We model two-dimensional systems of granular aggregates confined between two planes and demonstrate that at a critical grain volume fraction an abrupt rigidity transition occurs. This transition is observed both in static and shear tests. The grain volume fraction at which the transition occurs, νc, decreases with increasing friction between the grains. Densely packed grains, with a volume fraction ν>νc, display an elastic-plastic rheology. Dilute packings, with ν<νc, display gas-like characteristics. Packings with ν=νc display phase coexistance. It is shown that when volume fraction is allowed to change freely (using constant normal stress boundary condition), it evolves spontaneously to νc under a wide range of boundary conditions, exhibiting 'self-organized criticality'.
Cite
@article{arxiv.cond-mat/9812204,
title = {On Phase Transition and Self-Organized Critical State in Granular Packings},
author = {Einat Aharonov and David Sparks},
journal= {arXiv preprint arXiv:cond-mat/9812204},
year = {2007}
}