赵慧婷
, 章鹏
ZHAO Huiting, ZHANG Peng
中图分类号: TB324
文章编号: 1005-3093(2016)06-0457-08
通讯作者:
收稿日期: 2015-09-25
网络出版日期: 2016-06-25
版权声明: 2016 《材料研究学报》编辑部 《材料研究学报》编辑部
基金资助:
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摘要
制备了4种钕铁硼粉填充型磁敏弹性体和4种羰基铁粉与钕铁硼粉混合填充的磁敏弹性体, 对上述磁敏弹性体进行不同强度充磁, 并利用数码显微镜观察其微观结构, 使用振动样品磁强计测试了样品的磁化特性曲线, 采用流变仪对磁敏弹性体的力学性能进行测试, 分析不同充磁强度对钕铁硼粉填充型磁敏弹性体磁控力学性能的影响, 以及硬磁颗粒的质量分数与剩磁对磁敏弹性体磁控力学性能的影响。结果表明, 充磁强度越大, 钕铁硼粉填充型磁敏弹性体力学性能受磁场影响越大, 适量的硬磁颗粒、增大充磁能提高磁敏弹性体磁控范围。
关键词：
Abstract
Two types of magneto-active elastomers (MAEs) with fillers of NdFeB powder and powder mixture of carbonyl iron and NdFeB are prepared respectively, and then they were all magnetized by different magnetization intensities. The microstructure of MAEs is characterized by KEYENCE VHX-600 digital microscope. The magnetization characteristic curves and the mechanical properties of MAEs weremeasured by VSM and MCR-301 rheometer respectively. The influence of the fraction and magnetic remanence intensity of the hard magnetic fillers on the magneto-control mechanical behavior of the MAEs was carefully examined.The results demonstrated that the mechanical properties of MAEs filled with NdFeB powder were affected strongly by the intensity of magnetic field adoped for magnetization treatments. An appropriate amount of the hard magnetic fillers and the magnetization by higher magnetic field intensity are beneficial to the improvement of the shear storage modulus of the MAEs.
Keywords：
磁敏弹性体(Magneto-active elastomer, MAE)是一种新型的磁控智能材料, 它是将微米量级的铁磁性颗粒分散于高分子聚合物中, 在特定工艺下固化而成的力学性能受外加磁场控制的弹性体材料[1-4]。利用磁场来控制磁敏弹性体力学性能, 在减振、降噪等领域具有潜在的工程应用, 目前磁敏弹性体已初步应用于可变刚度轴衬、减振器、阀门等领域[5-7]。传统的磁敏弹性体采用羰基铁粉等软磁颗粒作为填充因子, 国内外学者针对软磁颗粒的形状、粒径、质量分数、磁学性质等对磁敏弹性体磁控力学性能的影响作了大量研究[8-10], 关于磁敏弹性体的研究包括磁控力学性能、电学性能等均是基于软磁颗粒填充材料开展的[11-14]。近年来, 一些学者开始将关注点转向硬磁颗粒填充。Stepanov 等人[15-18]不仅研究了纯NdFeB颗粒填充的磁敏弹性体的磁化特性曲线, 还探索了应变、频率以及外加磁场方向对材料磁致模量的影响。Borin等人[19]发现形变与剩磁对磁化后纯NdFeB颗粒填充的磁敏弹性体的拉伸模量有影响, 样品磁化后拉伸模量最大变化量为360%。虽然Stepanov 等人针对硬磁颗粒填充的磁敏弹性体作了一系列研究, 但其使用的材料弹性模量很小, 数量级仅为104 Pa, 机械性能不理想, 并且磁敏效应有限, 还无法投入应用。目前关于硬磁颗粒填充的磁敏弹性体研究还处于起步阶段, 针对其磁控力学性能的认识还很不足, 因此有必要进一步探讨, 为开发新型的磁控力学材料及器件提供技术基础。
