基础油对羰基铁磁流变液摩擦性能的影响

采用四球摩擦磨损试验机,在有外加磁场和无外加磁场条件下,考察了基础油对羰基铁磁流变液的摩擦系数的影响,记录了试验时间内摩擦系数随时间的变化曲线.结果表明,在较低载荷下,基础油的运动黏度值与磁流变液的流变性能有直接关系;基础油的摩擦性能决定了磁流变液的摩擦性能.     

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.     

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250mT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。     

磁场作用下磁流变液剪切性能的实验分析

本文研究了磁流变液的力学性能,制备了羰基铁粉体积分数为20%的硅油基磁流变液,观察了磁流变液在磁场作用下的微观变化,测试了磁流变液的剪切性能。实验表明,无磁场作用下,磁流变液为牛顿流体;在磁场作用下,随着剪切速率的增加,剪切应力趋于稳定,表观粘度呈现指数式下降,磁流变液具有剪切稀化效应,符合广义Bingham模型。磁流变液剪切应力和外加电流的依赖关系为:在电流较小时,剪切应力表现为指数增长,指数值约为1.5;随着外加电流的增大,剪切应力表现为线性增长,最终达到稳定值。     

磁流变液的流体动力学理论

在外加磁场作用下,磁流变液从牛顿流体变成了Bingham体,超过屈服应力开始流动,其的流变性(弹性、塑性、粘性)、磁化性、导电性、传热性以及其它的机械性质和物理学性质皆发生显著的改变.研究磁流变液在外加磁场作用下,流场分布规律随磁场强度变化的动态特性,建立磁流变液的流体动力学理论,对开发和设计磁流变器械至关重要.本文运用物理学和流体力学的基本理论,结合本构方程,考虑磁场对磁流变液的流动的影响,建立了磁流变液力磁耦合的流体动力学模型,给出了描述磁流变液流动的基本方程组.     

工作间隙对磁流变液联轴器的影响

对一种新型磁流变液传动器件——磁流变液联轴器的磁场进行了有限元分析,研究了工作区的间隙对磁流变液联轴器磁感应强度和剪切应力的大小及分布的影响。通过分析表明,当工作区间隙由0.2mm增加到2.0mm时,工作区的磁感应强度逐渐减小,而磁感应强度和剪切应力沿长度方向的分布却逐渐趋于均匀,磁感应强度最大值与最小值之差由0.65T减小到0.35T;无论是当工作区磁流变液的磁场达到饱和时,还是当磁感应强度使剪切应力达到屈服值时,剪切应力都不会再随磁感应强度升高而增大。通过计算可知,对于所研究的直径与长度之比为5/7的磁流变液联轴器,当工作区间隙由0.2mm增加到2.0mm时,它所能传递的工作扭矩仅降低25%。因此在设计其磁场时应综合计及加工、安装精度及生产成本等因素合理选择工作区的间隙,推荐选用1.2mm左右的工作间隙。     

磁流变液阻尼器响应时间的试验研究及其动态磁场有限元分析

摘 要：首先,试验测试了不同速度和电流变化下,大吨位磁流变液阻尼器的响应时间;然后,对激励电流变化时阻尼器的磁场变化进行了有限元模拟,基于阻尼器间隙内磁流变液剪切屈服强度的变化考察了阻尼器的响应时间,并与试验数据做了比较。最后,研究了涡流和阻尼器电磁回路中电流响应时间对阻尼力响应时间的影响。结果表明,可以用有限元模拟得到的间隙内磁流变液的平均有效剪切屈服强度的时程曲线来研究磁流变液阻尼器的响应时间;电磁响应时间是阻尼力响应时间的决定因素,减小阻尼器中的涡流是缩短磁流变液阻尼器响应时间的重要途径;电流下降时涡流对阻尼器磁路的影响要大于电流上升的情况;无论是上升还是下降,电流初值越小,涡流对阻尼器磁路的影响越大,阻尼力响应时间也越长。研究还表明,缩短电流的响应时间,会带来更大的涡流,并不一定能缩短阻尼力的响应时间。     

