镍粉填充型磁流变弹性体压敏与温敏电阻特性研究

磁流变弹性体具有良好的压致电阻敏感特性和温度-电阻敏感特性,在柔性触觉传感领域表现出应用潜力。以羰基镍粉作为导电填充颗粒,硅橡胶作为基体,分别制备了镍粉随机分散和磁致链化的磁流变弹性体样品,测试了磁流变弹性体在不同温度下的压力-电阻特性和定值压力下的温度-电阻特性。分析了镍粉体积分数、外加电压、镍粉磁致链化对磁流变弹性体压阻特性的影响和不同温度下磁流变弹性体的压敏电阻规律。研究表明,体积分数为26%的磁流变弹性体在较低加载电压下,不仅其对数电阻与压力具有较好的线性关系,而且压力感知范围较宽;磁致链化可显著提高MRE压阻灵敏度;在不同恒定压力下,温度-电阻曲线具有一致的变化规律,呈现出先降后升的特性。     

磁场退火对La_(0.7)Sr_(0.3)MnO_3低场磁电阻增强效应的研究

为了提高La0.7Sr0.3MnO3的低场磁电阻效应,将样品进行了磁场退火处理。实验结果表明,磁场退火并没有改变样品的磁矩,但对其磁各向异性产生了较大的影响。与零磁场下退火的样品相比,磁场退火样品的磁电阻明显提高。这种增强效应在低磁场下更加明显,在0.1 T的外磁场下,磁退火样品的磁电阻比零场退火的提高了140%。利用自旋极化隧穿机制解释了这种增强的磁电阻效应。     

制备具有“跳跃效应”Terfenol—D的研究

利用浮区法和布里奇曼法制备Ｔｂ０．３Ｄｙ０．７Ｆｅ１．９５的Ｔｅｒｆｅｎｏｌ－Ｄ，通过磁致伸缩系测定，发现利用浮区法制备的样品在一定的压应力下有“跳跃效 ”，利用布里奇曼法制备的样品具有较大的压力效应但没有出现“跳跃效应”。     

磁场对Ni/硅橡胶复合材料交流电导率及介电性质的影响

采用硅橡胶（110型）与金属（镍粉）按质量比为1∶2.7进行配料, 应用室温二次固化合成Ni/硅橡胶压敏复合材料样品。室温下测量了样品的压阻效应, 比较了外加0.024 T磁场前后样品的介电性质。结果表明, 当压强从3.75kPa到312.5kPa时, 样品直流电阻率下降了8个数量级。与加磁场前相比, 0.024T的磁场使得低频(40~104Hz)交流电导率提高了2.46倍, 介电常数提高了20%, 介电损耗提高了2倍, 这主要是由复合材料中铁磁绝缘体铁磁颗粒膜的隧道磁电阻效应以及磁电耦合引起的。撤去磁场后交流电导率、介电常数和介电损耗均不能回到加磁场前的初始值, 这与Ni粉的铁磁性有关。Ni/硅橡胶压敏复合材料的压阻、 磁电阻效应及磁电耦合等物理性质在磁传感器件、 信息储存等领域有潜在的应用价值。      

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.     

硅橡胶/镍粉复合材料的力敏性能

为探讨硅橡胶/镍粉复合材料的力敏性能,研究了不同掺量镍粉填充硅橡胶复合材料试样的电阻随拉应力、压应力的变化规律,并结合扫描电镜观察进行了机理分析。研究结果表明,所制备的硅橡胶/镍粉复合材料试样的电阻随拉、压应力的增加而减小,镍粉掺量越大,电阻对应力变化越敏感;在2MPa的拉、压应力作用下,硅橡胶/镍粉复合材料试样的电阻变化最大分别可达11个和12个数量级。硅橡胶/镍粉复合材料优异的力敏效应是由量子隧道效应导致的。     

