Viscoplasticity is a model for rate-dependent plasticity. Rate dependent plasticity is important for (high-speed) transient plasticity calculations. It should be used in combination with a plasticity law. Viscoplasticity influences the stresses via the plastic strains.
The group_materi_plasti_visco_exponential model reads
where and are material fluidity constants and is the pressure. This model was first developed for visco-plastic soil behaviour.
The group_materi_plasti_visco_power model reads
where (fluidity constant), (reference value for yield function, e.g. the yield stress for Von-Mises plasticity) and (power) are user specified parameters.