Chapter 5 - Effect of Hardness HV on Fatigue Limits of Materials Containing Defects, and Fatigue Limit Prediction Equations

Abstract

This chapter presents a simple and useful method, based on only two basic quantities, for the prediction of both ΔKth and fatigue limit σw for materials containing small defects and cracks. The materials having higher Vickers hardness show higher values of ΔKth, and concomitant higher fatigue strengths. The fatigue limit of a specimen, containing a notch or a defect, is not directly proportional to the Vickers hardness. This is presumably because the occurrence of nonpropagating cracks follows a different relationship. The fatigue limits of materials containing small defects and cracks are determined by the microstructure hardness and by the characteristic dimension for defects and cracks, √area. The prediction method based on this concept is named the √area parameter model. The fatigue limit for a specimen, containing a small hole or crack, is the threshold condition for nonpropagation of a crack emanating from an initial defect or crack, hence the initial value of √area is a more crucial geometrical factor than is the initial 3D defect shape.