Electro-Rheological Fluids and Magneto-Rheological Suspensions

The following sections are included:

• PREFACE

• In Memory of Dr. Frank E. Filisko

• CONTENTS

Recently, we developed a theory and new technology, which utilizes a pulsed electric field to change the rheology of complex fluid to reduce its viscosity, while keeping the temperature unchanged. The method is energy-efficient, universal, and applicable to all complex fluids with suspended particles in nano-meters, sub-micrometers, or micrometers. We have applied this technology to crude oil and refinery fuels. While the applications are still developing, the results are very impressive, indicating that electrorheology can play a very important role in energy production, transportation, and conservation.

This study addresses the nondimensional analysis of adaptive magnetorheological energy absorbers (MREAs) for drop-induced shock mitigation. The governing equation of motion of a single degree of freedom system with an MREA was derived. The Bingham number was defined and its effect on the system response was examined. A comprehensive nondimensional analysis was conducted using nondimensional stroke, velocity and acceleration, where Bingham number and time constant were key parameters. An optimal Bingham number-based on drop velocity, payload mass, and passive damping-minimized the drop-induced shock loads transmitted to the payload by utilizing maximum damper stroke.

Novel concepts for the magnetic circuit in magnetorheological dampers have been proven. In contrast to the known magnetic circuits where the magnetic field for the control of the magnetorheological fluid is generated by the coil of an electromagnet, hybrid magnetic circuits consisting of at least one permanent or hard magnet and an electromagnet are used in the new approaches. Three different technical configurations are distinguished: 1. The electromagnet is combined with two permanent magnets, whose magnetization cannot be modified even by strong magnetic fields of the electromagnet. The main advantage is the improved fail-safe behaviour of the damper in case of a power failure. 2. The electromagnet is combined with a hard magnet, whose magnetization can be modified by the electromagnet. This configuration leads to high energy efficiency, because electric power is only required in short pulses for the switching of the hard magnet. 3. All three types of magnetic field sources, permanent, hard and electromagnet are combined in the magnetic circuit, which gives the highest flexibility of the magnetic field generation and the damping control at the expense of a relatively large effort. Demonstrators for magnetorheological dampers with all three magnetic circuits were constructed and their performances were tested. The results of the investigations are described in this paper.

A new concept of material removal based on the principle of conservation of momentum is applied to analyze Magnetorheological Finishing (MRF^®) and Magnetorheological Jet (MR Jet^®) processes widely used in precision optics fabrication. According to this concept, a load for surface indentation by abrasive particles is provided at their interaction near the wall with heavier basic particles, which fluctuate (due to collision) in the shear flow of concentrated binary suspension. The model is in good qualitative agreement with experimental results.

Electrorheological (ER) suspensions, which behaves like a Bingham fluid having yield stress, is believed to be capable of applying to various mechanical systems since it can be rapidly change in reversible manner by applying electric field. In this research, a Braille display system driven by micro-diaphragm ER actuators which can be driven by relatively low supply pressure is developed. Since the diaphragm actuator uses a polyurethane film of 0.02 mm thickness and very low stiffness, it can be driven by about 240 kPa supply pressure. By using the actuator, experiments for displaying six tactile pins and step response of pin's height are performed.

A system to simulate crude oil flow in pipeline is established in our lab. The system measures the crude oil flow rate with or without the electric field treatment. With this system, it is demonstrated that the crude oil flow rate is increased by about 20% after a n electric field of 12000V/cm is applied in the direction parallel to the flow direction. The electric energy for this electric field treatment is very small and oil temperature is almost unchanged. The electrorheology induced thinning effect will have significant application in crude oil pipeline transportation.

Improving engine efficiency and reducing pollutant emissions are extremely important. Here we report our finding, using electrorheology to reduce the viscosity of diesel fuel. Diesel is made of many different molecules, 75% small molecules and 25% large molecules. In addition, it contains other nanoscale particles, such as sulfur. Therefore, diesel can be regarded as a liquid suspension. Under a strong electric field, the large molecules aggregate into small clusters, yielding a lower viscosity. This viscosity reduction leads to finer mist in fuel atomization, improving the combustion and engine efficiency.

E85 is an alternative fuel with 85% ethanol and 15% gasoline. However, it is widely reported that E85 vehicles have difficulties to start in winter and have poor performance. Here we report that with proper application of electrorheology, we can solve these issues. E85 vehicles all have port injected engines. The fuel is injected into cylinders as droplets. Before the ignition, the fuel evaporates. Because E85 is more viscous than gasoline, the injected E85 droplet size is not small. Especially, in winter the cold weather makes the viscosity even higher, leading the E85 droplets even bigger. Since evaporation starts from the droplet surfaces, large droplets are difficult to be evaporated before the ignition comes. When there are no enough fuel vapors, the engine cannot start. To solve this problem, we introduce a small device just before the fuel injection, which produces a strong electric field to reduce the fuel viscosity, leading to much smaller fuel droplets in atomization. The evaporation is much faster and the engine is easier to start. As the small fuel droplets produced by our device make the combustion fast and timely, engine efficiency and performance are also expected to be improved.

Recent advances in robotics have resulted in robots working in close proximity with humans. As a consequence, safety issues are becoming increasingly important, for example when a collision unexpectedly occurs between a robot and a person. To address such a scenario, a 3-DOF soft manipulator has been developed that incorporates an electrorheological (ER) clutch and a pneumatic sensor. The pneumatic sensor is used to decrease the impact force, while the ER clutch also decreases the collision force by making the robotic joint flexible during a collision. In this study, we aim to further improve the safety during collisions between a robot and a person by controlling the electric field applied to the ER clutch after a collision. We add energy dissipation to the robot arm by increasing the friction in the ER clutch. Moreover, we examine recoil of a robot arm just after a collision by reversing a motor. In this paper, we report on several reversal experiments conducted on a 1-link arm that does not undergo collision, and we investigate the energy dissipation effect that can be generated by an 45ER clutch.

This paper is concerning to a small pump for liquid crystal, which is called liquid crystal pump in the present paper. The mechanism of the induced flow of liquid crystal by application of electric fields on the liquid crystal is used to generate the rotational flow in the present pump. Liquid crystal pump has a channel to change rotational flow into one way flow from inlet to outlet of the pump. Rotational electric fields are used in the present study. The rotational electric fields are generated by circle-electrode structure fabricated on planar surface, which are applied three-phase alternating currents. Using integrated electrode plate, connection of pumps with plate type is easier than cylindrical one. The pressure-flow rate characteristics of the pump were measured. In addition the relation between non-dimensional flow rate and pressure of the pump were obtained. In order to obtain a high pressure and high flow rate, various shapes of electrode and channel were investigated and the measured results were compared each other. Besides connecting pumps with integrated circle electrode plate were designed to get the required pressure and flow rate.

Electro-rheological gel (ER gel) exhibits various adhesive characteristics according to the applied electric field. This characteristic is called the electro-adhesive effect (EA effect). The results of a recent study reveal that the EA effect also occurs in a vacuum. Therefore, it is expected that ER gel can be applied to a chucking or damping device in a vacuum process. However, the characteristics of ER gel in a vacuum have not been sufficiently clarified. The purpose of this study is to experimentally analyze the characteristic of ER gel in a vacuum. The performance of an ERG fixture element used for a silicon wafer in a vacuum is evaluated through shearing tests. The experimental results indicate that the ER gel demonstrates satisfactory performance in a vacuum. Moreover, the outgas released from the ER gel in a vacuum is evaluated, and the influence of the degassing time on the outgas is investigated.

Nowadays, due to the widespread use of rehabilitation and virtual reality technology, tactile display systems have attracted the attention of researchers from the medical and amusement fields. A clutch mechanism that employs ER and MR fluids is appropriate for force transmission in a tactile display device, because the ER and MR effects are passive and safe for the operator, as compared with an active actuator using motor. The developed ER gel (ERG) produces approximately twenty times higher shear forces than ER fluid and exhibit stable performance. In this research, an ERG multiple-disk clutch is fabricated and applied to a tactile display system. The experimental results of the control test indicate that the tactile display system with the proposed control method can exhibit the "sense of touch" of various viscous fluids.

