Spanning the Scales of Granular Materials: Microscopic Force Imaging

TL;DR

This paper presents a novel experimental method to measure three-dimensional forces inside granular materials like sand, linking microscopic forces to macroscopic mechanical responses and revealing a microscopic deformation enhancement mechanism.

Contribution

It introduces a new experimental approach for force imaging in granular materials and connects microscopic force measurements to macro-scale behavior with theoretical analysis.

Findings

Measured forces inside granular packings under controlled deformation.

Connected micro-scale forces to macro-scale response through mean field calculation.

Discovered a microscopic particle deformation enhancement mechanism.

Abstract

If you walk on sand, it supports your weight. How do the disordered forces between particles in sand organize, to keep you from sinking? This simple question is surprisingly difficult to answer experimentally: measuring forces in three dimensions, between deeply buried grains, is challenging. We describe here experiments in which we have succeeded in measuring forces inside a granular packing subject to controlled deformations. We connect the measured micro-scale forces to the macro-scale packing force response with an averaging, mean field calculation. This calculation explains how the combination of packing structure and contact deformations produce the unexpected mechanical response of the packing, and reveals a surprising microscopic particle deformation enhancement mechanism.