Title: Granular dynamics in compaction and stress relaxation

Author (Talk): Ping Wang, Physics Department, City College of New York

Abstract:

The nonlinear elastic and dissipative properties of cohesionless granular assemblies under uniaxial compression are studied both experimentally and by numerical simulations. As a prelude to granular dynamics measurements, we investigate system compaction through a novel procedure at varying conffining oscillatory pressures. Once the system is fully compactied we investigate the slow stress response under step-strain perturbations. We show that there is a two-step stress relaxation composed of an exponentially fast regime followed by slow logarithmic behavior with time. The origin of the slow relaxation dynamics is then studied with computer simulations which indicate that the coupling between damping and the collective nature of the motion and sliding of the constituent particles is responsible for the slowing down of the relaxation. We characterize an analogous "glass transition" for packed granular systems, below which the system shows aging in time dependent sliding correlation functions.