A new method for studying the effect of multiaxial strain states on low cycle non-proportional fatigue prediction

In this paper, a new method is put forward to predict fatigue life under low cycle non-proportional loadings. Modified from the thought of Modified Wöhler Curve Method, a multiaxial ASME strain based approach is presented to estimate low cycle fatigue damage under proportional loadings. Based on it, the new method can consider the multiaxiality effect on the determination of reference proportional strain path and the calculation of non-proportionality factor Fnp. For the first time, a viewpoint of inhomogeneous integral path for calculating factor Fnp is proposed, and a path-dependent weight factor is defined to describe this heterogeneity. The experimental tests on 3 sets of metallic materials with various loading cases are referenced to validate the present study. As a result, the proposed method can more accurately quantify the non-proportionality degree of loading paths.