Electrorheological Fluids and Magnetorheological Suspensions

The following sections are included:

• PREFACE

• CONTENTS

Magnetorheological finishing (MRF) is enabling technology that may produce surface accuracy of the order of 10 nm peak to valley and surface micro-roughness less than 10Å. In this technique, magnetorheological fluid performs the primary function, which is deterministic material removal. There are several auxiliary devices that also function on a "smartness" of magnetorheological fluid. A non-intrusive magnetorheological valve is an integral part of the finishing machine "circulatory system" and provides the pump "stiffness" and computer control of the flow rate. To provide MR polishing fluid continuous circulation, a special means for fluid removal from the polishing wheel and returning to the delivery system has been designed. Once the fluid leaves the polishing zone, it is removed from the wheel surface by a suction cup. The cup has a magnetic system that forms a dynamic magnetorheological fluid seal in the gap between the cup and the wheel surface. Finite element analysis software has been used for magnetic systems and flow design and optimization.

We propose a magnetic compound fluid (MCF) as a new smart fluid. This fluid includes nm size magnetite and μ m size iron particles in a solvent. The magnetic effects of this fluid can be expected to lie in the range between those of magnetic fluid (MF) and magneto-rheological fluid (MRF). Moreover, the magnitude of the shear stress to the shear rate under a steady magnetic field can be larger than that of MRF by varying the compound rate of the MF and MRF. This report shows an experimental application of microscopic polishing using MCF. We examined the surface roughness of flat titanium material attached to a rotating plate at 15 rpm under a magnetic field and found that MCF produced a more uniform surface polish than did MR. As well, the roughness of R_y and R_a are larger under a fluctuating magnetic field than under a steady magnetic field. This more effective polishing can be explained in terms of the cluster model of particles.

An experimental study is presented of the dynamic behavior of the impacting droplet of magneto-rheological suspension under applied magnetic fields. Effects of magnetic fields on the impact phenomena between a MR fluid droplet and paper on the hard rubber mat were revealed with a three-dimensional motion analysis system. In case of perpendicular magnetic field to a target surface, the MR fluid droplet did not collapse completely by its impact, but MR fluid spikes were formed by the magnetic field. In case of parallel magnetic field to a target surface, the MR fluid droplet showed complicated deformation. In case of strong parallel field, the MR fluid droplet showed breakup into few droplets.

A caster-walker with ER fluid brakes installed in the rear wheels has been developed and tested. The brake actuation is "intelligent", in response to signals from a speed sensor and microprocessor, permitting it to prevent stumbling by the patient in mounting or dismounting the walker and on downslopes due to walker acceleration. The walker also serves effectively as a walk trainer. The ER brake is advantageous for small-wheeled vehicles because it is compact and simple, and consumes very little power. In this report, we describe the structure and characteristics of the brake, and key points in the brake design and development.

This study focuses on the effect of semi-active magneto-rheological fluid (MRF) dampers in reducing the response of a scaled bridge structure subjected to a random loading. A fluid-mechanics based model that can characterize the nonlinear dynamic behavior of MRF dampers is employed. A state-variable model for an integrated system of a 1/12 scaled, two-span bridge and two MRF dampers is established. A feedback on-off control law is employed based on Lyapunov approach that guarantees the system stability for uncertain bounded input disturbances. An output feedback Lyapunov controller is implemented in the experimental study to verify the presented method. Both the theoretical and experimental studies show that the Lyapunov based control systems can effectively reduce the relative displacement between the deck and the abutment of the bridge when subjected to various input motions. In addition, when comparing to experiment results, it is demonstrated that the proposed analytical model can predict the response of the system, accurately.

To demonstrate the industrial application and benefits of the ERF-technology, a German Ministry of Research backed project was initiated with the working title "Adaptronic Transport Systems with electrorheological fluids (ERFs) for the transport of sensitive goods". This project was successfully completed by Schenck Pegasus GmbH and partners and resulted in a fully functional ERF-hydraulic transporter system. The general system design including the specific ERF-actuators with integrated ring-segment ER-valves is discussed. Parallel to fully active systems, research work is being carried out on ERF-damper design for commercial automobiles and on the development of an ERF-servovalve.

This paper presents vibration control of flexible structures using squeeze mode ER mounts. After devising the squeeze mode ER mount, its field-dependent damping forces are evaluated at various exciting frequencies. The ER mounts are then incorporated with a flexible beam structure. The governing equation of motion is obtained and an optimal controller which represents controllable damping force is designed to attenuate unwanted structural vibration. The controller is experimentally realized and control responses are presented in time and frequency domains. In addition, vibration control responses of a flexible frame structure integrating with the proposed ER mounts are investigated.

This paper is concerned with an experimental and theoretical determination of the rheological performance of an electrorheological (ER) fluid when subjected to time-dependent applied loads. The experimental facility was built as a squeeze cell in which the fluid is sandwiched between two electrodes, one fixed and the other moving, which permits the instantaneous measurement of the mechanical and electrical responses of the fluid. The transient rheological characteristics of the fluid were assessed for various mechanical force levels and for constant voltage excitation of the fluid. Input and output stress levels across the fluid were monitored enabling the dynamic response of the fluid to be determined using a combination of displacement, force, velocity and acceleration transducers. The experimental results were compared with the results from a modified theoretical analysis, which employs a bi-viscous shear stress/shear strain characteristic of the electrically stressed fluid together with a fluid yield stress, which has a strain-direction dependence on the electrical field.

Force display systems are important in virtual reality and other applications. Conventional force displays, however, are active systems with actuators, so that it may become danger inherently. Consequently, passive force display is effective method for assuring safety. In this paper, we developed a brake using ER fluid and passive force display using ER brakes. Then we discuss two degree of freedom passive force display and basic control experiments.

Experience in manufacturing MR fluids for commercial application has shown that some of the greatest barriers to commercial success are not factors or conditions normally considered in the laboratory. The present paper looks at conditions found in MR fluid devices operating in real-world applications where shear rates may exceed 10⁵ sec^-1 and devices are called upon to operate for very long periods of time. The problem of "In-Use-Thickening" wherein a MR fluid subjected to long-term use progressively thickens until it eventually becomes an unworkable paste is presented. The search for a solution to this heretofore unrecognized problem delayed commercial introduction of the Lord truck seat damper system for several years. Today, good fluids are able to operate for long periods with minimum in-use-thickening.

A seat suspension system with a controlled MR(Magneto Rheological) fluid damper is introduced to improve the ride quality and prevent the health risk of a driver compared to conventional seats. The system locates between a seat cushion and base, and is composed of a spring, MR fluid damper and controller. The MR fluid damper designed in valve mode is capable of producing a wide range of damping force according to applied currents. In experiments, a person was sitting on the controlled seat excited by a hydraulic system. The skyhook control, continuous skyhook control and relative displacement control were applied and the continuous skyhook control improved the vibration suppression by 36.6%.

We validate and assess the applicability of an Eyring constitutive model. The Bingham plastic model has a zero shear rate discontinuity, which leads to inaccuracies in modeling and simulation, and is characterized by two rheological constants for a constant field: yield stress and postyield viscosity. The Eyring model has a smooth transition through the zero shear rate condition, and also has two rheological constants for a constant field. An ER damper having a damping level comparable to a shock absorber for a small-sized passenger car damper is manufactured, and its performance is predicted using the Eyring model. To accurately identify the rheological parameters of the Eyring model, a parameter identification method was used. The daming force versus piston displacement and velocity behaviors of the ER damper are experimentally measured with respect to applied electric field and excitation frequency. To validate the Eyring model, the experimental results are compared with predictions in the damping force versus piston displacement and velocity behaviors.

A semi-active, controllable fluid dampers and their control devices are described and studied in this paper. Such dampers can be used to eliminate oscillations in different servo drive robots and machine tools systems, where their good dynamic parameters are required. In this paper a different control circuit and its influence on MR damper properties are investigated. The experimental results of coil current transients response during switching on and off with different circuits and elements are shown. Construction of the above mentioned damper is described and finally experimental results of control circuits influence on dampers dynamic performance are presented.

The apparent viscosity of the electrorheological(ER) fluids can be changed with the variation of applied electric field strength. The damping force offered by ER shock absorbers can then be controlled by using the characteristics. It is found that, besides the performance of the ER fluids, the construction design of the shock absorber also strongly affects the characteristics of ER shock absorbers. In this paper, this phenomenon is discussed in detail with different construction styles of ER shock absorbers and mechanical analysis is done with hydro-mechanical and rheological theories.

Friction and wear phenomena associated with electro-structured fluids (ESF) are reviewed with respect to operation in the boundary lubricated region. Opportunities for fundamental research into "system effects" are revealed in the light of recent results from magneto-rheological fluid, steel on steel, block on ring, sliding contact tests. Consideration of characterisation means and of conditions for best performance are stimulated by the wide ranging nature of the information presented.

The aim of this work was to investigate the rate of heat transfer from a moving radial plate clutch surface. The paper presents experimental results over a range of angular speeds (Ω) and fluid gap widths (h), which are then favorably compared to analytical and Computational Fluid Dynamics (CFD) solutions for the same geometry and operating conditions. Verifying the heat transfer capabilities of the latter goes some way towards validating a CFD package as a viable virtual prototyping method. In light of the results assumptions were established to allow the comparison of a duel channel radial and concentric clutch designs on a heat transfer basis.

This study demonstrates the feasibility and effectiveness of ER (electrorheological) and MR (magnetorheological) fluid-based landing gear systems on attenuating dynamic load and vibration due to the landing impact. First, the theoretical model for ER/MR shock struts, which are the main components of the landing gear system, is developed based on experimental data. With this theoretical model, the telescopic type landing gear system using the ER/MR shock struts is constructed and its governing equation is derived. Then, the robust sliding mode controller against parameter variations and external disturbances is designed and controlled performance of the ER/MR landing gear system is evaluated during touchdown of the aircraft.

The aim of this paper is to bring together various works on concentrically located rotating shaft seals which utilize electro-structured fluid sealant, in order to produce a generalized approach to their design, thus resolving seemingly incompatible reports on the effects of rotational speed on sealing capabilities. In turn the results from these works are reviewed, a viscoplastic analysis of the two dimensional problem is presented and the effects on leakage rate of radius ratio, rotational speed and axial pressure gradient as they interact with fluid properties are illustrated.

