【作者】 孙宏丽；

【导师】 朱石沙；

【作者基本信息】 湘潭大学 ， 机械电子工程， 2007， 硕士

【摘要】 电流变液体作为一种智能材料,其力学性能(粘度、剪切强度等)可以通过外加电场而得到连续调控。电流变器件已广泛应用到自动控制、汽车制造、机械传动、机器人等诸领域。电流变效应的机理研究,是电流变技术基础研究的核心内容。现有的静电极化模型和界面极化模型都强调电流变效应是由组成电流变液体二相成分的介电属性失配(mismatch)所引起的。无论是介电失配还是传导失配,都与电流变液体的介电常数有关。但这两个模型,是静态的,没有考虑到电流变液体在剪切场或压力梯度场下的动力传输过程。研究表明,颗粒以及由颗粒形成的大的聚集体在强力场的作用下(电场、剪切场、压力梯度场等)要重新取向,能导致液体的介电常数、介电损耗和松弛频率的变化,这就是FMP(flow-modified permittivity)效应。由于粒子极化速率是有限的,FMP效应必定对电流变效应产生重要影响。本论文围绕着以下几个方面进行展开:首先,本文详细地论述了FMP理论,并研究了流动场下,FMP效应对两电流变液颗粒间局部电场的影响。通过使用Matlab软件模拟得出,小介电失配比的情况下,FMP效应对局部电场的影响比较剧烈,大介电失配比时几乎不受影响。并且发现FMP效应与局部电场的关系并不是简单函数的问题。其次,研究FMP效应对Poiseuille流动场下电流变液颗粒的动力学的影响。经研究发现,FMP效应对电流变响应的强度影响并不是很大,而对电流变颗粒运动位置的影响较为明显。另外,进行了有关FMP效应的电流变液响应的动力传输实验,实验采用的是平行平板型和同心圆环型结构的电流变元件。通过理论和实验分析得出,电流变液的动力传输过程中,形成的链状网络结构将俘获上游的粒子,在这个过程中,FMP效应与俘获效应的耦合作用,共同对电介质的介电常数做出了贡献,宏观上表现为力学性能的动态变化。并首次推导出有关FMP效应与俘获效应耦合的动力学初步模型,提出用FMP技术来探测电流变液粒子成链信息的想法。最后,本文进行了有关FMP效应的电流变液的动力学仿真。以经FMP效应修正的静电极化模型为基础,采用分子动力学方法,对两平行极板间Poiseuille流场下的电流变液进行仿真。发现FMP作用下,电流变液终态结构有所改变,结构演变的时间和力学性能都受到了影响。并认证了刚进入界面或者界面中的孤立粒子被电流变液结构聚集体俘获的可能性。通过对不同弛豫时间下,剪切应力与压力梯度的关系曲线中,发现电流变效应的强度与粒子极化的弛豫时间关系密切,对于同种电流变液材料,应该有一最佳介电松弛频率。本文创新之处:提出电流变响应过程中的FMP效应与俘获效应的耦合作用,以及基于此的“结构-力”动态耦合。该课题研究的意义在于将电流变效应机理研究拓展到动力学领域,对电流变器件的设计具有指导意义,并对推动电流变技术的发展有着积极作用。更多还原

【Abstract】 Electrorheological fluids is an intelligent material, its mechanical performance (such as viscosity, shearing strength and so on) can be regulated continuously by the applied field. The electrorheological apparatus have been used in various fields such as the automation, automobile manufacture, mechanical transmission, robot and so on.The research on the mechanism of electrorheological effect is the core content of the basic study of electrorheological technology. Both the electrostatic polarization model and the interface polarization model emphasize that the electrorheological effect is caused by the mismatch of the two components of electrorheological fluids. It relates with the dielectric constant of the electrorheological fluids no matter what it is dielectric mismatch or conductive mismatch. But both of the two models are static states, no considering the dynamic transmission process of the electrorheological fluids in shear field or pressure gradient field. The investigation indicate that the particles or the congregating which built up by particles will reorient the new direction under strong field such as electric field, shear field or pressure gradient field and so on, and this process can alter the dielectric constant, the coefficient of dielectric loss and the relaxation frequency of electrorheological fluids, this is called flow-modified permittivity (that is FMP effect). Owing to the limit polarization speed of particles, the FMP effect plays an important role on the influence to the electrorheological effect. This paper carries through some aspect work about FMP effect as follows:First of all, this article detailedly expatiates the FMP theory, studies the influence of FMP effect to the local electric field of two particles in shear field, we obtain the result that the action of FMP effect is great when it is in small dielectric mismatch situation, it may be neglected in big dielectric mismatch situation by using the Matlab software, and the relationship between FMP effect and the local electric field is not a simple function.Secondly, this article studies the kinetic influence of electrorheological particles caused by FMP effect in poiseuille flow field, and finds that the action of FMP effect is not prominence, but it indeed does great contributions to the location of the particles.In addition, this article carries through the electrorheological power transmission experiment about FMP effect, the experiment uses the parallel-plate and the annular structure electrorheological elements, according to the results of experiments and theoretical analysis, we obtain that the chain-net structure will capture the particles from the upstream in the response of the dynamic transmission process, and during the process, the FMP effect and the capture effect both give contributions to the dielectric constant of the particles, and it expresses the changes of the mechanical performance on macroscopic. We get the control equation about the coupling dynamics process of FMP effect and capture effect for the first time, and propose the idea about getting information of the particles becoming chains by FMP effect.In the end, this article gives the results of dynamic simulation about FMP effect in the response of electrorheological fluids in poiseuille flow field between two parallel plates on the base of the modified polarization model by FMP, uses the molecule dynamics method and finds that the structure of electrorheological fluids will alter to some small extent by FMP effect, the time in which will alter too,also the mechanical performance suffer the influence, and testify the possibility that the particles which enters the screen just now or the isolation particles in the screen are captured by the electrorheological congregating. Through comparing the relation curves of shear strength and pressure gradient under the different dielectric relaxation time, we find that the electrorheological effect connects the relaxation time of particle intimately, and there must be an optimal dielectric relaxation rate.The innovation of this article is proposing the FMP effect and capture effect coupling process basing on this“the structure - strength”the dynamic coupling of electrorheological fluids. And the meaning of this research will develop the electrorheological mechanism into the kinetic field, it has the guiding significance to the design of electrorheological components and the active action for impelling the developing of electrorheological technology.更多还原