Non-monotonic Rheology and Stress Heterogeneity in confined Granular suspensions

TL;DR

This study reveals how boundary confinement influences the complex shear-thickening behavior and stress distribution in dense granular suspensions, showing size-dependent non-monotonic flow curves and stress heterogeneities.

Contribution

It demonstrates the impact of boundary confinement on rheology and stress heterogeneity, introducing boundary stress microscopy to connect microscopic stress patterns with macroscopic flow.

Findings

Confined suspensions exhibit non-monotonic, S-shaped flow curves.

Enhanced stress heterogeneity with stable high-stress domains.

Boundary confinement can control suspension rheology.

Abstract

We systematically investigated the impact of boundary confinement on the shear-thickening rheology of dense granular suspensions. Under highly confined conditions, dense suspensions were found to exhibit size-dependent or even rarely reported non-monotonic ($S$-shaped) flow curves in steady states. By performing in-situ boundary stress microscopy measurements, we observed enhanced flow heterogeneities in confined suspensions, where concentrated high-stress domains propagated stably either along or against the shear direction. By comparing the boundary stress microscopy results with macroscopic flow responses, we revealed the connection between non-monotonic rheology and stress heterogeneity in confined suspensions. These findings suggest the possibility of controlling suspension rheology by imposing different boundary confinements.