Rheology and Contact Lifetime Distribution in Dense Granular Flows

TL;DR

This study investigates the rheology and contact lifetime distribution in dense granular flows, revealing a transition from Bagnold to viscous-like behavior as particle softness increases, driven by changes in contact durations.

Contribution

It provides new insights into how particle softness affects rheology and contact lifetime distributions in dense granular flows through large-scale simulations.

Findings

Hard particles follow Bagnold scaling with quadratic shear stress.

Softer particles exhibit deviations towards viscous flow behavior.

Longer contact lifetimes correlate with the transition in rheology.

Abstract

We study the rheology and distribution of interparticle contact lifetimes for gravity-driven, dense granular flows of non-cohesive particles down an inclined plane using large-scale, three dimensional, granular dynamics simulations. Rather than observing a large number of long-lived contacts as might be expected for dense flows, brief binary collisions predominate. In the hard particle limit, the rheology conforms to Bagnold scaling, where the shear stress is quadratic in the strain rate. As the particles are made softer, however, we find significant deviations from Bagnold rheology; the material flows more like a viscous fluid. We attribute this change in the collective rheology of the material to subtle changes in the contact lifetime distribution involving the increasing lifetime and number of the long-lived contacts in the softer particle systems.