Electro-rheological (ER) gel is a relatively new type of functional material that has been developed. ER gel has a shear stress characteristic on the surface, which increases according to the applied electric field. Introducing the gel into the interface elements of a force transmission system facilitates the realization of functional clutches and brakes. This study aims to develop a linear actuator which is safe, can operate in reverse and can generate a large force using such a functional clutch. Applying an ER gel clutch in a force transmission system results in a decrease of inertia and the mechanical limits of the maximum speed not obstructing high controllability. This contributes to high safety. This paper reports, in particular, on stabilizing the output of the linear actuator.

An experimental device of rotary damper with one corrugated disc and another plate disc has been examined. The narrow gap between two discs is filled with electrorheological fluid (ERF) (or magnetorheological (MR) Liquid,); so electro-structural effect has to be taken into consideration. Computational fluid dynamics (CFD, FLUENT software) is the method used to produce comparative performance data between two types of dampers. Theoretical and numerical studies have been shown that the total output torque increment for corrugated disc rotary damper is significant larger than those of the dual-disc rotary damper at ignoring the impact of electric field strength. The research results help for optima design of a pre prototyping procedure with ER (or MR) fluid damper.

The anti-lock brake system (ABS) based on the conventional solenoid valve and hydraulic brakes in car agencies existed shiver during the breaking processing. Brake friction block and brake disc friction led to a sharp temperature rising and resulted in some brake lag phenomenon. In this paper, it has been proposed and developed an auto ABS brake based on electrorheological (ER) effect. The result shows that brake effect based on ER is superior to solenoid valve and hydraulic brake, and also it can be achieved an automobile anti-lock braking processing by adjusting voltage.

The actuation behavior of soft silicone-based magnetorheological eleastomers (MRE) in magnetic fields of variable strength was investigated. An inhomogeneous magnetic field gives rise to a reversible actuation effect, which is the result of the competition between magnetic and elastic forces in the material. MRE are capable to perform more sophisticated deformations than known rigid actuator materials. In this connection, the actuation behavior of MRE ring-shaped bodies in a valve-type device for the control of an air flow is demonstrated. For this purpose, MRE rings with different hardness were prepared and used in the valve. Additionally, the actuation of anisotropic MRE was compared with that of isotropic samples. The inhomogeneity of the magnetic field at the MRE material which is required for the actuation could be strongly influenced by the shape of the magnetic yoke. In the study, the closing characteristics of the valve with different yoke shapes and MRE materials were evaluated by measuring the dependence of the air flow rate on the magnetic field strength. It is demonstrated that the air flow through the valve can be controlled by the current in the field-generating coil, which yields the base for a new type of magnetic valves.

HYSCOM knee joint with stance and swing motion control system utilizing a developed compact MR fluid brake has been developed, and the details of the knee design and control system and results of its field walking test on some individual TF amputees are reported.

In this paper, developments of a MR mount for vibration attenuation are presented. First, an MR mount was designed, and analysis of the magnetic circuits by using the magneto V64 software was conducted, followed by calculating the corresponding magnetic flux density and the magnetorheological fluid yield shear stress. Then, this MR mount was manufactured and filled with MR fluid (MRF-122EG made by Lord Ltd), and a single degree of freedom system with the MR mount is set up for vibration validation. Utilizing various controllers like the skyhook, PID and self-tuning fuzzy PID controllers, the damping effects of the MR mount are conducted. Experimental results show that it has better damping effectiveness by using the self-tuning fuzzy PID controller than the other controllers for the semi-active control system with the MR mount.

An artificial rubber muscle was paid to attention as an actuator in the present study because human was safe for the manipulator to have come in contact with human. However, this actuator occurs easily the vibration, and is late the response because of applying the air pressure. Then, the MR brake that uses the MR fluid with an early response is built into the joint, and controls the vibration. In this paper, we have grasped a manipulator's dynamic characteristics by construction of a model for improvement in the control performance of MR brake. Furthermore, the simulation was performed using the model and efficient breaking of MR brake was examined.

This paper presents to the feasibility for improving the ride quality of railway vehicle equipped with semi-active suspension system using magnetorheological (MR) fluid damper. In order to achieve this goal, a fifteen degree of freedom of railway vehicle model, which includes a car body, bogie frame and wheel-set is proposed to represent lateral, yaw and roll. The MR damper system is incorporated with the governing equation of motion of the railway vehicle which includes secondary suspension. To illustrate the effectiveness of the controlled MR dampers on railway vehicle secondary suspension systems, the sky-hook control law using the velocity feedback is adopted as the system controller. Subsequently, computer simulation of performance evaluation such as vibration control of the car body is performed using Matlab. Various control performance are demonstrated under external excitation by creep force between wheel and rail.

This paper presents experimental evaluation of a magnetorheological (MR) damper designed for an integrated isolation mount for ultra-precision system. The vibration sources of the ultra-precision system can be classified as two. The one is the environmental vibration from the floor, and the other is the transient vibration occurred from stage moving. The transient vibration occurred from stage moving has serious adverse effect to the process because the vibration scale is quite larger than other vibrations. Therefore in this research, semi-active MR damper, which can control the transient vibration, is adopted. Also the stage needs to be isolated from tiny vibrations from the floor. For this purpose, dry friction of MR damper must be removed. In order to achieve this goal, a new type of MR damper is designed that the friction parts are eliminated and damping force range is optimally increased. Subsequently, the damping force characteristics of MR damper are experimentally evaluated.

Beside active dampers, rotating brake and clutch systems are the main field of application for magnetorheological fluids (MRF). Within this paper an idea is shown that uses the well known technology of MRF dampers and combines it with the also well known technology of common mechanical ball clutches. The result of this fusion is a new type of MRF-clutch design that has a lot of advantages compared to traditional MRF clutch designs. Additionally to show the potential of the idea for common applications, two demonstrator structures that had been investigated will be presented.

In this paper the servo property of a high performance magnetorheological valve will be evaluated by closing the pressure feed back loop. The magnetorheological valve developed for this study has two separately controllable fluid flow channels and is especially designed for high frequency applications. A state space model for the magnetorheological valve from the control signal to the pressure output will be indentified. The indentified model is used for tuning a PID controller and in simulating the closed loop system. Finally the controller will be implemented to a control computer and the pressure output will be controlled in a real time control loop. By analyzing the dynamic and static results of the magnetorheological servo valve, it can be stated that the magnetorheological valve has a good potential for pressure and force control applications.

Haptic units in small consumer electronic products (such as hand-held devices) require miniaturization of tactile and kinesthetic modules. However, it is quite challenging, particularly minimizing the size of kinesthetic actuators. Thus, this study investigates a miniature haptic button actuated by magnetorheological (MR) fluids with an aim to convey kinesthetic information or realistic button sensations to users in small electronic devices. To this end, a prototype haptic button was designed and constructed. The design focus was to maximize the resistive force generated by the fluids in a given size by using multiple operating modes of MR fluids. In order to evaluate the performance of the prototype button, a test setup consisting of a micro stage and a precision load cell was constructed. Using the setup, the resistive force of the button was measured by varying the indented depth and the input current. The results show that the force change (defined by the ratio of the difference between the maximum force and the minimum force to the maximum force) is over 72 % for all indented depths (up to 1.5 mm). This change is sufficient to create various button sensations. In other words, the proposed haptic button can offer a range of stiffness change that can be conveyed to human operators.

