Friction Behavior of Magnetorheological Fluids with Different Material Types and Magnetic Field Strength

Magnetorheological （MR） fluid is a type of a smart material that can control its mechanical properties under a magnetic field. Iron particles in MR fluid form chain structures in the direction of an applied magnetic field, which is known as MR effect, resulting in variation of stiffness, shear modulus, damping and tribological characteristics of MR fluid. As MR effect depends on the density of particles in the fluid or the strength of a magnetic field, the experiments are conducted to evaluate the friction property under reciprocating motion by changing the types of MR fluid and the strength of a magnetic field. The material of aluminum, brass, and steel are chosen for specimen as they are the most common material in mechanical applications. The surfaces of specimen are also observed by optical microscope before and after experiments to compare the surfaces with test conditions. The comparing results show that the friction coefficient increases as the strength of a magnetic field increases in regardless of types of MR fluid or the material. Also the density of particle in MR fluid affects the friction characteristic. The results from this research can be used to improve the performance of mechanical applications using MR fluid.

Preparation and Electrorheological Property of Y_4O(OH)_9(NO_3)-NH_4NO_3 Materials

The new electrorheologicai （ER） material, a particle material composed of Y4O（OH）9（NO3） and NH4NO3, was obtained. They display better ER performance. The shear stress of the suspension of Y4O （OH）9 （NO3） （ NH4NO3 ）2.8 material in dimethyl silicone oil reaches 1469 Pa at an electric field strength （E） of 4.2 kV·mm^-1 and the shear rate （7） of 150 s^-1 The relative shear stress, τ E/τ0（ τE and τ0 are the shear stresses at E = 4.2 and 0 kV·mm^-1 respectively）, is up to 29, which is 19 times that of pure Y2O3 material. The dielectric and conductive property of the materials play important roles in the modification of the ER effect of the particle materials. The researches on these new ER materials are very useful for obtaining a better understanding on the mechanism of the ER effect and finding an ideal ER material.

Relationship between subsurface damage and surface roughness of ground optical materials

A theoretical model of relationship between subsurface damage and surface roughness was established to realize rapid and non-destructive measurement of subsurface damage of ground optical materials.Postulated condition of the model was that subsurface damage depth and peak-to-valley surface roughness are equal to depth of radial and lateral cracks in brittle surface induced by small-radius(radius≤200 μm)spherical indenter,respectively.And contribution of elastic stress field to the radial cracks propagation was also considered in the loading cycle.Subsurface damage depth of ground BK7 glasses was measured by magnetorheological finishing spot technique to validate theoretical ratio of subsurface damage to surface roughness.The results show that the ratio is directly proportional to load of abrasive grains and hardness of optical materials,while inversely proportional to granularity of abrasive grains and fracture toughness of optical materials.Moreover,the influence of the load and fracture toughness on the ratio is more significant than the granularity and hardness,respectively.The measured ratios of 80 grit and 120 grit fixed abrasive grinding of BK7 glasses are 5.8 and 5.4,respectively.

Smart Property of Homogeneous Electrorheological Fluid and Its Application in Reducing Seismic Responses of Engineering Structures

The smart properties of homogeneous electrorheological fluid (HERF) containing side-chain type liquid crystalline polymer were studied and an actual HERF damper with an adjustable viscosity was produced.A mechanical model of the HERF smart damper was established on the basis of experiment and theoretical analysis.Then a controlled equation of SDOF structure by HERF damper was derived and a semi active control strategy based on optimal sliding displacement of damper was presented.The simulation results for a single story frame structure indicate that HERF,which may avoid some defects of common particles suspended ER fluids,is an excellent smart material with better stability.Using the semi active control strategy presented,HERF smart damper controlled could effectively reduce seismic responses of structures and keeps the control stable at all times.

