基于挤压模式下磁流变液力学行为的实验研究

对磁流变液在不同直流电流作用下的准静态挤压过程进行了实验研究.建立了用于测试磁流变液挤压模式下力学特性的实验装置,并通过ANSYS/Multiphysics对此实验装置磁路的磁感应强度分布进行了仿真分析.测试了压应力和压缩弹性模量各自随压应变的变化曲线.实验结果表明:压应力与压应变、外加电流大小和磁流变液本身的性能都有密切的关系.压应力与压应变、压缩弹性模量与压应变的曲线可以划分为3个不同的区域.在第1区域压应变小于0.025时,压应力和压缩弹性模量随压应变的增加而迅速增加;在第2区域压应力与压应变的曲线斜率近乎为零,而压缩弹性模量却随压应变的增大而下降,在压应变约为0.15时降到最低.随后在压应变大于0.15时压应力和压缩弹性模量与压应变显示为指数关系.     

改进型的磁流变液剪切应力测试仪

针对圆盘缝隙磁场分布不均匀、磁场强度低和注液不方便等问题,对自行研制的旋转圆盘式磁流变液剪切屈服强度测试仪进行了改进.运用ANSYS磁路仿真软件对剪切圆盘机构的磁路进行了优化设计分析,对产生漏磁的部件和结构进行了改进,使测试圆盘所在区域的磁场强度的均匀性得到了加强;当电流为1.6 A时,圆盘间隙处的平均磁感应强度可达0.9 T;同时该测试仪的测试结果表明,Herschel-Bulkley模型可以较好地拟合MRF屈服后区的非线性特性.     

改进型的磁流变液剪切屈服强度测试

根据两个相对运动的平行圆盘间的流体简单剪切流状态的原理,设计了一种改进型的旋转圆盘式磁流变液剪切屈服强度测试仪.测试仪采用可细分式步进电机驱动测试圆盘,通过扭矩传感器测量上下圆盘间的磁流变液发生流变后所产生的扭矩,从而计算出磁流变液的剪切屈服强度.对剪切圆盘机构和磁路进行了优化设计分析,将剪切圆盘置于电磁线圈内部的中间位置,将测试圆盘所在区域的磁场强度不均匀性降至1%,从而可大大降低测量误差.     

一种改进型的磁流变液制备工艺研究

分别以传统的磁流变液制备工艺和改进的磁流变液制备工艺,以羰基铁粉为软磁性颗粒,以专用减振液为母液,制备了2种磁流变液,并对其零场粘度、悬浮稳定性和剪切屈服强度进行了测试和分析。试验结果表明,改进型工艺制备的磁流变液零场粘度比传统工艺制备的磁流变液稍高,但其沉降稳定性和剪切屈服强度均优于以传统工艺制备的磁流变液。     

磁流变抛光液的研究

介绍了磁流变抛光的原理和特点,并由此提出了适于抛光的磁流变液的评价标准,根据这一标准选取了磁流变液的各组分,配制出了标准的光学抛光用磁流变抛光液.通过自行研制的磁流变仪测得该磁流变液在磁场为600mT,剪切率为110rad/s时的剪切屈服应力达到70kPa.用所配磁流变液对K9玻璃进行抛光实验,试验结果表明,磁流变抛光的材料最大去除率为0.4μm/min.     

挤压式磁流变液阻尼器--转子系统的动力学特性与控制

用磁流变液代替常规挤压油膜阻尼器的润滑油,可制成阻尼特性受磁场控制的挤压油膜阻尼器,用于转子系统的振动控制。依据Bingham模型推导了磁流变液挤压油膜的雷诺方程及其解的表达式,给出了油膜流速、压力分布、油膜反力和阻尼器内磁拉力等的计算公式;以磁流变液阻尼器—刚性转子系统为例,理论分析了挤压油膜的力学特性和转子系统的不平衡响应特性;设计和制造了一种用于转子振动控制的挤压式磁流变液阻尼器;试验研究了支承在该阻尼器上的单盘偏置柔性转子系统的不平衡响应特性和控制方法。研究表明,磁拉力可降低一阶临界转速和临界振幅;油膜反力可降低转子系统在无阻尼临界转速处的振幅,并使一阶有阻尼临界转速增大;通过开关控制能使阻尼器具有最佳的减振效果,使转子振幅在全转速区达到最小。     

