Rheology of periodically sheared suspensions undergoing reversible-irreversible transition

TL;DR

This study numerically investigates how cyclic shear affects the rheology of suspensions, revealing a critical strain amplitude that marks a reversible-irreversible transition with notable changes in viscosity and normal stress differences.

Contribution

It uncovers the relationship between rheological behavior and microstructural transitions in suspensions under cyclic shear, highlighting the critical strain amplitude scaling and the connection to reversible-irreversible dynamics.

Findings

Reduced viscosity near critical strain amplitude

Onset of finite normal stress difference and frequency doubling

Microstructure approaches hyperuniformity at transition

Abstract

The rheology of non-colloidal suspensions under cyclic shear is studied numerically. The main findings are a strain amplitude ($\gamma_0$) dependent response in the shear stress and second normal stress difference ($N_2$). Specifically, we find a reduced viscosity, an enhanced intracycle shear thinning, the onset of a finite $N_2$ and its frequency doubling, all near a critical strain amplitude $\gamma_c$ that scales with the volume fraction $\phi$ as $\gamma_c \sim \phi^{-2}$. These rheological changes also signify a reversible-irreversible transition (RIT), dividing stroboscopic particle dynamics into a reversible absorbing phase (for $\gamma_0<\gamma_c$) and a persistently diffusing phase (for $\gamma_0>\gamma_c$). We explain the results based on two flow-induced mechanisms and elucidate their connection in the context of RIT through the underlying microstructure, which tends towards hyperuniformity near $\gamma_0=\gamma_c$. Overall, we expect this correspondence between rheology and emergent dynamics to hold in a wide range of settings where structural organizations are dominated by volume exclusions.