Bridging the rheology of granular flows in three regimes

TL;DR

This paper explores the rheology of granular flows across three regimes using molecular dynamics simulations, revealing how stress behavior scales with jamming and particle softness, and proposing a comprehensive rheological model.

Contribution

It introduces a unified rheological model for granular flows across regimes, accounting for particle softness and friction effects, extending previous frictionless studies.

Findings

Three flow regimes identified with stress scaling near jamming

Pressure-strain rate relation independent of friction at jamming point

Departure from inertial scaling linked to particle softness

Abstract

We investigate the rheology of granular materials via molecular dynamics simulations of homogeneous, simple shear flows of soft, frictional, noncohesive spheres. In agreement with previous results for frictionless particles, we observe three flow regimes existing in different domains of particle volume fraction and shear rate, with all stress data collapsing upon scaling by powers of the distance to the jamming point. Though this jamming point is a function of the interparticle friction coefficient, the relation between pressure and strain rate at this point is found to be independent of friction. We also propose a rheological model that blends the asymptotic relations in each regime to obtain a general description for these flows. Finally, we show that departure from inertial number scalings is a direct result of particle softness, with a dimensionless shear rate characterizing the transition.