基于微孔金属材料的磁流变液阻尼特性研究

针对存于规则微孔板的磁流变液(MRF)在磁场作用下产生正应力的现象进行了实验研究,实验结果表明:以微孔金属铝板为载体储存的磁流变液在磁场作用下能从微孔中溢出并能在两平行板产生正应力从而实现阻尼功能,本文研究了产生正应力的大小与磁场强度、剪应变及工作间隙关系。     

磁流变液屈服应力测试仪磁路设计与仿真

分析了平行圆盘式磁流变液屈服应力测试仪的工作原理,结合磁路欧姆定律和安培环路定理,对一种圆盘式磁流变液屈服应力测试装置的磁路进行计算,确定励磁线圈的相关参数。在此基础上,运用有限元软件Ansys中的磁场分析单元对磁路进行建模和仿真。仿真结果表明,工作区间的磁场为匀强磁场,磁场强度随励磁电流的增大而增大。     

磁流变液密封技术概述

在外加磁场作用下,磁流变液因具有一定的黏性应力和可控的屈服应力,故能呈现出明显的耐压能力.即使发生瞬时过压,当压力回落时,磁流变液密封也可自动愈合,使得其在很多领域得到了广泛应用.介绍磁流变液的基本特征及其密封应用;对磁流变液密封结构设计相关事项进行了论述;针对如何提高磁流变液密封耐压压降方面,重点阐述影响其密封性能的...     

钛酸酯偶联剂含量对磁流变液性能的影响

分别以不同含量的钛酸酯偶联剂为稳定剂,以羰基铁粉为磁性颗粒制备了硅油基磁流变液,比较了不同体积分数钛酸酯偶联剂对磁流变液沉降稳定性和剪切性能的影响.结果表明:磁流变液的沉降稳定性随钛酸酯偶联剂含量增多而下降,添加2%时具有最好的沉降稳定性;添加4%钛酸酯偶联剂时,在400 mT磁场下剪切屈服强度可达20 kPa;并得到...     

Flow dynamics of magnetorheological fluids in throttle channels under external magnetic fields

We consider the results of our experimental studies of the throttling of magnetorheological fluids saturated with ferrous and ferric iron oxides, FeOFe₂O₃, through a channel of a rectangular cross section under normally directed quasi-stationary magnetic fields. We analyze the data obtained by taking into account previously constructed physical models for the dynamical processes of interaction between ferruginous solutions and external magnetic fields.     

Thrust bearing using a magnetic fluid lubricant under magnetic fields

This paper describes a thrust bearing using a magnetic fluid lubricant under a magnetic field. The critical pressures of the bearing versus the magnitude of the magnetic flux densities have been investigated experimentally. It is shown that the critical pressures of the proposed bearing are larger than those of the normal lubricated bearing under high speeds.     

A 3D model for magnetorheological fluid that considers neighboring particle interactions in 2D skewed magnetic fields

Magnetorheological (MR) fluid is used as the working medium in MR finishing. The viscosity of the MR fluid, which determines the shear acting on the workpiece surface stress, can be controlled by the intensity of the applied external magnetic field, and is thus an important design parameter in the finishing process. Most previous studies have used a shear stress value obtained experimentally under a limited set of conditions. Although a recent theoretical model that predicts the shear stress in an external vertical magnetic field has been developed, it treats the energy variation with respect to the strain and the intensity of the magnetic field only among the adjoining particles in a chain. Because that model assumes no multiparticle interactions, it is not well suited to a case in which the magnetic field is more than one dimension such as in MR finishing. In this study, a new three-dimensional model is proposed by expanding the one-dimensional model and considering multiparticle interactions. The proposed model assumes that each particle is surrounded by the 26 neighboring particles, and the total internal energy is estimated by calculating the magnetic dipole interactions among the particles. Therefore, the proposed model considers not only the particle-to-particle energy variations, but also the chain-to-chain energy variations. The behavior of MR fluid is evaluated using the proposed model in a two-dimensional skewed magnetic field.     

On developing a magnetorheological transformer that operates in orthogonal magnetic fields

The operation of a magnetorheological transformer in which choke channels are replaced with a cylindrical clearance between two coaxial cylinders is considered. The cylindrical clearance, as well as the working and compensation chambers, are filled with a magnetorheological fluid. It has been shown that this design of the magnetorheological transformer is preferable for damping impact loads.     

