Competition between Glassy Five-Fold Structures and Locally Dense Packing Structures Governs Two-Stage Compaction of Granular Hexapods

TL;DR

This study explores how granular hexapod particles compact through two stages, involving particle interlocking and dense aggregate formation, revealing glass-like disordered structures influenced by geometric frustration.

Contribution

It uncovers the two-stage compaction process and the role of five-fold symmetric structures in granular packings of complex-shaped particles.

Findings

Two distinct compaction mechanisms identified

Emergence of five-fold symmetric structures during densification

Granular packings exhibit glass-like disordered configurations

Abstract

Using X-ray tomography, we experimentally investigate the structural evolution of packings composed of 3D-printed hexapod particles, each formed by three mutually orthogonal spherocylinders, during tap-induced compaction. We identify two distinct structural compaction mechanisms: an initial stage dominated by enhanced particle interlocking, which yields local mechanically stable structures through strong geometric entanglement, and a later stage characterized by the formation of dense polytetrahedral aggregates and a sharp increase in the number of five-ring motifs. The emergence of these five-fold symmetric structures indicates that, despite their highly concave geometry, hexapod packings can be effectively treated as hard-sphere-like systems and exhibit similar glass-like disordered configurations. The frustration between local mechanically stable structures and global glassy order suggests a universal organizational principle underlying the structure of uniform and isotropic disordered granular materials.