Relationship Between Bending Fatigue Strength Expressed by Actual Stress and Stress Gradient at Critical Point

Abstract

When bending fatigue strength was evaluated using the actual stress (maximum stress) at the critical point, the bending fatigue strength depends on the geometry near the critical point. In order to propose a bending fatigue design method applicable to machine elements of arbitrary shape, it is necessary to verify the shape dependence of the bending fatigue strength. Since the notched bending fatigue specimen and the notched tensile fatigue specimen have similar normal stress distributions near the critical point, a correspondence is considered between the tensile fatigue strength and bending fatigue strength. In this study, the relationship between the fatigue strength and stress gradient was investigated by tensile and bending fatigue tests. As a result, the equivalence of tensile fatigue strength and bending fatigue strength was recognized, and a method to estimate the bending fatigue strength from the stress gradient was proposed.