磁流变弹性体基于卡方分布的磁偶极子模型

为了精确描述磁流变弹性体的磁致效应,从而使磁流变弹性体应用于工程实际,基于磁偶极子理论,结合铁磁颗粒在磁流变弹性体中的分布特点,引入分布参量n,假设相邻铁磁颗粒的间距满足卡方分布,提出基于卡方分布的磁偶极子模型,推导了磁致剪切模量的表达式。该模型弥补了"均匀分布"假设的不足且形式简单,适于工程应用,同时可以精确反映出各因素对磁流变弹性体磁致效应的影响规律,其中分布参量和外加磁场强度是影响磁致效应的关键因素。     

柱状和层状结构磁流变弹性体剪切模量的数值计算

从颗粒间的磁相互作用能出发,计算了磁流变弹性体的磁致剪切模量.考虑了链内颗粒和相邻链中颗粒的影响,修正了磁流变弹性体的磁偶极子模型.构建了体心立方结构和简单立方结构计算模型,分别考虑了柱和层状聚集结构的大小以及其间距,对含柱状结构和层状结构的磁流变弹性体的力学性能进行了计算.计算结果表明,单层模型的磁流变弹性体磁致剪切模量比单链模型的预报值高约48%.在提高磁流变弹性体的磁致剪切模量方面,层状结构优于柱状结构.     

基于链化模型的磁流变弹性体磁致效应影响因素分析

磁流变弹性体是磁流变材料中新的一员,它是由可磁化的铁磁性颗粒和橡胶基在外加磁场下固化而成的,固化后铁磁性颗粒在基体中形成链状等有序结构,因此其力学、电学、磁学等性质可由外加磁场控制.目前限制磁流变弹性体的大规模应用的一个重要因素是其磁致效应还不能够满足工程需要,制备出具有更大磁致效应的磁流变弹性体材料是当前的紧迫任务之一.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效应的影响,包括颗粒链的初始倾斜角、外加磁场强度、剪应变大小等,为材料的制备和性能的优化提供理论上的帮助.     

磁流变胶泥磁致流变学行为微观动力学模型研究

针对磁流变胶泥材料在外加磁场作用下悬浮相内磁相互作用机理和材料设计参数不确定的问题,根据磁流变材料微观偶极子理论,建立铁磁颗粒在磁场中的平板单链模型,结合链与磁场夹角之间满足指数分布的规律,得出了磁流变胶泥材料剪切屈服应力的理论表达式;根据磁流变胶泥材料的实验数据,对理论分析模型进行了修正,使模型能更好地预测不同影响因素下的剪切屈服应力值;对磁流变胶泥剪切屈服应力与铁磁颗粒、质量分数、基体粘度等因素进行分析,为高性能磁流变胶泥材料的设计、制备提供理论指导。     

基于颗粒动力学演化的磁弹体力磁耦合数值模型

基于颗粒动力学演化的磁致微观结构建立了横观各向同性磁弹体（MREs）三维几何模型,在考虑了磁场和变形耦合作用的基础上,依据当前MREs研究较热的两种磁颗粒作用模型构建了颗粒的控制方程,从而建立MREs多颗粒的力磁耦合数值模型,从细观角度研究MREs的力磁耦合性能。数值模型和剪切实验对比表明,点偶极子作用力模拟的MREs磁流变效应远低于实验数据,而多极作用力在量级上更接近实验数据。基于构建的数值模型,还详细探究了磁感应强度和颗粒浓度对磁致剪切模量的影响,模拟结果和实验趋势吻合较好,颗粒体积分数在20%附近时,相对磁流变效应达到最大。     

基于链化模型的磁流变弹性体磁致压缩模量分析

基于链化模型的磁流变弹性体,在受到压缩形变时,基体中的颗粒链会弯曲变形,变形后相邻颗粒间的相互作用力沿压缩方向和垂直于压缩方向的分量均不同。分析了压缩模式下链弯曲对磁流变弹性体磁致压缩模量的影响。随着磁场强度和压缩应变的增大,磁流变弹性体的磁致压缩模量在压缩方向的磁致力分量和垂直于压缩方向的磁致回复力的共同作用下逐渐变大。     