One of the key factors affecting the performance of ER fluid devices is the geometry of the electrodes, which also affects the geometry of the device itself. For an ERF valve, the pressure drop and the flow rate characteristics dictate the performance and efficiency of the device. The geometrical configurations considered in applications up to now mainly involve two parallel surfaces, most of these being parallel flat electrodes and annular electrode configurations. However, there are other electrode configurations that may be potentially more efficient than the traditional parallel flat electrode configurations. The static and dynamic yield stresses of different ER valve geometrical configurations were characterised. The efficiency considered is not the electrical efficiency of the structure, but rather the locking pressure efficiency of the geometry of the electrodes and the valve, closely linked with the pressure drops achieved at different applied electric fields. The data produced was processed, analysed and plotted to give the characteristic operation curves for the different electrode configurations. In this work, the performance of ERF valves based on the traditional parallel flat electrode configurations is compared with those of ERF valves based on square teeth and tapered electrode configurations.

The vibration transmissibility characteristics of a cantilevered brass tube are controlled by means of an electro-rheological fluid which is employed as a constrained layer damping medium. The ER fluid, which is a 50 wt % mixture of silicone oil and starch, was contained in the annular space formed between the outer surface of the tube and the inner surface of a bigger brass tube. It is shown that the modal characteristics of the tube depend on the electric field strength and on the height of the ER fluid. The modal frequencies of the tube increase as the electric field potential is increased and as the height of the ER fluid is increased. Also, the loss factors generally increase as the electric field is increased, but decrease as the height of ER fluid in the annular space is increased. When the annular space is 100% filled with ER fluid, the fluid effectively couples the inner and outer tubes into one vibrating system. Overall, the modal transmissibility of the tube is least when the annular space is filled with the ER fluid to a level of 12.5% of the maximum and an electric field potential of 3 kV is applied.

Stractural rearrangements of an electrorheological fluid (ERF) in an electric field cause a change not only in its mechanical characteristics (viscosity, elasticity, plasticity) but also in such physical properties as thermophysical, optical, electrical, heat-transfer, etc. We have considered the possibility of control of these parameters by an electric field on the basis of our experimental results and an analysis of the relevant data available in the scientific literature and in the patents.

This paper demonstrates a possible in-vitro cancer therapy by mechanically blocking the blood vessels to a tumor through injecting a model magnetorheological (MR) fluid and applying an external magnetic field. The biocompatible MR fluid is made of magnetite particles coated with starch and suspended in either water or sheep blood. Two particle sizes of 1.0 and 0.25 μm are used. A simple "blood" network consists of 4 branches of "blood" vessels made of silicone tubes of 0.4 mm in diameter. One of the branches contains a "tumor" made of a cylindrical cavity with a diameter of either 3.0 mm or 5.0 mm to simulate stage II or III tumors. The cavity is connected with either two or four vessels to the rest of the branch and is placed between two magnetic poles. By measuring the weight of the leaking fluid downstream from the magnets, the sealing quality is monitored. A dilute MR fluid (1.0% particle volume fraction) is pumped slowly through the network. As the fluid goes through the cavity, seals form within seconds after a magnetic field (0.43 - 0.62 T) is turned on. They block the fluid flow to the "tumor". With sheep blood as the suspension medium, both size of magnetite particles forms a good quality seal for the 3 mm cavity. Thus, a mechanical method for stopping "blood" flow is demonstrated in a multi-tube "blood" network for stage II tumor.

This study demonstrates the application of a precise and variable impedance control to the homogeneous ER clutch. The viscous coefficient of a homogeneous ER fluid can be changed by the application an electric field. However, the ER effect of the fluid is easily changed by shear rate variation or temperature variation. Therefore, some feedback compensations are necessary for these systems to maintain a more precise viscosity.

In this paper, we apply a force-based impedance control to the homogeneous ER clutch in order to more effectively use ER fluid. First, we study the fundamental characteristics of the homogeneous ER clutch. Next, we apply the viscous control based on the force control in order to maintain a more precise viscosity. The results of our experiment clearly show that the viscosity of the clutch has been accurately and stably controlled by the proposed control method.

The particle size distribution and magnetic susceptibility of some commercial carbonyl iron powders were measured. The polydispersity of the powders increased as follows: OX ≈ CS < HQ < SM ≪ CC. The magnetic susceptibility increased in the order: CC ≈ HQ < OX < SM. Three grades were chosen to prepare magnetorheological suspensions (MRS). Yield stress without magnetic field and at 100 and 200 Gauss were measured. The yield stress under field increased in the order: CC < SM < OX. This result suggests that particle size distribution plays a role at least as important as magnetic susceptibility on the performance of MRS's. Besides, a damper (Lord RD-1005-3) slightly modified and filled with an alternative MRS formulated with one of these powders was tested in a MTS 850 test system. Applying an electric current to the damper, ranging between 0 and 1 A, we measured a force of about 250 N between 0 and 100 mA, 500 N at 300 mA, 1000 N at 600 mA and 1300 N at 1 A. The behavior of the suspension is reproducible and reversible in this range of current, which suggests that it may be applied to manufacture controllable devices.

Solid electrorheological (ER) composites are prepared by arranging suspended particles in polymer melts with an electric field and cross-linking the obtained structure. Electrostriction phenomenon of ER composites is defined as a deformation effect on the dielectric properties. Composite materials with a chain-like structure demonstrate large electrostriction response to normal and shear deformations. High sensitivity of anisotropic composites to shear electrostriction can be utilized for vibration control and for shear stress/strain sensor applications. We model an electrostriction behavior and provide experimental data characterizing electromechanical properties of the synthesized ER composites.

Various devices and equipment using the ER effect have been developed and studied. When the ER fluid is used in shear mode, the ER fluid is filled between a pair of opposing parallel electrodes, and the rheological characteristics are controlled by applying an electric field across the electrodes. In general, a high voltage of a few kV is required to obtain an adequate ER effect. This causes problems associated with safty or cost. When a pair of opposing parallel electrodes is employed, use of a slip-ring or a brush is needed for the wiring to the moving part, again leading to problems associated with reliability or cost. In this paper, use of one-sided pattern electrodes is proposed as a solution to the above problems. A one-sided pattern electrode is an electrode in the form of a pattern arranged on only one of the two surfaces of a pair of disks, with an insulator arranged on the other surface. We developed two kinds of one-sided pattern electrodes and experimentally verified the manifestation of ER effects in liquid crystalline polymers.

This paper deals with the performance estimation of the semi-active suspension system considering the response time of Electro-Rheological fluid-based damper. The Bingham characteristics and response time of ER fluids are obtained experimentally. Then the ER damper is applied to the quarter car model and its performance using sky-hook control algorithm is compared to the system using conventional damper through computer simulation. As simulation results, the gain is improved above 50% but it is deteriorated rapidly with the increase of response time. So it is proved that the response time as well as the yield stress of ER fluids is the dominant factor to design the semi-active suspension system using the ER damper.

This paper presents the characteristics of ER (electrorheological) and MR (magnetorheological) fluid-based systems through comparative analysis considering time response phenomena. In doing so, a nondimensional analysis, based on parallel plate geometry, is used to characterize the field-dependent properties of ER and MR dampers. Experimental tests are conducted for ER and MR dampers in order to validate our analysis.

A conventional vehicle center bearing (CB) consists of a roller bearing that rests on a circular "U" shaped support, which includes a bladder formed by an elastomer, providing damping for radial vibrations between the roller bearing and the housing. In order to have a better control of the damping force of a CB, MR fluids can be used instead of the traditional elastomeric material. In this work we estimated the variation of the forces acting on a vehicle center bearing, performed the analysis of the magnetic field in a prototype bearing, and tested a MR CB prototype. We concluded that the major component of the reaction on a CB acts in the direction of the joint operating angle, and that MR fluids effectively can be used in vehicle center bearings to provide damping. Moreover, a design of a MR center bearing based in the shear mode is not the best option since weld of the plates may occur at high speeds of rotation of the shaft.

In order to understandthe effectiveness of MR fluids insome applications, such as bearings, this work focuses on the properties of MR fluids under squeeze mode, torsional mode and squeeze combined with torsional mode. A special device was designed and fabricated to performthese experiments, which were carried out on an Instron Multiaxial Testing Machine. The hysteresis loops of the MR fluids were studied for different intensities of magnetic field, frequencystrain amplitude and angle amplitude. The results showed that the damping force and the area of the hysteresis loop of MR fluids increase with the magnetic field andstrain amplitude. Changes on the frequency did not influence the stress values significantly, within the range of frequencies used in these experiments. These results were compared to the ones obtained in valve mode by means of a RD1005 damper manufactured by Lord Corporation. The shape of the hysteresis loop curves and the MR effect were found to be different for the squeeze film damper and the RD1005 damper.

The amount of electric power and the efficiency of a rotating disk under an A.C. electric field surrounded by suspension-type electrorheological fluid (ERF) were investigated. This report also dealt with the time lags of torque and current density from the applied electric field. Especially, the time lag of the current density was arranged by the power factor. The time lag of the torque becomes larger than that of current density. On the other hand, the data regarding torque and the current density have steady and varying characteristics as amplitude components. Therefore, four aspects of electric power require investigation: apparent power, effective power, steady power from the steady component of the current density, and total power. From the four electric powers, we can deal with four areas of efficiency regarding electric power in relation to torque. They depend on the angular velocity of the disk,,and frequency and intensity of the electric field. The results are explained using the particle aggregation model.

Torque and current density on a rotating disk immersed in suspension-type electrorheological fluid (ERF) under A.C. electric field with were measured. They have steady and varying characteristics as an amplitude components which depend on the angular velocity of the disk, and the frequency and intensity of the electric field. The results were demonstrated by means of a particle aggregation model. The constant torque and current density under D.C. electric field were compared to those under A.C. field. The magnitudes of the differences strongly depend on the angular velocity of the disk and the frequency of the electric field. When an A.C. electric field is used, a smaller frequency should be applied for the sake of greaten efficiency.

A three-ports micro ER valve has been fabricated by a photolithography, which is made of a patterned resist film between two-glass plates coated ITO electrode pattern. And one inlet channel (height h=0.1mm, width w=2mm) of the ER suspension diverges into two outlet channels having ER valves, so that the inflow of the ER suspension from the inlet port is divided into two outflows to the two outlet ports by synchronously controlling a pair of ER valves installed in the outlet channels. The PWM control strategy is applied to a pair of ER valves to change the flow rates, as proposed in our previous paper. The PWM control of each outlet micro-ER valve can realize the almost same changing characteristics of flow rate with the duty ratio as that of a conventional valve. The switching characteristics of a pair of ER valves have been investigated by measuring the flow rates from both outlet ports and visualizing the micro-flow behavior of ER suspension in the ER valves.

