Rheological Chaos of Frictional Grains

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.