Showing papers on "Magnetorheological fluid published in 2004"

On finitely strained magnetorheological elastomers

Abstract: Magnetorheological elastomers (MREs) are ferromagnetic particle impregnated rubbers whose mechanical properties are altered by the application of external magnetic fields. Due to their strong magnetoelastic coupling response MREs are finding an increasing number of engineering applications, thus necessitating appropriate theoretical descriptions which is the objective of this work. Two different continuum formulations for MREs are presented: an Eulerian (current configuration) based approach using the second law of thermodynamics plus the conservation laws method of mechanics and a new, Lagrangian (reference configuration) based formulation based on the unconstrained minimization of a potential energy functional. It is shown that both approaches yield the same governing equations and boundary conditions. Following a discussion of general properties of the free energy function of MREs, we use a particular such function to illustrate the magnetoelastic coupling phenomena in a cylinder subjected to traction or torsion under the presence of external magnetic fields.

Design and development of the magnetorheological abrasive flow finishing (MRAFF) process

Abstract: A new precision finishing process for complex internal geometries using smart magnetorheological polishing fluid is developed. Magnetorheological abrasive flow finishing (MRAFF) process provides better control over rheological properties of abrasive laden magnetorheological finishing medium. Magnetorheological (MR) polishing fluid comprises of carbonyl iron powder and silicon carbide abrasives dispersed in the viscoplastic base of grease and mineral oil; it exhibits change in rheological behaviour in presence of external magnetic field. This smart behaviour of MR-polishing fluid is utilized to precisely control the finishing forces, hence final surface finish. A hydraulically powered experimental setup is designed to study the process characteristics and performance. The setup consists of two MR-polishing fluid cylinders, two hydraulic actuators, electromagnet, fixture and supporting frame. Experiments were conducted on stainless steel workpieces at different magnetic field strength to observe its effect on final surface finish. No measurable change in surface roughness is observed after finishing at zero magnetic field. However, for the same number of cycles the roughness reduces gradually with the increase of magnetic field. This validates the role of rheological behaviour of magnetorheological polishing fluid in performing finishing action.

Experimental Research and Modeling of Magnetorheological Elastomers

Abstract: In this paper, new methods for fabricating magnetorheological (MR) elastomers are introduced. Two different MR elastomers, one made of polyurethane and the other made of natural rubber, are successfully fabricated. The experimental results show that the modulus of polyurethane MR elastomers can increase by 28% under a strong magnetic field. Comparatively, the rubber MR elastomer has low modulus change ability. A mathematical model to represent the stress-strain relationship of MR elastomers is presented. The model takes into account all the dipole interactions in a chain and the nonlinear properties of the host composite. The analytical results of the model are in agreement with experimental data.

Dynamic Modeling of Large-Scale Magnetorheological Damper Systems for Civil Engineering Applications

Abstract: Magnetorheological (MR) dampers are one of the most promising new devices for structural vibration mitigation. Because of their mechanical simplicity, high dynamic range, low power requirements, large force capacity, and robustness, these devices have been shown to mesh well with earthquake and wind engineering application demands and constraints. Quasistatic models of MR dampers have been investigated by researchers. Although useful for damper design, these models are not sufficient to describe the MR damper behavior under dynamic loading. This paper presents a new dynamic model of the overall MR damper system which is comprised of two parts: (1) a dynamic model of the power supply and (2) a dynamic model of the MR damper. Because previous studies have demonstrated that a current-driven power supply can substantially reduce the MR damper response time, this study employs a current driver to power the MR damper. The operating principles of the current driver, and an appropriate dynamic model are provided. Subsequently, MR damper force response analysis is performed, and a phenomenological model based on the Bouc-Wen model is proposed to estimate the MR damper behavior under dynamic loading. This model accommodates the MR fluid stiction phenomenon, as well as fluid inertial and shear thinning effects. Compared with other types of models based on the Bouc-Wen model, the proposed model has been shown to be more effective, especially in describing the force rolloff in the low velocity region, force overshoots when velocity changes in sign, and two clockwise hysteresis loops at the velocity extremes.