Among various materials suitable for an electrorheological (ER) fluid, polyaniline and its many derivatives based upon modification of oxidation state, dopant and polymerization conditions are of technological interest for their adaptation into ER fluids. This is because they have better thermal stability and smaller density than other potential ER materials. Furthermore, polyaniline is easy to polymerize by oxidation polymerization at relatively low temperature and can be doped from a conducting emeraldine hydrochloride form to an insulating state using simple protonic acids. In this study, we adapted the polyaniline based ER fluids for semi-active cylindrical flow-mode type ER damper. A cylindrical flow-mode type ER damper was chosen in this study because it has similar geometrical configuration to the conventional damper normally used for passenger vehicle. The damping forces measured using a semi-active ER damper with polyaniline based ER fluids were found to be controlled by tuning an applied electric field for different piston velocity.

Magneto-rheological (MR) suspensions are actively used in damping devices. As a rule suspensions are magnetic particles in a nonmagnetic environment. The control and field influence are carried out only at the expense of the MR effect. In this article the dissipative environment on a magnetic fluid basis is presented. This gives opportunity to use additional controlling mechanism by this environment at the expense (using) ponderomontive force. It will allow to create the local volume of magnetic environment in the given local place. The attention is given to account of the dissipation force at theoretical investigation of the plate oscillation and corresponding calculation of the damping decrement.

The Lyapunov type robust control is applied to the semiactive vibration control of a controllable seat system to accommodate the modeling uncertainty of system and time delay of the damper. The seat system has a flexible mechanism of a spring and MR fluid damper between a seat cushion and base. Simulation results show that the robust control considering the time delay of the damper suppresses the seat vibration effectively.

The viscous coefficient of a homogeneous ER fluid can be changed by the application of an electric field. However, the ER effect of the fluid is easily varied by temperature variation. Therefore, an envelopment and time in which the fluid is applied is limited.

In this paper, we examine the influence of the thermal effects induced on the fluid by the device, in order to construct more reliable homogeneous ER devices. We discuss two kinds of thermal effects caused by joule thermal and the dissipation of viscous energy.

The results of simulations and experiments suggest that the most of the exothermic elements of the homogeneous ER fluid are caused by the dissipation of viscosity energy in the fluid. Therefore, it seems reasonable to drive the clutch at a low rotating speed for short periods. We think that a robot arm for impedance control is more effective than a damper for vibration control.

Performance analysis for ER (electrorheological) and MR (magnetorheological) fluid-based impact damper systems is evaluated on the basis of the Herschel-Bulkley shear model. Generally, most ER/MR dampers have been analyzed based on simple Bingham-plastic shear model. However, the Bingham-plastic shear model cannot well describe the behavior of the damper in the condition of high velocity and high field input. Therefore, in this study, the Herschel-Bulkley shear model, in which the constant post-yield plastic viscosity in Bingham model is replaced with a power law model dependent on shear rate, is used to assess performance of ER/MR impact damper systems. In doing so, an ER/MR impact damper system is proposed and its governing equation of motion is derived on the basis of the Herschel-Bulkley shear model. Then, computer simulation is done to analytically evaluate characteristics of the ER/MR impact damper system under impact loads. As an important parameter in the Herschel-Bulkley shear model, effects of the flow behavior index, n, that is the degree of shear thinning or shear thickening, on impact damper system performance are shown.

A numerical simulation is conducted to clarify the unsteady flow behavior and drag force around the oscillating fiat plate immersed in MR fluids under the applied magnetic field. A modified Bingham model is adopted to take viscous flow behavior at the small shear rate and also yield stress into account. The experimental yield stress is given to the model as a function of magnetic field intensity. The governing equations for the oscillating flat plate and unsteady MR fluids flow are derived by modified Bingham model taking magnetic body force, yield stress and viscous force into account. The effects of magnetic field intensity, oscillating frequency and amplitude and further plate thickness on the fluid and damping characteristics around the oscillating flat plate are clarified by the numerical simulation.

The present work is aimed at elucidation of the specific features in propagation of ultrasound waves in an electrostructurized medium, of their dependence on an applied electric field and implementation of the effects obtained in practice.

A new high voltage amplifier/supply unit specifically for the demands of ERF applications and ER-fluid testing has been designed, developed and tested. This unit is now commercially available. The heart of the amplifier is a 60kHz clocked blocking oscillator (B.O.) type high voltage transformer operating in current-control-mode. Main attributes of this patented transformer are a low leakage inductance coupled with a reduced influence of the internal capacitance on the natural frequency of the transformer. The B.O. type transformer is fed by the rectified mains voltage (230V AC). Controlled switching of the transformer on the primary side and high voltage dependent forced discharge of the charging capacitor secondary-side via high voltage sink allow externally variable HV (0-6kV) modulation up to 1kHz which is independent of the load. For detailed ER-fluid investigation and exact mechatronic control, accurate load current and load voltage monitoring, flashover indication and minimal signal distortion were design feature requirements.

A high efficiency design was explored for meso-scale MR valves (<25 mm O.D.). The main design issues in the MR valve involve the magnetic circuit and nonlinear fluid mechanics. The performance of the MR valve will be limited by saturation phenomenon in the magnetic circuit and by the yield stress of the MR fluid. The non-dimensional plug thickness is evaluated as a basis for evaluating the valve efficiency. In this paper, design parameters of the MR valve were studied and an optimal performance was designed using these parameters. A maximum magnetic flux density at the gap was achieved in the optimized valve design based on a constraint on the outer diameter limitation. Valve performance was verified with simulation. A flow mode bypass damper system was fabricated and was used to experimentally validate the valve performance.

The use of magnetic fluids in controlling rod vibrations is investigated. A prototype of ferrofluid vibration damper is designed and experimentally set up based on the principle of anti-resonance. The efficiency of this damping system is verified in experiments and well explained with classical equations of motion. The improvement of the present system towards active control of rod vibration is also discussed.

This paper presents shock responses of a cylindrical shock damper featuring an electrorheological(ER) fluid. An appropriate size of the ER shock damper is designed and manufactured on the basis of the field-dependent Bingham model of the ER fluid. The damping force of the ER shock damper is evaluated with respect to the excitation frequency at various electric fields. Subsequently, the ER shock damper is incorporated with a 1 degree-of-freedom (DOF) dynamic system in order to investigate shock responses. A skyhook controller is formulated to attenuate acceleration level due to impulse excitation and empirically realized. Controlled acceleration magnitudes are evaluated and compared with uncontrolled ones at various excitation frequencies.

This paper presents vibration control responses of a commercial vehicle installed with ER primary suspensions and a MR seat damper. After formulating the governing equation of motion of the full-vehicle system associated ER and MR dampers, the sky-hook controllers are designed by imposing semi-active actuating conditions. The control algorithms are then implemented via the hardware-in-the-loop simulation, and control responses of vertical displacement and acceleration at the driver's seat are evaluated under two road conditions; bump and random road.

Underwater explosion that has high energy brings about the shock waves and the pulsating gas bubbles. In general, structural vibration from the shock waves is more serious than that of pulsating gas bubbles. The shock waves may damage the important fragile structures and equipment in the ship. This paper demonstrates the possibility of shock wave reduction in Magneto-Rheological (MR) inserts. To experimentally verify the MR insert, MR insert in an aluminum plate is made and two piezoelectric disks are used as wave transmitter and receiver. By measuring the transmission ratio between the transmitter and receiver, the shock wave attenuation possibility of MR insert in tested. Details of the experiments are addressed.

This paper presents vibration characteristics of a wire cut discharge machine in which an electrorheological brake actuator is used to control the wire tension. On the basis of the tension level required in the machine an appropriate size of the ER brake actuator is devised. The ER brake actuator is then incorporated with the machine and the field-dependent wire tension is experimentally evaluated. The straightness of the workpiece is also empirically investigated by changing the intensity of the electric field. In addition, the tension control performance of the discharge machine is simulated by utilizing a robust sliding mode controller.

The feasibility of using a well-known twin ER clutch linear reversing mechanism as a robotic actuator is demonstrated. High speed of response, displacement and positional accuracy can be obtained bi-directionally. A validated mathematical model of the apparatus provides a basis for the control strategy. Positional accuracy is enhanced by an ER brake which works in sequence with the clutch excitation switches. The robot arm, in rotational displacement is tested over a large number of cycles, speeds, displacements and inertial loads and the quality of control compared to that of competitive conventional servo motors.

Field induced structures are studied inside suspensions of magnetic colloidal particles of micronic size. We have characterized the average distance between aggregates in a thin cell with the magnetic field perpendicular to the plane and also in the presence of a rotating field with the plane of rotation perpendicular to the plane of the cell. The characteristic size of the mesostructure is predicted on the basis of a thermodynamic model. The theory well predicts the experimental results in the uniaxial case but not in the case of ae rotating field; in this last case, the surface tension which is needed to have a good fit is far too low compared to its expected order of magnitude. When the field is uniaxial and sinusoidal we have found a collective instability where all the aggregates are rotating simultaneously in a chaotic way.

In this article it will be demonstrated that columns of particles bridging the electrodes are not the characteristic feature of ER fluids under field. Instead a higher level of order, particle lamellae, must develop under shear and E field if a suspension is to be a legetimate ER fluid.

The dynamics of induced dipolar chains in magnetorhelogical suspensions subject to rotating magnetic fields has been experimentally studied combining scattering dichroism and video microscopy experiments. When a rotating field is imposed the chainlike aggregates rotate synchronously with the magnetic field. We found that the average size of the aggregates decreases with Mason number (ratio of viscous to magnetic forces) following a power law with exponent -0.5 being the hydrodynamic friction forces the cause of the chains break up. However the total number of aggregated particles shows two different behaviors depending on Mason number. For low Mason numbers, the total number of aggregated particles remains almost constant and above a critical Mason number, the rotation of the field prevents the particle aggregation process from taking place so the number of aggregated particles decreases with Mason number following a power law behavior with exponent -1. Athermal molecular dynamics simulations are also reported, showing good agreement with the experiments.

The dipole interaction between a pair of electrorheological (ER) particles under an external AC electric field was confirmed in a dynamic case using optical tweezers positioning and a system of high speed imaging and image processing. By measuring the interactions between two micron-sized ER particles with both central distance and structure forming time, the structure response time and the interaction strength were obtained for the particles under an AC electric field. The spacial resolution of the optical tweezers-high speed imaging-image processing system is 0.26μm. The sampling rate of the high-speed video recorder is up to 8000 frame/s with the corresponding time resolution being 0.125 ms.

General properties of sphere-chain and chain-chain structures are analysed for homogeneously magnetized spheres. For field aligned structures the local maximum of the magnetic force is observed at H₀/M_s ≈ 0.5. The magnetic saturation effects are accounted by the Frölich-Kennelly law. Outlines of the approximate methodology of multi-chain interaction are given together with the test results.