磁流变弹性体力磁耦合本构关系的研究进展

磁流变弹性体是一类力学特性能够被外磁场可逆调控的新型智能复合材料。将微米尺寸的磁性颗粒填充到橡胶类聚合物基体中制备的磁弹体材料,其模量、阻尼和形变可以由外加磁场快速、连续、可逆改变。目前,基于动力学实验的宏观力学元素组合模型分析方法、微观偶极子力学分析和宏观连续介质力学描述成为分析磁感应多场耦合复合材料本构关系的主要方法。同时,数值模拟也成为研究磁流变材料的颗粒聚集结构演化和磁致伸缩效应的有效手段。本文侧重于介绍磁弹体智能材料力磁耦合的基本理论和研究方法,总结相关研究工作并探讨研究趋势,为磁敏类多功能材料的应用研究提供理论基础。     

基于RVE方法的磁流变弹性体力学行为的预测

磁流变弹性体是一种在不同磁场条件下力学性能可控的智能材料。磁流变弹性体的模量为无磁场下材料的模量和磁场诱导产生的模量之和。运用基于周期性边界条件的代表性体积单元法,用理论和有限元两种方法对比研究了无磁场下磁流变弹性体的宏观弹性模量和剪切模量。通过引入Maxwell应力张量,研究了磁流变弹性体在不同磁感应强度下对磁场诱导产生的弹性模量和剪切模量的影响。用RVE的方法证明了,磁流变弹性体由于磁场诱导产生的弹性模量是负数,但总的弹性模量是正数,且其大小随磁感应强度的增大而增大。而其初始剪切模量则始终为正数,其大小随着磁场强度的增大而增大,这与偶极子理论推导得到的结论一致。     

基于Digimat中RVE模型的磁流变弹性体的磁致压缩力学性能的数值模拟

磁流变弹性体的宏观压缩力学性能受其组分材料的体积比、形态和外加磁场等因素的影响。从3方面系统的研究了磁流变弹性体在磁场和压缩条件下的静态磁致力学性能。首先运用Digimat软件中的均匀化方法和RVE研究零磁场条件下的磁流变弹性体力学性能。然后研究了磁场条件下各向同性和各向异性磁流变弹性的磁致力学性能。最后利用实验方法研究磁流变弹性体的力学性能。得到了磁场的施加使得各向同性和颗粒成链磁流变弹性体的压缩模量增大,同时颗粒成链比各向同性磁流变弹性体的磁流变效应更大的结论。     

磁流变弹性体的磁致性能

设计了一种聚氨酯基磁流变弹性体,利用设计的磁致力学性能测试装置,对剪切状态下磁流变弹性体的磁流变效应进行了系统的测试。结果表明,相对磁流变效应随着外加磁场强度的增大而增大,随着激励振幅的增大而减小。预加载位移的大小直接决定这相对磁流变效应,过大的变形会导致相对磁流变效应急剧减小。激励频率对相对磁流变效应影响不大。     

Investigation on magnetorheological elastomers based on natural rubber

Magnetorheological Elastomers (MR Elastomers or MREs) are a kind of novel smart material, whose mechanical, electrical, magnetic properties are controllable under applied magnetic fields. They have attracted increasing attentions and broad application prospects. But conventional MREs are limited to wide applications because their MR effects and mechanical performances are not high enough. This paper aims to optimize the fabrication method and to fabricate good natural rubber based MREs with high modulus by investigating the influences of a variety of fabrication conditions on the MREs performances, such as matrix type, external magnetic flux density, and temperature, plasticizer and iron particles. Among these factors, the content of iron particles plays a most important contribution in shear modulus. When the iron particle weight fraction is 80% and the external magnetic flux density is 1 T, the field-induced increment of shear modulus reaches 3.6 MPa, and the relative MR effect is 133%. If the iron weight fraction increases to 90%, the field-induced increment of shear modulus is 4.5 MPa. This result has exceeded the best report in the literatures researching the MREs on the same kind of matrix. The dynamic performances of MREs were also experimentally characterized by using a modified Dynamic Mechanical Analyzer (DMA) system. The effects of strain amplitude and driving frequency on viscoelastic properties of MREs were analyzed.     

硅橡胶基磁流变弹性体的研制

磁流变弹性体是一种新型的智能材料,它的力学性能可以受磁场控制,在需要变刚度的器件等方面有着广泛的应用前景.本文总结了一些制备高性能磁流变弹性体的基本方法,尝试采用不同的组份制备了以硅橡胶为基体的高性能磁流变弹性体.并使用改进的动态机械分析仪来测试分析所制样品的磁致剪切储能模量和损耗因子等性能.结果表明,所制备的磁流变弹性体在600mT磁感应强度下的剪切储能模量相对变化可达到501%.     

