Vibration-induced jamming transition in granular media

The quasistatic frequency response of a granular medium is measured by a forced torsion oscillator method, with forcing frequency f(p) in the range 10(-4) Hz to 5 Hz, while weak vibrations at high-frequency f(s), in the range 50 Hz to 200 Hz, are generated by an external shaker. The intensity of vibration Gamma is below the fluidization limit. A loss factor peak is observed in the oscillator response as a function of Gamma or f(p). In a plot of 1n f(p) against l/Gamma, the position of the peak follows an Arrhenius-like behavior over four orders of magnitude in f(p). The data can be described as a stochastic hopping process involving a probability factor exp(-Gamma (j)/Gamma) with Gamma (j) a f(s)-dependent characteristic vibration intensity. An f(s)-independent description is given by exp(- tau (j)/tau), With tau (j) an intrinsic characteristic time, and tau = Gamma (n)/2 pif(s), n = 0.5-0.6, an empirical control parameter with unit of time. tau is seen as the effective average time during which the perturbed grains can undergo structural rearrangement. The loss factor peak appears as a crossover in the dynamic behavior of the vibrated granular system, which, at the time scale 1/f(p), is solidlike at low Gamma, and the oscillator is jammed into the granular material, and is fluidlike at high Gamma, where the oscillator can slide viscously.