Electro-Rheological Fluids and Magneto-Rheological Suspensions

The following sections are included:

• PREFACE

• CONTENTS

To enhance the yield shear stress of magnetorheological (MR) fluids is an important task. Since thick columns have a yield stress much higher than a single-chain structure, we enhance the yield stress of an MR fluids by changing the microstructure of MR fluids. Immediately after a magnetic field is applied, we compress the MR fluid along the field direction. SEM images show that the particle chains are pushed together to form thick columns. The shear force measured after the compression indicates that the yield stress can reach as high as 800 kPa under a moderate magnetic field, while the same MR fluid has a yiled stress of 80 kPa without compression. This enhanced yield stress increases with the magnetic field and compression pressure and has an upper limit well above 800 kPa. The method is also applicable to electrorheological fluids.

The ability of magnetic-field-sensitive gels to undergo a quick controllable change of shape can be used to create an artificially designed system possessing sensor- and actuator functions internally in the gel itself. The peculiar magneto-elastic properties may be used to create a wide range of motion and to control the shape change and movement, that are smooth and gentle similar to that observed in muscle. Magnetic field sensitive gels provide attractive means of actuation as artificial muscle for biomechanics and biomimetic applications.

Electroactive elastomers are composites made of solid particles embedded in an elastomeric network whose mechanical or optical properties can be changed by the application of an electric or a magnetic field. These materials have obviously a strong connection with ER and MR fluids and can be more appropriated for some applications. We present recent results concerning two kinds of filled elastomer, one based on carbonyl iron particles and the second one on silica particles. In the first case we show that the change of elastic properties obtained by the application of a magnetic field depend dramatically on the way we have structured the suspension before the polymerization. We explain quantitatively these experimental results with the help of finite element calculation to predict the magnetic forces between the particles. In the second case we show how it is possible to modulate the transmission of a laser beam by shearing a thin elastomeric film whose particles have been initially aligned with the help of an electric field. Some applications related to the organization of the filler particles by the application of a field or a combination of a field and a flow before polymerization will be discussed.

Steady and oscillatory shear 3-D simulations of electro- and magnetorheology in uniaxial and biaxial fields are presented, and compared to the predictions of the chain model. These large scale simulations are three dimensional, and include the effect of Brownian motion. In the absence of thermal fluctuations, the expected shear thinning viscosity is observed in steady shear, and a striped phase is seen to rapidly form in a uniaxial field, with a shear slip zone in each sheet. However, as the influence of Brownian motion increases, the fluid stress decreases, especially at lower Mason numbers, and the striped phase eventually disappears, even when the fluid stress is still high. In a biaxial field, an opposite trend is seen, where Brownian motion decreases the stress most significantly at higher Mason numbers. To account for the uniaxial steady shear data we propose a microscopic chain model of the role played by thermal fluctuations on the rheology of ER and MR fluids that delineates the regimes where an applied field can impact the fluid viscosity, and gives an analytical prediction for the thermal effect. In oscillatory shear, a striped phase again appears in a uniaxial field, at strain amplitudes greater than ~0.15, and the presence of a shear slip zone creates strong stress nonlinearities at low strain amplitudes. In a biaxial field, a shear slip zone is not created, and so the stress nonlinearities develop only at expected strain amplitudes. The nonlinear dynamics of these systems is shown to be in good agreement with the Kinetic Chain Model.

The ER behavior of the water-free complex strontium titanate(STO) particles, which were synthesized by means of sol-gel technique with surface modification dispersed in silicone oil, was investigated systematically. It is found that this fluid has attractive ER properties with high shear stress, low leakage current, wide dynamic range in both temperature and shear rate, as well as good antisettling character.

Meso-scale metal phthalocyanine (MPc, M = Cu, Ni, Mn, or Co)-Fe₃O₄ nanocomposites for EMR fluids have been prepared and well characterized. The results indicate that there exists chemical bonding between MPc and Fe₃O₄ nanoparticles, and their strength of chemical bonding increases in the following order: NiPc < CuPc < CoPc ~ MnPc. Compared to Fe₃O₄ nanoparticles, MPc-Fe₃O₄ nanocomposites have superior ability to anti-oxidation and thermal stability, and show almost the same saturation magnetic strength, but much less coercive force. All MPc-Fe₃O₄ nanocomposites have irregular spherical shape with D of 0.2~0.4 μm. The EMR fluids containing MPc-Fe₃O₄ nanocomposites in chlorinated paraffin oil have excellent stability and redispersibilty. They show reversible significant field-induced shear stress, which increase linearly with the increment of electric field strength (E) or H and which are different for MPc-Fe₃O₄ nanocomposites containing various metal elements, when E or H is applied respectively. Furthermore, field-induced shear stress shows obvious synergetic effect when E and H are applied simultaneously.

The relations between the rheological and electrical properties of NaY zeolite electrorheological fluid and its solid phase are studied. It is found that there exist complex relations between its electrical and rheological properties. The temperature spectra of dielectric properties of the fluid under high AC electric field are strongly field strength dependent. The relation between the DC conductivity of the fluid and the exciting electric field is experimentally presented as log σ=A+BE^1/2, where A is a strong function, but B, a very weak function of temperature. The shear stress of the fluid under a fixed electric field and temperature decreases with shear rate. A relaxation time for the adsorbed charges is estimated to be about 0.3 to 6.6 s in the temperature range from 280 to 380 K. The relaxation time qualitatively corresponds to the shear rate at which the shear stress begins to drop. The time dependent leaking current of the ER fluids under DC electric field is also measured. The conductivity increase is mainly caused by the structure evolution of particles. The experimental results can be explained with the calculations of Davis (J. Appl. Phys. 81(1997) pp.1985-1991) and Martin (J. Chem. Phys. 110(1999) pp.4854-4866). It is predicted that the NaY zeolite ER fluid strength would get degraded slowly.

The associated effects of polarization strength, polarization rate, and dielectric loss on ER performance ware studied by means of the correlation of rheological properties of carbon-doped TiO₂ ER fluids with experimental results of flow-modified permittivity (FMP). We prepared ER fluids with carbon-doped TiO₂ powders of different conductivity via controlling carbonization temperature and organic contents. The experiments present the optimum organic contents of 4.6% to 9.2% and the optimum carbonization temperature of around 673 K for the better ER activity. The role of conductivity in ER performance is testified. FMP measurements of fluids were performed under weak and strong exciting fields respectively. Under weak exciting field, FMP effects are hardly detectable; while under high exciting field, FMP effects become significant which reflect ER particle configurations, particle orientations, and limited dielectric response time in the combined electric and shear fields. The shear field strength, exciting field strength and frequency are the three main factors influencing the FMP effects. The FMP data can be modeled and qualitatively explained by introducing two characteristic shear rates of D_c1 and D_c2, J=J₀+J₁exp(-D/D_c1)+ J₂exp(-D/D_c2) with D being shear rate.

Rheological, electric and dielectric properties of two groups of ER fluids containing zeolite or perovskite particles with different cation compositions are compared. The dielectric behaviour at low field strength and the dependence of shear stress and current density on field strength and temperature in strong electric fields have been investigated. The results show striking differences in the dielectric properties and the temperature dependence of shear stress and current density between the two groups of materials. These differences can be correlated with the crystal structures of the particles and the polarization mechanisms involved. The ER activity in zeolite-based fluids is dominated by the conductivity and attributed to the mobility of the cations. In contrast the ER activity in perovskite-based ER fluids is dominated by the dielectric constant and attributed to the local displacement of ions.

Using three different carbonaceous particles, we investigated the electrical and rheological properties of several ER fluids. Each of the carbonaceous particles, prepared from different treatment methods, possesses a different oxygen content or degree of crystallinity. These materials were prepared from mesophase pitch and were cationically polymerized with naphthalene and HF/BF₃ at high temperature (500~700 °C). Special focus was placed on the variables affecting ER properties, including current density, temperature, electric field strength, and volume fraction of the particles. Rheological properties were measured by a rotational rheometer equipped with a high voltage generator. To investigate the durability of the carbonaceous ER fluids, we also measured changes in shear stress, shear viscosity, and current density at the shear rate of 50 sec^-1 and different temperatures (from 20 to 100°C). Good thermal and electrical stability of the carbonaceous particle-based ER suspensions were observed.