采用羰基铁粉(型号: SQ, 粒径3.5 μm, BASF, 德国)和钕铁硼粉(粒径50 μm, 四川绵阳西磁有限公司)作为填充颗粒, 双组分室温硫化硅橡胶(深圳红叶杰科技)作为基体, 硅烷偶联剂作为钕铁硼粉的表面处理剂, 二甲基硅油作为增塑剂, 制备磁敏弹性体。
钕铁硼粉表面预处理: 由于钕铁硼颗粒粒径较大, 属亲水性, 硅橡胶为亲油性, 为提高钕铁硼粉与硅橡胶的结合程度, 采用硅烷偶联剂对钕铁硼粉作表面预处理。将钕铁硼粉在硅烷-乙醇混合溶液中浸泡搅拌10 min, 再置于真空干燥箱中在80℃下烘干1 h。
纯硬磁填充型磁敏弹性体的制备工艺流程如图1所示。首先根据配比称取各组分, 将称好的钕铁硼颗粒预处理, 再与硅油混合, 加入硅橡胶A组分、(mA+mSimethicone)
制备混合填充的磁敏弹性体的步骤与各向同性硬磁填充型磁敏弹性体一样, 唯一区别在于填充颗粒为钕铁硼粉与羰基铁粉。
为研究硬磁填充的磁敏弹性体的力学性能, 制备硬磁颗粒质量分数为70%的各向同性、各向异性的磁敏弹性体, 制备参数如表1所示。样品编号1对应各向异性硬磁MAE, 2、3、4分别对应不同电压充磁下的硬磁MAE。为探究剩磁大小对混合磁敏弹性体力学性能的影响, 制备了羰基铁粉(60%)+钕铁硼粉(20%)质量分数的混合磁敏弹性体, 样品编号分别为5、6、7、8, 进行不同电压充磁。为便于描述, 本文使用“60%+20%”的简称术语来指代该样品, 下文中其他样品用同样的方式描述。为探索硬磁颗粒质量分数对混合磁敏弹性体力学性能的影响, 制备羰基铁粉+钕铁硼粉质量分数为80%+0、70%+10%、40%+40%的混合磁敏弹性体。
表1 磁敏弹性体的制备参数
Table 1 Preparation parameters of MAEs
| Samples | Carbonyl iron powder | NdFeB powder | A component of RTV-2 | Simethicone | Magnetizing voltage |
|---|---|---|---|---|---|
| No. | /%,mass fraction | /%, mass fraction | /%, mass fraction | /%, mass fraction | /V |
| 1 | 0 | 70 | 15 | 15 | - |
| 2 | 0 | 70 | 15 | 15 | 0 |
| 3 | 0 | 70 | 15 | 15 | 700 |
| 4 | 0 | 70 | 15 | 15 | 1200 |
| 5 | 60 | 20 | 10 | 10 | 0 |
| 6 | 60 | 20 | 10 | 10 | 700 |
| 7 | 60 | 20 | 10 | 10 | 1000 |
| 8 | 60 | 20 | 10 | 10 | 1200 |
磁敏弹性体的动态力学性能表现为弹性体在交变应力(应变)作用下的响应, 通常用剪切储能模量
为了更清楚地认识磁敏弹性体的内部结构, 使用KEYENCE VHX-600数码显微镜对样品1、4的切面进行微观结构拍摄, 放大倍数取500倍, 结果如图2所示。
图2 硬磁填充的磁敏弹性体内部微观结构: (a)各向异性; (b)各向同性
Fig.2 Internal microstructures of MAEs with hard magnetic filler: (a) anisotropy and (b) isotropy
由图2可看出各向异性磁敏弹性体内部虽未呈现出明显的链状结构, 但部分硬磁颗粒沿着磁场方向形成较为有序的结构。部分硬磁颗粒被磁化, 并受到磁场力的作用, 克服基体阻力, 沿着磁场方向有序排列。
为了解充磁对各样品的剩余磁化强度及磁化特性的影响, 使用振动样品磁强计对样品进行磁化特性扫描, 测试磁场范围为0~12 koe, 结果如图3所示。磁化曲线的初始值(H=0)反映了样品的剩余磁化强度。从图3中的初始值可明显看出, 充磁电压越大, 充磁后样品的剩余磁化强度越大。而各向异性硬磁弹性体也呈现出弱磁化现象。因样品内仅NdFeB颗粒可被磁化, 故NdFeB的磁学性能对样品的磁化特性起决定性作用, 图4给出了NdFeB粉末的磁滞回线。由于NdFeB颗粒磁化强度随着磁场的增大而增加, 导致各样品的磁化强度也随着磁场的增加而增加, 且12 koe时磁化强度均未饱和。
使用型号为MCR-301的流变仪在振荡剪切模式下测试硬磁填充的磁敏弹性体。预应力设置为5 N, 应变幅值取0.01%, 频率为10 Hz, 样品尺寸为
图5 硬磁弹性体剪切储能模量与磁场的关系
