Showing papers on "Magnetorheological fluid published in 1999"

Properties and applications of commercial magnetorheological fluids

Abstract: The rheological and magnetic properties of several commercial magnetorheological (MR) fluids are presented and discussed. These fluids are compared using appropriate figures of merit based on conventional design paradigms. Some contemporary applications of MR fluids are discussed. These applications illustrate how various material properties may be balanced to provide optimal performance.

Model of magnetorheological elastomers

Abstract: Magnetorheological elastomers consist of natural or synthetic rubber filled with micron-sized magnetizable particles. During curing of the elastomer, an applied magnetic field aligns the particles into chains. The shear modulus of the resulting cured material is sensitive to magnetic fields of several kOe magnitude. Such sensitivity to magnetic field makes these materials attractive for applications in automotive mounting components. At large fields (magnetic induction B>1 T), the Fe particles are completely magnetized or saturated. Calculations using finite element analysis show that for typical elastomers the increase in shear modulus due to interparticle magnetic forces at saturation is about 50% of the zero-field modulus. The optimum particle volume fraction for the largest fractional change in modulus at saturation is predicted to be 27%. Calculations of the zero-field shear modulus perpendicular to the chain axis indicate that it does not exceed the modulus of a filled elastomer with randomly disper...

Magnetorheological elastomers : Properties and applications

Abstract: Magnetorhelogical (MR) elastomers are viscoelastic solids whose mechanical properties are controllable by applied magnetic fields. We have developed a family of MR elastomers, comprising micrometer-sized carbonyl iron particles embedded in natural rubber, that can be processed using conventional rubber-mixing techniques. By crosslinking the elastomer in the presence of an applied magnetic field, field-induced interparticle interactions promote the formation of particle chains and columns aligned along the field direction. The resulting composites possess field- dependent of the mechanical properties of MR elastometers enables the construction of controllable elastomeric components, such as suspension bushings, that may prove advantageous in some automotive applications.

Magnetorheological finishing (MRF) in commercial precision optics manufacturing

Abstract: Finish polishing of highly precise optical surfaces is one of the most promising uses of magnetic fluids. We have taken the concept of magnetorheological finishing (MRF) from the laboratory to the optical fabrication shop floor. A commercial, computer numerically controlled (CNC) MRF machine, the Q22, has recently come on-line in optics companies to produce precision flat, spherical and aspheric optical components. MRF is a sub-aperture lap process that requires no specialized tooling, because the magnetically-stiffened abrasive fluid conforms to the local curvature of any arbitrarily shaped workpiece. MRF eliminates subsurface damage, smoothes rms microroughness to less than 1 nm, and corrects p-v surface figure errors to (lambda) /20 in minutes. Here the basic details of the MRF process are reviewed. MR fluid performance for soft and hard materials, the removal of asymmetric grinding errors and diamond turning marks, and examples of batch finishing of glass aspheres are also described.

Magnetorheology in viscoplastic media

Abstract: Suspensions of iron particles in media with yield stresses were investigated to determine the effect of the continuous phase yield stress on the magnetorheological (MR) response. The steady-shear MR response was independent of the continuous phase yield stress for yield stresses in the range 0.9–37 Pa. The field-induced suspension yield stress increased sub-quadratically with the flux density. The small amplitude oscillatory shear response exhibited history dependence. The storage modulus depended not only on the magnitude of the applied magnetic field, but also on its history. This history dependence can be explained in terms of the field-dependent evolution of the suspension microstructure.

Magnetorheological and electrorheological materials in adaptive structures and their performance comparison

Abstract: Magnetorheological (MR) and electrorheological (ER) materials show variations in their rheological properties when subjected to varying magnetic and electric fields, respectively. They have quick time response, in the order of milliseconds, and thus are potentially applicable to structures and devices when a tunable system response is required. When incorporated into an adaptive structural system, they can yield higher variations in the dynamic response of the structure. This study presents a detailed analysis of vibration control capabilities of adaptive structures based on MR and ER materials, and compares their vibration minimization rates, time responses and energy consumption rates. Homogeneous one-dimensional MR and ER adaptive beam configurations were considered. A structural dynamic modeling approach was discussed and vibration characteristics of MR and ER adaptive beams were predicted for different magnetic and electric field levels. In addition to the model predictions, actual MR and ER adaptive beams were fabricated and tested. Both studies illustrated the vibration minimization capabilities of the MR and ER adaptive beams at different rates and environmental conditions. The relative performances of both MR and ER adaptive beams were discussed in detail and their advantages and disadvantages were listed.