Various ER fluids were prepared based on polyethers such as polypropylene glycol and polytetramethylene glycol. The polyethers were modified with isocyanates to give homogeneous liquids which show a positive or a negative ER effect depending on the molecular structure. The molecular motion of an urea-derivative of the polyether was analyzed with the NMR relaxation method. The modified polyethers were also used as a component of immiscible blends with silicones and suspensions. The immiscible blends showed a positive ER effects even when the polyether showed a negative ER effect. The suspensions tended to show a positive ER effect, which is similar to usual ER suspensions.

Copolyanilines are synthesized by a chemical oxidation of aniline and o-ethoxyaniline with various molar ratios in an acidic media, and then characteristics of these polymers such as chemical structure, particle size and the particle size distribution were examined by using FT-IR, SEM and particle size analyzer, respectively. Suspensions of copolyaniline containing ethoxy group, namely poly(aniline-co-o-ethoxyaniline), in silicone oil have been investigated as one of many potential candidates for dry-base electrorheological (ER) fluid systems. Rotational rheometer (Physica) equipped with a high voltage generator was used to characterize the rheological properties of ER fluids from both steady shear and dynamic tests. From the steady shear experiment, we obtained flow properties and found that ER fluids exhibited the yield phenomenon. On the other hand, viscoelastic property was also obtained from the dynamic experiment. Since viscoelastic properties for ER fluids are mainly dominated by the particle chain structure, the state at different time scale was analyzed from the rheological parameters such as storage modulus (G'), loss modulus (G") and tanδ. We conducted a strain amplitude sweep at 1Hz under an applied electric field to determine a linear viscoelastic region first. The G' and G" were then measured by a frequency sweep from 0.1 to 100 Hz in the linear viscoelastic region.

Polyaniline-Na⁺-montmorillonite nanocomposite particles were synthesized using an emulsion intercalation method, and electrorheological (ER) fluids were produced by dispersing the synthesized nanocomposite particles in an electrically-insulating silicone oil. The emulsion of an aniline monomer with dodecyl benzenesulfonic acid was inserted into the layers of clay, and polymerization was processed by adding the oxidant initiator solution. DBSA as a emulsifier and a dopant took a important role for polyaniline clay nanocomposite. This insertion of polyaniline was confirmed by X-ray diffraction. To observe its ER properties, we measured the shear viscosity and the shear stress by controlling shear rate. Furthermore, we conducted dynamic tests to investigate the viscoelastic properties of the ER fluid under an electric field in the linear viscoelastic region.

ER fluids (ERFs) typically consist of a concentrated dispersion of solid particles in a nonconducting base fluid. As a result, particle sedimentation represents a significant problem for many formulations since, in most cases, the particulate phase is of higher density than the base fluid. To remedy this situation, higher density fluids have been widely used in ERFs (ρ > 1.1 g / cc) rather than less expensive mineral oils that display lower densities (0.8 - 0.9 g / cc). An alternative approach to density "matching" has been explored by Qi and Shaw who have successfully developed ERF particles based on low density, micron-sized hollow glass "balloons" that are polymer coated. These microballons are commercially available from the PQ Corporation and they exhibit an effective density of 0.7 g / cc. Using these materials, it becomes possible to engineer ERF particles that are "neutrally buoyant" in mineral oils by adjusting the coating weight of an ER active polymer on the glass spheres.

In this study, a simple solution coating process was developed exploiting the unique surface chemistry of glass which contains -Si-O-Si- and -Si-OH sites capable of hydrogen bonding with hydrophillic polymers. A number of water-soluble ionic polysaccharides were evaluated as coatings because of their ability to form hydrogen bonds with glass surfaces. A synthetic alcohol-soluble polymer, sulfonated polyphenylene oxide, was also evaluated because of its thermal stability and mechanical durability.

By the classical electrodynamics, the expression of interaction energy and force between two dipoles located arbitrary orientations are derived. Using direct polymerization method, we have prepared the metal/microcapsule-particles. Meanwhile an electrorheological fluid (ERF) made up by these composite particles is prepared. The ER behaviors were investigated by microscope and mechanical test, it is found that the very visible chain's structure of ERF can observe and the induced yield stress increased with the electric field and the particles' volume fraction.

The eletronic band calculations of noble metal halides are studied to make the high ionic conducting origin of silver and cupper ions clear using the tight-binding method. The d bands of Ag ions are much more weakly coupled with the p bands of halogen ions, while those of Cu ions are much more strongly coupled with the p bands. The strength of p-d hybridization is discussed to connect with the activation energy for the ionic conduction. It is shown that the high ionic conductivity of AgX primary stems from combination of the deformability of the d shell and the weakness of the p-d hybridization.

Under static conditions, ER suspensions form columns under electric field. However under the combined stimulii of a shear and electric field, the particles assemble into lamellar structures. The morphology of these structures are complex functions of electric field, shear rate, time of shear, electrode gap, particle concentration, and others. In this paper we present information regarding the field dependence, the concentration dependence, and the sequence of application of the electric and shear fields. A alternative model for ER activity, other than chain breaking, is presented which incorporates this lamellar texture.

It was reported that under the simultaneous stimulus of an electric field and shear, the particles in an ER fluid form lamellar formations in the direction of shear (adhered to one of the electrodes) which may be responsible for the ER activity more than the strength of the chains. In this way, it would be expected that the shear stress should change consistently with the morphology of the formations. In this work we studied the effect of shearing time, electric field strength and shear rate on the shear stress. We suggest that changes on shear stress with time are due to changes of the morphology of the lamellar formations.

We propose an analytical conduction model describing particle-particle interactions for the case of electrorheological fluids based on surface conducting particles. The system consisting of two contacting spheres immersed in a dielectric liquid is modeled by a distributed impedances network, from which we derive analytical expressions for the potential at the spheres surface, for the electric field in the liquid phase, and finally for the interaction force. The theoretical interaction force is compared with experimental results obtained on insulating spheres coated with a thin conducting polyaniline film. A good agreement is found between the theory and experiment.

In this work, the mechanical properties of an anhydrous electrorheological fluid made of carbonaceous particles dispersed in silicone oil were determined in tensile, compression and oscillatory squeeze tests. The mechanical tests were carried out on a Mechanical Testing Machine and the device developed for measuring the ER properties was composed of two parallel steel electrodes between which the ER fluid was placed. The mechanical properties were measured for different DC electric field strengths, velocity and initial gap between the electrodes, and the ERF was tested in two different ways: (a) the fluid was placed between the electrodes (configuration 1) and (b) the electrodes were immersed inside the ERF (configuration 2). The results showed that the ER fluid is more resistant to compression than to tensile, and that the shape of the tensile stress-strain curve and the tensile strength varies with the electric field strength and the initial gap between the electrodes. The compressive stress increased with the increase of the electric field strength and with the decrease of the gap size and upper electrode velocity. In oscillatory tests, for both configurations 1 and 2, increasing the oscillation frequency f and the number of cycles N produced a decrease of the damping performance of the ER fluid. Besides this, the damping force of each cycle in oscillatory tests increased with N. The electric field also played an important role on the shape of the hysteresis loop (stress as a function of fluid strain) for both configurations.

We have examined ER effects in very small parallel and non-parallel gaps utilizing conventional ER suspensions. The flow rate reduction due to the electric field applied is measured as the ER effect for parallel, converging, diverging and combined channels. The test with the parallel channel under AC or rectangular pulse wave electric fields shows that the ER fluids are helpful for the flow rate control even in a narrow gap with the size about 10 times of particle diameter. In comparison between a converging channel and a diverging one, the former has advantages in magnitude and stability of ER effect. Moreover, the converging channel generates larger ER effect than that of the parallel channel with same flow characteristics under no electric field. It is considered that a small area with a higher electric field in the non-parallel channel makes it easy to control the flow rate. Further, the multiplier effect of the converging flow of particles and the increase in electric field along the flow direction generates a larger and stable ER effect. We have also examined with a combined converging and diverging channel and confirmed the similar enhancement in ER effect to the single converging one without the unsymmetrical ER effect due to the flow direction.

The use of computational fluid dynamics (CFD) software for modelling the flow of electro-structured fluids is introduced. A non-Newtonian fluids package written specifically to model Bingham plastics is validated for several flow rates between stationary parallel plates for varying yield stresses, plate separations and lengths. The computing procedure is rationalised in terms of grid fitting of the 'plug' edge. The programme is modified to include an analytical expression which relates delectro-rheological fluid parameters. This approach is then used to predict valve flow rates from small sample, Couette viscometer produced data: its output compares with experimental results.

