Showing papers on "Magnetorheological fluid published in 2010"

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.

Generality of shear thickening in dense suspensions

Abstract: Suspensions are of wide interest and form the basis for many smart fluids. For most suspensions, the viscosity decreases with increasing shear rate, that is, they shear thin. Few are reported to do the opposite, that is, shear thicken, despite the longstanding expectation that shear thickening is a generic type of suspension behaviour. Here we resolve this apparent contradiction. We demonstrate that shear thickening can be masked by a yield stress and can be recovered when the yield stress is decreased below a threshold. We show the generality of this argument and quantify the threshold in rheology experiments where we control yield stresses arising from a variety of sources, such as attractions from particle surface interactions, induced dipoles from applied electric and magnetic fields, as well as confinement of hard particles at high packing fractions. These findings open up possibilities for the design of smart suspensions that combine shear thickening with electro- or magnetorheological response.

New Composite Elastomers with Giant Magnetic Response

Abstract: Novel magnetorheological elastomers (MRE) based on a highly elastic silicone rubber filled with carbonyl iron magnetic particles of 3―5 and 3―50 μm are synthesized. The effect of an external homogeneous magnetic field on the viscoelastic properties of these materials is studied by dynamic experiments (shear oscillations on a rheometer). It is shown that the magnetic response of the MRE increases with a decrease of the strain. At 1% deformation both the storage and loss moduli of the new MRE demonstrate a giant response to the magnetic field, namely, an increase of more than two orders of magnitude in both moduli in a field of 300 mT is observed. In addition, these new MREs show a twofold increase of the damping ratio, which is important for their application as tunable vibration absorbers.

Tunable elastic stiffness with microconfined magnetorheological domains at low magnetic field

Abstract: Surface micropatterning enhances the interfacial sliding resistance of magnetorheological fluid at low magnetic field (10–35 mT). Fluid is confined to surface microchannels, resulting in the formation of spatially aligned magnetic domains. The channels are supported by a pair of overlapping ribbons, which, along with the surrounding fluid, are enclosed in a soft elastomer. The embedded elastomer represents an electromagnetic alternative to current methods of active stiffness control that are based on principles of gel hydration, particle jamming, and pneumatics.

Effect of particle shape in magnetorheology

Abstract: Magnetorheological (MR) properties were investigated for sphere, plate, and rod-like iron particles in suspension under the presence of magnetic fields to ascertain the effect of particle shape in MR performance. A novel two-step synthesis route for micrometer sized iron particles with different morphologies is described in detail. Small-amplitude dynamic oscillatory and steady shear flow measurements were carried out in the presence of external magnetic fields. Finite element method calculations were performed to explain the effect of particle shape in the magnetic field-induced yield stress. Compared to their sphere and plate counterparts, rod-like particle based MR fluids present a larger storage modulus and yield stress. The effect of particle shape is found to be negligible at large particle content and/or magnetic field strengths.

Optimal design of an automotive magnetorheological brake considering geometric dimensions and zero-field friction heat

Abstract: This paper presents an optimal design of a magnetorheological (MR) brake for a middle-sized passenger car which can replace a conventional hydraulic disc-type brake. In the optimization, the required braking torque, the temperature due to zero-field friction of MR fluid, the mass of the brake system and all significant geometric dimensions are considered. After describing the configuration, the braking torque of the proposed MR brake is derived on the basis of the field-dependent Bingham and Herschel–Bulkley rheological model of the MR fluid. The optimal design of the MR brake is then analyzed taking into account available space, mass, braking torque and steady heat generated by zero-field friction torque of the MR brake. The optimization procedure based on the finite element analysis integrated with an optimization tool is proposed to obtain optimal geometric dimensions of the MR brake. Based on the proposed procedure, optimal solutions of single and multiple disc-type MR brakes featuring different types of MR fluid are achieved. From the results, the most effective MR brake for the middle-sized passenger car is identified and some discussions on the performance improvement of the optimized MR brake are described.

