The Competing Roles of Microstructure and Flaw Size on the Fatigue Limit of Metals

Abstract

Research includes the development and verification of an analytical model that addresses the fatigue process, namely the threshold condition of non-propagating cracks. Two parameters are identified to govern the fatigue resistance: non-propagating crack size and crack barrier strength. The concept of three defect types associated with three different flaw dominated fatigue regimes is introduced. Furthermore, application of the model to fatigue mechanisms in high strength steels, synergistic effects of surface finish and intergranular cracks, competition between surface and subsurface fatigue nucleation, and unexplained observations and scatter in fatigue behavior is demonstrated. Overall, the model is proven as a simple and robust tool for qualifying and statistically quantifying material behavior. In addition, the model can be implemented in material screening, selection, and processing as well as a guide for future material research and design.