Shearing of frictional sphere packings

TL;DR

This study investigates the shear response of glass bead packings, revealing velocity-independent yield stress that exponentially increases with packing density and a transition point around phi 0.595, highlighting differences between shear and bulk moduli.

Contribution

It provides experimental measurements of shear response in granular packings, identifying a transition in behavior and quantifying the relationship between yield stress and packing fraction.

Findings

Yield stress is velocity independent over four decades.

Yield stress increases exponentially with packing fraction.

Shear modulus is significantly smaller than bulk modulus.

Abstract

We measure shear response in packings of glass beads by pulling a thin, rough, metal plate vertically through a bed of volume fraction phi, which is set, before the plate is pulled, in the range 0.575 to 0.628. The yield stress is velocity independent over 4 decades and increases exponentially with phi, with a transition at phi approximately 0.595. An analysis of the measured force fluctuations indicates that the shear modulus is significantly smaller than the bulk modulus.