Stress fluctuations in a 2D granular couette experiment: A continuous transition

Abstract

Experiments on a slowly sheared 2D granular material show a continuous transition as the packing fraction γ passes through γc ≃ 0.776. The mean stress, σ, plays the role of an order parameter. As γ → γc from above, (1) the compressibility becomes large, (2) a slowing down of the mean velocity occurs, (3) the force distributions change, and (4) the network of stress chains changes from intermittent long radial chains near γc to a tangled dense network for larger γ. © 1999 The American Physical Society.