Electrorheological Fluids and Magnetorheological Suspensions

Foreword

Organization

Contents

The transient response of electrorheological suspensions in shear flow subjected to a suddenly imposed electric field is investigated experimentally. Barium titanate/silicone oil and alumina/mineral oil suspensions are employed. The evolution of both the rheological properties and suspension structure are investigated. Transient responses appear above a critical field field strength, and the critical Mason number for the onset of a transient rheological response is equivalent to the critical Mason number for the onset of lamella formation, within experimental uncertainty. These results are consistent with previous predictions. However, the shear rate and volume fraction dependence of the critical Mason number deviate from that predicted.

Electro-rheological Fluid (ERF) is the functional fluid that can change its viscoelastic property by applying electric field. However, ERF shows the sedimentation of the ER particles in long time use, and it caused the unstable ER effect. The Gel-structured ERF (ERG) has been developed to solve this problem. When a metallic flat plate is placed on the ERG sheet, ERG shows the high shear force due to the occurrence of the contact between the gel and the plate in response to the applying electric field (ERG effect). ERG effect can be obtained not only for metallic materials but also non-metallic materials by applying the one-sided electrode, and the ER effect is supposed to be considerably influenced by the material and geometrical properties of flat plate on the ERG sheet. In this study, the influences of the material and geometrical properties of sliding plate are experimentally analyzed from the viewpoint of the relative permittivity, surface roughness and flatness, and the design instruction for the selection of materials and their geometrical issues are proposed.

ER fluids under shear are often approximated by the Bingham model with the electric field induced yield stress. This approach, however, neglects the properties of the solid phase created. The oscillation measurements taken under field below the yield point and leading to calculation of storage and loss moduli of the electrified solid do not allow for determination of the full stress–strain relationship of the solidified ER suspension. In order to overcome this problem and collect information about the mechanical properties of this solid a dedicated rheometer was constructed capable of measuring small strains under moderate stresses and under electric field. Full shapes of the stress–strain curves were recorded leading to determination of storage modulus, linearity range, maximum deformation and yield point. Looking for relations between the viscoelastic behavior of ER suspensions and properties of their material components a series of fluids comprising silicone oil dispersions of conductive polymers (polyaniline, poly(p-phenylene), pyrolysed polyacrylonitrile) and polymer electrolytes (polyacrylonitrile complexes with inorganic salts) was studied. It was found that the viscoelastic responses of ER fluids were affected by material characteristics of the dispersed phase.

Reducing the viscosity of liquid suspensions is vital in science and engineering. This paper explores the physical mechanism for the viscosity reduction method in liquid suspension by pulsed electric or magnetic field. The key is that the maximum volume fraction to be available for the suspended particles in the suspension increases with the particle size and the polydispersity in the particle size distribution. Positive experimental results with various liquid suspensions indicate that this method, developed from the basic mechanism of viscosity, is universal and powerful for all liquid suspensions with broad applications.

Iron nanoparticles dispersed in hydraulic oil were prepared by mixing two microemulsions containing iron (II) sulfate and sodium borohydride at a temperature of 60°C. Six values of ω_o = [water]/[surfactant] were used, namely 5, 10, 15, 20, 25, and 30. Dynamic light scattering measurements of the hydrodynamic radius of the reverse micelles showed that the average size, surfactant shell thickness and water core radius, increased with ω_o. The micelle size distribution for ω_o values of 5, 10, and 15, was in the nanometer regime, while for ω_o values of 20, 25, and 30 it was in the micrometer regime. Scanning electron microscopy showed that the nanoparticle diameters were around 30 nm. In addition, a comparison between the particle size distribution of the iron nanoparticles dispersed in isopropyl alcohol and the iron nanoparticles in the reverse micellar solution was made. It was shown that once the particles are cleaned and separated from the micellar solution, they agglomerate into particles that are about 1 μm in size.

No abstract received.

In this study, electrorheological (ER) behaviour of silica nanocomposite suspensions treated with urea and N, N – dimethylformamide (DMF) in DC electric field has been investigated. While the ER effect of the neat silica itself was very low, the modification of silica nanoparticles improved compatibility of the solid and liquid phase and increased considerably ER activity of the system. In contrast to maximum possible concentration about 5 wt.% of neat silica due to particle aggregation 20 wt.% suspension of treated particles with low field-off viscosity could be prepared. The dielectric measurements showed that with increasing amount of urea deposited on the silica particles both the difference between the limit values of the relative permittivities and the relaxation frequency increased. This indicates a great influence of both particle polarizability and the rate of rearrangement of the ER structure in the electric field on the ER intensity. After DMF addition the changes in dielectric properties reflected the higher ER activity. At higher particle loading (25 wt.%) mutual particle interaction increased and field-off viscosity steeply rose. The comparison of the behaviour of 20 and 25 wt.% suspensions of modified particles showed that even if high yield stress at higher particle content under electric field application sets in, its relative increase indicating the ER efficiency due to high field-off value may be much lower than at lower suspension loading.

Magnetorheological (MR) elastomers are composite materials consisting of magnetic particles in elastomer matrices, whose mechanical properties can be influenced by applying a magnetic field. Main parameters which determine the behavior of these smart materials are the concentration of the magnetic particles and the mechanical stiffness of the elastomer matrix. The viscoelastic properties of silicone-based MR elastomers are outlined in terms of their storage and loss moduli. The mechanical behavior of the material is also influenced by a magnetic field during the curing of the elastomer matrix, which leads to materials with anisotropic microstructures. The storage and loss moduli of soft elastomer matrix composites can be significantly increased in the presence of a magnetic field by considerably more than one order of magnitude. This increase exceeds that of all previously reported data. A shape memory effect, i. e. the deformation of an MR elastomer in a magnetic field and its return to original shape on cessasion of the magnetic field, is described.

The Ferrofluid-based magnetorheological suspensions (F-MRS) have been newly developed, in which ferrofluids were used as the carrier media, and microsized iron particles as the magnetic material. The advantageous properties of the F-MRS were presented by comparing with commercial mineral oil based MR suspension (M-MRS). Furthermore, the static yield stresses τ_sy of four F-MRS samples were measured in fixed shear rate method and step-increased strain method. The different behaviors under the two methods were analyzed. And finally the dependence of the static yield stress on the magnetic induction B and the sample weight fractions φ were summarized.

Understanding ER behavior remains theoretically and mechanistically unsatisfactory. Although E induced particle aggregation is material dependent, shear yield stresses appear independent of materials, around 3-5 kPa . Recent studies of ER dispersions under compression and shear report higher yield values, 50 - 300 kPa. Some studies report ER fluids in preyield show shear moduli in the MPa range. ER/MR fluids of commercial concentration and at high field strengths at static conditions on microscope slides do not show single chains or columns but a dense continuous particulate network. However exposing certain dispersions to E/M and shear fields simultaneously aggregates particles into lamellar structures(walls) oriented in the shear direction. Such structures vs. columns require a much greater FORCE to shear which must be transmitted from the electrodes to the particulate structures by a “frictional force”. Although non-slip conditions are assumed, this is mostly an unproven theoretical convenience. An alternate view suggests these “forces” may be inadequate to shear the particulate structures, the yield mechanism being slippage between electrodes and adjacent particle lamellae. Thus the strength limiting feature of ER/MR fluids is not particle lamellae shear strength, but “force of adhesion” between electrodes and lamellar surfaces. This is discussed and substantiated with experimental results.

The static and dynamic shear stress of newly developed electrorheological (ER) fluids can reach more than 100 kPa and over 60 kPa at 3 kV/mm, respectively. The high yield stress of those ER fluids and its near linear dependence on the electric field are different from the conventional ER fluids and can not be explained with traditional dielectric theory. Experiment demonstrates that the polar molecules adsorbed on the particles play crucial role in those ER fluids, which can be named as polar molecule type electrorheological (PM-ER) fluids. To explain PM-ER effect a model is proposed based on the interaction of polar molecule-charge in between the particles, where the local electric field is much higher than the external one and can cause the polar molecules aligning. The main effective factors for achieving high-performance PM-ER fluids are discussed.

This paper describes the dynamic behavior of permanent magnets encompassed with magnetic fluid subjected to the alternating magnetic fields. The dynamic behavior of NdFeB magnet encompassed with magnetic fluid in the magnetic fields is a fascinating subject that is attracting the attention of robot researchers and micromachine engineers. This subject is concerned with the development of the micro actuators driven by the wireless energy supply system. A permanent magnet adsorbs magnetic fluid, and it is suspended in magnetic fluid. The permanent magnet in the self-levitation phenomenon can be easily controlled by the external magnetic fields. Some basic responses of permanent magnets encompassed with magnetic fluid subjected to the alternating magnetic fields are studied with a high speed video camera system. Experimental results show the possibility of the control of the permanent magnet motions by the external magnetic field. According to the frequency of external alternating magnetic field, the responses of permanent magnet show reciprocating, rotary and metronomic motions. The effects of the magnetic fluid volume and magnetic field intensity on the dynamic behavior of permanent magnet are revealed experimentally.

In this study, the performance of a new design concept utilizing a magnetorheological (MR) fluid composite material is examined through encapsulating a MR fluid into an elastomer. A prototype MR Fluid-Elastomer Vibration Isolator is built and its dynamic behavior is studied in oscillatory compressions for a wide range of frequencies under various applied magnetic fields. The experimental results show that both the stiffness and the damping capability of the MR Fluid-Elastomer Vibration Isolator is a function of the displacement amplitude and magnetic field strength, and only weakly dependent upon the frequency of excitation. This demonstrates that the new vibration isolator, whose mechanical properties can be controlled by an applied magnetic field, has potential in applications where tuning vibration characteristics are desired.

The electric field strength and shear rate dependence of the apparent shear viscosity of electrorheological (ER) suspensions can often be represented by a function of only the Mason number. A Mason number defined for magnetorheological (MR) suspensions by direct substitution of magnetostatic variables for electrostatic variables does not produce a similar collapse of shear viscosity data for MR suspensions. We show that a Mason number defined in terms of the suspension magnetization can be employed to produce a collapse of experimental data at various magnetic field strengths and shear rates. As for ER suspensions, the new Mason number can be calculated from experimentally measured quantities.

MRF performance requirements for a commercial 4WD clutch are outlined and appropriate characterization methods presented, a prerequisite to identify and overcome shortcomings of MRF formulations, popped up in a clutch test rig. These methods include the response to rapidly changing shear rates and switching magnetic flux densities as well as a characterization of durability and redispersibility. Parallel to the improvement of the MRF performance, design studies of the 4WD clutch with regard to the required torque, maximum allowable weight/dimensions, and benchmark to alternative technologies were conducted, making intensive use of computer aided design. Combining the expertise of the collaborating parties, a 12 kg 700 Nm 4WD clutch was realized and the expected performance based on CAD simulations verified, demonstrating the feasibility of a new technology.

