Showing papers on "Magnetorheological fluid published in 2011"

Magnetorheological fluids: a review

Abstract: Magnetorheological (MR) materials are a kind of smart materials whose mechanical properties can be altered in a controlled fashion by an external magnetic field. They traditionally include fluids, elastomers and foams. In this review paper we revisit the most outstanding advances on the rheological performance of MR fluids. Special emphasis is paid to the understanding of their yielding, flow and viscoelastic behaviour under shearing flows.

Magnetorheological fluid dampers: a review of parametric modelling

Abstract: Due to the inherent nonlinear nature of magnetorheological (MR) dampers, one of the challenging aspects for developing and utilizing these devices to achieve high performance is the development of models that can accurately describe their unique characteristics. In this review, the characteristics of MR dampers are summarized according to the measured responses under different conditions. On these bases, the considerations and methods of the parametric dynamic modelling for MR dampers are given and the state-of-the-art parametric dynamic modelling, identification and validation techniques for MR dampers are reviewed. In the past two decades, the models for MR dampers have been focused on how to improve the modelling accuracy. Although the force–displacement behaviour is well represented by most of the proposed dynamic models for MR dampers, no simple parametric models with high accuracy for MR dampers can be found. In addition, the parametric dynamic models for MR dampers with on-line updating ability and the inverse parametric models for MR dampers are scarcely explored. Moreover, whether one dynamic model for MR dampers can portray the force–displacement and force–velocity behaviour is not only determined by the dynamic model itself but also determined by the identification method.

Homogenization-based constitutive models for magnetorheological elastomers at finite strain

Abstract: This paper proposes a new homogenization framework for magnetoelastic composites accounting for the effect of magnetic dipole interactions, as well as finite strains. In addition, it provides an application for magnetorheological elastomers via a “partial decoupling” approximation splitting the magnetoelastic energy into a purely mechanical component, together with a magnetostatic component evaluated in the deformed configuration of the composite, as estimated by means of the purely mechanical solution of the problem. It is argued that the resulting constitutive model for the material, which can account for the initial volume fraction, average shape, orientation and distribution of the magnetically anisotropic, non-spherical particles, should be quite accurate at least for perfectly aligned magnetic and mechanical loadings. The theory predicts the existence of certain “extra” stresses—arising in the composite beyond the purely mechanical and magnetic (Maxwell) stresses—which can be directly linked to deformation-induced changes in the microstructure. For the special case of isotropic distributions of magnetically isotropic, spherical particles, the extra stresses are due to changes in the particle two-point distribution function with the deformation, and are of order volume fraction squared, while the corresponding extra stresses for the case of aligned, ellipsoidal particles can be of order volume fraction, when changes are induced by the deformation in the orientation of the particles. The theory is capable of handling the strongly nonlinear effects associated with finite strains and magnetic saturation of the particles at sufficiently high deformations and magnetic fields, respectively.

A high-performance magnetorheological material: preparation, characterization and magnetic-mechanic coupling properties

Abstract: A novel high-performance magnetorheological material, named as magnetorheological plastomer (MRP), was developed by dispersing iron particles into a plastic polyurethane (PU) matrix. The dynamic properties (including storage modulus and loss factor) of the MRP material were systematically tested and the influences of the iron particle content and magnetic field were analyzed. It is found that the anisotropic MRP product with 80% iron particle weight fraction (A-MRP-80), shows a high dynamic property: the maximum magneto-induced storage modulus is 6.54 MPa; the relative MR effect reaches as high as 532%; the loss factor can be reduced to 0.03 by adjusting magnetic field. This kind of MRP shows a much higher magnetorheological performance than the previously reported magnetorhelogical elastomer (MRE). The mechanism for its high MR performance was proposed and the influence of the iron particle distribution and temperature on the dynamic properties were discussed.

Core-shell structured carbonyl iron microspheres prepared via dual-step functionality coatings and their magnetorheological response.

