To supplement what Bruno has already mentioned, deal.II provides some of the tools what you might find useful to implement constitutive laws or specific governing equations. To get some feeling as to what is possible, I would suggest that you take a look through the
list of publications to see what the community has achieved using deal.II. There are also several
tutorials and
code-gallery contributions (current and pending) that might give you insights into how you might go about implementing such a constitutive law within a solid-mechanics code. You might also with to look at the “Applications” listed in the top bar on the
home page (I can’t give you a clickable link, I’m afraid). I believe that at least one of them (PRISMS) has a partial focus on plasticity.