Fig.5 Magnetic field dependence of shear storage modulus for MAE with hard magnetic filler
由图5可看出各向异性硬磁弹性体的剪切储能模量大于各向同性硬磁弹性体, 原因是各向异性硬磁弹性体内部分硬磁颗粒在固化磁场作用下成链后, 使得样品抵抗剪切应变的能力增强, 宏观表现为剪切模量更大。但各向异性硬磁弹性体的磁场扫描曲线不平缓, 存在一些下降点。由于样品的剪切储能模量表征的是样品的刚度, 并与样品内部结构及颗粒间的相互作用力有关, 而颗粒间的相互作用力不会随着磁场增大而减小, 故上述现象意味着在磁场增大过程中, 样品的内部结构出现了微调导致某些磁场下样品刚度下降, 说明样品内部受力不均, 结构不稳定。这是因为固化磁场磁化了部分硬磁颗粒, 并带动其周围的束缚橡胶在局部形成链状后, 导致弹性体内某些位置链状颗粒聚集, 某些位置出现缺陷。当磁场增大到一定值时, 颗粒链多的地方吸引力足够大到使周围被磁化的粒子靠近, 形成更粗壮的链, 而此结构微调的过程中弹性体较为松散。当流变仪的转子对弹性体施加载荷时, 会感受到弹性体的刚度下降, 因此剪切模量会出现某些分立的下降值。结构微调后的弹性体, 颗粒链间相互作用力随着磁场的增大继续增大, 剪切模量增加。
对于各向同性硬磁弹性体来说, 结合图3、4、5分析可知, 由于未充磁样品的磁化强度在低磁场下较小, 颗粒间的相互作用很弱, 磁场较大时磁相互作用力才足够大到使得剪切模量开始增加。充磁电压越大, 充磁后样品的剩余磁化强度越大, 颗粒间的相互作用越大, 因此剪切模量随着充磁电压的增大而增大。由图5可看出, 充磁样品的剪切模量的最小值并不在磁场扫描曲线的零点, 当测试磁场方向与剩磁方向一致时, 硬磁颗粒的磁化强度随测试磁场的增加而增大, 硬磁颗粒间的相互吸引力增强, 并趋于沿着磁场方向排列, 在竖直方向上将橡胶束缚得更紧, 刚度更大, 因此剪切模量随着测试磁场的增大而增大。而当测试磁场方向与颗粒磁化方向相反时, 硬磁颗粒在力矩的作用下, 趋于旋转到与测试磁场方向一致, 初始排列被破坏, 同时在测试磁场增大的起始阶段, 硬磁颗粒的磁化强度随磁场的增大而减小, 刚度减小, 剪切模量随着测试磁场的增大而减小。当测试磁场增大到一定值后, 硬磁颗粒被反向磁化, 内部颗粒重新排列到达稳定状态, 此时硬磁颗粒的磁化强度随着磁场的增大而增大, 颗粒间的磁相互作用力开始随着测试磁场的增加而增加。因此当测试磁场方向与颗粒剩磁方向相反时, 剪切模量随测试磁场的增加先减小后增大。由图5还可看出, 充磁电压越大, 剪切模量随磁场变化越大, 因为由图3可知, 相同磁场下, 充磁电压越大, 样品的磁化强度与初始值相比变化越大, 说明硬磁颗粒磁化强度变化越大, 颗粒间磁相互作用力变化越大, 反映在剪切模量上变化越大。
综上所述, 与软磁弹性体不同的是, 硬磁弹性体的力学性能表现出对磁场方向的依赖性。由此可知剩磁影响了硬磁弹性体的磁控力学行为。充磁电压越大, 硬磁颗粒的剩磁越大, 剪切模量对测试磁场的作用越敏感, 受测试磁场的影响越大。
为更清楚的认识混合磁敏弹性体, 使用数码显微镜对样品5、8的内部结构进行拍摄, 结果如图6所示。
图6 混合磁敏弹性体内部微观结构: (a) 未充磁; (b)充磁
Fig.6 Internal microstructures of mixed MAEs: (a) non-magnetize and (b) magnetized
因混合磁敏弹性体固化后填充颗粒被基体束缚, 充磁也无法使颗粒摆脱基体的阻力, 因此充磁前后弹性体结构并未改变, 仍为各向同性磁敏弹性体。为观察充磁对混合磁敏弹性体磁学性能的影响, 使用振动样品磁强计对样品进行磁化特性测试, 测试结果如图7所示。由图7中各样品的初始磁化强度可知, 充磁电压越大, 充磁后样品剩余磁化强度越大。
按照3.2节同样的测试条件, 取测试磁场为0~1.2 T, 对样品5~8进行磁场扫描, 实验结果如图8所示。可以看出, 相同磁场下, 混合磁敏弹性体的剪切储能模量随着剩磁的增大而增大。原因是充磁使混合磁敏弹性体内部的硬磁颗粒被磁化, 由于硬磁颗粒具有高剩磁, 充磁后类似“小磁铁”, 即使无外加磁场, 颗粒也会在其周围局部提供一个“内置磁场”, 将包覆在硬磁颗粒表面的羰基铁粉磁化, 在硬磁颗粒“内置磁场”作用范围内, 硬磁颗粒之间、硬磁颗粒与羰基铁颗粒之间、羰基铁颗粒之间都会产生磁相互作用力。充磁电压越大, 剩磁越大, “内置磁场”越大, 样品更结实、紧密。磁致剪切模量和磁流变效应是评价磁敏弹性体的重要参数, 可分别由式1、式2算出, 计算结果如表2所示。
图8 不同充磁电压混合磁敏弹性体的剪切储能模量与磁场的关系
