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.