Abstract: The dispersion stability of soft magnetic carbonyl iron (CI)-based magnetorheological (MR) fluids was improved by applying a unique functional coating composed of a conducting polyaniline layer and a multiwalled carbon nanotube nest to the surfaces of the CI particles via conventional dispersion polymerization, followed by facile solvent casting. The coating morphology and thickness were analyzed by SEM and TEM imaging. Chemical composition of the polyaniline layer was detected by Raman spectroscope, which also confirmed the coating performance successfully. The influence of the functional coating on the magnetic properties was investigated by measuring the MR performance and sedimentation properties using a vibrating sample magnetometer, rotational rheometer, and Turbiscan apparatus. Improved dispersion characteristics of the MR fluid were observed.

Material removal in magnetorheological finishing of optics

Abstract: A concept of material removal based on the principle of conservation of particles momentum in a binary suspension is applied to analyze material removal in magnetorheological finishing and magnetorheological 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 (magnetic) particles, which fluctuate (due to collision) in the shear flow of concentrated suspension. The model is in good qualitative and quantitative agreement with experimental results.

Magnetomechanical properties of anisotropic and isotropic magnetorheological composites with thermoplastic elastomer matrices

Abstract: In this paper the magnetomechanical properties of magnetorheological (MR) elastomers with isotropic and anisotropic structure are examined A method for manufacturing magnetorheological elastomers (MRE) with thermoplastic elastomer matrix and 60 µm iron particles is presented The influence of various chemical compositions on the material parameters is investigated The properties of isotropic and anisotropic MR elastomers are examined in a wide range of mechanical and magnetic stimulations Test samples are subjected to cyclic shearing with a constant frequency of 1 Hz The change in magnetomechanical properties is expressed by the relative change of hysteresis loop area δW and stress amplitude δτ

A rheological model of the dynamic behavior of magnetorheological elastomers

Abstract: A rheological model is described that was developed to simulate the dynamic behavior of magnetorheological elastomers (MREs). The viscoelasticity of the polymer composite, magnetic field-induced properties and interfacial slippage between the matrix and particles were modeled by analogy with a standard linear solid model, a stiffness variable spring, and a spring-Coulomb friction slider, respectively. The loading history and rate dependent constitutive relationships for MREs were derived from the rheological model. The hysteresis loop from shear strain-shear stress plots, which determines the shear modulus and loss factor, were obtained from substituting cyclic loading into these constitutive relationships. The dynamic behavior of MREs was simulated by changing parameters in the rheological model to influence MREs’ performance. The simulation results verified the effectiveness of the model.

Experimental investigations into forces during magnetorheological fluid based finishing process

Abstract: Magnetorheological fluid based finishing process is a fine finishing process that has been applied to a large variety of brittle materials, ranging from optical glasses to hard crystals. Under the influence of a magnetic field, the carbonyl iron particles (CIPs) and non-magnetic polishing abrasive particles remove material from the surface being polished. Knowledge of forces acting is important to understand the mechanism of material removal. A dynamometer and virtual instrumentation are used to on-line record the normal force and tangential force acting on the workpiece through the magnetorheological (MR) fluid. A full factorial design of experiments is used to plan the experiments and ANOVA to correlate the forces and process parameters. The selected process parameters (volume concentration of CIPs and abrasives, working gap, and wheel rotation) are varied over a range to measure forces during experimentation. The maximum contribution is made by a working gap on the forces developed on the workpiece surface followed by CIP concentration while the least contribution is noticed by the wheel speed.

