Particle shape dependence in 2D granular media

Particle shape is a key to the space-filling and strength properties of granular matter. We consider a shape parameter eta describing the degree of distortion from a perfectly spherical shape. Encompassing most specific shape characteristics such as elongation, angularity and non-convexity, eta is a low-order but generic parameter that we used in a numerical benchmark test for a systematic investigation of shape dependence in sheared granular packings composed of particles of different shapes. We find that the shear strength is an increasing function of eta with nearly the same trend for all shapes, the differences appearing thus to be of second order compared to eta. We also observe a non-trivial behavior of packing fraction which, for all our simulated shapes, increases with eta from the random close packing fraction for disks, reaches a peak considerably higher than that for disks, and subsequently declines as eta is further increased. These findings suggest that a low-order description of particle shape accounts for the principal trends of packing fraction and shear strength. Hence, the effect of second-order shape parameters may be investigated by considering different shapes at the same level of eta. Copyright (C) EPLA, 2012