Gardner-like transition from variable to persistent force contacts in granular crystals

TL;DR

This study provides experimental evidence of a Gardner-like transition in granular crystals, showing how force contacts evolve from variable to persistent with increasing density and compression, linked to microscopic asperities.

Contribution

First experimental observation of a Gardner-like transition in a granular crystal, analyzing force contact variability and linking it to microscopic asperities.

Findings

Force contacts are undetermined below the transition density.

Contacts become persistent above the transition, fully so after jamming.

Disorder is related to microscopic asperities of the particles.

Abstract

We report experimental evidence of a Gardner-like transition from variable to persistent force contacts in a two-dimensional, bidisperse granular crystal by analyzing the variability of both particle positions and force networks formed under uniaxial compression. Starting from densities just above the freezing transition, and for variable amounts of additional compression, we compare configurations to both their own initial state, and to an ensemble of equivalent, reinitialized states. This protocol shows that force contacts are largely undetermined when the density is below a Gardner-like transition, after which they gradually transition to being persistent, being fully so only above the jamming point. We associate the disorder that underlies this effect to the size of the microscopic asperities of the photoelastic disks used, by analogy to other mechanisms that have been previously predicted theoretically.