Thermal properties of athermal granular materials

TL;DR

This study investigates aging and stress relaxation in athermal granular materials, revealing that thermal molecular processes at contact points influence their mechanical strengthening over time.

Contribution

It demonstrates that aging and stress relaxation in athermal granular systems are driven by thermal processes at contact points, a novel insight into their dynamics.

Findings

Interparticle force evolution leads to increased yield stress.

Aging and stress relaxation follow logarithmic time dependence.

Thermal effects influence the rate of strengthening.

Abstract

Dry granular materials consist of a vast ensemble of discrete solid particles, interacting through complex frictional forces at the contact points. The particles are so large that these systems are believed to be completely athermal. Here, we arrest the dynamics of a flowing granular material in a steady-state flow configuration, enabling an isolated examination of aging at the particle contacts without granular rearrangements. Our findings reveal that the evolution of interparticle forces within the arrested athermal granular network results in the spontaneous increase of the system's yield stress. This strengthening process is logarithmic in time with a rate that depends on temperature. We demonstrate that the material's stress relaxation exhibits similar time- and temperature-dependent behavior, suggesting a shared origin for aging and stress relaxation in these systems governed by thermal molecular processes at the scale of the grain contacts.