ASME STP-PT-081

Abstract

Scope: INTRODUCTION AND DESCRIPTION OF THE PROBLEM Cyclic stress-strain curves describe the stress-strain behavior under cyclic loads. Usually, the cyclic stress amplitude Δσ/2 is plotted as a function of the cyclic strain amplitude Δε/2 for a defined cycle. The fact that the stress-strain response of a material is usually cycle-dependent requires a reference cycle which can be considered as representative for the cyclic stress-strain curve. In contrast to monotonic stress-strain curves which deliver a unique relationship between the stress and strain of a material, the cyclic stress-strain relationships may undergo cycle-dependent changes. The material can be: Cyclic hardening Cyclic softening Cyclic stable Combinations of cyclic softening and cyclic hardening This means that the stress-strain relationship determined in strain fatigue tests is usually cycle dependent. Figure 1-1 shows the change of stress amplitude with a number of cycles for a low carbon steel as an example [1].