Vibration analysis of a multi-layer beam containing magnetorheological fluid

Abstract: Magnetorheological (MR) materials exhibit rapid variations in their rheological properties when subjected to varying magnetic field and thus offer superior potential for applications in smart structures requiring high bandwidth. MR sandwich structures can apply distributed control force to yield variations in stiffness and damping properties of the structure in response to the intensity of the applied magnetic field and could thus provide vibration suppression over a broad range of external excitation frequencies. This study investigates the properties of a multi-layered beam with MR fluid as a sandwich layer between the two layers of the continuous elastic structure. The governing equations of a multi-layer MR beam are formulated in the finite element form and using the Ritz method. A free oscillation experiment is performed to estimate the relationship between the magnetic field and the complex shear modulus of the MR materials in the pre-yield regime. The validity of the finite element and Ritz formulations developed is examined by comparing the results from the two models with those from the experimental investigation. Various parametric studies have been performed in terms of variations of the natural frequencies and loss factor as functions of the applied magnetic field and thickness of the MR fluid layer for various boundary conditions. The forced vibration responses of the MR sandwich beam are also evaluated under harmonic force excitation. The results illustrate that the natural frequencies could be increased by increasing the magnetic field while the magnitudes of the peak deflections could be considerably decreased, which demonstrates the vibration suppression capability of the MR sandwich beam.

Vibration characteristics of MR cantilever sandwich beams: experimental study

Abstract: The concept of vibration controllability with smart fluids within flexible structures has been of significant interest in the past two decades. Although much research has been done on structures with embedded electrorheological (ER) fluids, there has been little investigation of magnetorheological (MR) fluid adaptive structures. In particular, a body of research on the experimental work of cantilever MR beams is still lacking. This experimental study investigates the controllability of vibration characteristics of magnetorheological cantilever sandwich beams. These adaptive structures are produced by embedding an MR fluid core between two elastic layers. The structural behaviour of the MR beams can be varied by applying an external magnetic field to activate the MR fluid. The stiffness and damping structural characteristics are controlled, demonstrating vibration suppression capabilities of MR fluids as structural elements. MR beams were fabricated with two different materials for comparison purposes. Diverse excitation methods were considered as well as a range of magnetic field intensities and configurations. Moreover, the cantilever MR beams were tested in horizontal and vertical configurations. The effects of partial and full activation of the MR beams were outlined based on the results obtained. The controllability of the beam's vibration response was observed in the form of variations in vibration amplitudes and shifts in magnitudes of the resonant natural frequency.

A geometrical optimization of a magneto-rheological rotary brake in a prosthetic knee

Abstract: Magneto-rheological (MR) fluids have been successfully introduced to prosthetic devices. One such device is a biomechanical prosthetic knee that uses MR fluids to actively control its rotary stiffness. The brake is rotational, utilizing the MR fluid in shear mode. In this study, the geometrical design of the MR brake is addressed. This includes the design of the magnetic circuit and the geometry of the fluid chamber. Mathematical models are presented that describe the rotary torque of the brake. A novel perfluorinated polyether (PFPE)-based MR fluid is introduced, whose properties are tailored for the prosthetic knee. On-state and off-state rheological measurements of the MR fluid are presented. The finite element method is used to evaluate the magnetic flux density in the MR fluid. The design is formulated as an optimization problem, aiming to maximize the braking torque. A parametric study is carried out for several design parameters. Subsequently, a multi-objective optimization problem is defined that considers three design objectives: the field-induced braking torque, the off-state rotary stiffness and the weight of the brake. Trade-offs between the three design objectives are investigated which provides a basis for informed design decisions on furthering the success of the MR prosthetic knee.

