Fluctuations, Jamming, and Yielding for a Driven Probe Particle in Disordered Disk Assemblies

TL;DR

This study uses simulations to analyze how a driven probe particle behaves near the jamming transition in disordered disk assemblies, revealing critical fluctuations, velocity distribution changes, and local yielding phenomena.

Contribution

It provides detailed insights into velocity fluctuations, distribution characteristics, and local shear banding near the jamming point in disordered systems.

Findings

Velocity fluctuations become intermittent near jamming.

Velocity distributions transition from exponential to power-law close to jamming.

A critical force threshold exists for probe motion above jamming.

Abstract

Using numerical simulations we examine the velocity fluctuations of a probe particle driven with constant force through a two-dimensional disordered assembly of disks which has a well-defined jamming point J at a density of \phi_J=0.843. As \phi increases toward \phi_J, the average velocity of the probe particle decreases and the velocity fluctuations show an increasingly intermittent or avalanchelike behavior. When the system is within a few percent of the jamming density, the velocity distributions are exponential, while when the system is less than a percent away from jamming, the velocity distributions have a non-exponential or power law character. The velocity power spectra exhibit a crossover from a Lorentzian form to a 1/f shape near jamming. We extract a correlation exponent \nu which is in good agreement with recent shear simulations. For \phi > \phi_J, there is a critical threshold force F_c that must be applied for the probe particle to move through the sample which increases with increasing \phi. The onset of the probe motion above \phi_J occurs via a local yielding of the particles around the probe particle which we term a local shear banding effect.