Seismic Control of a Nonlinear Benchmark Building using Smart Dampers

Abstract: This paper addresses the third-generation benchmark problem on structural control, and focuses on the control of a full-scale, nonlinear, seismically excited, 20-story building. A semiactive design is developed in which magnetorheological (MR) dampers are applied to reduce the structural responses of the benchmark building. Control input determination is based on a clipped-optimal control algorithm which employs absolute acceleration feedback. A phenomenological model of an MR damper, based on a Bouc–Wen element, is employed in the analysis. The semiactive system using the MR damper is compared to the performance of an active system and an ideal semiactive system, which are based on the same nominal controller as is used in the MR damper control algorithm. The results demonstrate that the MR damper is effective, and achieves similar performance to the active and ideal semiactive system, while requiring very little power.

Benchmark Problem for Response Control of Wind-Excited Tall Buildings

Abstract: This paper presents an overview and problem definition of a benchmark problem for the response control of wind-excited tall buildings. The building considered is a 76-story 306 m concrete office tower proposed for the city of Melbourne, Australia. The building is slender with a height to width ratio of 7.3; hence, it is wind sensitive. Wind tunnel tests for such a 76-story building model have been conducted at the University of Sydney and the results of across-wind data are used in the present benchmark problem. Either active, semiactive, or passive control systems can be installed in the building to reduce the wind response, although only an active control sample problem has been worked out to illustrate the control design. In the case of active control systems, either an active tuned mass damper or an active mass driver can be installed on the top floor. In the case of passive or semiactive systems, such as viscous dampers, viscoelastic dampers, electrorheological, or magnetorheological dampers, etc., c...

Vibration suppression capabilities of magnetorheological materials based adaptive structures

Abstract: This paper discusses the investigation of vibration suppression capabilities of magnetorheological (MR) materials in adaptive structures. Homogeneous three-layered adaptive beams with MR materials sandwiched between two elastic layers were considered. By varying the externally applied magnetic field level over the MR layer, the stiffness and damping properties of the adaptive beam can be varied. These variations in the damping and stiffness properties can be used to tune the vibration characteristics of the adaptive beams such as natural frequencies, vibration amplitudes, mode shapes and loss factors. In this study, theoretical investigation of the MR adaptive beams vibration behavior based on the energy approach is accomplished. Experiments were performed to observe the theoretically predicted vibration responses in real time. From both studies, vibration suppression capabilities of MR adaptive beams were observed in the forms of shifts in natural frequency values, variations in loss factors, and vibration amplitudes.

Viscoelastic properties of magnetorheological fluids

Abstract: We have studied the rheological properties of some magnetorheological fluids (MRF). MRF are known to exhibit original rheological properties when an external magnetic field is applied, useful in many applications such as clutches, damping devices, pumps, antiseismic protections, etc. While exploiting parameters such as magnetic field intensity, particle concentration and the viscosity of the suspending fluid, we highlighted the importance of each one of these parameters on rheology in the presence of a magnetic field. We made this study by conducting rheological experiments in dynamic mode at very low strain which facilitates the comprehension of the influence of the structure on MRF rheology. Our results confirmed the link between the magnetic forces which ensure the cohesion of the particles in aggregates, and the elastic modulus. Moreover, we found that the loss modulus varies with the frequency in a similar manner than the elastic modulus. The system, even with the smallest deformations, was thus not purely elastic but dissipates also much energy. Moreover, we demonstrated that this dissipation of energy was not due to the matrix viscosity. Actually, we attributed viscous losses to particle movements within aggregates.

Encapsulation of spherical iron-particle with PMMA and its magnetorheological particles

Abstract: Composite magnetic particles (CMP) with carbonyl iron (CI) core and poly(methyl methacrylate) shell were prepared by an in-situ dispersion polymerization method via surface treated CI with acrylic acid. These CMP were adopted as dispersed phase of magnetorheological (MR) fluids, and has better MR fluids characteristics than fluid with CI alone as they have severe sedimentation and poor dispersion quality. Flow properties of the MR fluids were analyzed via a rotational rheometer equipped with a magnetic field supplier in parallel plate geometry.

Deformation in magnetorheological elastomer and elastomer?ferromagnet composite driven by a magnetic field

Abstract: Magnetorheological elastomer (MRE) is a new class of smart materials, whose modulus can be controlled by the applied magnetic field. In this paper, using a white light speckle technique for deformation analysis, we present the real-time dynamic deformation progress (the vector diagram of the displacement or the whole-field quantitative displacement distribution) of the MRE and the elastomer?ferromagnet composite (EFC) while the magnetic field is turned on. The experimental results verify the prediction presented in a recently published paper, (Borcea and Bruno 2001 J.?Mech.?Phys.?Solids 49 2877?919), and reveals some interesting phenomena which will give us a deeper understanding for such smart materials.

