Non-uniqueness of critical solid fraction considering boundary conditions and strain-rate effects

Abstract

The critical solid fraction (ϕJ), which marks the transition between the solid and liquid phases in the jamming diagram, is influenced by several factors. In this study, the dependency of ϕJ on strain rate and boundary conditions is examined through discrete element method simulations considering a frictionless polydisperse granular system. Different approaches are used to determine ϕJ. The observed boundary effect is due to the nonuniform solid fraction distribution induced by the clustering of particles close to rigid-wall boundaries at high compression rates. The solid fraction distribution within the sample in the rigid-wall simulations approaches that in the periodic-boundary simulations as the compression rate decreases. With increasing compression rate, the major force transmission network contains fewer mechanically stable particles and a less stable force transmission network. This causes jamming of the granular assembly at a lower solid fraction. These force transmission networks, however, are fragile and disintegrate quickly upon relaxation.