Micromechanics of compressive and tensile forces in partially-bonded granular materials

TL;DR

This study investigates how partial bonding in granular materials affects their mechanical properties, revealing that bonded particles increase local forces and rigidity, with implications for understanding material strength and jamming behavior.

Contribution

It provides a detailed particle-scale analysis of how partial bonding influences force distribution, jamming, and local rigidity in granular media.

Findings

Bonded particles increase bulk strength and stiffness.

Local pressure and connectivity are enhanced near bonded dimers.

Force distributions broaden with more bonded particles.

Abstract

In granular media, the presence of even small amounts of interparticle cohesion manifests as an increase in the bulk strength and stiffness, effects that are typically associated with an increase in the average number of constraints per particle. By performing an ensemble of isotropic compression experiments, all starting from the same initial particle configuration but with varying fraction of bonded particles, we use photoelastic force measurements to identify the causes of this phenomenon at the particle-scale and meso-scale. As a function of the percentage of bonded particles, we measure a small decrease in the critical packing fraction at which jamming occurs. Above jamming, the local pressure increases predominantly for the bonded particles, measured relative to the unbonded case, through approximately equal contributions of both tensile and compressive forces. Histograms of the magnitude of the interparticle forces become broader for systems with more bonded particles. We measure both pressure and coordination number as a function of distance from a bonded dimer, both of which are locally enhanced for nearest neighbors, indicating that dimers appear to act as areas of concentrated force and connectivity that improve rigidity.