Using diffusing-wave spectroscopy (DWS), we studied experimentally the particle dynamics for a density matched superparamagnetic polystyrene colloid in a refractive index nearly matched multiple-layered cell. Particle dynamics is probed during structure formation and disintegration, when a 0.2 Hz square-wave magnetic field was turned on for 4 s and off for 1 s. The correlation function shows that the particles move slower and more restricted when the magnetic field is on. Even during the off cycle of the magnetic field, the particles' motion is not free but still constrained with a less degree than that when the field is on. Thus, it takes more than 1 s for the induced structure to disintegrate. As the magnetic field strength increases, so does the degree of constrain for both the on and off cycle of the magnetic field and the differences between them. Modified telegrapher theory is found to be valid for our strongly absorbing and limited multiple scattering sample.

A new method of doing DWS (diffusing wave spectroscopy) measurement has been developed by using high speed CCD to investigate the structure and the dynamics of nonergodic and concentrated system such as electrorheological (ER) fluids under high electric field. The DWS results from the CCD method and the traditional method using a single-mode optical fiber agree well for ergodic system. The structure response time is obtained by measuring the transmittance of the sample under different electric field. The force response time of about 100ms is obtained from the time-dependent diffusion coefficient. In this paper, by comparing the time variation of transmittance and diffusion coefficient obtained under different conditions, a criterion of fast and strong responses of practical ER fluids to electric field is provided.

Colloidal particle coordinates in three dimensions can be obtained in 3D samples with a combination of the increased resolution and optical sectioning capabilities of confocal microscopy and fluorescently labeled model core-shell silica colloids. In this work we show how this capability can be used to analyze structure formation in electrorheological fluids on a quantitative basis. We find body-centered-tetragonal (BCT) crystals for colloidal particles in an electric field. Metastable sheet like structures were identified as an intermediate phase prior to BCT crystal formation. Due to finite-size effects induced by the electrode surface the sheets are not randomly oriented, but grow preferentially with a 60° tilt with respect to the electric field. Preliminary measurements indicate that flow-aligned sheets form under shear. Finally, we show that in the case that the ionic strength is very low, electric-field-induced dipolar interactions can be present in addition to long-range repulsions between the colloids leading to interesting metastable and equilibrium structures with possibilities for applications in photonic bandgap crystals as well as in model ER studies.

Non-equilibrium polarizability of a polyelectrolyte ball is calculated in the framework of a quasi-onedimensional model, taking into account the concentration polarization phenomenon. This non-equilibrium polarizability is shown to be proportional to the volume of a polyball and to have a negative sign. Based on these results, the available experimental data on the aggregation phenomena in DNA solutions are considered in terms of the electric field induced phase separation. Numerical estimates for the critical electric field strength necessary for the aggregation to take place and the frequency range where it is observed are in a reasonable agreement with experiment. In the framework of this model, the internal circulations observed in the DNA aggregates are interpreted as being due to the spontaneous rotation of polyelectrolyte balls with a negative polarizability.

A lamellar pattern can form in a thin magnetic fluid layer when the applied electric field is above a critical value. A 2D simulation is performed to study the field-induced phase separation and the pattern by using the mass continuity equation. The simulation produces the similar structure in field but does not match the experimental growth law.

The phase diagram of the magnetorheological suspension allowing for the modulated phases in the Hele-Shaw cell under the action of the normal field is calculated. The phase boundaries between the stripe, the hexagonal and the unmodulated phases in dependence on the layer thickness and the magnetic field strength are found. The existence of the transitions between the stripe and the hexagonal phases at the corresponding variation of the physical parameters is illustrated by the numerical simulation of the concentration dynamics in the Hele-Shaw cell. It is remarked that those transitions in the case of the magnetorheological suspensions can be caused by the compression or the expansion of the layer. Among the features noticed at the numerical simulation of the concentration dynamics in the Hele-Shaw cell are: the stripe patterns formed from the preexisting hexagonal structures are more ordered than arising from the initial randomly perturbed state; at the slightly perturbed boundary between the concentrated and diluted phases the hexagonal and the inverted hexagonal phases are formed and others.

We carry out Monte Carlo simulations of a ferromagnetic colloidal system, which is subjected to an external magnetic field, to investigate the structures formed by chain clusters. The control parameters are the ratio of the dipole moment energy to thermal energy, λ, and the ratio of the interactive energy between the dipole and the external magnetic field to thermal energy, ξ. We investigate the effect of the system height on the pattern formations for λ = 18 and ξ = 30, ∞. Note that the system becomes paramagnetic when ξ = ∞. We find that as the system height increases, chains coagulate to form fat clusters and spatially ordered structures are created when ξ = 30, whereas chains form thin meandering walls when ξ = ∞.

We investigate equilibrium and dynamic magnetic characteristics of a triangular ferromagnetic lattice system by the Monte Carlo and Brownian dynamics methods. We find that dipoles form hexagonal vortex structures under certain conditions. We investigate the effect of the control parameters on the specific heat and linear and nonlinear magnetic susceptibilities. We also investigate the effect of an external dc magnetic field on the magnetization. We find that when the dipole-dipole interaction is strong, an hysteresis appears in the magnetization-magnetic field relation, which is similar to the magnetic characteristics of spin glass.

W have developed a new Ewald summation for a three-dimensional dipolar system with two-dimensional periodicity in a uniaxial field and a rotating field in a horizontal plane. Under a constant pressure and temperature, Monte Carlo simulation has been carried out; phase transitions are found and chainlike structure for a uniaxial field and monolayer or multilayer for rotating field are obtained, which are well consistent with experiments.

Different concentration of spherical iron particles (7 to 8 μ m) are dispersed in silicone oil to increase the stability with smectite. The concentration of iron particles is maintained between 2 to 40 volume %. The solenoid coil surrounding the cylinders applies the magnetic field in the longitudinal direction of cylinder, when the cylindrical viscometer is employed. As the magnetic field increases, the diameter of chain structure also increases. The shear stress versus shear rate is proportional relation since the viscosity enlarges as the magnetic field increases at small concentration of iron in MR fluid. Additionally, the more increase of the magnetic field strength caused the decrease of the shear stresses at large concentration of iron in MR fluid, while the share rate is increased for the open system of the cylinders. It is assumed that wider clusters or wider chain structures are partly produced in the cylinder under the certain magnetic field. Therefore, the shear stress is not uniformly increased. On the other hand, when the cone and plate viscometer is used, the magnetic field direction is perpendicular to the flow direction. The shear stress versus share rate behaves like a Bingham fluid type under the effect of the magnetic field. As increasing the iron particles volume %, the chain structures cannot increase and make other ring type structures. When the magnetic field is measured by hall probe, the magnetic field decreased at some amount of volume percent of iron in suspension because of shield effect.

This paper describes a new class of water-free electrorheological (ER) fluids based on nonaqueous doped TiO₂ with rare earth (RE) in silicone oil. The thermal character and crystal structure of these materials are investigated with DSC, TG and XRD. The doped TiO₂ crystals possess anatase phase and their lattice spacing varies significantly with the content of rare earth. The rheological measurements show that the doped TiO₂ ER fluid exhibits an obviously higher shear stress than that of pure TiO₂ ER fluid under dc electric field. Especially, substitution with 10mol% cerium or 8mol% lanthanum for Ti can obtain a relatively high shear stress. On the basis of dielectric and conduction measurements, we preliminarily discuss the influence of the doping of rare earth on ER effects of TiO₂.

The ER effect results from bulk and surface electric polarization processes in solid grains of ER suspensions but detailed mechanisms are not very clear. The aim of the present study was to find correlations between the character of bulk charge transport processes (electronic and/or ionic) in particles of a dispersion and parameters of the ER effect. As the dispersed phase we used glasses comprising oxides of silver, vanadium and phosphorus with addition of silver iodide. Bulk electric properties of this material could be modified without changing other properties influencing the ER effect like porosity, shape of grains, hardness, affinity to a liquid matrix etc. Variations of concentration of the components result in changes of ionic and electronic conductivity whilst other properties remain constant. The suspensions of the powdered glasses showed relatively high ER effect. The dynamic yield stress figured from 35 to 160 Pa at 2.0 kV/mm for 12% concentration by volume. The highest values were observed for ionically conducting samples. The values of relaxation frequencies (f_R) based on bulk properties of the glass samples were calculated and correlated with the yield stress whose maximum was obtained for samples of f_R close to 100 kHz. High ER effect was observed also for samples of f_R in the MHz range but in this case different polarization mechanism was postulated. The influence of polarization mechanisms on rheologjcal behavior of the prepared fluids was discussed.

Water-soluble urethane-modified polyethers were prepared by addition of poly(ethylene oxide)-co-poly(propylene oxide) and aromatic isocyanate compounds. These polymers were found to dissolve in water at lower temperature and separate from solution upon heating. The temperature showing this unusual solubility change is called lower critical solution temperature (LCST). These chemical structures of thermo-responsive polymers were similar to those of urethane-modified ER active polymers containing poly(tetramethylene oxide) and aromatic urethane moiety. The thermo-responsive and ER polymers may have various intra- and intermolecular interactions through the urethane moiety. It is considered that both thermo-responsivility and ER effect are dependent on the conformational stability of the polymers under different conditions possibly related to these stimuli-responsivility through the molecular interactions. In order to clarify molecular motion of thermo-responsive polymers near the LCST, ¹H-NMR spin-lattice relaxation time (T₁) was measured in D₂O. The result indicated that hydrophobic interaction of terminal urethane moiety would strongly affect the LCST behavior.

Iron nanopowders for use in magnetorheological (MR) fluids were synthesized using a Microwave Plasma Synthesis technique developed at Materials Modification Inc (Fairfax VA). Transmission electron microscopy and surface area analysis measured iron particle size at 15-25 nm. The nanopowders were mixed into hydraulic oil to create nano-scale MR fluid. A micron-scale fluid was created using 45 μm iron particles as well as a hybrid fluid using a 50/50 mix of micro- and nanoparticles. All three fluids had a solids loading of 60% (w/w or weight by weight fraction). The fluids were tested in a flow mode rheometer fabricated from a modified damper using a sinusoidal input dynamometer over a speed range of 12.7 to 177.8 mm/s (0.5 to 6 in/s) and an input current range of 0 to 2 A. The yield stress and plastic viscosity of the MR fluid were characterized using a Bingham plastic model.

The MRF consisted of protein-Fe particles prepared by micro emulsion technique has been studied. The process of protein-Fe preparation and its characterization with XRD, SEM and IR analysis are reported. The magnetorheological and temperature effects, as well as sedimentation stability of protein-Fe MRF have been investigated. The results show that the protein-Fe particles are composite of crystalline α-Fe coated with non-crystalline protein. The protein-Fe MR fluid has strong magnetorhological effect, while its sedimentation stability is much improved comparing to that of carbonyl iron MRF.

