negative elasticity modulus

[Krzyszof]

?
How I can use a stress-strain curve in the plastic region with the negative elasticity modulus to material’s modelling

 

[brad]

There is no constitutive basis for a negative modulus. Materials do not behave this way, neither in reality nor in proper modeling.
Further, the use of such a construct (even when allowed by codes) almost guarantees severe convergence problems. It completely freaks out the yield surface when solving Mises plasticity problems.

I would discourage this approach.

Brad