The two dimensional flow of an electrorheological fluid in a concentric cylinder, Couette type apparatus is investigated at different inter-plate speeds, voltages and axial pressure gradients. Test results at low, but realistic, loading conditions correlate with Bingham plastic computer fluid dynamics (CFD) package predictions, at each field strength. The package had been pre verified against an analytical solution for the same flow field. In all cases the liquid is taken to be isothermal. Indications are that the rate of throughflow should not interfere severely with the voltage set magnitude of torque transmission. Hence the cooling of slipping clutches by through flow can be contemplated. At present the investigation covers only the case of one stationary and one moving plate with no heat transfer or centrifugal terms.

The formation and orientation of field-induced structures in magnetorheological (MR) fluids subject to rotating magnetic fields have been studied using two optical methods: scattering dichroism and small angle light scattering (SALS). The SALS patterns show how these chain-like aggregates follow the magnetic field with the same frequency but with a retarded phase angle for all the frequencies measured. Using scattering dichroism two different behaviors for both, dichroism and phase lag, are found below or above a critical frequency. Experimental results have been reproduced by a simple model considering the torques balance on the chain-like aggregates.

In recent years, it has been found that ER effects can be induced by attaching fabrics on the electrodes. In this paper, the mechanism of this effect is studied in detail. The fluid studied was dimethylsiloxane, which shows no ER effect without the fabric. Velvet fabric was attached on one of the electrodes, and the shear and the normal stresses were measured with various gap distances, shear rates and the field strengths. The results show that ER effect strongly depends on the gap distance but only weakly on the shear rate. A simple model which can explain these results are presented and discussed.

We derived a scaling relation in cluster-cluster aggregations from a modified Smoluchowski's coagulation equation and obtained the relation between the scaling exponents and the control parameter. The power laws in cluster-cluster aggregations derived from the scaling relations agreed with those of ferromagnetic colloidal particles obtained by a numerical calculation.

We present an experimental evidence of a "colloidal motor" behavior of a suspension. Previous attempts to observe such a phenomenon with ferrofluids under alternating magnetic fields have failed. Here, negative viscosity is obtained by making use of Quincke rotation: the spontaneous rotation of insulating particles suspended in a weakly conducting liquid when the system is submitted to a DC electric field. In such a case, particles rotate around any axis perpendicular to the applied field, nevertheless, when a velocity gradient (simple shear rate) is applied along the E field direction, the particles rotation axes will be favored in the vorticity direction (the direction perpendicular to the suspension velocity and the velocity gradient). The collective movement of particles drives the surrounding liquid and then leads to a reduction of the apparent viscosity of the suspension. The decrease in viscosity is sufficiently important for the liquid to flow while no submitted to any mechanical stress.

A theoretical method is developed to calculate the interaction force between coated particles in a host liquid under an electric field. With the nonlinear conduction effect of the oil taken into consideration, the Poisson's equation of the potential φ is transformed into a Laplace's equation. At the same time, the multipolar expansion method is applied to solve the problem. By self-consistent calculation, the conductivity of the host liquid and the local field strength can be obtained simultaneously. On the basis of the model, a single chain structure spanning two parallel electrodes is dealt with. We find that the interaction between neighboring particles is strengthened when a dielectric layer is coated on the surface of the metallic spheres in comparison with that of the dielectric particles, and the interaction force is nearly independent on the dielectric constant of the coating layer except that the layer is a sort of insulator and its dielectric constant is rather small. Further, the interaction force in a dc field varies with the field strength more slowly than a parabola, and approaches a straight line in some cases, even has a maximum.

An equilibrium thermodynamic approach is employed to derive a continuum-level expression for the field-induced stress in uniaxial anisotropic materials, such as electro- and magnetorheological suspensions. This model introduces new electro-and magnetostriction coefficients, which are material parameters that describe the strain dependence of the dielectric and permeability tensors as well as the field-induced stresses. An idealized microscopic model illustrates the relationships between microscopic parameters and the macroscopic magnetostriction coefficients. The model is used to determine the stresses in common applications; predictions from the continuum approach agree with direct calculations of the normal stress and static shear modulus of magnetorheological suspensions.

Halsey and Toor theoretical model (HT) predicts that a thermally induced long-range chain-chain interaction might be responsible for chain-chain lateral aggregation in dipolar fluids. However, this model fails with experiments. To characterize thermally induced chain vibrations, we measured the dynamics of particles in a chain configuration in a very dilute ferrofluid emulsion using Dynamic Light Scattering (DLS). The transverse particle diffusion coefficient at short times is studied as a function of the scattering wave vector, q, and the coupling constant, λ. By varying q, transverse motions of the whole chain can be well separated from transverse motions of the chain components (particles). The results show that the characteristic frequency of particle position fluctuations scales as , where a is the particle radius. This is interpreted using a polymer analogy including Hydrodynamic Interactions (HI) known as Rouse-Zimm model. Since HI are not included in HT model, HI could be responsible for the discrepancy with experiments. When the volume fraction increases, chains gather and DLS is inappropriate to study the system. A more recently developed technique, known as Diffusing Wave Spectroscopy (DWS) is used to obtain the mean square displacement of particle within columns. Since the particle dynamics is closely related to the viscoelastic properties of the system, studying particle dynamics may help us to understand better the rheological properties of MR fluids.

The apparatus to measure interaction forces under an electric field at small distance between a conductive hemisphere and a flat plate has been developed. The surface forces at small distance sandwiched ER fluid dispersing ultrafine smectite particles (20 to 50 nm thickness) in silicone oil has been measured. This fluid shows 0.7kPa of apparent yield stress by applying 2.5kV/mm of DC electric field. When an electric field applies to this ER fluid, the repulsive energy curves shows inflection points at about 0.2 μ m distance periodically at small distance of less than 1 μ m because the repulsion force decreases for a vacancy of particles after the particles are pushed out and the dipole attraction force acts between hemisphere and plate. On the other hand, when the electric field becomes off and it passes enough time, the inflection points is observed more shorter distance of about 0.15 μ m periodically. The coagulated particle size is estimated about 0.15 μ m under no electric field and becomes larger by applying electric field.

An exercise for balancing the heat generated in and the cooling capacity of a digitally operated, clutch based, ER variable motion configuration mechanism is highlighted. Both electrical and mechanical loadings are considered in conjunction with the natural cooling from a rotating cylindrical clutch surface, temperature dependant fluid properties and inertial parameters. The methodology developed applies to both ER and MR type fluids and indicates pointers to the future development of these fluids for high speed machines and vice versa.

A couple of concentric cylinders with "double gap" geometry, of the rheometer Rheotest 2.1 (MLW Werk Medingen GmbH) was modified in order to control the temperature and the applied magnetic field. A sample of the magneto-rheological suspension MRF-132LD (from Lord Corp., USA) was tested under shear flow and magnetic fields of 50, 100, 200, 300, 400 and 500 Gauss. The fluid was tested at 10, 20, 30, 40, 50, and 60°C, ± 1°C. The shear stress (τ) was measured in 24 different shear rates between 2.3 and 2,018 s^-1 . At all temperatures, and for all magnetic field intensities tested, the shear stress is a logarithmic function of the shear rate and the viscosity is shear thinning. With the same applied field, at a given shear rate, the viscosity seems to remain constant between 10 – 60°C.

We carried out Brownian dynamics simulations of a ferromagnetic colloidal system and investigated the particles' motions and the magnetic structures of the system. The particles' pair correlation functions and the magnetic correlation functions are calculated and the formations of chain clusters and magnetic domains are analysed quantitatively. Investigating the magnetic susceptibility, the specific heat of the system, the magnetic moments' ordering and the magnetisation of the system, the cluster and magnetic characteristics of the highly frustrated ferromagnetic system are made clear.

We carried out Brownian dynamics analysis of a ferromagnetic colloidal system which is subjected to both shear flow and external magnetic fields and investigated the magnetic and rheological characteristics. The effects of the strength of magnetic field, particle interactions and shear rate on the magnetisation, the viscosity and the cluster formations are examined and discussed. The cluster structures in the ferromagnetic colloidal system and rheological characteristics of the system in both low and high shear rate regions are made clear.

The cluster structure is visualized and the physical properties of new two types of nano MR fluids are measured in the applied magnetic fields. Correlating to these measurements, the damping characteristics of an oscillating flat plate immersed in two types of nano MR fluids such as damping amplitude, phase difference, viscous damping coefficient and viscous drag force acted on a flat plate are experimentally clarified, comparing with those of commercial magnetic fluid from the fluiddynamic points of view. It is shown that the resonance of damping amplitude and phase difference are very sensitive to the applied magnetic field, and further the damping effect of MR fluid is about ten times stronger than that of the commercial magnetic fluid even in low magnetic fields of 50-100 Gauss due to the robust cluster formation.

