Sensitivity of Granular Force Chain Orientation to Disorder-induced Metastable Relaxation

TL;DR

This study investigates how force chain orientations in a granular system respond to disorder and tapping, revealing that force chain reorientations serve as indicators of metastability without significant changes in packing fraction or coordination number.

Contribution

The paper introduces an experimental approach to monitor force chain orientation and demonstrates its sensitivity to disorder-induced metastability in granular materials.

Findings

Force chain orientation parameter $S$ sharply transitions with disorder.

Tapping causes measurable changes in force chain orientation, not in packing fraction or coordination number.

Disorder-induced metastability is detectable via force chain reorientations, not configurational relaxation.

Abstract

A two-dimensional system of photoelastic disks subject to vertical tapping against gravity was experimentally monitored from ordered to disordered configurations by varying bidispersity. The packing fraction $\phi$, coordination number $Z$, and an appropriately defined force chain orientational order parameter $S$, all exhibit similar sharp transition with small increase in disorder. A measurable change in $S$, but not $\phi~\&~Z$, was detected under tapping. We find disorder-induced metastability does not show configurational relaxation, but can be detected via force chain reorientations.