Fig.8 Magnetic field dependence of storage modulus for 60%+20% mixed MAE of different magnetizing voltages
表2 混合磁敏弹性体的初始剪切储能模量、磁致剪切模量、磁流变效应
Table 2 Initial shear storage modulus, magneto-induced shear modulus and MR effect for 60%+20% mixed MAEs
| Samples No. | Initial shear storage modulus ( | Magneto-induced shear modulus ( | MR effect ( |
|---|---|---|---|
| 5 | 0.18 | 1.47 | 817 |
| 6 | 0.27 | 1.50 | 556 |
| 7 | 0.31 | 1.52 | 490 |
| 8 | 0.35 | 1.55 | 443 |
结合图8和表2可知, 对于软/硬磁颗粒质量分数为60%+20%的混合磁敏弹性体来说, 剩磁增加使磁场扫描曲线整体向上平移, 而磁致模量改变不大, 但也表现出了一定的增加趋势, 并且由于受到了初始剪切模量的影响, 磁流变效应随着剩磁增大反而减小。磁致模量与样品总磁相互作用力的变化量直接相关, 当各成分质量分数相同时, 磁致模量主要取决于样品的磁学性能以及内部结构。由之前的分析可知, 充磁前后弹性体内部结构不变, 因此样品的磁学性能起主导作用。由图5可观察到, 充磁电压越大, 硬磁弹性体的磁致模量越大, 即颗粒间作用力变化越大, 故硬磁颗粒间的作用力对混合磁敏弹性体磁致模量随剩磁增加有一定贡献。由图3可知, 相同磁场下, 充磁电压越大, 样品的磁化强度与初始值相比变化越大, 说明硬磁颗粒磁化强度变化越大。弹性体内羰基铁颗粒受到的总磁场为
采用上节同样的测试条件, 对羰基铁粉+钕铁硼粉质量分数为80%+0、70%+10%、40%+40%的混合磁敏弹性体进行磁场扫描, 得到如图9、10所示的实验结果。由图9(a-d)可看出, 硬磁颗粒质量分数大的混合磁敏弹性体的剪切储能模量在低磁场时较大, 由于羰基铁颗粒磁化强度随磁场增加的幅度大于NdFeB, 因此当磁场大于600 mT后, 羰基铁粉质量分数越大, 总磁相互作用力越大, 样品的剪切储能模量越大, 磁致模量也越大。在填充颗粒总质量分数不变的前提下, 样品的磁致模量、磁流变效应主要取决于羰基铁粉在弹性体内的质量分数, 但由图9(b)~(d)可知, 充磁后, 硬磁颗粒质量分数大的样品在低磁场下剪切模量更大。
图9 不同配比的混合磁敏弹性体的储能模量与磁场的关系
Fig.9 Magnetic field dependence of storage modulus for Mixed MAE of different proportions
图10 剩磁对70%+10%、40%+40%混合磁敏弹性体的储能模量与磁场关系的影响
Fig.10 Influence of remanence on magnetic field dependence of storage modulus for 70% + 10%, 40% + 40% mixed MAEs
图10显示了剩磁对软/硬磁颗粒质量分数为70%+10%、40%+40%的混合磁敏弹性体的剪切储能模量与磁场关系的影响。填充颗粒质量分数相同时, 剩磁越大, 相同外加磁场下弹性体的剪切模量越大。而钕铁硼颗粒质量分数越大, 不同剩磁引起的磁敏弹性体的剪切模量的差异越大, 弹性体的力学性能对剩磁越敏感。对于70%+10%、60%+20%的样品, 不同的剩磁使得磁场扫描曲线在未充磁样品的基础上附加不同的初始模量, 磁致模量变化不大, 充磁的钕铁硼颗粒起到补强剂的作用。但当羰基铁粉与钕铁硼粉配比为1:1时, 由于硬磁颗粒质量分数较大, 充磁后“内置磁场”作用范围增大, 大多数羰基铁粉包覆在硬磁颗粒周围并被磁化, 较小的充磁电压已大幅提高样品的初始模量, 当测试磁场增大时, 根据软磁材料的磁学特性可知, 羰基铁颗粒的磁化系数先增加后减小, 颗粒间作用力的变化率也表现出了同样的趋势, 因此在磁场增大到一定程度后, 剩磁越大的样品的储能模量的变化率越小, 当测试磁场为1.2T时, 储能模量已相差不大, 导致充磁样品的磁致模量和磁流变效应减小。因此在软磁弹性体内适当添加硬磁颗粒, 增大充磁可起到补强效果。
1. 各向异性纯硬磁弹性体的剪切储能模量要高于各向同性纯硬磁弹性体。各向同性硬磁弹性体的剪切储能模量具有磁场方向的依赖性, 剪切储能模量的最小值并不在零场, 在外磁场方向与弹性体剩磁方向相反时, 弹性体在低磁场下表现出负磁流变效应, 超过某一临界磁场后, 剪切模量随着磁场的增大而增大。
