Unjamming due to local perturbations in granular packings with and without gravity

TL;DR

This study uses simulations to analyze how local perturbations cause unjamming in granular packings, revealing long-range effects and the influence of friction, gravity, and contact network structure on system stability.

Contribution

It provides new insights into the unjamming process by comparing zero gravity and gravity conditions, highlighting the role of friction and contact network connectivity.

Findings

Long-range stress and displacement effects observed.

Penetration depth and critical force depend on friction coefficient.

Nonmonotonic friction dependence with different extrema in gravity and zero gravity.

Abstract

We investigate the unjamming response of disordered packings of frictional hard disks with the help of computer simulations. First, we generate jammed configurations of the disks and then force them to move again by local perturbations. We study the spatial distribution of the stress and displacement response and find long range effects of the perturbation in both cases. We record the penetration depth of the displacements and the critical force that is needed to make the system yield. These quantities are tested in two types of systems: in ideal homogeneous packings in zero gravity and in packings settled under gravity. The penetration depth and the critical force are sensitive to the interparticle friction coefficient. Qualitatively, the same nonmonotonic friction dependence is found both with and without gravity, however the location of the extrema are at different friction values. We discuss the role of the connectivity of the contact network and of the pressure gradient in the unjamming response.