Neural network control for a semi-active vehicle suspension with a magnetorheological damper

Abstract: Semi-active vehicle suspension with magnetorheological dampers is a promising technology for improving the ride comfort of a ground vehicle. However, the magnetorheological damper always exhibits nonlinear hysteresis between its output force and relative velocity, and additional nonlinear stiffness owing to the state transition from liquid to semi-solid or solid, so that the semi-active suspension with magnetorheological dampers features nonlinearity by nature. To control such nonlinear dynamic systems subject to random road roughness, in this paper we present a neural network control, which includes an error back propagation algorithm with quadratic momentum of the multilayer forward neural networks. Both the low frequency of road-induced vibration of the vehicle body and the fast response of the magnetorheological damper enable the neural network control to work effectively on-line. The numerical simulations and an experiment for a quarter-car model indicate that the semi-active suspension with a magnetorheological damper and neural network control is superior to the passive suspensions in a range of low frequency.

Semi‐active fuzzy control for seismic response reduction using magnetorheological dampers

Abstract: A semi-active fuzzy control strategy for seismic response reduction using a magnetorheological (MR) damper is presented. When a control method based on fuzzy set theory for a structure with a MR damper is used for vibration reduction of a structure, it has an inherent robustness, and easiness to treat the uncertainties of input data from the ground motion and structural vibration sensors, and the ability to handle the non-linear behavior of the structure because there is no longer the need for an exact mathematical model of the structure. For a clipped-optimal control algorithm, the command voltage of a MR damper is set at either zero or the maximum level. However, a semi-active fuzzy control system has benefit to produce the required voltage to be input to the damper so that a desirable damper force can be produced and thus decrease the control force to reduce the structural response. Moreover, the proposed control strategy is fail-safe in that the bounded-input, bounded-output stability of the controlled structure is guaranteed. The results of the numerical simulations show that the proposed semi-active control system consisting of a fuzzy controller and a MR damper can be beneficial in reducing seismic responses of structures.

Volume-constrained optimization of magnetorheological and electrorheological valves and dampers

Abstract: This paper presents a case study of magnetorheological (MR) and electrorheological (ER) valve design within a constrained cylindrical volume. The primary purpose of this study is to establish general design guidelines for volume-constrained MR valves. Additionally, this study compares the performance of volume-constrained MR valves against similarly constrained ER valves. Starting from basic design guidelines for an MR valve, a method for constructing candidate volume-constrained valve geometries is presented. A magnetic FEM program is then used to evaluate the magnetic properties of the candidate valves. An optimized MR valve is chosen by evaluating non-dimensional parameters describing the candidate valves' damping performance. A derivation of the non-dimensional damping coefficient for valves with both active and passive volumes is presented to allow comparison of valves with differing proportions of active and passive volumes. The performance of the optimized MR valve is then compared to that of a geometrically similar ER valve using both analytical and numerical techniques. An analytical equation relating the damping performances of geometrically similar MR and ER valves in as a function of fluid yield stresses and relative active fluid volume, and numerical calculations are provided to calculate each valve's damping performance and to validate the analytical calculations.

Modelling the hysteresis phenomenon of magnetorheological dampers

Abstract: Recently, magnetorheological (MR) dampers have emerged as a potential technology to implement semi-active control in structures and vehicle applications in order to efficiently suppress vibration Perfect understanding about the dynamic characteristics of such dampers is necessary when implementing MR struts in application One of the important factors to successfully attain desirable control performance is to have a damping force model which can accurately capture the inherent hysteresis behavior of MR dampers Different models have been proposed to simulate the hysteresis phenomenon in such a kind of damper The Bouc–Wen model has been extensively used to simulate the hysteresis behavior of MR dampers However, considerable differences still exist between the simulation and experimental results In this work, a methodology to find the characteristic parameters of the Bouc–Wen model in the attempt to better characterize the hysteresis phenomenon of MR dampers has been proposed The methodology takes into consideration the effect of each individual term of the Bouc–Wen model over the hysteretic loop to estimate the appropriate values of the parameters The Bouc–Wen model in which the new established characteristic parameters have been used has been validated against experimental data and an excellent agreement has been shown between the simulation and experimental results Moreover, the findings pointed towards the fact that linear or exponential relationships exist between the estimated parameters and the current excitation Considering this, a new model based on the Bouc–Wen model has been proposed in which the excitation current has been incorporated as a variable This proposed modified Bouc–Wen model has also been validated against the experimental results and a good correlation has been found

