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 behaviorand 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 time- and (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 isclose to linear, for non-cohesive granular materials, and nonlinear with peculiarpressure dependence, for adhesive powders – due to the nonlinear dependenceof the contact adhesion on the confining forces.Introduction
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