Flow analysis of field-controllable, electro- and magneto-rheological fluids using Herschel-Bulkley model

Abstract: The Bingham plastic constitutive model has been widely used to predict the post-yield behavior of electro- and magneto-rheological fluids (ER and MR fluids). However, if these fluids experience shear thinning or shear thickening, the Bingham plastic model may not be an accurate predictor of behavior, since the post-yield plastic viscosity is assumed to be constant. In a recent study, it was theoretically and experimentally demonstrated that the Herschel-Bulkley fluid model can be successfully employed when evaluating non-Newtonian post-yield behavior of ER and MR fluids. In this paper, we extend our previous work and adopt the Herschel-Bulkley model to include a detailed analysis of ER and MR fluid dynamics through pipes and parallel plates. Simplified explicit expressions for the exact formulation are also developed. It is shown that the proposed simplified model of the Herschel-Bulkley steady flow equations for pipes and parallel plates can be used as an accurate design tool while providing a convenient...

Fundamentals of Magnetorheological Fluid Utilization in High Precision Finishing

Abstract: Magnetorheological finishing (MRF) is an enabling technology that may produce surface accuracy on the order of 30 nm peak to valley (p-v) and surface micro-roughness less than 10 A rms. In MRF, mec...

Viscoelastic properties of MR fluids

Abstract: Mechanical properties of magnetorheological (MR) fluids are classified into pre-yield and post-yield regions according to whether the shear stress is below or above the yield stress. MR fluids within the pre-yield region exhibit viscoelastic properties; and these properties are important for understanding MR suspensions, especially for vibration damping applications. MR suspensions composed of reduced iron powders dispersed in silicone oil are utilized to study the viscoelastic properties with the help of a strain-controlled rheometer with plate-plate configuration. Two types of experiments, i.e. strain-amplitude sweep mode and frequency-sweep mode, were carried out to investigate the viscoelastic properties of MR fluids: (a) strain-amplitude sweep mode, the strain amplitude was swept from 0.0001 to 0.001 at a fixed driving frequency of 10 Hz. (b) Frequency-sweep mode, the driving frequency was swept from 1 Hz to 100 Hz at a constant strain amplitude of 0.001. The results show that both storage modulus G´ and loss modulus G´´ decrease with the increment of the strain amplitude, however, the loss factor increases with the increment of the strain amplitude. On the other hand, both the storage modulus and loss modulus increase with the increment of frequency, which is different from the loss factor. Moreover, the effects of magnetic field and volume fraction on the viscoelastic properties are also investigated. The higher the magnetic field, the higher the storage modulus and loss modulus, and the lower the loss factor. The higher the volume fraction, the higher the storage modulus and the loss factor.

Progress Update in Magnetorheological Finishing

Abstract: In magnetorheological finishing (MRF), magnetically stiffened magnetorheological (MR) abrasive fluid flows through a preset converging gap that is formed by a workpiece surface and a moving rigid wall, to create precise material removal and polishing. Theoretical analysis of MRF, based on Bingham lubrication theory, illustrates that the formation of a core attached to the moving wall results in dramatically high stress on the workpiece surface. A correlation between surface stress on the workpiece and material removal is obtained. A unique attribute of the MRF process is its determinism. MRF has been successfully implemented to polish optical surfaces to very high precision. MRF reduces the surface micro roughness of optical materials to ≤ 10A. Figure errors are corrected to a fraction of a wavelength of light and subsurface damage is removed. A wide range of optical surface shapes, including aspheres, has been polished on many different materials. Other applications in precision finishing are being considered, including integrated circuits and advanced ceramics.