Recent experimental as well as theoretical investigations have shown that the formation of structures of magnetic nanoparticles has significant influence on the behaviour of ferrofluids. The dependence of this structure formation on the magnetic field strength and shear stress applied to the fluid leads to strong changes of the viscosity and to the appearance of viscoelastic effects in the fluids. The actual approaches for a description of the effects vary in the basic modeling of the fluid and its behaviour. Some models base on microscopic assumptions, other model the fluid on a mesoscale and even macroscopic descriptions abstaining from microscopic assumptions have been suggested. A point in which the predictions of the models differ is the question of an appearance of a magnetic field dependent yield stress in ferrofluids. For investigations concerning the appearance and field dependence of a yield stress a special stress controlled rheometer for ferrofluids has been designed. The preliminary results presented here, show a dependence of the yield stress on magnetic field strength for different kind of ferrofluids and magnetorheological fluids.

This study intends to identify the behavior of MR fluid subject to high rates of shear and high flow velocities. A high shear rheometer is built which allows for the high velocity testing of MR fluids. The rheometer is capable of fluid velocities ranging from 1 m/s to 37 m/s, with corresponding shear rates ranging from 0.14×10⁵ s⁻¹ to 2.5×10⁵ s⁻¹. Fluid behavior is characterized in both the off-state and the on-state. The MR fluid is run through the rheometer at various flow velocities and a number of magnetic field strengths. The term “dwell time” is introduced and defined as the amount of time the fluid spends in the presence of a magnetic field. Two active valve lengths were considered, which when coupled to the fluid velocities, generated dwell times ranging from 12 ms to 0.18 ms. The yield stress is found from the experimental measurements and the results indicate that the magnitude of the yield stress is sensitive to fluid dwell time. As fluid dwell times decrease, the yield stress developed in the fluid decreases. The results from the on-state testing clearly demonstrate a need to consider fluid dwell times in high velocity applications. Should the dwell time fall below the response time of the fluid, the yield stress developed in the fluid may only achieve a fraction of the expected value. These results imply that high velocity applications may be subject to diminished controllability for falling dwell times.

Despite its wide application as a suspended particle in magnetorheological (MR) fluids along with its extensive investigations on MR characteristics and dispersion stability, the pristine carbonyl iron (CI)-based MR fluid still possesses several drawbacks, including severe sedimentation of the CI particle due to its high density. To resolve these problems, we prepared poly(methyl methacrylate) (PMMA) coated-CI composite particles, possessing different shell thicknesses onto iron particles. The polymer coated composite magnetic particles (CIPMMA) were synthesized via an in-situ dispersion polymerization method using CI dispersions in methyl methacrylate monomer, and then adopted as dispersed phase of MR fluids. The CIPMMA was found to potentially resolve several problems of CI only based MR fluids such as severe sedimentation problem and poor dispersion stability. Flow and viscoelastic properties of the MR fluids were analyzed via a rotational rheometer equipped with a magnetic field suppler using measuring system of a parallel plate in both steady and oscillatory shear modes. Main focus was put on studying the effect of shell thickness in the internal structure formation and sedimentation characteristics. The MR characteristics including a yield stress were found to be affected by the CI contents in the composite particles.

Modeling dynamic behavior of magnetorheolgocial (MR) fluids frequently based on a two-phase flow approach which homogenizes the particles' dynamics and ignores their individual motions. Particles motion in moving carriers was primarily studied in pure cylindrical tubes under the influence of inform magnetic field. The objective of this paper is to simulate flow of a MR-fluid consisting of a magnetically neutral carrier and ferrous particles in micro-tubes with rough wall under the influence of a non-uniform magnetic field developed by a permanent magnet. Carried in MATLAB simulations show that ferrous particles are concentrated around the magnets poles and bumps or dents of the tube wall which could clot the tube. A computationally efficient but simplified model developed in this study provides qualitative insights in behavior of MR-fluids while its quantitative accuracy declines if MR-particles form substantial clots that alter flow patterns. Analysis of these phenomena requires more accurate accounts of particles-fluid interaction and lead to more complex and computationally extensive models; the corresponding results are presented in a subsequent paper in this proceeding.

A series of ER fluids materials with high shear stress have been developed recently, which named as polar molecule dominated electrorheological (PM-ER) fluids. Difficulties have been met in shear stress measurement process due to the slide of PM-ER fluids on the surface of metallic electrodes. In this paper, two shearing configurations have been developed to remove the interface effect. The intrinsic shear stress of ER fluids can be obtained by using the devices.

A novel magnetorheological fluid, in which the surface of iron particles is coated with poly (butyl acrylate) by surface initiated atom transfer radical polymerization (ATRP), is investigated. The polymer coating procedure includes two steps, which are immobilization of initiator: 2-4(-chlorosulfonylphenyl)-ethytrichlorosilane (CTCS) on the iron particles surface and graft polymerization of butyl acrylate from the surface. The surface coating is characterized by FTIR and SEM. This magnetorheological fluid has controllable off-state viscosity and high shear yield stress. Coating polymer on the iron particles surface by ATRP can significantly reduce iron particles settling and improve stability of the MR fluid. Polymerization kinetics of bulk butyl acrylate are investigated using differential scanning calorimetry (DSC). Glass transition temperature is obtained using the step-scan DSC method. The molecular weight and conversion can be controlled by the molar ratio of monomer to initiator, reaction temperature and time. The reaction is first order determined by the plot of In (M/M₀) against polymerization time. The overall activation energy is found to be 126kJ/mol by Kissinger's Method.

By using a perturbation approach, we investigate dynamic effects on nonlinear alternating current (ac) responses in electrorheological (ER) fluids under an ac or a direct current electric field. We show that the dynamic effect due to a shear flow plays a significant role in the responses. Our results can be well interpreted in the dielectric dispersion spectral representation, and they offer a convenient method to determine the relaxation time and rotation velocity of ER particles by measuring the nonlinear ac responses.

Properties of a magnetorheological (MR) fluid synthesized by dispersing a mixture of two carbonyl iron powders (CIP) in an ionic liquid have been investigated. At first, mixtures of CM (d₅₀ = 7 μm) and HQ (d₅₀ = 1.1 μm) CIP powders, prepared at the same solid weight fraction but at various weight fractions of large particles, were dispersed in the ionic liquid (N,N-Diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate), which is stable even at high temperature. Then, the magnetic clusters of the synthesized MR fluids were observed by using an optical microscope, whereas the magnetorheological properties were investigated by using a bi-cylindrical viscometer. Each apparatus was equipped with a magnetic field generator to create a uniform magnetic field. After finding the most suitable mixing ratio of powders, a new batch of MR fluid was synthesized by the addition of surfactant (ETC-7) to enhance its stability. Finally, the properties of the MR fluid with or without addition of surfactant were compared. The experimental results showed that the MR fluid with 60 wt% fraction of large particles exhibited the highest MR response.

Magnetorheologioal fluids are known to respond in a matter of milliseconds to the application of a magnetic field. To date, however, very little work has been done to study the time dependence of the MR response. The purpose of this study is to investigate the response time of the fluid. Experiments were conducted on a high shear rate rheometer capable of fluid speeds in excess of 35 m/s. With an MR valve length of 6.35 mm, the resulting dwell times were as low as 0.18 ms. For each of three magnetic field strengths, a reduction in yield stress is observed as dwell time decreases. A model is proposed to represent the time response of the fluid to the application of the magnetic field. The experimental data and the proposed model are used to identify the response time of the fluid for each field strength. Results indicate that as the magnetic field increases, the response time of the MR fluid decreases. For the range of magnetic field strengths considered in this study the response time of the fluid ranged from 0.24 ms to 0.19 ms.

We employ particle-level simulations to show that body forces, such as gravity or centrifugal forces, can significantly influence the structure and rheology of ER and MR suspensions even when the magnitude of the body force acting on a particle is small compared to the field-induced force. We also report an experimental investigation of the effects of body forces on the structure of ER suspensions. Experimental results agree qualitatively with predictions.

The rheological properties of various novel MR fluids are characterized using a parallel plate MR shear rheometer. In these MR fluids the surface of iron particles is coated with a polymer. The Theological properties are measured and compared at various magnetic field strengths shear rates and strain amplitudes. It has been shown that these MR fluids exhibit stable and desirable rheological properties such as, low viscosity and high yield stress which are comparable to or higher than the conventional MR fluids.

Two types of carbonyl iron powders, (CIP's, BASF AG), the HS and HS-I (I = insulated, due a coating with phosphate), and two kinds of silica, one hydrophobic (Cab-O-Sil^® TS610) and other hydrophilic (Cab-O-Sil^® M5), were used to evaluate the influence of the surface treatment of the magnetic particle and the kind of fumed silica on the formulation of some magnetorheological suspensions (MRS). Oscillatory measurements at no field showed an evident difference between the silicas, but not a specific interaction with the phosphate coating on HSI. On the other hand, steady flow experiments also without magnetic field showed that the kind of silica and its specific interactions with the coating on iron powder drove the rheological behavior of the MRS on all region of the shear rate. Under magnetic field, the flow curves differences will be due to the iron particles and its magnetic properties, mainly on the region of higher shear rate.

We describe two different systems, the first one based on a magnetorheological elastomer and the second one on magnetic particles inside a liquid crystal. In both system we manage to have chain structures with particles that are not in contact. The effect of the gap on the viscoelastic properties. We show in particular how in magnetorheological elastomers, the energy dissipation is closely related to the creation and the motion of cavities in the gap between the particles. In liquid crystal chaining of particles can occur without applying a magnetic field. This happens if the anchoring of liquid crystal on the surface of the particles is homeotropic. We demonstrate how the combination of elastic defects and of a magnetic field allow to obtain microscopic springs made of a pair of magnetic spheresp.