Energy conversion in magneto-rheological elastomers

Abstract

Magneto-rheological (MR) elastomers contain micro-/nano-sized ferromagnetic particles dispersed in a soft elastomer matrix, and their rheological properties (storage and loss moduli) exhibit a significant dependence on the application of a magnetic field (namely MR effect). Conversely, it is reported in this work that this multiphysics coupling is associated with an inverse effect (i.e. the dependence of the magnetic properties on mechanical strain), denoted as the pseudo-Villari effect. MR elastomers based on soft and hard silicone rubber matrices and carbonyl iron particles were fabricated and characterized. The pseudo-Villari effect was experimentally quantified: a shear strain of 50 % induces magnetic induction field variations up to 10 mT on anisotropic MR elastomer samples, when placed in a 0.2 T applied field, which might theoretically lead to potential energy conversion density in the mJ cm^-3 order of magnitude. In case of anisotropic MR elastomers, the absolute variation of stiffness as a function of applied magnetic field is rather independent of matrix properties. Similarly, the pseudo-Villari effect is found to be independent to the stiffness, thus broadening the adaptability of the materials to sensing and energy harvesting target applications. The potential of the pseudo-Villari effect for energy harvesting applications is finally briefly discussed.     

磁流变弹性体隔振缓冲器设计及实验研究

磁流变弹性体是一种剪切模量可由外加磁场控制的智能材料,在半主动控制、着陆缓冲等方面具有广阔的应用前景。本文在此基础上探讨了基于磁流变弹性体的隔振器的磁路计算方法和结构设计准则,并设计出隔振器原型样机,通过改变控制电流和正弦波激振频率,考察隔振器的振动控制响应特性。实验结果表明在一定的频率范围内,该隔振器具有良好的隔振效果。     

Dynamic viscoelastic modeling of magnetorheological elastomers

A micromechanics-based viscoelastic constitutive model is proposed to estimate the zero-magnetic-field- and magnetic-field-dependent dynamic shear stiffness and damping behavior for magnetorheological elastomers (MREs). The effect of imperfect interfacial condition between the ferromagnetic particles and the elastomeric matrix on those properties is incorporated in the proposed model. A concept of effective volume fraction of particles is introduced to take into account the particle agglomeration in MREs. The magnetic dipole interaction is further employed to evaluate the magnetic-field-induced increase in shear stiffness of MREs. Numerical simulations are conducted and compared with experimental data to verify the proposed model.     

磁流变液及其阻尼器的制备与性能研究

研究了一种新型MR液和MR阻尼器;用振动样品磁强计测试了MPS-MRF-25羰基铁粉的磁性能;用磁流变仪测试了MR液的表观粘度和磁致剪切应力;用静置沉降法分析了MR液的抗沉降稳定性;用电液伺服材料性能试验机测试了MR阻尼器的性能.结果表明MPS-MRF-25羰基铁粉具有优良的磁性能;以其制备的MR液具有较好的抗沉降稳定性和温度稳定性;MR阻尼器在2A电流下可以达到15kN的阻尼力.     

Novel Magnetorheological Suspensions Based on Co-Phthalocyanine/Fe Nanocomposite Particles

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Rheological Characterization of MR Polishing Fluid Used for Silicon Polishing in BEMRF Process

The finishing mechanism of the ball-end magnetorheological finishing (BEMRF) process mainly depends on the stiffened hemispheroid, which is formed at the tool tip. Magnetorheological (MR) polishing fluid imparts strength to the polishing spot because of the effect of magnetic field strength. Behavior of this polishing fluid mainly depends on the size and shape of its constituents, volume concentration, particle size distribution, and applied magnetic field strength. A detailed study was undertaken on the role of carbonyl iron particle (CIP) size on the rheological behavior of the MR polishing fluid under various magnetic flux densities. Evaluation of the behavior of MR polishing fluid for silicon polishing was attempted through designing and fabrication of a parallel-plate magnetorheometer. Rheological characterization study was carried out using the Casson fluid model and the MR polishing fluid rheological properties, namely field-induced yield stress and shear viscosity were evaluated.     

磁流变液流变特性的数值模拟分析

建立了微观颗粒的动力学模型,提出了相应的算法,模拟了二维状态下颗粒成链及其剪切流动过程,表明剪切过程中存在旧链断裂和新链形成,得到了流动时磁流变液的剪切应力,并模拟了高剪切速率下微结构的演变过程,发现新链形成速度小于旧链断裂速度,出现了剪应力下降现象.