Continuum modeling of mechanically-induced creep in dense granular materials

TL;DR

This paper demonstrates that a nonlocal granular rheology model can accurately predict mechanically-induced creep phenomena in dense granular materials, including rate independence and force-dependent creep speeds.

Contribution

It extends the nonlocal fluidity model to capture creep behavior in granular media, including the effects of intruders and force application.

Findings

Model captures all salient experimental features.

Creep rate is independent at slow driving.

Creep speed increases faster than linearly with force.

Abstract

Recently, a new nonlocal granular rheology was successfully used to predict steady granular flows, including grain-size-dependent shear features, in a wide variety of flow configurations, including all variations of the split-bottom cell. A related problem in granular flow is that of mechanically-induced creep, in which shear deformation in one region of a granular medium fluidizes its entirety, including regions far from the sheared zone, effectively erasing the yield condition everywhere. This enables creep deformation when a force is applied in the nominally quiescent region through an intruder such as a cylindrical or spherical probe. We show that the nonlocal fluidity model is capable of capturing this phenomenology. Specifically, we explore creep of a circular intruder in a two-dimensional annular Couette cell and show that the model captures all salient features observed in experiments, including both the rate-independent nature of creep for sufficiently slow driving rates and the faster-than-linear increase in the creep speed with the force applied to the intruder.