Two-scale evolution during shear reversal in dense suspensions

TL;DR

This paper investigates the complex shear reversal behavior of dense suspensions through simulations that resolve lubrication forces and particle contacts, revealing distinct microstructural responses at different strain scales.

Contribution

It introduces a detailed simulation approach capturing both hydrodynamic and contact forces, highlighting the two-scale evolution during shear reversal in dense suspensions.

Findings

Hydrodynamic and contact stresses evolve over different strain scales.

Distinct microstructural responses are observed at small and large strains.

Particle roughness and repulsion significantly influence stress response.

Abstract

We use shear reversal simulations to explore the rheology of dense, non-Brownian suspensions, resolving lubrication forces between neighbouring particles and modelling particle surface contacts. The transient stress response to an abrupt reversal of the direction of shear shows rate-independent, nonmonotonic behaviour, capturing the salient features of the corresponding classical experiments. Based on analyses of the hydrodynamic and particle contact stresses and related contact networks, we demonstrate distinct responses at small and large strains, associated with contact breakage and structural re-orientation, respectively, emphasising the importance of particle contacts. Consequently, the hydrodynamic and contact stresses evolve over disparate strain scales and with opposite trends, resulting in nonmonotonic behaviour when combined. We further elucidate the roles of particle roughness and repulsion in determining the microstructure and hence the stress response at each scale.