Rheological Chaos of Frictional Grains

TL;DR

This paper demonstrates that a dense fluid of frictional grains exhibits chaotic and heterogeneous flow behavior under certain stress conditions, with a phase diagram showing reentrant flow and jamming phenomena.

Contribution

It introduces a hydrodynamic model coupling stress and microstructure to explain chaotic flow and jamming in frictional granular materials.

Findings

Chaotic, heterogeneous flow occurs in a specific stress range.

Reentrant stationary flow observed at low and high stresses.

Model predictions agree with simulation results.

Abstract

A two-dimensional dense fluid of frictional grains is shown to exhibit time-chaotic, spatially heterogeneous flow in a range of stress values, $\sigma$, chosen in the unstable region of s-shaped flow curves. Stress controlled simulations reveal a phase diagram with reentrant stationary flow for small and large stress $\sigma$. In between no steady flow state can be reached, instead the system either jams or displays time dependent heterogeneous strain rates $\dot\gamma({\bf r},t)$. The results of simulations are in agreement with the stability analysis of a simple hydrodynamic model, coupling stress and microstructure which we tentatively associate with the frictional contact network.