International Journal of Modern Physics B

A series of high performance ER fluids newly manufactured in our laboratory are presented. The yield stress of those ER fluids can reach several tens of kPa, 100 kPa and even 200 kPa, respectively. For understanding the high shear stress effect a model is proposed base on the electric field induced molecular bounding effect. The main effective factors in fabricating the high performance ER are discussed.

Considering the importance of large interfacial or surface polarization to strong electrorheological (ER) effect, we developed a high surface area mesoporous doped TiO₂ ER material by using block-copolymer. By comparing the ER experiments between samples with mesopore and without mesopore, we demonstrate a very large enhancement in ER activity of mesoporous ER material and its yield stress is 100 times that of the pure TiO₂ ER material and 5-8 times that of single doped TiO₂ without mesoporous structure. We give a preliminary discussion about the improvement in ER activity based on previous dielectric analysis.

As a novel candidate of electrorheological (ER) material, core/shell composite particles (PAPMMA) of poly(methyl methacrylate) (PMMA) core and polyaniline (PANI) shell were prepared and adopted as a dispersed phase. PAPMMA particles, obtained by a dispersion polymerization method, were spherical and possessed a monodisperse particle size distribution, in which the PANI shell was introduced on the surface of PMMA via an in-situ polymerization of aniline by adding an oxidant in an aqueous acidic solution. Yield stress of the PAPMMA suspensions under an applied electric field was observed to be increased with a particle size. In addition, monodisperse acrylic microspheres with aniline moiety on the surface were prepared by a seeded emulsion method, and then composite particles possessing chemically bonded PANI shell (PA-PGMA) were prepared via an in-situ polymerization of aniline. Their ER characteristics were also examined.

An electrorheological (ER) effect in suspensions of solid particles is related to electric polarization processes within the bulk of grains of the solid phase or/and on their surface. The nature of these processes is governed by dopants, functional groups or structure of the solid particles and the solid-liquid interface. The purpose of our investigations was to find correlations between material properties of the solid phase and the parameters of the ER effect. We focused on the role of electrical conductivity and permittivity of the dispersed phase as well as chemical nature of surface groups. As the solid phase we chose an acrylic copolymer whose properties were modified by pyrolysis in controlled conditions or by doping with a salt, and silicone oil as the liquid matrix. The prepared materials were characterized by physical and chemical methods. The impedance spectroscopy was applied to estimate the electric conductivity and permittivity of the prepared materials. The characterized powders were then dispersed in silicone oil and their flow curves in the presence of electric field were recorded. The values of yield stress of the ER fluids containing pyrolized materials ranged from 40 Pa to 300 Pa at 3kV/mm for 15% w/w concentrations of solids. The ER effect of the ionic material suspensions was strongly influenced by salt concentration in the polymer. It was also found that samples of higher electronic conductivity exhibited higher currents in comparison to other samples but not higher shear stresses. The current densities in the ionic materials suspensions were significantly lower than in the annealed samples. Pyrolized and oxidized polyacrylonitrile samples contained polar functional groups. Some of the samples were chemically treated in order to modify polarity of the functional groups and the influence of this treatment on the ER effect was studied.

ER properties of suspensions of four conjugated polymers - polyaniline, polyphenylene, polythiophene and pyrolysed polyacrylonitrile - in relation to their electric properties and chemical nature were studied. The polymer samples were synthesized and characterized by various methods and flow curves of their mixtures with silicone oil were recorded under electric field. It was found that the ER activity resulted from surface polarization processes due to presence of polar species (polyaniline and pyrolysed polyacrylonitrile) or bulk polarization related to mobile ions (polyphenylene). Polythiophene, despite its conjugation, showed only residual ER effect. The main conclusion is that many conducting (conjugated) polymers exhibit ER activity but the most characteristic and important feature of these materials – the conjugated system of multiple bonds – does not seem to be responsible for that. The electronic conductivity resulting from the conjugation contributes to higher currents which is unfavourable for technical applications. Conjugated polymers are ER active due to the enhanced mobility of ions within the bulk of particles dispersed in a liquid matrix and/or polar groups present on their surface.

Investigation of the electrorheological effect of silicone-oil suspensions of silica particles coated with polyaniline base in a DC electric field revealed that breaking stress, as a criterion the intensity of the electrorheological phenomenon, steeply increased at first with coating thickness. At relatively low polyaniline content (volume fraction ≈ 0.05), it has reached a value several times higher than that with suspension of pure silica. Then they became virtually constant or slightly increased. The frequency spectra of dielectric characteristics of these systems reflect high relaxation times. The results suggest that the interfacial polarization of particles is predominantly controlled by polarizability of their surface layer, and the influence of the thickness is of secondary importance.

We have fabricated several TiO₂ based ER fluids with doping and without designed doping, which exhibit the high yield stress up to more than 100kPa. The titanium oxide nanoparticles were synthesized by using wet chemical method. The ER effect of those materials is dominated by the special additives, such as amide or its ramification, as well as the remained molecules or ions in the sample preparation. It is found that the yield stress is also strongly dependent on the viscosity of the oil. The prepared ER fluids possess other attractive characters, for instance the current density is low and against sedimentation.

A type of calcium titanate (CTO) nanoparticles was synthesized by means of wet chemical method [1] without coating on the particles. The CTO/silicone oil ER fluid exhibits excellent electrorheological properties: high shear stress (~50-100 kPa) under dc electric field, a low current density (less than 2μA/cm2 at 5kV/mm), and long term stability against sedimentation. Although there are not special additives in the ER fluids, it is found from the chemical analysis that a trace of alkyl group, hydroxyl group, carbonyl group and some ions is remained in the particles which may dominate the ER response.

A kind of magnetorheological elastomers based on polyurethane (PU)/silicone rubber (Si-rubber) hybrid is fabricated without applying magnetic fields. The MR effect is improved by optimizing preparation conditions, in particular by adjusting PU/Si-rubber ratio, and improving compatibility between PU and Si-rubber. The influences of the preparation condition and the relationship between the microstructure and MR effect of this kind of magnetorheological elastomers are discussed in detail. The results show that this kind of MR elastomers has better MR effect than that of MR elastomers based on pure Si-rubber or PU matrix with same testing conditions. SEM analysis indicates that the former forms a peculiar interpenetrating microstructure in the presence of PU in the matrix. The maximum increase in shear modulus of this kind of MR elastomers can be up to 0.5MPa when exposed to a magnetic field of about 0.2T.

In this study, a magneto-rheological fluid dispersed by silica-coated iron was developed and its properties such as fluid viscosity (shear stress or shear rate) and abrasion were investigated. The metallic iron coated by silica dispersed in magneto-rheological fluid was prepared by H₂ reducing of precipitated magnetite (Fe₃O₄). Then, the magneto-rheological fluid (MR fluid) for the seal was prepared with silica-coated iron or carbonyl iron (HQ type; diameter of 1.6-1.9 10^-6m) and two solvent oils i.e. silicon oil (SH200cv, 10000cSt) and CVT oil (T-CVTF, automobile transmission oil). It was observed that the MR fluid viscosity of CVT oil with HQ particles is lower in every fluid condition. Furthermore, the surface roughness of polyvinyl plate after abrasion test for MR fluid with silica coated iron and CVT oil as solvent was higher compared to the other types of MR fluids. The results indicated that carbonyl iron (spherical particles) and silica-coated iron particles dispersed in silicon oil are feasible to be used where the low abrasion in mechanics is required.

As an organic/inorganic hybrid possessing advantages from the combination of their own unique properties, conducting polyaniline (PANI)-titanium dioxide (TiO₂) hybrid particles were synthesized by an oxidation polymerization of aniline, and their ER characteristics were examined. Our aim was to study the ER behavior of highly potential ER-active particles using conducting polymer and TiO₂ nanoparticle with relatively high dielectric constant. In addition, we also investigated its ER behavior as a function of particle fraction of TiO₂ under an applied electric field. The result was interpreted in terms of the dielectric relaxation mismatch. The fast relaxation time of PANI/TiO₂ hybrid was considered to enhance electrostatic force over shear force under a hydrodynamic flow, showing its improved ER performance.

Hybrid electrorheological fluids comprising powdered conjugated polymers dispersed in solutions of a liquid crystalline polymer were prepared and studied. FeCl₃ doped poly(p-phenylene) and pyrolised polyacrylonitrile were chosen as the dispersed phase and poly(n-hexyl isocyanate) dissolved in xylene was used as the active liquid matrix. All the component materials were extensively characterized by various methods. Flow curves of the hybrid ER fluids were recorded under electric field and compared with analogous curves obtained for dispersions of the powders in silicone oil and with homogeneous solutions of the LC polymer in xylene. A very significant enhancement of the ER effect in the studied hybrid fluids was observed.

