Quantifying interparticle forces and heterogeneity in 3D granular materials

Abstract

Extensive theoretical, numerical, and experimental research has examined interparticle forces in granular materials. Interparticle forces are intimately linked to mechanical properties and are known to self-organize into heterogeneous structures, or force chains, under external load. Despite progress in understanding the statistics and spatial distribution of interparticle forces in recent decades, a systematic method for measuring forces in opaque, 3D, frictional, stiff granular media has yet to emerge. In this Letter, we present results from an experiment that combines 3D X-ray diffraction, X-ray tomography, and a numerical force inference technique to quantify interparticle forces and their heterogeneity in a granular material composed of quartz grains undergoing a 1D compression cycle. Forces exhibit an exponential decay above the mean and partition into strong and weak networks. We find a surprising inverse relationship between macroscopic load and the heterogeneity of interparticle forces, despite the clear emergence of two force chains that span the system.

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