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1.
Effects of electric field on the rheology, electrorheological effects, are investigated on ferroelectric smectic C* phase of 4-(6-methyl)octyl-resorcylidene-4′-octylaniline (MORA-8). When an electric field is applied in smectic C* phase, an increase of the shear stress is observed with its behavior depending on the shear rates; at higher shear rates the shear stress increases monotonously with the electric field strength, but at lower shear rates the shear stress increases monotonously until about 2 kV mm−1, but above this field it discontinuously decreases to lower values, which is followed by an increase at higher electric fields. In close vicinity of the smectic C* to isotropic phase transition point, a field induced decrease of the shear stress is observed. These ER behaviors are discussed on the basis of the field induced orientational changes of the smectic layer and the director and a possible field induced structural change. 相似文献
2.
Electrorheological effects in carbon, barium titanate, and nickel coated with barium titanate suspensions 总被引:1,自引:0,他引:1
Effects of the electric field on the rheology, electrorheological (ER) effects, are investigated on carbon, barium titanate (BaTiO3) and BaTiO3-coated nickel (BT-Ni) suspensions. Among some electroreological properties, electric field frequency dependence of the induced shear stress (yield stress) observed for three suspensions shows a contrasting behavior. With increase in the electric field frequency, the yield stress decreases above 100 Hz in the carbon suspension, monotonously increases in the BaTiO3 suspension, and is almost constant in the BT-Ni suspension. The difference in the frequency dependence and magnitude of the yield stress is discussed on the basis of the magnitude and relaxation time of the interfacial polarization and the effect of the particle rotation under the shear flow. 相似文献
3.
Electrorheological(ER) fluid is a type of smart fluid whose shear yield stress relies on the external electrical field strength. The transition of ER fluid microstructure driven by the electrical field is the reason why viscosity changes.Experimentally, the transparent electrodes are used to investigate the column size distribution where an external electric field is applied to a colloidal suspension, i.e., ER fluid is increased. The coarsening profile of ER suspensions is strongly related to electrical field strength, but it is insensitive to particle size. In addition, in a low field range the shear stress corresponding to the mean column diameter is studied and they are found to satisfy a power law. However, this dependence is invalid when the field strength surpasses a threshold value. 相似文献
4.
The results of positive/negative Fowler-Nordheim high electric field stress and thermal post-high electric field stress annealing of commercial n-channel power VDMOSFETs have been presented. They have shown that gate bias sign has an influence on the fixed trap behavior during high electric field stress, but has no influence on any defect type behavior during thermal post-high electrical field stress annealing. In addition, slow switching traps have different behavior, but fast switching traps have the same behavior during thermal post-high electrical field stress annealing and thermal post-irradiation annealing. 相似文献
5.
极性分子型电流变液 总被引:2,自引:0,他引:2
电流变液在电场作用下软硬连续可调的奇特性质具有广泛和重要的应用价值。传统电流变液是基于颗粒极化产生的相互作用,根据介电理论预测,其剪切屈服强度的上限约为10kPa。电流变液被发明50年来,阻碍其应用的主要原因是剪切强度低。近年来发明的"极性分子型电流变液"是一类新型电流变液,其屈服强度比传统电流变液大一个数量级以上,且与电场强度呈线性关系,这一点和传统电流变液中的平方关系也明显不同。文章作者提出了极性分子在颗粒间强局域电场中的取向并与极化电荷作用的模型,成功地解释了观察到的实验现象。根据这一原理,有可能制备出屈服强度高达MPa的电流变液。 相似文献
6.
Electrorheological (ER) fluids are a class of materials whose rheological properties are controllable by the application of an electric field. A dielectric electrorheological (DER) fluid is the simplest type of ER fluid, in which the material components follow a linear electrostatic response. We review and discuss the progress of the studies on physics of this type of material. A first-principles theory of DER fluids, along with relevant experimental verifications, are presented in some detail. In particular, the properties presented include static equilibrium structure, shear modulus, static yield stress and its variation with applied electric field frequency, and structure-induced dielectric nonlinearity. 相似文献
7.
8.
The yield stress of our newly developed electrorheological (ER)
fluids consisting of dielectric nano-particles suspended in silicone oil
reaches hundreds of kPa, which is orders of magnitude higher than that of
conventional ones. We found that the polar molecules adsorbed on the
particles play a decisive role in such new ER fluids. To explain this polar
molecule dominated ER (PM-ER) effect a model is proposed based on the
interaction of polar molecule-charge between the particles, where the local
electric field is significantly enhanced and results in the polar molecules
aligning in the direction of the electric field. The model can well explain
the giant ER effect and a near-linear dependence of the yield stress on the
electric field. The main effective factors for achieving high-performance
PM-ER fluids are discussed. The PM-ER fluids with the yield stress higher
than one MPa can be expected. 相似文献
9.
The interaction between nanoparticles and an electric field is explored from the electrorheological (ER) point of view, using variational formulations for both the static and dynamic characteristics. In the first part the static characteristics of the ER fluid, consisting of a dispersion of solid particles in a liquid, is detailed by using the spectral representation approach for the effective dielectric constant. Predictions concerning the ground state structure, yield stress, upper bounds on the ER effect are presented together with comparisons to experimental results. The giant ER effect, involving a different paradigm of permanent electric dipoles, is described phenomenologically. In the second part the ER fluid dynamics is formulated via the variational principle of Onsager. Predictions of the model are compared with experiments. It is shown that the phenomenon of the diminishing ER effect at high shear rates may be mitigated by the planar interdigital electrode configuration. 相似文献
10.