Carbonyl-iron (CI) based magnetorheological (MR) fluid containing submicron-sized additive particles was prepared. The flow behavior at steady and oscillatory shear modes was investigated by comparing flow properties of CI-mineral oil suspensions without an additive via precise control of magnetic field strength. To enhance the dispersion stability and to examine submicron-sized filler effect for the CI suspensions, organically modified montmorillonite (organoclay) was added to the CI suspensions. In addition, with the precision control of magnetic field strength, we examined the novel features of submicron-sized particle filled CI suspensions, especially under weak magnetic field strengths, in steady shear modes; a temporal decrease of steady shear viscosity in sweeping magnetic field strengths was observed.

Semiconducting phosphoric acid doped polyaniline (PANI-H₃PO₄) particles were synthesized by chemical oxidation polymerization, and their chemical structure and particle size were examined via Fourier transform IR spectroscopy (FT-IR) and scanning electron microscopy (SEM), respectively. Electrorheological (ER) fluids were prepared by dispersing the synthesized PANI-H₃PO₄ particles in kerosine, and their steady shear rheological properties under applied electric fields were investigated using a rotational rheometer with a high-voltage generator. The PANI-H₃PO₄ synthesized in this study possesses a typical ER behavior: large increase of shear stress with applied electric field strengths.

We propose a model of surface saturation polarization as the mechanism for the giant electrorheological (GER) effect, recently discovered in suspensions of coated nanoparticles dispersed in silicone oil. On the basis of this model, the distinguishing features of the GER fluid, such as the extremely high value of the static yield stress (exceeding the theoretical upper-bound) and its linear field-dependence, can be explained quantitatively. The current-field relation and the particle size-scaling effect are also addressed. The agreement between theory and experiments is excellent. We give a brief discussion on the role of electrowetting effect in the formation of surface aligned dipole layer(s).

Particle rotation leads to a steady-state which is different from the equilibrium state in the absence of rotational motion. The change of the polarization of the particle due to the rotational motion is called the dynamic electrorheological effect (DER). There are three cases to be considered: rotating particles in a dc field, particle rotation due to a rotating field and spontaneous rotation of particle in dc field (Quincke rotation). In the DER of rotating particles, the particle rotational motion generally reduces the interparticle force between the particles. The effect becomes pronounced when the frequency is on the order of the relaxation rate of the surface charges. In the electrorotation of particles, the mutual interaction between approaching particles will change the electrorotation spectrum significantly. The electrorotation spectrum depends strongly on the medium conductivity as well as the conductivity contrast between the particle and the medium. In the collective behaviors of Quincke rotors, the mutual interactions between the individual rotors lead to the assembly of chain-like structures which make an angle with the applied field. This has an implication of a new class of material.

An alternative explanation of the giant eletrorheological (GER) effect is proposed using the van der Waals interaction which can lead to a yield stress of at least 50 kPa when the gap between two colloid spheres 60 nm in diameter is about 0.1 nm. This effect is in addition to the saturation dipole polarization in. When the electric field is removed, an elastic force would allow the colloid particle system to balance in a new position, which makes a larger gap than the one under the field, and the van der Waals force decreases dramatically. When the Laplace equation and the van der Waals interaction are considered, it is proposed that the gap between the colloidal ER particles would change with the external electric field to match the experimental result of the giant ER effect. An attempt is also shown to understand the size effect, base oil effect and tailing phenomenon of GER effect.

Interactive surface force between each particle in suspension is very important to explain the dispersion and flocculation phenomena in fluid. The new equipment has been developed to measure the interactive surface force of particles, which was calculated by using Derjaguin's formula, in Electro-Rheological (ER) Fluid and Magneto-Rheological (MR) Suspensions/fluids under electric and magnetic fields, respectively. Firstly, the interactive force of particles in ER fluid dispersed by melamine particles under electric fields was measured. Secondly, the interactive force of particles in MR suspensions dispersed by carbonyl iron particles under magnetic field was investigated. Considering the measurement of interactive surface force of ER and MR fluids, they have a original characteristic frequency due to the attractive and repulsive force of particles interactions initiated by the electric, magnetic and compressive force. Moreover, clusters formed according to the size of particles, particles movement model and formation are estimated by the characteristic frequency of ER fluid and MR suspensions under various electrical and magnetic fields. It indicates that these estimation models might be lead to the interaction kinetics of suspended particles in ER/MR under electrical and magnetic fields.

An electrorheological fluids (ERF) are the suspensions consisting of dielectric rigid particles in the viscous (or viscoelastic) media. Based on the three-dimensional well-ordered multi-particle model (the crystal model) we describe rheological properties of ERF. We use the model of cubic body-centered lattice. We also assume that the electric field is orthogonal to the velocity of shear of fluid's layers. The displacement gradients are assumed to be different (from small to finite values). For small deformations in the framework of the approach proposed and under assumptions made it was stated that the ERF can be treated as a viscoelastic body and it is consequently described on the basis of the linear theory of viscoelasticity. We obtain a complex dynamic shear modulus as a function of the electric field strength, volume fraction of filler, electric properties of components of ERF and viscosity of the fluid phase. For finite deformation the relation between stresses and shear rate gradients has also been made. The relation does not keeps whatever phenomenological or arbitrary parameters and takes into account contribution an electrostatic interaction painted by external field dipoles. From other side a bunch of computational experiments by Monte-Carlo approximation to model both the structure and the peculiarities of ERF were made. We use a procedure by Metropolis for canonic NVT ensemble and parallel computational technologies. The structural characteristics, density, energetic parameter and others for system under consideration have been estimated. In order to verify a theoretical predictions we compare both approaches and some experimental data.

Determined were the effects of preparation procedure and electric field frequency f=dc to 10⁵ Hz on the dielectric constants and ER response (shear rate ) of a suspension in silicone oil of 23 wt.% zeolite particles originally containing 19 wt.% H₂O. Heating the oil and the zeolite particles at 110°C both prior to, and following, mixing decreased the conductivity of the suspension more than simply heating the suspension following mixing. The double heating procedure reduced the complex dielectric constant of the particles and the complex mismatch parameter β*. The ER shear stress τ_E was proportional to for the single heating and for the double heating, where is the complex dielectric constant of the silicone oil. The lower exponent corresponds to a higher water content and in turn higher conductivity of the suspension. Erratic ER response occurred for f=10 Hz in tests with , but not in tests with .

The paper presents investigation of dynamic properties of MR fluids by using a rheometer with parallel-plate geometry. The sample is reduced iron powder based MR suspensions. Linear viscoelastic properties of such sample, which can be variably controlled using a magnetic field, are obtained and summarized based on oscillatory tests. Four field-induced regimes, I, II, III, and IV, are found in the system, which are defined by three critical field strengths: B_C1 < B_C2 < B_C3. MR fluids in regime I through IV experience four typical structural convolutions: coexisting of particles and random chains; coexisting of chains and random clusters; coexisting of clusters and chains; stable clusters. Such results are in good accord with experimental results achieved by Liu's group using light scattering techniques.

We have studied magnetic force on sperical magnetic fluid samples with a wide range of concentrations by pendulum method. The results demonstrate good agreement with Kelvin body force and show that other force expressions clearly deviate from experimental data for large sussceptibility values.

An apparatus is developed to study field-induced forces between two spheres. The mutual forces of a couple of identical spheres made of different materials in various media have been measured precisely as the function of inter-spherical spacing, field strength and field frequency. The respective dependences of the forces on inter-spherical spacing, field strength, field frequency and sphere size are obtained. By comparing the measured results with available theoretical calculations we conclude that a further improvement on the theoretical model should be carried out for explaining the most experimental results when the particle nearly contact.

Precise measurement of the attracting force between two spheres inside an electric field indicates that the rotation of one sphere along the axis perpendicular to the electric field reduces the attracting force between them. This reduction becomes smaller as the distance between the two spheres increases. In the limit of infinite rotational speed, the attracting force seems to tend to a non-zero constant.