When a DC electric field is applied perpendicular to a thin film of ferrofluid constrained between two conducting plates, the ferrofluid separates into phases that are concentrated and dilute in magnetic particles for field strength above a critical value. The phase separation stems from the competition between the electrostatic energy and entropy of the induced dipoles. The entropy around the critical value of the phase separation is continues in our experiment indicating the transition is second order.

The computer simulation method has been used to study the structural formation and transition of electro-magneto-rheological (EMR) fluids under compatible electric and magnetic fields. When the fields are applied simultaneously and perpendicularly to each other, the particles rapidly arrange into two-dimensional close-packed layer structures parallel to both fields. The layers then combine together to form thicker sheet-like structures, which finally relax into three-dimensional close-packed structures with the help of the thermal fluctuations. On the other hand, if the electric field is applied firstly to induce the body-centered tetragonal (BCT) columns in the system, and then the magnetic field is applied in the perpendicular direction, the BCT to face-centered cubic (FCC) structure transition is observed in very short time. Following that, the structure keeps on evolving due to the demagnetization effect and finally form the three-dimensional close-packed structures.

Molecular dynamics simulations were carried out to find the underlying structures of a Magnetorheological (MR) fluid while taking into account dipolar forces, viscous drag, and the Brownian force. Three different structures were found: the bct lattice, chains, and a liquid state. The conditions under which these structures are found is based on two parameters A and B which are the ratios of the dipolar force to the viscous drag force and the Brownian force to the dipolar force respectively.

Blends of immiscible liquids with different dielectric constants and viscosities were known to show the ER effect due to the change of the domain structure by the electric field. In this paper, we report on our attempt to explore the possibility of the magnetic analog of these blend-type ER fluids. Water-based ferrofluid was blended with silicone oil with higher viscosity than the ferrofluid, in order to see whether the negative MR effect can be induced. The domain structure and the viscosity under the magnetic field and shear flow were studied. Growth of the droplet due to coalescence was observed under the field, which resulted in the gradual decrease of the shear viscosity.

In general, immiscible liquid blends form a domain structure; for example, in a binary blend, one component fluid forms droplets, and another forms the matrix. We investigated the change of this domain structure induced by an electric field. The domain structure change depended strongly on the mixing fraction and electric field strength. The resulting viscosity change of the blend was also reported.

The experiemental shear stress versus shear rate curves of MR fluids are analysed with the help iof a chain model. Two critical shear rates are found, one corresponding to the onset of agregate breaking and the other corresponding to the total disappearance of aggregates. Above this second critical shear rate we observe an abrupt jump of stress and the onset of a layered stripe pattern This novel shear induced transition can be observed by using a cone-plate geometry but is usually smeared out in a plate-plate geometry. Still in a plate plate geometry we also have observed a similar phase separation in ER fluids but without a clear rheological signature. We show that this phase separation can be explained by the transition from a nematic like order induced by the field to an isotropic state which is obtained when the shearing hydrodynamic forces on a pair of particles overcome the magnetic or electrostatic forces. The critical shear stress predicted on this basis is in good agreement with the experimental results. We find a similar layered pattern in a rotating magnetic field. The connection between the two situations is explained .

This paper investigates the influence of static and dynamic structures on Rheology in a model magnetorheological fluid. Dynamic structures generated under shear are studied using first a rotational rheometer then an optical image processing system. A microscope allowed us to visualize the different patterns thus generated and compare these results to the measurements obtained with the rheometer. It also enabled us to analyze the various initial static structures formed by an externally applied magnetic field. Besides the well known column-dominated and bent-wall dominated static structures we were able to observe novel, concentric, ring like formations under shear. A dynamic yield stress analysis was conducted for each type of structure along with a statistical approach to further characterize and differentiate the various types of magnetic particle arrangements.

Efficient numerical simulations of microstructure development in magnetorheological (MR) fluids are conducted. The simulations, which are based upon a fast multipole algorithm, treat the magnetic inclusions as two-dimensional continuum magnetic entities. The development of microstructure is quantified by computing and recording the time evolution of the effective permeability of the composite fluid. Such a principle has been previously exploited for the experimental measurements of microstructure development [Jolly, Bender and Mathers, ERMR'97, Yonezawa, Japan 1997]. As was observed experimentally, numerical simulations reveal the evolution of microstructure to be multimodal in nature. Unlike the experiments, the numerical simulations afford us the ability to observe the physical mechanisms associated with various modes.

The dynamics of the structure formation of an electrorheological fluid consisting of either one type of particles or with two types of particles is studied numerically. In the latter case half of the suspension particles have dielectric constants greater and the the other half smaller than that of the base fluid. In such a system the potential energy between interacting particles depends also on the type of the particles such that the direction of the force between different types of particles is complementary to the force between identical particles. The simulation model is based on a dipole model by utilizing an Ewald method for taking long range interactions into account. The dipoles are not fixed but they are allowed to adapt to local surroundings.

We developed a statistical model of the cluster formation of ferromagnetic particles and analysed the cluster structures. We investigated the effect of the control parameter λ, that is, the ratio of magnetic dipole moment energy to thermal energy, and external magnetic fields on the fractal dimensions of three-dimensional ferromagnetic clusters. We found that the fractal dimension of clusters, D, changes from 5/3 to 2 as λ increases in the absence of a magnetic field. We also found that when clusters are subjected to a magnetic field, the fractal dimension decreases and the transition region from high fractal dimension to D = 1 becomes shorter as λ increases.

This paper is concerned with an experimental comparison of the dynamic performance of an Electrorheological and a Magnetorheological fluid when subjected to impulsively applied loads. The ER device was built as a squeeze cell incorporating an ER fluid sandwiched between two electrodes which, during impact, move towards each other, whilst the MR device was a commercially available vibration absorber. Each device was mounted in an experimental rig which was capable of determining the instantaneous responses of the fluids. The transient characteristics of the devices were assessed for various mechanical force levels and, for the ER device, under DC excitation of the fluid in conjunction with a digital controller to provide a constant applied electrical field.

The behavior of an electrorheological (ER) chain under a shear force is investigated theoretically and experimentally. Contrary to the conventional assumption that the ER chain under a shear force becomes slanted and breaks at the middle, we have found that there is symmetry breaking. When the shear strain is small, the chain becomes slanted with a space gap between the first and second particles (or between the last and next last particles). As the shear strain increases, the gap becomes wider and wider. When the shear strain exceeds a critical value, the chain breaks at the gap. The experiment also confirms that an ER chain under the shear breaks at either end, not at the middle. This symmetry breaking reflects the space's anisotropy, which is the result of the applied electric field.

The steady and transient stress responses were investigated from lower shear rates to higher shear rates at a given strength of the electric field, and the individual experimental conditions were reduced to Mason number (M_n). The electro-rheological response was found in the region with higher M_n of the order of 10, and the transient response became faster as the shear rate increased. These results show that the effect of chance of collision among the polarized particles would play an important role even in the region.

The purpose of this paper is to study the characteristics and performance of pine oil and its ester as a base fluid material for electrorheological fluids. Here, all the tested fluids had a relatively low concentration level of between 5-15% of weight to study the electrorheological strength and phenomena for rotary machines as an application for keeping the working fluid in a steady position while the machine is not working.

The objective of this basic study is to give an introduction to the electrorheological fluids based on polyaniline particles and pine oil and to measure their dependencies on changes in the applied external electric field, temperature, shear rate, dynamic viscosity and concentration, and to study the influence of grinding the particles.

By measuring the shear stress of a ferroelectric particle/silicone oil ER fluid varying with the temperature across Tc, the dependence of ER effect on permittivity mismatch is quantitatively obtained. The dielectric property of ferroelectric material behaves a dramatic change at Curie temperature (Tc) either in the dielectric constant and the conductivity. TGS and KNO₃ ferroelectric particles are chosen for studying the dielectric constant and conductivity dependence of the shear stress in ER fluids respectively. The measured results are more reliable, because the conditions, such as size, shape, composition of particles, especially chemical nature of particles and interface property between particles and liquid, all are same. The available theoretical calculations can not well fit our measured results. In order to consider the properties of whole suspensions, the orientation of the particles with spontaneous polarization under an electric filed was studied in advance.

