A constitutive model of cyclic viscoplasticity considering changes in subsequent viscoplastic deformation due to the evolution of dislocation structures

This paper presents a unified constitutive model for cyclic viscoplasticity and changes occurring in subsequent viscoplastic deformation due to the evolution of dislocation structures. The model considers the viscoplastic potential and a modified Ramberg–Osgood law. Stress is assumed to divide into three components: back stress (the center of the yield surface), flow stress (the radius of the yield surface), and viscous stress (overstress). The modification of the Ramberg–Osgood law is carried out employing memorized back stress. The applicability of the model to monotonic loading, pure creep, tension–compression cyclic loading, subsequent creep, and subsequent stress-relaxation were verified by comparing the predictions with experiments of Type 316L stainless steel at room temperature. The relationships between the internal variables in the model and the dislocation structures organized by cyclic deformations are also discussed.