Hysteresis and competition between disorder and crystallization in sheared and vibrated granular flow.

Experiments on spherical particles in a 3D annular shear cell vibrated from below and sheared from above show a hysteretic freezing or melting transition. Under sufficient vibration a crystallized state is observed, which can be melted by sufficient shear. The critical line for this transition coincides with equal kinetic energies for vibration and shear. The force distribution is double peaked in the crystalline state and single peaked with an approximately exponential tail in the disordered state. Continuous relations between pressure and volume (with dP/dV>0) exist for a continuum of partially and/or intermittently melted states over a range of parameters.