Analysis and Verification on the Chain-like Model with Normal Distribution of Magnetorheological Elastomer

在磁流变弹性体链化模型的基础上,引入斜链夹角的正态分布,采用偶极子法从理论上分析了诸多因素对磁流变弹性体磁致剪切模量的影响,包括颗粒链的初始倾斜角、外加磁场强度、剪应变大小等,并进行了实验验证.     

Enhancement in Magnetorheological Effect of Magnetorheological Elastomers by Surface Modification of Iron Particles

为了研制具有高磁流变效应的磁流变弹性体,从新的化学修饰的角度制备了各向异性的橡胶基磁流变弹性体. 阴离子表面活性剂、非离子表面活性剂和复合表面活性剂等三种不同类型的表面活性剂分别用于修饰铁颗粒. 使用力磁耦合动态测试仪测量磁流变弹性体的动态剪切模量,并计算材料的磁流变效应. 测试结果表明,当Span 80的含量为15%时,材料的相对磁流变效应可达到188%,除了表面活性外,Span 80的增塑效应也有利于相对磁流变效应的增加. 当使用具有强表面活性的复合表面活性剂修饰铁颗粒时,用量只需0.4%,便可使相对     

基于分布链修正的磁流变弹性体的物理模型

在考虑磁流变弹性体中链的方向分布的基础上,对磁流变弹性体的偶极子模型作出了修正.用局部场的方法计算了链的势能,引入了分布函数来描述链的分布,并分析了与磁场方向不一致的斜链的磁流变效应,进而通过积分叠加求得含有分布链的磁流变弹性体的磁流变效应.在磁流变弹性体的理论模型中,引入了制备磁场和基体性质等影响因素.     

Radiation Vulcanization of Magnetorheological Elastomers Based on Silicone Rubber

介绍了两种制备磁流变弹性体的硫化方法即高温硫化和辐射硫化. 研究中采用动态力学分析仪(DMA)测量了样品的动态力学特性.特别是对样品的磁流变效应和耐久性进行了详细的测试. 实验结果表明,经过辐射硫化的样品具有更大的零场模量和磁致模量,以及更好的磁流变效应和耐久性. 为了解释这些结果,文章对样品的体积形变和增塑剂渗出都作了详细的分析. 在硫化过程中样品的体积保持稳定是辐射硫化样品具有大磁致模量的重要原因,而增塑剂渗透性小也是辐射硫化样品具有高磁流变效应和耐久性的重要因素.     

基于链化分析的磁流变液剪切屈服应力模型

基于磁性颗粒在磁场作用下的链化分析和统计分析方法,建立了磁流变液的宏观屈服剪应力的分析模型.模型考虑了磁感应强度、颗粒尺寸、体积分数、剪应变率以及饱和磁化强度等因素,能描述不同剪切应变率下剪切应力的变化及在高应变率下可能出现的剪切稀化效应.分析了不同因素对剪切屈服应力的影响,讨论了提高磁流变液剪切屈服应力的途径.分析表明,该模型的计算结果能较好地描述有关实验现象,并可用于高性能磁流变液的设计分析.     

Damping of Magnetorheological Elastomers

利用改装后的力磁耦合动态测试系统实验研究了磁流变弹性体在磁场下的阻尼性能. 实验得出了外加磁场的磁感应强度、基体的本征阻尼、铁粉含量、动态应变以及激励频率对磁流变弹性体阻尼的影响规律. 发现了磁流变弹性体的阻尼在很大程度上是由基体和颗粒之间的界面滑移所决定的. 而且该界面滑移不同于一般复合材料,它会受到外加磁场的影响..     

磁性纳米颗粒膜的微磁学模拟

用微磁学方法对磁性纳米颗粒膜的磁特性进行了模拟，采用的模型是由122个磁性纳米颗粒组成的面心立方(fcc)结构体系.结果表明：在该体系中，偶极相互作用对体系的静态磁结构的影响显著，而交换相互作用的影响表现不明显.在此基础上，本文还采用有效媒质理论计算分析了磁性合金颗粒不同体积比时颗粒膜的磁谱和表征电磁参量发生显著变化的逾渗现象和逾渗阈值.并完成了对高磁损耗磁性纳米颗粒膜的材料设计. 关键词： 微磁学 纳米颗粒膜 逾渗阈值 磁导率 材料设计     

对称磁电层合板磁电转换效应理论研究

磁致伸缩和压电层合材料通过磁致伸缩和压电效应的乘积可以获得大的磁电效应.通过材料的力学本构方程，建立了对称磁电层合板磁电耦合的静态力学模型；采用ANSYS 80多物理场有限元分析软件，对层合结构的磁电转化效应进行了数值计算，并与理论计算值进行了对比.研究结果表明：磁致伸缩/压电的厚度比增加使磁电电压系数增大；所推导的磁电电压系数公式的计算值与等效电路模型推导的公式计算值符合很好；有限元数值计算结果介于两种模型的计算结果之间. 关键词： 磁电效应 层合板 本构方程 有限元分析     

酞菁钴/铁纳米填充母粒组成的磁流变液性能

采用有机／无机原位（ｉｎ ｓｉｔｕ）复合方法制备得出本菁钴／铁纳米填充母粒,与甲基硅油组成磁流变液（ＭＲＳ）。ＭＲＳ的附加动态剪切应力（△τ）与分散介质浓度、外加磁场强度呈正比例关系;剪切速率对△τ的影响表明磁致流变为链状结构特征;△τ的对温度不敏感;ＭＲＳ对外加磁场有可逆的开／关变化特征,无记忆效应,磁流变响应时间小于０．１ｓ。     

