Viscoplastic strain rate formulation (VP)

In the standard strain rate formulation (VP=0), the effective strain rate is calculated based on the components in the current strain rate tensor. In the viscoplastic strain rate formulation (VP=1), the effective strain rate is calculated based on the plastic part of the strain rate tensor. In this latter formulation, the code iterates on the effective plastic strain rate during the corrector state of the backward euler integration scheme typically used in material models for metals. In general, VP=1 is recommended since the default strain rate formulation (VP=0) often produces noisy effective strain rates.