Response Of Electrorheological Fluids Research Articles

Effects of electrode surface morphology on electrical response of electrorheological fluids

In an attempt to enhance the electrical response of electrorheological (ER) fluids under DC electric field conditions, the influence of the electrode surface morphology has been studied using a rheometer in which the electrode surface was covered with a thin metallic net. The test fluids consisted of microsphere particles suspended in two insulating oils, dimethylsilicone oil and fluoridated dimethylsilicone oil. The aggregation of particles and the ER responses in these fluids revealed the effect of local changes in the electric field on the metallic net surface. It is shown that a metallic net on the electrode surface is effective for further promoting the rheological response of the ER fluid suspended in fluoridated dimethylsilicone oil. The responses appear to depend on the material properties of the ER fluids and the mesh size of the metallic net.

The response of electrorheological fluid under oscillatory squeeze flow

The behaviour of an electrorheological fluid under oscillatory squeeze flow is experimentally examined using a new instrument, the Micro-Fourier Rheometer. Under high voltages a distinct flattening of the waveforms of the transmitted force is observed. The amplitude and harmonic composition are investigated as functions of voltage, frequency and amplitude of the input oscillation, and show qualitative agreement with the theoretical bi-viscous model for a Bingham-type fluid. Differences in the waveforms indicate that the actual yielding process is considerably more gradual than for a Bingham material.

Enhanced electrorheological fluids using anisotropic particles

The electrorheological (ER) phenomenon is widely attributed to the chaining of micron-sized polarizable particles when subjected to an external electric field. It has been hypothesized that the strength of the particle–particle interactions determines the rheological properties of ER fluids. On the basis of an electrostatic polarization model, we proposed that by controlling the geometry of the particles, the dielectric properties of ER fluid can be enhanced, resulting in increased strength of the particle–particle interactions. In this work, we have developed systems featuring anisotropic particles and conducted a systematic study of the role of particle geometry in the response of ER fluids. Our findings appear to be in agreement with the electrostatic polarization model.

Mathematical Modelling of the Dynamic Response of Electro-Rheological Fluid

The dynamic response of electro-rheological (ER) fluid is studied and it is shown that the current response to a change in the applied voltage can be modelled accurately by a simple nonlinear RC network. Various models proposed in the literature are studied and are compared with the simple model. When the voltage is applied across the electrode of an ER device the yield stress changes from a zero to a finite value. It is concluded that the dynamic response of the yield stress cannot be measured from test in flow mode. However, by employing a simple signal processing technique the dynamic response can be estimated in shear mode. The dynamic response of the yield stress is modelled by a second order transfer function characterized by a natural frequency and a damping ratio.

A Non-Linear Model for Dynamic Response of Electro-Rheological Fluid in Flow Mode

In this paper a model is presented for the electrical and mechanical properties of ER fluid in flow mode and it is concluded that a similar model must also govern the properties of ER fluid in shear mode of operation. A settling time constant is defined for the fluid which determines the speed of response. The model has been derived from several years of experience gained working with ER fluid and has not been verified experimentally. The proposed model is based on the theory that the electrical properties of ER fluid such as resistance and capacitance are functions of the applied voltage and time. This function is characterised by a time constant (TR) for a simple model and may be characterised by a natural frequency and a damping ratio for more complex model. The numerical solution of these functions when compared with the experimental results obtained from large step input confirm the viability of the proposed model. Further work, however, is required to identify the coefficients numerically from data obtained on a special test rig.

Influence of orientation of electric field on shear flow of electrorheological fluids

It is possible, in experimental flows of electrorheological (ER) fluids or in actual ER devices based on shear flows, that the electric field may have a component normal to and/or parallel to the fluid velocity. An analytical study of this possibility is presented here. The analysis is carried out using a constitutive equation for the three‐dimensional response of ER fluids [Rajagopal and Wineman, Acta Mechanica 91 (1992)] in which the electric field influences the response in two ways: (a) by affecting the material parameters, and (b) by contributing to stress components because of the interaction of the electric field vector and the shearing. It is shown that the viscosity is altered by a component of the electric field in the direction of the fluid velocity. Moreover, the viscosity is changed if the shear direction is reversed. The model is used in a study of the flow between parallel plates. It is found that the velocity field need not be symmetric about the midplane and the tractions on the plates may differ.