Title: Entangled Granular Materials

Abstract: 

A jumble of clothes hangers is a nightmare to untangle, as the individual hangers hook onto and become entangled with one another. Entanglement-driven cohesion is a general phenomenon, occurring in many different systems involving irregularly shaped particles. I'll present a variety of studies on "geometrically cohesive” granular materials (GCGM), defined by the ability to cohere due to the particle shape. These include long, thin rods, which can be surprisingly rigid, and U-shaped staples (pictured) that resist being pulled apart. The statistical theories that explain how these piles melt and disentangle are reassuringly simple and capture the fundamental mechanism of entanglement and "weakest link” behavior. More recently, GCGM have been used to model the network behavior of fire ants, which form self-healing piles capable of supporting both compressional and extensional forces to migrate across rivers.