Stress propagation in locally loaded packings of disks and pentagons

TL;DR

This study investigates how grain shape affects stress transmission and force chain structures in granular packings, revealing that pentagons transmit stresses over shorter distances and have fewer back-bending force chains compared to disks, with implications for material strength and flow.

Contribution

It provides quantitative experimental analysis of stress propagation in granular packings of disks and pentagons, highlighting shape-dependent differences in force chain behavior and stress transmission.

Findings

Pentagons resist intruders at lower packing fractions than disks.

Pentagons have fewer back-bending force chains than disks.

Stress transmission scales with packing fraction related to open channel formation.

Abstract

The mechanical strength and flow of granular materials can depend strongly on the shapes of individual grains. We report quantitative results obtained from photoelasticimetry experiments on locally loaded, quasi-two-dimensional granular packings of either disks or pentagons exhibiting stick-slip dynamics. Packings of pentagons resist the intruder at significantly lower packing fractions than packings of disks, transmitting stresses from the intruder to the boundaries over a smaller spatial extent. Moreover, packings of pentagons feature significantly fewer back-bending force chains than packings of disks. Data obtained on the forward spatial extent of stresses and back-bending force chains collapse when the packing fraction is rescaled according to the packing fraction of steady state open channel formation, though data on intruder forces and dynamics do not collapse. We comment on the influence of system size on these findings and highlight connections with the dynamics of the disks and pentagons during slip events.