Yield stress and shear-banding in granular suspensions

TL;DR

This study investigates how gravity and viscous stresses induce a yield stress and shear banding in dense granular suspensions, revealing that density matching can suppress yield stress development up to high volume fractions.

Contribution

It combines local MRI measurements with rheometry to elucidate the origin of yield stress and shear banding in dense suspensions, highlighting the role of density mismatch.

Findings

Yield stress arises from gravity-viscous stress competition.

Shear banding occurs alongside yield stress development.

Density matching delays yield stress onset until 62.7% volume fraction.

Abstract

We study the emergence of a yield stress in dense suspensions of non-Brownian particles, by combining local velocity and concentration measurements using Magnetic Resonance Imaging with macroscopic rheometric experiments. We show that the competition between gravity and viscous stresses is at the origin of the development of a yield stress in these systems at relatively low volume fractions. Moreover, it is accompanied by a shear banding phenomenon that is the signature of this competition. However, if the system is carefully density matched, no yield stress is encountered until a volume fraction of 62.7 0.3%.