ABSTRACT
Extensive experiments, simulations, and models address the transition between ‘fluid’ and ‘solid’ states of granular material. Using horizontal shaking a material layer undergoes a backward bifurcation between a solid-like state stationary in the frame of the shaker and a fluid-like state moving/sloshing on top of a solid layer. Both the solid/fluid transition and the reverse fluid/solid transition have similar divergent time scales τ = τ*|ϵ|− β , where e is a small change past either critical point. For both transitions β = 1 and τ* = 0.5 sec. Before transition there is a ‘gas’ of free particles sliding on the bulk material surface. Although these particles are few in number, suppressing them with a thin plastic strip removes the hysteresis: the fluidization transition becomes forward. A Coulomb friction model predicts a forward rather than a hysteretic transition. A model with friction changing continuously between static and dynamic values produces the hysteresis seen in experiments.