磁流变液颗粒成链过程的理论和实验研究

通过计算机模拟及实验研究了磁流变液颗粒在渐变磁场作用下的成链过程。首先从理论上建立了磁流变液成链过程的物理模型,采用蒙特卡罗方法模拟了其在渐变磁场作用下成链的详细过程。其次,采用光学显微镜观察了磁流变液在渐变磁场作用下的成链过程。数值模拟和实验结果表明,在平行磁场中,当外部磁场为零时,磁流变液的磁性颗粒处于随机分布状态。随着磁场强度的增加,磁性颗粒产生磁团聚形成链状絮凝体,进而由二连体或三连体发展到多连体,甚至网状及柱状结构;在倾斜磁场中,磁流变液中的聚合链也同时旋转,磁性颗粒沿着磁场方向从小链逐渐增大到大链,最后全部沿着磁场方向呈链状或柱状排列。研究结果对优化磁流变液材料的配置和设计高性能磁流变液装置具有重要意义。     

磁流变液的流变特性分析和实验验证

本研究制备了羰基铁粉体积分数为10%的硅油基磁流变液,使用Physica MCR 301流变仪测试其流变性能,用Bingham模型和Casson模型对磁流变液的流变性能进行拟合计算。实验表明,Bingham模型和Casson模型均可较好地描述磁流变液的流变行为,在磁场作用下,随着剪切速率增加,剪切应力增大并趋于稳定,表观粘度显著减小,磁流变液存在剪切稀化现象。通过对数拟合的方法,得出磁流变液剪切应力和磁场的关系,剪切速率恒定时,随着磁场增大,磁流变液剪切应力显著增加。     

磁流变液的流变学性质研究

用球形羧基铁颗粒、硅油和油酸制备了磁流变液（ＭＲＦ），该ＭＲＦ不加外磁场是就呈现非牛顿性，ＭＦＲ的剪切应力τ随剪切率γ的变化关系为一曲线，其表观粒度ηａｐ随剪切速度的增大而减小，在外磁场作用作用，ＭＲＦ的ηａｐ迅速增大两个数量级，ＭＲＦ呈现一定的屈服应力τｙ＝９４．７Ｐａ，当τ〉τｙ后，ＭＲＦ的流变特性满足Ｂｉｎｇｈａｍ模型。     

Principles and Methodology for the Simultaneous Determination of Thickness and Dielectric Constant of Coatings With Capacitance Measurements

We propose a new methodology to measure both the dielectric constant and thickness of dielectric coatings on a flat conducting substrate from two capacitance measurements. We discuss the principles of the method and demonstrate its feasibility using 2-D numerical simulations. We present a proof of principles experiment confirming the viability of the method in practice. Finally, we propose and analyze a multisphere electrode geometry     

中温烧结耐高温陶瓷电容的制备及性能研究

在BaTiO3(BT)BNT-Nb2O5-Zn系统中改变Nb、Zn掺杂量,对BTBNT-Nb-Zn进行介电性能研究,以期获得中烧耐高温陶瓷电容.研究发现,Nb2 O5、ZnO对BTBNT-Nb2O5-ZnO陶瓷介电性能以及电容量温度变化曲线的影响主要体现在居里温度和居里峰的变化.它们的改性机理可用掺杂后晶粒壳与晶粒芯体积分数的变化来解释.对比不同掺杂后钛酸钡陶瓷的SEM照片可以得出:陶瓷的室温介电常数与掺杂后钛酸钡陶瓷的晶粒生长情况密切相关.     

A planar applicator for measuring surface dielectric constant ofmaterials

An applicator is described which allows the surface dielectric constant of a body to be measured simply by putting the device upon the body itself and by measuring the resulting capacitance value using a hand-held portable capacitance meter. The performances of the sensor were first verified by testing materials with known dielectric properties. Its particular use in measuring the dielectric constant of ceramic materials, plastic materials and of commonly used marbles and stones was then considered. Such application may be of interest in the case where the surface dielectric constant of marble and stone can be related to alterations of the external layer of these materials caused by atmospheric pollutants     

Elimination of the anomalous humidity effect in precisioncapacitance based transducers

An anomalous humidity effect has been observed in a precision capacitor-based displacement transducer. This effect displays a threshold, well below the dew point, above which the capacitance change exceeds by far the increase in moisture-caused dielectric constant of the air dielectric. This effect, common to air capacitors in general, results from water vapor adsorption on insulator surfaces. It can be eliminated by shielding the capacitor in a way which removes the humidity sensitive flux from the internal electric field of the capacitor     

