Stiffness matrix in plasticity region

[kushwah_dk]

Hello,
I just wanted to ask that the stiffness matrix in the plasticity region will be symmetric or not?
As we know the stiffness matrix or [C] is symmetric for elastic region.

 

[FEA way]

It depends. It's symmetric when the flow rule is associated (e.g. Mises plasticity) and unsymmetric when the flow rule is non-associated (e.g. Drucker-Prager model).