磁流变弹性体中结合胶的存在及其对材料性能的影响

为了提高磁流变材料的力学磁学性能，在大量的实验和观测过程中，发现了在磁流变弹性体的内部存在结合橡胶现象．进一步的实验证实了铁磁性颗粒表面的确存在结合橡胶，并且这层结合橡胶的厚度和铁磁性颗粒的大小之间的相互关系对材料的性能有显著的影响．通过理论分析和实验测试发现，通过提高颗粒半径和结合橡胶厚度的比率，可以显著提高磁流变弹性体的磁流变性能．     

A Gaussian distribution model of anisotropic magnetorheological elastomers

A Gaussian distribution model was developed to examine the field-induced performance of anisotropic magnetorheological elastomers. The developed model was based on the assumption that the iron particles in magnetorheological elastomers aggregate into a large number of parallel body-centered tetragonal structure columns whose length obeys the Gaussian distribution. By using multi-pole approximation with local field effect and taking into account the nonlinearity and saturation of particle magnetization, the field-induced shear modulus was calculated as a function of distribution and dimension of the particle structures, the external magnetic field and the dynamic shear strain. Compared with other modes as well as the published experimental results, this model shows a remarkable improvement in accurately predicting the behavior of the magnetorheological elastomers.     

Importance of depletion interactions for structure and dynamics of ferrofluids

The influence of attractive depletion forces on the structure and dynamics of ferrofluids is studied by computer simulations. In the presence of a magnetic field, we find that sufficiently strong depletion forces lead to an assembly of particle chains into columnar structures with hexagonal ordering inside the columns. In a planar shear flow, this ordering is destroyed, leading to strong shear thinning behavior. A pronounced anisotropy of the shear viscosity is observed. The viscosity is found to be largest when the magnetic field is oriented in the gradient direction of the flow.     

Rheological properties of polydisperse magnetic fluids. Effect of chain aggregates

A theoretical model of medium-density polydisperse magnetic fluids is proposed. The model takes into account that the major fraction of particles in typical ferrofluids is characterized by a magnetic core diameter of about 10 nm. In addition, there is a certain proportion of large particles with a core diameter of about 16 nm. As a result of the magnetic dipole interaction, the large particles form chain aggregates. Small particles, for which the magnetic dipole interaction energy (both with each other and with large particles) is smaller than the thermal energy, remain in the individual nonaggregated state. The distribution of chains with respect to the number of (large) particles and some rheological characteristics of the ferrofluids are determined. The proposed model is capable of explaining, in principle, the giant magnetoviscosity effect and a strong dependence of the rheological properties of ferrofluids on the shear rate observed in some recent experiments.     

Influence of composition of carbonyl iron particles on dynamic mechanical properties of magnetorheological elastomers

Magnetorheological elastomers (MRE) are known as smart materials. However, the magnetorheological (MR) effect of MRE is not high enough at present, which limits its engineering applications. Prior studies have shown that magneto-induced shear storage modulus and MR effect were mainly determined by the performance of the ferromagnetic particles. In this paper, MRE samples were prepared by carbonyl iron particles (CIP) of different compositions based on silicon rubber under external magnetic field. Their microstructures were observed using an optical digital microscope and a scanning electron microscope. The dynamic mechanical properties of MRE samples were measured using a modified dynamic mechanical analyzer under varying magnetic field strength and frequency. The results show that the carbon content of CIP have a greater impact on the dynamic mechanical properties of MRE. The magneto-induced shear storage modulus and MR effect can be increased by selecting CIP of low carbon content. In addition, the damping property is also significantly influenced by the carbon content of the CIP. This study is expected to provide guidance for fabrication of high performance MRE.     

A Diffusion Model of Field-Induced Aggregation in Ferrofluid Film

By introducing Arrhenius behaviour to the ferroparticles on the surface of the aggregated columnar structure in a diffusion model, equilibrium equations are set up. The solution of the equations shows that to keep the aggregated structures stable, a characteristic field is needed. The aggregation is enhanced by magnetic fields, yet suppressed as the temperature increases. Analysing the influence of the magnetic field on the interaction energy between the dipolar particles, we estimate the portion of the diffusing particles, and provide the agreeable ratio of the column radius over the centre-to-centre spacing between columns in a hexagonal columnar structure formed under a perpendicular magnetic field.     

In situ imaging of field-induced hexagonal columns in magnetite ferrofluids

Field-induced structures in a ferrofluid with well-defined magnetite nanoparticles with a permanent magnetic dipole moment are analyzed on a single-particle level by in situ cryogenic transmission electron microscopy (2D). The field-induced columnar phase locally exhibits hexagonal symmetry and confirms the structures observed in simulations for ferromagnetic dipolar fluids in 2D. The columns are distorted by lens-shaped voids, due to the weak interchain attraction relative to field-directed dipole-dipole attraction. Both dipolar coupling and the dipole concentration determine the dimensions and the spatial arrangement of the columns. Their regular spacing manifests long-range end-pole repulsions that eventually dominate the fluctuation-induced attractions between dipole chains that initiate the columnar transition.     

ANALYSIS OF PARTICLE-PARTICLE FORCES IN ELECTRORHEOLOGICAL FLUIDS

The Rayleigh identity, based on a multipole expansion theory, is extended to analyse the forces between particles in an electrorheological system. The shear modulus for chains of particles arrayed on a square lattice is calculated. It is found that the modulus increases linearly with the ratio of dielectric constants of the dispersed particles to that of the continuous phase; as the ratio becomes larger, contrary to the expectations from a simple dipole approximation, the modulus would saturate. In the case of conducting particles, the modulus varies with the frequency of the applied field. In a limiting case of perfectly conducting particles, the conductivity is also considered. It is found that the particle-particle forces are extremely sensitive to their separations from each other.