理论计算表明,介质包覆导体颗粒用作电流变液的分散相,可以获得高剪切应力的电流变液.采用溶胶-凝胶技术在尺度为5—10μm的石墨颗粒表面成功地包覆了TiO2,获得了金红石相TiO2包覆石墨的复合颗粒.配制成复合颗粒/硅油电流变液,其剪切应力与纯TiO2/硅油电流变液相比,可提高一个数量级.当电场强度为1.7kV/mm时,复合颗粒/硅油电流变液的剪切应力可达1.25kPa,电流密度小于10μA/cm2.
关键词:
电流变液
包覆
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石墨 相似文献
11.
Yield stress fluids have proven difficult to characterize, and a reproducible determination of the yield stress is difficult. We study two types of yield stress fluids (YSF) in a single system: simple and thixotropic ones. This allows us to show that simple YSF are simply a special case of thixotropic ones, and to pinpoint the difference between static and dynamic yield stresses, one of the major problems in the field. The thixotropic systems show a strong time dependence of the viscosity due to the existence of an internal percolated structure that confers the yield stress to the material. Using loaded emulsions to control the thixotropy, we show that the transition to flow at the yield stress is discontinuous for thixotropic materials, and continuous for ideal ones. The discontinuity leads to a critical shear rate below which no steady flows can be observed, accounting for the ubiquitous shear banding observed in these materials. 相似文献
12.
This paper reports on the results in investigations into the properties of piezoelectric textured materials that are formed through technological treatment of a mixture of components of dispersed poly(vinyl chloride) and a ferroelectric powder with the application of an external mechanical shear stress and an electric field. 相似文献
13.
利用基于密度泛函理论的第一性原理方法,系统研究了变形、电场及共同作用对石墨烯电学特性影响的电子机理.研究表明,本征石墨烯的能隙及态密度值在费米能级处均为0,呈现出半金属特性;在一定的变形量下对石墨烯施加剪切、拉伸、扭转及弯曲变形作用,发现剪切和扭转变形对打开石墨烯能隙的作用明显;对本征石墨烯施加不同方向的电场,可知010电场方向对打开石墨烯能隙的作用效果最强.这是因为该电场方向下石墨烯C-C原子间的布居数正值较大,成键键能较高,而负值数值较小,反键键能较低;线性增加电场强度,石墨烯的能隙呈线性增长势;变形及电场共同作用下,外加电场提高了变形对打开石墨烯能隙的作用效果,但不及两种外场叠加的作用效果. 相似文献
14.
Measurements of electric field fluctuations, Reynolds stress and poloidal flow have been performed in the boundary region of the HT-7 tokamak using a Langmuir probe array.Sheared radial electric field and poloidal flow have been found in the vicinity of the limiter and the turbulence has been clearly modified in this region. Furthermore,the electrostatic Reynolds stress component shows a radial gradient close to the velocity shear layer location.All results here indicate that the radial gradient of Reynolds stress may play an important role in the driving of poloidal flows in the plasma boundary region. 相似文献
15.
In the squeeze-flow mode of operation, electrorheological (ER) fluid is placed between two electrodes, which are free to translate in a direction roughly parallel to the direction of the applied electric field. Consequently, the ER fluid is subjected to alternate tensile and compressive strokes and shearing of the fluid also occurs. Available displacements are small but large forces are available from compact devices and there are many potential applications, notably in vibration isolation.The present authors have spent several years developing mathematical models to account for the observed behaviour of ER fluids in squeeze-flow. Previous attempts at modelling squeeze-flow behaviour have been partially successful but there have always been discrepancies. These discrepancies have generally been attributed to the difficulty of estimating the yield stress developed within the ER fluid when an electric field is applied.In the present paper, the authors describe a new approach in which the yield stress is determined iteratively by minimizing the difference between observed and predicted values of the transmitted force. Using this technique, force/displacement and force/velocity plots are predicted and compared with values from an experimental facility. It is shown that agreement between model predictions and experimental observation is excellent and significantly better than those obtained using existing models. 相似文献
16.
17.
Local friction at a sliding interface between an elastomer and a rigid spherical probe 总被引:1,自引:0,他引:1
This paper reports on spatially resolved measurements of the shear stress distribution at a frictional interface between a
flat rubber substrate and a glass lens. Silicone rubber specimens marked close to their surface by a colored pattern have
been prepared in order to measure the surface displacement field induced by the steady-state friction of the spherical probe.
The deconvolution of this displacement field then provides the actual shear stress distribution at the contact interface.
When a smooth glass lens is used, a nearly constant shear stress is achieved within the contact. On the other hand, a bell-shaped
shear stress distribution is obtained with rough lenses. These first results suggest that simple notions of real contact area
and constant interface shear stress cannot account for the observed changes in local friction when roughness is varied. 相似文献
18.
19.
We discuss the coupling between flow and other hydrodynamic variables that can occur in the optically isotropic tetrahedratic
phase (Td) characterized by a third rank tensor order parameter Tijk. We point out that an applied electric field or an applied temperature gradient will lead to flow. Reciprocally we predict
that, for example, a shear flow applied to a tetrahedratic phase leads to an induced electric field and a temperature gradient.
Similarities to recent experimental observations in the vicinity of the isotropic-B7 phase transitions in materials formed
by banana-shaped molecules are discussed.
Received 31 July 2001 相似文献
20.
The electro-elastic interaction between a piezoelectric screw dislocation and an elliptical piezoelectric inhomogeneity, which contains an electrically conductive confocal elliptical rigid core under remote anti-plane shear stresses and in-plane electrical load is dealt with. The analytical solutions to the elastic field and the electric field, the interfacial stress fields of inhomogeneity and matrix under longitudinal shear and the image force acting on the dislocation are derived by means of complex method. The effect of material properties and geometric configurations of the rigid core on interfacial stresses generated by a remote uniform load, rigid core and material electroelastic properties on the image force is discussed. 相似文献