Weakly nonlocal continuum theories of granular media: restrictions from the Second Law

The classical continuum mechanical model of granular media of rational thermodynamics results in a Coulomb-Mohr type equilibrium stress-strain relation. The proof is based on a two component material model introducing a scalar internal variable. Here we will show how one can get similar stress-strain relations without assuming a balance of substructural interactions, considering only the restrictions of the Second Law of thermodynamics.