Experimental exploration of geometric cohesion and solid fraction in columns of highly non-convex Platonic polypods

TL;DR

This paper explores how non-convex particles shaped like Platonic solids with arms, called polypods, can form stable columns through geometric cohesion without adhesives, influenced by particle geometry and friction.

Contribution

It introduces the concept of geometric cohesion in non-convex granular columns and analyzes how particle shape and friction affect stability and solid fraction.

Findings

Certain non-convex particles exhibit geometric cohesion leading to stable columns.

Stable structures can form at very loose packing fractions, unlike traditional granular materials.

Friction coefficient influences the stability and solid fraction of the columns.

Abstract

In this study, we investigate the stability and solid fraction of columns comprised of highly non-convex particles. These particles are constructed by extruding arms onto the faces of Platonic solids, a configuration we term \emph{Platonic polypods}. We explore the emergence and disappearance of solid-like behavior in the absence of adhesive forces between the particles, referred to as \emph{geometric cohesion}. This investigation is conducted by varying the number of arms of the particles and the thickness of these arms. To accomplish this, columns are assembled by depositing particles within a cylindrical container, followed by the removal of the container to evaluate the stability of the resulting structures. Experiments were carried out using three distinct materials to assess the influence of the friction coefficient between the grains. Our findings reveal that certain granular systems exhibit geometric cohesion, depending on their geometrical and contact properties. Furthermore, we analyze the initial solid fraction of the columns, demonstrating that these arrangements can achieve stability even at highly loose states, which contrasts with traditional granular materials.