磁流变弹性体及其振动控制应用综述

磁流变弹性体是将磁性颗粒(微米级)分散到聚合物弹性体中制备而成的一种磁控智能材料,其不仅拥有颗粒增强复合材料的优异力学特性,还具备迅速、连续且可逆的磁控特性,在智能传感、电磁屏蔽及缓冲减振等领域具有广泛的前景。为了促进磁流变弹性体及其振动控制技术的发展,综述了磁流变弹性体的材料组成,制备方法。总结了磁流变弹性体在振动控制领域的应用现状及对应用前景进行了展望。

磁流变抛光技术研究进展

表面质量是精密零部件最重要的性能之一,零件的表面质量主要是由加工过程中不同的工艺参数和方法决定的。传统的磨抛工艺由于作用在工件上的力很大、嵌入的磨料颗粒、对工艺的控制有限等原因很难使表面粗糙度降低到精密零部件的要求精度。磁流变抛光(MRF)提供了一种新型高效的方法使工件加工质量达到预期的精度水平。MRF对工艺控制具有更大的灵活性,并且可以在不破坏表面形貌的情况下完成加工。综述了磁流变抛光液组分对加工效果的影响、材料去除模型的建立和发展、不同的MRF加工方式和未来磁流变抛光技术发展的新方向,最后总结了目前MRF技术存在的问题总结,并提出了MRF技术未来可能的发展方向。

调控界面应力分布增强干黏附材料的黏附力

干黏附材料利用分子间作用力产生黏附性能,凭借其可重复使用等特点,在机器人技术及精密制造中有着重要的应用。为使干黏附材料受拉时接触界面应力更加均匀,提高其黏附力,对微米级羰基铁粉颗粒/聚二甲基硅氧烷磁流变弹性体干黏附材料进行结构设计,通过改变羰基铁粉的质量分数和外加磁场,制备了弹性模量沿半径方向变化的多级复合样品和梯度模量样品,黏附强度分别达到8.0 N/cm^(2)和11.4 N/cm^(2),相较于羰基铁粉质量分数(60%)相同的均质样品,多级复合样品和梯度分布样品的黏附强度分别提升了35%和77%。结合有限元仿真结果可知,弹性模量径向分布设计能有效降低边缘应力集中,由于梯度模量样品界面正应力分布更均匀,因此其黏附增强效果比多级复合样品更显著。

基于MRG/CNT复合材料的磁电阻效应研究

通过在磁流变胶泥(MRG)中加入碳纳米管(CNT)组成复合材料,结合MRG的优良磁响应特性与CNT的电导特性,以复合材料作为填充材料设计实验敏感元件,建立实验表征系统对复合材料磁电阻效应的静态与动态特性开展了实验研究,并从微观层面分析了磁电阻效应机理,揭示了激励磁场影响复合材料电阻的关键因素。结果表明:复合材料处在磁工作区范围内,敏感元件的电阻值随磁场的增强而衰减,相对变化量达到了62.2%,同时表现出良好的时间稳定性;实验的动态响应输出与激励磁场的变化趋势高度一致,证明了复合材料具有良好的动态磁电阻响应特性。

单晶SiC磁流变弹性抛光垫的磁控抛光性能研究

将智能可控材料磁流变弹性体(MRE)作为化学机械抛光中的抛光垫,研究不同磁控参数(颗粒类型、颗粒质量分数、颗粒粒径、固化磁场强度)的MRE抛光垫对单晶SiC的磁控抛光效果,并分析MRE抛光垫的磁控材料去除机制。结果表明:相比四氧化三铁磁性颗粒,羰基铁粉(CIP)磁性颗粒制备的MRE抛光垫,在抛光SiC时材料去除率(MRR)提高了52.2%;CIP质量分数越大,抛光的MRR越大,表面粗糙度越小,抛光的表面质量越好,因为CIP质量分数高时具有更大的材料模量和更多的CIP颗粒接触;不同磁性颗粒粒径的MRE抛光垫磁控抛光效果差异并不大,粒径通过颗粒的大小和接触概率影响着抛光加工的去除效果,这和表面的接触状态有关;相比各向同性MRE,施加固化磁场制备的各向异性MRE能获得更好的磁控抛光效果;在固化磁场为140 mT时制备的MRE抛光垫具有最好的抛光效果,其在抛光磁场为335 mT的条件下,可使SiC的MRR相比无磁场抛光时提升31.0%,表面粗糙度下降50.0%。MRE抛光垫磁控抛光材料的去除机制为,外加磁场增加了MRE抛光垫的机械力学性能,磨料对SiC表面具有更大的切削力和正压力,从而能够获得更大的材料去除。

磁流变脂组分对其动态流变性能的影响

采用原位皂化工艺制备了基于不同类型载液和磁性颗粒的磁流变脂,使用智能磁流变仪分别考察了基础油类型及黏度、磁性颗粒粒径对磁流变脂流变性能的影响,并用自然沉降法考察了基于不同组分的磁流变脂的沉降稳定性。实验结果表明,通过改变基础油类型和调节基础油的黏度可控制磁流变脂的内部骨架结构,有效地改善磁流变脂的磁流变性能和沉降稳定性;增大磁性颗粒的粒径可提高磁流变脂的流动性,增大磁场下磁流变脂的结构强度,增强其磁流变效应。