2. 相同配比的混合磁敏弹性体的剪切储能模量随着剩磁的增大而增大。硬磁颗粒质量分数越大, 剪切储能模量越大, 受磁场的影响越敏感。
3. 适当增加硬磁质量分数, 增大充磁电压有助于提高混合磁敏弹性体剪切模量的同时保证磁致模量, 过量的硬磁颗粒会导致零场模量过大使磁致模量及磁流变效应大幅下降。
The authors have declared that no competing interests exist.
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A. Szilagyi and M. Zrinyi, Magnetic field-responsive smart polymer composites , |
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Nonlinear magneto-viscoelasticity of transversally isotropic magneto-active polymers ,
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Kramarenko and A. R. Khokhlov, New composite elastomers with giant magnetic response , |
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Magnetoviscoelasticity parametric model of an MR elastomer vibration mitigation device ,
Both experimental and modeling studies of magnetic field induced viscoelastic properties of magnetorheological (MR) elastomers under different loading cases are discussed. Anisotropic MR elastomer (MRE) samples with different concentrations of carbonyl iron powder, natural rubber and additives are fabricated and four MRE vibration mitigation devices are manufactured to investigate the dynamic viscoelastic properties of MREs under varying magnetic fields, displacement amplitudes and frequencies in the shear mode. The characteristics of the dynamic properties of the MRE devices are obtained in terms of the experimentally determined shear storage modulus and loss factor. These results demonstrate that the MREs exhibit variable stiffness and damping properties. Based on the studies of properties of viscoelastic materials and the experimental results of MREs, a parameter model is proposed to describe MRE performances. The four parameters under various working conditions, such as magnetic field, displacement amplitude and frequency, are identified by using the Matlab optimization algorithm. Comparisons between experimental and numerical results are discussed, and the results show that the proposed parameter model can describe the performances of MRE devices very well.