Synthesis and Properties of Novel Magnetorheological Fluids Having Improved Stability and Redispersibility

Abstract: A novel class of relatively stable and redispersible MR fluids based on meso-scale magnetic particles of iron or nickel zinc ferrite and nano-scale additives is described. For a flux density B ~ 1 Tesla, the iron based MR fluids exhibited yield stresses of ~100 kPa. For ferrite based fluids the yield stress values were as high as ~15 kPa at B ~ 1T. The yield stresses at the flux density required for magnetic saturation increase quadratically with the saturation magnetization of the particulate material, in good agreement with a model for the yield stress of uniformly saturated particle chains. At lower flux densities, the yield stress was generally observed to increase as B3/2, consistent with models of the role of local saturation of the particle magnetization. The additives were found to enhance the stability and redispersibility of the MR fluids: they appeared to promote a small non-zero yield stress in the absence of a field but were found not to have a substantial effect on the field-dependent yield stresses.

Controllable viscous damping: an experimental study of an electrorheological long-stroke damper under proportional feedback control

Abstract: It is now well known that smart fluids (electrorheological (ER) and magnetorheological) can form the basis of controllable vibration damping devices. With both types of fluid, however, the force/velocity characteristic of the resulting damper is significantly nonlinear, possessing the general form associated with a Bingham plastic. In a previous paper the authors suggested that by using a linear feedback control strategy it should be possible to produce the equivalent of a viscous damper with a continuously variable damping coefficient. In the present paper the authors describe a comprehensive investigation into the implementation of this linearization strategy on an industrial scale ER long-stroke vibration damper. Using mechanical excitation frequencies up to 5 Hz it is shown that linear behaviour can be obtained between well defined limits and that the slope of the linearized force/velocity characteristic can be specified through the choice of a controller gain term.

Design Analysis and Experimental Evaluation of an MR Fluid Clutch

Abstract: An MRC (Magneto-Rheological Clutch), a device to transmit torque by shear stress of MR fluids, has the property that its power transmissibility changes quickly in response to control signal. In this study, we consider methods to predict performance of an MRC. First, we anticipate the performance of an MRC with a simplified mathematical model and second, we predict the performance in consideration of the applied magnetic field and viscosity distribution of fluids caused by the field. Between the two methods, compared with experimental results, it is shown that the numerical method is closer to reality than the simplified one.

Micromechanics of Dipolar Chains Using Optical Tweezers

Abstract: Here we present our initial study of the micromechanical properties of dipolar chains and columns in a magnetorheological (MR) suspension. Using dual-trap optical tweezers, we are able to directly measure the deformation of the dipolar chains parallel and perpendicular to the applied magnetic field. We observe the field dependence of the mechanical properties such as resistance to deformation, chain reorganization, and rupturing of the chains. These forms of energy dissipation are important for understanding and tuning the yield stress and rheological behavior of an MR suspension.

Low-Cost MR Fluid Sponge Devices:

Abstract: A variety of robust, high-strength, MR fluids and devices that enable the benefits of controllable fluid technology are now commercially available. Commercial, mass-produced devices include rotary brakes for use in exercise equipment, real-time controllable vibration dampers for truck seats and adjustable linear shock absorbers for racing cars. Recently, a new way of using MR fluids in which the fluid is contained in an absorbent matrix has been developed. Such MR fluid sponge devices enable the benefits of controllable MR fluids to be realized in cost sensitive applications. Most of the high-cost components normally associated with a fluid filled device can be eliminated with this approach. Low-cost, controllable MR fluid sponge dampers are particularly appropriate for moderate-force vibration control problems where a high degree of control authority is desired such as a new generation of high-performance, home washing machines now being developed.

Magnetorheological fluid apparatus, especially adapted for use in a steerable drill string, and a method of using same

Abstract: A rotatable steerable drill string in which guidance module controls the direction of the drilling. A magnetorheological fluid in the module supplies pressure to pistons that apply forces to the wall of the bore and thereby alter the direction of the drilling. The pressure applied by the magnetorheological fluid is regulated by valves that apply a magnetic field to the fluid so as to increase or decrease its fluid shear strength thereby controlling the actuation of the pistons and the direction of the drilling.

