REVERSIBILITY AND IRREVERSIBILITY IN THE PACKING OF VIBRATED GRANULARMATERIAL

We report on the settling of loosely packed, cohesionless granular mat erial under mechanical vibrations. Monodisperse spherical beads were c onfined to a long vertical cylinder that was driven by an electromagne tic vibration exciter. Under vibrations the bead packing evolves from an initial, low-density configuration towards higher density. Ramping the vibration intensity repeatedly up and back down again reveals the existence of both an irreversible and a reversible branch in the respo nse. The reversible branch represents a steady state in which the pack ing density depends monotonically on the vibration intensity. We have investigated the bead size, depth, and ramp rate dependence of the com paction process. Our results indicate how the occupied volume fraction can be optimized by slowly reducing the vibration intensity along the reversible branch. (C) 1997 Elsevier Science S.A.