A Model for Evaluation of Low Cycle Fatigue Lives under Nonproportional Straining
Takamoto ITOH
Abstract:This paper develops a damage model for evaluation of low cycle fatigue lives under complex cyclic multiaxial loadings. The author has proposed the equivalent strain parameter for the life prediction of the nonproportional low cycle fatigue. This strain parameter could evaluate the dependence of fatigue lives on strain history and material, and correlate the fatigue lives within a small scatter band under 15 kinds of proportional and nonproportional strain paths. However, the parameter was applicable to the life prediction under the limited nonproportional strain history, so that some modifications were required. In this study, a simple damage model for the life prediction by combining the equivalent strain parameter with Miner's law in order to apply the life prediction under more complex nonproportional loadings. The applicability of the proposed model was examined for life evaluation of nonproportional low cycle fatigue for different materials; type 304 stainless steels, copper, aluminum alloys, chromium-molybdenum and carbon steels, which were obtained from different research institutes. The model could correlate most of all the fatigue data within a factor of two scatter band and has a possibility to become a good damage model for nonproportional low cycle fatigue. Key Words:Low cycle fatigue, Life prediction, Multiaxial strain, Nonproportional loading, Additional hardening, Slip system