A viscoplastic constitutive model for cyclic hardening in the dynamic strain aging regime

Negative strain rate sensitivity in certain temperature regimes is considered to be a manifestation of dynamic strain aging. Within the framework of unified state variable theory, viscoplastic constitutive equations incorporating the Mises yield criterion are presented to model negative rate sensitivity of the flow stress and its gradual variation with cyclic loading. The modeling capabilities are essentially accomplished by introducing a rate sensitivity parameter into the evolution law of the back stress. The influence of the drag stress and the isotropic stress as well as the rate sensitivity parameter both on the cyclic hardening and the variation of strain rate sensitivity is systemically investigated. Excellent agreement between experimental results reported in the literature and model simulations is obtained, confirming the efficacy of the proposed constitutive model.