Dynamic Susceptibilities in Dense Soft Athermal Spheres Under a Finite-Rate Shear

Norihiro Oyama,Takeshi Kawasaki,Kuniyasu Saitoh

doi:10.3389/fphy.2021.667103

Abstract

The mechanical responses of dense packings of soft athermal spheres under a finite-rate shear are studied by means of molecular dynamics simulations. We investigate the volume fraction and shear rate dependence of the fluctuations in the shear stress and the interparticle contact number. In particular, we quantify them by defining the susceptibility as the ratio of the global to local fluctuations. The obtained susceptibilities form ridges on the volume fraction-shear rate plane, which are reminiscent of the Widom lines around the critical point in an equilibrium phase transition.

Highlights

Soft condensed matters comprising bubbles, emulsions, or powder particles are generally referred to as “soft athermal particle systems." Soft athermal particles are characterized by their elastic interactions, and thermal motion is negligible since they are large in size
We measure the volume fraction dependence of the shear stress under a constant shear rate, and near the jamming transition point, which is characterized by the athermal quasistatic (AQS) limit, we find that the fluctuation of the stress exhibits a peak
We find that the peak height diverges and the peak position converges to the jamming transition point when we decrease the shear rate toward the AQS limit, which is reminiscent of the Widom line near the critical point in an equilibrium phase transition

Summary

Introduction

Soft condensed matters comprising bubbles, emulsions, or powder particles are generally referred to as “soft athermal particle systems." Soft athermal particles are characterized by their (quasi-) elastic interactions, and thermal motion is negligible since they are large in size. When their density increases quasistatically, a transition from the liquid state, where the stress is zero, to the amorphous solid state, where the stress is finite, occurs. This work focuses on the fluctuation of the physical quantities and clarifies the jamming transition behavior under a finite shear rate

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