分形结构颗粒团聚体分散行为的三维离散元法数值模拟研究

发布时间：2018-01-04 00:05

本文关键词：分形结构颗粒团聚体分散行为的三维离散元法数值模拟研究　出处：《华南理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：纳米尺度填充颗粒在聚合物基体中的分散效果直接影响了聚合物基纳米复合材料的综合性能,由于纳米颗粒表面能极高,并且在范德华力和静电力的作用下极易团聚形成颗粒团聚体。因此,提高填充纳米颗粒在聚合物基体中的分散均匀性对于聚合物加工领域来说是一项十分重要的课题。目前,实验手段难以精确测得纳米颗粒在加工过程中的位移、速度和接触力等动态信息,并且难以评估团聚体结构对颗粒分散效果的影响。随着离散元法(Discrete Element Method,DEM)发展和逐渐成熟,许多学者开始利用离散元法对团聚体的分散过程展开研究。但是以往所研究的团聚体通常为简单结构或是致密结构,与通过随机运动凝聚形成的团聚体的结构存在一定差别,因此所得结果还不能够完全反映出团聚体的分散特征,同时,未深入揭示团聚体的分散机理,即颗粒究竟以何种分散方式脱离团聚体没有提出明确的判断标准。随着分形凝聚计算机模拟技术的发展完善,采用颗粒分形凝聚模型能够生成与真实颗粒团聚体结构十分相似的分形结构团聚体,因此,对具有分形结构的团聚体在流场中的分散行为进行研究,将有助于揭示团聚体在真实加工流场中的分散机理。将颗粒分形凝聚计算机模拟技术和离散元法数值模拟技术相结合,在Visual Studio2010编程环境中,采用C++编程语言开发颗粒凝聚与分散模拟软件(Particles Aggregate and Disperse,PAD),利用OpenGL实现颗粒运动行为的可视化。利用PAD软件模拟了分形结构团聚体凝聚过程,研究了分形结构团聚体在流场中的分散行为及其力链结构演变规律。结果表明,相同凝聚体系条件下,团聚体的分形维数随着颗粒数量的增多而提高;扩散指数的取值直接影响DLCA团聚体的凝聚机制;强弱力链交织形成了团聚体复杂的力链网络形态,分散过程中,团聚体力链结构的变化决定了颗粒的分散机制;DLCA团聚体最终的碎片加权颗粒数随着流场强度的增大以幂函数规律降低;相同流场强度下,拉伸流场对DLCA团聚体的分散效果优于剪切流场。
[Abstract]:The nano scale dispersion effect of particles in the polymer matrix directly affects the performance of polymer nanocomposites, because nano particle surface energy is extremely high, and extremely easy in the van Edward force and electrostatic force under the effect of agglomeration of particles. Therefore, improving the filling nano particles in polymer matrix, the dispersion uniformity is a very important task for the polymer processing field. At present, it is difficult to accurately measure the displacement experiments of nano particles in the machining process, the speed and force of dynamic information, and it is difficult to assess the impact of aggregate structure on dispersing of particles. With the discrete element method (Discrete Element Method, DEM) development and gradually mature and many scholars have started research on the discrete element method of dispersion on aggregate. But previous studies usually aggregate simple structure or Compact structure, and there are some differences of structure formation of aggregates by the random motion of cohesion, so the results can not fully reflect the characteristics of dispersion, polymer group at the same time, did not reveal the dispersion mechanism of aggregates, namely the particle dispersion from the aggregates with what made no clear criteria. With the development of computer simulation of fractal aggregation the improvement of technology, adopting the particle fractal aggregation model to fractal structure formation and the real particle aggregates, aggregate structure is very similar to the result, to study the dispersion behavior of aggregates with fractal structure in the flow, will help to reveal the aggregates in the real processing flow field the dispersion mechanism of the particles. The computer simulation technology and discrete fractal aggregation finite element method combining numerical simulation technology in Visual Studio2010 programming environment, using C++ programming language development Particle agglomeration and dispersion simulation software (Particles Aggregate and Disperse, PAD), visualization of particle movement is simulated by OpenGL. The fractal structure of aggregates condensation process by using PAD software, the dispersion behavior and force chain structure evolution of the fractal structure of aggregates in the flow field. The results show that the same system under the condition of fractal dimension the aggregates increase with the number of particles; value of diffusion index directly affects the coagulation mechanism of DLCA aggregates; force chain intertwined to form the force chain network form aggregates complex, the process of dispersion, agglomeration changes in physical chain structure determines the mechanism of particle dispersion; DLCA aggregates the final weighted number of particles increases with debris flow intensity of power-law flow is reduced; the same strength, tensile flow of DLCA aggregates dispersed better than shear flow Field.

【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TB383.1

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