Dynamics of Self-Assembled Chaining in Magnetorheological Fluids

Abstract: The aggregation dynamics of paramagnetic spherical particles embedded in a viscous fluid is investigated via numerical simulations using a fully coupled three-dimensional model. Particles experience simultaneously Brownian motion, dipolar magnetic attraction, and multibody hydrodynamic interactions. When the dipole strength characterizing the ratio of magnetic attraction to random diffusion exceeds a critical value, particles join together forming supraparticle structures. As time evolves, particle/chain and chain/ chain interactions lead to a continuous increase of the cluster size. The mean length of particle chains has a power-law dependence with respect to time, as predicted by the theory of diffusion-limited aggregation. Both the exponent and the characteristic time scale agree very well with the experimental results of Promislow et al. (J. Chem. Phys. 1995, 102, 5492).

A Magnetorheological Fluid Damper for Rotor Applications

Abstract: Even though we are still far from industrial applications, in the last decade there has been increasing attention directed toward the employment of electrorheological (ER) and magnetorheological (MR) fluids in active bearings and active squeeze film dampers in rotordynamics. MR fluids react to magnetic fields undergoing reversible changes in their mechanical characteristics, viscosity, and stiffness in particular. In previous literature, some applications of ER fluids in rotor squeeze film dampers can be found; however, on the contrary, little is reported on similar test rigs set up for MR dampers. In this work, the design of an MR squeeze film damper is presented and discussed. A numerical simulation has been carried out in order to evaluate the dynamic behavior of the damped rotor as a function of the magnetic field strength. The test rig is made of a slender shaft supported by two oilite bearings and an unbalanced disk. The damper is interfaced with the shaft through a rolling bearing. Electric coils generate the magnetic field whose field lines cross the MR film. Since the damping characteristics can be varied continuously by controlling the magnetic field, it is possible to have the optimum conditions for each regime of rotational speed. Preliminary tests are encouraging.

Study on the mechanism of the squeeze-strengthen effect in magnetorheological fluids

Abstract: Current magnetorheological (MR) fluids have the limitation that their yield stresses are not strong enough to meet some industrial requirements. X. Tang, X. Zhang, and R. Tao [J. App. Phys 87, 2634 (2000)] proposed a method to achieve high-efficiency MR fluids by study of squeeze-strengthen effect. But there is little report on its mechanism. This paper aims to investigate this effect through experimental and theoretical approaches. For this purpose, an apparatus is designed to experimentally study the mechanism of this squeeze-strengthen effect. Taking account of a modified magnetic dipole model and the friction effect, a semiempirical model is proposed to explain this effect. In addition, this model is expected to study the squeeze-strengthen effect in electrorheological fluids.

Series damper actuator: a novel force/torque control actuator

Abstract: A novel force/torque control actuator called series damper actuator (SDA) is proposed, modeled and analyzed Compared to conventional force/torque control schemes and series elastic actuator (SEA), SDA has good output force/torque fidelity, low output impedance and large force/torque range Furthermore, varying damping coefficient endows the SDA with more advantages and makes the system more versatile An experimental SDA system is developed, in which a magnetorheological (MR) fluid damper is employed as the series damper The experimental results show that SDA system is an effective force/torque control actuator

State-of-the-art of semiactive control systems using MR fluid dampers in civil engineering applications

Abstract: Semiactive control systems have received considerable attention for protecting structures against natural hazards such as strong earthquakes and high winds, because they not only offer the reliability of passive control systems but also maintain the versatility and adaptability of fully active control systems. Among the many semiactive control devices, magnetorheological (MR) fluid dampers comprise one particularly promising class. In the field of civil engineering, much research and development on MR fluid damper-based control systems has been conducted since this unique semiactive device was first introduced to civil engineering applications in mid 1990s. In 2001, MR fluid dampers were applied to the full-scale in-service civil engineering structures for the first time. This state-of-the-art paper includes a detailed literature review of dynamic models of MR fluid dampers for describing their complex dynamic behavior and control algorithms considering the characteristics of MR fluid dampers. This extensive review provides references to semiactive control systems using MR fluid dampers. The MR fluid damper-based semiactive control systems are shown to have the potential for mitigating the responses of full-scale civil engineering structures under natural hazards.

