Spanning the scales of granular materials through microscopic force imaging

• Published in: Nature communications Vol. 6; no. 1; p. 6361
• Main Authors: Brodu, Nicolas, Dijksman, Joshua A., Behringer, Robert P.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 05.03.2015; Nature Publishing Group; Nature Pub. Group
• Subjects: 639/301/119; 639/301/930/328; Computer Science; Condensed Matter; Humanities and Social Sciences; Mechanics; Mechanics of materials; media; multidisciplinary; Physics; Sand; Science; Science (multidisciplinary); Signal and Image Processing; Soft Condensed Matter; system
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms7361

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. Here we describe 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 observed nontrivial mechanical response of the packing, revealing a surprising microscopic particle deformation enhancement mechanism. One major challenge for granular materials is how their microscopic contact forces respond to applied stress or strains at the macroscopic scale. Here, Brodu et al . map the contact forces of deformable hydrogel particles in three-dimensions and identify nonlinear stiffening of packing under compression.