This study presents an application of magnetorheological elastomer (MRE) on the development of an Adaptive Tuned Vibration Absorber (ATVA) for torsional vibration reduction of vehicle powertrains. The MRE used for the ATVA development consists of a silicone polymer, silicone oil and magnetic particles with the weight fractions are 60%, 20%, 20%, respectively. The experimental testing was conducted to obtain MRE properties such as elastic modulus and damping ratio. Also, effective formulas for elastic modulus, damping ratio were derived to facilitate ATVA design. Numerical simulation show that the ATVA works effectively for powertrain vibration reduction.

In this study, a new magnetorehological elastomer (MRE) based absorber is proposed and its vibration isolation performance is investigated. The MRE absorber with a compact structure is firstly designed in order to accomplish the maximization of the variable stiffness range. The working characteristics of the MRE are then measured. On the basis of the experimental data, the control model of the MRE is also formulated. Finally, the drop test is carried out to check the actual impact isolation performance.

Magneto-rheological fluid squeeze mode investigations at CVeSS have shown that MR fluids show large force capabilities in squeeze mode. Theoretical and experimental study of MR fluids in squeeze mode has previously been limited to quasi-static conditions. It was found that MR fluids in squeeze mode can be used in a wide range of applications such as engine mounts and impact dampers. In these applications, MR fluid is flowing in a dynamic environment due to the transient nature of inputs and system characteristics. The research presented in this paper undertakes the problem of dynamic testing and modeling of MR fluid squeeze mounts. Dynamic tests of the MR mount are studied for different densities of magnetic field, frequencies and excitation amplitudes. An effective mathematical model of MR mount for steady state was built which contains inertial effect. The results show the compression force and the area of the hysteresis loop increase when increasing the density of magnet field or excitation amplitude. Also, the inertia effect becomes more significant for higher displacement frequencies.

Based on results obtained from testing MR fluid in a squeeze mode rheometer, a novel compression-adjustable element has been fabricated and tested, which utilizes MR fluid in squeeze mode. While shear and valve modes have been used exclusively for MR fluid damping applications, recent modeling and testing with MR fluid has revealed that much larger adjustment ranges are achievable in squeeze mode. Utilizing squeeze mode, an MR squeeze mount was developed and tested. Test results show the device was capable of varying the compression force from less than 8lbs to greater than 800lbs when the pole plates were 0.050" apart. Test results showed that the mount tends to achieve higher forces after each repeat of test. This behavior, called "clumping", was studied and solutions to minimize this effect are discussed.

This study experimentally investigates the dynamic performance of a semiactive control system consisting of an MR damper and an electromagnetic induction (EMI) device. The EMI system, consisting of permanent magnets and coils, is capable of converting reciprocal motions (kinetic energy) of the MR damper into useful electrical energy (electromotive force or emf). The emf signal is an alternating voltage signal, proportional to the velocity of the motion. Thus, the EMI can act as a relative velocity sensor for the implementation of a control algorithm for the MR damper system. However, this sensing capability of the EMI has not been evaluated in control experiments with a building structure. Thus, this study intends to investigate the performance of an MR damper system, solely operated by an EMI device (without a conventional velocity sensor) using a three storey shear building structure under scaled historic earthquake loadings. To this end, an MR damper and an EMI device are installed in the building structure, and a semi-active control algorithm, maximum energy dissipation algorithm, is implemented based on the EMI signal. The experimental results show that the MR-damper system with an EMI device outperformed a passive "optimal" control system, implying that the EMI can replace conventional velocity sensors in MR damper systems.

MR damper has brought out new challenges for development of the recoil mechanisms and vibration stability control of weapons because of its good electromechanical coupling performances. At present, it has been an urgent task during automatic firing to ensure its dynamic performance and its reliability of gun recoil mechanism under continuous fastly impact. For recoil mechanisms applications, MR dampers are desired to provide optimal damping force to control the recoil dynamics, so that large peak of recoil forces can be avoided with a certain limited stroke, and the firing stillness and stability are ensured. According to its vibration and shock mechanics process of gun recoil mechanism, the measurement method of its vibration-reduction and shock-resistant properties of gun recoil mechanism based on MR damper is analyzed. The results show that a gun recoil mechanism based on MR damper is quite a good vibration-reduction and shock-resistant equipment when the vibration and shock energy dissipation by damp is considered.

In the previous works, we suggested a compact MR fluid brake (CMRFB) in which multi-layered disks and narrow gaps of 50 μm are used. This device has a great advantage in its small size and high torque. However, there are unignorable errors between analytical results and experimental results in its torque. To clarify the reason of this phenomenon, and decide the practical limitation of the gap-size for the CMRFB, we developed new CMRFB whose gap-size is 100 μm. In this paper, we analytically and experimentally compared torque characteristics of these two types of CMRFB. The braking torques of these brakes show approximately same level. According to the comparison of analytical and experimental results for 50 micro-gaps brake shows a large error. Flow observation tests shows a possibility that the fluid is not sufficiently filled into the 50μm-gap.

Driver fatigue is one of the leading factors contributing to road crashes. Environmental stresses such as unwanted seat vibration is a key contributor to fatigue. This paper presents the design and development of a MR elastomers isolator for seat suspension system. By altering the system's stiffness and damping, the vehicle's vibration energy input to seat is reduced, which then suppresses the seat's response. Results shown that the proposed isolator can reduce vibration further comparing with a passive isolation system, indicating the significant potential of its application in vehicle seat vibration control.

For implementing intelligent control of the longitudinal vibration for the Tianxingzhou Bridge, which is a double-decker railway and highway cable-stayed bridge, twelve MR dampers were fabricated and identified, and installed between the deck and lower cross beam of the bridge. The results show that the MR fluid, manufactured in a 500 l quantity, exhibited high stability, high yield stress and suitable viscosity. The MR dampers had excellent mechanical characteristics; the maximum damping force was 537 kN for an applied current of 1.0 A, and the damping increased by a factor of 18 when the current was increased from 0 A to 1.0 A. Simulation results show that installing these twelve MR dampers maintains the longitudinal vibration below the maximum allowable value of 30 mm, even for a worst case scenario when two trains brake at the same time, in the same direction and in the middle of the bridge span.

This paper proposes a driver supportive device with haptic cue function to achieve optimal gear shifting in manual transmission vehicles. This function is implemented on accelerator pedal by utilizing magnetorheological (MR) clutch mechanism. In order to achieve this goal, an MR fluid-based clutch is devised to be capable of rotary motion of accelerator pedal. The proposed MR clutch is then manufactured and its transmission torque is experimentally evaluated according to field intensity. Then the manufactured MR clutch is integrated with accelerator pedal to establish the haptic cue device. A virtual environment emulating 4-cylinder 4-stroke engine is constructed and communicated with the haptic cue device. Control performances such as torque tracking are experimentally evaluated via simple feed-forward controller.

In this paper, the graphite based Magnetorheological Elastomer (Gr MREs) is presented to study the sensing capability of MREs. With the help of graphite, the giant resistance of MREs is reduced to kΩ level. When either the magnetic field or the external force is applied on to the Gr MREs, its resistance is changed. This finding opens up possibilities for the design of a force sensor combining Gr MREs. A representative unit model is addressed to express the phenomenon theoretically.

The yield stress of the electrorheological fluid based on the powder of the precursor of CaTiO₃, the main component of which is calcium oxalate monohydrate, has being measured for different treating temperature. It is found that the yield stress decreases dramatically as the treating temperature increases to 160 °C. The components of the vaporized materials during heating process are analyzed by thermogravimetry-mass spectrum method and also thermogravimetry-infrared spectrum method. Both of the methods show that the vaporized material is almost water before the temperature rising to 200 °C. These results suggest that the water adsorbed in the dispersed particles plays a decisive role in this type of electrorheological fluids.

