Effect of particle shape on the density and microstructure of random packings

Abstract

We study the random packing of non-spherical particles by computer simulation toinvestigate the effect of particle shape and aspect ratio on packing density andmicrostructure. Packings of cut spheres (a spherical segment which is symmetric about thecentre of the sphere) are simulated to assess the influence of a planar face onpacking properties. It turns out that cut spheres, in common with spherocylindersand spheroids, pack more efficiently as the particle’s aspect ratio is perturbedslightly from unity (the aspect ratio of a sphere) to reach a maximum density at anaspect ratio of approximately 1.25. Upon increasing the aspect ratio further thecut spheres pack less efficiently, until approximately an aspect ratio of 2, wherethe particles are found to form a columnar phase. The amount of ordering issensitive to simulation parameters and for very thin disks the formation of longcolumns becomes frustrated, resulting in a nematic phase, in marked contrastto the behavior of long thin rods which always randomly pack into entangledisotropic networks. With respect to coordination numbers it appears that cut spheresalways pack with significantly fewer contacts than required for isostatic packing.