ER fluids of three types, composed of liquid crystalline polymethylsiloxanes (LCSs) differing in the range of polysiloxane chain length and mesogenic group content diluted by polydimethylsiloxanes (DMSs) with or without phenyl groups, were prepared and the ER effect of each was investigated in terms of its temperature dependence and rise time. Type A fluid exhibited an ER effect with a short rise time but a strong temperature dependence. The ER effect of the Type B fluid showed little temperature dependence but a comparatively long rise time. The Type C fluid exhibited a short rise time, comparable to that of Type A, and a temperature independence similar to that of Type B. For all three types, the decay time of the ER effect was long. Investigation of the decay time for the Type A fluid showed that it was affected particularly by shear rate and DMS dilution ratio and also by temperature and DMS viscosity, and indicated that deformation by shear stress was necessary for a return of the fluid to its orignal non-viscous structure.

Particle and electrode surfaces were altered to examine the effects on the electrorheological response of barium titanate/silicone oil suspensions. Unmodified suspensions exhibited nonlinear conduction. The dynamic yield stresses scaled as Eⁿ, where n < 2 at all electric field frequencies, and the current had substantial harmonic content, a hallmark of nonlinear conduction. Modifying the particle surfaces did not affect these nonlinear responses. Casting polymers on the electrode surfaces changed the responses. With polymer coatings, the dynamic yield stresses scaled as Eⁿ, where n ≥ 2 at some frequencies and increased with coating thickness. With coated electrodes, the current harmonic contents were significantly decreased. These results suggest that nonlinear conduction in ER suspensions is associated with charge injection at the electrode/liquid interface.

Homogeneous ER fluid is an ER fluid which consists of a homogeneous fluid only; it is neither a suspension nor a blend of immiscible liquids. Various liquid crystals are typical examples of homogeneous ER fluids. Recently, we have found that urethane-modified polypropylene glycol (UPPG) is one of the very few examples of homogeneous ER fluids which show no liquid crystalline order. In order to clarify the mechanism of the ER effect in this fluid, we have studied, in this paper, electrohydrodynamic flow under shear and electric field.

An experimental investigation is conducted to clarify the hydrodynamic characteristics of ERF with elastic particles of smectite in a two-dimensional parallel duct of various widths. Experimental data on pressure difference to a volumetric flow rate in a supplying D.C. electric field are measured. These data are arranged to obtain the apparent viscosity by using the integral method of rheology. From the data of apparent viscosity, the wall friction coefficient is obtained. The increment of the apparent viscosity caused by the applying electric field is a function of shear rate as well as the electric field strength and the width of the duct. However, the wall friction coefficient is not a function of electric field strength and the width of the parallel duct, but only of shear rate. The yield stress is a function of the width of the parallel duct as well as of electric field strength. The ratio of Non-Newtonian viscosity in the apparent viscosity is varied by the intensity of the shear rate.

We report our experimental results on the electrorheological (ER) characteristics of ER fluids consisting of suspensions of semiconducting polyaniline and copolyaniline particles in silicone oil. Ionic sodium diphenylamine sulfonate and nonionic o-ethoxyaniline were introduced to synthesize copolyanilines, i.e. N-substituted copolyaniline and poly (aniline-co-o-ethoxyaniline), respectively. ER fluids using these particles were compared. ER fluids, which contain the ionic copolymer, showed the highest ER performance among polyaniline and its copolymer systems. This result was interpreted in terms of the conductivities of the particles and their dielectric spectra.

A historical survey is made of the works devoted to physico-mathematical modeling of transfer processes of the ER-fluids whose peculiarities are determined by the regularities in changing the internal structure of a liquid carrier in the presence of an electric field. The difficulties encountered in the statement and complete solution of a system of the Maxwell equations and the motion equation of a fluid with complicated rheology are discussed.

For the first time the hydrodynamic characteristics (flow rate, pressure drop, velocity profile) of an ER-fluid in a channel-condensor of the simplist form, i.e. with a rectangular cross-section are calculated using the most complicated phenomenological equation of state, i.e. having the exponential – law dependence of shear stress on shear rate and applied electric field intensity. The relations obtained can be employed in designing the hydrodynamic systems in a wide range of flow velocities and electric-field intensities.

The electrorheological (ER) behavior of suspensions in silicone oil of phosphoric ester cellulose powder (average particle size : 17.77 μm) was investigated at room temperature with electric fields up to 2.5 kV/mm. For development of anhydrous ER fluids using at wide temperature range, it was sought the effect of activation time of phosphoric ester cellulose particles on the ER activities. Anhydrous ER fluids based on the phosphoric ester cellulose particles made from cellulose particles treating in chemical solution of 2M phosphoric acid and 4M urea and heating at 150°C were measured. After activating the phosphoric ester cellulose anhydrous ER fluids at 120°C, not only analysis of dispersing cellulose particles but also electrorheological characteristics of ER fluids such as dielectric constant, current density, electrical conductivity and rheological properties were studied. Activation time had a large influence to ER properties of anhydrous ER fluids based on phosphoric ester cellulose. As the activation time went by, particle size and number of dispersing particles, electrical properties, dynamic yield stress on electric field, initial apparent viscosity (η₀) and electrorheological effect (τ_A/τ₀) of phosphoric ester cellulose ER fluids increased with increasing activation time at 120°C till activation time over 5 hours.

This paper presents field-dependent Bingham and response characteristics of ER fluid under shear and flow modes. Two different types of electroviscometers are designed and manufactured for the shear mode and flow mode, respectively. An ER fluid consisting of soluble chemical starches (particles) and silicon oil is made and its field–dependent yield stress is experimentally distilled at two different temperatures using the electroviscometers. Time responses of the ER fluid to step electric fields are also evaluated under two operating modes. In addition, a cylindrical ER damper, which is operated under the flow mode, is adopted and its measured damping force is compared with predicted one obtained from Bingham model of the shear and flow mode, respectively.

The electrorheological (ER) behavior of chitosan and chitosan phosphate suspensions in silicone oil was investigated. Chitosan and chitosan phosphate suspensions showed a typical ER response (Bingham flow behavior) upon application of an electric field. However, chitosan phosphate suspension exhibited excellent shear yield stress compared with chitosan suspension. The difference in behavior results from the difference in the conductivity of the chitosan and chitosan phosphate particles due to their degree of the polarizability. The shear stress for chitosan and chitosan phosphate suspensions showed a linear dependence on the volume fraction of particles. The values of structure factor, A_s obtained 1 and 3~4 for chitosan and chitosan phosphate suspensions and it may be due to the formation of single-row chains and multiple chains upon application of the electric field. Throughtout the experimental results, chitosan and chitosan phosphate suspensions were shown to be an ER fluid.

The electric potential in a granular system consisting of spherical inclusions in the presence of an external applied electric field is studied in detail within the framework of the Rayleigh identity. The effects of induced charges on the inclusions are taken into account explicitly. The method, in principle, includes the effects of all multipoles. The method is applied to study the interaction between two inclusions. The standard form of interaction between inclusions widely used in studying ER fluids is recovered as an approximation of our general approach. We then apply the method to a chain of inclusions. Analytic expressions for the electrostatic energy per inclusion and the electric field are obtained for the case in which the chain is parallel to the applied field. Our result reduces to the form used in the literature when appropriate approximation is taken. The method is further extended to study the interaction between chains of inclusions. An approximate expression is obtained for the force between two chains of inclusions. Our approach provides a rigorous framework for determining the interaction between inclusions and chains of inclusions to arbitrary accuracy.

Electrorheology (ER) was studied for 3 fluids consisting of dispersoids having different functional groups and the same alkyl chain (C₁₆H₃₃-X; X= -OH, -COOH, -CN) dispersed in dimethylsilicone oil. Fluids changed from dispersed to homogeneous with increasing operating temperature because dispersoids melted at higher temperatures. Both the ER effect and dielectric properties changed drastically with the change from dispersed to homogeneous. Both their ER effect and Δε′ increased with temperature below their melting points, becoming almost zero above their melting points. The ER effect of –OH was the highest and that of –CN lowest. The ER effect of fluids were largely explained by Δε′ , the difference in dielectric constant ε′ at 10² and 10⁵ Hz.