A new type of electrorheological (ER) fluid consisting of lanthanum titanate (LTO) nanoparticles is developed. The ER Fluids were prepared by suspending LTO powder in silicon oil and the particles are fabricated by wet chemical method. This ER fluid shows excellent ER properties: The static yield stress reaches over 150kPa under 5kV/mm with linear dependence on the applied DC electric field, and the current density is below 10μA/cm2. In order to investigate the affect factor on the ER behavior the LTO powder were heated under different temperatures. The ER performances of both two particles treated under different temperatures were compared and the properties of those particles were analyzed with TG-FTIR technique. It was found that the static yield stress of the suspensions fell from over 150kPa to about 40kPa and the current densities decreased prominently as the rise of the heating temperature. TG-FTIR analysis indicated that organic groups remained in the particles such as alkyl group, hydroxyl group and carbonyl group and etc, may contribute to the ER effect significantly. The experimental results are helpful to understand the mechanism of the high ER effect and synthesize better ER material.

The model of an artificial cilia as a flexible ferromagnetic filament in a rotating magnetic field is proposed. Numerical algorithm for the simulation of its behavior is developed and the characteristic shapes of the filament with one fixed end under the action of a rotating field are found. It is concluded that ferromagnetic filaments may be used as mixers in microfluidics.

This study was aimed on the preparation of titanate/polypyrrole core-shell rod-like composite particles. The mere titanate rod-like particles were prepared as a core material and PPy was polymerized on their surface in different amounts. Rheological measurements showed that under an applied external electric field, shear stress of these materials significantly increased with amount of PPy in the shell layer. The yield stresses obtained from the Cho-Choi-Jhon model were correlated with dielectric properties of suspensions. Polarizability as a measure of particle polarization obtained from Havriliak-Negami model of dielectric spectra increases with the content of PPy in the samples. Furthermore, role of particle concentration and silicone oil viscosity was also investigated.

Here, we have fabricated carboxyl-group-immobilized hollow polyaniline (PANI) spheres with various alkyl chain lengths. The hollow PANI sphere was fabricated by the extraction of polystyrene (PS) spheres after polymerization of aniline on PS sphere. And then, carboxyl-group was immobilized on the surface of hollow PANI sphere. After the application of an electric field, the shear stress of carboxyl-group-immobilized hollow PANI spheres was higher than hollow PANI spheres in the following order: PANI adipate > PANI glutarate > PANI succinate > PANI malonate > PANI.

The thermal stability of ERF based on oxyhydroxides of metals has been established. It increases in the row of metals Al < Fe < Cr < Ni. It is shown that hydrates of oxyhydroxides of polyvalent metals that are characterized by a laminated structure and by the presence of a potential charge carriers as a result of the formation of the hydrogen bonding of the OH groups of unstructured water molecules are efficient thermally stable fillers of ERFs for various technological facilities.

Molecule-based electrorheological (ER) materials as a novel type of ER materials, a series of compounds using melamine (C₃N₆H₆) as the substrate, have been synthesized using orthophosphoric acid (H₃PO₄), oxalic acid (H₂C₂O₄), 4-toluenesulfonic acid (PTA, C₇H₈O₃S) and 5-sulfosalicylic acid (SSA, C₇H₆O₆S), respectively, as starting materials. The ER performance and dielectric property of materials have been studied. The results show that these materials have ER activity. The unusual relationship between dielectric property and ER property of these materials was found and discussed. The composition and structure of molecule are the dominant factors, the function group plays an important role, in influencing ER performance of the molecule-based ER material.

The aim of this contribution is to find a correlation between shear rheological characteristics of polymer solutions and spinnability. Specifically it describes the suitability of various polyvinylbutyral (PVB) solutions for the process of electrospinning in which, under a strong electrostatic field, fibres are generated and deposited on a template as a non-woven sheet.

A series of experiments were conducted to determine the impact of various lubricant additives on the oxidative stability of LORD MR fluids. Oxidative stability was assessed by measuring the oxidation induction time (OIT) by pressure differential scanning calorimetry, and experiments were designed using DOE methodology to determine the effects of and interactions between various fluid components. A variety of anti-oxidants, anti-friction agents, and metal passivators were screened in several designed experiments. Metal passivators and anti-friction agents had little effect on OIT, but a combination of particular primary and secondary anti-oxidants was observed to extend the OIT of a test MR fluid threefold. MR fluids with OIT of greater than two hours were prepared, as compared to the test fluid with an OIT of about 50 minutes.

Our aim in this work was propose the use of a ternary blend of two carbonyl iron powder CIP, mixed with water atomized iron powder (WAIP), to reduce the off-state viscosity, without prejudice of MRF performance in terms of yield stress and torque output. The idea of mix water atomized iron powder with carbonyl iron powder is not new. The US Pat. # 5,900,184 by Weiss et al (1999) describes that a binary blend, half-to-half, can reduces the viscosity of MRF in the absence of magnetic field, and increase the torque output under field.

A MR suspension was prepared by dispersing silica-coated iron alloy particles into a liquid gallium. In other words, the iron alloy particles of 30 to 50 nm in diameter were first prepared and then coated with silica. Next, the particles were then suspended in a liquid Ga (assay: 99.9999%). In addition, the magnetic properties of the synthesized particles and suspension under the influence of the magnetic field were investigated. One of the main findings of this study is that the prepared powder showed a temperature sensitive of magnetization within the testing temperature range of 293 - 353 K. The saturation magnetization of silica-coated FeNbVB particles was about 0.55 T, whereas the saturation magnetization (297 K) of the synthesized MR suspension was 0.019 T.

In a novel approach, electrorheological (ER) fluids based on doped polyurethane (PUR) particles were prepared and described. The dopants were electrically polar and polarizable organic substances either as guest molecules or as modifying agents of the PUR network. The ER properties of these ER fluids were investigated and compared with those of salt-doped and non-doped reference samples. It was found that organic compounds, in particular those with a highly conjugated π-electron system, as guest molecules of PUR delivered remarkable improvements of the ER activity. In some ER fluids, the PUR particles were modified by covalent bonding of polar organic molecules to the polymer network. These modifying compounds are equipped with one or several reactive hydroxyl or amine groups. Furthermore, the influence of the number of chemical bonds of the modifying agents to the PUR network on the ER properties was also studied. Upon the application of modifying agents, which serve as plasticizer in the PUR particles, ER fluids with significantly improved electrorheological properties were obtained. The most promising ER fluid exhibited an extraordinary high shear stress of more than 10 kPa and simultaneously a very low current density below 4 μA/cm² at 40°C, which strongly improves the two basic features of ER activity in comparison to the known salt-doped ER fluids.

In this work the preparation and characterization of magnetorheological (MR) fluids constituted by CoNi nanofibers (56 nm length, 6.6 nm width) are reported. The properties of these new fluids were characterized by usual techniques (including magnetometry and magnetorheology). The results where compared with those obtained for conventional magnetic suspensions constituted by CoNi nanospheres. We found a remarkable effect of particle shape on the magnetic properties of the compressed powders: suspensions of nanofibers showed a weaker magnetic response than suspensions of nanospheres at low and medium applied field. This difference is probably due to the strong influence that nanofiber orientation could have on the demagnetizing field and, thus, on the internal field that governs the magnetization of the particles. This result was corroborated by means of finite element method simulations. Steady-state and oscillatory experiments were carried out in the presence of applied fields in order to characterize the MR response of the fluids. We found that the MR response of suspensions of nanofibers was considerably enhanced as compared to suspensions of nanospheres, in agreement with the results reported previously for microfibers.

This work reports the experimental and theoretical results on the steady-state shear flow of the suspension of magnetic fibers in the presence of a homogeneous magnetic field perpendicular to the flow. In experiments, we did not observe a significant static yield stress. However, the experimental flow curves show a steep initial section corresponding to gap-spanning aggregates formed in the fiber suspension under a magnetic field. At higher Mason numbers, aggregates are not more confined by the walls and the flow curves become linear manifesting a Bingham behavior with the dynamic yield stress growing with the magnetic field intensity. This yield stress for the fiber suspension appears to be about three times the yield stress for the suspension of spherical particles. Such difference is explained in terms of the enhanced magnetization of the aggregates composed of fibers compared to the aggregates composed of spherical particles.

