Emergence of multi-contact interactions in contact dynamics simulations of granular shear flows

We examine the binary collision assumption of hard-sphere kinetic theory in numerical simulations of sheared granular materials. For a wide range of densities and restitution coefficients we measure collisional and non-collisional contributions to the stress tensor and find that non-collisional effects dominate at large density and small restitution coefficient. In the regimes where the non-collisional contributions disappear, we test kinetic theory predictions for the pressure without any fitting parameters and find remarkable agreement. In the regimes where the non-collisional contributions become large, we observe groups of simultaneously interacting grains and determine the average multi-contact cluster size using measurements of spatial force correlations.