Flow, arrest, and dynamics near the jamming transition in sheared granular materials*

With a decreasing pressure-normalized shear stress or stress ratio, the strain rate in granular materials decreases and approaches zero as the system nears a critical stress ratio. This critical stress ratio is the threshold for the system to flow and depends not only on material properties such as the friction coefficient but also on the type of flow, whether a planar pure or simple shear flow or a non-planar triaxial flow. Using discrete element method simulations of large systems, we characterize how the critical stress ratio depends on these parameters and then discuss the dynamics of granular systems both above this critical stress ratio where the system flows at a near-quasistatic rate and below where the system eventually arrests. Near this limit, the system experiences bursts of motion and spatial inhomogeneities. We isolate these events to examine the spatial-temporal rearrangement of grains and explore their statistics.