Influence of shape and cohesion on rheophysics of granular materials

International audienceWe describe the results of two separate studies of the influence of shape and cohesion on therheophysics of granular materials, both based on discrete numerical simulations. The fist onecompares dense flows of dry frictional spheres and polyhedra down a rough inclined plane.The flow diagrams and constitutive laws previously established for spheres are extended topolyhedra : in both cases, solid fraction and effective friction variations with inertial numbercan be described as linear over a certain range. In the case of polyhedra, there is a significantincrease of the effective friction, while the wall roughness tends to jam the flow in a bottomlayer, a few diameters thick. The second study investigates steady - state, pressure - controlledsimple shear flows of frictional cohesive disks or spheres. Interparticle cohesion may resultfrom van der Waals or capillary forces, and introduces a dimensionless cohesion numbercomparing confining forces to contact tensile strength. It is shown that the rheophysics is welldescribed by simple dependencies of solid fraction and effective friction on both inertial andcohesion numbers. Moreover, both studies provide microstructural insight on the origin of theconstitutive laws : role of face-to-face contacts in polyhedral assemblies, characterisation ofdensity inhomogeneities and sensitivity to attractive force range in cohesive flow