Granular failure from micro- to meso- to macro-scale

When a granular material suddenly fails at the macroscopic scale, the rupture begins as some microscopic frictional/energetic failure criterion is surpassed, which locally mobilizes particles and results in macroscopic structural changes. I will present a series of experiments which start at this smallest scale and proceed through the force chain scale to elucidate how failure nucleates. Our experiments are performed on photoelastic particles which allow us to measure both the dynamics (normal and tangential forces at each contact) and kinematics (particle trajectories), and thereby quantify which failure criteria are at work under various conditions. Importantly, rigidity is a mesoscale property and it is therefore necessary to consider the network of interactions, which we achieve through the use of the Pebble Game.