We made an experimental investigation of the steady characteristics of torque, current density, and response time of ERF on rotational flow of the disk and the concentric cylinder. We used smectite particles suspension ERF and D.C. electric field. We compared the steady shearstress, current density, and the rise and settling time of the concentric cylinder and with those of the rotating disk. Then we clarified the differences. At a larger electric field strength, the shear stress, yield stress, and apparent viscosity to a constant shear rate in the case of the rotating disk are larger than they are in the case of the rotating concentric cylinder. However, at a larger electric field strength, the current density to a constant shear rate in the case of the rotating disk is smaller than it is in the case of the rotating concentric cylinder. Rise time of torque in the case of the rotating disk is faster than it is in the case of the rotating concentric cylinder. However, rise time of current density in the case of the rotating disk is slower than it is in the case of the rotating concentric cylinder at a small electric field strength. On the other hand, the difference of settling time of torque and current density between the rotating disk and the rotating concentric cylinder is changed by the electric field strength and shear rate. The settling time of torque in the case of the rotating disk is faster than it is in the case of the rotating concentric cylinder at a large electric field strength and large shear rate. The settling time of current density in the case of the rotating disk is slower than it is in the case of rotating concentric cylinder at a small electric field strength. Based on these results, the rotating disk has an efficiency of obtained torque to given electric power greater than that of the rotating concentric cylinder.

In this paper, the adjustable double refraction phenomenon of Electrorhological fluids (ERF) was investigated. The measurements have been made of He-Ne laser through suspension of silica and pentaerythrite in silicone oil. When electric field was applied perpendicular to the laser beam, it was found that no light gets through the pair of perpendicular polarizing plate and analyzer plate without electric field. But when ERF is brought to bear electric field, the transmission light intensity increases with the electric field to be rising. For ERF of the same material, the double refraction phenomenon is more obviously to the low concentration. It is thought that the double refraction phenomenon of ERF is due to the fact that the particles link together to form thin chains or thick columns.

Bingham plastic constitutive model has been widely used to predict the post-yield behavior of electro- and magneto-rheological fluids (ER and MR fluids). However, if these fluids experience shear thinning or shear thickening, Bingham plastic model may not be an accurate predictor of behavior, since the post-yield plastic viscosity is assumed to be constant. In a recent study [4,5], it was theoretically and experimentally demonstrated that the Herschel-Bulkley fluid model can be successfully employed when evaluating non-Newtonian post-yield behavior of ER and MR fluids. In this paper, Herschel-Bulkley model is adapted to include a detailed analysis of ER and MR fluid dynamics through pipes and parallel plates. In addition, non-dimensionalized equations are derived. Moreover, simplified explicit expressions for the exact formulation are developed. It is shown that the proposed simplified model to the Herschel-Bulkley steady flow equations for pipes and parallel plates can be used as an accurate design tool while providing a convenient and generalized mathematical form for modeling ER and MR fluid materials.

Electrorheological (ER) and magnetorheological (MR) fluid-based dampers are typically analyzed using Bingham-plastic shear flow analysis under quasi-steady fully developed flow conditions. An alternative perspective, supported by measurements reported in the literature, is to allow for post-yield shear thinning and shear thickening. A Herschel-Bulkley constitutive shear flow relationship is used to account for such post-yield shear thinning or thickening behavior. The objective of this paper is to develop a theoretical method for predicting the force-velocity characteristics of an ER/MR flow mode damper utilizing a Herschel-Bulkley model. Then, analytical damping predictions are compared using the nonlinear Bingham-plastic and nonlinear Herschel-Bulkley analysis models.

A blend of two immiscible liquid forms a domain structure. The domain structure strongly affects the macroscopic properties of the blend. We focused on the domain structure and viscosity change by applying an electric field in a urethane-modified polypropylene glycol (UPPG) and dimethylsiloxane (DMS) immiscible liquid blend. In the case that UPPG forms droplets, the domain structure changed drastically by the electric field application and the resulting viscosity change was observed.

The ER fluids containing sulfonated polymer particles were continuously sheared at increasing and decreasing shear rates using a rotary concentric cylinder rheometer and the hysteresis in the up- and down-flow-curves were analyzed. The ER fluids show hysteresis of shear stress and current density. The up-curve (when shear rate increased) was located below the down-curve (when shear rate decreased). As the electric field increased, the area in the hysteresis curves increased. The hysteresis depended on the electric field strength, the time of the applied electric field, the volume fraction of particles and the water content of the particles. Hysteresis phenomenon was explained, based on the formation of agglomerations of dispersed particles in the ER fluid and on changes of the lamellar formations

This paper presents torque control characteristics of ER(electro-rheological) and MR(magneto-rheological) clutches. As a first step, Bingham properties of ER and MR fluids are experimentally distilled under the shear mode. A nondimensional model of the clutches is established for the reasonable comparison. Two clutches have same principal design parameters such as outer radius of the disc and electrode gap size. Following the manufacturing two clutches on the basis of the nondimensional model, field-dependent torque levels are experimentally evaluated. A PID(proportional-integral-derivative) controller is designed and experimentally realized to achieve desired torque. Both regulating and tracking torque control responses of the two clutches are evaluated and compared. In addition, control durability for torque tracking is undertaken to provide a practical feasibility of the proposed clutches.

A method and a device for measuring a true static yield stress in magnetorheological (MR) fluids are proposed. The data obtained by means of this device are compared with the measured values of the dynamic yield stress for similar compositions as well as with the quantities calculated by the reported models. It is shown that the dynamic yield stress exceeds the static one. The experimental data better agree with Rosensweig's model.

A variety of robust, high-strength, MR fluids and devices that enable the benefits of controllable fluid technology are now commercially available. Commercial, mass-produced devices include rotary brakes for use in exercise equipment, real-time controllable vibration dampers for truck seats and adjustable linear shock absorbers for racing cars. Recently, a new way of using MR fluids in which the fluid is contained in an absorbent matrix has been developed. Such MR fluid sponge devices enable the benefits of controllable MR fluids to be realized in cost sensitive applications. Most of the high-cost components normally associated with a fluid filled device can be eliminated with this approach. Low-cost, controllable MR fluid sponge dampers are particularly appropriate for moderate-force vibration control problems where a high degree of control authority is desired such as a new generation of high-performance, home washing machines now being developed.

This paper presents an experimental study on heat generation and dissipation of controllable magneto-rheological (MR) fluid shock absorbers. Since MR fluid dampers are energy-dissipating devices, the issues of heat generation and dissipation are important. The viscosity of MR fluid is highly sensitive to temperature, therefore, the damping force is a function of temperature. Only limited studies have been performed on heating of electro-rheological (ER) dampers. In this study, experiments are conducted on a variety of MR fluid dampers that have been designed, developed, and tested at the University of Nevada, Reno (UNR) for specific applications. Each unique MR fluid damper is experimentally evaluated for temperature changes that results from various types of sinusoidal input motions. The experimental analysis is used to develop and verify a theoretical analysis. The temperature effect on the damping force is significant.

MR dampers have potential benefits in soft-inplane rotors such as hingeless and bearingless rotors. An experimental performance characterization of MR dampers for the l/6th scale Comanche wind tunnel model rotor has been presented. MR lag dampers were tested with preload with the magnetic field turned on (ON condition) and off (OFF condition). Damping was characterized for single frequency sinusoidal excitation at lag/rev (10 Hz). Dual frequency testing was also carried out at 10 Hz and 15 Hz corresponding to the model rotor lag/rev and RPM respectively. In all of these tests, the force versus displacement hysteresis cycle or energy diagram was measured for the MR dampers. Two non-linear models: 1. A viscoelastic-plastic model and 2. A stiffness-viscosity-elastoslide model have been developed to capture the non-linear behavior of these dampers. The model parameters were identified using single frequency test data from the MR dampers. Model validation for both single and dual frequency data was carried out. Both models accurately capture the non-linear behavior of the damper and can be used in rotorcraft analyses codes.

An MR(Magneto-Rheological) fluids damper is designed and applied to vibration suppression of a 1/4 car model. The damping constant of the MR damper changes according to the input current which is controlled in a semi-active way. Several control algorithms are compared in simulations and experiments. The advantage of the proposed Frequency shaped LQ control is that passenger ride comfort is emphasized in the frequency range of 4 and 8Hz and driving safety is emphasized around the resonance frequency of unsprung mass. When the frequency shaped LQ control is applied, simulations of a typical passenger car show that the passenger comfort improves in the frequency range of 4 and 8 Hz and experiments of a quarter car model show the similar results.