This paper presents two kinds of magnetorheological elastomers (MREs). One is composed of appropriate silicon rubber, carbonyl iron particles and some other materials. It is cured under a strong magnetic field at a room temperature. Its relative modulus increment reaches 878%. Such high MR effect has not been reported until now. The other is composed by appropriate natural rubber, carbonyl iron particles and some other materials. After the compositions are mixed in a two-roll mill, they are cured under a strong magnetic field according to a temperature profile. Its relative modulus increment reaches 133%. Furthermore, it has enough hard strength to load bearing and absorb vibration energy. To measure their dynamic viscoelastic properties, DMA (Dynamic Mechanical Analyser) has been developed. A special magnetic field is fit to DMA. Its field intensity can reach 1.1T. This setup can measure the dynamic magnetoviscoelasticity of MREs under tension, compression, bending, and shear deformation modes. The shear mode results meet well with that measured by our previous self-developed measurement system. Electronic Pull Test Machine, Shaw's LX-A Rubber Hardness Gauge, Akron Abrasion Test Machine, Thermal Ageing Test Oven, Rubber Fatigue Test Machine, and Impact Elasticity Test Machine are also set up to measure their corresponding mechanical properties. All observed results show that the fabricated MREs are utilizable. They have successfully been utilized to adaptive tuned vibration absorbers, which will serve for vibration absorption of vehicles.

The paper deals with the effect of two conductive polymers (polyaniline, PANI, and polypyrrole, PPy) in combination with inorganic particles on the response of silicone-oil suspensions. Conductive polymers cause a significant increase in electrorheological response. PANI combined with silica is much more efficient when in the form of a thin layer on the particle surface than if the two components are simply mixed. All combinations are followed from the viewpoint of viscosity and yield stress.

This computational study focuses on the dynamics of individual ferrous particles and the flow of the incompressible Newtonian fluid under the effect of an externally applied magnetic field and pressure gradient in a micro tube with smooth wall. The particle dynamics is simulated as a discrete phase using MATHLAB code and the fluid flow is solved as a continuous phase using Computational Fluid Dynamics Software FLUENT. Interaction between the particle and fluid phases are included as hydrodynamic forces predicated by the fluid phase simulation and updated particle locations determined by the particle phase solution under non-uniform magnetic field. Non-uniform magnetic field forces the particles to move to poles of the magnet, and results in their accumulation. This causes drastic change on the continuous phase flow and pressure distribution, which in turn influences the particle motion. Predicted dynamics of the suspended ferrous particles under magnetic field and flow of the carrier fluid with pressure gradient is in reasonably well agreement with previous work. The results show that non-uniform magnetic field generated by externally placed magnets can be used to control the locations of the particles and flow of the fluid in a micro tube.

Electrosensitive compounding of lubricants were developed for use in the friction pairs in the transitive regimes of their work. The investigation of their viscoplastic properties and friction coefficients in the electric field was made.

The discovery of the giant electrorheological (GER) effect poses a challenge to the theorists for an explanation of its physical underpinnings. This is particularly the case as the GER effect breaks the yield stress upper bound predicted on the basis of induced polarization mechanism. The GER effect was observed in suspensions of coated nanoparticles, each consisting of a core particle of barium titanyl oxalate (20-50 nm), coated with a 5-7 nm layer of urea. The suspending oil is also very important, as the “wrong” oil can mean no electrorheological effect at all. Our prior work has shown the GER data, on the field dependence of yield stress, to be quantitatively accountable by the formation of aligned molecular dipolar layers in the region of particle-particle contact. Here we justify this picture through microscopic statistical mechanic considerations. We present a model of hydrogen bonding which can give rise to both electrowetting between the particles and the oil, as well as inducing the formation of aligned surface molecular dipolar layers. Monte Carlo simulation is used to account for both the entropy and energetic effects. It is shown that the formation of aligned surface dipolar layers can indeed be a robust phenomenon

Magnetorheological Finishing (MRF) is a precision finishing process that has become an industry standard tool for polishing high quality optical surfaces. This novel technology utilizes a magnetorheological (MR) fluid and a magnetic field to generate material removal for this sub-aperture polishing process. The properties of the MR fluid provide a significant number of advantages for generating a flexible and stable tool making it uniquely suitable for finishing a wide range of optics to extremely high precision. This includes diverse applications such as finishing flats/prisms, spheres, aspheres, and cylinders of materials that range from glass, single crystals, ceramics and some metals – all of which could be polished on the same platform. What is more, the unique attributes make it a valuable tool for lightweight optics and high-energy applications. The original MRF platform was developed to make routine work of finishing high precision optics (flats, spheres, aspheres etc.) ∼20-200mm in size. Since then, the size of optic that can be finished with this technology has been scaled to both larger and smaller sizes over a range of less than 5 mm to more than 2000 mm. A number of technical challenges have been realized and overcome as the platform geometry has been modified. An overview of some of these challenges, and their solutions will be presented.

The properties of ultrasonic propagation velocity in water-based and kerosene-based magnetic fluids and an MR fluid are examined experimentally. The ultrasonic frequency used is 1 MHz and the measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 mT to 550 mT and is swept at a constant rate dB / dt (sweep rate). The ultrasonic propagation velocity changes with applied magnetic field and hysteresis is observed. The properties of ultrasonic propagation seem to be highly influenced by the formation of chain-like clusters (in the magnetic fluids) and robust clusters (in the MR fluid).

In recent years, the automation of polishing and finishing technologies has become a requirement because polishing and finishing with high accuracy takes a long time and often depends on the experience and special skills of technical engineers. One of the most promising polishing technologies is Field-assisted Fine Finishing (FFF), which has attracted a lot of attention from many researchers. In FFF, an electric field or a magnetic field is applied for finishing, polishing, and so on. In this study, a new polishing technology using Electro-rheological Gel (ERG) is proposed. The ERG we have developed is a functional material whose induced shear force changes according to the applied electric field intensity. A thin ERG sheet with abrasive grains is applied to the polishing pad of a rotary polisher. The properties of the ERG polishing pad can be changed by adjusting the intensity of the electric field applied to the ERG pad. We conducted experiments to analyze the basic performance of the ERG polishing method. The results show that the polishing efficiency can be improved by applying an electric field

Our bidisperse magnetorheological fluids are suspensions of micron (2-10μm) and nanometer (∼40n m) scale magnetic iron particles in silicone or hydraulic oil. Earlier studies were conducted to determine the yield stress of these fluids at low magnetic field induction. These studies have shown the absence of saturation yield stress implying the possibility of a higher yield stress by increasing the applied field. In this study, three different bidisperse MR fluids were investigated to determine the maximum available yield stress that can be obtained at or near saturation magnetic flux density. The iron loading in the fluids varied from 50% to 80% by weight. Two types of MR cells, a low field and a high field cells, were used for the investigation. Using a parallel disc rheometer alternatively equipped with one of the two MR cells, the flow curves of the MR fluids were obtained and their yield stress determined. The yield stress of the MR fluids as a function of applied magnetic field was identified using the Bingham-Plastic constitutive model. Results show that the high field cell (maximum 1 Tesla) was able to measure shear stress up to saturation, whereas the low field cell (maximum 0.26 Tesla) could not.

A prototype of a cylindrical ERF coupling was fabricated, and its transmission capability in steady and unsteady running conditions was investigated. The torque transmitted by the coupling with viscous force in wide ranges of driving speed and field strength was measured. The relationship between the transmission torque, the zero field viscosity of ERF and the shear yield stress of ERF under field was obtained, and was compared with theoretical prediction. Moreover, by modulating the strength of the applied DC field, under a fixed load and input speed, the output speed of the coupling was controlled in the range of transmission ratio from 0 to 1. This provides a means to construct transmission systems in which the output speed can be conveniently adjusted and controlled. Further, square wave electric pulses were applied on the ERF coupling, with a fixed external load added on the output shaft, a uniform stepping rotation of the output shaft has been realized. Experiments showed that under certain conditions the rotation angle of the output axle can be precisely controlled.

For polar molecule dominated electrorheological (PM-ER) fluids [1], the surfaces of ordinary metallic electrodes cannot satisfy the condition of polar molecules' aligning and interaction. Slide must occur at the interface between PM-ER fluids and electrodes so that the measured shear stress is much lower than the true value. Several modified electrodes are developed and tested for increasing the adhesion of PM-ER fluids to the electrodes and weakening the slide in shearing. The modified electrodes can not only improve the measured shear stress to approach the intrinsic one, but also greatly reduce the current density of PM-ER fluids. Using the modified electrodes is certainly necessary for measuring and applying the PM-ER fluids.

We have examined the small strain response of an inverse ferrofluid system, consisting of micron-sized inert particles dispersed in a ferrofluid, which is a magnetisable liquid consisting of single domain magnetite nanoparticles. Under a magnetic field the inert particles will form elongated aggregates in the field direction, analogous to a magnetorheological fluid. It was found that the fluid appeared to have a Bingham fluid-like yield stress when analysed using the flow curve. However careful study of the behavior at very low shear rates revealed an ever decreasing shear stress. In addition, the behavior of conventional magnetorheological fluids at large strains under steady shear flow and constant magnetic field was also studied, and the results compared to particle-level computer simulations.

Nano-sized TiO₂ particle materials doped with Na₂O or ZrO₂ have been synthesized. The electrorheological (ER) properties of the materials have shown that both Na-doping and Zr-doping can effectively enhance the ER performance of TiO₂ materials with suitable degree of doping. A material, the suspension of which has a high relative shear stress (τ_r=84.0), has been obtained. Such high ER activity is advantageous in its application as an ER fluid. The composition, especially the composition in the surface layer of particles, plays a dominant role in influencing the ER performance of the particle materials.

The paper introduces a kinetic theory based particle pair model for magnetorheological fluid characterization. Fluid constitutive equations are derived from an analysis of the motion of a pair of particles subject to hydrodynamic and magnetic field forces. The effect of neighboring particles from the same chain on the magnetic force is included. The model can predict fluid behavior when particles separate or remain in contact during flow. For yield stress predictions, the case when particles separate is considered. Predictions for the yield stress are compared with experimental data and with other theoretical models. Predictions from the proposed model are in good agreement with experimental data.

The sol-gel method was used to prepare amorphous TiO₂ powders with sub-micrometric grain size. These powders together with commercial nanometric TiO₂ were characterized with FT-IR spectroscopy, X-ray diffraction, scanning electron microscopy, and a light scattering method. Then electrorheological suspensions were composed out of these powders and their flow curves under electric field were recorded. The ER activity of the synthesized powders was relatively high which probably resulted from residual amounts of polar organic matter present in the prepared titania. It was found, however, that the studied suspensions underwent a very well pronounced agglomeration process clearly observed in suspensions of higher concentrations and particularly in those fluids which were exposed to electric field for some time. Therefore, the studied ERFs which were originally prepared out of nanometric powders contain in fact aggregated particles of considerably bigger size. The agglomeration process is hardly reversible and strongly influences all basic properties of the studied electrorheological suspensions.