FeGa/BTO/FeGa层状复合结构中的磁电效应

采用区域熔炼法制备了FeGa磁致伸缩材料并测量了其磁致伸缩性能.利用该材料制备了FeGa/BTO/FeGa层状复合结构,并对该样品的磁电性能进行了系统研究.结果表明,该材料在共振频率95kHz下,磁电性能高于低频下性能7～10倍.磁电电压随直流偏磁场的变化发生明显变化,出现5.97×104A/m的优化偏置场,这主要是由FeGa层的压磁系数q随偏磁场的变化所致.3层复合材料的磁电系数与交流驱动场变化呈线性关系.另外,较薄的BTO压电层可以提高压应力,从而获得较高的磁电性能.     

Fe为过渡层的Co/Cu/Co三明治巨磁电阻效应的研究

用超高真空电子束蒸发方法成功制备了以不同厚度Fe为过渡层的Co/Cu/Co三明治巨磁电阻样品,与以Cr为过渡层的Co/Cu/Co三明治巨磁电阻样品比较,样品的矫顽力大大减小,因而样品的磁灵敏度有了较大地提高。当Fe过渡层的厚度为7nm时样品的磁电阻值最大。另外,温度更强烈地影响以Fe为过渡层样品的磁电阻值,在77K下样品的磁电阻曲线表现出明显的不对称性,它来源于低温下fcc Fe过渡层的反铁磁性转变。     

[Co80Fe10Ni10]20Cu80-xCrx块体合金的巨磁电阻效应研究

在氩气气氛中用熔炼法制备了[Co80Fe10Ni10]20Cu80-xCrx系列Cu基巨磁电阻合金．通过光学显微镜、透射电子显微镜、场致发射扫描电镜和电子探针研究了[Co80Fe10Ni10]20Cu80-xCrx合金在1000℃均匀化处理6h后水淬．以及随后的300～700℃，30～150min回火处理的微观结构及组分。用直流四探针法测量了合金的室温巨磁电阻效应(GMR)。结果表明．合金在回火时从基体相中析出了高度弥散的含Fe、Ni、Co的纳米磁性新相。回火温度对合金的磁电阻效应影响很大，样品在600℃温度回火90min时，合金的室温GMR效应最好，可达8．61％。少量合金元素Cr的添加替代(Cr代Cu)消除了Co-Fe-Ni—Cu合金中的混溶裂隙，改善了合金的加工性但也降低了合金的磁电阻效应。     

粘结Sm-Dy-Fe合金的磁致伸缩性能研究

采用粘结法制备了Sm_(1-x)Dy_xFe_2合金样品,测量了粘结合金样品的静态磁致伸缩、动态磁致伸缩系数、增量磁导率和磁-机械耦合系数,研究了磁致伸缩性能等随磁场H的变化规律。发现当x<0.12时合金的低场磁致伸缩随x的增加而增加,高场磁致伸缩随x的增加而降低。棒状Sm_(0.88)Dy_(0.12)Fe_2合金在H=200kA/m时的磁致伸缩达405×10~(-6),磁-机械耦合系数和动态磁致伸缩系数分别达到0.34和1.28nm/A,因而粘结Sm_(0.88)Dy_(0.12)Fe_2合金具有一定的实用价值。     

Smart composites of urethane elastomers with carbonyl iron

Smart composites based on carbonyl-iron particles in a polyurethane matrix, known as magnetorheological elastomers (MREs), were manufactured and studied. The influence of ferromagnetic particle content and particle arrangement in relation to an external magnetic field was investigated. Several different elastomers with different stiffnesses were used as matrices. It was found that the structure of a fabricated MRE depends on the viscosity of the matrix before curing and the flux density of the applied magnetic field. Two different magnetic field strengths were used: 0.1 and 0.3 T. The amount of carbonyl iron particles was varied from 1.5 to 33.0 vol%. Scanning electron microscopy technique was used to observe MRE microstructure. The particles’ orientation and their arrangement were also investigated by vibrating sample magnetometer. A correlation was found between MRE microstructure and magnetic properties. Compression tests on cylindrical samples in the presence and absence of a magnetic field showed that a magnetic field increased the stiffness of the material. Additionally the rheological properties of MREs were tested in a magnetic field. It was found that the amount of ferromagnetic particles and their arrangement have a significant influence on the rheological properties of MREs. The highest relative change of storage modulus under 200 mT magnetic field, equal to 282%, was recorded for samples with 11.5 vol% of particles.     

