Forms of the dissipation function for a class of viscoplastic models

The minimum properties that allow a dissipation functional to describe a behavior of viscoplastic type are analyzed. It is considered a material model based on an internal variable description of the irreversible processes and characterized by the existence of an elastic region. The dissipation functional derived includes the case of time-independent plasticity in the limit. The complementary dissipation functional and the flow rule are also stated. The model analyzed leads naturally to the fulfillment of the maximum dissipation postulate and thus to associative viscoplasticity. A particular class of models is analyzed, and similarities to and differences from diffused viscoplastic formats are given.