# CSMm 2.5.Constitutive Laws

For the moment one can use a simple elastic model or a more complex elasto-plastic model with a VonMisses yield criterion:

• Elastic model

$\boldsymbol{\sigma = D \cdot \epsilon}$

• Elasto-Plastic model:

It uses a Von Mises yield criterion: plastic yielding starts when the elastic energy stored in changes of shape reaches a critical value.