Fatigue life prediction of magnetorheological elastomers subjected to dynamic equi-biaxial cyclic loading

Prediction of fatigue life is of great significance in ensuring that dynamically loaded rubber components exhibit safety and reliability in service. In this text, the dynamic equi-biaxial fatigue behaviour of magnetorheological elastomer (MREs) using a bubble inflation method is described. Wöhler (S–N) curves for both isotropic and anisotropic MREs were produced by subjecting the compounds to cycling over a range of stress amplitudes (σ_a) between 0.75 MPa and 1.4 MPa. Changes in physical properties, including variation in stress–strain relations and complex modulus (E*) during the fatigue process were analysed. It was found that the complex modulus of MRE samples decreased throughout the entire fatigue test and failure took place at a limiting value of approximately 1.228MPa ± 4.38% for isotropic MREs and 1.295 ± 10.33% for anisotropic MREs. It was also determined that a dynamic stored energy criterion can be used as a plausible predictor in determining the fatigue life of MREs.     

磁场对磁流变弹性体表面特性的影响

为探究磁流变弹性体在磁场作用下的表面特性,制备体积分数为5%,10%,15%,20%,25%和30%的磁流变弹性体(MRE)样本,分别在施加磁场前后进行金相显微镜、白光干涉仪表面观察实验以及滑动摩擦验证实验。表面观察实验表明:样本的表面磁性颗粒随组分体积分数的增加而增加,并且各组分样本表面在磁场下粗糙度均降低,5%MRE的样本降低最多,约20%;摩擦实验结果表明:摩擦因数随着体积分数增加和在磁场作用下均出现降低趋势,30%MRE的摩擦因数相比于5%的摩擦因数约减小了38%, MRE表面铁磁颗粒含量是影响其摩擦特性的主要因素。     

各向同性磁流变橡胶材料的摩擦实验研究

分别从宏观和微观角度研究磁场对各向同性磁流变橡胶摩擦性能的影响.搭建了磁流变橡胶的摩擦实验平台,在外加磁场下进行滑动摩擦实验.实验结果表明,磁流变橡胶在轻载且低速条件下,摩擦系数随正压力增大呈减小趋势,而且磁场会使得磁流变橡胶表面的摩擦系数减小,且减小趋势随羰基铁粉体积比的增加呈现非线性变化,当羰基铁粉体积比为10％、正压力为0.25N、磁场强度为250 mT时,其摩擦系数变化最大,减小约25％.通过金相显微镜进一步观测施加磁场前后的磁流变橡胶表面,检测表明磁场使得羰基铁粉在磁流变橡胶表面产生聚集,从而使其表面材料属性及微结构发生变化,该变化是促使磁流变橡胶的摩擦性能发生改变的重要原因.     

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。     

Comparison of dynamic properties of magnetorheological elastomers with existing antivibration rubbers

Tan δ and energy dissipated during hysteresis testing of isotropic and anisotropic MREs containing silane modified iron sand particles in a natural rubber matrix were compared with existing antivibration rubbers. Tan δ was measured using dynamic mechanical analysis (DMA) over a range of frequency (0.01–130 Hz), strain amplitude (0.1–4.5%), and temperature (−100–50 °C). Energy dissipated was measured using a universal tester under cyclic tensile loading. The chosen antivibration rubbers for comparison contained different contents of carbon black filler (30, 50 and 70 phr) in a natural rubber matrix. It was found that energy absorption for comparative samples was generally higher than isotropic and anisotropic MREs over the range of frequency and strain amplitude explored, as well as in hysteresis testing and this was believed to be largely due the presence of carbon black in the formulation. Further assessment was carried out on materials that were the same as anisotropic MREs except they had additions of carbon black. The energy absorption was found higher than comparative samples with the same carbon black contents, supporting the use of iron sand to improve damping. However, trends for energy absorption at around T_g were found to reverse which is considered to be due to the segmental motion of rubber chains being by far the most significant influence on energy absorption in the glass transition zone.     