The electrorheological (ER) and dielectric properties were measured simultaneously on carbon and BaTiO₃ suspensions to investigate the relationships between the ER effect and the dielectric permittivities at high electric field strength. In the carbon suspension, frequency dependence of the ER effect and the 1st order dielectric permittivity shows a relaxation type of spectra, while in the 3rd order dielectric permittivity a resonance type of spectrum due to shear-induced particle rotation is observed. On the other hand, in BaTiO₃ suspension, a resonance type of spectrum is observed in each spectrum of the ER effect, 1st order and 3rd order dielectric permittivities. These resonance spectra are also attributed to the shear-induced particle rotation. From a theoretical analysis, it is indicated that the magnitude of the relaxation time of the interfacial polarization is responsible for the difference in the type of the spectra. It is also suggested that the shear-induced particle rotation would be a general property of the ER suspension since the resonance peak in the 3rd order dielectric permittivity, which is caused by the particle rotation, is observed in most of ER suspensions.

In this paper we analyze efficiency of a magnetorheological (MR) fluid valve consisting of a flow channel placed inside a solenoid. The scope of the optimization is to find a proper geometry and dimensions of the flow channel in order to achieve the highest possible inlet pressure ΔP(H) at a given field strength H. We analyze two types of flow channels: spiral channels with different helix angles and packed beds of spherical and cylindrical particles with different aspect ratios, both nonmagnetic and paramagnetic. For the prediction of the valve discharge characteristics in the presence of the magnetic field of an arbitrary orientation, we have used our recent physical models for MR fluid flows through capillaries and porous media. We show that among spiral channels the most efficient is the one having the minimal helix angle, i.e. the densest winding of the spiral. At H=20 kA/m this channel provides the inlet pressure 9 times the pressure in the absence of the field. Comparing the porous beds, we conclude that those made of superparamagnetic material are always more effective than nonmagnetic beds. The shape of the bed particles has also been found to affect the inlet pressure by affecting porosity and tortuosity of the beds. The most effective bed consists of packed cylinders made of magnetically soft steel and having the length-to-diameter ratio of either 0.5 or 5. At H=20 kA/m these beds give the pressure near 40 times the pressure at zero field and thus show a higher effectiveness compared to spiral channels.

The modeling and vibration properties of rotating electrorheological (ER) sandwich beams are discussed. The proposed beam is composed of three layers with ER fluids sandwiched between two elastic layers. Based on the Hamilton's principle and finite element method (FEM), the equations of motion of ER beam are derived. The effects of different electric fields, rotating speed and thickness ration on the resonant frequencies and modal loss factors are presented. The results of numerical simulation show that the model loss factor of rotating ER beam can be substantially increased when applied an electric field. The ER materials have a significant effect on the vibration suppression of rotating composite beam.

Back scattering of diffusing wave spectroscopy (DWS) method is employed to measure the mean square displacements of the colloidal particles in electrorheological fluid systems right after an electric field is applied and removed. An electrorheological fluid consisting of colloidal particles 30-40 nm in size shows a tailing phenomenon, namely the clusters of the colloidal ER particles do not return to their original state of Brownian motion as soon as the electric filed is removed. The DWS results of above ER fluid shows that the mean square displacement remains small and changes slowly with time right after the electric field is removed. The Van der Waals attractive force between colloidal particles is used to explain this tailing phenomenon.

The oscillatory squeeze flow of electrorheological (ER) fluid between two parallel discal electrode with transitional electric field is studied numerically in this paper. The ER fluid is modeled as Bingham-like fluid with the continuous modification model proposed by Papanastasiou. The numerical solutions based on the Navier-Stokes equations are presented by using the finite volume methods on the deforming grid. The force transmitted across the fluid under dc and ac electric fields are calculated. The effects of the electric field frequency and the phase difference between the ac electric field and mechanical oscillation are studied. The magnitude and the shape of the transmitted forces is shown to be not only a function of the applied voltage and the mechanical frequency but also the phase difference.

In most studies, a bilateral electrode system in which an electrorheological fluid (ERF) is filled between a pair of electrodes has been used for application of the ERF. Some troubles exist in this configuration of the electrodes, for example a short-circuit. We have, therefore, proposed "one-sided pattern electrodes", or "OSPE" that are arranged on the only one-side surface. In order to use efficiently them for any controllable systems, characteristics of the ERF on OSPE should be cleared and a design procedure for it will be needed. In this paper, we proposed a total force calculation method for the one-sided patterned electrode (OSPE) system in which a liquid crystalline polymer (type-A LCP) was used. Experimental results and simulation results are compared on a force transmission system using the OSPE. In the proposed simulation method, we improved a mathematical model of the characteristics of the type-A LCP, "two phased viscosity model". By using this model, we improved the accuracy of a simulation result. These simulation methods will enables to design an optimal electrode pattern.

The description of ER response in a flow field is a key issue in researching control technology of ER fluid. In this paper, an experimental work on controlling flow field in fluid power transmission has been carried out. The results of research show that the control flow field differs from the rotary shearing flow field in an experimental instrument. Besides the ER effect there is a concomitant-effect of ER response called "capture effect" in the field, which is unbeneficial to the control on fluid power transmission.

Suspensions of carbonyl iron powder in oil (CIP/O) have a very promising application on controlled fluids processes, as a very high local viscosity can be produced in the region in which the magnetic field is applied, allowing some control of the flow. In experiments performed in tube viscometers the flow can be completely stopped in some circumstances, such as specific pressure, magnetic field strength and particles concentration. This work presents our initial results of the jet morphology produced at the tip of the tube of a CIP/O, in terms of the applied pressure or of the applied magnetic field. A 3-CCD camera positioned in front of the jet collected "frozen" pictures of the jets produced in different conditions. Morphologic parameters of the jet such as the angle of the cone and the amplitude of the jet oscillation can be measured. Thus, the effect of the magnetic field on the fluid can be visualized and parameterized. It was observed that the perturbation due to the application of the magnetic field on the tip of the tube causes large changes on the jet oscillation. The amplitudes of the oscillations are very sensitive to the parameters described above.

Governing equations of MR fluids using improved Bingham model and considering anisotropic rheological properties in the applied magnetic field are proposed to analyze MR fluids flow in a rectangular channel. It is found that the flow rate decreases linearly with magnetic field intensity, which is remarkable for large anisotropic parameter of shear stress and small aspect ratio of channel cross section in the strong magnetic field intensity and small pressure gradient. The pressure gradient becomes steep in the applied magnetic field region, which results from large viscous drag force caused by increasing yield stress. The pressure distribution shows the same tendency as experimental result.

Reducing the viscosity of liquid suspensions is of great importance in science and engineering. We present a theory and experiments that a suitable electric or magnetic field pulse can effectively reduce the viscosity for several hours with no appreciable change of temperature. Positive experimental results with magnetorheological fluids and crude oil suggest a broad range of practical applications.

Measurement of average interparticle gap in chains of colloidal particles is realized by means of light scattering in silica suspensions or dynamic mechanical analysis in MR elastomers. For a silica volume fraction of 10% we find that the mean distance between particles inside chains drop off sharply with the increase of field; this behavior is attributed to the presence of a long range ionic repulsive force. We show that this experiment allows to obtain information about interparticle forces between colloidal particles. On the other hand the transmitted light is very sensitive to the size of the particles in the chain and to the gap between particles. In an other domain, namely elastomers containing chains of magnetic particles, the magnetostriction is also found to be determined by the interparticle gap.

The focus of this work is to study surface effects on the friction factor a magneto-rheological (MR) fluid flowing through a grooved channel under various magnetic fields and volumetric flow rates. Based on the experimental data, a relation is developed for the friction factor of MR fluid in channel flow in terms of Mason number evaluated at the surface, and the depth of the grooves. Using this relation, the pressure loss of a MR fluid flowing through a channel with grooved walls can be determined without implementing a constitutive model for MR fluids or utilizing the concept of shear yield stress. Several grooves with different configurations in channel walls have been considered. From the experimental results it has been demonstrated that under an applied magnetic field, the grooved surface would increase the friction factor of MR fluid flow significantly when comparing to the surface without grooving. The depth of grooves plays an important role in this increment.

Magnetorheological elastomers' mechanical property is greatly influenced by the microstructure of magnetizable particles embedded in the rubber matrix. When synthesizing magnetorheological elastomers, usually the mixture is cured in the presence of a magnetic field and particles are arranged in chainlike or columnar structure after the crosslink, in order to get remarkable effect controlled by the magnetic field. However curing under the magnetic field will face some problems, e.g. the preparation will become not convenient.

