Consequences of Dynamic Yield Surface in Viscoplasticity

A theory of viscoplasticity is formulated within a thermodynamic concept. The key point is the postulate of a dynamic yield surface, which allows us to take advantage of the postulate of maximum dissipation to derive an associated formulation of the evolutions laws for the internal variables without using penalty techniques that only hold in the limit it when viscoplasticity degenerates to inviscid plasticity. Even a non-associated formulation is presented. Within this general formulation, a particular format of the dynamic yield function enables us to derive the static yield function in a consistent manner. Hardening, perfect and softening viscoplasticity is also defined in a consistent manner. The approach even includes associated and non-associated viscoplasticity where corners exist on the yield and potential surfaces.