The evolution of the yield stress in Equation 3–59 can be modeled using different isotropic hardening laws:
Voce nonlinear isotropic hardening:
(3–71)
See for Rate-Independent Plasticity in the Material Reference further details. The parameters
, 
, 
, and 
are fitting parameters.Multilinear isotropic hardening: The multilinear hardening behavior is described by a piece-wise linear stress-plastic strain curve, see Rate-Independent Plasticity in the Material Reference for further details. The plastic strain and stress values are directly taken from the experimental data.
Inverse polynomial nonlinear isotropic hardening:
(3–72)
as proposed by [Schmachtenberg, 1985] and [Dillenberger, 2020]. The parameters
, 
and 
are fitting parameters. However, since this hardening
law is not available in the Mechanical APDL solver, it is then approximated
using a multilinear isotropic hardening model.
In the equations above, 
denotes the accumulated equivalent plastic strain.