Charles Voivret

Effect of shape nonconvexity on the shear strength of granular media

We investigate the influence of particle shape nonconvexity on the shear strength and texture of granular materials. We consider regular trimers (clumps composed of three circular particles) described by a nonconvexity parameter depending on the relative positions of the particles. The contact dynamics method is used to shear large samples of trimers with different levels of nonconvexity. The solid fraction is a nonmonotonous function of nonconvexity. The shear strength increases with nonconvexity and saturates. We show that the increase of shear strength results from the presence of multiple contacts between trimers leading to enhanced frictional interlocking. The double and triple contacts are less in proportion but carry the largest forces in the packing. The saturation is related to the fact that the contact orientation anisotropy declines and compensates the increase of the normal force anisotropy, so that the shear strength remains constant.

Force transmission in highly polydisperse granular media

This work is devoted to the numerical modeling of highly polydisperse granular materials in view of investigating the texture and mechanical behavior in quasi‐static shearing. The polydispersity is modeled in terms of size span and curvature of the particle size distributions. A method is proposed to generate representative size distributions both in number and volume of size classes, and the accessible polydispersity parameters are determined for tractable number of particles. A geometrical method is used to construct large samples and to study the resulting texture in a systematic manner as a function of size distribution. These samples are then subjected to simple shear with periodic boundary conditions by means of the contact dynamics method. We show that: 1) The highest level of solid fraction corresponds to uniform distribution by particle volume fractions; 2) The shear strength in the steady state is independent of polydispersity; 3) A detailed analysis of the texture and force transmission indicat...

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.