Numerical Simulation Of Highly Dense Particle Packing Under Vibration

In this paper, numerical simulation of monosize particle packing under three dimensional (3D) vibration was carried out by using Discrete Element Method (DEM). The aim is to realize high packing density, followed by the characterization of the formed dense structure, and finally the identification of the hard sphere crystallization mechanism.Here mainly focus on the packing of 2500 monosize glass beads with 1 cm in diameter under 3D interval vibration and batch-wised feeding with the aid of DEM modeling. By properly choosing the vibration parameters such as amplitude A and frequencyω, highly dense packing with the packing density of 0.728 can be realized, which is much denser than the maximum packing density of random close packing. Through the analyse on both the macro-property, e.g. packing density, and the micro-properties, e.g. Coordination Number (CN), Radial Distribution Function (RDF), Angle Distribution Function (ADF), Voronoi/Delaunay pore size distribution, and the variation of accompanied force field and velocity field, the following conclusions are obtained.(1) Ordered structure beyond the maximum random packing density (p≈0.64) can be numerically achieved under special conditions, and the packing density can reach 0.728.(2) The CN and Voronoi/Delaunay distributions show that the created structure of simulation is quite different from that of random packing, and through comparison it can be found that the macroscopic property is in good agreement with microscopic ones at both the dense and loose packings.(3) The analyse on RDF and ADF further proves that ordered structure is formed, which can be identified by their correlation either at long distance or at specific angle, which is the characteristic of ordered structure. From their distributions some local disorder structures are also obtained, and they are the so called defects.(4) The pore size distribution shows a high and narrow main peak, which indicates that the pore distribution is narrow and uniform. The Voronoi curve corresponds to a sub-peak structure, and this implies that there exist large pores in the packing structure.(5) The properties of Voronoi polyhedron have been analyzed and compared with those of loose packing as well. These properties include:vertex distribution, perimeter distribution, surface area distribution, face number distribution, volume distribution of each Voronoi polyhedron; and edge distribution, perimeter distribution, face area distribution of each face on Voronoi polyhedron. They all showed large difference from those of loose structure. For highly dense packing, these distributions tend to be more uniform, which is a typical characteristic of ordered structure.(6) The properties of Delaunay tessellation have been analyzed and compared with those of loose packing as well. These properties include:area, volume, diameter, and sphericity of each tetrahedron. They all showed large difference from those of loose structure. For highly dense packing, these distributions tend to be more uniform.(7) Through the static and dynamic analysis, it is found that the obtained packing structure is FCC crystal, but with a small amount of defects. The crystallization mechanism can be ascribed to the formation of small ordered islands (core) and then their growth. During the growing, one grain is devoured by another to form a large one.