Shear thickening of highly viscous granular suspensions

TL;DR

This study experimentally explores shear thickening in dense granular suspensions, revealing the roles of dilation, confining stress, and viscosity contributions, and how liquid viscosity influences the shear thickening behavior.

Contribution

It provides a detailed analysis of the mechanisms behind shear thickening, including the effects of dilation and confining stress, and how viscosity variations soften the shear thickening response.

Findings

Dilation occurs beyond a critical strain, ending shear thickening.

Viscosity contributions from hydrodynamics and dilation determine shear thickening.

Higher liquid viscosity softens the discontinuous shear thickening.

Abstract

We experimentally investigate shear thickening in dense granular suspensions under oscillatory shear. Directly imaging the suspension-air interface, we observe dilation beyond a critical strain $\gamma_c$ and the end of shear thickening as the maximum confining stress is reached and the contact line moves. Analyzing the shear profile, we extract the viscosity contributions due to hydrodynamics $\eta_\mu$, dilation $\eta_c$ and sedimentation $\eta_g$. While $\eta_g$ governs the shear thinning regime, $\eta_\mu$ and $\eta_c$ together determine the shear thickening behavior. As the suspending liquid's viscosity varies from 10 to 1000 cst, $\eta_\mu$ is found to compete with $\eta_c$ and soften the discontinuous nature of shear thickening.