Shear stress fluctuations in the granular liquid and solid phases

TL;DR

This paper investigates shear stress fluctuations in granular materials, revealing non-Gaussian behavior in solid states due to force chains and a transition to Gaussian stress distribution in fluid states, with models predicting this behavior.

Contribution

It provides experimental evidence of stress fluctuation behavior across solid and fluid phases and links these to structural mechanisms and predictive models.

Findings

Non-Gaussian stress fluctuations in solid phase

Gaussian stress distribution in fluid phase

Force chains influence shear rigidity and stress distribution

Abstract

We report on experimentally observed shear stress fluctuations in both granular solid and fluid states, showing that they are non-Gaussian at low shear rates, reflecting the predominance of correlated structures (force chains) in the solidlike phase, which also exhibit finite rigidity to shear. Peaks in the rigidity and the stress distribution's skewness indicate that a change to the force-bearing mechanism occurs at the transition to fluid behaviour, which, it is shown, can be predicted from the behaviour of the stress at lower shear rates. In the fluid state stress is Gaussian distributed, suggesting that the central limit theorem holds. The fibre bundle model with random load sharing effectively reproduces the stress distribution at the yield point and also exhibits the exponential stress distribution anticipated from extant work on stress propagation in granular materials.