Unified Constitutive Equations of Viscoplastic Deformation: Development and Capabilities

This paper addresses a viscoplastic constitutive model that allows a consistent way of modeling positive and negative rate sensitivities of flow stress, which is associated with dynamic strain aging occurring in a certain regime of loading rates and temperatures. Based on the concept of continuum mechanics, a phenomenological constitutive model includes the use of a yield surface within the framework of unified viscoplastic constitutive equations. An extension of modeling capability to negative rate sensitivity of flow stress is accomplished through a rate-dependent format of nonlinear kinematic hardening rule that causes the back stress to be rate-dependent. The negative rate sensitivity of the back stress enable to predict the influence of prior strain rate on relaxation behavior, which means that the relaxed stress of the fastest prior strain rate has the smallest magnitude at the end of relaxation period.