The spinel cobalt ferrite (CoFe₂O₄) nanoparticles were prepared via a sol-gel method followed by the annealing process. Their structural, magnetic and magnetorheological (MR) properties depending upon the annealing temperature were investigated. The X-ray diffraction analysis revealed that the higher annealing temperature, the larger grain size of CoFe₂O₄ particles resulting in larger magnetic domains in particles. The saturation magnetization, determined via a vibrating sample magnetometry, increased with annealing temperature and, in contrast, the coercivity decreased. The rheological behavior of CoFe₂O₄ particles based MR suspensions determined under the small-strain oscillatory shear flow in magnetic field showed that higher annealing temperature reflects in larger changes of rheological properties.

Fe₃O₄ nanoparticles (NPs) were synthesized via chemical co-precipitation in an aqueous solution, and were characterized by scanning electron microscope (SEM). Bidisperse magnetorheological (MR) fluids were prepared with Fe₃O₄ NPs, silicone oil and micron scale carbonyl iron particles (CIPs). Their rheological properties were experimentally investigated via a rheometer equipped with an electromagnet. Results show that the sedimentation stability and yield stress of the bidisperse MR fluids were increased when adding small concentrations of Fe₃O₄ NPs.

Magnetorheological fluids (MRFs) were characterized in this study to investigate the effect of replacing magnetic particles with nonmagnetic micro-scale glass beads to increase yield stress, while also reducing density and settling rate. Two MRF samples were prepared. MRF-40 had a Fe concentration of 40 vol% while the second fluid had a total Fe concentration of 37 vol% and a glass bead concentration of 3 vol%. A comparative study of MRF characteristics was conducted to determine the impact of the nonmagnetic glass beads on yield force, as well as viscosity, and settling rate. Both MRFs were characterized as follows: 1) magnetorheology as a function of magnetic field, 2) sedimentation analysis conducted with an inductance-based sensor, and 3) cycling of a small-scale damper undergoing sinusoidal excitations at frequencies of 1 Hz for characterization and 4 Hz for fatigue tests. Further investigation of the glass beads was conducted to examine their durability post-cycle. The goal of this study is to analyze the effectiveness and feasibility of replacing magnetic particles with micro-scale glass beads in MR fluids as a means to reduce the specific gravity and increase the yield stress.

Magnetorheological elastomeric (MRE) composites composed of a silicon rubber matrix with dispersed Co particles of different morphology and weight fraction: (a) spherical microparticles of 10, 30, and 50 wt% and (b) nanowires of 10 wt% were subjected to compressive pre-strain with normalized amplitudes of 1, 2, or 3 % while held in the magnetic cell. The deformation frequency ranged from 0-20 Hz, while the magnetic flux density was fixed at discrete values of 0, 0.1, and 0.2 T. Our investigation of the spherical microparticle-based composites show that the dynamic stiffness and equivalent damping increase with the particle weight fraction for all strain amplitudes. The most significant magnetorheological (MR) effect on dynamic stiffness is observed for 10 wt% samples at strain amplitude of 1 %. This effect highly decreases with both weight fraction and strain amplitude. The MR effect on equivalent damping is much higher than that on dynamic stiffness and it only slightly decreases with particle weight fraction and strain amplitude. To assess the dependence of MR properties on Co particle morphology, the 10 wt% spherical microparticle- and nanowire-based composites were compared. The dynamic stiffness and equivalent damping coefficient values are much higher for the nanowire-based MRE compared to the spherical microparticle-based MRE for all strain amplitudes. However, the MR effect on dynamic stiffness and equivalent damping coefficient is slightly smaller for the nanowire-based composite.

Titanate nanotube (TN) synthesized by hydrothermal reaction of titania nanoparticles in alkali solution, then the TNs were modified by acetamide. X-ray diffraction analyses, scanning electron microscopy and Fourier transform infrared spectrometry are used to determine the structure of the TNs. Under DC electric field, the yield stress of these acetamide-modified TN suspensions shows large yield stress. It is also found that the ER effect is sensitive to the wettability of the TNs.

In this paper, we studied the effects of heat treatment on the ER performance, electrical and dielectric properties of a type of polar molecule dominated-TiO₂ ER fluids. It was found that the permittivity of unheated TiO₂ ER fluids was large and there was a clear dielectric loss peak between 10³ to 10⁴ Hz. However, for heat-treated ER fluids, the permittivity moves up to a relative low value from 40 to 10⁴Hz. No dielectric relaxation process was observed at low frequency range. The distinct changes of polar molecule dominated-TiO₂ electrorheological fluids before and after heat treatment are due to the presence of water absorbed on the surface of particles, which play an important role in improving the ER effects.

Electrorheological (ER) fluids are a type of colloids whose rheological characteristics can be varied reversibly with the application of an electric field. The traditional ER mechanism is based on induced polarization arising from the dielectric constant contrast between the suspended solid particles and the fluid. However, for induced polarization there is a maximum value for the dimensionless electric susceptibility χ ~0.24. That implies an upper bound for the traditional ER effect. For permanent molecular dipoles, χ can be as high as 4-50. Thus, one to two orders of magnitude higher electric energy can be gained by harnessing the molecular dipoles. Indeed, the recent discovery of the giant electrorheological (GER) effect, in nanoparticles of urea-coated barium titanate oxalate suspended in silicone oil, has shown that the theoretical upper bound of the traditional ER effect is no longer applicable to this new type of electrorheological fluid. A phenomenological model of the GER mechanism, based on aligned molecular dipoles of urea molecules in the contact regions of the nanoparticles, yields an adequate account of the observed effect but without a microscopic picture on how this can occur. More recently, by using molecular dynamics (MD) to simulate the urea-silicone oil mixture confined between two bounding surfaces of a nanocontact, we find that the urea molecules, which has a molecular dipole moment of 4.6 Debye, can form aligned dipolar filaments that penetrate the oil film to bridge the two substrates, with the attendant lowering of the aligning field for the urea dipoles. This phenomenon is explainable on the basis of a 3D to 1D crossover in urea molecules' microgeometry, realized through the confinement effect provided by the oil chains. The resulting electrical energy density is shown to give an excellent account of the observed yield stress variation as a function of the electric field.

The aggregation of magnetic particles in the presence of a magnetic field is the basic phenomenon which underlies all the physics of magnetorheological (MR) fluids. Although these interactions are well understood when the suspending fluid is a simple liquid, new MR fluids based on dispersion of magnetic microparticles in a ferrofluid or MR elastomers based on dispersion of magnetic particles in a rubber matrix, present some unusual properties which are not well described by conventional theories. We analyze in this work the motion of magnetic particles dispersed in a ferrofluid and submitted to a magnetic field and discuss the possible applications.

Experimental and simulation results are presented that illustrate how the addition of non-magnetizable particles to a magnetorheological (MR) fluid can enhance the field-induced yield stress. Efforts to understand the underlying mechanisms are described.

An electrorheological gel (ERG) is a functional material that changes its surface adhesive property according to the intensity of the applied electric field. It is a composite material consisting of ER particles and silicone gel. Under no electric field, the surface adhesion is low because the slippery ER particles protrude from the gel surface. When an electric field is applied to an ERG, silicone gel around ER particles rises and covers the ERG surface such that the surface adhesion becomes high. The surface adhesion of ERGs can be changed quickly and reversibly by adjusting the electric field. This unique property is called the electro adhesive (EA) effect. However, although this electro adhesive phenomenon has been experimentally confirmed, the physical theory has not been sufficiently developed. In this study, the theory of the EA effect based on electromagnetics is developed and validated using a numerical analysis. Simulation results show that ER particles sink into silicone gel, and silicone gel around ER particles heaves due to the Maxwell stress and gradient force of the applied electric field.

