John Doyle
Ansys Employee

For metal plasticity, the input should be True Stress-True Strain.  If your test data is Engineering Stress-vs-Strain, you should convert this to True Stress-vs-True Strain.  If you really need to model material softening, you can do this with the Voce Hardening model (Nonlinear Isotropic Hardening).  See TB command (TB,NLISO,,,,VOCE) and Section 4.4 of Material Reference Guide for more information.

For post buckling simulation, consider Stabilization Damping and/or Arc Length Method.