MRE properties under shear and squeeze modes and applications

Abstract: Magnetorheological elastomers (MREs) are smart materials whose mechanical properties, like their modulus and elasticity, can be controlled by an external magnetic field. This feature has resulted in a number of novel applications, such as adaptive tuned dynamic vibration absorbers for suppressing unwanted vibrations over a wide frequency range. MRE-based devices operate in different modes, such as shear mode and squeeze mode; however, the study of mechanical performances of MREs under squeeze mode is very rare. This article aims to investigate MRE performances under both shear and squeeze modes. Experimental studies and simulations were conducted to analyze the MR effect in both modes. These studies indicate a different working frequency ranges for both modes. In a case study, a MRE-based vibration absorber was built up in a simulation and its mechanical performances were analyzed, which demonstrated good capabilities in reducing vibrations.

A study of the magnetorheological effect of bimodal particle based magnetorheological elastomers

Abstract: This paper presents theoretical and experimental studies of the mechanical performance and magnetorheological effects of magnetorheological elastomers (MREs) fabricated with mixtures of large and small particles. First of all, an effective permeability model was developed to theoretically analyze the MR effect of bimodal particle based MR elastomers. From the theoretical analysis, an optimum volume fraction was derived which resulted in enhanced MR effects. Two categories of iron products with different particle sizes of 50 and 5? ?m were used to fabricate a series of bimodal MRE samples. Their mechanical performances were characterized by using an MR rheometer. Experimental results agreed fairly well with theoretical analysis. The theoretical prediction of the optimum mixture ratio between large and small size particles was experimentally verified.

Rheological properties of magnetorheological suspensions based on core–shell structured polyaniline-coated carbonyl iron particles

Abstract: The sedimentation caused by the high density of suspended particles used in magnetorheological fluids is a significant obstacle for their wider application. In the present paper, core–shell structured carbonyl iron–polyaniline particles in silicone oil were used as a magnetorheological suspension with enhanced dispersion stability. Bare carbonyl iron particles were suspended in silicone oil to create model magnetorheological suspensions of different loading. For a magnetorheological suspension of polyaniline-coated particles the results show a decrease in the base viscosity. Moreover, the polyaniline coating has a negligible influence on the MR properties under an external magnetic field B. The change in the viscoelastic properties of magnetorheological suspensions in the small-strain oscillatory shear flow as a function of the strain amplitude, the frequency and the magnetic flux density was also investigated.

Comparison of some existing parametric models for magnetorheological fluid dampers

Abstract: Magnetorheological dampers have received a great deal of attention in the last two decades due to their being a potential technology to conduct semi-active control. It is therefore vitally important to understand the dynamic behavior of such devices whose nonlinear hysteresis is a rather complicated phenomenon. Hence, this paper aims at conducting a comparative evaluation of the currently available parametric models that have been widely used to develop control algorithms that take maximum advantage of the unique features of MR dampers. The comparisons showed that the simple algebraic parametric models exhibited considerably better predictions than the much more complicated ordinary differential parametric models.

Enhanced hardening of soft self-assembled copolymer gels under homogeneous magnetic fields

Abstract: The rheological response of highly swollen physical gels obtained by self-assembling of triblock copolymers containing low remanence ferromagnetic particles was investigated in the presence of external homogeneous magnetic fields. Three different types of sample geometries with distinctive magnetic particle orderings were investigated: isotropic (no magnetic field present during synthesis), parallel to the plane of the gel film and perpendicular to the plane of the gel film. Both the storage and loss moduli exhibit a strong increase with magnetic field strength for all geometries. Dependence of the rheological response on particle volume fraction was also investigated. The strength of such rheological hardening, as well as its saturation behaviour, depend strongly on the relative orientation between particle strings, shear and external field. In some cases a very strong relative increase of storage modulus, up to 6000% was obtained. Further transient rheological studies suggest that strong rearrangement of the particle network is largely responsible for the enormous increase in elastic modulus. Parallel to that, a maximum in the loss factor was observed as a function of particle volume fraction and field strength and it was interpreted in terms of a competition between an increase in string (clusters) hardening and a decrease in their ability to deform and flow. These results suggest that magnetorheological gels are an intermediate system between magnetorheological elastomers (MREs) and magnetorheological fluids (MRFs) with directional dependent rheological response and partial rearrangement of the particle network.