Experimental investigation of the vibration characteristics of a magnetorheological elastomer sandwich beam under non-homogeneous small magnetic fields

Abstract: In this study, a magnetorheological elastomer (MRE) was manufactured and tested, and a MRE sandwich beam was also fabricated from a MRE between two thin aluminum layers An experimental test rig was set up to investigate the vibration response of the MRE sandwich beam under a non-homogeneous magnetic field The experimental results show that the first natural frequency of the MRE sandwich beam decreased as the magnetic field applied to the beam was moved from the clamped end of the beam to the free end of the beam It is also noted that the MRE sandwich beam had the capability to left shift the first natural frequency when the magnetic field was increased in the activated regions

An adaptive tuned mass damper based on the emulation of positive and negative stiffness with an MR damper

Abstract: This paper presents a new adaptive tuned mass damper (TMD) whose stiffness and damping can be tuned in real-time to changing frequencies of a target structure. The adaptive TMD consists of a tuned mass, a tuned passive spring and a magnetorheological (MR) damper. The MR damper is used to emulate controlled friction?viscous damping and controlled stiffness. The controlled positive or negative stiffness emulated by the MR damper works in parallel to the stiffness of the passive TMD spring. The resulting overall TMD stiffness can therefore be varied around the passive spring stiffness using the MR damper. Both the emulated stiffness and friction?viscous damping in the MR damper are controlled such that the resulting overall TMD stiffness and damping are adjusted according to Den Hartog's formulae. Simulations demonstrate that the adaptive TMD with a controlled MR damper provides the same reduction of steady state vibration amplitudes in the target structure as a passive TMD if the target structure vibrates at the nominal frequency. However, if the target structure vibrates at different frequencies, e.g.?due to changed service loads, the adaptive TMD with a controlled MR damper outperforms the passive TMD by up to several 100% depending on the frequency change.

Magnetorheological transmission device

Abstract: The invention relates to a magnetorheological transmission device and to a method for influencing the coupling intensity of two components that can be coupled and the coupling intensity of which can be influenced. In order to influence the coupling intensity, a channel is provided, which contains a magnetorheological medium that can be influenced by a magnetic field and that has particles that can be magnetically polarized. A magnetic-field generating apparatus is provided in order to generate a magnetic field in the channel in order to influence the magnetorheological medium in the channel by means of the magnetic field. A rotary body is provided in the channel. A free distance between the rotary body and the component is at least ten times as large as a typical average diameter of the particles that can be magnetically polarized in the magnetorheological medium. An acute-angled region containing the magnetorheological medium is provided between the rotary body and a component. The magnetic field of the magnetic-field generating apparatus can be applied to said region in order to optionally link the particles into chains and/or to wedge the particles with the rotary body or to release the particles.

Sensing capabilities of graphite based MR elastomers

Abstract: This paper presents both experimental and theoretical investigations of the sensing capabilities of graphite based magnetorheological elastomers (MREs). In this study, eight MRE samples with varying graphite weight fractions were fabricated and their resistance under different magnetic fields and external loadings were measured with a multi-meter. With an increment of graphite weight fraction, the resistance of MRE sample decreases steadily. Higher magnetic fields result in a resistance increase. Based on an ideal assumption of a perfect chain structure, a mathematical model was developed to investigate the relationship between the MRE resistance with external loading. In this model, the current flowing through the chain structure consists of both a tunnel current and a conductivity current, both of which depend on external loadings. The modelling parameters have been identified and reconstructed from comparison with experimental results. The comparison indicates that both experimental results and modelling predictions agree favourably well.

Modeling of a magnetorheological damper by recursive lazy learning

Abstract: Nowadays dampers based on magnetorheological (MR) fluids are receiving significant attention specially for control of structural vibration and automotive suspensions systems. In most cases, it is necessary to develop an appropriate control strategy which is practically implementable when a suitable model for MR dampers is available. It is not a trivial task to model the dynamic of MR dampers because of their inherent non-linear and hysteretic dynamics. In this paper, a recursive lazy learning method based on neural networks is considered to model the MR damper behavior. The proposed method is validated by comparison with experimental obtained responses. Results show the estimated model correlates very well with the data obtained experimentally. The method proposed learns quickly that it is only necessarily a learning cycle, it can learn on-line and it is easy to select the network structure and calculate the model parameters.

