Solid-fluid transition and surface melting in wet granular matter

By means of molecular-dynamics simulations, we study the transition from solid-like to fluid-like behavior in sinusoidally vibrated wet granular matter. We find that the peak acceleration at which the transition occurs depends not only on the capillary bridge force but also on the driving energy of the bottom plate, which reduces the effect of the capillary bridge force. A simple argument based on the balance of the maximal forces acting on a one-dimensional column is able to predict the transition found in simulations surprisingly well. Furthermore, it predicts surface melting to occur at this transition, which is also found in simulations.