Morphology of Polydisperse Granular Media

We investigate the morphology and space-filling properties of polydisperse densely-packed granular media in 2D. A numerical procedure is introduced to generate collections of circular particles with size distributions of variable size span. This particle generation procedure is used with a geometric deposition protocol in order to build large close-packed samples of prescribed polydispersity. The solid fraction is a strongly nonlinear function of the size span, and the highest levels of solid fraction occur for the uniform distribution by volume fractions. A transition occurs from a regime of topological disorder where the packing properties are governed by particle connectivity to a regime of metric disorder where pore-filling small particles prevail. The polydispersity manifests itself in the first regime through the variability of local coordination numbers. In the second regime, the material is homogeneous beyond only a few average particle diameters. We also show that the fabric anisotropy declines with size span.