Magnetorheological (MR) and electrorheological (ER) dampers are a promising class of devices for the control of civil engineering structures for earthquake hazard mitigation. ER and MR dampers exhibit both viscous damping and friction damping, where the friction damping level is controlled by an applied electric or magnetic field, respectively. These unique characteristics lend them to be very suitable devices for the semi-active control of such seismically loaded structures. Inspection of the equation of motion for such a system yields a non-dimensional variable, β, which is the ratio of the yield force of the damper to the forcing input (the product of a characteristic mass of the building and the seismic acceleration). During seismic loading, this input force is larger in magnitude than the yield force of most dampers. Therefore, practical values of β are less than one. This value of β is useful because it can be used to scale a damper to a structure for a desired response reduction, and it can be used as a non-dimensional control parameter. It is also shown that for lightly viscous damped structures (like most civil structures), the response reduction is approximately linear with β. Numerical analyses are performed on a three-story model structure for different damper locations. It is shown that placing dampers toward the base of the structure will minimize interstory drift, as well as floor accelerations. Lastly, it is shown that passively controlling structures undergoing seismic accelerations with constant field applied to the damper greatly reduces the seismic response.

The dynamic nonlinear viscoelasticity of an MR fluid in oscillatory slit flow under magnetic flux normal to the flow has been investigated by using a newly developed oscillatory pressure flow type rheometer. The MR fluid consisting of micron-sized magnetically polarizable particles (carbonyl iron) dispersed into a carrier medium (hydrocarbon oil) was evaluated. The dependence of viscoelasticity of the MR fluid on magnetic field strengths, fluid strain amplitudes and fluid oscillation frequencies have been already investigated. Generalized viscoelastic mechanical models of the MR fluid in oscillatory slit flow are very important for analyzing various MR dampers using MR valves. In this work, a nonlinear dynamic viscoelastic mechanical model of the MR fluid in oscillatory slit flow is proposed, based on the data which have already been measured. The proposed viscoelastic mechanical model of an MR fluid is discussed and compared with the experimental results.

An MRC(Magneto-rheological Clutch), a device to transmit torque by shear stress of MR fluids, has the property that its power transmissibility changes quickly in response to control signal. In this study, we consider methods to predict performance of an MRC. Firstly, we expect the performance of an MRC with a simplified mathematical model and secondly, we predict the performance in consideration of the applied magnetic field and viscosity distribution of fluids caused by the field. Between two methods, compared with experimental results, it is shown that numerical methods are closer to the real than the simplified.

Magnetorheological finishing (MRF) is an enabling technology that may produce surface accuracy on the order of 30 nm peak to valley (p-v) and surface micro-roughness less than 10 Å rms. In MRF, mechanical energy for material removal over the portion of the workpiece surface is generated by the magnetically controlled hydrodynamic flow of a magnetorheological polishing fluid. A fundamental advantage of MRP over existing technologies is that the polishing tool does not wear, since the recirculated fluid is continuously monitored and maintained. Polishing debris and heat are continuously removed. The technique requires no dedicated tooling or special setup. A unique attribute of the MRF process is its determinism that is attained through the use of a well-defined material removal function to eliminate known surface error. The efficiency of material removal and the removal process stability are the crucial factors in MRF. In turn, they are primarily dependent on MR polishing fluid stability. It is shown that the joint use of physicochemical and rheological factors along with specially developed methods of the slurry handling, pumping, and in-line monitoring and maintaining provides a level of MR slurry stability that is quite adequate for high precision finishing. Attention is given to methods of MR slurry property measurements.

In order to polish complicated-shaped inner surfaces of molds, a new polishing method with magnetic congelation liquid was invented. Magnetic congelation liquid which is magnetic fluid at high temperature, but it can be solidified by cooling. If abrasives are in the magnetic congelation liquid, the distribution of abrasives in the liquid can be controlled by magnetic field. Therefore we can make special polishing tool which has well arranged abrasives inside after cooling. In order to know the fundamental polishing properties of this new polishing tool, brass plate was polished with this tool. The polishing tool was pressed and rotated against the brass plates in certain polishing time. After plenty of experiments, it was found that this type polishing tool provided enough removal rate and surface roughness. Also it was confirmed that the alignment of abrasives in the polishing tool affected removal rate and surface roughness strongly.

In manufacturing, fixtures are required to locate parts in a correct position to ensure machining accuracy. Especially for machining on irregular-shaped work-pieces and fine parts, flexible fixtures are at demand to reduce non-machining time. The quick phase change and strong yield strength of MR fluids lead us to investigate the possibility to produce MR-fluid-flexible-fixture. The yield strength and pre-yield elastic modulus are the key issues for a flexible fixture. However, a typical MR fluid currently has yield stress about 100 kPa that is not sufficient for flexible fixtures. To overcome the difficulties, we apply pressure to force single chains into thick columns. This produces a structure-enhanced yield stress. MR fluids in this process produce a yield stress of 800 kPa or above under a moderate magnetic field. The three-dimensional load capacity of MR fluids in this process is strong enough to ensure precision manufacturing. In addition, MR-fluid-flexible-fixtures are environmentally friendly and work at room temperature.

Magnetorheological suspension (MRS) dispersing spherical several μ m of iron particles in the low vapor pressure of dimethylpolysiloxane has been prepared. Yield stress has been proportional to square of magnetic field intensity and increases as containing larger volume fraction of iron particles and using solvent that is more viscous. The plastic viscosity increased linearly as a function of volume fraction of iron particles. The burst pressure of MRF seal is related on the dispersed iron particle size. The burst pressure is related on the magnetization curve in the MRS dispersing less than several μ m of iron particles. On the other hand, the surface tension of solvent influences on the burst pressure in the MRS dispersing more than several μ m of iron particles. Also the burst pressure is affected on the seal gap. In the large gap, the burst pressure in stationary condition adds the pressure by the yield stress of MRS. However, in the small gap the burst pressure of rotating condition is almost the same as that of stationary condition because the arranged iron particles can not be reconstructed in a small gap. The larger viscosity of solvent and volume of iron in MRS increases the burst pressure.

This work demonstrates the principle of a novel cancer therapeutic method using magnetic fluids to block the blood supply to a tumor in order to starve it. Plastic tubes are used to simulate the simplest blood network. The sealing effect to the fluid flow is easily achieved at low particle concentrations with strong pressure resistance and reasonable sealing times at low flow rate (Q = 0.078 ml/min). At high flow rate (Q ≥ 0.62 ml/min), oscillations in Pressure and step increases in Weight of the fluid are found.

A haptic device based on an electrorheological fluid has been designed and tested. The device is similar to a joystick which controls the motion of a cursor on a computer screen. In electric fields of different strength the shear stress of the electrorheological fluid is increased accordingly, which is perceived by the user by different resistance forces against the motion of the joystick. Controlled by the software the user can feel if the cursor enters a selected field on the screen. Such haptic devices can be useful in various possible applications like supporting tools for the operation of machines, assisting interfaces for blind persons working with a computer, virtual reality or computer games. The design of the haptic device, its components and the electrorheological fluid used are described.

By employing ER fluids as working fluids in fluid power systems, direct interface can be realized between electric signals and fluid power without the need for mechanical moving parts like spools in control valves. In this paper, first, novel hydraulic actuators with ER fluids and with movable electrodes (METERA: Movable Electrode-Type ER Actuator) are proposed, which are classified into a linear type (L-METERA) and a rotary-type (R-METERA). Secondly, a design method of L-METERA is described and a small sized L-METERA is fabricated, whose size is 40mm×l8mm×16mm. Thirdly, a design method of R-METERA is described and a small sized R-METERA is fabricated, whose size is ɸ67mm×53mm. Principles of METERA are confirmed with the fabricated METERA.

We developed ER actuators with high performance. An ER actuator consists of ER clutch, reduction gear unit and electric motor. The electrodes of the output-shaft side in the developed ER actuators are made of light material such as CFRP, and the moment of inertia of the ER actuators with respect to the output-shaft becomes very small. As a result, the large torque/inertia ratio can be obtained, compared with conventional actuators. When comparing with powder clutches in which the torque/inertia ratio is considered to be extremely high, the torque/inertia ratio of small-size ER actuators is not inferior. Considering the slow response property of powders in powder clutches, it can be stated that ER actuators are devices with extremely high response characteristics. Firstly we discuss the design and structure of ER actuators. Secondly the experimental results are presented. Then, the control experiments are executed. The developed ER actuators are used in order to develop the new force display system which has high-fidelity force-presentation ability.

