Compaction of anisotropic granular materials : experiments and simulations

TL;DR

This study combines experiments and simulations to explore how rod-shaped granular materials compact in tubes, revealing how aspect ratio influences packing density and phase transitions, supported by a simplified lattice model.

Contribution

It introduces a comprehensive experimental and numerical analysis of anisotropic granular compaction, highlighting the impact of particle aspect ratio and proposing a lattice toy model for understanding behaviors.

Findings

Packing volume fraction varies with aspect ratio.

A phase transition occurs at aspect ratio 1.

The toy model replicates key experimental behaviors.

Abstract

We present both experimental and numerical investigations of compaction in granular materials composed of rods. As a function of the aspect ratio of the particles, we have observed large variations of the asymptotic packing volume fraction in vertical tubes. The relevant parameter is the ratio between the rod length $\ell$ and the tube diameter $D$. Even the compaction dynamics remains unchanged for various particle lengths, a 3d/2d phase transition for grain orientations is observed for $\ell/D = 1$. A toy model for the compaction of needles on a lattice is also proposed. This toy model gives a complementary view of our experimental results and leads to behaviors similar to experimental ones.