Granular materials: micromechanical approaches of model systems

International audienceAn overview is given of micromechanical approaches to the rheology of granular materials, from solidlike granular packs to large plastic strains and dense inertial flows, which essentially relies on the numerical simulation (by the "discrete element method" or DEM) of simple model systems. The main features of contact laws are presented, and then it is insisted on the importance of the geometry of disordered granular assemblies, such that some details of contact interactions are in fact often irrelevant. Some salient results, as obtained from DEM studies over the last decades, are presented about the variety of microstructures and internal states, depending on assembling processes; on elasticity and its (limited) role in quasistatic granular behavior; on plastic strains and the fon-damental concept of critical states, and on its recent applications to the rheology of dense granular flows and suspensions