In this paper magnetorheological elastomers are prepared in various volume fractions in the absence of a magnetic field. Their dynamic viscoelastic properties are tested by a system designed by ourselves. Their microstructures are observed by scan electronic microscope. Finally the inherent relation is revealed between the magnetoviscoelasticity and the distribution of particles in the matrix as well as the components of the mixture and the chemical technique. A kind of typical microstructure is found to be relative to the magnetoviscoelasticity of magnetorheological elastomers prepared in the absence of a magnetic field. This study also provides a guide when designing and preparing this kind of smart materials.

Electrorheological (ER) fluids are usually described by the continuous theory, Newtonian model and Bingham model. But during recent years, experiments showed that the mechanical properties of ER fluids were much complex than the traditional definitions. Many-body effect, modeling mechanical properties of ER fluids from particle chains or columns, and other problems are thought to be some key issues in ER effect and for ER mechanism.

When a magnetic field is applied across MR fluids, a yield stress is developed, and their rheological properties can then be categorized into two distinct regimes; pre-yield and post-yield. This paper concerns the viscoelastic behaviour of MR fluids in the pre-yield region. Oscillatory tests were carried out to determine the complex shear modulus properties of MR fluids between the temperature range of -20°C and +50°C. The test results show that the storage modulus and loss modulus increased in value as the excitation frequency was increased from 5Hz to 50Hz. The complex modulus was also found to be influenced by changes in temperature; the higher the temperature, the lower the complex modulus. This is consistent with the behaviour of viscoelastic polymers. The sets of temperature-dependent and frequency-dependent data were subsequently condensed using the method of reduced variables into master curves of complex modulus which effectively extended the frequency coverage of the data at the reference temperature.

This paper presents a new approach for hysteresis modeling of an electro-rheological (ER) fluid. The Preisach model is adopted to describe change of an ER fluid hysteresis with temperature, and its applicability is experimentally proved by examining two significant properties under two dominant temperature conditions. As a first step, the polymethylaniline (PMA)-based ER fluid is made by dispersing the chemically synthesized PMA particles into non-conducting oil. Then, using the Couette type electroviscometer, multiple first order descending (FOD) curves are constructed to consider temperature variations in the model. Subsequently, a nonlinear hysteresis model of the ER fluid is formulated between input (electric field) and output (yield stress). A compensation strategy is also formulated in a discrete manner through the Preisach model inversion to attain desired shear stress of the ER fluid. In order to demonstrate the effectiveness of the identified hysteresis model and the tracking performance of the control strategy, the field-dependent hysteresis loop and tracking error responses are experimentally evaluated in time domain and compared with responses obtained from Bingham model.

Magnetorheological suspensions (MRS) based on mixtures of two commercial carbonyl iron powders (BASF grades CL and SU) as magnetic phase and hydrocarbon oil as liquid phase were prepared. CL and SU are both soft magnetic powders, but CL is a coarse powder, while SU is a fine one. The total mass fraction of iron was 80% w/w each formulation. Hydrophilic fumed silica (5% w/w of Aerosil^® 200) was used to reduce the settling. The mixing ratios were: CL 0%, CL 20%, CL 40%, CL 60%, CL 80% and CL 100%. A MRS, the mixture CL 80%, showed considerable reduction of the plastic viscosity without field, in the range of 100 – 500 s^-1, when compared to the MRS with just one powder. The yield stress values under applied field H ~ 340 kA/m were: 18.1 kPa for the MRS CL 0%, 18.3 kPa for the MRS's CL 20% and CL 40%, 20.0 kPa for the MRS CL 60%, 22.3 kPa for the MRS CL 80% and 23.3 kPa for the MRS CL 100%, respectively. For comparison, a sample of commercial MRF-132LD (Lord Corp.) in the same conditions showed yield value of 21.2 ± 0.6 kPa. On the other hand, another MRS, CL 60%, showed an increment of ~ 33% on the normal force, with relation to the MRS prepared with just CL or just SU powders, above 150 kA/m. Therefore, mixing carbonyl iron powders with different particle sizes can improve the performance of MRS, decreasing the 'off' plastic viscosity, and increasing the MR effect.

Electra-rheological fluids (ERFs) are composed of a functional fluid and colloidal suspension. Their rheological properties vary rapidly and reversibly with the applied electric field intensity. ERFs are mixtures of nonconductive silicone oil and inorganic/organic composite electro-rheological particles. Investigations into the properties of ERFs have led to remarkable advances in their performance in recent years. However, ERFs exhibit an undesirable property that obstructs the long-term use of ERF devices, namely the sedimentation and separation of ER particles from the silicone oil. The sedimentation of ER particles reduces the electro-rheological effect. In order to suppress the sedimentation and thereby improve the performance of ERF devices, a new functional material called Gel Structured ERF (ERG) is developed and its basic properties are analyzed in this study. The ER particles are sustained in the gel component, and thus will not precipitate out. This suppresses the decrease in ER effect associated with precipitation. The developed ERG shows large shear stress variation in response to the applied electric field. This high performance of ERGs involves a different mechanism than that observed in ERFs. In order to elucidate the mechanism in ERGs, the behavior of ER particles was observed under an electric field. Conditions at the interface between the electrode and ERG were found to change rapidly in response to the applied electric field, resulting in the variation of shear force.

A circular pipe electrode was developed to control the pressure and the flow rate of the ER(Electro-rheological) fluids by one of the authors. The shape of the electrode is a circular pipe and some parts of the inner surface of the pipe are the electrode. The diameter of the tube is 1mm and the four pairs of the electrode are used. In the present study a liquid crystal mixture is selected for a homogeneous ER fluid and the pressure drop of the circular pipe electrode is measured for the constant flow rates under application of the voltages. The voltages are added in the peripheral direction. The director which is the average direction of the molecular of the liquid crystal is perpendicular to the flow direction. On the other hands, numerical analysis of the electric fields and the flow in the circular pipe electrode is conducted and the relations between the flow rate and the pressure are obtained for various electric field intensities, which almost agree with experimental results. The emphasized point of the present flow analysis is assuming that the viscosity of a liquid crystal mixture distributes in the flow field. Furthermore the pulse-wave voltages are added to the electrodes to control the pressure drop using the pulse width modulation. It is found that the pressure can be controlled using the pulse width modulation in the some range of the parameters.

A new magneto-rheology device (MRD) was constructed, which can be used in combination with a Physica MCR roational rheometer form Anton Paar. The MRD is build around a parallel-plate measuring geometry. Maximum magnetic flux densities of up to 1 Tesla in the air gap between the two plates are possible. The distribution of the magnetic flux density in the measuring gap has been evaluated with the help of a three-dimensional Hall sensor. The MRD system allows simultaneous software controlled setting of the magnetic field strength and the use of all possible rheological test modes of the rheometer. In the past mostly flow curves based on purely rotational measurements have been used to investigate the rheological behavior of MRFs giving only limited information. A measuring method is introduced, which is based on oscillatory measurements and thus allowing an exact determination of a substance's visco-elastic properties as a function of the magnetic field strength. In addition to structure investigations at various magnetic field strength with standard oscillatory strains sweeps an oscillation measurement with constant amplitude and constant frequency was performed while changing the magnetic field strength in a logarithmic ramp (magneto-sweep). On a typical MRF significant transition points are observed which distinguish different regions. These transitions can directly be correlated to corresponding changes in the material's structure resulting from the increase in the magnetic flux density.

The effect of a uniform magnetic field on the elastic and viscous properties of new magnetocontrolled materials (magnetoelastics) was studied. It was found that the application of a magnetic field leads to a considerable rise both in Young's modulus and in the viscosity of these materials. We investigated the samples prepared both in the absence of magnetic field and in the magnetic field applied during magnetoelastic curing.

Experiments were performed to examine the influence of external homogeneous magnetic field on ferrofluid convection in thin cylindrical layer heated from one wide sidewall and cooled from another. Gravitational and magnetic mechanisms of convection as well as the influence of gravitational sedimentation of particles and their aggregates on stability and structure of fluid flows are studied. The integral and local temperature sensors were used for measurement of heat transport across the layer. Visualization of flow patterns was provided by a temperature-sensitive liquid crystal sheet. The results indicate that with the help of a magnetic field it is possible to control the stability and the form of convection motions. Besides, the concentration gradients of solid phase can have material role to convection instability and heat transfer.

