The effect of grain shape and material on the nonlocal rheology of dense granular flows

TL;DR

This study investigates how particle shape and material influence the parameters of nonlocal rheology in dense granular flows, revealing that shape and material significantly affect flow behavior and failure conditions.

Contribution

It provides experimental data showing the impact of particle shape and material on nonlocal rheology parameters in granular flows, highlighting geometric friction effects.

Findings

Nonlocal rheology fits well for all particle types.

Nonlocal parameter A varies with shape and material.

Critical stress ratio mu_s depends on particle shape.

Abstract

Nonlocal rheologies allow for the modeling of granular flows from the creeping to intermediate flow regimes, using a small number of parameters. In this paper, we report on experiments testing how particle properties affect model parameters, using particles of three different shapes (circles, ellipses, and pentagons) and three different materials, including one which allows for measurements of stresses via photoelasticity. Our experiments are performed on a quasi-2D annular shear cell with a rotating inner wall and a fixed outer wall. Each type of particle is found to exhibit flows which are well-fit by nonlocal rheology, with each particle having a distinct triad of the local, nonlocal, and frictional parameters. While the local parameter b is always approximately unity, the nonlocal parameter A depends sensitively on both the particle shape and material. The critical stress ratio mu_s, above which Coulomb failure occurs, varies for particles with the same material but different shapes, indicating that geometric friction can dominate over material friction.