DEM study of crystallization of monosized spheres under mechanical vibrations

The crystallization (disorder-order transition) of monosized spheres under three-dimensional (3D) mechanical vibrations is studied using discrete element method (DEM). The crystallization dynamics and final structure are analyzed for two selected conditions: i.e. the packing of rough spheres (glass beads) with interval vibration and batch-wise feeding (Case I) and the packing of smooth spheres with continuous vibration and total feeding (Case II). The final packing densities are 0.728 and 0.712 for Cases I and II, respectively, higher than that of random close packings. Partial crystallization characterized by the {111}-oriented face centered cubic (FCC) structure can be observed in both packings, which is further confirmed from the analyses of coordination number, radial and angular distribution functions, and Q₆ bond order. Through the tracing of the particles (e.g. the evolutions of velocity and force fields), two crystallization mechanisms are identified: engulfed growth of two adjacent small crystals and epitaxial growth from existing ordered structures (nuclei).