Some functional fluids that respond to both magnetic and electric fields have been prepared and their characteristics are described. In this study, an electro-magnetorheological fluid (EMRF) dispersing zeolite particles containing metallic iron by reducing precipitated magnetite has been investigated. When the viscosity is measured by cone plate viscometer and cylindrical viscometer, electric and magnetic fields are applied both between cone and plate or two cylinders. In case of cone plate, the shear stress at constant shear rate increased with the increase of both magnetic field and electric field. On the other hand when the viscosity is measured by cylindrical viscometer, the shear stress at constant shear rate increased with the increase of electric field, however, the increase rate of shear stress by magnetic field is very small. In this case the magnetic field direction is perpendicular to electric field. The EMRF has typical characteristics to respond with magnetic and electric field. The shear stress of EMRF in electric field is stronger than that of magnetic field. Additionally, the inflection and peak point in the shear rate-shear stress curve are appeared and the behaviors of the clusters in the electric field are observed. The experimental results suggested that the fluid viscosity (shear stress/shear rate) is affected by the arrangement of clusters parallel or perpendicular to the direction of the EMRF flow.

A host of fascinating and useful magnetic phenomena are found in composites containing magnetizable particles in viscoelastic solids. Embedding magnetically soft iron particles in natural rubber produces a class of magnetostrictive composites sometimes termed magnetorheological (MR) elastomers. We have previously shown that these materials can exhibit viscoelastic moduli that increase substantially in an applied magnetic field. In this paper, we incorporate MR elastomers in a simple resonant structure called a tuned vibration absorber to measure the complex dynamic shear moduli of these materials at high frequencies. We find that the field-induced modulus increase in MR elastomers is substantial even at kilohertz mechanical frequencies. As in previous measurements at low frequencies, the moduli are generally found to decrease with strain amplitude. We also report preliminary measurements of the relatively large elongation of these materials in applied magnetic fields.

The mechanical properties of magnetic gel have been investigated. Magnetic gels, which consist of finely dispersed powder of barium ferrite (BaFe₁₂O₁₉) and poly vinyl alcohol (PVA), have been synthesized. The diameter of barium ferrite is less than 45 μm. The magnetic gels varying with ferrite concentration, crosslinking densities were prepared by mixing 10 wt.% PVA aqueous solution and barium ferrite using glutaraldehyde as a crosslinking agent in the presence of HCl. The diameter of barium ferrite is large enough to have a permanent magnetic moment. We applied a 10 kOe magnetic field in order to saturate the magnetic moment of barium ferrite. After magnetization, the compressive modulus was estimated with an ultrasonic method in order to find the influence of magnetization. Ultrasonic measurements were carried out using burst waves at 10 MHz and 295.5 K. The modulus of magnetized gel was found to depend on the concentration of magnetic substance, the crosslinking density, and the degree of swelling. It was clear that the modulus of magnetized gel was higher than the gel without magnetization for all samples. The change in modulus to the initial modulus ΔM'/M'0 for 10 wt.% and 15 wt.% of ferrite concentration was about 0.28% and 0.4% in a lower density region, respectively. Moreover, the change in modulus ΔM'/M'0 was constant in a lower density region however it strongly depends on the density in a higher density region. When the stress direction is perpendicular to the magnetization, the change in modulus increased. On the contrary, the change in modulus decreased when the stress direction is parallel to the magnetization. As increasing the density, the distance between magnetic substances become short and therefore the magnetic interaction is more significant in a higher density region.

We introduce a new technique for probing the microscopic relaxation of magneto-viscoelastic materials consisting of magnetic particles embedded in a natural rubber matrix. Transversely coherent x-rays from a high brilliance synchrotron source are scattered by the magnetic particles, forming a speckle pattern at low scattering angles. The time dependence of this pattern is recorded with a CCD area detector while the sample is cyclically perturbed by a reversal of the magnetic field direction. The corresponding time-resolved scattering pattern probes both the dynamics of the particles and the relaxation of the matrix in which they are embedded. X-ray photon correlation spectroscopy (XPCS) reveals characteristic time scales for this relaxation by applying the intensity auto-correlation function to the time dependent speckle pattern. For low angle scattering, the wave vector dependence of the relaxation rate exhibits power law length scaling.

The silicone oil-based electrorheological (ER) gel containing the non-aqueous fine particles was newly created in the present study. After these particles were dispersed at 30wt.% in the dimethylsilicone oil, the ER gel was produced by the hydrosilylation reaction in the mixture of the modified silicone oil. This reaction could considerably be promoted by heating at 90°C.

The behavior of particles in the ER gel was observed by a microscopical method. When an electric field was applied to the ER gel, the gap between the electrodes was bridged by the chains of particles arranged in the direction of the electric field. The dynamic properties of the ER gel were also examined under the applied dc electric field up to 2kV/mm using the oscillating rheometer with the low frequencies of 1Hz or less. Consequently, it is shown that the electroviscoelastic effect of the gel can be controlled by the electric field strength.

For a number of years we and others have investigated electrorheological (ER) gel systems comprising low-modulus elastomers mixed with various particles. Unlike ER fluids, the particles in gels do not change relative positions, thus creating model systems that can be used to check equilibrium theories of ER response. To make such materials, a magnetic field was used to align iron particles during the cure of a liquid silicone prepolymer in a sheet mold. Particle chains were made with as little as 0.5% particles, and aligned at angles from 0 to 45° to the normal. The gap between the particles was controlled by swelling the crosslinked material with additional prepolymer. The dependence of the ER effect on particle structuring in these materials was investigated experimentally using rheometry and dielectrometry. Also investigated were the properties of these materials as transducers and actuators.

A magnetoactive elastomer made of micronic carbonyl iron particles, structured in elongated clusters and embedded in a silicon elastomer matrix is studied under traction both in static and dynamic modes. The application of a magnetic field of 120kA/m induces a change in elastic moduli of about 0.6MPa at strains of 4 to 5%. Still higher changes(4MPa) are observed in dynamic storage modulus at low strains (10^-4 to 10^-3). The shape of the stress-strain curves are explained by taking into account the existence of a fiber like structure.

Magnetorheological rubber is the solid analog of magnetorheological suspensions. The incorporation of magnetically polarizable particles in a rubber matrix results in a material for which the shear modulus can be increased by an applied magnetic field. The main advantage of magnetorheological rubbers in comparison with magnetorheological suspensions is that since the matrix is crosslinked the particles do not sediment. However, magnetorheological work only in the pre-yield region while suspensions typically work in the post-yield region, so the two groups of materials are more complementary than competitive.

We have produced and analyzed magnetorheological rubbers, made from nitrile rubbers with different acrylonitrile content and large (over 50 µm) iron particles. The acrylonitrile content in the material influences material properties as the modulus and the damping. The materials were conventionally sulfur vulcanized. The increase in the dynamic shear modulus caused by a magnetic field of 0.2T was measured. Even though the particles have not been aligned within the material by an applied magnetic field during the curing, the increase in modulus is substantial.

In-situ sol-gel method to prepare colloidal hybrids of surfactant modified polysucchride and titanium oxide has been presented, and experiments indicated these highly ER active particles exhibited a remarkable ER effect. The static shear stress can be up to 37 k Pa (shear rate 5 S^-1) under DC field of 4 kV/mm at room temperature, well above that of simple blends of starch and TiO₂. In the meanwhile, temperature dependence and sedimentation stability were also greatly improved. Based on recent experimental facts, we find that dielectric properties and surface (interface) activity are two necessary conditions fulfilling the requirement of high ER activity. Adequate grinding of particles with oil can effectively enhance the shear stress, which may be owed to the decline of the activation energy needed for restructuring. It has provided us a new horizon for preparation of excellent ER materials and further studies should be continued to make.

Sedimentation which is a natural process in most of ER fluids can be reduced by addition of surfactants that influence also other properties of the fluids. To study both the ER effect and the rate of sedimentation was the aim of the investigations. The ER fluids comprised powdered polyaniline and silicone oil to which surfactants of different polarity were added. The rate of sedimentation was measured by a sedimentation balance. The flow curves were recorded under electric field up to 2.5 kV/mm. Current density was also measured as a function of shear rate. It was found that the activity of a surfactant depends strongly on its polarity. The lipophylic surfactants stabilized the suspension very well but about 30% decrease of the dynamic yield stress was observed. The current density was reduced as well by almost one order of magnitude. The hydrophylic surfactants hardly stabilized the suspension but increase of yield stress was observed that was not followed by increase of current density. The role of different types ofnon-ionic surfactants was discussed.

Blends of immscible liquids with different dielectric constants and viscosities were known to show the ER effect due to the change of the domain structure by the electric field. One of major problems of this type of ER fluids is that the stress dose not drops to the original value even long after the removal of the field. In this paper, we report on our attempts to improve the reversibility of the ER effect in immiscible blends.

The ER effects were studied for various immiscible blends composed of urethane-modified polyethers and silicones. Some polyethers and silicones were prepared from polypropylene glycol (PPG) and modified poly(dimethyl siloxane) having terminal hydroxyl groups, respectively. The influence of blend composition on the ER effects were examined for some binary and ternary blends based on these materials. The ER effects of these blends varied with the modification of polyethers and silicones, and also with the blend composition. In particular, the response of viscosity on applying or removing an electric field was found to vary with the blend composition, which should reflect some time-dependent change in the phase structure during the application and removal of the electric field. The variety of field response are discussed on the basis of the miscibility of the blend components.

Ternary ER blends composed of two different liquids and solid dispersoid were prepared by blending silicone oil, viscous polyether liquid, and urethane powder at various compositions. The polyether liquid used here was polytetramethylene glycol modified with phenyl isocyanate, and the powder was urethane derivative of 4,4'-diphenylmethane diisocyanate. Under certain conditions, some of the ternary blends showed larger increase of viscosity under an electric field than those of binary mixtures prepared from each component of the ternary one. In this case, the viscous polyether and urethane powder act cooperatively by forming some particular structures within the blends. Microscopic observation revealed that each urethaneparticle was covered with polyether liquid in the absence of electric field, and that the binary droplets aggregated to form viscous bridges between the electrodes keeping powders within them.

In order to investigate relationship electro-rheological (ER) response and stiffness of matrix gel (ex. silicone gel) we synthesized two types of silicone gel containing dielectric particles as a sample and measured modulus of these samples. We suggested ER response does not depend on modulus of matrix gel but structures in matrix.