An Active-damping-compensated Magnetorheological Elastomer Adaptive Tuned Vibration Absorber

Abstract: This article presents the development of an active-damping-compensated magnetorheological elastomer (MRE) adaptive tuned vibration absorber (ATVA). The principle and the vibration attenuation performance of the proposed active-damping-compensated ATVA were theoretically analyzed. Based on the analysis, a prototype was designed and manufactured. Its dynamic properties and vibration attenuation performances were experimentally investigated. The experimental results demonstrated that the damping ratio of the prototype was significantly reduced by the active force. Consequently, its vibration attenuation capability was significantly improved compared with a conventional MRE ATVA.

Nano-finishing of stainless-steel tubes using rotational magnetorheological abrasive flow finishing process

Abstract: A new polishing method called Rotational (R)-Magnetorheological Abrasive Flow Finishing (MRAFF) process has been proposed by rotating a magnetic field applied to the Magnetorheological polishing (MRP) medium in addition to the reciprocating motion provided by the hydraulic unit to finish internal surface of cylindrical stainless steel (non-magnetic) workpiece. By intelligently controlling these two motions uniform smooth mirror-like finished surface in the range of nm has been achieved. For parametric analysis of the process, the experiments have been planned using design of experiments technique and response surface regression analysis is performed to analyze the effects of process parameters on finishing performance. Analysis of Variance (ANOVA) is conducted and contribution of each model term affecting percent improvement in surface finish is calculated. The experimental results are discussed and optimum finishing conditions are identified from optimization study. The present study shows that rotationa...

Anisotropic polyurethane magnetorheological elastomer prepared through in situ polycondensation under a magnetic field

Abstract: Highly filled polytetramethylene ether glycol (PTMEG)-based polyurethane (PU) magnetorheological elastomers (MREs) with anisotropic structure and good mechanical properties were prepared. The difficulty in dispersion and orientation of iron particles in the PU elastomer was overcome by ball milling mixing and further in situ one-step polycondensation under a magnetic field. The microstructure and properties of the composite were characterized in detail. Scanning electron microscopy (SEM) showed that a chain-like structure of carbonyl iron was formed in the PU matrix after orientation under a magnetic field of 1.2 T. The aligned chain-like structure of carbonyl iron in PU greatly enhanced the thermal conductivity, the compression properties and the magnetorheological (MR) effect of anisotropic PU MREs compared to that of the isotropic one. When the test frequency is 1 Hz, the maximum absolute and relative MR effect of anisotropic PU MREs with 26 wt% hard segment and 70 wt% carbonyl iron were ~ 1.3 MPa and ~ 21%, respectively.

Process parameter effects on material removal in magnetorheological finishing of borosilicate glass.

Abstract: We investigate the effects of processing parameters on material removal for borosilicate glass. Data are collected on a magnetorheological finishing (MRF) spot taking machine (STM) with a standard aqueous magnetorheological (MR) fluid. Normal and shear forces are measured simultaneously, in situ, with a dynamic dual load cell. Shear stress is found to be independent of nanodiamond concentration, penetration depth, magnetic field strength, and the relative velocity between the part and the rotating MR fluid ribbon. Shear stress, determined primarily by the material mechanical properties, dominates removal in MRF. The addition of nanodiamond abrasives greatly enhances the material removal efficiency, with the removal rate saturating at a high abrasive concentration. The volumetric removal rate (VRR) increases with penetration depth but is insensitive to magnetic field strength. The VRR is strongly correlated with the relative velocity between the ribbon and the part, as expected by the Preston equation. A modified removal rate model for MRF offers a better estimation of MRF removal capability by including nanodiamond concentration and penetration depth.

