Emergent plasticity and hysteresis in disordered packings of filaments.

A bird's cup-nest can be viewed as a disordered packing of slender grains, defined by average quantities -- coordination number and packing fraction; and dependent on grain properties -- flexibility, friction, and aspect ratio. Experimental data from packings of varying aspect ratio grains, subject to cyclic, quasi-static, oedometric compression reveal two distinctly meta- mechanical responses: plasticity associated with rearrangement without damage; and hysteresis associated with static friction rather than viscoelasticity. These qualitative behaviors appear to be common across systems of round grains to extremely fine fibers. One-to-one numerical simulations allow us to relate otherwise inaccessible micromechanical quantities such as contact distributions to bulk behaviors, confirming underlying assumptions regarding their origin.