Investigating Wide Shear Zones in Slow Granular Flow by Discrete Element Simulations
Jeremy B. Lechman1, Gary S. Grest1, Martin Depken2, and Martin Van Hecke3. (1) Surface and Interface Science Department, Sandia National Laboratories, PO Box 5800, MS 1415, Albuquerque, NM 87185-1415, (2) Instituut-Lorentz for sTheoretical Physics, Leiden University, PO Box 9506, NL-2300 RA, Leiden, Netherlands, (3) Kamerlingh Onnes Lab, Leiden University, PO Box 9504, 2300 RA, Leiden, Netherlands
While the rheology of rapid granular flows is becoming well established, slow, dense flows are not well characterized in part because the strain localization (i.e., shear bands) they often exhibit is not easily amenable to continuum descriptions. Recently, a novel experimental system (split-bottom Couette Cell) was developed with promising potential to give new insight into these flows due to its wide, smooth shear zones. We describe numerical studies undertaken to understand the nature of the flow in this device. In particular, Depken et al. have proposed a set of testable constitutive relations between the internal stresses and flow field. In particular, they suggest that the bulk, effective friction coefficient between sliding layers of particles is not constant, but has a subtle dependence on the orientation of the layers with respect to the bulk force. Here we present large-scale Discrete Element Simulations to analyze the bulk flow in both circular, above and below the critical height, and linear, where no critical height for slip at the base is found, split-bottom geometries. We check the proposed form of the stress tensor and assess the validity of the claim that the effective friction coefficient depends on the shape of the shear zone with respect to gravity.
1Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract No. DE-AC04-94AL85000.