Force Chain Evolution in a Two-Dimensional Granular Packing Compacted by Vertical Tappings

TL;DR

This study experimentally investigates how force chains in a two-dimensional granular packing evolve under vertical tapping, revealing relationships between packing isotropy, force-chain disorder, and force magnitude during compaction.

Contribution

It provides new experimental insights into the evolution of force chains and grain configurations in tapped granular materials, highlighting universal correlations.

Findings

Force chains increase and saturate with packing fraction.

Grain configurations and force chains become isotropic and disordered during compaction.

Positive correlation between grain isotropy and force-chain disorder.

Abstract

We experimentally study the statistics of force-chain evolution in a vertically-tapped two-dimensional granular packing by using photoelastic disks. In this experiment, the tapped granular packing is gradually compacted. During the compaction, the isotropy of grain configurations is quantified by measuring the deviator anisotropy derived from fabric tensor, and then the evolution of force-chain structure is quantified by measuring the interparticle forces and force-chain orientational order parameter. As packing fraction increases, the interparticle force increases and finally saturates to an asymptotic value. Moreover, the grain configurations and force-chain structures become isotropically random as the tapping-induced compaction proceeds. In contrast, the total length of force chains remains unchanged. From the correlations of those parameters, we find two relations: (i) a positive correlation between the isotropy of grain configurations and the disordering of force-chain orientations, and (ii) a negative correlation between the increasing of interparticle forces and the disordering of force-chain orientations. These relations are universally held regardless of the mode of particle motions with/without convection.