Force chain structure in a rod-withdrawn granular layer

TL;DR

This study visualizes and analyzes the development of oblique force chains in a granular layer during rod withdrawal, revealing consistent force chain angles and a correlation between force chain forces and withdrawal force.

Contribution

It provides experimental insights into force chain structures and their relation to withdrawal forces in a granular layer using photoelastic techniques.

Findings

Force chains develop obliquely at about 20° from horizontal.

Total force in chains increases with withdrawal.

Force chain force component correlates with withdrawal force.

Abstract

When a rod is vertically withdrawn from a granular layer, oblique force chains can be developed by effective shearing. In this study, the force-chain structure in a rod-withdrawn granular layer was experimentally investigated using a photoelastic technique. The rod is vertically withdrawn from a two-dimensional granular layer consisting of bidisperse photoelastic disks. During the withdrawal, the development process of force chains is visualized by the photoelastic effect. By systematic analysis of photoelastic images, force chain structures newly developed by the rod withdrawing are identified and analyzed. In particular, the relation between the rod-withdrawing force $F_\mathrm{w}$, total force-chains force $F_\mathrm{t}$, and their average orientation $\theta$ are discussed. We find that the oblique force chains are newly developed by withdrawing. The force-chain angle $\theta$ is almost constant (approximately $20^{\circ}$ from the horizontal), and the total force $F_\mathrm{t}$ gradually increases by the withdrawal. In addition, $F_\mathrm{t}\sin\theta$ shows a clear correlation with $F_\mathrm{w}$.