As a candidate for the development in electrorheological (ER) materials, phosphate cellulose (PC) particles were synthesized from the phosphate–ester reaction between cellulose particles and ammonium phosphate solution prepared from six different molar concentrations of phosphoric acid. The synthesized particles were then dispersed in silicone oil to prepare the PC- based anhydrous ER fluid. The effects of electric field strength and particle concentration on the ER performance were investigated with both steady shear and dynamic oscillatory shear modes. The ER system with PC particles formed with a 2 M phosphoric acid solution exhibited the highest yield stress. A difference in the flow behavior of the PC-based ER fluids was also analyzed via the dielectric spectra using an impedance analyzer. We adapted the PC-based ER fluids to the the semi-active ER damper and then examined their damping characteristics.

Electrorheological (ER) effect of surface modified silica particles dispersed in silicone oil was experimentally studied. Monodispersed silica particles were prepared by hydrolyzing tetraethylorthosilicate in an ethanol solution. Rheometry measurements of shear stress and viscosity under shear rates of the suspensions were carried out with a rotational double concentric rheometer. Electric field is applied transverse to the direction of the shear. Flow curves reveals that there is no field effect on dispersion of dried particles. When water is adsorbed on the silica particles surface, the ER effect exists, but beyond a rate of 5 wt% of water, the capillary forces produce the aggregation of the particles. This agrees with the theory where it has been shown that the ER behaviour is proportional to the dielectric constant of the particles. Moreover hydrated lithium cations adsorbed on the silica surface involve a reversible ER effect with short relaxation times.

The electrorheological (ER) behavior of amine coated chitosan phosphate suspension in silicone oil was investigated. Amine coated chitosan phosphate suspension showed a typical ER response (Bingham flow behavior) upon application of an electric field due to the polarizability of phosphoryl polar group. The shear stress for the suspension exhibited a linear dependence on an electric field power of 1.94. The values of structure factor, A_s obtained 2 for amine coated chitosan phosphate suspension and it may be due to the formation of multiple chains upon application of the electric field. Throughtout the experimental results, The suspension showed good dispersion stability and found to be an anhydrous ER fluid.

The electrorheological (ER) behavior of chitosan dicarboxylate suspensions in silicone oil was investigated by varying the electric fields, volume fractions of particles, and shear rates, respectively. The chitosan dicarboxylate susepnsions showed a typical ER response caused by the polarizability of an amide polar group and shear yield stress due to the formation of multiple chains upon application of an electric field. Of these, chitosan malonicate suspension represented slightly higher rheological performance than any other suspensions due to dependent upon the carbon chain length. The shear stress for the suspension exhibited a linear dependence on an electric field power of 1.88. On the basis of the results, the newly synthesized chitosan dicarboxylate suspensions were found to be an anhydrous ER fluid.

Electrorheological (ER) suspensions containing spherical-monodispersed polymer particles in silicone oil were investigated. The core was poly(methylmethacrylate) (PMMA), obtained by dispersion polymerization method, and the shell, coated on monodisperse PMMA particles, was polyaniline(PA) prepared by in-situ polymerization of aniline in aqueous acidic medium. Both steady shear and dynamic tests were conducted under various electric field strength and particle concentrations in order to study flow and viscoelastic properties of the PAPMMA based ER fluids. Dielectric spectra of the ER fluids obtained were found to give a clue both to analyze their electrical polarization properties and to interpret flow behavior of the PAPMMA ER fluids.

Electrorheological (ER) properties of a fluid composed of mesoporous MCM-41 particles suspended in silicone oil under a high electric field were investigated. Typical properties of ER fluids such as viscosity enhancement and viscoelasticity under applied electric fields in MCM-41/silicone oil suspensions were observed. In the dynamic and static yield stress measurements, a strain hardening effect was also observed and subsequently confirmed by elasticity measurement as a function of time under a linear viscoelastic condition.

Polyaniline-montmorillonite nanocomposite (PANI-MMT) particles were synthesized by an emulsion intercalation method and characterized by IR, XRD and TEM spectrometry. TEM showed that the particle's size of MMT-PANI particles was about 100 nm. The dielectric constant of PANI-MMT nanocomposite was increased 2.4 times than that of MMT and 7 times than PANI, the conductivity of PANI-MMT particles was increased 10 times than that of MMT. Meanwhile, the dielectric loss tangent was also increased about 1.36 times than that of PANI. The electrorheological behaviors of the suspensions of PANI-MMT nanocomposite particles in silicone oil with a 30% weight fraction were investigated under DC electric fields. In 3 kV/mm DC field at room temperature, the yield stress was 8.26 kPa (shear rate 5 s^-1). In 4 kV/mm DC field, the shear strength was 8.30 kPa (γ=103.1 s^-1, T=20 °C), and much higher than that of pure polyaniline (PANI), montmorillonite (MMT) and mixture of polyaniline with clay (MMT+PANI). The sedimentation experiment showed that the PANI-MMT nanocomposite particles did not deposit during about two months. The relevant influential factors between shear stress and electric fields, between shear stress and shear rate, between shear stress and temperature was also discussed preliminarily. The results showed that the MMT-PANI ER fluid displays a notable ER effect under DC electric field.

When a strong electric field is applied to a suspension of micron-sized high T_c superconducting particles in liquid nitrogen, the particles quickly aggregate together to form millimeter-size balls. The balls are sturdy, surviving constant heavy collisions with the electrodes, while they hold over 10⁶ particles each. The phenomenon is a result of interaction between Cooper pairs and the strong electric field. The strong electric field induces surface charges on the particle surface. When the applied electric field is strong enough, Cooper pairs near the surface are depleted, leading to a positive surface energy. The minimization of this surface energy leads to the aggregation of particles to form balls.

The granular flow in a vertical pipe in the presence of electric field E is studied. Depending upon its initial state and the applied field voltage the controlled flow rate remains in two phases, dilute flow or dense flow. For dilute flow, the electric field has no effect on the flow rate until V reaches a critical value V₁. At V = V₁, the flow rate drops abruptly and a transition of the particulate from dilute to dense flow occurs. For dense flow, the flow rate decreases monotonically with increasing V. A two-dimensional computer simulation has been done and the results agree qualitatively well with the experimental measurements.

The bridging of electrodes by the columns of highly viscous polymer is dominant feature of the response of most electro-rheological liquid polymeric blends to the imposed electric field. To link the columnar structure and its deformation to the macroscopic shear stress, the transitory process of structure reorganization is described as a stochastic process determining rheological properties of the blend. The shear stress predictions are compared to the experimental data for steady and start up shear flows. The data support the assumption that only viscous deformation prevails in shear flow.

The effects of shape and size of dispersoids on electrorheology were investigated. In order to study the effect of shape on electrorheology, three kinds of hydroxy-zinc complexes were used for dispersoids. Hydroxy-zinc complexes were Zn₅(OH)₈Cl₂ • H₂O(1), Zn₅(OH)₈(NO₃)₂ • 2H₂O(2), and Zn₅(OH)₈(CH₃COO)₂ • 2H₂O(3). Shapes of (1) and (2) are plate. The shape of (3) is rod. The ER fluid containing (3) showed the lowest permittivity and the lowest ER effect. The ER phenomena containing dispersoids with different shapes were independent of their shapes and were explained by their dielectric properties. Zinc oxides prepared by the heat treatment of (1), (2), and (3) were used for studying the effect of size on electrorheology. The particle size influenced their dielectric property and influenced their electrorheology. The dielectric properties were responsible for the ER effect.

When an electrorheological fluid between two parallel disk electrodes is subjected to squeeze mode excitation, the microstructural flow behavior of the ER fluid has been investigated in close relation to the measured electrorheological properties. A dilute anhydrous ER fluid made of 10 vol% carbonaceous particles dispersed in silicone oil and two ITO glass disk electrodes are used to visualize the microstructural flow behavior. The squeeze tests are carried out on a mechanical testing machine in tensile, compression and oscillatory squeeze modes. The ER properties and the associated flow-induced microstructures are measured and visualized for different initial DC electric field strengths and initial gap h_i=0.5 mm between the electrodes in two different configurations: (a) the fluid is placed only between the electrodes (conf-1) and (b) the two electrodes are immersed in the ERF (conf-2).

We propose a model that takes into account the effect of flow-modified permittivity on electrorheology (ER). Due to dielectric relaxation, a shear flow causes the induced particle dipole moments in an ER fluid to tilt in a direction away from the direction of the applied DC electric field. Results from our computer simulation indicate that at high shear rates this misalignment (tilt angle) between the particle dipole moments and the applied electric field plays a crucial role in producing ER effects. By choosing particle-fluid dielectric and conductive mismatches to optimize the tilt angle, our simulation produces ER effects at much higher shear rates than those in earlier simulation work, even though there is no chain structure at these high shear rates. The increase in shear stress due to the applied electric field in our simulation is nearly constant over the wide range of shear rates examined, in qualitative agreement with experimental results. In addition, our model generates results that agree with earlier simulation work at low shear rates, where the particle dipole moments are essentially aligned with the field and the chain model is adequate.

Liquid crystal is one of homogeneous ER(Electro-rheological) fluids in some range of temperature. Transient responses of pressure drop are examined when liquid crystal flows between two parallel-plate electrodes for constant flow rates. When voltages are applied on the liquid crystal and removed, the pressure responses of the inlet of electrodes are measured with the pressure transducer. At the same time, liquid crystal between the transparent electrodes made of glass is visualizedwith the high-speed video camera to investigate the time history of the director of the liquid crystal. Outlet of the flow channel with two parallel-plate electrodes is atmosphere. Relation between the flow visualization results and the changes of pressure drop is investigated especially for transient period. In the present experiment the flow rates change from 0.001cc/sec(velocity is 1mm/sec) to 0.003cc/sec and the electric field intensity is from 0.2kV/mm to 1kV/mm. The gap of the electrodes is 0.2mm. The isotropic-nematic transition is 35.5°C and smectic-nematic transition is 23.1°C. The open-loop test facility with the liquid crystal is set in a pyrostat to keep the temperature constant.

An experimental investigation is described concerning the effect of the existence of a remanent magnetization of the dispersed particles on the rheological properties of magnetorheological fluids (MRF). Two MRF's were used: (1) solid phase: cobalt ferrite particles + silica gel (1.5 % w/w); liquid phase: silicone oil (viscosity 20 mPa·s); and (2) solid phase: carbonyl iron + silica gel; liquid phase: silicone oil. The cobalt ferrite particles were synthetized as monodisperse colloidal spheres with an average diameter of 850 nm. The dependence of the dimensionless shear stress (τ*/Φ) vs. Mason number (Mn) fails to scale when a "magnetorheological hysteresis procedure" is followed, specially for the higher volume fractions used (≈ 7.5 %). The yield stress (τ_y) is first estimated from successive rheograms obtained decreasing the external field (H₀) values for different Φ. A more precise determination can be done by applying a stress ramp in the oscillatory regime. The critical stress amplitude (τ_c) needed to exceed the viscoelastic linear region (VLR) is obtained. It is found that both τ_y and τ_c strongly depend on the magnetic history of the sample. As expected, the previous results were not obtained in aclassical MRF of carbonyl iron particles since they do not present magnetic hysteresis. We conclude that cobalt ferrite suspensions are an other kind of MRF which works at low fields (0 - 17.8 kA/m) with the opposite effect: decrease of the yield stress with the field. This property can be improved using particles with stronger remanent magnetization.

