Studies on the macroscopic and microscopic packing properties of nonconvex particles are scarce. As a common concave form, the curved spherocylinder is used in the simulations, and its bending and elongation effects on the random packings are investigated numerically with sphere assembly models and a relaxation algorithm. The aspect ratio is demonstrated to be the main factor regarding the packing density. However, at certain aspect ratios of low densities around 0.3–0.4, the density of curved spherocylinders may increase by 15% more than that of the straight ones, indicating that bending is also a contributor to the packing density. The excluded volume of the curved spherocylinder decreases with the increase of the bending angle, indicating that the excluded volume is applicable in explaining the bending effect on the packing density variation of nonconvex particles. The packings are verified to be randomly distributed in orientation with no significant layering or in-plane order. The local arrangements are further analyzed from the radial distribution function and contact results. The results show that the random packings of nonconvex particles have significant differences and richer characteristics on both the macroscopic and microscopic properties compared with convex objects.

Regular tetrahedra have been demonstrated recently giving high packing density in random configurations. However, it is unknown whether the random-packing density of tetrahedral particles with other shapes can reach an even higher value. A numerical investigation on the random packing of regular and irregular tetrahedral particles is carried out. Shape effects of rounded corner, eccentricity, and height on the packing density of tetrahedral particles are studied. Results show that altering the shape of tetrahedral particles by rounding corners and edges, by altering the height of one vertex, or by lateral displacement of one vertex above its opposite face, all individually have the effect of reducing the random-packing density. In general, the random-packing densities of irregular tetrahedral particles are lower than that of regular tetrahedra. The ideal regular tetrahedron should be the shape which has the highest random-packing density in the family of tetrahedra, or even among convex bodies. An empirical formula is proposed to describe the rounded corner effect on the packing density, and well explains the density deviation of tetrahedral particles with different roundness ratios. The particles in the simulations are verified to be randomly packed by studying the pair correlation functions, which are consistent with previous results. The spherotetrahedral particle model with the relaxation algorithm is effectively applied in the simulations.