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Mechanical Property of Magnetorheological Elastomer and its Application in Vibration Control ,
磁流变弹性体的力学性能及其在振动控制中的应用 ,URL 摘要
磁流变弹性体(MRE)是一种 主要由微米级的铁磁性颗粒和橡胶类基体构成的智能复合材料,其性能(模量、阻尼、变形、电阻抗等)可以由外加磁场快速、连续和可逆地控制,因此MRE在工 程实践中具有广泛的应用前景。目前对MRE力学性能的研究主要集中在其剪切力学性能上,对法向力学性能的研究较少。此外,MRE在剪切状态下的承载能力较 差,而在压缩状态下能承受较大的载荷。因此,MRE在压缩状态具有更好的工程应用价值。针对MRE可能的工程应用,本文首先对MRE的法向力和高应变率下 的压缩性能进行了研究。在此基础上,结合前人的研究成果,针对MRE在振动控制应用中存在的问题,对MRE在吸振和隔振方面的应用展开了讨论,解决了 MRE在振动控制应用中面临的器械设计和控制算法问题,初步实现了MRE的工程应用。本文的主要内容如下： 1.采用安东帕MCR301流变仪研究了MRE在压缩状态、准静态剪切状态和动态剪切状态下的法向力,得到了MRE的法向力与外加磁场、剪切应变、温度和 颗粒分布等的关系。在压缩状态下,MRE的法向力随着外加磁场的增大而增大,当铁颗粒达到磁饱和时,法向力也表现出饱和的趋势。此外,预压力、颗粒分布、 外界环境温度和磁场的循环加载对MRE的法向力行为均有影响。在准静态剪切下,MRE的法向力与剪切应变密切相关。低磁场时,法向力随着剪切应变的增大而 减小；高磁场时,法向力随着剪切应变的增大而增大。法向力的这种变化趋势与预压缩方向的弹性模量和颗粒链在外加磁场下受到的力矩相关。这两个因素的共同作 用导致了MRE在准静态剪切下的法向力行为。在振荡剪切下,MRE的法向力与振荡剪切的幅值密切相关。当应变幅值低于7%时,法向力随剪切应变的变化趋势 与准静态时类似。但是,当剪切应变幅值大于7%时,法向力随着剪切应变的增加急剧地减小,这与MRE内部铁颗粒链的断裂密切相关。该部分的研究工作为 MRE在作动器和减振器等工程器械方面的应用奠定了基础。 2.采用改进的SHPB测试系统研究了MRE在高应变率条件下的动态压缩力学性能,得到了MRE的动态压缩力学性能与外加磁场和应变率的关系,并提出了相 应的本构方程。在屈服前的阶段,MRE的动态压缩力学性能具有明显的磁场相关性和应变率相关性。随着外加磁场的增加,杨氏模量增加,屈服应力增加,而屈服 应变减小。随着应变率的增加,杨氏模量增加,屈服应力增加,而屈服应变减小。为了描述MRE在屈服前的动态压缩力学性能,提出了一个由超弹性、粘弹性和磁 致应力组成的本构模型。实验和理论的对比表明,所提出的本构模型可以很好地描述MRE在高应变率下的动态压缩力学性能。在屈服后的阶段,当应变大于屈服应 变时,MRE的应力表现出逐渐减小的趋势。随着应变的进一步增加,应力达到最小值。当应变大于0.2时,应力表现出逐渐增加的趋势。MRE屈服后的过程可 以看作是其内部铁颗粒链逐渐被破坏和MRE逐渐被压实的过程。该部分的研究工作为MRE在抗冲击方面的应用提供了实验基础。 3.在传统MRE吸振器的基础上,通过增加主动力控制,设计了移频范围宽且阻尼小的MRE主动自调谐式吸振器。主动自调谐式吸振器采用音圈电机作为阻尼补 偿元件,通过主动力控制使得所设计的吸振器在保留传统MRE吸振器固有频率快速可调特点的同时又克服了传统MRE吸振器阻尼大、减振性能差的缺点。该部分 研究对于解决工程实践中振动控制相关的问题具有一定的意义。 4.为了提高半主动吸振器刚度控制的精度和速度,设计了一种基于相位差的MRE吸振器刚度控制算法。该算法不依赖于吸振器控制量与固有频率的精确模型,具 有调整时间快、稳定性好和易实现等优点。实验和仿真的结果都验证了算法的可行性和有效性。该部分研究不仅可用于MRE吸振器的刚度控制,对所有的半主动吸 振器均具有较好的控制效果,对于提高半主动吸振器刚度控制的速度和精度具有重要的意义。 5.采用MRE作为变刚度元件,音圈电机作为变阻尼元件设计了刚度和阻尼实时可控的MRE隔振器原理样机及其控制算法。实验结果表明在ON-OFF控制 下,MRE隔振器具有较好的隔振效果,可以有效地减小负载的振动响应。尤其对负载在固有频率附近的振动也具有较好的隔振效果。该部分研究对于解决工程实践 中振动控制相关的问题具有一定的意义。
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Development of a real-time tunable stiffness and damping vibration isolator based on magnetorheological elastomer ,
A tunable stiffness and damping vibration isolator based on magnetorheological elastomers (MREs) is developed. In this isolator, four MRE elements are used as the tunable springs, whose stiffness can be controlled by varying the magnetic field. A voice coil motor, which is controlled by the relative velocity feedback of the payload, is used as the tunable damper of the isolator. Under the combined ON-OFF control, the proposed vibration isolator shows satisfying isolation effect. The experimental results indicate that the responses of the payload are suppressed significantly in comparison to the passive system. The transmissibility of the payload around the resonant frequency is decreased by 61.5%. The root mean square (RMS) value and the maximum value of the displacement responses of the payload are decreased by 36.0% and 50.0%, respectively. In addition, the RMS values and maximum values of the velocity responses are decreased by 45.4% and 52.5%, respectively.
