On universal structural characteristics of granular packs

TL;DR

This study reveals that the structural characteristics of granular packs are primarily governed by the packing protocol and the higher moments of the size distribution, rather than initial conditions or grain parameters, indicating a universal behavior.

Contribution

It demonstrates that key structural features of granular packs are universal across different conditions when the size distribution variance is fixed.

Findings

Mean coordination number vs. packing fraction is protocol-independent.

Quadrons and cell distributions collapse to universal forms.

Structural properties depend mainly on packing protocol and DSD moments.

Abstract

Dependence of structural self-organization of granular materials on preparation and grain parameters is key to predictive modelling. We study 60 different mechanically equilibrated polydisperse disc packs, generated numerically by two protocols. We show that, for same-variance disc size distributions (DSDs): 1. the mean coordination number of rattler-free packs vs. the packing fraction is a function independent of initial conditions, friction and the DSD: 2. all quadron volume and cell order distributions collapse to universal forms, also independent of the above. We conclude that, contrary to common wisdom, equilibrated granular structures are determined mainly by the packing protocol and higher moments of the DSD.