Identification of Material Properties under Strain-Controlled Non-Proportional Cyclic Loading

Abstract

In most cases of non-proportional cyclic loading, the investigated materials show additional hardening in comparison to the hardening observed under proportional loading path. For some materials, however, an opposite effect is observed. In the present paper, the above mentioned phenomena are experimentally investigated under non-proportional cyclic loading in form of circular path in a strain space and proportional cyclic loading (tension-compression) for three different commercial materials, i.e., brass, steel, and an aluminium alloy. An evolution of the mechanical properties due to cyclic loading is assessed using the concept of the yield surface determined in the two-dimensional stress space (sigma, tau). Effects of strain rate and magnitude of cyclic loading amplitude are also investigated. Analysis of the stress and strain signals during non-proportional cyclic loading has shown significant eflect of a phase shift of the maximum stress with respect to the corresponding maximum strain, which was not observed during tests carried out along proportional loading paths.