About contacts of adhesive, elasto-plastic, frictional powders

Granular materials can be studied in a split-bottom ring shear cell geometry, where they show wide shear bands under slow, quasi-static, large deformation. The contact models are at the basis of their interesting collective behavior and flow-rheology as well the core ingredient for the discrete element method (DEM). The contact mechanics used involves elasto-plastic, viscous, frictional, and torque contributions. From a single simulation only, by applying timeand (local) space-averaging, and focusing on the regions of the system that experienced considerable deformations, the critical-state yield stress (termination locus) can be obtained. It is close to linear, for non-cohesive granular materials, and nonlinear with peculiar pressure dependence, for adhesive powders – due to the nonlinear dependence of the contact adhesion on the confining forces.