Peter I am using multilinear isotropic hardening plasticiy, but I could not see the nonlinearity.

The model is a beam, fixed in both extreme, but I modeled only the half, and use a plane of symmetry,

I could not see the nonlinear curve in equivalent total strain neither nonlinearity in the equivalent stress:

In spite of reach the yeld and rupture stress, the curve is linear, I am not understanding why.