Shear thickening and migration in granular suspensions

TL;DR

This study investigates shear thickening and particle migration in dense granular suspensions, revealing heterogeneity, fast grain migration, and transient shear thickening phenomena linked to Bagnoldian rheology.

Contribution

It combines local MRI measurements with rheometry to show that shear thickening involves rapid particle migration and heterogeneity, challenging the view of intrinsic discontinuous shear thickening.

Findings

Heterogeneous material in steady state

Transition from viscous to Bagnoldian behavior at low shear rates

Fast particle migration linked to Bagnoldian rheology

Abstract

We study the emergence of shear thickening in dense suspensions of non-Brownian particles. We combine local velocity and concentration measurements using Magnetic Resonance Imaging with macroscopic rheometry experiments. In steady state, we observe that the material is heterogeneous, and we find that that the local rheology presents a continuous transition at low shear rate from a viscous to a shear thickening, Bagnoldian, behavior with shear stresses proportional to the shear rate squared, as predicted by a scaling analysis. We show that the heterogeneity results from an unexpectedly fast migration of grains, which we attribute to the emergence of the Bagnoldian rheology. The migration process is observed to be accompanied by macroscopic transient discontinuous shear thickening, which is consequently not an intrinsic property of granular suspensions.