(8)
in which c and d are isotropic hardening parameters. This
term represents the saturated value of the isotropic softening stress
with increasing visco-plastic multiplier and the decay-rate, d ,
that leads to the softening saturation, c . The UVP model has been
numerically implemented in ABAQUS FE user subroutine UMAT using an
implicit integration scheme1,3,49.