恒流放电法测量超级电容器静电容量的影响因素分析与不确定度评定

静电容量是超级电容器的主要电气参数之一,相关标准中均推荐采用恒流放电法对超级电容器静电容量进行测量。介绍了恒流放电法的测量原理和测量电路,通过实验分析了放电电流、充电电流、初始电压对测量结果的影响,并对静电容量测量不确定度进行了评定。结果表明:放电电流对测量结果有较大影响,静电容量随放电电流的增大而减小;充电电流和初始电压对测量结果的影响影响较小;恒流放电法测量静电容量的相对扩展不确定度为2.2%(k=2)。     

稀土氧化物掺杂对钛酸钡基陶瓷电容器材料性能的影响

研究了 BaTiO_3基陶瓷电容器材料掺杂稀土元素对介电常数,热稳定性和介电损耗的影响。分别在 Ba-TiO_3ZnNb_2O_6中加入稀土氧化物 CeO_2、Sm_2O_3、Dy_2O_3等,测量了它们的介电常数和介电损耗及其与温度的关系(ε～T、tanδ～T),比较了三种稀土氧化物对陶瓷材料介电性质的影响,得到了一些有益的结果。     

Synthesis and structure characterization of low dielectric constant MSQ films by using octamethyl cyclotetrasiloxane (D4) as a porosity promotion agent

Low dielectric methylsilsesquioxane (MSQ) film can be synthesized by spin-coating on P–Si (100) wafer. Octamethyl cyclotetrasiloxane (D4) was used as a porosity promotion agent to MSQ film. Seven samples with different treatment were prepared. The dielectric constants of these MSQ films significantly lowered from 3.0 to 2.1. Fourier transform infrared spectroscopy was used to identify the Si–O–Si network structure, Si–O–Si cage structure and other bonds. The change of structure resulted in significant lowering of the dielectric constant (k). The capacitance–voltage (C–V) characteristic by HP4294A was used to determine the dielectric constant. Current–voltage (I–V) measurement by Keithley6517A was used to determine the breakdown electric field.     

Ferroelectric gated electrical transport in CdS nanotetrapods

Complex nanostructures such as branched semiconductor nanotetrapods are promising building blocks for next-generation nanoelectronics. Here we report on the electrical transport properties of individual CdS tetrapods in a field effect transistor (FET) configuration with a ferroelectric Ba(0.7)Sr(0.3)TiO(3) film as high-k, switchable gate dielectric. A cryogenic four-probe scanning tunneling microscopy (STM) is used to probe the electrical transport through individual nanotetrapods at different temperatures. A p-type field effect is observed at room temperature, owing to the enhanced gate capacitance coupling. And the reversible remnant polarization of the ferroelectric gate dielectric leads to a well-defined nonvolatile memory effect. The field effect is shown to originate from the channel tuning in the arm/core/arm junctions of nanotetrapods. At low temperature (8.5 K), the nanotetrapod devices exhibit a ferroelectric-modulated single-electron transistor (SET) behavior. The results illustrate how the characteristics of a ferroelectric such as switchable polarization and high dielectric constant can be exploited to control the functionality of individual three-dimensional nanoarchitectures.     

Dielectric engineering of Ge nanocrystal/SiO2 nanocomposite thin films with Ge ion implantation: Modeling and measurement

Ge nanocrystal (nc-Ge) embedded SiO₂ nanocomposite thin films have been synthesized with the ion implantation technique. The distribution profile of nc-Ge in the SiO₂ matrix can be tailored by varying the implantation energy and dose in the Ge ion implantation process; thus the effective dielectric constant of the nc-Ge/SiO₂ nanocomposite thin films can be engineered. The effective metal–oxide-semiconductor (MOS) capacitance of the nanocomposite thin films has been calculated using the sub-layer model and the Maxwell–Garnett effective medium approximation, taking the reduced dielectric constant corresponding to the nanometer size of nc-Ge into account. On the other hand, capacitance–voltage measurements on the MOS structures based on the nc-Ge/SiO₂ thin films have been conducted to extract the capacitance experimentally. The modeling and measurement results have shown good agreement, suggesting that the nanocomposite dielectric engineering can be easily realized through the energy- and dose-controlled Ge⁺ implantation technique.     

钛酸钡陶瓷介温特性测试技术

钛酸钡陶瓷介温特性测试系统主要由介电性能测试软、硬件平台构成,具有信号调理、采集、分析处理、自动生成测试报告等功能,可以实现钛酸钡陶瓷的室温介电常数、相变温度、介电常数-温度特性、介电损耗-温度特性、容量温度变化率特性等多项参数的综合自动测试.系统硬件平台主要包括计算机、参数转换装置、LCR仪、温控箱、显示终端等.自动...