The effects of substitution of micron size powder by nanometer size powder in magnetorheological (MR) fluids are investigated in this study. Three MR fluid samples containing iron powder with 45% weight fraction in a carrier fluid were made by Materials Modification Inc. The difference among these three fluids is size of the magnetic particles. The first MR fluid sample contained only micron size iron powder with 10μm particle size. In the second sample, 5% micron iron was substituted with nano powders having 30~40nm mean diameter, while the third sample had 37.5% micron powder and 7.5% nano powder. Rheological tests were conducted on the three samples using a parallel disk rheometer. Highest yield stress was observed in the second MR fluid sample containing 40% micron and 5% nano iron powder. By replacing only 5% micron iron powder with nanoparticles, we achieved substantial increment in yield stress. However, when nano powder content is increased to 7.5%, the yield stress decreases and is lower than that in the all micron MR fluid. Thus, by doping a reasonable percent of nano iron powder in the MR fluid, a substantial change in the rheological characteristics is obtainable. Further investigations of effects of nano iron powder in MR fluids for higher weight fraction MR fluids will be carried out in future.

MR suspension systems have significant non-linearity and time-delay characteristics. For this reason, linear feedback control of an MR suspension has limited vibration control performance. To address this problem, a four DOF half car suspension model with two MR dampers was adopted. Having analyzed non-linearity and time-delay of the MR suspension, a Human-Simulation Intelligent Control (HSIC) law with three levels was designed. Simulation verified effects of HSIC in solving the problem of non-linearity and time-delay of MR dampers. In comparison, simulation of linear-quadratic gaussian (LQG) without considering the non-linearity and time-delay of MR suspension is also made. The simulation results show that the HSIC controller is faster than LQG controller under bump input and has better stability and accuracy, and it can achieve smaller acceleration peak value and root mean square (RMS) and better ride comfort compared with LQG controller under random input.

Experimentally the filling of a single capillary-condenser in the transverse to the gradient of electrical field current was studied. ERF on the basis of polymethyloxane fluids or mineral oil that consist of activated particles of SiO₂ with the weight concentration 5-30% were observed. The dependence of position of meniscus, its crookedness and the height of near-wall layer on the tension of electrical influence and time were measured. The variants of usage of homogeneous and gradient on the axis of the capillary electrical fields were studied. In the experiments consolidation of the middle area of meniscus and lengthening of its near-wall area and also the change of the speed of its filling while the intensity of electrical influence increased was found.

The objective of this work is to characterize the performance of MR fluid at high shear rates and high velocities. A slit-flow rheometer has been built which allows for high speed testing of MR fluid under varying field strengths. Fluid velocities range from 3.9 m/s to 27 m/s with resulting shear rates ranging from 0.23×10⁵s^-1 to 1.6×10⁵s^-1. In order to evaluate the performance of the fluid, the force required to drive the fluid through the slit is measured and force-velocity characteristics are generated. The zero-field viscosity is found and results indicate that shear thinning is still present even at these high shear rates. Two magnetic field strengths were considered for the field testing (50 kA/m and 100 kA/m). Results indicate that a yield stress is still being developed in the fluid. However, as fluid velocity increases, the yield stress being developed in the fluid decreases. This reduction in the yield stress could be attributed to the dwell time, or the amount of time the fluid spends in the presence of a magnetic field.

The influence of the type and concentration of activator (substance used to provide sensitivity of ferromagnetic particles to electric field) on the electrorheological (ER), magnetoelectrorheological (MER) and dielectric properties of MERFs have been investigated. Non-colloidal particles of -iron oxide or magnetite are used as a dispersed phase. An organic acid activator and two types of amine-based activators have been studied. MERFs with amine-based activators exhibit stronger ER effect. It has been found that the minima in the dependencies of dielectric constant on the activator concentration are strongly correlated with maxima in the correspondent dependencies of MER and ER effects.

By means of the combination of mechanochemical method and sol-gel technique the modified kaolinite/titanium oxide composite was prepared. The structure analyses XRD, EDS showed that composite was consisted of the mechanochemically activated kaolinite/NaCl complex coating with titanium oxide. A distinct enhancement in the electrorheological effect under DC electric field was found by using such particles dispersed in silicone oil. The shear stresses of modified kaolinite/titanium oxide suspension were about 9.5 kPa at 4kV/mm, which are 11.5 times of that of pure kaolinite ERF and 2.2 times of that of kaolinite/TiO₂ ERF reported previous respectively.

Magnetorheological suspensions with different particle sizes including bimodal particle size distributions have been rheologically investigated. The results show a continuous decrease in the base viscosity without magnetic field when increasing the ratio of coarse to fine particles, which is in accordance with the observed trend of sedimentation stability of the samples. However, measurements of the shear stress with a rising magnetic flux density demonstrate higher values for MR suspensions with special mixtures of coarse and fine particles indicating a strengthening of the particle interactions in the magnetic field. The change of the viscoelastic properties of the MR suspensions in dependence on the field strength and shear load (amplitude) have been studied with oscillatory experiments. As expected, at low field strengths, the viscous behavior dominates and, at high field strengths, the elastic behavior, but differences in the crossover field strengths between the two regimes occur for the different particle size distributions. The shear load variation also shows differences between the various MR suspensions indicating the highest yield stress for the sample with only fine particles without magnetic field, but the lowest yield stress at moderate field strengths.

Coated-PAn particles consisting of polyaniline(PAn) core and barium titanate (BaTiO₃) shell were synthesized by modified sol-gel processing. The shear stress and current density of the suspensions of Coated-PAn particles and pure PAn particles in silicone oil with a 20vol% were investigated at different conductivity and environment temperature. The dielectric and the conductance behavior of coated PAn particles as a function of temperature we also investigated. The results showed that the ER effect of BaTiO₃ coated PAn particles was far stronger than that of pure polyaniline synthesized by the same method. Meanwhile, the BaTiO₃ coated-PAn particles also showed favorable temperature stability and low current loss at the high electric field, which is rather important for the ER fluids application.

The heat convection, which can be provided from a magneto-rheological (MR) fluid, is a useful process in converting heat from high to low temperature and vice versa. In this work, the property and preparation of liquid gallium-based MR fluid is presented. The prepared MR fluid disperses micron-sized iron or nicked metal powders in liquid gallium (Ga). In this experiment, supercooling of MR fluid was investigated in order to obtain the condition under which the liquid state can be kept below the melting point. Moreover, the viscosity and elasticity of the prepared MR liquid were measured as a function of magnetic flux density. Finally, it was demonstrated that liquid Ga is a useful base for preparing a new type MR fluid.

In the present study, we sysnthesize two types of MR fluids with different particle shapes and sizes. The magnetic functions are evaluated circulatingly by the analysis of cluster formation, rheological properties in the applied magnetic field and damping characteristics in the MR damper, comparing with those of commercial MR fluids. Final objective is to provide the fundamental data for the development of newly advanced MR fluids. The main topics consist of geographycal cluster formation depending on particle shapes and sizes, relating to the apparent viscosity and yield stress with magnetic flux density and further equivalent damping coefficient of two newly sysnthesised MR fluids comparing with those of LORD MR fluid.

Varying the electric field strength (E), the ER effect, the dielectric permittivity, and the electrical conductivity were simultaneously measured on the Ba_0.75Sr_0.25TiO₃ suspension. It was found that at high E the ER effect increased with the frequency (f), while at low E it once decreased and then increased with increase in f. At high E, the dielectric permittivity at low frequencies was much larger than that at high frequencies, indicating that an electrode polarization was formed as a result of accumulations of ions, which were dissociated from the liquid at high E, near the electrodes. This electrode polarization was further confirmed in the time dependence of the electrical conductivity after the electric field was switched on. From these results it is suggested that the E-dependent frequency dependence of the ER effect may be due to the electrode polarization, which causes larger shielding of the applied electric field at lower f while smaller shielding at higher f.

The aqueous ER elastomers, containing crude organic starch particles which dispersed in gelatin/glycerin/water matrix, were prepared with or without the applied DC electric field. The responses of the composite systems to the electric field were tested by the compression modulus and resistance of the elastomers. The result shows that they are enhanced and controlled evidently under an applied DC electric field. The strongest responses appear at 25% weight fraction of starch. In addition, the increment modulus of the elastomer increases with the strength of the applied field within 0.5~1.5 kV/mm, while after the field is stronger than 1.5 kV/mm it doesn't increase with field, appearing "saturation".

By using a modified conduction model and the dipole approximation model respectively, we simulate the stress-strain curve and evaluate the dynamic yield stress through an ideal microstructure model of electrorheological fluid. The static yield strain is larger in our modified conduction model than in the dipole approximation model. Besides, the dynamic yield stress and static yield stress nearly linearly vary as volume fraction in the dipole model, while in our modified model they both exhibit a maximum at about volume fraction ϕ=0.45. Interpretation about these results is associated with the conduction effect and the inter-chain interactions.