When neutrally buoyant poly alpha olefin particles in corn oil were exposed to a gradient ac electric field generated by a spatially periodic electrode array, these particles experienced the negative dielectrophoresis and instability in all the suspensions of concentration range from 0.01% to 5% (v/v). One critical particle concentration was experimentally determined as 1% (v/v) below which the particles in corn oil were segregated to form island-like structures in the lower electric field regions; and above which, particles only formed straight stripes. The island-like structure was suspended in the lowest electric field area. Specially designed experiments with a suspension of 1.126% (v/v) confirmed that there exists particle instability. Anisotropic properties of electric interactions are responsible for particle instability in all the suspensions of different concentrations and island-like structures were formed only in the dilute suspensions in which the particle instability has enough space to be developed.

We used numerical simulations of a continuous model and the molecular dynamics model to understand the particle instability, formation of island-like structures and existence of one critical particle concentration of 1% (v/v) for formation of island-like structures in the suspension in a gradient ac electric field reported in Paper I. The simulations of the continuous model show that the critical concentration of 1% (v/v) is the concentration of which the particles of a suspension are just fully filling the lower field region finally. According to the MD simulations, the particles instability does exist in the corn oil in a gradient ac electric field, anisotropic polarization interactions among the particles are responsible for the particle instability and have memory, and the memory is still kept even when the particles are transported by a dielectrophoresis force. The island-like structures can be regarded as signature of the memory. We explored possibilities to apply our findings in biomedical fields.

The multiple scattering method is used in calculating the electric field distribution for the systems composed of spheres. According to the calculation result, we propose a new mechanism of the electrorheological effect and show that the yield stress induced by this mechanism exhibits the typical characteristics of that observed in experiments.

The influence of centrifugal accelerations on the particles in magnetorheological fluids due to high rotational speeds in brakes and clutches is often described with an undesirable increase of the off-state torque or an irreversible decomposition of the MRF when no magnetic field is applied. In this contribution this effect is studied by analyzing the flow fields caused by the rotary motion of the enclosed boundaries in radial and axial shear gaps from the fluid dynamics point of view. By an analytical approach for describing the particle behavior, changes in the particle distribution can be calculated. The approach is based on the simulation of several tracks of individual particles for different rotational speeds. The results of the simulation are compared with measurements performed on a test actuator for identifying a move of the particle concentration in radial shear gaps by measuring changes in magnetic flux density distribution.

This study presents adaptive sliding mode fault tolerant control for magneto-rheological (MR) suspension system considering the partial fault of MR dampers. After formulating the full car dynamic model featuring four MR dampers, the fault model of the MR damper due to the varying working temperature was derived. An adaptive sliding model fault tolerant control strategy was then proposed after the occurrence of a fault. Its performance was evaluated and compared under the bump road condition and presented in time domain. The results show that significant gains are made in the presence of partial fault of the MR damper. The control scheme could reduce the effect of the partial fault of the MR damper on the system performance.

The effect of residual structure on properties of magnetorheological (MR) fluids, based on carbonyl iron (CI) particles, was investigated using a magneto-sweep technique and initial magnetic susceptibility measurements. The shear rate, particle size and the CI surface properties were among the experimental variables. A mechanical hysteresis, associated with the irreversible residual structure formation, was observed. The hysteresis was most pronounced at the creeping flow as compared to high shear conditions. Regardless of experimental settings, the level of the hysteresis was the same at high shear rate, while the fluids containing larger particles and higher CI concentrations demonstrated stronger residual effect at slow flow. The hysteresis loop was slightly wider for the silica treated particles suggesting that chemical (non-magnetic) interaction might contribute to the fluid irreversible behavior. Existence of some residual structure has been also shown in measurements of initial magnetic susceptibility of MR fluids. After exposure to a sequence of DC magnetic fields, fluids exhibited higher susceptibility presumably caused by the formation of residual structures of larger size than those in the initial state.

This research is focused on mathematical modeling of MR fluids in squeeze mode. There is no universally accepted mathematical model of squeeze flow of MR fluids to date. In this research, the squeeze flow problem of MR fluids is solved using perturbation techniques and squeeze force, flow field, and plug flow region are determined.

This study investigates the field-induced rheological characteristics of perfluorinated polyether (PFPE) based magnetorheological (MR) fluids. Four PFPE based MR fluid samples were prepared, each with a different solid loading. All samples contain a single grade of carbonyl iron powder with an average particle diameter of 2 μm. The PFPE base fluid enhances sedimentation stability and its composition and qualities are introduced in the paper. The magnetization characteristics of a fluid sample are measured and its magnetic properties are compared to known models from the literature. The shear yield stress in all fluid samples is investigated experimentally, as a function of solid loading and the magnetic flux density. The results are compared to established shear stress models for MR fluids. Model parameters are set to conform to the PFPE based MR fluids. The PFPE based MR fluids are shown to have a comparable shear yield stress, when compared to commercially available MR fluids with a comparable particle loading and particle size.

This article refers to the field of apedal ferrofluid based locomotion systems. An analytical solution shall be given on the matter of flow manipulation by an alternating magnetic field. The problem involves the causative magnetic field leads to the correspondingly deformed free ferrofluid surface contour and presents the evidence of an effective flow, meaning a non-zero average flow rate.

The performance of most commercial MR fluid devices depends on the shear strength of the MR fluid. The field-induced yield stress can be accurately characterized experimentally by a magneto-rheometer. However, as a number of factors, for example, particle volume ratio and particle size, are known to affect the rheological properties of the fluid, such measurements can be very time consuming. Hence, computational models represent a valuable tool in the design of MR fluid devices. This study provides a computational model to quantitatively predict the shear yield stress for MR fluids. The configuration is a representative unit cell in the form of a cube of a visco-plastic material which contains a number of rigid spherical particles. The cube undergoes a simple shear deformation and the mean induced shear stress is calculated. The model is used to study the effect of particle size and volume ratio on the dynamic yield stress of MR fluids.

In recent years, a new type ER fluids named as polar-molecule-dominated electrorheological (PM-ER) fluids have been developed, of which the yield stress can reach more than 100 kPa and behaves a linear dependence on the electric field. A brief description on the composition and synthesizing method for the materials is given. The main merits of PM-ER fluid are as follows: high yield stress, the shear stress increasing with shear rate up to more than 10³s^-1, low current density, rapid electric response and anti-sedimentation. Some perspectives on PM-ER fluid and its applications are presented.

The progress in the synthesis of new magnetic nanoparticles and agglomerates stimulates the development of novel ferrofluids with enhanced rheological properties. In the current work ferrofluids based on Co-nanoplatelets and clustered iron oxide nanoparticles have been considered. Steady-shear experiments and yield stress measurements of these ferrofluids have been performed using rotational rheometry.

This study is focused on the behavior of magneto-rheological (MR) grease flow through microchannels with nominal internal diameters ranging from 75μm to 1mm. A PAO-based grease is synthesized and mixed with iron micro-powders with 1.1μm average particle size to create a MR suspension with 80% solids loading. A magnetic field is applied midway along the microchannel by an electromagnet, and the pressure gradient of the flow is measured across the microchannel for different channel diameters. The results show significant pressure drops for different magnetic field strengths. It is also demonstrated that there is good agreement between the experimental data and the macroscale theory, using the Hershel-Bulkley model for flow through a circular cross section. In addition, the effect of surface roughness on the pressure gradient is examined by evaluating different microchannels made of stainless steel, PEEK, and fused-silica with different values of surface roughness. It is observed that surface effect diminishes as the microchannel diameter decreases.

To understand the dynamic rheological behavior of polar molecular electrorheological (PMER) fluids, the shear stress and viscosity of the colloids are compared with the parameters of their lamellar structures which are obtained simultaneously with the rheological characteristics using an electrorheoscope. The results of the experiments and molecular dynamics simulation indicate that the shear stress is mainly contributed by the moving particle rings, and there is an inverse correlation between the width of the moving particle rings and the shear stress.