A novel water-based magnetorheological (MR) suspension is based on the poly(ethylene glycol)-coated carbonyl iron particles, which is prepared by the co-sol-gel reaction using carbonyl iron particles as raw materials, and water without any other additive. The microstructure, anti-oxidation properties, magnetic and magnetorheological properties of the core-shell particles are characterized by scanning electronic microscopy, transmission electronic microscopy, Fourier transform infrared spectroscopy, thermogravimetric-differential thermal analysis, vibrating sample magnetometer, and ARES2000 rheometer, respectively. The results show that the as prepared particles have core-shell structure with a polymer shell of less than 100 nm and its anti-oxidation property is enhanced due to the compound coating. Both the core-shell particles and its based MR suspension exhibit excellent soft magnetic performance. The based MR suspension shows low zero viscosity and high MR effects, especially greatly improved anti-settlement and redispersibility. The phenomena are attributed to the hydrophilic thin shell of the core-shell particles.

The self-assembly properties and ER effects of the Polyaniline-Poly(ethylene glycol)-Polyaniline (PAn-PEG-PAn) triblock copolymers were studied in this paper. The results indicate that with the increase of solubility parameter of the solvent, PAn-PEG-PAn copolymers form into different morphologies of spheriods, vesicles and rods. PAn-PEG-PAn copolymers with vesicles morphology show the highest polarization strength, while those with rods have the most rapid polarization rate. Among the PAn-PEG-PAn copolymers of different morphologies, the PAn-PEG-PAn copolymer vesicles show the strongest ER effect.

In this paper, a magnetorheological (MR) torque transfer device is designed, modeled, and controlled. MR fluids possess the unique ability to undergo dramatic and nearly completely reversible changes in their rheological properties under the application of a magnetic field. These controllable fluids can serve as quiet, rapid interfaces between electronic controls and mechanical systems. One area of application is to use these fluids as actuators. The MR torque transfer device can function as either a clutch or a brake. This coupling device was designed and built using a parallel plates configuration, and uses a stationary electromagnetic coil to activate the fluid. A PID controller is designed and experimentally evaluated. In the experimental control setup, the output variables are the position, velocity, and torque at the output shaft and the control input is the electromagnet current. Angular position of the output shaft and the transferred torque are measured using an encoder and a torque transducer, respectively. A dSpace control system was used to experimentally implement the control algorithms. The closed loop performance of system was studied for both torque regulation as well as torque tracking.

Magnetorheological (MR) dampers have been successfully used in vibration control of civil and mechanical structures. Application examples include vibration control of stay cables in cable-stayed bridges, vibration damping of automotive seats and suspension systems, and vibration isolation of automation and precision equipment/machines. While usefulness, the existing MR dampers are incapable of self-sensing structural vibration for implementing real-time, closed-loop vibration control. This paper describes the development of a kind of novel MR dampers possessing the attractive sensing-while-damping function with a high degree of sensor-damper collocation. Lead zirconate titanate (PZT) piezoceramic sensors and PZT/polymer piezocomposite sensors have been embedded, respectively, with actuation-only MR dampers to form two self-sensing MR dampers. The sensors have specifically designed geometry and electrode pattern to provide an optimal sensibility. Performance tests have been conducted by mounting the self-sensing MR dampers on a material test system operating in various displacement-controlled excitations, including sinusoidal and ramp excitations with different combinations of frequency and amplitude. Good agreements between the sensor outputs and the force inputs have been observed. The damper embedded with piezocomposite sensor has shown a higher sensitivity and a better reliability than the one integrated with piezoceramic sensor. The self-sensing MR dampers have great potential to be used in real-time close-loop vibration control of civil and mechanical structures.

One suitable way to polish optics of complex shapes is by using a jet of abrasive fluid. In doing so, the energy required for polishing is supplied by the radial spread of the jet, which impinges upon a surface to be polished. Generally, the jet instability results in a non-deterministic polishing process. A method of jet stabilization has been proposed, developed and demonstrated whereby the round jet of MR fluid is magnetized by an axial magnetic field as it flows out of the nozzle. It has been experimentally shown that in this case a stable and reproducible material removal function can be achieved at a distance of several tens of centimeters from the nozzle. At the same time, the interferometrically derived distribution of material removal for the MR Jet coincides well with distribution of the fluid power density calculated using CFD modeling. Polishing results support the assertion that the MR Jet finishing process may produce high precision surfaces on glasses and single crystals.

A fuzzy finite element (FFE) based method is used for modeling Magnetorheological(MR) Dampers performance with vague or imprecise uncertainties. The successful performance of MR devices or dampers requires them to be tested under imprecisely defined conditions. However, physical prototyping and testing under vague conditions are expensive and time consuming. The limitations associated with physical prototype testing can be circumvented through numerical studies.

In this work, fuzzy sets are used to represent the uncertainties present in the MR fluid, piston, housing properties (magnetic properties) and material property of magnet wire (electric resistance). The first vertex fuzzy analysis technique is used to compute the possibility distributions of a specific function that reflects some characteristics of an MR damper (electrical power and time constant). The finite element analysis of electromagnetic circuit is done by ANSYS Parametric Design Language (APDL) to obtain the magnetic flux density and to perform the optimization process. Next a new method is proposed for reducing uncertainties effects. The results show that the FFE method and the proposed method found to be useful and suitable for use in the design of MR dampers.

The primary purpose of this study is to provide an experimental evaluation of some of the characteristics and benefits of magneto-rheological tuned vibration absorbers (MR TVAs). Tuned vibration absorbers (TVAs) often provide a simple and elegant solution to many vibration problems. To extend the concept of passive TVAs to MR TVAs, we discuss four different control methods, called velocity-based on-off groundhook control, velocity-based continuous groundhook control, displacement-based on-off groundhook control, and displacement-based continuous groundhook control. Using the test apparatus, a series of tests were conducted to investigate the dynamics of the MR TVA with each control policy. The performances of each of the cases were then analyzed along with the equivalent passive TVA. The performance index was the transmissibility between the input and the output displacement of the structure. The experimental results indicate that the most suitable control method for MR TVAs is the displacement-based groundhook control.

The performance of teleoperation systems can be improved if force feedback is employed. When the operator controlling the master has the feeling of direct interaction with the remote environment, the system is called “transparent”. The goal of this paper is to combine novel magnetorheological (MR) fluid-based haptic systems with microstructural analysis and modern control techniques to design and develop a transparent haptic system. For this purpose, a MR fluid-based joystick is designed. The work in this paper overcomes the sticky wall phenomena, adds restoring force feeling to the user by using a variable compliance, and increases the overall transparency of the system.

Magnetorheological (MR) fluids provide a means for controlling properties of dampers to achieve various performance objectives. Some applications that require dampers may benefit from an additional actuation capability. While MR fluid alone is not sufficient for actuation, it can be used in combination with other components to create an actuator while adjustable damping properties are retained. A concept for a device that serves as both a controllable damper and a linear actuator is described. Such a device might be useful in a suspension or leveling system, or a repositioning system incorporated in a recoil damper. Basic design considerations are reviewed and the particular step-and-repeat architecture, in which two MR damper subassemblies are used as variable holding clamps, is presented. Two candidate actuator cores are considered. A voice coil core was used in a prototype unit, and a magnetostrictive or piezoelectric core is suggested for a higher-force device. Prototype design features and results of testing are described. A test unit achieved speeds up to 10 mm/s. Several non-ideal effects were noted, and must be addressed to make the technology practical.

This study presents the experimental and theoretical evaluation of an MR (magnetorheological) isolator using multiple fluid modes including shear, flow and squeeze. For doing so, a novel type of multi-mode MR isolator against multi-degree-of-freedom excitations is proposed and fabricated. The experimental testing of the proposed MR isolator is conducted by an MTS machine and its damper characteristics are experimentally evaluated by equivalent damping and complex stiffness methods. To construct a theoretical model of the MR isolator, its dynamic equation is derived and important model parameters are identified by the force averaging method using the force-displacement or the force-velocity plots. Using the theoretical model, the damper characteristics of the MR isolator are also predicted and compared with those using the experimental data.

This paper presents force feedback control performance of a spherical haptic device featuring an electrorheological (ER) fluid that can be used for minimally invasive surgery (MIS). As a first step, a spherical ER joint composed of rotational and stationary electrodes is designed and optimized based on the mathematical torque modeling. The active force produced in MIS is generally small, even though the passive force is large. In order to meet this agreement, both clutch and brake mechanism are adopted for the ER joint. In this operation, the active (small) force feedback by the rotational electrodes and/or semi-active (large) force feedback are achieved by the stationary electrode. Subsequently, the master device is manufactured by integration the spherical ER joint with AC motor. In order to achieve desired force trajectories, a sliding mode controller, which is robust to uncertainty, is formulated by considering mechanical friction and hysteretic behavior of the ER fluid as uncertainty. The controller is then experimentally realized. Tracking control performances for various force trajectories are presented in time domain.

Large-scale, commercial use of magnetorheological (MR) fluids to provide semi-active control in mechanical systems is now a reality. This is due primarily to their application in controllable, automobile suspension systems. Controllable MR fluid dampers are presently available on a number of General Motors vehicles as well as the new Ferrari Fiorano and Audi TT Coupe. Commercial MR fluid production is presently on the order of 100,000 liters per year. The number of MR devices in use worldwide is estimated to be in excess of 250,000.

A comparison of the mechanical performances of radial plate and concentric clutches is made on the basis of: torque/size, acceleration, control ratio and maximum casing temperature – for both a single clutch pair and multi plate models, all with double acting surfaces. The various embodiments examined herein assume a constant rotor and case thickness, negligible inertial effects of the fluid and the clutches are, in the main, always slipping steadily. Electrical heating is not considered.

CFD is used for the computations and is verified against analytical solutions and experimental data where possible. The fluid, which may be MRS or ERF is taken to be a Bingham plastic with temperature invariant plastic viscosity and yield stress. Where acceleration is calculated the initial value (when full excitation is just applied to an already slipping clutch) is given. Input and output shafts are not included in the comparisons though they may have some effect on acceleration and heat transfer: Casing temperatures are taken to be uniform, as they approximately will be in the steady state, as highly conductive materials of construction being used. Through these simplified models some idea of this relative overall performances of the two clutch forms can be gleamed. Perhaps more importantly the CFD method is shown to be useful for detailed investigation of more specific situations. FLUENT [1] was chosen as the operating programme with sub-routines to handle the non Newtonian nature of the fluid. No regulation of the input drive speed due to loading is accounted for.

