Translational and rotational velocities in shear-driven jamming of ellipsoidal particles.

Yann-Edwin Keta,Peter Olsson

doi:10.1103/physreve.102.052905

Abstract

We study shear-driven jamming of ellipsoidal particles at zero temperature with a focus on the microscopic dynamics. We find that a change from spherical particles to ellipsoids with aspect ratio α=1.02 gives dramatic changes of the microscopic dynamics with much lower translational velocities and a new role for the rotations. Whereas the velocity difference at contacts-and thereby the dissipation-in collections of spheres is dominated by the translational velocities and reduced by the rotations, the same quantity is in collections of ellipsoids instead totally dominated by the rotational velocities. By also examining the effect of different aspect ratios we find that the examined quantities show either a peak or a change in slope at α≈1.2, which thus gives evidence for a crossover between different regions of low and high aspect ratio.

Highlights

Dense collections of circular disks in two dimensions (2D) and spheres in 3D with contact interaction at zero temperature have been studied extensively during the past decades with the aim to understand the jamming transition
We have shown that a change from spherical to slightly ellipsoidal particles with aspect ratio α = 1.02 gives an altogether different microscopic dynamics
Comparing spheres and ellipsoids close to jamming it is found that the translational velocity is reduced by 80%, and that the rotations get a different role for the ellipsoids, contributing to the particles ability to fit together

Summary

Introduction

Dense collections of circular disks in two dimensions (2D) and spheres in 3D with contact interaction at zero temperature have been studied extensively during the past decades with the aim to understand the jamming transition. It has already been argued that the spherical limit is singular [17,18,19,20] and the purpose of the present paper is to explore further consequences of this change to aspherical particles. In the present paper we do shearing simulations of both spherical and ellipsoidal particles to examine how the asphericity affects the microscopic dynamics. Since the quartic modes found in static packings are primarily rotational in character [21,22] we believe that these effects are consequences of the quartic modes on the shear-driven dynamics. When doing simulations with a set of larger aspect ratios we find several quantities to have features at α ≈ 1.2, which suggests the existence of different regions of high and low aspect ratio

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Results

Conclusion