Microscopic insights into the structure and stability of granular materials

Dense granular materials, such as piles of sand, coffee beans, or powders, often exist at the critical boundary between solid and liquid-like behavior. When subjected to forces like gravity or external loading, these materials display heterogeneous force transmission patterns, forming intricate force networks. These networks are not homogeneous and typically exhibit structures that depend on the material's loading history. The intrinsic heterogeneity of particulate materials complicates the use of system-wide averages, presents challenges for continuum modeling, and often necessitates particle-scale knowledge of force distribution and particle placement. We demonstrate how photoelastic granular experiments allow us to directly observe these force networks, map the material's structure and stability, and provide insights into other particulate systems, such as cellular tissue, colloids, or foams.