Contacts, motion and chain-breaking in a two-dimensional granular system displaced by an intruder

TL;DR

This study uses numerical simulations to analyze how an intruder's motion in a 2D granular system influences contact networks, force transmission, and chain-breaking, revealing mechanisms behind force percolation and chain collapse.

Contribution

It introduces detailed analysis of force networks and chain-breaking mechanisms in a driven granular system, highlighting the roles of bearing and dissipative networks and the effects of friction.

Findings

Force networks percolate from intruder to walls, creating jammed regions.

Lower basal friction reduces the extent of force networks and cavity size.

Chains break and creep, explaining the collapse mechanism of bearing chains.

Abstract

We investigate numerically how the motion of an intruder within a two-dimensional granular system affects its structure and produces drag on the intruder. We made use of discrete numerical simulations in which a larger disk (intruder) is driven at constant speed amid smaller disks confined in a rectangular cell. By varying the intruder's velocity and the basal friction, we obtained the resultant force on the intruder and the instantaneous network of contact forces, which we analyze at both the cell and grain scales. We found that there is a bearing network that percolates forces from the intruder toward the walls, being responsible for jammed regions and high values of the drag force, and a dissipative network that percolates small forces within the grains, in agreement with previous experiments on compressed granular systems. In addition, we found the anisotropy levels of the contact network for different force magnitudes and regions, that the force network can reach regions far downstream of the intruder by the end of the intruder's motion, that the extent of the force network decreases with decreasing the basal friction, and that the void region (cavity) that appears downstream the intruder tends to disappear for lower values of the basal friction. Interestingly, our results show that grains within the bearing chains creep while the chains break, revealing the mechanism by which bearing chains collapse.