We present the design and evaluation of a controllable, semi-active magnetorheological (MR) fluid shock absorber. This study experimentally validates asymmetric quasi-steady MR damper model, using an idealized Bingham plastic shear flow mechanism, for the flow mode damper configuration. Essentially, the MR valve within the piston of the damper comprises a magnetic circuit and annular orifice, where the inlet and outlet geometry of the MR valve can be the same (symmetric) or different (asymmetric). In the asymmetric model, geometric properties of active valve length and gap, as well as the magnetization are different at each end of the MR valve, so that the field dependent yield stress is also different. Two dampers were tested using a MTS machine for sinusoidal stroke of 30mm, over a range of velocities below 0.4m/s. The damping force and damping effectiveness vs. velocity diagram was experimentally validated using the data over a range of applied magnetic field.

This study focuses on the theoretical analysis, design, fabrication and characterization of a magnetorheological (MR) fluid damper for a horizontal axis, front-loading washing machine. In such washing machines, there are two main cycles; washing and spin cycles. During acceleration from washing cycle to high-speed spin, the tub passes through its resonant speed requiring relatively high damping. On the other hand, high damping results in increased force transmission to the housing and noise at high-speed spin cycle. Controllability of the MR fluid damper allows adjustment of damping requirements for different cycles and helps reduce the noise at high speed spin cycle while limiting the tub motion at resonance. A new MR valve is used for the design of the MR fluid damper for washing machine to satisfy the requirements of the application. Fabricated prototype damper is characterized using harmonic displacement input. Test results are in good agreement with the theoretical predictions.

Electro-rheological gel (ERG) is a functional material whose induced shear force is changed according to the intensity of the applied electric field. One-sided patterned electrodes have been proposed in a recent study of ERF, in order to simplify the structure of the wiring. In this study, one-sided patterned electrodes were applied to the ERG and the ER effect was experimentally confirmed. The frictional characteristics of the ERG surface vary in response to the electric field applied to the one-sided patterned electrodes, and a very small change in the ERG thickness occurs due to contraction of the ERG. Performance of the ERG in a micro alignment and fixture device was experimentally investigated. The results show that ER effects are obtained not only for metallic materials, but also for nonmetallic materials, such as glass, bakelite and so on, as sliding objects on the ERG surface. Based on these results, a new fixture device with micro positioning for micro machining of glass is proposed and its performance is experimentally analyzed.

Strengthening muscle force by training, e.g., an isokinetic exercise is effective for not only healthy persons but also those who need rehabilitation. The isokinetic exercise is a training method under the restriction of constant rotational speed of a joint during the exercise. This enables dynamic trainings and at the same time, trainings at maximum output force over the whole range of motion. In many conventional isokinetic exercise systems, a high-power servomotor is used for an exact speed control. These systems are useful in clinical and investigative researches. However, these systems can be dangerous due to system trouble. Therefore, safety countermeasures are extremely important but lead to system complexity and higher costs. In this study, we developed an isokinetic exercise system using an “ER brake”. This brake includes particle-type ER fluid as the working fluid. Because of the rapid response of the ER fluid, the ER brake shows superior response performance compared with conventional brakes. In other words, a simple and safe training system with accurate rotational speed can be realized with this brake. In addition, a high-speed (800 deg/sec at an elbow joint) control was realized with this system.

A half-car vehicle model with variable dampers placed between the sprung mass and the unsprung masses was considered in the study. A suitable set of state variables were defined and state equations of the system were obtained. An integral performance index involving a weighted combination of the average squared heave accelerations of the sprung mass, and squares of suspension deflections was defined. The closed loop optimal control law which gives the optimal value of the damping coefficients of the variable dampers was obtained by using Pontryagin principle. The performance of a vehicle with an optimally controlled semi-active suspension was calculated for measured road profile inputs, and trade-off curves were obtained between the average sprung mass acceleration and suspension deflections. Performance of the vehicle with semi-active system was compared to the corresponding performance of a vehicle with a passive suspension system. Then, a time delay was introduced to the response of the damper and its effect on the performance of the semi-active system was investigated. The results of the study have shown that performance of the vehicle with variable damping semi-active suspension is much better than that of the vehicle with a passive suspension.

Damper behavior of a magnetorheological (MR) bypass damper is analyzed using hydro-mechanical modeling approach. An MR bypass damper consists of piston and double end rods in a hydraulic cylinder, and a bypass comprising cylindrical tubing and an MR valve. Damping forces are developed in the annular bypass via Poiseuille flow. A hydro-mechanical model for the MR bypass damper is derived by considering lumped hydraulic parameters, which are compliance of MR fluids inside the cylinder and flow resistance through the MR bypass valve. Numerical simulations are conducted to predict the controllable damping force due to variable yield shear stress of MR fluid, the post-yield damping due to viscosity of MR fluid, and hysteresis behavior in the low velocity domain due to the compliance effect of the fluid. A laboratory-scale MR bypass damper will be fabricated and tested in order to validate the hydro-mechanical MR damper model.

In this study, nondimensional analysis of shear-mode type rotary drum dampers using MR (magnetorheological) fluids is theoretically conducted. A shear-mode type rotary drum MR damper is constructed and its governing equation of motion is derived based on three different constitutive flow models: Bingham-plastic, biviscous, and Herschel-Bulkley. The damping performance of the rotary drum MR dampers is characterized in terms of the damping coefficient, which is the ratio of the equivalent viscous damping at field-on status to the damping at field-off status. To this end, the damping coefficient for the rotary drum MR damper is theoretically obtained using a key nondimensional parameter, the Bingham number. The performance characteristics of the rotary drum MR dampers are evaluated with respect to different constitutive flow models.

A unique MRF by-pass damper for heavy vehicle controllable suspension systems is designed, manufactured and tested. The damper can generate nearly 8000 N which meets the maximum force requirement for preventing the heavy vehicle rollover under certain crucial circumstance. A dynamic simulation of the roll over performance of a heavy vehicle incorporated with four MR dampers is carried out using vehicle dynamic software. Emergency maneuver and roll over scenario are simulated. The results show that the controllable MRF dampers could achieve better performance for protection from the vehicle rollover, which the roll angle can be reduced by 45% compared to the regular OEM dampers.

The characteristics of a tuned magnetic fluid damper (TMFD) are examined experimentally. Using a tuned mass damper analogy, the concept of effective and non-effective masses is introduced and the qualitative relation among fluid mass ratio, the natural frequency and magnetic field intensity are demonstrated. Effective damping is realized by using a suitable application of magnetic fields based on a frequency response diagram.

This study is to explore the controllable ratio of damping characteristics based on a serial multielectrode electrorheological(SMER) flow mode damper. The SMER damper is applied to the two-degree-of-freedom model of a suspension system. Semi-active suspension control system equipped with the SMER damper and the fuzzy controller is designed for the evaluation of the performance of the SMER damper. The SMER damper is designed, fabricated and tested. The design method for ER dampers based on the requirements of the system damper such as controllable damping force, controllable ratio and the ratio of rebound damping force and compression damping force is described. The experimental results of the semi-active control system have demonstrated that the displacement and the acceleration power spectral density are significantly reduced by applying the semi-active control on the SMER dampers. The simulation and experimental time and frequency response of the displacement and the acceleration indicate the effectiveness of the design of the SMER damper.

A magnetorheological fluid (MRF) fan drive prototype for automotive truck application was designed and tested for both performance and durability. A dual concentric gap with drum rotor design was chosen to meet the required torque capacity, packaging, and mass constraints. Finite element magnetostatic modeling was performed to size the electromagnetic circuit and achieve the desired flux density levels in the MR fluid gaps. The clutch was filled with a custom-formulated MR fluid. Performance testing showed excellent speed control and response. The required 40 N-m torque capacity was achieved along with low drag speed, which is a key design characteristic of the fan drive. The clutch successfully passed several 500-hour durability tests in a test cell environment. Performance testing indicated that the MRF clutch maintained its required torque capacity with very little increase in drag speed over the duration of the tests indicating no fluid thickening issues. The total dissipated energy in these tests is about 3.8 GJ. The total specific dissipated energy for these tests is more than seven times higher than the 10⁷ J/cm³ upper limit previously suggested in the literature.

A fuzzy-sliding mode controller is presented to control the dynamics of semi-active suspension systems of vehicles using magneto-rheological (MR) fluid dampers. A full-car model is used to design and evaluate the performance of the proposed semi-active controlled suspension system. Four mixed mode MR dampers are designed, manufactured, and integrated with four independent sliding mode controllers. In order to overcome the chattering of the sliding mode controllers, a fuzzy logic control strategy is merged into the sliding mode controller. The proposed fuzzy-sliding mode controller is designed and fabricated. The performance of the semi-active suspensions is evaluated in both the time and frequency domains. The obtained results demonstrate that the proposed fuzzy-sliding mode controller can effectively suppress the vibration of vehicles and improve their ride comfort. Furthermore, it is shown that the “chattering” of sliding mode control is smoothed when it is integrated with a fuzzy logic control strategy.

This paper presents vibration control responses of a passenger vehicle equipped with continuously controllable electrorheological (ER) shock absorbers. As a first step, four ER shock absorbers (two for front parts and two for rear parts) are designed and manufactured based on the damping force levels and mechanical dimensions required for the middle-sized passenger vehicle. After experimentally evaluating the field-dependent damping force property and controllability, the manufactured ER shock absorbers are incorporated with the suspension of a car to be tested. Subsequently, the skyhook control algorithm, which is simple, but very effective in rear field, is formulated by considering vertical, pitch and roll motions. The controller is then realized by integrating feedback sensors such as accelerometer and the field test is undertaken under bump and random road conditions. The control responses for the ride quality and steering stability are evaluated in both time and frequency domains. In addition, the performance comparison between conventional suspension and ER suspension is carried out.

A prototype clutch having horizontal rotational axis and a narrow gap between its two parallel radial disks is examined using CFD. The narrow gap between the discs is filled with an unexcited electro structured fluid (ESF); the through flow of {electrorheological (ERF) or magnetorheological (MRF)} fluid that would arise is contemplated as a means of contributing towards the cooling of the clutch. The throughflow, caused by body /centrifugal force action, is examined firstly when both plates rotate together at speed Ω. The aim is to estimate the flow rates arising under conditions of different rotational velocities, clutch geometries and fluid properties. Following this the cooling of the clutch is examined for the case of one plate fixed and the other rotating at a constant speed throughout. The inlet and outlet port pressures are made the same and the fluid is taken to be unexcited / Newtonian with viscosity μ.