行星式磁流变抛光装置设计及试验验证

为减少磁流变抛光过程中磁链屈服及磨粒沉降对材料去除效果的影响,提高磁流变抛光加工效率,基于磁流变抛光液的剪切应力模型和材料去除机理,结合工件Preston方程,建立了磁流变抛光材料去除模型;依据所建立的材料去除模型和行星式磁流变抛光加工原理,设计一种行星式磁流变抛光装置,并对抛光装置的关键参数进行计算;制作抛光装置样机并进行试验验证。结果表明,材料去除率与载液盘转速、工件转速及旋转半径呈正相关,所建立的材料去除率模型计算结果与试验结果一致性较好,所设计的装置能够达到精加工效果。

明胶基磁流变胶柔性砂带抛光头的制备及其抛光性能研究

针对复杂曲面零件抛光困难的问题,制备了以明胶基磁流变胶和砂带为柔性抛光头的新型抛光头,并研究了该柔性抛光头在不同加工工艺参数下对3D曲面铝合金表面质量和材料去除率的影响规律。方法:使用自制柔性抛光头以不同的主轴转速、进给速度对3D曲面铝合金进行抛光,测量不同加工参数下的表面粗糙度值和材料去除率。结果:当主轴转速增加时,工件表面的表面粗糙度值有明显的降低,但是当主轴转速超过1000 rpm时表面粗糙度值下降趋势变缓,与此同时材料去除率也下降。当进给速度变大时,工件的表面粗糙度值变大,材料去除率也不断变大。

Topology optimization of magnetorheological smart materials included PnCs for tunable wide bandgap design

Design and application of tunable phononic crystals(PnCs)are attracting increasing interest due to their promising capabilities to manipulate acoustic and elastic waves effectively.This paper investigates topology optimization of the magnetorheological(MR)materials including PnCs for opening the tunable and wide bandgaps.Therein,the bandgap tunability of the PnCs is achieved by shear modulus variation of MR materials under a continuously changing applied magnetic field.The pseudo elemental densities representing the bi-material distribution inside the PnC unit cell are taken as design variables and interpolated with an artificial MR penalization model.An aggregated bandgap index for enveloping the extreme values ofbandgap width and tunable range of the MR included smart PnCs is proposed as the objective function.In this context,the sensitivity analysis scheme is derived,and the optimization problem is solved with the gradient-based mathematical programming method.The effectiveness of the proposed optimization method is demonstrated by numerical examples,where the optimized solutions present tunable and stably wide bandgap characteristics under different magnetic fields.The tunable optimized PnCs based device that can provide a wider tunable bandgap range is also explored.

Material removal model of magnetorheological finishing based on dense granular flow theory

Magnetorheological finishing(MRF)technology is widely used in the fabrication of high-precision optical elements.The material removal mechanism of MRF has not been fully understood because MRF technology involves the integration of electromagnetics,contact mechanics,and materials science.In this study,the rheological properties of the MR polishing fluid in oscillation model have been investigated.We propose that the shear-thinned MR polishing fluid over the polishing area should be considered a dense granular flow,based on which a new contact model of MRF over the polishing area has been constructed.Removal function and processing force test experiments were conducted under different working gaps.The normal pressure and effective friction equations over the polishing area were built based on the continuous medium and dense granular flow theories.Then,a novel MRF material removal model was established.A comparison of the results of the theoretical model with actual polishing results demonstrated the accuracy of the established model.The novel model proposed herein reveals the generation mechanism of shear force over a polished workpiece and realizes effective decoupling of the main processing parameters that influence the material removal of MRF.The results of this study will provide new and effective theoretical guidance for the process optimization and technology improvement of MRF.

A novel multifunction material with both electrorheological performance and luminescence property

A multifunctional material with both electrorheological（ER） performance and luminescence property was synthesized by a simple coprecipitation. The tetrabutyl titanate, as well as the Tb（NO3）3·6H2O and sulphosalicylic acid（C7H6O6S·2H2O, SSA） were chosen as starting materials. The composition, ER performance and luminescence property of the material were studied. The results showed that a novel material（TiTbSSA） with both ER performance and luminescence property was obtained. The relative shear stress τr（τr=τE/τ0, τE and τ0 were the shear stresses of the suspension with and without an applied electric field） of the suspension（30 wt.%） of the material in silicone oil reached 32.7 at a shear rate of 12.5 s–1 and an electric field strength of 4 kV/mm（DC electric field）. The material containing the rare earth（RE=Tb） complex exhibited fine luminescence performance and higher ER activity. Therefore, it is a novel multifunction material which would have wide application prospect.

