Effect of shape and friction on the packing and flow of granular materials

KM Salerno and DS Bolintineanu and GS Grest and JB Lechman and SJ Plimpton and I Srivastava and LE Silbert, PHYSICAL REVIEW E, 98, 050901 (2018).

DOI: 10.1103/PhysRevE.98.050901

The packing and flow of aspherical frictional particles are studied using discrete element simulations. Particles are superballs with shape vertical bar x vertical bar(s )+ vertical bar y vertical bar(s )+ vertical bar z vertical bar(s)= 1 that varies from sphere (s = 2) to cube (s = infinity), constructed with an overlapping-sphere model. Both packing fraction, phi, and coordination number, z, decrease monotonically with microscopic friction mu, for all shapes. However, this decrease is more dramatic for larger s due to a reduction in the fraction of face-face contacts with increasing friction. For flowing grains, the dynamic friction fl-the ratio of shear to normal stresses- depends on shape, microscopic friction, and inertial number I. For all shapes, A grows from its quasistatic value (mu) over tilde (0) as ((mu) over tilde - (mu) over tilde (0)) = dI(alpha), with different universal behavior for frictional and frictionless shapes. For frictionless shapes the exponent alpha approximate to 0.5 and prefactor d approximate to 5 (mu) over tilde (0) while for frictional shapes alpha approximate to 1 and d varies only slightly. The results highlight that the flow exponents are universal and are consistent for all the shapes simulated here.

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