This paper investigates the effects of dissipativity on the seismic performance of the base isolated benchmark building controlled by magnetorheological (MR) fluid dampers. In the past decade, MR dampers have received special attention in the structural control community due to the advantages over other control strategies from a seismic mitigation perspective. However, due to their nonlinear behavior, which is mainly characterized by their dissipative nature, development of control strategies for MR dampers may be challenging. In general, dissipativity is never taken into account in the design process; therefore, control of the damper may not be efficient in some cases. Recently, several dissipativity measures are introduced to aid the selection of control design for smart dampers. While, these indices have proved to be useful for simple structures and idealized dampers, they have not yet been investigated for realistic building and damper models. The recently introduced base isolated benchmark building and the 20-ton MR damper model are realistic and very suitable for the investigation of dissipativity. In this study, the linear quadratic regulator (LQR) is selected as the control strategy to command several MR dampers to control the base isolated benchmark building. It is shown that control designs with higher dissipativity characteristics are more suitable for MR dampers than the ones that have lower dissipativity.

Particle type ER fluids commonly have about 5-mili seconds response times. This delay needs to be taken into consideration when electric fields to energize ER fluids are controlled in real time. Especially, servo systems with ER fluid devices have a sampling time for the control loop that is about 1-mili second and so is shorter than the response time of ER fluids. Though the delay in this case has a great possibility of having effects on the performance or stability of servo systems, most research in this area has not mentioned the problem. We previously developed a particle ER fluid damper for fast and precise positioning of a direct-drive motor; its viscosity was controlled continuously in real time. In this paper, we investigated how the time delay affected damping performance and stability of this system.

The paper presents the design and development of a 2-DOF magnetorheological fluid (MRF) based haptic joystick and studies its applications in virtual reality. The developed system consists of three main parts: MR joystick, control hardware, and software. The MR joystick is composed of two actuators with disc shape positioned perpendicularly with a gimbal structure. The dimensions of the actuators were optimized using finite element analysis and their steady-state performances of the actuator were measured. The kinetics of the joystick in terms of working space and resistance force were discussed, where a subhysteresis model and a compensation technique were employed. The applications of the MR joystick in virtual reality were demonstrated using two interface examples.

The purpose of this study is to develop a prosthetic ankle joint intelligently controlled by the specially designed linear MR brake of flow-type. MR fluid changes its rheology depending on the intension of an applied magnetic field. The brake using MR fluid has a simple structure and can control its braking force with a low voltage. Prosthesis users often tumble because they don't have dorsiflexon during swing phase, so that we propose putting a MR brake to keep dorsiflexion in order not to tumble. We hope that prosthesis users can walk more naturally and smoothly by use of developed intelligent prosthetic ankle joint with MR brake. We developed a prototype of the intelligent prosthetic ankle joint with the MR brake and evaluated it in walking experiments and obtained good results.

This study focuses on the design and characterization of magneto-rheological (MR) fluid dampers for a mini-bus based on mixed operational mode. The theoretical fluid mechanics-based model is developed and used to predict the performance of these MR dampers. The arrangement of coils in the piston and winding orientation are discussed and identified by electromagnetic finite element analysis. As a verification of the theoretical prediction, two prototypes of MR dampers are designed, manufactured and characterized. The theoretical results are compared with the experimental results for different input frequency and electric current. The theoretical predictions are shown to be in excellent agreement with the experimental data. The obtained results indicate that the performance of the MR damper with two coils is better than a damper with a single coil of the same activation length. Furthermore, the developed dynamic damping force is found to be controllable over a wide range suggesting that these proposed MR dampers can be used as a good actuator for the semi-active suspension system of the mini-bus Changan 6350.

The dynamic behavior of a two-layered fluid in a laterally oscillated rectangular container under a vertical non-uniform magnetic field was studied experimentally. The two-layered fluid was formed of water based magnetic fluid and silicone oil. The dynamic behaviour was studied by measuring the velocity profile of the two-layered fluid using an ultrasound velocity profile measuring technique while varying the vertical magnetic field. The displacement of the free surface was measured using a laser sensor. The effect of the magnetic field on the sloshing of the two-layered fluid was considered.

In this study, a normally closed (NC) type clutch using magnetorheological (MR) suspension and a rare-earth permanent magnet is proposed as a safety device for human-collaborative robots. This clutch can transmit an effective torque under various conditions and function as a holding brake and a changeable torque limiter. To design this clutch to achieve both good controllable characteristics and safety performance, the normally closed structure with a permanent magnet was realized by placing two facing magnetic poles asymmetrically for efficient generation of the magnetic field, and by adopting the multi-sheet rotor for the improvement of the torque output. As the analysis results show, it was confirmed that the three-sheet rotor obtained about 1.5 times torque output as much as the single-sheet rotor. When the exciting current was 0.8A, the transmitted torque marked the minimum; when the exiting current was 0A, the torque output of approx. 41Nm was generated with the time constant of 0.15s.

This paper presents the design and fabrication of a flow-mode bifold magnetorheological (MR) damper for shock and vibration mitigation for high piston velocity (15mph or 6.71 m/s) as well as an evaluation of its performance at low speed. Based on a Bingham-plastic model, as well as a Bingham-plastic model coupled with a low speed hysteresis model, two theoretical MR damper models for flow-mode MR dampers are constructed. Using the design strategy associated with the Bingham-model based damper model, two MR damper designs for achieving the performance requirement with a limited space are considered: first, the conventional MR damper that has an MR valve inside the piston head and second, the bifold MR damper that has MR valves at each end of the damper. After numerically comparing the damping performances of two MR damper designs, the bifold MR damper was chosen because its dynamic range was better at high speed. The bifold MR damper was tested at relatively low piston velocity using an MTS testing machine under sinusoidal loading. Experimental data are compared well with the results predicted by the theoretical models.

The paper presents the design and of a magnetorheological (MR) fluid based damper that operates in squeeze and flow modes. The damper has been designed to reduce vertical vibrations, namely displacement/force transmissibility, from a pneumatic hammer to the operator body. The mount governing equations have been derived and the effect of system parameters on its performance was analyzed. Particular attention was given to the effect of the operator mass and the magnitude of the magnetic field on the mount response. Results analysis indicated that the resonant peak decreases as the applied magnetic field increases. Simultaneously, the resonance frequency decreases.

In this paper, the innovative principle of a magnetoelectric relative displacement self-sensing magnetorheological damper (MSMRD), through integrating an integrated relative displacement sensor (IRDS) into a commercially available MR fluid damper, is realized and experimentally tested. The prototype of MSMRD and the testing setup with the rapid control prototyping (RCP) technique are established using 849 Shock Absorber Test System from MTS and the DS1103 PPC controller board from dSPACE GmbH under MATLAB/SIMULINK/RTW from MathWorks. Finally, the experimental testing on the first assembled prototype of MSMRD and the corresponding results are presented and analyzed.

The main objective of this study is to experimentally quantify the feasibility of using ER fluids for suppressing vibrations of the rotating beams. An ER sandwich beam specimen, in which an ER fluids layer is sandwiched between two elastic surface layers, is constructed. An experiment set-up is established to investigate the effect of the ER fluids on vibration suppression of the rotating beams with point-to-point motion. The vibration response performances of the beam subjected to different electric field intensity, rotating speed, and acceleration are demonstrated and evaluated. The experimental results obtained indicate that significant vibration attenuation is achieved at different operating conditions by applying an electric field to the rotating beam.

Microfluidic manipulation is one of the main concerns in lab-chip society. This paper presents the design, fabrication and testing methodologies of electrorheological (ER) fluid-controlled active microfluidics chips. All of the fundamental building blocks, such as microvalves, micropumps and micromixers, are fabricated with similar processes in PDMS-based chips for easy integration. Such building blocks can be digitally controlled by on-off switching of electric fields applied on the parallel electrodes along the ER fluid channels. Experimental results show reliable functionalities of these devices. The ER active control scheme supplies additional flexibilities over the passive control of microfluidics. A hybrid approach active mixers, combining the ER active actuation with the passive baffle structures, was applied to achieve more efficient chaotic mixing than the passive mixers available.

In this study, a response-dependent MR damper of which frictional force is determined according to the assumed shape function composed of displacement and velocity of the damper piston itself, is designed and its performance is compared to the passive one and semi-active one using linear quadratic regulator. Numerical analysis results from SDOF system indicate that passive MR damper designed to have appropriate frictional force of which magnitude is less than about 30% of the base shear force, provides the smallest displacement response spectrum over all structural periods and response-dependent MR damper show better control performance in reducing absolute acceleration spectrum with increasing frictional force for the long period structure. Also, seismic analysis of a three story structure with the MR damper shows that well designed response-dependent MR damper provides performance equivalent to or better than the semi-active MR damper operated by LQR controller in spite of using only the structural response transferred to the damper.

This paper proposes a control strategy for systems of automotive active suspension using fuzzy logic and shows how to generate the necessary rules. Conventional control algorithms for active or semi-active suspension, such as on/off and continuously variable will be shown. The results of the control laws are compared with the fuzzy strategy through numeric simulations and experimental tests. Analyses of results show the advantages and disadvantages of the used methods.

Magnetorheological model suspensions with different contents of iron particles have been investigated. The results show an increase of the shear stress by increasing the magnetic field and the solid content, which was mathematically modelled. The influence of the solid content is approximately exponential without magnetic field and linear in strong magnetic fields. The effect of the temperature and of the base oil viscosity on the shear stress is negligible in the field but decisive without field. The sedimentation behavior also strongly depends on the iron particle content, where MR fluids with a higher concentration settle with a lower intensity due to the higher sediment height. The response time of the magnetorheological model suspensions could not be clearly determined, but it is less than 10 milliseconds.

This paper presents a robust and superior control performance of a quarter-vehicle electrorheological (ER) suspension system. In order to achieve this goal, a moving sliding mode control algorithm is adopted, and its moving strategy is tuned by fuzzy logic. As a first step, ER damper is designed and manufactured for a commercial suspension system, and its field-dependent damping force is experimentally evaluated. The ER damper is then incorporated to a commercial quarter-vehicle suspension system, which is composed of sprung mass, spring and tire. After formulating the governing equation of motion for the quarter-vehicle ER suspension system, a stable sliding surface and moving algorithm based on fuzzy logic are formulated. The sliding mode controller is then synthesized and experimentally realized with a quarter-vehicle for the demonstration of a practical feasibility. Control performances such as vertical displacement and acceleration are evaluated in time and frequency domains under various road conditions such as bump and random road.

