A micromechanical study on the flow rule for granular materials

The authors have performed a set of numerical probe tests in terms of the Granular Element Method. These test results help explaining the internal mechanism hidden behind the macroscopic behaviors. This paper deals with the plastic behavior whose mechanism has its main origin on the slipping between grains. A theoretical yielding condition, which explains the result obtained by the simulation, is derived from non-slipping condition for stable assemblies of rigid particles. Performing eigen-value analyses of the instantaneous stiffness matrix utilized in the Granular Element Method, the authors demonstrate the similarity of displacement fields accompanied by plastic deformations for different loading directions.