Packings of 3D stars: Stability and structure

TL;DR

This study investigates the stability of cylindrical packings of star-shaped particles with varying properties through experiments involving loading, tipping, and vibration, revealing a stability diagram and factors influencing stability.

Contribution

It introduces a comprehensive experimental analysis of star-shaped particle packings, establishing a stability diagram and examining effects of friction, vibration, and particle size.

Findings

Stability boundary follows a power-law relation between height and diameter.

Friction and vibration enhance pile stability.

Larger particles can destabilize the packing under certain conditions.

Abstract

We describe a series of experiments involving the creation of cylindrical packings of star-shaped particles, and an exploration of the stability of these packings. The stars cover a broad range of arm sizes and frictional properties. We carried out three different kinds of experiments, all of which involve columns that are prepared by raining star particles one-by-one into hollow cylinders. As an additional part of the protocol, we sometimes vibrated the column before removing the confining cylinder. We rate stability in terms of r, the ratio of the mass of particles that fall off a pile when it collapsed, to the total particle mass. The first experiment involved the intrinsic stability of the pile when the confining cylinder was removed. The second kind of experiment involved adding a uniform load to the top of the column, and then determining the collapse properties. A third experiment involved testing stability to tipping of the piles. We find a stability diagram relating the pile height, h, vs. pile diameter, delta, where the stable and unstable regimes are separated by a boundary that is roughly a power-law in h vs. delta with an exponent that is less than one. Increasing friction and vibration both tend to stabilize piles, while increasing particle size can destabilize the system under certain conditions.