Along with rheological properties, dielectric spectra of the ER fluids were found to provide additional information on both analyzing their electrical polarization properties and interpreting their flow behavior. Dielectric properties of three different material systems such as spherical-monodisperse polymer microshperes (PAPMMA) consisting of a poly(methyl methacrylate) (PMMA) core and a polyaniline (PANI) shell, single-doped and mesoporous-doped TiO₂ system and copper phthalocyanine-doped mesoporous TiO₂ suspensions based ER fluid were analyzed via dielectric spectra of permittivity and loss factor as a function of the frequency, and Cole-Cole plots. Polarizability which is defined as a difference of dielectric constant at both zero frequency and infinite frequency was found to be a proper parameter to understand a better ER fluid. Using the Cole-Cole plot we were able not only to fit the dielectric spectra, but also to deduce the achievable polarizability by explaining the higher ER performance of the ER fluids.

Iron containg hexagonal mesoporous silica particle (Fe-MCM-41) was prepared and adopted into carbonyl-iron (CI) based magnetorheological (MR) suspension as an additive to improve the sedimentation problem of the CI based MR fluid. Structural properties and morphology of the synthesized Fe-MCM-41 particles were observed using SEM. Their MR properties such as oscillation characteristics and flow response (shear stress and shear viscosity) were examined via a rotational rheometer in parallel plate geometry equipped with a magnetic field supplier under external magnetic field strengths ranging from 0 to 257 kA/m. The addition of Fe-containing mesoporous particles into CI suspension was found to improve not only MR behaviors but also sedimentation problem of the CI based MR fluid.

This paper presents robust control performance of a direct current (DC) motor with brake system adopting the giant electrorheological (GER) fluid, whose distinguished feature is an extremely high value of yield stress. As a first step, Bingham characteristics of the GER fluid is experimentally investigated using the Couette type electroviscometer. A cylindrical type of ER brake is then devised based on the Bingham model, and its braking torque is experimentally evaluated. The ER break is then incorporated with a DC motor. After formulating the governing equation of motion for the DC motor with ER brake system, a sliding mode control algorithm, which is very robust to external disturbances and parameter uncertainties, is synthesized and experimentally realized in order to achieve desired rotational speed trajectories. The tracking responses of the control strategy are then evaluated for various sinusoidal trajectories. In addition, their tracking errors are evaluated and compared with those obtained from traditional PID controller.

A magnetorheological (MR) damper with a bypass valve containing porous media is developed. Movement of the piston forces MR fluid to flow from one side of the piston to the other, through an externally mounted bypass packed with magnetic spheres. The passageways between the spheres provide narrow, tortuous channels that act as a controllable valve when subjected to a magnetic field. A stationary magnetic coil is wrapped around the so called porous valve, isolated from the MR fluid and external to the device. While flowing through the tortuous channels in the porous media created by the packed spheres, the MR fluid experiences varied local flow directions, and thus an external field can be applied in any direction and still achieve variable damping. Additionally, the use of long channels tightly packed to create narrow passageways allows a very high damping force to be generated by a relatively compact damper. Furthermore, use of an externally mounted coil allows for maintenance accessibility, and the magnetic flux return path can be either empty (air) or any high permeability material. The damper is tested for steady state sinusoidal displacements, and equivalent viscous damping and complex stiffness are computed. It is shown that the porous bypass valve MR damper can provide high controllable damping force and a wide force range.

This paper presents an adaptive tuned vibration absorber (ATVA) which based on magnetorheological elastomer (MRE). Traditional dynamic absorber has limited its application and vibration absorption capacity for its narrow working frequency bandwidth. MRE is a kind of smart material whose modulus can be controlled by applied magnetic field. Based on MREs, an adaptive tuned vibration absorber which works on shear mode is proposed in this paper. After the vibration mode shapes of the ATVA are analyzed, the mechanical structure of the ATVA is brought forward. Then the magnetic circuit of the ATVA is identified by ANSYS software. By using of a modified dipole model, the shift-frequency properties of the ATVA versus magnetic field and strains are theoretically analyzed and simulated. Further more, by employing a beam with two ends supported, its shift-frequency property and vibration absorption capacity are experimentally justified. The experimental results demonstrate that the designed ATVA has better performance than traditional passive absorber in terms of frequency-shift property and vibration absorption capacity.

Recently many researches on ER fluids (ERF) are developed for applications of clutches, brakes, dampers and other kind of mechatronics technologies. In many applications, these devices are constructed with bilateral electrodes to apply electric field in ERF. However, the electric field of several kV/mm may be necessary to generate an ER effect sufficiently for practical purposes. The gap between a pair of electrodes should be, therefore, maintained narrowly and exactly for fears of short-circuit. At the same time, this electrode system also requires an interconnection on driving parts. To dissolve these disadvantages on the conventional configuration of the electrodes, we have been proposing an “one-sided patterned electrode” (OSPE) system. In this report, we confirmed the flow characteristics of low molecular liquid crystal (LMLC) on OSPE. Next, we also confirmed the different characteristics depending on the pattern type. According to results of electro-static analysis, we conclude that such a difference may results from directors of LC molecules derived by electric field.

MR Fluid (MRF) is suitable material for some mechatronics device, for example clutches or brakes because of its rapid response and large viscosity change. However, total response speed will grow worse due to the affect of eddy current at magnetic circuit. Realization of high torque devices requires large area of magnetic circuit. However, the larger the area becomes, the larger the effect of eddy current grows with reduction of electric resistance. To dissolve this problem, we propose to use laminated silicon steel sheets (LSSS) for yokes of electro-magnets. By using LSSS, we developed high-torque (> 30Nm) and high-speed (< several m illiseconds) MRBrake (MRB). In this paper, the design guideline of the MRB is described. In this guideline, we use FEM analysis to design shapes and location of yokes. In addition, experimental results of MRB are presented. As a result, high performance MRB, whose maximum output torque is 36Nm and output response speed is several milliseconds, was realized.

The results of experimental research of the process of capillary rise of magnetorheological suspensions in the vertical cylindrical capillary in the magnetic field were presented. It was shown that under small magnetic fields the speed of capillary filling increased. Under big values of magnetic induction this process is slowed down. In the capillaries of a small diameter the influence of magnetic field leads to the decrease of the height of capillary rise which is due to the overlapping of wall menisci and the change of the coefficient of surface tension.

This paper presents control characteristics of a commercially available magnetorheological (MR) damper which can be directly applied to passenger vehicles. After evaluating the field-dependent damping force, the damping force controllability is experimentally investigated. Subsequently, a quarter-car model which is composed of sprung mass, MR damper, spring and tire is constructed and the governing equation of motion is derived in order to investigate vibration control of a vehicle. A discrete-time fuzzy sliding mode control algorithm is then designed by considering system uncertainties such as the variation of the sprung mass. The controller consists of a discontinuous part and an equivalent part. In addition, the fuzzy algorithm is adopted to increase system robustness to the uncertainties and achieve faster reaching to the sliding surface. Control performances of the proposed sliding mode controller are experimentally evaluated under various road conditions and compared with continuous-time sliding mode controller.

This paper presents vibration control of a real-scaled five-story steel structure subjected to horizontal excitation using a semi-active magneto-rheological (MR) damper. A large-sized double-rod MR damper, which is applicable for vibration control of the real-scaled five-story structure, is designed and manufactured on the basis of the field-dependent Bingham model of the MR fluid. The damping force of the MR damper is experimentally evaluated with respect to the excitation frequency at various magnetic fields. After formulating the governing equation of motion for the five-story structure associated with the MR damper, displacement and acceleration responses of the structure are discussed under pseudo earthquake excitation in which a hybrid mass damper is designed to reproduce seismically excited structural responses. The controllers which require only structural response of the damper installed floor for calculating the input current of the MR damper are designed to effectively suppress unwanted structural vibrations.

Since the force generated by a MR damper has large nonlinearity, the performance of the MR damper is dependent on the response characteristics such as frequency and amplitude. Soil-structure interaction (SSI) is generally known to have large effect on the seismic response of building structure. In this study, the performance of MR damper in mitigating seismic response of a building structure is evaluated considering SSI effect. Firstly, the performance variance of a MR damper due to the change of natural period is investigated by constructing its normalized response spectrum through the numerical analysis for many earthquake wave records and the natural period of structure. The variable friction force of a MR damper is normalized by the structural base shear force, and its amplitude and the decrement of response are quantitatively evaluated. Then, the response characteristics of SSI system due to the lengthening of structural natural period and various soil conditions are numerically evaluated based on the response spectrum analysis. Finally, the numerical results with and without considering the SSI effects are comparatively evaluated for the building structure with a MR damper. The comparison results show that the SSI effect should be considered in order that the undesirable effect of MR dampers on the structural control should not be neglected.

This paper presents control characteristics of a quarter-vehicle Electrorheological (ER) suspension system by adopting a discrete-time fuzzy sliding mode control algorithm. A cylindrical ER damper is designed and manufactured by incorporating Bingham model of the ER fluid. After evaluating the field-dependent damping characteristics of the ER damper, a quarter-vehicle ER suspension system is constructed which is composed of sprung mass, ER damper, spring and tire. After deriving the governing equation of motion for the quarter-vehicle ER suspension system, a discrete-time control model with system uncertainties is formulated in a state space. A stable sliding surface is then designed followed by the formulations of a discrete-time sliding mode controller which consists of a discontinuous part and an equivalent part. In the controller formulation, the fuzzy control algorithm is also adopted to increase system robustness to the uncertainties and achieve faster reaching to the sliding surface. The controller is then experimentally realized and control performance is evaluated under various road conditions.

Magnetorheological (MR) fluids consist of suspensions of micron scale magnetic particles (iron or cobalt) in a fluid medium such as silicone oil or mineral oil. MR fluids are used as dampers in vibration absorption applications as well as active valves in hydraulic applications. Nevertheless, one limitation preventing the broader use of MR fluids is the gradual sedimentation of the particles as a function of time. Typical MR fluids utilize micron scale particles at high weight fractions (as much as nominally 80wt% (app. 34vol%)). A reduction in sedimentation rate can be achieved by substituting nanometer scale particles in bi-disperse MR fluids (i.e., a mixture of micron-scale and nanometer scale particles). The nanometer scale particles reduce sedimentation rate, because nanometer scale particles fill in the voids between the micron scale particles, thereby reducing creeping flow. In this study we investigate and quantify the effect of substitution of micro-particles with nanometer scale particles on the sedimentation rate of the MR fluid. Different MR fluids varying from pure micron scale to nanometer scale particle loading of 10% and 15% are investigated. In order to measure sedimentation, a sedimentation rate measurement device was constructed. The device measures sedimentation magnetically utilizing the reduction in permeability with sedimentation. The flow curves of the MR fluids are determined using a Paar-Physica Rheometer and data is fitted with the Bingham-Plastic flow model to estimate yield stress.

