The Gurson model is for apdl so can be used as you did within a Static say Workbench Mechanical system.
Explicit Dynamics (Autodyn) does not have this material model (Gurson).
LS-Dyna (say used within Workbench) has it though (*MAT_GURSON) so we can use that if you have access to LS-Dyna inside Workbench (WB).
The graph you show is that Abaqus /Standard or Explicit?
Also what is the point of going further done the softening part, we have reached the max load it can take (and that is often what we want), and we see softening. So pushing it down further the softening part of the curve.
All the best