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).
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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