Isotropic magnetorheological elastomers with thermoplastic matrices: structure, damping properties and testing

Abstract: This paper presents a procedure for manufacturing composites, a methodology for testing them and the cyclic properties of isotropic magnetorheological elastomers. The choice of a thermoplastic matrix and magnetically active iron powder as the filling (much larger than the carbonyl iron powder filling used so far) is expounded. A manufacturing technology has been developed. Possibilities for the experimental investigation of magnetomechanical properties have been created by building a measuring system enabling the testing of various elastomers in a wide range of mechanical and magnetic parameters. The effect of the magnetic field and that of the stress frequency on the damping properties of a selected elastomer (considered to be optimal) were examined.

A shear thickening phenomenon in magnetic field controlled-dipolar suspensions

Abstract: A shear thickening phenomenon in dipolar suspensions of magnetorheological (MR) fluid is reported. The stress of the MR fluid abruptly decreases when the applied magnetic field increases to above a critical value under a small constant shear rate. It abruptly increases when the shear rate is higher than a critical value under a constant magnetic field, accompanied by a change in normal stress during shear thickening or unshear thickening processes. A shear-thickened structure is important for an MR fluid to obtain a high yield stress, which is beyond the prediction of a traditional dipole or multipole interaction model.

Vibration power generator for a linear MR damper

Abstract: The paper describes the structure and the results of numerical calculations and experimental tests of a newly developed vibration power generator for a linear magnetorheological (MR) damper. The generator consists of permanent magnets and coil with foil winding. The device produces electrical energy according to Faraday's law of electromagnetic induction. This energy is applied to vary the damping characteristics of the MR damper attached to the generator by the input current produced by the device. The objective of the numerical calculations was to determine the magnetic field distribution in the generator as well as the electric potential and current density in the generator's coil during the idle run and under the load applied to the MR damper control coil. The results of the calculations were used during the design and manufacturing stages of the device. The objective of the experimental tests carried out on a dynamic testing machine was to evaluate the generator's efficiency and to compare the experimental and predicted data. The experimental results demonstrate that the engineered device enables a change in the kinetic energy of the reciprocal motion of the MR damper which leads to variations in the damping characteristics. That is why the generator may be used to build up MR damper based vibration control systems which require no external power.

Thixotropy of MR shear-thickening fluids

Abstract: Particle sedimentation is a key issue of conventional magnetorheological (MR) fluids. We recently fabricated MR shear-thickening fluids (MRSTF), which can work as novel MR fluids without particle settling. This merit of the material against particle settling is attributed to the thixotropy property. By using shear-thickening fluids as a base medium, a series of MRSTF samples was prepared and their rheological properties were tested. It was found that when the weight fraction of the STF base is above a threshold value of 15%, the MRSTF exhibits a significant thixotropy phenomenon, which greatly reduces the settling problem of MR fluids and consequently increases the stability of MR fluids. A theoretical approach was proposed to verify the experimental studies.

Stiffness and Damping in Fe, Co, and Ni Nanowire-Based Magnetorheological Elastomeric Composites

Abstract: The stiffness and damping properties of the aligned magnetorheological (MR) elastomer composites filled with 10 wt% Fe, Co, and Ni nanowires were investigated under normalized strain amplitude of 1, 2, and 3%, cyclic deformation frequency of 1 Hz, and magnetic flux density of 0, 0.1, and 0.2 T. The highest values of the dynamic stiffness are observed for the Ni- and the lowest for the Fe-based composites within the whole range of strain amplitude and magnetic flux density. The MR effect on the dynamic stiffness is the most significant for 1% strain amplitude and it almost completely disappears for 3% amplitude for all composites. The equivalent damping coefficient values have maxima for 1% strain amplitude for all composites. These values abruptly drop with an increase of strain amplitude to 2% and only slightly change as strain amplitude is further increased to 3%. The MR effect on the equivalent damping coefficient is high for all composites and strain amplitudes.