取向磁场对钴颗粒填充硅橡胶磁流变弹性体动态黏弹性的影响

为了研究取向磁场强度对磁流变弹性体（MRE）动态黏弹性的影响规律及影响机制,采用溶剂热法制备球状钴颗粒,SEM和XRD表征结果显示,其粒径为1~2 μm,呈密排六方结构。以硅橡胶为基体,以钴颗粒为填充相,分别在0 mT、480 mT、1 154 mT取向磁场强度下制备MRE,并在不同工况下测试其动态黏弹性。实验结果表明,Co颗粒填充的MRE微观结构的有序性随取向磁场强度增大而增加,其储能模量G'、损耗模量G ″和磁流变效应也随之提高;当取向磁场强度增大到一定程度,由于有序结构趋于稳定,动态黏弹性随取向磁场的变化较小。     

Mechanical properties of magnetorheological elastomers under shear deformation

In this paper, urethane magnetorheological elastomers (MREs) consisting of carbonyl-iron particles in a polyurethane matrix were studied. The volume fraction of particles was equal to 11.5%. Three types of ferromagnetic particles were used, with average particle size ranging from 1 to 70 μm. The elastic (storage) modulus G′ was measured as a function of angular frequency ω and strength of magnetic field. The measured G′ values were approximated with empirical model. The highest magnetorheological effect has been found for samples with 6–9 μm carbonyl-iron powder. The highest increase in the yield stress is observed for samples with particles aligned at 30° to the magnetic field lines. It has been found that rheological properties strongly depend on the MRE microstructure, in particular on the size/shape of particles and their arrangement. By optimizing the particles size, shape and alignment, the stiffness of MREs has been increased under applied magnetic field.     

Implementation of functionalized multiwall carbon nanotubes on magnetorheological elastomer

This work studies the effects of loading various functionalized multiwall carbon nanotubes (carboxyl, –COOH-MWCNTs) on the morphological and the field-dependent rheological properties of magnetorheological elastomers (MREs). A new type of MRE, which is reinforced by various loading from 0 to 1.5 wt% of COOH-MWCNT, is fabricated and experimentally investigated. The morphology of COOH-MWCNT and MRE with COOH-MWCNTs is characterized using field emission scanning electron microscopy and transmission electron microscopy. The results indicate that the COOH-MWCNTs are well embedded and dispersed randomly in the MRE structures. The rheological properties under different magnetic fields are evaluated using parallel plate rheometers. The influence of COOH-MWCNT content on the viscoelastic performance of the MRE is systematically investigated. It is found that when a higher content of COOH-MWCNT (up to 1.0 wt%) is added in the MRE, the MRE exhibits a higher MR effect of up to 17.5%. It is also shown that COOH-MWCNT acts as a reinforcing agent that leads to an enhancement in MR performance.     

磁流变弹性体调频吸振器的研制

传统的动力吸振器吸振频带较窄,限制了稳定性和吸振效果的提高,影响了其应用范围.而磁流变弹性体是一种剪切模量可由外加磁场可控的智能材料.本文利用磁流变弹性体作为动力吸振器的弹性元件和阻尼元件,并采用移频调谐的控制方法,设计了一种可调频的动力吸振器.对其进行的动力特性的研究表明,该吸振器移频范围较宽,在较宽的吸振带宽内具有较好的吸振效果.