Core–shell-structured silica-coated magnetic carbonyl iron microbead and its magnetorheology with anti-acidic characteristics

Abstract: We synthesized silica-coated soft magnetic carbonyl iron (CI) particles through a modified Stober method, in which the CI particles were pretreated with a grafting agent to enhance the affinity of a precursor of silica. Synthesized magnetic microbeads were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and anti-acid test in HCl solution. Silica-coated CI shows not only improved wettability to silicone oil with a lower off-state shear viscosity as a better magnetorheological fluid under an applied magnetic field but also enhanced anti-acidic property.

Interfacial friction damping properties in magnetorheological elastomers

Abstract: In this study, the interfacial friction damping properties of magnetorheological elastomers (MREs) were investigated experimentally. Two kinds of carbonyl iron particles, with sizes of 1.1 µm and 9.0 µm, were used to fabricate four MRE samples, whose particle weight fractions were 10%, 30%, 60% and 80%, respectively. Their microstructures were observed using an environmental scanning electron microscope (SEM). The dynamic performances of these samples, including shear storage modulus and loss factor were measured with a modified dynamic mechanical analyzer (DMA). The experimental results indicate that MRE samples fabricated with 1.1 µm carbonyl iron particles have obvious particle agglomeration, which results in the fluctuation of loss factor compared with other MRE samples fabricated with large particle sizes. The analysis implies that the interfacial friction damping mainly comes from the frictional sliding at the interfaces between the free rubber and the particles.

Temperature-Dependent Mechanical Properties and Model of Magnetorheological Elastomers

Abstract: Magnetorheological elastomers (MREs) are composed of magnetizable particles (iron particles) and a soft rubberlike matrix. Their mechanical properties, including modulus and damping capability, dep...

Analysis and Experimental Study of Magnetorheological-Based Damper for Semiactive Suspension System Using Fuzzy Hybrids

Abstract: In this paper, the development and implementation of a novel semiactive suspension control of a quarter-car model using a hybrid-fuzzy-logic-based controller have been done. The proposed quarter-car model can be described as a nonlinear two-degree-of-freedom system, which is subject to system disturbances from different road profiles. In order to implement the suspension system experimentally, the magnetorheological (MR) fluid has been used as an adjustable damper. The MR damper is a control device that consists of a hydraulic cylinder filled with magnetically polarizable particles suspended in a liquid. The MR damper rapidly dissipates vibration by absorbing energy. In this paper, proportional-integral-derivative (PID), fuzzy logic, and hybrid controllers are used to control the semiactive car suspension system. The results show that both fuzzy logic and hybrid controllers are quite suitable to eliminate road disturbances for the semiactive suspension system considerably as compared to the conventional PID controller.

Experimental study of a self-powered and sensing MR-damper-based vibration control system

Abstract: The paper deals with a semi-active vibration control system based on a magnetorheological (MR) damper. The study outlines the model and the structure of the system, and describes its experimental investigation. The conceptual design of this system involves harvesting energy from structural vibrations using an energy extractor based on an electromagnetic transduction mechanism (Faraday's law). The system consists of an electromagnetic induction device (EMI) prototype and an MR damper of RD-1005 series manufactured by Lord Corporation. The energy extracted is applied to control the damping characteristics of the MR damper. The model of the system was used to prove that the proposed vibration control system is feasible. The system was realized in the semi-active control strategy with energy recovery and examined through experiments in the cases where the control coil of the MR damper was voltage-supplied directly from the EMI or voltage-supplied via the rectifier, or supplied with a current control system with two feedback loops. The external loop used the sky-hook algorithm whilst the internal loop used the algorithm switching the photorelay, at the output from the rectifier. Experimental results of the proposed vibration control system were compared with those obtained for the passive system (MR damper is off-state) and for the system with an external power source (conventional system) when the control coil of the MR damper was supplied by a DC power supply and analogue voltage amplifier or a DC power supply and a photorelay. It was demonstrated that the system is able to power-supply the MR damper and can adjust itself to structural vibrations. It was also found that, since the signal of induced voltage from the EMI agrees well with that of the relative velocity signal across the damper, the device can act as a 'velocity-sign' sensor.

