【作者】 易成建；

【导师】 彭向和；

【作者基本信息】 重庆大学 ， 固体力学， 2011， 博士

【摘要】 磁流变液是一种由软磁性颗粒、基液以及添加剂组成的悬浮液,在外加磁场作用下可形成有序结构,且该结构随外加磁场的变化而变化。作为一类性能可控的智能材料,因其独特的磁流变效应和良好的流变性能,被认为是最具发展潜力的新型材料之一,国外已有较多的工程应用,国内也有一些尝试性的使用,并展现出广阔的应用前景。随着磁流变液工程应用研究的深入,提供性能可靠的磁流变液材料和建立合理实用的理论模型显得尤为重要。本文基于国家自然科学基金资助项目“多场耦合下磁流变液特性的微结构机理及跨尺度分析”,从实验测试、理论计算和数值模拟三个方面对磁流变液的机理和性能进行了比较全面的研究。为了对磁流变液的力学性能进行评估,本文首先利用旋转碟片式磁流变液性能测试装置,测试了不同颗粒体积分数、不同载液及不同添加剂含量磁流变液样品的力学性能。然后利用自行研制的透明观测装置和图像采集及处理技术,观测了低体积分数磁流变液在不同外加磁感应强度下的微结构链化特点,以及在剪切条件下磁流变液动态微结构的演化规律。针对工程应用中对高性能磁流变液的需求,以解决磁流变液在应用研究中遇到的各种稳定性问题为目的,从材料设计的角度出发,以国内先进产品为对照,围绕改善磁流变液体系沉降稳定性的同时增强其屈服应力,全面优化各制备工艺及组合,制备了性能良好的BGS-1型系列磁流变液。基于磁性物理学的基本理论,推导了不简化情况下的偶极子理论,得到了两个偶极子之间的相互作用力,将其与简化偶极子理论和Maxwell理论的结果进行对比,分析得出简化偶极子理论在一定程度上更加简洁和实用,并运用有限元的手段对其进行了验证。然后从微观角度入手,考虑磁流变液的微结构形态和体系的磁能,建立了基于微结构和统计力学方法的磁流变液微-宏观特性分析模型,模型能考虑磁感应强度、颗粒尺寸、体积分数、剪应变率以及饱和磁化强度等因素,计算结果表明,此模型能较好的描述实验现象及各主要因素的影响,不仅可用于计算剪切应力,而且可为优化磁流变液设计参数提供参考依据。利用磁流变液的链化模拟程序,模拟了两个颗粒的运动规律,以及多个颗粒的链化情况,并对链化过程中系统磁能的变化趋势进行了分析,结果表明该数值模拟平台能有效模拟磁流变液的微结构。然后从能量的角度出发,对外加静磁场下磁流变液具有单链、多链密排、立方、面心立方和体心立方胞元的微结构的磁能进行了分析,依据最小能量原理,得出不同微结构的稳定性特点。通过对链化程序的分析,采用OpenMP方法开发了基于曙光4000A集群系统的并行数值模拟平台,模拟和分析了在外加静磁场作用下大颗粒数磁流变液样本的运动规律和宏观力学特性。更多还原

【Abstract】 Magnetorheological fluids (MRFs) are dispersions composed of carrier liquid, ferromagnetic particles and additives. The apparent yield strength of MRFs can be changed significantly within milliseconds by the application of an external magnetic field. As a kind of designable and property-controllable smart materials, MRFs have been extensively used for different purposes in various fields and shown brilliant prospects.It is important to provide high-performance MRFs and establish reliable theoretical models for the design and engineering application of MRFs and MRF based devices. In this dissertation, consistent with the research of the project“Coupled-multi-field properties of magnetorheological fluids: microstructural mechanism and trans-scale analysis”, which was financially supported by the Natural Science Foundation of China, the properties of MRFs were systematically studied through experimental investigation, theoretical modeling and numerical simulation.In order to evaluate the mechanical properties of MRFs, the rheological properties of some MRFs were tested with a specially designed testing system, with which the effects of various influencing factors, such as the intensity of the applied magnetic field, the shearing strain rate, and the temperature, etc, can be investigated. On the other hand, the evolution of microstructures of MRFs subjected to static magnetic fields and shearing strain was also observed instantaneously with a specially developed device and a stereomicroscopy, as well as the image acquisition technology.Making use of the knowledge of physical chemistry and material design, some high-performance MRFs of good sedimentation stability were studied, the effects of the influencing parameters, such as ferromagnetic particles, the carrier liquids and additives, are investigated systematically and optimized for the purpose of achieving better mechanical properties and sedimentation stability.The interaction between two dipolar particles based on the exact dipolar model was formulated, under the consideration that the conventional simplified dipolar model may involve remarkable error when the spacing between two dipolar particles is much less than the sizes of the particles. However, the comparison between the results obtained with the exact dipolar model, the simplified dipolar model and that obtained with FE approach based on the Maxwell theory showed that the simplified dipolar model may provide better approximation. Then, considering the microstructures under magnetic field fields and shearing deformation, a micro-macro model was developed for the constitutive behavior of MRFs and the effects of the main influencing factors, such as the intensity of magnetic induction, the size and the volume fraction of dispersed particles, shearing strain rate and saturation magnetization on the macroscopic behavior of MRFs can be considered.The mechanism of chain formation was analyzed based on the simulation of the movement of two dipolar particles. Then the chain formation process and the variation of the magnetic energy in a 600-particle system under an applied magnetic field were simulated. The magnetic energy of some typical microstructures of dipolar particles in a static magnetic field was analyzed. It shows that, among the microstructures composed respectively of single-column, compact two-column, compact three-column, cubic-lattice, BCT and FCC cells, the average magnetic potential energy of the microstructure with cubic-lattice cells is the largest and that with BCT cells is the lowest. It indicates that the microstructures composed of BCT cells and compact multi-column cells are the most possible microstructures in MRFs under static magnetic fields. Through the analysis of the chain formation program, a parallel algorithm was developed based on the OpenMP method. With the developed approach, the response of MRF samples with a large number of particles subjected to applied magnetic field and shear deformation were numerically simulated on a Dawning 4000A cluster. The obtained overallτ–γrelationship and the microstructures are in reasonable agreement with that obtained in experiment and other analyrical approach, demonstrating the validity of the proposed approach.更多还原