基于磁流变复合材料的磁流变阻尼器设计

为解决传统磁流变阻尼器存在工作介质易沉降、密封要求较高,且中高频激励下阻尼器刚度快速增大,能耗衰减严重的问题,制备并测试了一种沉降稳定性能良好且密封要求低的磁流变复合材料,建立改进的Herschle-Bulkley模型用以表征复合材料的力学性能;基于该复合材料设计加工出一种剪切式磁流变阻尼器,并设计实验测试中、高频激励下阻尼器的性能响应规律.研究结果表明:3 A电流激励下,当测试频率由5 Hz增大至20 Hz时,阻尼器动态刚度由4.87×10^(5) N/m增加到6.29×10^(5)N/m,且全频段阻尼器单周期耗能均在0.04 J左右,验证了所设计的磁流变阻尼器在中高频振动工况下的耗能能力.

磨料颗粒增强磁流变弹性体的磨抛应用研究

针对常规刚性磨具对复杂面型、硬脆难加工材料工件进行磨抛加工时,难以兼顾加工效率、表面质量以及完整性的问题,提出了一种基于磨料颗粒增强磁流变弹性体材料(A-MRE)的磨抛加工方法。首先,基于磁性颗粒与磨料颗粒在硅橡胶基体中的链网组装与夹持行为,设计了A-MRE材料制备工艺流程;然后,基于微观组织结构观测,建立了A-MRE材料代表体积单元(RVE)模型,结合理论分析与有限元仿真研究了磁场条件对基体软固结磨粒把持行为的影响;最后,采用A-MRE磨具对SiC材料开展磨抛加工实验,分析了不同磁场条件下的表面加工质量与材料去除效率。研究结果表明:磁场方向与A-MRE基体磁性颗粒链方向夹角为0°时磨粒把持应力最大,且随磁场强度的增加而增大,对A-MRE基体施加1.5μm压缩量时,磨粒最大把持应力可达396.63 kPa;磁场强度为0.35 T时,采用A-MRE磨具加工的SiC材料表面粗糙度比无磁场条件下的降低了80.3%,材料去除效率提高了28.6%,磨具损耗量降低了56.1%,验证了A-MRE作为弹性磨具基体材料的可行性。

A novel method of water bath heating assisted small ball-end magnetorheological polishing for hemispherical shell resonators

Hemispherical shell resonator(HSR)is the core component of hemispherical resonator gyro.It is aφ-shaped small-bore complex component with minimum curvature radius less than 3 mm.Thus,traditional polishing methods are difficult to polish it.Small ball-end magnetorheological polishing method can polish the small components with complicated three-dimensional surface and obtain non-destructive surface.Therefore,this method is suitable for polishing HSR.However,the material removal rate of the ordinary small ball-end magnetorheological polishing is low,leading to long polishing time and low output of HSR.To solve this problem,a water bath heating assisted small ball-end magnetorheological polishing method is proposed in this research.The influence rule of processing parameters on the material removal rate is studied experimentally.A set of optimal processing parameters is obtained to maximize the material removal rate.Compared with the ordinary method,the material removal rate of the new method can be improved by 143%.Subsequently,an HSR is polished by the new method.The results show that the polishing time can be reduced by 55%,and the polished surface roughness can reach 7.7 nm.The new method has the great potential to be used in actual production to improve the polishing efficiency of HSR.

汽车半主动悬架系统研究进展

基于系统工程理论 ,论述了汽车半主动悬架系统的研究和动态 ,分析了目前电 磁流变液减振液的研究及减振器开发现状。在分析了一些较为成功的半主动悬架控制策略的基础上 ,论述了经典控制、线性最优控制、自适应控制和智能控制方法在半主动悬架系统中的应用前景 ,提出了基于天棚阻尼控制理论、模糊控制理论和自适应控制理论为主线的复合控制策略。此外 ,提出了基于磁流变液减振器的半主动悬架系统研究与开发的整体思路 ,探讨了值得研究的若干理论和应用问题。