Shear flow behavior of confined magnetorheological fluids at low magnetic field strengths

Abstract: The non-linear properties of iron based magneto-rheological (MR) fluids are investigated at low magnetic field strengths (0–1.7 kA/m) and different gap thickness (0–500 μm) in a plate-plate configuration. Single-width chain models qualitatively predict the low-shear flow behavior when plotting the field-specific viscosity, ηF, as a function of the Mason number, Mn: a slope close to −1 is observed in log-log representations. Wall depletion effects are observed when the suspensions are sheared under the presence of low external magnetic fields applied and/or large gap distances. These results are correlated to frictional yield stress measurements and chain length distribution calculations in the presence of the external magnetic field. Finally, an equivalent slip layer thickness is calculated using the method of Yoshimura and Prud’homme.

Surface Finishing and Evaluation of Three-Dimensional Silicon Microchannel Using Magnetorheological Fluid

Abstract: A surface-finishing method for three-dimensional microchannel structures is proposed. The method utilizes magnetorheological fluid mixed with abrasives as a polishing tool. The influences of the process parameters on the material removal were investigated, and the surface topographies before and after finishing were compared. When a microchannel was finished by proposed method, the roughness of bottom and side surfaces of the silicon channel was reduced by a factor of 5-10, and the pressure drop of a gas flow through the single microchannel was lowered to 26.7% of the pressure drop in an unfinished microchannel. The experimental results demonstrated that the proposed method was effective in finishing of microstructures.

Biviscous damping behavior in electrorheological shock absorbers

Abstract: Electrorheological (ER) and magnetorheological flow mode dampers can exhibit biviscous damping behavior. Such behavior is characterized by a high damping pre-yield region for low velocities, with a transition to a relatively lower post-yield damping, once the damper force exceeds the static yield force of the damper. The biviscous damping behavior is typically the result of leakage, that is, a second path of Newtonian flow in addition to the Bingham plastic flow through the ER or MR valve. We experimentally demonstrate such bilinear damping behavior in a monotube ER shock absorber. Leakage is typically introduced to smooth the force response of the damper as the damper undergoes transitions through the low velocity. The ER fluid is typically assumed to behave as a Bingham plastic fluid. Thus, two perspectives are examined for modeling damping performance of the ER monotube shock absorber. First, the quasisteady Bingham plastic analysis is coupled with a mechanical analysis of the leakage effects. Second, a biviscous constitutive perspective is described that allows the leakage effects to be described as an apparent pre-yield viscosity of the ER fluid. Both perspectives prove to be useful in describing damping performance of the ER monotube shock absorber.

A unified modelling and model updating procedure for electrorheological and magnetorheological vibration dampers

Abstract: Magnetorheological (MR) and electrorheological (ER) dampers are known to exhibit nonlinear behaviour which can make it difficult to predict their performance, particularly when they are integrated into engineering structures. As a result it can be impossible to properly assess the feasibility of using such semi-active devices to solve practical engineering problems. In this paper, a new model format is proposed which represents an extension of earlier work by the authors. The proposed model is more general and yet maintains the physical significance of key parameters. A novel model updating (or system identification) technique is developed so that the model can account for the behaviour of various configurations of device without the need for prior knowledge of the fluid properties. The technique relies upon the iterative adjustment of the model's stiffness parameter so that the quasi-steady behaviour of the device can be estimated. Correlation between a bi-viscous model and the estimated quasi-steady behaviour is used as the criterion for choosing the most suitable value of stiffness. The modelling technique is completed by establishing empirical shape relationships between the pre-yield parameters, post-yield parameters, yield force and the applied excitation conditions. The modelling and identification procedures are applied to an MR damping device and the results are validated by comparing predicted and experimental responses under both non-sinusoidal and broadband excitation conditions.