In this study, the behavior of thick magnetorheological elastomers (MREs) has been experimentally investigated. Two types of MRE specimens of varying concentrations, with circular and rectangular shapes having thicknesses from 6.35mm to a maximum of 25.4mm are prepared. These samples are evaluated under quasi-static compression and double lap shear tests. The shear and the Young's moduli of the MREs are obtained under different applied magnetic fields. It is observed that the field induced change in modulus is independent of the thickness of the MRE and only dependent on the iron particle concentration and the magnetic field strength. With the increase in applied magnetic field, it is observed that the change in modulus from a linear trend at lower field to a non-linear trend at higher field. It is found that thick MREs are more controllable in compression mode than in shear mode.

Many efforts have been spent on developing high-performance positive ER materials. In those efforts, change of functional groups of ER materials is the easiest method to approach developers' satisfaction. However, the mechanism of functional group's effect has not clearly investigated. In this study, we introduced benzene ring or triazine group into amine or carboxyl groups immobilized chitosans to observe their influence on the shear stress under an electric field. All of the curves of the shear stress plotted against shear rate were fitted well by our suggested spring-damper model.

The compatibility of solid phase – liquid medium appears to be an important factor for controlling the electrorheological efficiency of electrorheological fluids. Controlled protonation of polyaniline particles with perflourooctanesulfonic, tartaric or sulfamic acid provides particles in a broad range of hydrophobicity as a suitable model to study this phenomenon. The relation between organization of such particles in silicone oil suspensions in on/off electric field at rest and during flow at various volume concentrations was demonstrated.

Electrorheology (ER) of ferroelectric materials such as nanometric BaTiO₃ is still not fully understood. In this work, nanoparticles of Ba_XSr_(1-X)TiO₃ (where x = 0.8, 0.9 or 1.0) were synthesized using the method of Pechini, calcinated at 950°C, and after, lixiviated under pH 1 or pH 5. A controlled stress rheometer (MCR-301) was used to make the ER characterization of dispersions made of Ba_xTi_1-xO₃ in silicone oil (30% w/w), where (a) shear stress as a function of DC electric field (under constant shear rate) or (b) shear stress as a function of shear rate (under constant AC or DC electric field) were measured. We observed that electrophoresis occurred under electric field DC, creating a concentration gradient which induced phase separation in ER fluid. On the other hand, under AC fields above 1 kV/mm, the ER effect is stronger than for DC field, and almost without electrophoresis. Furthermore, there is an AC frequency, dependent on the disperse phase, where the ER effect has a maximum.

Pectinated electrode was designed to measure the rheologcal property of PM-ER fluids. The principle of this measurement is based on the effect that the outside electric field near the edges of parallel electrode can contribute a considerable value of the field. The relation of the yield stress and the gap between pectinated electrode and workpiece, the variations of the yield stress vs the parameters of pectinated electrodes are obtained. We believe that knowledge of the pectinated electrodes and the ER behavior in between the electrode and workpiece are helpful for the application of ER fluid-assisted polishing.

In this work, a new method to determine the wall shear stress was developed step by step. To determine the wall shear stress, methods of the suspension rheology are being used for the first time to characterize ER fluids. This work focuses on investigations of the flow behavior of electrorheological suspensions in flow channels with different geometries at different electrical field strengths. Careful interpretation of the results with respect to different gap geometries has shown that the measured flow curves should undergo a combination of corrections. As a result it can be shown that wall slip effects can be measured under application like conditions on a hydraulic test bench.

In this work, dynamic modeling of mono-tube magnetorheological (MR) damper is performed using a lumped parameter method. After describing configuration and quasi-static modeling of the MR damper based on Bingham model, the integrated lumped parameters model of the whole damper system is obtained by taking into account the compressibility and dynamic motions of MR fluid in the annular duct, upper chamber, lower chamber and dynamics of pistons. In order to demonstrate the effectiveness of the proposed dynamic model, a comparative work between simulation and experiment is undertaken. In addition, the effect of MR fluid compressibility on the hysteresis of MR damper is investigated through computer simulations.

Large, high-force, controllable MR fluid dampers often present the device designer significant challenges. This is particularly true if a significant range of force control is required at high speeds. In many instances, achieving a sufficiently high on-state force while maintaining an acceptably low off-state force can lead to device dimensions that are unreasonably large. A balance must be struck between the iron loading needed to meet the on-state force requirement and the viscosity needed to meet the off-state force requirements. A further complication is that very large diameter dampers can encounter Reynolds numbers high enough to cause significant turbulence which further compromises off-state performance. Very large, high-force dampers also present challenges relating to high static and dynamic pressures and ensuring that MR fluid in all parts of the damper does not suffer from particulate settling. In this paper we present evidence of new MR fluid valve and damper designs that allow LORD Corporation to achieve significantly enhanced performance in large, high-force dampers. We will present data that shows that an appropriately designed MR valve can appear to enrich the fluid, thus providing higher apparent yield stresses in the fluid.

We present details of a new, high-shear-rate, valve-mode MR fluid rheometer capable of measurement at rates appropriate to high-speed dampers and shock absorbers. The instrument is modular and allows for choosing from a number of well-defined magnetic valve geometries or a capillary tube. It requires only a modest amount of MR fluid and is easily cleaned to allow rapid testing of different fluid formulations. Of particular importance is the means for applying and accurately determining the magnetic field H applied to the fluid and provision for demagnetizing the system between measurements.

A twin gap plate-plate shear cell, developed by BASF, meets the requirements for reliable durability testing on magnetorheological fluids. The possibility to test the effect of life time energy input to MR-formulations within a few days is demonstrated for commercial MRF formulations (Basonetic^®). MRF durability measurements as well as further analytical characterization of the sheared MRF prove that magnetorheological fluids with high content of magnetisable particles, as required for clutch/brake applications, are able to withstand specific energy intakes of more than 5·10¹² J/m³. This remarkable result should encourage designers in industry and automotive to explore new MRF applications.

In the paper the results of investigation of structural interactions, generated by simultaneous impact of electric and magnetic fields on fluids containing a two-component dispersed phase are presented. Dielectric, magnetic and rheological characteristics of these fluids are considered. The characteristic features of the formed structures depending on the filler type, deformation conditions and intensity of application external fields are discussed.

Durability is an essential issue of magnetorheological fluids (MR fluids) especially in brake and clutch applications. To investigate the lifetime dissipated energy (LDE) within a technical relevant scale, considering the volume of MR fluid and the transmitted torque, a long-term measuring system is developed which is based on a continuous load cell (CLC). An advantage is the possibility to vary the influencing quantities, which enables the characterization of the MR fluid during a durability experiment and application oriented load cases with changing influencing quantities. Measurements show the dependency of the attainable LDE on the power dissipation and a pressure increase, indicating wear processes of the MR fluid.

This study investigates a new generation of magnetorheological elastomers (MREs) based on hard magnetic materials. The type and dispersion of the filler material affects how the MREs respond to an applied magnetic field. A random dispersion of soft magnetic particles, such as iron, results in a MRE with stiffness that varies with the applied magnetic field. Unlike "soft" MREs, a dispersion of hard magnetic materials aligned in an electromagnetic field will produce an MRE with magnetic poles. When a magnetic field is applied, perpendicularly to these poles, the filer particles generate torque and cause rotational motion of the MRE blend. The primary goal of this project is to fabricate and test the properties of MREs filled with hard magnetic particles (or H-MREs). This experimental work investigated the effect of different types of filler materials by measuring the blocked force and the displacement of H-MREs with varying magnetic fields. The linear trends in the displacement and blocked force over the respective ranges give good indication of the application of H-MRE materials as bending type actuators.

A finite element transient analysis together with the unit cell modeling method has been employed to simulate the damping properties of magnetorheological elastomers (MREs). The influence on the damping effect of MREs of frequency and amplitude of an applied load, the shape of ferromagnetic particles, damping of the rubber matrix and properties of the interfacial layer has been investigated. The results indicated that damping in MREs is generally increased with frequency and amplitude of the external load and is more sensitive to the load at low frequencies and high amplitudes. The results also demonstrated that MREs fabricated with regular shaped particles and low damping matrix materials had the smallest damping effect. Additionally, dependence of the damping properties of MREs on the thickness and damping characteristics of the interfacial layer were also discussed.