Details of the polishing spot in magnetorheological finishing (MRF)

Abstract: Magnetorheological Finishing (MRF) is a novel process for deterministic figure correction and polishing of optical materials that utilizes a sub-aperture lap created by moving a magnetic field-stiffened magnetorheological (MR) fluid ribbon against an optical surface. MRF has been successfully applied to a wide range of optical materials. A new research platform has been designed and built that is used to generate sub-aperture polishing profiles, i.e., polishing 'spots,' on optical flats under well-controlled conditions. This platform uses the same fluid circulation and conditioning system as the commercial computer numerically controlled MRF machine, thereby allowing fluid performance issues to be investigated. This new machine complements the capabilities of the original MRF research platform that has been in continuous use for over six years. These two machines have been used to generate polishing spots on a variety of optical materials. The spot profiles were measured to calculate material removal rates and the quality of the polished surfaces characterized by measuring the microroughness within the polishing spots. Examples are presented which illustrate how the evaluation of polishing spots was used to develop MR fluids and operating conditions for calcium fluoride, CaF2, and potassium dihydrogen phosphate, KDP.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Heating of Magnetorheological Fluid Dampers

Abstract: This paper presents experimental and theoretical studies on heat generation and dissipation of fieldcontrollable, magneto-rheological (MR) fluid shock absorbers. Since MR fluid dampers are energy-dissipating devices, the issues of heat generation and dissipation are important. In this study, experiments are conducted on a variety of MR fluid dampers that have been designed, developed, and tested at the University of Nevada, Reno (UNR), for specific applications. Each MR fluid damper is experimentally evaluated for temperature changes that result from various types of sinusoidal input motions. In addition a theoretical model is developed which predicts the temperature increase of the MR fluid dampers. This model is solved numerically, and is compared with experimental results. Also, a non-dimensional form of the governing equations is developed to assess the effect of physical parameters on the heat dissipation as well as heat generation within the MR fluid damper. Moreover, the theoretical results for tem...

Method and apparatus for chemical polishing using field responsive materials

Abstract: A process for, and apparatus for, Chemically-Mechanically Polishing (CMP) a semiconductor wafer with a slurry including ElectroRheological (ER) and/or MagnetoRheological (MR) fluids. The combination of the materials and an electric field provides inherent tuning of polishing rates, locally and globally, and improves flatness and uniformity, as well as minimizing recession and erosion.

Seismic response control using smart dampers

Abstract: Presents the results of a numerical study conducted to demonstrate the capabilities of multiple magnetorheological (MR) devices for seismic control of civil engineering structures when used in conjunction with a clipped optimal control algorithm. The study employs an identified model of the integrated structural system that is shown to accurately predict the responses of the experimental setup in the Washington University Structural Control and Earthquake Engineering Lab. Four parallel-plate, shear-mode MR dampers are used to control a six-story structure. The control devices are arbitrarily located in the structure. Through simulation, the performance of the controlled system is examined. The results indicate that high performance levels can be achieved, and the responses of the semi-active system are significantly smaller than that of comparable passive systems.

The role of the dispersed-phase remnant magnetization on the redispersibility of magnetorheological fluids

Abstract: The influence of the remnant magnetization of the soft magnetic particulates, used as a dispersed phase, on the redispersibility of magnetorheological (MR) fluids is discussed. Calculations of the magnetic interaction energy showed that for 33-vol% MR fluids based on particles of iron (∼6 μm), manganese zinc ferrite (∼2.3 μm), and nickel zinc ferrite (∼2.1 μm), the ratios of the magnetic interaction energy to the thermal energy were 161,000, 6400, and 3900, respectively. These calculations showed that even the seemingly small levels of remnant magnetization, associated with particulates employed in MR fluids, introduced significant dipole–dipole interparticle interactions. It is proposed that this interaction causes most MR fluids to show a tendency for “cake formation,” which makes it difficult to redisperse these fluids. Our modeling presented here also suggests practical strategies to enhance the redispersibility of MR fluids.

