Local rheological measurements in the granular flow around an intruder

TL;DR

This study experimentally investigates the local rheological behavior of granular flow around a moving intruder, revealing inhomogeneous stress and strain distributions and highlighting the need for non-local rheological models.

Contribution

It provides detailed grain-scale measurements of stress and strain in granular flow around an intruder, emphasizing the limitations of local rheology models.

Findings

Inhomogeneous shear rate and localized stress fields observed.

Significant dilation rate comparable to shear strain rate.

Deviations from local rheology suggest the need for non-local models.

Abstract

The rheological properties of granular matter within a two-dimensional flow around a moving disk is investigated experimentally. Using a combination of photoelastic and standard tessellation techniques, the strain and stress tensors are estimated at the grain scale in the time-averaged flow field around a large disk pulled at constant velocity in an assembly of smaller disks. On the one hand, one observes inhomogeneous shear rate and strongly localized shear stress and pressure fields. On the other hand, a significant dilation rate, which has the same magnitude as the shear strain rate, is reported. Significant deviations are observed with local rheology that justify the need of searching for a non-local rheology.