Squeeze flow magnetorheology

Abstract: This paper is concerned with an investigation of the rheological performance of magnetorheological fluids under squeeze flow. Preliminary results on Newtonian fluids are first compared to Stefan’s equation. Then, unidirectional monotonic compression tests are carried out in the presence of uniaxial external magnetic fields at slow compression rates under constant volume operation. Results are compared to Bingham plastic, biviscous, and single chain micromechanical squeeze flow models. Measurements using combined deformation modes (compression+small-strain oscillatory shear) suggest a compression-induced shear strengthen effect up to strains of ∼0.5. Particle-level dynamic simulations are in qualitatively good agreement with experimental observations.

Magnetorheology: Materials and Application

Abstract: As one of the most important field-responsive intelligent and smart soft matter materials, magnetorheological (MR) fluids, consisting of magneto-responsive magnetizable particles suspended in non-magnetic fluids, have drawn a lot of attentions in both academia and industry as their physical and rheological characteristics can be controlled with external magnetic field strength. In this highlight, preparation methods and MR properties of various magnetic composites with soft magnetic particles and polymers are reviewed. In addition, some industrial applications, such as a MR dampers and a MR polishing, are briefly summarized.

Investigating new symmetry classes in magnetorheological elastomers: cantilever bending behavior

Abstract: This work defines and examines four classes of magnetorheological elastomers (MREs) based upon permutations of particle alignment‐magnetization pairs. Particle alignments may either be unaligned (e.g. random) or aligned. Particle magnetizations may either be soft-magnetic or hard-magnetic. Together, these designations yield four material types: A‐S, U‐S, A‐H, and U‐H. Traditional MREs comprise only the A‐S and U‐S classes. Samples made from 325-mesh iron and 40 μm barium hexaferrite powders cured with or without the presence of a magnetic field served as proxies for the four classes. Cantilever bending actuating tests measuring the magnetically-induced restoring force at the cantilever tip on 50 mm × 20 mm × 5 mm samples yielded ∼350 mN at μ0 H = 0.09 T for classes A‐H, A‐S, and U‐S while class U‐H showed only ∼40 mN. Furthermore, while classes U‐S and A‐S exerted forces proportional to tip deflection, they exerted no force in the undeformed state whereas class A‐H exerted a relatively constant tip force over its entire range of deformation. Beam theory calculations and models with elastic strain energy density coupled with demagnetizing effects in the magnetic energy density were used to ascertain the magnitude of the internal bending moment in the cantilever and to predict material response with good results. This work highlights the ability of the newly developed A‐H MRE materials, and only that material class, to operate as remotely powered bidirectional actuators. (Some figures in this article are in colour only in the electronic version)

Seismic Performance Analysis of A Smart Base-isolation System Considering Dynamics of MR Elastomers

Abstract: This article investigates a smart base-isolation system using magnetorheological (MR) elastomers, which are a new class of smart materials whose elastic modulus or stiffness can be adjusted dependi...

Soft magnetic carbonyl iron microsphere dispersed in grease and its rheological characteristics under magnetic field

Abstract: Magnetorheological (MR) grease, comprised of a suspension of soft magnetic carbonyl iron (CI) microspherical particles dispersed in a grease medium, was fabricated by a mechanical stirring method. As potential medium oil for MR system, shear viscosity of the pure grease was measured as a function of temperature. Its MR characteristics were investigated using a rotational rheometer under an external magnetic field. Flow curve responses (shear stress and shear viscosity), yield stress, and elasticity were investigated using various magnetic field strengths ranging from 0 to 342 kA/m. It was confirmed that MR grease has a yield stress under no external magnetic field due to the inherent property of grease. In addition, CI based MR grease exhibited a characteristic of a Bingham fluid.