Linear viscoelasticity of an inverse ferrofluid

Abstract: A magnetorheological fluid consisting of colloidal silica spheres suspended in an organic ferrofluid is described. Its linear viscoelastic behavior as a function of frequency, magnetic field strength, and silica volume fraction was investigated with a specially designed magnetorheometer. The storage modulus G′ is at least an order of magnitude larger than the loss modulus G″ at all magnetic field strengths investigated. G′ does depend only weakly on frequency, and linearly on volume fraction. A model is presented for the high frequency limit of the storage modulus G∞′. In the model our system is treated as a collection of single noninteracting chains of particles. Assuming a dipolar magnetic interaction, theory and experiment show reasonable agreement at high frequencies.

Non-linear magnetorheological behaviour of an inverse ferrofluid

Abstract: The non-linear magnetorheological behaviour is studied of a model system consisting of monodisperse silica particles suspended in a ferrofluid. The stress/strain curve as well as the flow curve was measured as a function of volume fraction silica particles and field strength, using a home-made magnetorheometer. Both curves were found to scale linearly with the volume fraction and quadratically with the magnetic moment of the silica particles. Affine deformation cannot lead to the observed yield stresses. Instead, a bead–rod model is described that gives results closer to what is observed experimentally. A master curve for the viscosity was obtained by plotting the dimensionless viscosity versus the Mason number, Mn. The free single chain model of Martin and Anderson does not give a good description of the measured curves. This may be due to the simplifications with respect to the microstructure of and processes in the suspension.

Analysis and Testing of Electrorheological Bypass Dampers

Abstract: We experimentally validate nonlinear quasi-steady electrorheological (ER) and magnetorheological (MR) damper models, using an idealized Bingham plastic shear flow mechanism, for the flow mode of damper operation. An electrorheological valve or bypass damper was designed, and fabricated using predominantly commercial off-the-shelf hydraulic components. Both the hydraulic cylinder and the bypass duct have cylindrical geometry, and damping forces are developed in the annular bypass via Poiseuille (flow mode) flow. Damper models assume parallel plate geometry. Three nondimensional groups are used for damper analysis, namely, the Bingham number, Bi, the nondimensional plug thickness, 6, and the area coefficient defined as the ratio of the piston head area, AP, to the cross-sectional area of the annular bypass, Ad. In the flow mode case, the damping coefficient, which is defined as the ratio of equivalent viscous damping of the Bingham plastic material, Ceq, to the Newtonian viscous damping, C, is a function on...

Vibration Suppression in an MR Fluid Damper Suspension System

Abstract: An MR(Magneto-Rheological) fluid damper is designed and applied to a semi-active suspension system of a quarter car model. The damping constant of the MR damper changes according to the input current and the time delay of the damper is included in the system dynamics. The passive method, LQ control and frequency shaped LQ control are compared in experiments. The advantage of the proposed frequency shaped LQ control is that the ride comfort improves in the frequency range of 4 and 8 Hz where a human is most sensitive and the driving safety improves around the resonance frequency of unsprung mass, 11 Hz. The experiments using a quarter car model show the effectiveness of the algorithm.

System for abrasive jet shaping and polishing of a surface using magnetorheological fluid

Abstract: A fluid (40) having magnetorheological (MR) properties and including a finely-divided abrasive material is directed through a non-ferromagnetic nozzle (30) disposed axially of the helical windings of an electric solenoid (28). A magnetic field created by the solenoid orients and aligns the magnetic moments of the particles to form fibrils thereby stiffening the flowing MR fluid (40) which, when ejected from the nozzle (30), defines a highly collimated jet. Collimation of the MR material persists for a significant time outside the magnetic field, permitting use of the abrasive jet to shape and/or polish the surface of a workpiece (12) at some distance from the nozzle (30). The jet (35) is directed into a shroud (20) against a workpiece (12) mounted for multiple-axis rotation and displacement to meet predetermined material removal needs for shaping.