【作者】 于丹；

【导师】 邹宗树； 安希忠；

【作者基本信息】 东北大学 ， 钢铁冶金， 2008， 硕士

【摘要】 在本文中采用离散元方法,数值模拟了单一尺寸球在三维振动条件下的堆积。其目的是实现高堆积密度,表征其形成的致密结构,并最终确定硬球结晶机理。在三维间歇振动和批量加料条件下,使用DEM模型研究了2500个直径为1厘米玻璃球的堆积。通过适当选择振动参数如振动振幅A和振动频率ω,可以实现堆积密度0.728的高密度堆积,它是比最大随机紧密堆积更致密的堆积。通过宏观特征如堆积密度ρ、微观特征如配位数(CN, Coordination Number)、径向分布函数(RDF, Radial Distribution Function)、角分布函数(ADF, Angle Distribution Function)及Voronoi/Delaunay孔尺寸分布以及伴随力场和速度场的变化发现：(1)可以数值实现超越最大无规密排(p≈0.64)的有序结构,堆积密度可达0.728。(2)CN和Voronoi/Delaunay分布表明,模拟产生的结构与随机堆积结构有很大不同,通过对比发现不论是致密堆积还是松散堆积,其宏观特征与微观特征是相互对应的。(3)RDF和ADF的进一步分析证明所获得的结构并不是纯随机的,RDF和ADF曲线分布证明了堆积结构无论是在较大距离上还是在特定角度上都存在相关性,这是有序结构所具有的特点。从它们的分布上还发现一些局部的无序结构,即所谓的缺陷。(4)孔的尺寸分布呈现出高且窄的主峰,表明孔分布小且均匀。Voronoi曲线有一个子峰,表明堆积结构中有较大孔存在。(5)对致密和松散堆积进行了Voronoi多面体的特征分析和对比。这些特征包括：每个Voronoi多面体顶点分布,周长分布,面积分布,面数分布,体积分布；每个Voronoi多面体面的边分布,周长分布,面积分布。它们与松散结构相比表现很大差距。对于高密度堆积,它们的分布更趋于均匀,这是有序结构的一个典型特点。(6)对致密和松散堆积进行了Delaunay四面体的特征分析和对比。这些特征包括：每个Delaunay四面体的面积、体积、直径、球形度。它们与松散结构相比差别很大,堆积密度越高其分布越均匀。(7)通过静态和动态分析发现获得的堆积结构是FCC晶体,但内有少量的缺陷。结晶机理可以归因于小岛(核)的形成及生长,在长大过程中,一个晶粒被另一个晶粒吞并形成一个大的晶粒。更多还原

【Abstract】 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.更多还原