Interacting jammed granular systems

TL;DR

This study tests Edwards' statistical model of jammed granular systems through experiments and simulations of confined spheres, revealing limitations and counterintuitive effects in coupled systems.

Contribution

It introduces a simple experimental and numerical system to evaluate Edwards theory and explores the behavior of coupled jammed granular systems.

Findings

Edwards theory describes the joint system only when considered as a single entity.

Counterintuitive change in order parameter relative to compactivity in coupled systems.

Analytical calculations align with simulation results, validating the approach.

Abstract

More than 30 years ago Edwards and co-authors proposed a model to describe the statistics of granular packings by an ensemble of equiprobable jammed states. Experimental tests of this model remained scarce so far. We introduce a simple system to analyze statistical properties of jammed granular ensembles to test Edwards theory. Identical spheres packed in a nearly two-dimensional geometrical confinement were studied in experiments and numerical simulations. When tapped, the system evolves towards a ground state, but due to incompatible domain structures it gets trapped. Analytical calculations reproduce relatively well our simulation results, which allows us to test Edwards theory on a coupled system of two subsystems with different properties. We find that the joint system can only be described by the Edwards theory if considered as a single system due to the constraints in the stresses. The results show counterintuitive effects as in the coupled system the change in the order parameter is opposite to what is expected from the change in the compactivity.