Most industrial robots are driven through reduction gear units by DC or AC servomotors. The elasticity of the drive systems including these reduction gear units cannot be ignored when the high-speed and precise motion control is required for robots. Due to the elasticity of the drive systems, the vibratory behaviors are caused, and the control performances of robot systems are deteriorated. In this study, we develop a new actuator, which consists of an AC servomotor, a harmonic drive gear and an ER damper. Since the gap between electrodes of the ER damper is 80[μm], only the voltage of 80[V] is needed for the electric field of 1[kV/mm]. And this ER damper consumes little electric power. The actuator is installed to the one-link robot arm. The mathematical model of the robot arm is derived, and the eigenvalues of the robot system are analyzed. The experiments are conducted, and the effectiveness of the actuator is shown.

Since a direct-drive (DD) motor system doesn't have the reduction gear, the structure of the servo system can be simple and stiff. On the other hand, in the DD system, the disturbance torque directly influences the accuracy of the motor control. The high servo gain is effective and important for reducing the influence of the disturbance torque. However, the high servo control often makes the control system unstable or vibratory. Therefore, the servo gain must be lowered for assuring stability, and the influence of the disturbance becomes serious. In this study, the DD motor system using an ER fluid damper is discussed. By applying the ER damper to the DD motor system, it is possible to obtain the mechanical damping and to realize a high servo gain in the motion control. Finally, the effectiveness of the proposed system is confirmed experimentally.

This paper presents the position control of a cylinder system using electro-rheological (ER) valves with application to a seaport cargo handling system. On the basis of the field-dependent yield stress of the ER fluid, cylindrical ER valves are designed and manufactured. The ER valve bridge circuit for the position control of the cylinder is formulated and its governing equation of motion is derived. In order to demonstrate the position controllability, the bridge circuit is applied to a laboratory model of cargo handling system consisting of two principal components: container palette transfer car and platform controlled by ER valve-bridge cylinder. After describing the principle of loading and unloading procedures, a sliding mode controller is designed for the platform which needs to be tracked the position of the cargo ship subjected to time-varying tide and wave motion. The controller is experimentally realized and position control results are presented.

This paper describes the performance estimation of semi-active suspension system using Electro-Rheological fluid-based damper which is continuously variable according to the electric field strength. ER fluid characteristics is formulated by incorporating Bingham-plastic model and a dynamic model of ER damper is achieved. Then the ER damper is applied to the quarter car model. A sky-hook control algorithm is applied to improve the ride quality through computer simulation. And vibration tests are carried out to compare their performance with conventional passive suspension systems.

Double adjustable shock absorbers allow for adjustment of their yield force and post-yield damping. To emulate the performance of a conventional double adjustable shock absorber, an electrorheological (ER) automotive shock absorber was designed and fabricated at the University of Maryland. An applied electric field between two tubular electrodes, located in the piston head, increases the force required for a given piston rod velocity. Two different shaped gaps, between the cylinder electrodes, meet the controllable performance requirements of a double adjustable shock. Concentric electrodes adjust the yield force of the shock absorber and eccentric cylinders allow for control of the post-yield damping. Force measurements from sinusoidal displacement cycles, recorded on a 5HP mechanical dynamometer, validate the performance of the concentric and eccentric cylinders for yield force and post-yield damping adjustments.

As an application of the ERF to a practical device, coaxial twin rotary cylinders, in which the rotation of an inner driving cylinder is transmitted to an outer rotary cylinder through the medium of an ERF, was designed, and the revolution rates of both cylinders were examined. As another application, a simple shock absorber having coaxial cylindrical electrodes without the bypass was designed and the falling time of an inner moving rod was measured.

The quantitative relationship between the applied electric field and the revolution rate and the falling time was obtained experimentally.

This study presents a new type ER suspension with energy generator which does not require external power sources. This is accomplished by converting kinetic energy into electrical energy. In order to do this, a semi-active suspension with an appropriate size of the ER damper is manufactured. A mechanical mechanism which changes the linear motion of the ER damper to the rotary motion is then constructed. This rotary motion is amplified by gears and makes a generator produce electrical energy. The efficiency of energy generation is experimentally evaluated and the field-dependent damping force of the ER damper operated by the generated power is also investigated. Subsequently, the ER suspension system is applied to a quarter car model, and its vibration isolation is experimentally evaluated in frequency domain.

Experiments on a cone-shaped squeeze-film mode ER damper are reported. An analytical model is developed to calculate the damping force as a function of the vibration amplitude, frequency, the yield stress of the ER fluid. Our calculations agree with the experiments very well at small amplitudes. The cone-shaped electrodes make the damper benefit from both shear mode damper and squeeze-film mode damper. The azimuth angle θ of the cone electrodes plays am important role in magnifying the damping coefficient of this new type of ER damper.

This paper proposes a new type of an ER (electro-rheological) engine mount which has a mixed mode as fluid working mode (the combination of shear and flow modes). As a first step, a mixed mode ER engine mount which is applicable to a medium-sized passenger vehicle is designed and manufactured by incorporating Bingham model of the ER fluid. The vibration isolation performance of the ER engine mount with different intensity of electric fields is evaluated in the frequency domain and compared with that of conventional hydraulic type engine mount. Subsequently, a full car system installed with the proposed ER engine mounts is constructed and modeled by considering engine excitation forces. After deriving its governing equations of motion, H_x control algorithm is formulated by taking into account the semi-active actuating condition. The vertical engine displacement and body acceleration are evaluated via hardware-in-the-loop simulation (HILS) at various engine excitation frequencies.

The solids in the particle dispersion type functional fluid have been found to reciprocate between electrode under AC field at low frequencies. This promotes the continued dispersion of the solids. Here, we have tested the positive use of this phenomenon in finishing process and have found that the process is assisted positively or negatively depending on the strength of applied electric field and the pressure applied to the finishing pad. The optimum electric field strength and pressure are 3.5 kV/mm and 24 kPa.

This paper is an extension of the author's papers from the previous ERMR Conference in Yonezawa, Japan 1997, related only to a cylindrical electro-rheological clutch (ERC) without heat transfer.

Input and output of an ERC (cylindrical or radial) are supposed to be connected with an electrodrive and a loading machine (brake) respectively. Driving moment is described by a nonlinear dynamic moment characteristics and loading moment is assumed to be harmonic in time with adjustable mean value, amplitude and frequency. Also friction moments on input and output shafts are taken into account, consisting of a dry and viscous components. Thus the relative angular velocity between ER clutch rotors is not an input parameter (as it used to be) but it emerges from the dynamic state of all complex system in question. This system is called a thermo-electro-rheological aggregate (TERA), because now (on the contrary to previous papers) also heat transfer in ERC via conduction and convection are taken into account. ER fluid is taken as usually as a Bingham plastic, but a gap in ERC is not necessarily narrow. More detailed list of assumptions is presented.

Not only two types of ERC (cylindrical and radial with unified geometry), but also two arrangements of TERA for each type are considered, when outer rotor of ERC (casing) is connected with an electrodrive and inner rotor with a brake and vice versa.

One starts to build up unified model of ERC from the very general Navier-Stokes equations in cylindrical coordinates applied for ERC. Afterwards nonlinear dimensional dynamic model of TERA is completed with equations of drive and motion. The model is of 7th order in time and contains 44 dimensional input parameters (their list is given).

An electro-rheological clutch (ERC) is inserted an investigated in a broader system called a thermo-electro-rheological aggregate (TERA), with an electrodrive (ED) on the input side and a loading machine (brake B) on the output one (Fig. 1). Driving moment is given by a nonlinear dynamic moment characteristic and loading moment is taken as harmonic in time with adjustable mean value, amplitude and frequency. On the input and output shafts also friction moments with dry and viscous friction components are considered. ERC itself can be cylindrical or radial, with a common geometry and a gap (not necessarily narrow) between input and output rotors, filled by an electro-rheological fluid (ERF), Fig. 2, left. Within and out of ERC heat transfer (hTr) via conduction and convection is taken into account Two structural arrangement of TERA with ERC casing, connected either to ED or B, are considered (Fig. 2, right).

One starts from a survey of a dimensional dynamic model of TERA, derived thoroughly in the twin paper of this Proceedings [6]. The model is nonlinear of the 7th order relative to time, with 48 dimensional parameters. This model is further developed and made more precise. Then a nondimensionalization of the model is performed, which reduces the number of nondimensional parameters to 37 (their list is given). Quasi-steady (qs) solution of ERC itself is given and corresponding transferred moments for cylindrical and radial ERC are determined and compared.