A unified constitutive law for cyclic viscoplasticity

A phenomenological constitutive model for cyclic viscoplasticity is presented within the framework of unified state variable theory. The model utilizes three distinct parameters to account for the cyclic (isotropic) hardening: drag stress, isotropic stress and rate sensitivity parameter causing the back stress to be rate-dependent. With the help of a rate-dependent format of the back stress, the constitutive model can reproduce positive, zero and negative strain rate sensitivity of the flow stress in a concise manner. The purpose of the paper is to investigate the influence of the three parameters on stress relaxation behavior and rate-dependent cyclic hardening concerned with the variation in strain rate sensitivity. The applicability of the model to monotonic and cyclic loading is validated by comparing the predictions with experiments of two stainless steels and an aluminum alloy reported in literature.