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The effect of particle shape and distribution on the macroscopic behavior of magnetoelastic composites ,
The magnetoelastic homogenization framework and the partial decoupling approximation proposed byare used to estimate material properties for a class of magnetically susceptible elastomers. Specifically, we consider composites consisting of aligned, ellipsoidal magnetic particles distributed randomly with “ellipsoidal” symmetry under combined magnetic and mechanical loading. The model captures the coupling between the magnetic and mechanical fields, including the effects of magnetic saturation. The results help elucidate the effects of particle shape, distribution, and concentration on properties such as the magnetostriction, actuation stress, magnetic modulus, and magnetization behavior of a magnetorheological composite.
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Calculations of magnetoactive elastomer reactions in a uniform external magnetic field ,
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Magnetorheological effect of magneto-active elastomers containing large particles, J .
The magnetorheological effect of elastomer composites containing a mixture of large (50-80 ?m) and small (3-5 ?m) particles has been experimentally examined. The data shows that elasticity in the range of small deformations (1%) for a magnetic field strength of 290 mT increased by two order of magnitude. This effect can be explained with the presence of the large particles in the structure of the composite assisting the aggregation effect. Due to the strong increase of the interparticle interaction compared with the restoring elastic forces, the presence of the large particles leads to the observed steep increase of Young's modulus.
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D. Lewandowski and A. Gasperowicz, Isotropic magnetorheological elastomers with thermoplastic matrices: structure, damping properties and testing , |
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Kramarenko and A. R. Khokhlov, Low-frequency rheology of magnetically controlled elastomers with isotropic structure , |
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Magnetorheological elastomer-based quadrupolar element of electric circuits ,
The author of this paper describes a quadrupolar electric circuit element ( Q ) based on electroconductive magnetorheological elastomer. It is shown by means of the experimental setup presented in the paper, that the electrical resistances, measured at the gates of Q , decrease with the increase of the strength H of the transverse magnetic field. But, for intensities of the control current ( I c =const.) injected into Q along the direction normal to H 鈫 mathContainer Loading Mathjax , the voltage at the outlet of Q decreases as the strength of the magnetic field increases. The as-obtained experimental results are presented and discussed.