Hybrid magnetic particles of carbonyl iron (CI) /poly(vinyl butyral) (PVB) with core/shell microstructure (CI-PVB) were prepared in order to enhance the dispersion stability of the magnetorheological (MR) fluids. Since the composite particles of CI-PVB have a lower density than that of the pristine CI particles, they are regarded to improve the sedimentation problem of magnetic particles in the MR fluid when the particles are dispersed in a mineral oil and to make easy redispersion after caking. The PVB coating layers were found to play an important role in the steric repulsion between the relatively large CI particles. Morphology and composition of the CI-PVB particles were observed via SEM and TGA, respectively. Flow properties of both CI and CI-PVB based MR fluids were examined via a rotational rheometer in parallel plate geometry equipped with a magnetic field supplier.

We prepared polyaniline (PANI) /multi-walled carbon nanotube (MWNT) nanocomposites of both PANI pierced MWNT nanocomposites synthesized using poly(vinyl alcohol) as a polymeric stabilizer and PANI/MWNT nanocables via an in-situ oxidative polymerization directed by a cationic surfactant of cetyltrimethylammonium bromide (CTAB). In addition to chemical analysis of the products, the formation of nanocomposite nanocable and their morphology in which the MWNTs were entirely encapsulated by amorphous PANI, were confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrorheological (ER) fluids were prepared by dispersing both of these synthesized MWNT/PANI nanocomposites in insulating silicone oil and their ER properties were investigated by controlling applied DC electric field strengths. The synthesized nanocomposite particles have enhanced interparticle interactions, and the shear stresses increase with the electric field strength for a broad range of shear rate. Among three different constitutive equations adopted, the Cho-Choi-Jhon model was found to fit the flow curves quite well.

This paper presents vibration control responses of a hybrid engine mount utilizing ER fluid and piezoelectric actuator to isolate the vibration of wide frequency range with various amplitudes. The function of ER fluid is to isolate vibration from engine unbalance force for low frequency range with large amplitude, while the piezoelectric actuator for high frequency range with small amplitude. The ER fluid part operating under the flow and shear modes is devised and the piezoelectric part is integrated with the magnification mechanism. After establishing the dynamic model of the proposed engine mount, both field-dependent dynamic stiffness of the engine mount are evaluated for various conditions. Then, in order to investigate the effectiveness of the proposed hybrid mount, one degree of freedom (DOF) system is established. The governing equation of motion of 1DOF system is formulated and then robust controller to attenuate vibration of wide range frequency component is designed. The vibration control performances such as displacement transmissibility are evaluated and presented in frequency domains.

Electro-Rheological Fluids (ERFs) are functional fluids that change their apparent viscosity by applying electric field. ERF is composed of ER particles and silicon oil. ERF shows reversibility and high responsiveness of ER effects, but has a defect that passage of time causes sedimentation of ER particles. Electro-Rheological Gel (ERG) has been developed to overcome the defect of ERF. ERG is composed of ER particles and silicon gel. A flat plate placed on the ERG sheet clings to the gel by applying an electric field and ERG produces the shear force to the plate. The one-sided pattern of electrodes, which has been developed for ERF devices, is a very useful idea to free sliding or rotating parts from wiring arrangements. In this study, the optimum design of one-sided pattern electrodes for ERG is carried out by means of a numerical analysis. The general-purpose tool for the analysis of electric and magnetic field ‘ANSYS Emag’ is used. The influences of the electrodes pattern on the performances of ERG are analyzed and the yield forces are estimated from electric field intensity at the interface between the electrodes and ERG. Some experiments are also carried out to examine the validity of the numerical analysis.

This paper presents performance characteristics of a MR impact damper for controllable bumper in vehicle systems. Recently, several mechanisms are proposed in order to minimize the injury of vehicle occupants during frontal collision. One of promising candidates is to adopt MR fluid which undergoes significant instantaneous reversible changes in material characteristics when subjected to magnetic field. Using this salient property, a new type of MR impact damper is devised in this work. The proposed MR impact damper is integrated with bellows to induce the flow motion and the motion is operated under flow mode. The field-dependent damping force is evaluated by computer simulation with various conditions. In order to investigate the effectiveness of the proposed impact damper, a lumped parameter mathematical model of frontal vehicle crash system including MR impact damper is developed and realized in order to evaluate acceleration peak reductions and transmitted force in the frontal collision.

Magnetorheological elastomers (MREs) consist of ferromagnetic particles embedded in a compliant matrix (i.e. elastomer). Due to the magnetic interaction of the ferromagnetic particles, MREs exhibit field dependent physical properties. Very significant changes in the modulus and loss factor of the elastomer can be realized. This makes MREs a promising candidate for active vibration control mechanisms. One factor currently limiting the implementation of this technology is the lack of an efficient manufacturing method that is practical for mass production. Most of the specimens created for previous MRE research were made using simple casting or mechanical mixing methods that are not ideal. In this research a new methodology for producing MREs using Vacuum Assisted Resin Transfer Molding (VARTM) was investigated. The method was used with a range of iron particles sizes and silicon elastomer systems and found to be effective within certain limits of applicability. The specimens produced were tested in compression under a range of magnetic fields to validate the presence of the MR effect. Changes in compressive modulus ranging from 35% to 150% (depending on volume fraction) under fields of around 0.3T were observed.

Compression Studies of electrorheological (ER) fluids have been impeded by not knowing the concentration of particles held between the plates. This paper presents a technique that calls for using a constant volume setup that solves the problem. This paper also includes results on the effects of changing concentration of particles and changing the viscosity of the oils used in compression of an ER fluid. The conclusions of this paper were that the constant volume squeeze flows of ER fluids were significantly different than what has been predicted with constant volume squeeze flow theories.

Carbonaceous condensed species, which include single-walled carbon nanotubes, produced by electric arc deposition (EAD) are subjected to thermogravimetric analysis at varying heating rates. It will be shown that the heating rate is critical when predicting the types and amounts of single-walled carbon nanotubes present in the sample. Examination of EAD products (from various applied currents) with TGA plots concludes that the 70-90 A current regime is the optimum operating parameter and the web-lid faction is the richest region of SWNT concentration.

This paper presents the development and performance testing and modeling of a position-feedback MR actuator. The MR actuator, in disc-shape, composes of rotary shaft and plate, an electromagnetic coil, MR fluids, and casings. The working principle of the actuator was discussed and the transmitted torque equation was employed by using the Bingham plastic model. The optimal dimensions of the actuator were obtained by finite element analysis using COSMOSEMS package. Following the manufacturing and fabrication of the actuator prototype, the steady-state performance of the MR actuator was measured using a force gauge. The experimental results show that the actuator exhibit hysteresis behavior. A sub-hysteresis model was then proposed and the model parameters were identified using the experimental results. The comparison between experimental results and model-prediction value demonstrated that the model could accurately predict the steady-state performances of the MR actuator.

We present preliminary studies of the rheological properties and dispersion stability of MR fluids as a function of particle shape by comparing fluids made with uniform nickel spheres to those employing nickel microrods suspended in silicon oil. The rods were fabricated using template-based electrodeposition having diameters in the range 300 ± 30 nm and lengths in the range of 5 – 25 μm. The properties of these rods were compared to commercial nickel carbonyl spheres (1–10 μm dia.). Qualitatively, the off-state (field off) viscosity of fluids containing only rods was found to be substantially greater than those that contain only spherical particles. Rheological measurements of the on-state viscosities were conducted using a custom rheometer equipped with an electromagnet capable of magnetic fields up to 0.6 T. Placed in this field, we observed yield stresses of 1.88 ± 0.23 and 1.86 ± 0.26 kPa, respectively for 7.6% volume fraction of pure nickel spheres and rods, respectively. Due to limitations of the testing apparatus, only the on-state properties of these fluids were investigated. For this reason, the yield stress values reported do not account for the difference in off-state viscosity. While the fluids containing spherical nickel particles tended to settle rather quickly (< 20 minutes), those containing only rods remained suspended even after 48 hours.

Recently, Wang and Liao (2005) proposed a new damper controller for MR fluid dampers based on signum function and the control algorithm and simulation results are analyzed. In this paper, the experimental setup to validate the signum function based damper controller is established and the testing results are presented. The experimental results show that the signum function based damper controller for MR dampers can let the controlled damping force track the desired damping force very well and the effectiveness of the damper controller based on the signum function is verified.

Encapsulated polypyrrole (PPy) with different amount in the channels of mesoporous silica (SBA-15) was synthesized. The XRD and N₂ adsorption/desorption isotherms analysis show that PPy with different loadings in the channels does not affect the ordered hexagonal structure of resultant PPy/SBA-15 nanocomposites. Further, the electrorheological (ER) properties of the nanocomposites with different PPy loadings were investigated by steady and oscillatory shear experiments. The results reveal that PPy/SBA-15 fluids exhibit typical ER and viscoelastic behavior under the applied electric field and ER response depends mainly on PPy loadings and there is an optimum PPy loading for strong ER effect.

Seismic control performance of MR dampers, which have severe nonlinearity, changes with respect to the dynamic characteristics of earthquake excitations such as magnitude and frequency contents. In this study, effects of excitation characteristics on the equivalent linear system represented by an equivalent damping ratio for single-degree-of-freedom (SDOF) systems with a MR damper are investigated through extensive numerical analysis for various natural frequencies of the structures and design parameters of the MR damper. In addition, to implement an equivalent linearization procedure considering non-stationarity and frequency contents of the earthquake excitation, seismic response reduction factors for artificial earthquake ground motions are proposed using regression analysis of linear structural responses obtained from numerical analysis. Equivalent linearization results show that the relative magnitude of the excitation compared with the friction force of the MR damper and the frequency contents of the excitation affect the equivalent damping ratio considerably, and appropriate combination of the friction and the viscous damping produces additional damping effect.

Electrorheological activity of suspensions, which have inorganic natural (glauconite, kaolin) and synthetic (frame aluminosilicates and hydrated aluminum oxides) fillers as dispersed medium, has been investigated. The dependences of electrorheological activity of the fillers on their composition, structure and the presence of different types of water have been found. It was assumed that the presence of solid phase of the coordinated water in the structure of synthetic compounds leads to the its protolytic dissociation (under the influence of metal ions) with the formation of H⁺ protons, responsible for the appearance of electrorheological effect of the electrorheological fluids investigated.