Is there a fatigue limit in metals? This question is the main focus of this book. Written by a leading researcher in the field, Claude Bathias presents a thorough and authoritative examination of the coupling between plasticity, crack initiation and heat dissipation for lifetimes that exceed the billion cycle, leading us to question the concept of the fatigue limit, both theoretically and technologically. This is a follow-up to the Fatigue of Materials and Structures series of books previously published in 2011. Contents 1. Introduction on Very High Cycle Fatigue. 2. Plasticity and Initiation in Gigacycle Fatigue. 3. Heating Dissipation in the Gigacycle Regime. About the Authors 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). This new, up-to-date text supplements the book Fatigue of Materials and Structures, which had been previously published by ISTE and John Wiley in 2011. A thorough review of coupling between plasticity, crack priming, and thermal dissipation for lifespans higher than a billion of cycle has led us to question the concept of fatigue limit, from both the theoretical and technological point of view. This book will address that and more.
ACKNOWLEDGEMENTS vii CHAPTER 1. INTRODUCTION ON VERY HIGH CYCLE FATIGUE 1 1.1. Fatigue limit, endurance limit and fatigue strength 1 1.2. Absence of an asymptote on the SN curve 5 1.3. Initiation and propagation 6 1.4. Fatigue limit or fatigue strength 7 1.5. SN curves up to 109 cycles 8 1.6. Deterministic prediction of the gigacycle fatigue strength 10 1.7. Gigacycle fatigue of alloys without flaws 12 1.8. Initiation mechanisms at 109 cycles 13 1.9. Conclusion 13 1.10. Bibliography 14 CHAPTER 2. PLASTICITY AND INITIATION IN GIGACYCLE FATIGUE 17 2.1. Evolution of the initiation site from LCF to GCF 17 2.2. Fish-eye growth 20 2.2.1. Fracture surface analysis 20 2.2.2. Plasticity in the GCF regime 23 2.3. Stresses and crack tip intensity factors around spherical and cylindrical voids and inclusions 29 2.3.1. Spherical cavities and inclusions 29 2.3.2. Spherical inclusion 31 2.3.3. Mismatched inclusion larger than the spherical cavity it occupies 31 2.3.4. Cylindrical cavities and inclusions 33 2.3.5. Cracking from a hemispherical surface void 35 2.3.6. Crack tip stress intensity factors for cylindrical inclusions with misfit in both size and material properties 38 2.4. Estimation of the fish-eye formation from the Paris–Hertzberg law 42 2.4.1. “Short crack” number of cycles 47 2.4.2. “Long crack” number of cycles 48 2.4.3. “Below threshold” number of cycles 48 2.5. Example of fish-eye formation in a bearing steel 49 2.6. Fish-eye formation at the microscopic level 52 2.6.1. Dark area observations 53 2.6.2. “Penny-shaped area” observations 54 2.6.3. Fracture surface with large radial ridges 56 2.6.4. Identification of the models 59 2.6.5. Conclusion 62 2.7. Instability of microstructure in very high cycle fatigue (VHCF) 62 2.8. Industrial practical case: damage tolerance at 109 cycles 69 2.8.1. Fatigue threshold in N18 70 2.8.2. Fatigue crack initiation of N18 alloy 71 2.8.3. Mechanisms of the GCF of N18 alloy 73 2.9. Bibliography 74 CHAPTER 3. HEATING DISSIPATION IN THE GIGACYCLE REGIME 77 3.1. Temperature increase at 20 kHz 77 3.2. Detection of fish-eye formation 81 3.3. Experimental verification of Nf by thermal dissipation 83 3.4. Relation between thermal energy and cyclic plastic energy 85 3.5. Effect of metallurgical instability at the yield point in ultrasonic fatigue 89 3.6. Gigacycle fatigue of pure metals 91 3.6.1. Microplasticity in the ferrite 95 3.6.2. Effect of gigacycle fatigue loading on the yield stress in Armco iron 97 3.6.3. Temperature measurement on Armco iron 98 3.6.4. Intrinsic thermal dissipation in Armco iron 102 3.6.5. Analysis of surface fatigue crack on iron 105 3.7. Conclusion 109 3.8. Bibliography 110 INDEX 113
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).