The Effect of the Shape of Granular Particles on Density

We investigate the packing densities of non-elongated regular polyhedra and spheres via discrete element simulations. It turns out that the limit of many (hundred) corners does not correspond to that of spheres with the same Young's modulus. However, if the Young's modulus is simultaneously decreased, the packing density of polyhedra approaches that of (harder) spheres. We conclude that the mechanism for the higher packing density is the higher mobility of particles, in the case of round particles due to rolling. While rolling can occur at vanishing energetic costs for perfect spheres, the mobility of polyhedra in packings is determined by the height differences between corners and faces, as well as due to the possibility that corners of neighbouring polyhedra to move through each other via deformation: reducing material strength therefore improves mobility. Additionally, we present finding about the influence of the walls and about the relation between filling height and surface roughness.