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Kramarenko and A. R. Khokhlov, Strong magneto dielectric effect in magneto-rheological elastomers , |
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Magnetorheological and deformation properties of magnetically controlled elastomers with hard magnetic filler ,
Viscoelastic and deformational behavior of soft magnetic elastomers with hard magnetic fillers under the influence of a magnetic field is studied by different experimental techniques. The magnetic elastomers used in this work were synthesized on the basis of silicone rubber filled with FeNdB particles and were magnetized in a field of 3 and 15 kOe. We have shown that due to high residual magnetization the materials demonstrate well pronounced non-elastic behavior already in the absence of any external magnetic field. In particular, in contrast to magnetic elastomers based on soft magnetic fillers their elastic modulus is strain-dependent. Under the influence of external magnetic field the storage and loss moduli of magnetic elastomers with hard magnetic filler can both increase and decrease tremendously.
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| [16] |
Magnetoactive elastomer based on magnetically hard filler: synthesis and study of viscoelastic and damping properties ,
This work is focused on the magnetic response of magnetoactive elastomer (MAE) based on silicone polymer matrices filled with magnetic particles of magnetically hard NdFeB-alloy. Viscoelastic properties of MAE were studied by the method of oscillation shear. After magnetization in an external magnetic field of 2 T MAE samples demonstrate more than two-time increase in the storage and loss moduli and 25% increase in the loss factor. Performed study of the damping properties of the materials has shown that the oscillation time of the pendulum hammering the magnetized sample is in two times shorter than in case of the non-magnetized sample. Viscoelastic and damping properties of MAE are defined by magnetic interactions between the magnetized particles of the magnetic filler.
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| [17] |
Magnetic and viscoelastic response of elastomers with hard magnetic filler ,
Magnetic elastomers (MEs) based on a silicone matrix and magnetically hard NdFeB particles have been synthesized and their magnetic and viscoelastic properties have been studied depending on the size and concentration of magnetic particles and the magnetizing field. It has been shown that magnetic particles can rotate in soft polymer matrix under applied magnetic field, this fact leading to some features in both magnetic and viscoelastic properties. In the maximum magnetic field used magnetization of MEs with smaller particles is larger while the coercivity is smaller due to higher mobility of the particles within the polymer matrix. Viscoelastic behavior is characterized by long relaxation times due to restructuring of the magnetic filler under the influence of an applied mechanical force and magnetic interactions. The storage and loss moduli of magnetically hard elastomers grow significantly with magnetizing field. The magnetic response of the magnetized samples depends on the mutual orientation of the external magnetic field and the internal sample magnetization. Due to the particle rotation within the polymer matrix, the loss factor increases abruptly when the magnetic field is turned on in the opposite direction to the sample magnetization, further decreasing with time. Moduli versus field dependences have minimum at non-zero field and are characterized by a high asymmetry with respect to the field direction.
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| [18] |
Motion of ferroparticles inside the polymeric matrix in magnetoactive elastomers ,
Ferroelastic composites are smart materials with unique properties including large magnetodeformational effects, strong field enhancement of the elastic modulus and magnetic shape . On the basis of mechanical tests, direct microscopy observations and magnetic measurements we conclude that all these effects are caused by reversible motion of the magnetic particles inside the polymeric matrix in response to an applied field. The basic points of a model accounting for particle structuring in a magnetoactive elastomer under an external field are presented.
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| [19] |
Tuning the tensile modulus of magneto-rheological elastomers with magnetically hard powder ,
It has been experimentally determined the tensile modulus of magnetorheological elastomers based on magnetically hard particles. Samples of the elastomer consisting of a soft elastic matrix and micron-sized particles of FeNdB powder have been magnetized in uniform magnetic fields of varying strength in order to provide different remanence magnetizations. The tensile modulus of these samples was measured small and large strain regimes (up to 6.6%) through mechanical elongation with a table top machine. The relative change in the tensile modulus after the sample was magnetized can reach 360%, depending on the remanence magnetization and the strain.
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