Magnetorheological (MR) fluids are now well established as one of the leading materials for use in controllable structures and systems. Commercial application of MR fluids, particularly in the automotive industry, has grown rapidly over the past few years. Today, MR fluid devices can be found in tens of thousands of vehicles. Experience in developing commercially successful MR fluids and devices has led to the creation of a series of figures-of-merit, design guidelines and empirical equations for describing MR fluids. Such experience-based guidelines have proven to be invaluable tools in all phases of MR fluid device development from initial concept feasibility to production engineering. These tools are easily integrated into design spreadsheets that enable the simultaneous optimization of MR fluid, device geometry, device size, device materials and electromagnet parameters.

The feasibility of utilizing a composite magnetorheological fluid plus elastomeric (MRFE) damper is assessed. To emulate the loading conditions for a helicopter lag damper, the MRFE damper emulation was subjected to single frequency (lag/rev) and dual frequency (lag/rev and 1/rev) sinusoidal loading, and equivalent viscous damping was used to compare the MRFE damping characteristics with a conventional elastomeric damper. The preliminary MRFE damper showed nonlinear behavior: damping was reduced as displacement amplitude increased. Upon application of a magnetic field, the damping level was controlled according to a specific damping objective as a function of the excitation amplitude. Under dual frequency conditions, damping degradation at lag frequency due to 1/rev motion was also mitigated by magnetic field input to the MR damper.

This paper presents the development of an interactive MR (Magneto-Rheological) fluid experiment. The hands-on experiment is developed to introduce MR fluids to students who are interested in this smart fluid. This apparatus is also used as a teaching tool for courses in smart materials. The experiment is designed to show students the basic operations of MR fluids and some common applications. This interactive experiment includes three devices with associated control buttons and all the devices are housed in a clear display case for easy visualization. 1) MR fluid morphing device, which clearly shows the morphing of MR material between fluid and semi-solid with the control of the electromagnet. 2) MR brake, which allow a user clearly feel the change of resistance level of the crank shaft with increasing of current to the electromagnets. 3) Vibration damping using MR fluid damper, which shows that the vibration of a platform induced by a rotating motor with an imbalanced mass can be suppressed by a simple MR fluid damper. This interactive experiment is fully autonomous and has been used in University of Houston. It has been demonstrated that it is an effective tool to assist student to learn MR fluids.

Force display systems are a kind of robot systems, which share the space with people while they are working, and which directly touch and display force-senses to their users. For such a robot system, it is important to estimate safety quantitatively and to assure mechanically safety. The safety can be assured by using MR actuator because MR actuator is one of clutch type actuators. And, the features of MR actuator are very preferable to those of ER actuator and other clutch type actuators, to improve the performance of force display systems. In this study, we developed an MR actuator with low inertia, high torque/inertia ratio and high responsibility. Then, a 2-D force display system using the MR actuator was developed. The characteristics of the MR actuator that are low inertia, high torque/inertia ratio and high responsibility contribute to improve the performance of force display systems.

In this paper, a preliminary design procedure of magnetorheological (MR) dampers is developed for controlling building response induced by seismic excitation. Hysteretic biviscous model which is simple and can describe the hysteretic characteristics of MR damper, is used for parametric studies. The capacity of MR damper is determined as a portion of not the building weight but the lateral restoring force. A method is proposed for the optimal placement and number of MR dampers, and its effectiveness is verified by comparing it with the simplified sequential search algorithm. Numerical results indicate that capacity, number and placement can be reasonably determined using the proposed design procedure.

In this paper, we suggest the new intelligent fluid applying MR fluid, and new base-isolation system using that new intelligent fluid. At first, new intelligent fluid suggested in this paper as MSF (Magnet Solidification Fluid) consist of some magnetic fluid and special particles. The most remarkable characteristic of the MSF is that this fluid gives stable and optional yield sharing stress by gathering the properties of containing materials.

By the way, in the region where the earthquake often occurs, buildings and industrial equipments must be provided for earthquakes. Then, fuse property is considered as the most anticipative idea for base-isolation system at present. That is, base-isolation system holds an upper structure by stable holding force at usual condition or slight earthquake. On the other hand, when a severe earthquake occurs, it releases holding force and insulates transfer of excitation force of earthquake at the isolation layer of system by yielding relative displacement between ground and an upper structure. According to such idea, we developed new base-isolation system utilizing characteristic of MSF.

The response time of a rotor system supported upon a disk-type magnetorheological fluid damper operating on shear mode is measured experimentally. The effects of rotating speed, step current and magnetic particle volume fraction, on the response time are dealt with. It is shown that the dynamic response can be described by first 10% response time and rapid response time. Generally, the first 10% response time and the rapid response time are in order of less than 0.1 second and 0.1~0.4 second. The magnetic field strength, magnetic particle volume fraction and power supply have a great effect on the response time. The response time in dropping step current is several times longer than that in applying step current. There is a zero initial delay time at either applying or dropping the current, which is caused by the magnetizing or de-magnetizing process.

MR (Magneto-Rheological) dampers have turned out to be a promising device for improving the ride comfort of ground vehicles. However, the current control algorithms for MR dampers, including on-off control and clipped-optimal control, are not sufficiently effective. This paper presents a fuzzy control strategy for an MR damper in order to determine the input voltage according to the desired restoring force. It then goes on using this new strategy to reduce the suspension vibration of a full-vehicle model equipped with 4 MR dampers, where the desired restoring forces are determined through the optimal control of suspension system. The numerical simulations indicate that the optimal fuzzy control can effectively reduce the suspension vibration of the full-vehicle model, especially the pitch angular acceleration and the roll angular acceleration of the sprung mass, and offers better ride comfort, running safety and handling stability than the clipped-optimal control. The design of the fuzzy controller is independent of the control system. Furthermore, fuzzy controller can also be extended to other applications of MR dampers, together with other control strategies.

This paper is concerned with the development of a damper with excellent characteristics. The vibration characteristics of the damper element composed of two annular permanent magnets and magnetic fluid are studied experimentally using a vibration testing system. The vibration amplitude of the upper magnet-magnetic fluid system is measured with an optical displacement detector system. It was found that the element of two annular permanent magnets adsorbed magnetic fluid is very effective over the wide frequency range.

In order to capture MR lag damper behavior accurately in the context of helicopter rotor dynamic analyses, a physically motivated rate-dependent elasto-slide model was developed based on the Bingham plastic model. This time-domain model uses a rate-dependent slide and a parallel viscous damper to simulate the yield behavior of the MR fluid and uses a stiff spring in series with the slide to represent the preyield stiffness. A method of determination of the model parameters was introduced using MR damper single frequency hysteresis data. The fidelity of the model was justified by the good correlation between modeling results and experimental steady-state data over a wide amplitude and moderate frequency range. Significantly, the rate-dependent elasto-slide model is applicable in predicting response under single and dual frequency loading conditions encountered by an MR lag damper.

During launching, a payload is submitted to large vibrations, which may damage it. To get rid of the problem, a solution would be to put an appropriate vibration isolator at the payload/launcher interface. Thus, a soft Isolating Payload Attach Fitting (IPAF) using Magneto-Rheological (MR) dampers is envisaged. In a pre-design phase for the launcher application, a preliminary study of the behaviour of a commercial MR damper (RD-1005-3) and its use in a 1-dof vibration isolator is carried out. In this paper, we report the MR damper behaviour analysis based on fluid and solid mechanics equations. In particular, we investigate chambers fluid compressibility and inertia effects. Then the damper model is used to evaluate the performance of a MR isolator in terms of equivalent transmissibility in passive mode and using skyhook control. The theoretical results will be soon compared to those from an experimental bench in construction.

Numerical dynamic simulation of a full vehicle incorporating a magneto-rheological damper in the primary suspension is studied using the package ADAMS and SIMULINK. The full vehicle model is built under ADAMS. The interaction between the tire and the road profile is simulated using the ADAMS/TIRE capabilities. The UA tire model is used to model the dynamic characteristics of the tires. A 3-D road profile model is built based on the spatial power spectrum density of a random road profile. In order to model the dynamic characteristics of the primary suspension MR damper, a non-parametric model of an MR damper is proposed which can conveniently be incorporated into the vehicle dynamic model. Two kinds of control policies, a common skyhook and the so-called non-jerk skyhook, are adopted to control the current applied to the MR damper. The simulation results imply that either one of the two skyhook control policies can obtain a good compromise between so-called "soft damping" and "hard damping", and non-jerk skyhook control policy can curb some higher frequency components which are observed in the acceleration response of the chassis. This study demonstrates that virtual prototype technology is an effective approach for investigating the dynamic behavior of MR dampers for complex systems.