Development and characterization of hydrocarbon polyol polyurethane and silicone magnetorheological polymeric gels

Abstract: Magnetorheological polymeric gels (MRPG) have been developed for use in semi-active magnetorheological fluid (MRF) dampers and other magnetorheological (MR) devices The novel MRPGs are prepared by suspending iron particles in polymeric gels Off-state (ie, no applied magnetic field) viscosity and settling behavior can be controlled through the selection of polymeric gels In this study, tunable rheological properties were investigated with a piston-driven flow type rheometer with a shear rate varying from 20 s−1 to 6,000 s−1 Silicone MRPG (with 845 wt % iron particles) has controllable viscosity and a high shear yield stress over a wide range of shear rates Silicone MRPG (795 wt % iron particles) has the lowest viscosity of those studied Polyurethane MRPG has the lowest settling rate The order of addition of magnetic particles and polymer during the polymerization process affects the MRPG final off-state apparent viscosity (80% increase in apparent viscosity for silicone MRPG polymerized after adding iron particles) This indicates that polymer gels modify the surface properties of the magnetic particles, causing interaction among particles The dynamic shear yield stress is higher for fluids with better dispersion stability Polyurethane MRPG, which has the lowest settling rate, has a high dynamic yield stress (23 kPa at 350 mT) Both dynamic and static shear stress values of the MRPGs were found to be similar in magnitude (5–8 kPa at 120 mT for silicone MRPG with 845 wt % iron particles and polyurethane MRPG), indicating that MRPGs can provide consistent performance in devices © 2004 Wiley Periodicals, Inc J Appl Polym Sci 92: 1176–1182, 2004

Investigations of a magnetorheological fluid damper

Abstract: This paper presents the results of a study of a magnetorheological fluid (MRF) damper. The principle could be used for such applications as seismic protectors for civil structure (where the dimensions are chosen to handle the greatest forces) or shock absorbers for the automotive industry (where the dimensions are chosen to accommodate heating effects). We describe the preparation method and some characteristics of the MRF, the experimental method (we used a hydraulic linear motor and pressure measurements), and the main experimental results. The external force required to move the damper increases several times when the magnetic field is applied.

Shear-Mode Rotary Magnetorheological Damper for Small-Scale Structural Control Experiments

Abstract: In an attempt to validate the effectiveness of a magnetorheological (MR) damper in controlling the wind-induced response of a building model in a wind tunnel, it is necessary to have a damper which produces a range of small forces so that it can be used to control the light-weight building model. In this study, a small-scale rotary type of MR damper is designed, manufactured, and tested. The damper uses shear-mode behavior of the MR fluids and is designed based on the simple Bingham viscoplastic model. A prototype damper that can produce forces in the order of a few newtons is made and tested in the laboratory. It is found that the Bouc-Wen model, which has been used to emulate linear valve-mode MR dampers, can also portray the hysteretic behavior of the shear-mode rotary damper. A simplified yet relatively accurate inverse dynamic model that can directly relate the damper force to the input voltage is proposed. Experiments demonstrate that a MR damper using this inverse model can closely reproduce prescribed forces. This inverse model provides an alternative means of commanding the MR damper for control applications.

Dynamic behavior of MR suspensions at moderate flux densities

Abstract: In many proposed applications, magnetorheological (MR) fluids are subjected to a dynamic stimulus with finite deformation. Dynamic behavior of reduced iron based MR suspensions under oscillatory shear is experimentally investigated using a parallel-plate rheometer. The effects of strain amplitude, oscillation frequency, and magnetic field strength on the dynamic behavior are studied. MR fluids behave as linear viscoelastic materials for only sufficiently small strain amplitudes. At large strain amplitudes, MR fluids are nonlinear viscoelastic or viscoplastic, where the storage modulus shows a decreasing trend with the strain amplitude. At large enough strain rate amplitudes, the yield stress contribution is negligible and the suspension response is Newtonian. The dependence of the dynamic behavior on the strain amplitude and oscillation frequency is qualitatively summarized in the form of a Pipkin diagram.

Development of Large Capacity Semi-Active Seismic Damper Using Magneto-Rheological Fluid

Abstract: In recent years, there has been increasing research in several industrial fields for development of semi-active vibration control devices. In particular, devices using magneto-rheological (MR) fluid have been attracting great research interest because they can realize high performance as capacity-variable dampers. MR fluids are controllable fluids that respond to applied magnetic fields. Applied magnetic fields drastically change the viscosity ofMR fluids from an oily state to a semi-solid state. This paper describes a study on a large capacity device using an MR fluid, i.e., an MR damper This developed MR damper provides a maximum damping force of 300 kN. Various tests were carried out and the dynamic characteristics, force-displacement hysteresis loops and controllable forces were investigated. These tests verified that the MR damper provides a technology that enables effective semi-active control of large-scale structure systems, i.e., real buildings and civil engineering structures.