismatched inclusion larger than the spherical cavity it occupies 312.3.4. Cylindrical cavities and inclusions 332.3.5. Cracking from a hemispherical surface void 352.3.6. Crack tip stress intensity factors for cylindrical inclusions with misfit in both size and material properties 382.4. Estimation of the fish-eye formation from the Paris–Hertzberg law 422.4.1. “Short crack” number of cycles 472.4.2. “Long crack” number of cycles 482.4.3. “Below threshold” number of cycles 482.5. Example of fish-eye formation in a bearing steel 492.6. Fish-eye formation at the microscopic level 522.6.1. Dark area observations 532.6.2. “Penny-shaped area” observations 542.6.3. Fracture surface with large radial ridges 562.6.4. Identification of the models 592.6.5. Conclusion 622.7. Instability of microstructure in very high cycle fatigue (VHCF) 622.8. Industrial practical case: damage tolerance at 109 cycles 692.8.1. Fatigue threshold in N18 702.8.2. Fatigue crack initiation of N18 alloy 712.8.3. Mechanisms of the GCF of N18 alloy 732.9. Bibliography 74CHAPTER 3. HEATING DISSIPATION IN THE GIGACYCLE REGIME 773.1. Temperature increase at 20 kHz 773.2. Detection of fish-eye formation 813.3. Experimental verification of Nf by thermal dissipation 833.4. Relation between thermal energy and cyclic plastic energy 853.5. Effect of metallurgical instability at the yield point in ultrasonic fatigue 893.6. Gigacycle fatigue of pure metals 913.6.1. Microplasticity in the ferrite 953.6.2. Effect of gigacycle fatigue loading on the yield stress in Armco iron 973.6.3. Temperature measurement on Armco iron 983.6.4. Intrinsic thermal dissipation in Armco iron 1023.6.5. Analysis of surface fatigue crack on iron 1053.7. Conclusion 1093.8. Bibliography 110INDEX 113