Entangled granular media

TL;DR

This study investigates how geometrically induced cohesion in granular u-particles affects their stability under vibration, revealing an optimal particle shape for maximum strength due to packing and entanglement effects.

Contribution

It introduces a combined experimental and simulation approach to understand the role of particle shape in granular cohesion and stability.

Findings

Collapse time depends exponentially on vibration parameters.

Optimal particle shape maximizes cohesion due to packing and entanglement.

Activation energy-like parameter peaks at intermediate particle aspect ratios.

Abstract

We study the geometrically induced cohesion of ensembles of granular "u-particles" which mechanically entangle through particle interpenetration. We vary the length-to-width ratio $l/w$ of the u-particles and form them into free-standing vertical columns. In laboratory experiment we monitor the response of the columns to sinusoidal vibration (frequency $f$, peak acceleration $\Gamma$). Column collapse occurs in a characteristic time, $\tau$, which follows the relation $\tau = f^{-1} \exp(\Delta / \Gamma)$. $\Delta$ resembles an activation energy and is maximal at intermediate $l/w$. Simulation reveals that optimal strength results from competition between packing and entanglement.