In paper we present the results of investigations of viscoelastic properties of magnetorheological elastomer containing carbonyl iron particles. Frequencies of natural vibrations of three layered beam, supporting constructions of which are made from aluminum and the inner layer – from magnetorheological elastomer are calculated, the dependence of vibrations on induction of the applied magnetic field is obtained. Non stationary vibrations of the beam at pulse impact of magnetic field are found.

The study of rheological characteristics for two types of magnetorheological polishing fluids (MRPF), MRPF-1 based on cerium oxide abrasive particles and MRPF-2 based on nano-diamond abrasive particles, was carried out. Experiments on polishing of a polycrystalline sitall laser mirror substrates with these fluids using magnetorheological finishing process were executed. The surface structure of the samples after the polishing was investigated with the atomic force microscope. The results of surface measurements for the samples under the study polished with both MRPF-1 and MRPF-2 fluids are reported in comparison with existed data obtained with regular pitch polishing method. The lowest root-mean-square roughness of 0.2 – 0.4 nm was obtained for the samples polished with MRPF-2.

The study addresses experimental characterization of magnetorheological elastomers (MRE) with six different particle loadings under various magnetic field intensities. The MREs consisted of spherical iron particles, 6 to 10 μm in diameter, ranging from 0.25 to 30% weight fraction, cured in a nonmagnetic silicone rubber host elastomer. Mechanical properties of MREs such as equivalent viscous damping and complex stiffness were experimentally determined by using an Instron material testing machine with a magnetic cell. The effects of weight fraction of particles, displacement excitation frequencies, and pre-strain on the field-dependent properties of MREs were experimentally evaluated.

In this study, the temperature dependent dynamic behavior of a magnetorheological (MR) damper was characterized. To this end, an MR damper, which was designed and fabricated for a ground vehicle seat suspension application, was tested over temperatures ranging from 0 °C to 100 °C at a constant frequency of 4 Hz and a constant amplitude of 7.62 mm on an MTS-810 material testing system equipped with a temperature-controlled environmental chamber. And, the widely adopted Bouc-Wen model was assessed to characterize the temperature dependency of the MR damper through examining the trends of the model parameters. It was observed that although mBW model could capture the MR damper behavior well, some of the model parameters did not represent the physical realization of the damper based on the physical structure of the model. This is attributed to the fact that mBW has differential terms and thus, an infinite solution space and different combinations of the model parameters may yield similar results. Therefore, it was concluded that mBW model was not successful to model the temperature dependency of MR damper behavior.

The high shear rate behavior of MR fluids is investigated using a concentric rotational cylinder viscometer fabricated in-house. The rotational cylinder viscometer is designed such that a high shear rate of up to 30,000 s^-1 can be applied to the MR fluid in a pure shear flow mode. As a comparison, the maximum shear rate of a commercially available parallel disk type rheometer is only up to 1,000 s^-1. To determine the shear rate of the MR fluid in the viscometer, an exact expression between torque and angular velocity is established. The yield stress and viscosity of the MR fluid is determined by fitting the expression into the measured torque and angular velocities, and the shear stress as a function of the shear rate is further derived. The magnetic filed strength across the fluid gap is determined based on an electromagnetic field analysis, and the yield stress and viscosity of the fluid as a function of the magnetic filed is established. Specifically, the stability of the MR fluid at high shear rate is also evaluated. Two commercially available MR fluids, i.e. Lord's MRF-132DG and MRF-140CG, are investigated using the rotational cylinder viscometer, and the testing results are compared to the manufacturer's data.

This study investigates the off-state rheological characteristics of magnetorheological (MR) fluids. Various carbonyl iron powder grades are tested, both micron- and nano-sized. The study considers both monodisperse and bidisperse MR fluid samples. The bidisperse MR fluids are both micron-sized only compositions and mixed micron- and nano-sized compositions. All fluid compositions employ a novel perfluorinated polyether (PFPE) oil as a base fluid. This base fluid is introduced and its qualities discussed. An off-state experimental investigation is conducted, for shear-rates from 0 to 200 s^-1. All samples exhibit the well known shear-thinning property of MR fluids but with varying proportions. The off-state viscosity is of importance in a particular application, in an MR prosthetic knee. It determines how fast the knee joint can rotate in the absence of a magnetic field. A prominent MR fluid composition is selected for the proposed application which aims to maximize to rotational speed of the MR knee joint in the absence of a magnetic field.

The dynamic behavior of the commercially used electrorheological fluid RheOil3.0 is measured under well defined conditions. Measurements were carried out in shear mode as well as in flow mode using flow channels that provide similar flow conditions to many electrorheological applications. The response time of the change in flow behavior upon a changed electric field are measured. Measurements were carried out in time domain (single step response) as well as in frequency domain (sinusoidal frequency sweep). In most flow conditions, the observed dynamic behavior is characterized by two leading response times of which the fast one is in the millisecond range. Under stable flow or constant shear rate conditions, ionic conductivity is found to be a limiting factor for a quick step response.

The development and character of secondary electrorheological structures in the flow field under various conditions were investigated. For that purpose, suspensions of glass beads in two mediums significantly differing in viscosity have been used The influence of sequences of electric field and shear rate applications, as well as the intensity of the shearing with respect to development of electrorheological patterns is discussed.

Particle slip on boundaries would strongly affect the strength of electrorheological (ER) effect leading to shear thinning phenomenon under high shear rate. We modified a confocal microscope allowing samples to experience high electric field and strong shearing. This white light scattering confocal microscopy makes possible to view three dimensional lamellar structures of polar molecular electrorheological (PMER) fluids under both electric and shear fields. The particle slip length on boundaries is obtained and compared with the viscosity change measured separately to find out their relation which is further compared with the corresponding result of molecular dynamics simulation.

This paper presents an experimental study on the cavity generated with water entry of a magnetic fluid coated cylindrical magnet. The permanent magnet is cylindrical NdFeB magnet with the magnetic flux density B=390mT. The kerosene-based magnetic fluid is adsorbed to the permanent magnet. This projectile collided with the surface of water in the rectangular container made of the transparent acrylic plastic. The cavity of air in water created by the impact of the magnetic fluid coated cylindrical magnet was observed with high-speed video camera system. The experiments were performed under nonmagnetic and alternating magnetic fields. The effect of the hydrodynamic forces on the cavity formation was clarified. The effect of the alternating magnetic fields on the pinch-off time of an air cavity was also revealed.

A kind of amorphous titanium oxide particles with different sizes (30nm, 80nm, 240nm and 640nm) was prepared using a hydrolysis method. The microstructure, dielectric properties and ER performance were investigated. The results show that the suspensions composed of smaller particles have higher yield stress at DC electric field, but also possess higher zero field viscosity. The maximal ER efficiency of the ER fluids with the larger particle size is higher than that for the smaller particles. The particles with the sizes of 30nm, 80nm, 240nm possess an excellent antisedimentation stability, while the particle with the size of 640nm shows a poor antisedimentation stability. The particle with size of 240nm has the best comprehensive performance.

The interaction between magnetorheological (MR) fluid particles and the device walls that retain the fluid is critical as this interaction provides the means for coupling the physical device to the controllable properties of the fluid. This interaction is often enhanced in actuators by the use of ferromagnetic walls which generate an attractive force on the particles in the field-on state. The aggregation dynamics of MR fluid particles and the evolution of microstructure in pressure-driven flow through ferromagnetic channels were studied for the first time using custom-built microfluidic devices. The aggregation of the particles is studied in rectilinear, expansion and contraction channel geometries. With the results of this study, methods for improving MR actuator design and performance are also identified.