An Effective Plastic Strain Component for Low Cycle Fatigue in Metals

Abstract

Low cycle fatigue tests were performed on several kinds of metal materials, and fatigue life was considered in terms of cyclic hardening property. The cumulative plastic strain energy to failure increases with a decrease in the plastic strain range controlled. The rate of the increase in that amount is influenced by the slip character of materials. Such a difference in the rate is reasonably interpreted by considering the shape of stress-strain hysteresis loop dependent on the slip character. A new criterion for low cycle fatigue was proposed on the basis of the effective plastic strain, ε_pe which is obtained through an analysis of the profile of the hysteresis loop. A simple equation of ε_pe·N_f= Constant is established in the life range from 10³ to 10⁷ cycles. This means that fatigue failure results from the linear accumulation of the effective plastic strain during strain cycling.