Magnetorheological (MR) based semi-active dampers for the protection of sensitive devices against high shock and impact is examined from design considerations to characterization testing. Shock and impact dampers should be able to produce a high damping force at high velocities. However, a specification requiring high damping force generally causes an increase in the size of shock and impact dampers, which motivates the study of MR dampers to retrofit existing or conventional passive shock and impact dampers. A novel MR damper design was developed in this study for achieving both design goals: high force and compactness. The novel MR damper design increases the number of magnetically active volumes through which fluid to passes while minimizing damper length. Through FEM (Finite Element Method) analysis, the magnetic properties of the proposed design are investigated prior to actual fabrication. In addition to the unique magnetic circuit, other considerations stemming from the high pressures and velocities expected in this device are addressed. Characterization testing was performed up to 12 Hz with 1 inch sinusoidal stroke on a servo-hydraulic testing machine. These tests demonstrate that the MR damper is able to provide a high damping force at high velocity.

In this work, three different magneto-rheological(MR) dampers, which are applicable for vibration control of a multi-story structure, are devised and their performance characteristics are compared. As a first step, the schematic configurations of the shear, flow, and mixed mode MR dampers are described with design constraints. The analytical models to predict the field-dependent damping forces are derived for each type and their damping forces are evaluated. The field-dependent damping forces are compared in terms of the damping force magnitude and the mixed-mode type of MR damper is chosen as an optimal candidate for the vibration control of the multi-story structure. An appropriate size of the mixed mode MR damper is manufactured and its field-dependent damping characteristics are evaluated in time domain. In addition, the displacement vs. damping force cycles of the piston are observed at various field intensities.

According to Bingham rheological model, the paper describes the technique of hydraulic power transmission based on the Magnetorheological fluid (MRF). As we all know, the MRF is an intelligent material, and it is used as the medium by which the power and signal can pass. Therefore, utilizing rheological behavior of MRF, the rheological state and viscosity of MRF can be directly modulated by electromagnetism field to control the speed, move direction and pressure of hydraulic system. We can gain an intermediate drive -control mode, which possesses many advantages such as: super stability, accurate precision, fine reliability, cheap cost and quick response and so on. It can overcome a series of disadvantages of the traditional hydraulic power transmission system. In addition, the paper introduces the operation principle of MRF power transmission, and researches the working performance and the fundamental factors that affect the properties of MRF by modeling and simulation. Finally, the paper explores theory and method of optimum design for MRF power transmission.

The magnetic droplet should be held in position against the flow of the blood for the magnetic drug targeting. In the present research, as the basis of this problem three types of experiments were conducted. In the first and the second experiments, a two-dimensional and a three-dimensional droplet are placed on the inclined flat plate and are supported by the magnetic force against the gravity. The maximum inclination for the droplet to flow down is measured. In the third experiment, a two-dimensional droplet is placed on the floor of the channel and is held in position by the magnetic force against the flow of the water. The droplet itself can be held at the position of the magnet, but, as the flow is faster, the spikes on the droplet move downstream with the water flow as if they rotate around the droplet.

Approximate analytical expressions describing MR/ER damper performance for an axisymmetric annular duct under the assumption of uniform field are presented. The key performance metric is the damping coefficient, which is the ratio of the equivalent viscous damping constant, C_eq, to the Newtonian viscous damping constant, C. To develop these approximations, a quadratic equation was used to approximate the center of the plug location in the annular duct. This equation simplified the calculation of the annular duct solution without resorting to numerical methods to solve the boundary value problem. Approximations for the damping coefficient are developed on this basis.

This paper addresses nondimensional analysis of a magnetorheological (MR) dashpot damper. An MR dashpot damper consists of a loosely fitting piston within a hydraulic cylinder or reservoir of MR fluids. The fluid flow within such a damper presents both Poiseuille (flow mode or pressurized flow through the duct) and Couette (shear mode or shear flow due to relative motion between piston and hydraulic cylinder wall) simultaneously. Thus, an MR dashpot damper, which mixes both shear and flow modes of behavior, is called a mixed mode damper. In this study, a quasi-steady analysis of MR dashpot dampers was revisited based on the utilization of the Bingham-plastic constitutive model to assess performance metrics such as damping capacity. For the mixed mode MR damper, key physical quantities are derived: fluid velocity profile, shear stress profile, and damping coefficient. In addition, the plug thickness equation to characterize the relationship between the Bingham number and the plug thickness is constructed. Through computer simulation, damping characteristics of the mixed mode MR dashpot damper are evaluated and compared to the flow mode case.

New training methods and exercises for upper limbs rehabilitation are made possible by application of robotics and virtual reality technology. The technologies can also make quantitative evaluations and enhance the qualitative effect of training. We have joined a project managed by NEDO (New Energy and Industrial Technology Development Organization as a semi–governmental organization under the Ministry of Economy, Trade and Industry of Japan) 5-year Project, "Rehabilitation System for the Upper Limbs and Lower Limbs", and developed a 3–DOF exercise machine for upper limbs (EMUL) using ER actuators. In this paper, we also present the development of software for motion exercise trainings and some results of clinical evaluation. Moreover, it is discussed how ER actuators ensure the mechanical safety.

A basic experiment for the gap flow in a closed piston - cylinder system of ER fluid was carried out with regard to engineering application to dampers. The purpose of this study is to gain system characteristics and to elucidate flow behaviors of ER fluid in the piston–cylinder system; the model damper. Pressure, which is the system characteristic, was examined in the present study. The test fluid was a smectite ER fluid in silicone oil base of the 3wt% particle dispersion concentration. In the apparatus the piston moves in the vertical direction at a given speed. Theoretical formula of pressure difference is considered by the one-dimensional analysis of the ER flow in the gap of cylinder. It was shown that the response of the pressure was retarded with strong electric field. In comparison with the theoretical estimation and experimental value, the theoretical pressure difference was in good agreement with experimental data. For a sake of giving an insight to flow phenomena, visualization was also achieved using model Newtonian fluid in the piston-cylinder system, and shown that vorticity generated at the rear corner of the piston plays an important role for the pressure characteristic.

A feasibility investigation into modelling ER/MR devices in transient operation using CFD is summarised. This particular study is one part of a project which has previously included examining 1D and 2D steady state flow, heat transfer, and field distributions using CFD. Though developed piecewise, these various CFD approaches can be integrated to allow a full pre-prototype assessment programme for almost any device conceived, in any mode or sequence of operation. Solutions which include translating boundary motion and inertial boundaries are introduced. In order to verify the CFD results, some new experimental works were carried out on a hydrodynamic bearing and clutch apparatus.

This work presents a design and analysis program for vehicle devices utilizing an electrorheological (ER) fluid. The program is operated in graphic user interface (GUI) environment and the initial window is consisted of four subprogram modules which are related to ER shock absorber, ER seat damper, ER engine mount, and ER anti-lock brake system (ABS), respectively. In order to execute each module, both material properties and design parameters are to be chosen by the user. Then, the output display window shows the field-dependent performance characteristics to be considered as design criteria. In addition, control performances of the vehicle system equipped with ER devices are displayed in time and frequency domain. In order to demonstrate the effectiveness of the proposed program, ER shock absorber and ER ABS are designed and manufactured and their performance characteristics are evaluated.

The data of previous researchers on the structure formation of electro sensitive suspensions under the action of an external electric field and on the resulting changes in the mechanical parameters of the fluid (viscosity, plasticity, elasticity) were used to develop a method of damping in a special clutches, which were used for fixing complicated shape construction (blade), that surfaces are to undergo fine turning. As demonstrated, the use of a fluid, the structure of which responds to an electric field as a clutching layer, improves the technological characteristics of the product and increase its reliability.