The rheological and dielectric behavior of novel electrorheological suspensions composed of non-colloidal silica gel particles of irregular shape and oil-in-oil emulsions with different electrical conductivity (and permittivity) are studied in this work. The rheological behavior of the suspensions is examined in systems with various compositions of the oil phase under different intensities of constant DC electric fields. Results reveal that the electrorheological (ER) response of the oil-in-oil emulsion increases with the applied voltage but is affected negatively when the concentration of the oil with higher conductivity is increased. When a small volume fraction of silica gel is added, the ER response increases considerably and its magnitude is strongly dependent on the electric field. In this case, however, larger concentrations of the oil with the higher conductivity, in the presence of silica particles, increase the relative viscosity of the suspensions. The dielectric properties of the suspensions are examined to elucidate the relation between the dielectric relaxation process and the relative composition of liquid drop phases. The mechanisms responsible of the ER response are explained in terms of the relationship between the microstructure changes in the suspensions and their rheological and dielectric properties.

The optical attenuation of light passing through a magnetic fluid film under a perpendicular magnetic field was investigated by measuring the optical transmission. A light with a wavelength of 1557 nm is normally incident to the magnetic fluid film, which is subjected to the magnetic fields perpendicular to the plane of the film. The experimental results show that the transmission I/I_o of a given magnetic fluid film decreases exponentially with the increasing thickness L of the film under a fixed magnetic field. By fitting the experimental I/I_o(L) data to the equation I/I_o = exp(-L/δ), the attenuation length δ can be obtained. It was found that the attenuation length could be reduced by raising the magnetic field strength, whereas the optical trnasmittance and attenuation length of magnetic fluids are independent of the sweep rate of the field. According to the experimental data, the optical attenuation length of the magnetic fluid ranges from tens to hundreds of micrometers.

In the paper half of a radial electro-structured fluid (ESF) clutch with vertical axis, consisting of a lower stationary disc and upper rotating disc is examined for constant speed of rotation. The narrow gap between the discs is filled with a viscous liquid, so electro-rheological effect is not taken into consideration. Frictional tangential forces in the fluid generate heat which is transferred through the fluid and rotating disc (by conduction) into surrounding air (by convection).

A steady state model of heat transfer for the system in question is built up and solved to enable the establishment of heat transfer prediction to be achieved. Several novelties in approach and solution relative to existing ones are adopted and realized. For some particular cases theoretical results are compared with experimental values by means of a table and gaphically and a good agreement is achieved.

The paper is the second part of a double paper, the first part of which is focused more upon general philosophy and experimental side of the problem in question.

An improvement of liophobic capillary-porous systems using magnetic fluids is proposed. The cycle of non-wetting liquid penetration and displacement is realized experimentally in the presence of the uniform magnetic field. Experimental investigations of the effect of the external uniform magnetic field on dynamics of capillary penetration of the Newtonian magnetic fluid into cylindrical capillaries at zero gravity and under gravity are presented. It is found that the pressure difference in the magnetic fluid between a meniscus and a free surface in a vessel increases in the field longitudinal to the capillary and decreases in the transverse one. In the longitudinal field, the velocity of penetration increases at zero gravity and does not vary under gravity. The transverse field slows down the process.

We present a model to investigate the induced interaction between rotating particles in ER fluids. For particle undergoes uniform rotation or harmonic oscillation, the effects due to dipole relaxation are studied analytically. The induced interaction between particles which are rotating uniformly is derived. The result shows that the dynamic effect reduces the interaction between particles. A proof on the consistency of the relaxation equation with charge conservation upon rotation is also given.

When particles immersed in a semi-insulating liquid are submitted to a sufficiently high DC field, they can rotate spontaneously around any axis perpendicular to the field (Quincke rotation). Recently we have shown that due to Quincke effect the effective viscosity of a colloidal suspension could be reduced. When the suspension is submitted to a shear, the particles rotation is amplified by the electric torque and drives the suspending liquid. For a flow in a capillary, this effect manifests itself by an increase of the flow rate. We present the results of our experiments carried out with a rectangular cross section capillary. These results are compared with the direct determination of the apparent viscosity in a Couette flow rheometer.

We investigate numerically the effect of an external ac magnetic field on the rheological characteristics of a ferromagnetic colloidal system which is subjected to a shear flow field. We carry out Brownian dynamics simulations, in which both translational and rotational motions of ferromagnetic particles are taken into account. The nondimensional parameters, which govern the problem, are the ratio of the magnetic dipole energy to thermal energy, λ, the ratio of the interactive energy between the magnetic field and the dipole moment to thermal energy, ξ, and the ratio of the shear rate to the viscosity, Pe, which is called the Peclet number. We analyse the dependence of the apparent viscosity on the frequency of the external magnetic field for λ= 1.5, ξ = 2 and Pe = 1. We find that when λ is as small as 1.5, in which case large clusters are not formed in the system, the apparent viscosity increases at low frequencies and becomes almost zero at high frequencies. The viscosity starts decreasing and becomes negative at intermediate frequencies.

Polymer gels swollen with a magneto-rheological suspension are highly elastic materials with considerable magnetic susceptibility. In this work the magnetic field induced deformation and motion of these magnetic polymer systems is discussed. We present a continuum material model by introducing magnetic equations into non-linear elasticity theory. The material properties of these magnetic rubber-like substances are characterized with a Langevin type magnetization and a neo-Hookean strain energy function. The non-linear character of the equations that describe the material properties and the nonhomogeneity of the deformation lead to a unique deformation mechanism. In order to demonstrate the characteristics of the magnetic field induced deformations we present numerical and finite element calculations and compare them with experimental results.

A new technology, compression-assisted aggregation, is developed to enhance the strength of electrorheological(ER) fluids. The yield shear stress of ER fluids depends on the fluid microstructure. The unassisted electric-field induced ER structure mainly consists of single chains, whose weak points are at their ends. This new technology produces a structure consisting of robust thick columns with strong ends. As the weak points of the original ER structure are greatly enforced, the new structure makes ER fluids super-strong: At a moderate electric field and moderate pressure, the yield shear stress of ER fluids at 35% volume fraction exceeds 100 kPa, well above any requirement for major industrial applications.

Oscillatory convection in viscoelastic ferromagnetic and dielectric liquids of the Rivlin-Ericksen, Maxwell and Oldroyd types is studied analytically by considering free-free, isothermal boundaries with idealized conditions on the magnetic/electric potential. The linear theory reveals the stabilizing nature of the strain retardation parameter and the destabilizing nature of the stress relaxation and magnetization/dielectric parameters. The Maxwell liquids are found to be more unstable than the one subscribing to the Oldroyd description whereas the Rivlin-Ericksen liquid is comparatively more stable. The results have implications in many non-isothermal applications of ferromagnetic and dielectric liquids especially in energy conversion devices.

The electrorheological (ER) fluids exhibit a drastic change in rheological and electrical properties. Among these properties, yield stress is one of the critical evaluation parameters of the performance of ER devices. The published experimental data of yield dependence on the electric field strength and particle volume fraction are inconsistent due to the time dependence of material properties and measuring conditions. In this paper, we present a universal function, descriptive of the normalized yield stress, via scaling of the applied electric field strength. This scaling equation hybridizes both the polarization and conductivity models. Yield stress data for various ER fluids are collapsed onto a single curve for a broad range of electric field strengths, suggesting that the proposed scaling equation is adequate for predicting the ER property. Furthermore, the yield stresses, obtained from two different measuring techniques (static and dynamic methods), were also examined.

We construct a microscale model for a rigid particle suspension in a viscous fluid that includes Maxwell electrostatic forces. Via homogenization techniques we characterize the properties the material exhibits at the macroscale. The change in the effective constitutive equations is due to the highly oscillating electrostatic forces. The material properties are determined by both hydrodynamic and electrostatic particle interactions.

A thermodynamical continuum modelling is proposed for electrorheological fluids. This thermodynamical approach tries to describe the response of an electrorheological fluid in the solid phase (which means with an applied adequate electric field) under mechanical solicitations. Thermodynamic formulations distinguish the contributions due to reversible and irreversible process. In an electrorheological fluid the microstructure generated by the application of an electric field introduces parameters whose the evolution of which influence the behavior. These parameters will be defined as internal variables, or hidden variables, in the formulation of thermodynamics. They are used for the description of dissipative effects. The choice and the number of pertinent parameters are crucial and need to be selected according to the nature of microscopic mechanism and experimental observations. The presence of fibrous structures in the E.R. fluid, when an electric field is applied, is an observed fact. In the theory of thermodynamics with internal variables, the introduction of internal variables doesn't modify, by hypothesis, the balance equations. Nevertheless, the experiments show the existence of hysteresis phenomenon due to the reorganization, at the microscopic level, of the particles that compose the fibers. In order to describe these phenomena, we introduce two internal variables following an idea of Kiryushin.

In this paper, the experimental and modeling study and analysis of the stress relaxation characteristics of magnetorheological (MR) fluids under step shear strain are presented. The experiments are carried out using a rheometer with parallel-plate geometry. The applied strain varies from 0.01% to 100%, covering both the pre-yield and post-yield regimes. The effects of step strain, field strength, and temperature on the stress modulus are addressed. For small step strain ranges, the stress relaxation modulus G(t, γ) is independent of step strain, where MR fluids behave as linear viscoelastic solids. For large step strain ranges, the stress relaxation modulus decreases gradually with increasing step strain. Moreover, the stress relaxation modulus G(t, γ) was found to obey time-strain factorability. That is, G(t, γ) can be represented as the product of a linear stress relaxation G(t) and a strain-dependent damping function h(γ). The linear stress relaxation modulus is represented as a three-parameter solid viscoelastic model, and the damping function h(γ) has a sigmoidal form with two parameters. The comparison between the experimental results and the model-predicted values indicates that this model can accurately describe the relaxation behavior of MR fluids under step strains.