剪切阀式磁流变液减振器磁路设计方法

激流变液减振器是新型的智能化减振装置，在汽车、机械以及土木工程减振领域具有广泛的应用前景。设计磁路是设计此类减振器一个关键技术。这里研究了在土木及汽车减振领域最具应用潜力的剪切阀式磁流变液减振器的磁路设计计算方法。发现了磁路最小断面面积是影响磁场强度的的关键因素之一，进而提出了磁路设计中应该注意的几个基本问题。     

一种磁流变液性能测试用的凹字型磁路结构设计与研究

剪切屈服应力是反映磁流变液流变特性的主要参数之一,稳定可控的磁场直接影响磁流变液剪切屈服应力的测量精度,因此磁场设计是否合理对磁流变液的流变性能测试具有重要的影响。针对外置式线圈产生的磁场强度较低且存在漏磁现象、对称式线圈中磁流变液装载不便导致测量过程持续性差等问题,设计了一种凹字型磁路,通过调整线圈位置来改变磁场结构,使磁力线垂直穿过磁流变液流动方向,同时可拆卸的组合式磁路设计在保证磁场强度需要的前提下实现了磁流变液的连续性测量。此外,还分析了不同电流下的磁场强度分布规律,并基于优化的磁路开展了磁流变液剪切屈服应力等力学性能参数的测试。与主流标准测试仪器相比,具有凹字型磁路结构的磁流变液测试系统所测得的剪切屈服应力平均相对偏差值约为10%,重复误差在6.34%以内,说明该磁路结构是磁流变测试中磁场装置设计的一种可行方法。     

新型磁流变阻尼器设计及磁场有限元分析

磁流变液是一种新型的智能材料,在外加磁场作用下其流变学特性如屈服强度能够在毫秒级时间内发生连续可逆的变化.利用磁流变液的这种特殊性能,针对力觉再现技术的要求,设计了一种新型的磁流变阻尼器结构.详细阐述了该阻尼器的工作原理和力矩模型,并完成了有限元模型的建立.运用磁场有限元分析软件Ansoft对阻尼器进行了磁场强度检验并进行了相应的结构改进.仿真结果表明该阻尼器设计结构合理,为磁流变阻尼器的准确设计提供了保证.     

Analysis of magnetorheological fluid behavior in chemo-mechanical magnetorheological finishing (CMMRF) process

Advanced nanofinishing is an important process in manufacturing technologies due to its direct influence on optical quality, bearing performance, corrosion resistivity, bio-medical compatibility and micro-fluidics attributes. Chemo-mechanical magnetorheological finishing (CMMRF) process, one of the advanced nanofinishing process, was developed by combining essential aspects of chemo-mechanical polishing (CMP) process and magnetorheological finishing (MRF) process for surface finishing of engineering materials. The CMMRF process was experimentally analyzed on silicon and copper alloy to generate surface roughness of the order of few angstroms and few nanometers respectively. However, the process needs theoretical exploration towards better understanding, process optimization and result prediction. Hence, an attempt has been made for theoretical study of CMMRF process to analyze the effects of MR fluid under various process parameters. The present theoretical work is split as per following two sub-activities to simplify intricacy of the work.1) FEA-CFD simulation to analyze magnetism, polishing pad formation and polishing pressure during the CMMRF process. The simulation results are used to conduct experiments on aluminium alloy.2) A mathematical model has been developed to predict material removal as well as surface roughness during the CMMRF process. Model validation is conducted by comparing finite element simulation results with the experiments on aluminium alloy.The theoretical results show good agreement with the experimental data and the same has been discussed in this paper.     

Polishing characteristics and mechanism in magnetorheological planarization using a permanent magnetic yoke with translational movement

Translational movement was integrated into a magnetorheological planarization process that uses a permanent magnet yoke with a straight air gap as magnetic source in order to improve surface planarity. The effects of the process conditions, including stroke and velocity of the translational movement, work and excitation gaps and concentration of carbonyl iron particles, on the polishing forces, surface roughness and volumetric removal rate were systematically investigated. The results showed that translational movement had insignificant effect on the polished surface finish, but considerably improved the surface planarity. The surface quality and volumetric removal rate were found to be affected by carbonyl iron particles concentration, and work and excitation gaps. Based on the parametric study, theoretical and empirical models were established for predicting the polishing forces, surface roughness and volumetric removal rate in this magnetorheological process.