The concept and some steps in the development of a new actuator system which enables the haptic perception of mechanically inhomogeneous virtual objects are introduced. The system consists of a two-dimensional planar array of actuator elements containing an electrorheological (ER) fluid. When a user presses his fingers onto the surface of the actuator array, he perceives locally variable resistance forces generated by vertical pistons which slide in the ER fluid through the gaps between electrode pairs. The voltage in each actuator element can be individually controlled by a novel sophisticated switching technology based on optoelectric gallium arsenide elements. The haptic information which is represented at the actuator array can be transferred from a corresponding sensor system based on ultrasonic elastography. The combined sensor-actuator system may serve as a technology platform for various applications in virtual reality, like telemedicine where the information on the consistency of tissue of a real patient is detected by the sensor part and recorded by the actuator part at a remote location.

In this paper, the problem of Electrorheological(ER) technology's application in the vibration isolation system is empirically studied. Based on the particular characteristics of the Electrorheological Fluids (ERF) tunable damping, a metal-spring ER isolator was designed and its working principle is mainly discussed. By theoretical analysis of its simplified physical model, the dynamic response of an ER isolator is frequency- and amplitude- dependent and sensitive to structural parameters. The controllable parameters here can be the system equivalent spring stiffness K and damping coefficient C of ERF. With experiment, the exertion of ER effect was controlled through the change of K and C. Consequently, the system dynamic stiffness, which is used to describe the dynamic properties of system isolation performance, can be changed obviously. According to the dynamic performance tests, the result confirmed that applying different electric field strength could change the dynamic peculiarity of the metal-spring ER isolator. The configuration design of the ER equipment, such as stiffness ratio of two fluid chambers and the size of the electric field, which are important factors for the tunable range of ER isolator.

Passive type systems are essentially safe, and expected that the system generating large force can be developed easily. We had developed ER fluid brakes and a 2-DOF (degrees of freedom) passive type force display system using ER brakes, and had made a presentation on it at ERMR2001. In this paper, we introduced progress of our study from ERMR2001.

Rolling element linear guide systems are widely used in the industrial machines such as machine tools for the advantages of high-precision, high-rigidity and low-friction. However, the principal disadvantage of such systems is their inferior damping characteristics, which cause the degradation of working efficiency and quality in certain circumstances, especially where vibration is to be expected. To meet the demands of increasing speed together with higher precision, a rolling element linear guide system with electrically controllable additional damping element (ER damper) is developed in this study. Liquid crystalline polymer, a sort of homogeneous ER fluid, is used because this fluid is thought be suitable for industrial positioning systems for the characteristics of high out-put, nearly-linearity, no sedimentation and no particle-crushing. Some basic experiments were carried out and the good characteristics were ascertained.

Some recent work has involved the incorporation of solids into soft matrices in order to acquire an improvement in their mechanical and damping performances [R. S. Lakes et al, Nature, Vol. 410, 565-567]. Other more general analytical works have dealt with the application of electrical and magnetic fields to susceptible materials, usually involving a relatively hard fluid filled sandwich. In the present note the effect of soaking soft porous solids in magneto or electro-rheological fluids (MRF or EFG respectively) on their stiffness is announced. In this case the pores or cells of the carrier soft solid hold polarisable solids. When the resulting composites are excited by a magnetic (MRF) or electric field (ERF) the stiffness of the sections thus produced are increased (in a passive sense) under loading. Unique results are obtained when auxetic MR soft soaked foams are excited – significant magnetostrictive effects are measured.

In most of robotic systems in industrial applications, vibratory problems occur at high-speed motion, because of elasticity of drive systems like reduction gear units and mechanical structures. Also friction and backlash in the drive systems cause serious problems. On the other hand, since direct-drive (DD) motor systems do not use reduction gears, those are effective for high-speed and high-precision control. In DD motor systems, however, low damping ratio, or large time delays of computers and amplifiers causes another type of problem at precise positioning phase. In this study, a particle type ER fluid damper was introduced to a DD motor system to compensate damping ratio mechanically. Because controlling viscosity of ER damper according to status of motion did not disturb advantage of the DD system that can move fast, the performance of the DD system was improved. The effectiveness of the proposed system was confirmed experimentally. The method of our study can contribute to expansion of usability of ER fluid dampers on industrial applications not limited to DD systems.

This work concentrates on the development of an uncommon type of electrodes to be used in electrorheological devices. Rather than using electrodes with constant gap, pin electrodes are used, in order to achieve variation in the gap. The device described has pins running across the direction of the flow. The ER fluid moves through rows and columns of pin electrodes of different polarities. One of the main problems would be the development of the head pressure drop as the number of rows of pins increases. The work presents different configurations that could be constructed using pin electrodes. One of the configurations is developed and tested as to the pressure gradients that could be achieved when different magnitudes of electric potentials are applied. The results are compared to the ones obtained when two of the constructed modules are aligned one after the other for the tests.

A key function of engine mount of vehicle systems is to support engine mass and isolate noise and vibration from engine disturbance forces. One of attractive candidates to achieve this goal is to utilize a semi-active ER engine mount. By applying this, we can effectively control damping force and hence the noise and vibration by just controlling the intensity of electric field. However, control performance of the engine mount may be very sensitive to temperature variation during engine operation. In this work, we investigate dynamic and control performances of ER engine mount with respect to the temperature variation. In order to undertake this, a flow-mode type of ER engine mount is designed and manufactured. Displacement transmissibility is experimentally evaluated for 1 degree of freedom. The ER engine mount is then incorporated with full-vehicle model in order to investigate vibration control performance. After formulating the governing equation of motion, a semi-active controller is designed. The controller is implemented through a hardware-in-the-loop simulation (HILS), and control responses such as acceleration level at various engine speeds are evaluated in the frequency and time domains.

ER slurry, which is composed of an ER fluid and abrasive grains, is available for efficient polishing or finishing. In this study, we propose a final process with the ER slurry and one-sided patterned electrodes. Characteristics of the ER slurry were investigated. And, ER polishing, which is a polishing using the ER slurry, was carried out. Results showed that the impression of the electric field can accelerate the polishing.

This paper presents robust control performances of a semi-active electro-rheological (ER) seat suspension incorporating vibration model of human-body. A cylindrical type of ER seat damper is manufactured for a commercial vehicle seat suspension system and its field-dependent damping force is experimentally evaluated. A human-body model is then derived and integrated with the governing equations of the ER seat suspension system. The integrated seat-driver model featured by a high order degree-of-freedom (DOF) is reduced through a balanced model reduction to design robust controller. By imposing semi-active actuating conditions, a sliding mode controller which is very robust to external disturbances and parameter uncertainties is synthesized and experimentally realized with the state observer. In the experimental configuration, a driver directly sits on the controlled seat. Control results for ride quality considering response of each human body segment are evaluated in both time and frequency domains. In addition, a comparison of the proposed semi-active ER seat suspension to a conventional passive seat suspension system is undertaken.

In this work, an electrically controllable anti-lock brake system (ABS) for passenger vehicle is developed by utilizing electrorheological (ER) fluid. A pressure modulator which consists of a cylindrical ER valve and the hydraulic booster is constructed in order to achieve sufficient brake pressure variation during ABS operation. The principal design parameters of the modulator are determined by considering ER properties as well as required braking pressure. After investigating pressure controllability of the modulator, a vehicle model which is integrated with the proposed pressure modulator is formulated to design yaw rate controller. A sliding mode controller is designed to obtain desired yaw rate, and the friction forces between roads and wheels are estimated via the estimator. Braking performances of the proposed ABS under various roads are evaluated through the hardware-in-the-loop-simulation (HILS) and the steering stability during braking operation is demonstrated by undertaking split-μ test.

The work presented in this paper bears on the feasibility and the operative technology of embedding electro-rheological (ER) fluids into cement mortar. We have made a cantilever mortar beam with controllable ER fluids filled in a central crack for the purpose of investigation on the evolutional rule of frequencies under different electric field strength by hammering test. The experimental results indicated that the influence of electric field strength upon the first frequency is more evident than that upon the second one, whereas that upon the third frequency is very little. In addition, the physical mechanism of the impact of the change of voltage on the frequency of smart beam structures embedded with ER fluids was discussed. This research sets up an experimental basis for the application of ER fluids in the domain of structural vibration control.

The better mechanical properties of Electrorheological fluid (ERF) are critical for its engineering application. In this paper, the effects of electric field strength and circumstance temperature on steady flow characteristic of ERF are analyzed; the effects of electric field strength, vibration amplitude, vibration frequency and circumstance temperature on ERF's dynamic mechanical properties are investigated using orthogonal tests. In addition, the ERF damper of lathe tool slide worked on shear-mode is developed; the turning experiments with the damper are performed in order to validate the suppressive effect of vibration. The experimental results demonstrate that ERF dampers can decrease the machining vibration response effectively.