We examine the interaction force between spheres of a slightly conducting material immersed in a dielectric liquid when subjected to a DC field. An approach is developed which refines the previous two-zone model retaining only the electrical conduction of the solid and liquid phases and taking into account the field enhanced dissociation of electrolytic impurities. Approximations on the shape of the equipotential surfaces inside the solid lead to a system of ordinary differential equations governing the distribution of the electrical potential along the sphere surface. Estimates are derived for the attraction force between spheres in contact, for the current and for the electric stress in the liquid lying between the spheres in the "contact zone". This field takes values in the range 200 - 300 V/μm which correspond to extremely high levels of salts dissociation. The different conduction phenomena in the liquid are then discussed and their role in limiting the interaction force is emphasized.

A two-fluid continuum model is developed to describe mass transport in electro-and magnetorheological suspensions. The particle flux is related to the field-induced stresses. Solutions of the resulting mass balance show column formation in the absence of flow, and stripe formation when a suspension is subjected simultaneously to an applied electric field and shear flow.

The three-dimensional multi-particle well-ordered model could be considered as an analogy to a crystal body. We use this model for describing rheological properties of concentrated electrorheological fluids (ER fluids). According to this model, the particles of the suspension take their places at sites of a grid with specified type of symmetry and then an electric field is applied to the fluid. Taking into account hydrodynamic couple interaction of particles and forces of electrostatic interaction of particles polarized under the action of an external electric field and employing the mathematical apparatus of the microscopic theory of crystals, we construct the basic relationships for describing viscoelastic electrorheological properties of ER fluids.

The steady stress under static electric fields and the conduction current passing through the electrorheological (ER) suspensions with cation exchange resin particles were investigated simultaneously as a function of the shear rate. The shear thinning behavior was found for a suspension with a higher viscosity of the continuous phase. Further, a remarkable dip behavior was found for a dilute ER suspension. The apparent conductivity, which was calculated from the conduction current, probed sensitively the corresponding behavior to the stress responses.

Anisotropic solid-state magnetorheological (MR) composites are prepared by applying magnetic fields to isotropic suspensions in polymer melts and preserved by cross-linking the melts. The composites are studied through a continuum-level perspective at various magnetic field strengths under oscillatory shear. The minimum number of constraints are applied in the derivation of the magnetic and rheological invariants, which relate the measured macroscopic magnetostriction coefficients to the discrete parameters of any microscopic model. The field-induced stress is defined by magnetostriction coefficients, which are material parameters that describe the strain dependence of the magnetization tensor. A comparison of the independently measured rheological and magnetic properties allow for the determination of the magnetostriction coefficients.

The movement of particles in electrorheological (ER) fluids is analyzed by means of molecular dynamic simulations. We found that the velocity profile of particles can be divided into two zones. One zone near electrodes where particles' velocity profiles change periodically like "breathing type" is called transition zone. The other in the middle of two electrodes where particles move smoothly like a plug is called "plug zone". In addition, the relationship between volume flow rate and relative pressure gradient is simulated out. Factors such as volume flow rate, critical electric field, critical pressure gradient and response time of shutting up were also analyzed respectively.

When Electrorheological fluids are subjected to electric fields (E) and/or shear fields ( ), that is, when they are under an electro-hydrodynamic (EHD) field, they present changes in their rheological properties. By making theapparent viscosity (which varies under EHD) as an indication of the ER structure state, and considering that it is composed of a dielectric polarizability component, an electric conductivity component and the original apparent viscosity of the suspension, it is possible to obtain an equation (derived from an equilibrium relation) that describes the dynamics of ER fluidsIn this article we present an analysis of the factors that influence the dynamics of structure formation in ER fluids We concluded that the particle'selectric conductivity proved to be fundamental for the understanding of the general behavior of the fluid, and that there is aroptimum structuring level per unit applied field ratio , no matter whether the ER fluidis more characteristically dielectric or conductive. These conclusions explain the deviation of the resistance to shear of ER fluids from a quadratic relation (E²), experimentally detected some time ago.

The behavior of MR fluids involved in industrial devices is often modeled by analogical models which do no link the parameters with the physical properties of the fluid. From the equations of fluid mechanics, we give a physical meaning to parameters such as friction, elastic and mass coefficients used in the mentioned models. The predictions are checked with experimental data which mimic the behavior of devices such as antiseismic systems. The viscoelastic behavior of MR fluids is characterized by mechanical spectroscopy. The complex shear modulus G*(ω) contains all the information about the restoring and viscous forces. For example, the relation between elastic modulus, yield stress and magnetic force is discussed in terms of strain amplitude.

This paper is concerned with the dynamic behavior of a magnetic fluid-permanent magnet system subjected to the vertical vibration. The surface response of magnetic fluid adsorbed to a disc permanent magnet is investigated experimentally. Experiment is performed on a vibration-testing system. The electrodynamic shaker is operated at a given frequency, displacement, and acceleration. The dynamic behavior of magnetic fluid surface is analyzed by a three-dimensional motion analysis system. The displacement of the permanent magnet is also measured with an optical displacement detector system. It is shown that the response amplitude depends on the excitation frequency at the constant excitation amplitude. The 1/2-subharmonic response on the surface of magnetic fluid is observed at higher frequencies. This response is observed as polygonal modes with large amplitude azimuthal waves. The response of the system such as jumping motion is also shown at the resonance frequency of the system.

A Physical and Mathematical model of the process of fluid drop spreading is suggested which quantitatively describes all the stages of spreading kinetics on the basic of a unified approach. It has been established that gravitational forces exert a pronounced influence on the process of fluid drop spreading over a horizontal solid surface.

Theoretical analysis and experimental research of the film flowing of magnetorheologic fluids when infinitive solid plate is retrieving from the former mediums were carried out. We have got dependencies of fluids mass losses m vs: velocity of moving plate V ; magnitude of magnetic intensity, its gradient and angle φ between direction of intensity lines and normal vector to plane of plate. It is shown that theoretical and experimental function m(φ) is anisotropy one and may change its magnitude more than 10 times. Real behavior and extreme characteristics of m(φ) depends on rhelogiacal parameters of MRS and its magnetization. Obtained experimental data of dependence m(V) are in qualitative and quantitative agreement with the modernized theory.

The rheological properties of MR fluids, MRF-132LD, are investigated under the steady shear and oscillatory shear for arange of operating temperatures from 20°C to 60°C. This was accomplished by using an advanced rheometer with the parallel-plate configuration. Under the steady shear, the Herschel-Bulkley model is used to model the rheology of the MR fluid. The corresponding parameters namely, τ_yd, K and n were determined at various temperatures, in an attempt to minimize the discrepancies between the experimental results and that predicted by the model. The results show that τ_yd, K and n all show decreasing trend with temperature. The results suggest that the MR fluid get "thinner" with increasing temperatures. Under the oscillatory shear, viscoelastic properties of the MR fluid were studied in the frequency sweep mode. The storage modulus, G′, decreases with increasing temperatures in both the linear viscoelastic region and the nonlinear viscoelastic region. In addition, two critical frequencies, ω_cr and ω_m, were identified in the latter region. They were found to decrease with increasing temperatures. Finally, thermodynamics are used to explain temperature dependence of MR properties.

A method for simulating the steady-shear behavior of bidisperse, nonlinearly magnetizable MR suspensions is described. Results show that the yield stress of suspensions containing mixtures of large and small particles is larger than that of monodisperse suspensions, in agreement with previous experimental results.

The quasi-static shear stress-strain property of magnetorheological fluids is analyzed, based on the calculation of the interaction energy of chains of equi-spaced magnetic spheres with the applied uniform magnetic field. First, the dipole moment of a chain of equi-spaced magnetic spheres imposed to a uniform magnetic field is determined, and simple expressions are given. Then, the interaction energy of a chain with the forcing field is determined, and the restoring force is calculated when the chain is slanted and elongated. In our analysis, only the contributions from the mutual interaction of the particles in chains are considered. Comparison with experimental results is made, and good agreement is obtained.

The effect of a regular surface micro topography on a magnitude of surface shear stress in a normal magnetic field under MR fluid deformation between two magnetic plates has been experimentally investigated. It was revealed that the static yield stress was increased by a factor of 2.8 for radially grooved plates as against smooth ones. The effect was most conspicuous at small iron particles volume fractions and strong magnetic fields. It is assumed that grooves create a magneto mechanical barrier that prevents the slip of particle aggregates against the wall.

The rheological and electric properties of various ER fluids in strong electric fields have been investigated simultaneously. From the measured data the dependences of shear stress and real and imaginary part of the high field permittivity on field strength, temperature and frequency have been derived. One group of ER fluids containing perovskite type particles obeys a polarization mechanism which is attributed to the local displacement of ions in the crystal structure of the particles. The contribution of conduction to ER activity is low and the electric properties of these ER fluids are nearly constant. The increase of shear stress with frequency is in accordance with the polarization model. In contrast, another group of ER fluids containing zeolite or ion conducting polymer particles shows a strong dependence of the complex permittivity on field strength and temperature demonstrating the pronounced nonlinearity of the electric properties. It is assumed that both conduction and polarization contribute to the ER activity in these systems. The relative extent of the contributions changes with external conditions like field strength and temperature.

The magnetorheology of a "suspension" of millimetric-size steel spheres in oil has been studied. After a precise measurement of the magnetic properties of the particles we show that the yield stress is well characterized and that it can be predicted by a finite element method and a non-affine model where the chains break in the middle. Some experiments in microgravity confirm that the sedimentation does not alter our results and also shows that the magnetic stress decreases with the shear rate.

In this work, mechanical fatigue properties of a chemical starch-based ER fluid are empirically investigated. To do this, a flow-mode type electroviscometer, which has the same working mode as the cylindrical ER damper, is constructed. The linear reciprocating motion is obtained by driving a hydraulic power unit, and the number of fatigue cycle is measured by the limit switch. The field-dependent yield stress and response time to step input are evaluated as a function of the operating cycle. In addition, the vibration control performance of ER suspension for a passenger car is analyzed by incorporating the full-vehicle model with the yield stresses evaluated at different operating cycles.

Rheological and magnetorheological behaviour of monolayer and double layer sterically stabilized magnetic fluids, with transformer oil (UTR), dioctilsebacate (DOS), heptanol (Hept), pentanol (Pent) and water (W) as carrier liquids, were investigated.

The data for volumic concentration dependence of dynamic viscosity of high colloidal stability UTR, DOS, Hept and Pent samples are particularly well fitted by the formulas given by Vand (1948) and Chow (1994). The Chow type dependence proved its universal character as the viscosity data for dilution series of various magnetic fluids are well fitted by the same curve, regardless the nonpolar or polar charcater of the sample.

The magnetorheological effect measured for low and medium concentration water based magnetic fluids is much higher, due to agglomerate formation process, than the corresponding values obtained for the well stabilized UTR, DOS, Hept and Pent samples, even at very high volumic fraction of magnetic nanoparticles.

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