Showing papers on "Magnetorheological fluid published in 1996"

Modeling and Control of Magnetorheological Dampers for Seismic Response Reduction

Abstract: Control of civil engineering structures for earthquake hazard mitigation represents a relatively new area of research that is growing rapidly. Control systems for these structures have unique requirements and constraints. For example, during a severe seismic event, the external power to a structure may be severed, rendering control schemes relying on large external power supplies ineffective. Magnetorheological (MR) dampers are a new class of devices that mesh well with the requirements and constraints of seismic applications, including having very low power requirements. This paper proposes a clipped-optimal control strategy based on acceleration feedback for controlling MR dampers to reduce structural responses due to seismic loads. A numerical example, employing a newly developed model that accurately portrays the salient characteristics of the MR dampers, is presented to illustrate the effectiveness of the approach.

A model of the behaviour of magnetorheological materials

Abstract: Magnetorheological materials are a class of smart materials whose rheological properties may be rapidly varied by application of a magnetic field These materials typically consist of micron-sized ferrous particles dispersed in a fluid or an elastomer A quasi-static, one-dimensional model is developed that examines the mechanical and magnetic properties of magnetorheological materials This model attempts to account for magnetic non-linearities and saturation by establishing a mechanism by which magnetic flux density is distributed within the composite material Experimental evidence of the viscoelastic behaviour and magnetic properties of magnetorheological fluids and elastomers suggests that the assumptions made in the model development are reasonable It is shown that the model is semi-empirical in that it must be fit to the experimental data by adjusting a parameter that accounts for unmodelled magnetic interactions

Phenomenological Model of a Magnetorheological Damper

Abstract: Semi-active control devices have received significant attention in recent years because they offer the adaptability of active control devices without requiring the associated large power sources. Magnetorheological (MR) dampers are semi-active control devices that use MR fluids to produce controllable dampers. They potentially offer highly reliable operation and can be viewed as fail-safe in that they become passive dampers should the control hardware malfunction. To develop control algorithms that take maximum advantage of the unique features of the MR damper, models must be developed that can adequately characterize the damper’s intrinsic nonlinear behavior. Following a review of several idealized mechanical models for controllable fluid dampers, a new model is proposed that can effectively portray the behavior of a typical magnetorheological damper. Comparison with experimental results for a prototype damper indicates that the model is accurate over a wide range of operating conditions and is adequate for control design and analysis.

Commercial magneto-rheological fluid devices

Abstract: Controllable magnetorheological (MR) fluid devices have reached the stage where they are in commercial production. Such devices are finding application in a variety of real world situations ranging...

Rheology of magnetorheological fluids: models and measurements

Abstract: Numerical and analytical models of magnetorheological fluid phenomena that account explicitly for the effects of magnetic nonlinearity and saturation are described. Finite-element analysis was used to calculate the field distribution in chains of magnetizable particles. The field-dependent stress required to shear the chains was then obtained using the Maxwell stress tensor. Three regimes are identified: at low applied fields, the stress increase quadratically, as expected from linear magnetostatics. In intermediate fields, the contact or polar regions of each particle saturate, reducing the rate of increase of the stress with increasing field. At high fields, the particles saturate completely, and the stress reaches its limiting value. Approximate analytical expressions for the yield stress and shear modulus in these regimes are also derived. The predictions of these models are compared to magnetorheological experiments in the literature and from our laboratory. These models predict successfully the magn...

Magnetorheological Fluids: Materials, Characterization, and Devices:

Abstract: Magnetorheological (MR) fluids consist of stable suspensions of magnetic particles in a carrying fluid. Magnetorheological effect is one of the direct influences on the mechanical properties of a f...

Multi-degree of freedom magnetorheological devices and system for using same

Abstract: A semi-active device (20) for damping motion between structures having multi-degrees of freedom. A magnetic field produced by a permanent magnet, a coil, or a combination thereof, change the rheological properties of an MR fluid (40) to effectively lock up the components and the structures to which they are attached to serve as a brake or damper of the associated compound motion. A system (21) employing the MR devices (20) includes a motion detection sensor (15) and a controller (19) to actuate the MR devices (20) when a predetermined motion threshold is exceeded.

Simulation of the formation of nonequilibrium structures in magnetorheological fluids subject to an external magnetic field.

Abstract: We developed a computer model to understand the nonequilibrium structures induced in a magnetorheological (MR) fluid by rapidly applying an external magnetic field MR fluids consist of particles suspended in a liquid where particles interact through dipole moments induced by the external magnetic field We have simulated these induced structures in both directions, parallel and perpendicular to the field, in the limit of fastest response, by neglecting thermal motion and applying the field instantaneously Our results show that the process of structure formation starts with particles forming chains aligned with the external field The chains then coalesce to form columns and wall-like structures (``worms'' as viewed from the top) The complexity of this pattern is found to depend on the concentration of particles and the confinement of the cell in the direction of the external field These results are consistent with experimental observations [GA Flores et al, in Proceedings of the Fifth International Conference on ER Fluids, MR Suspensions, and Associate Technology, University of Sheffield, Sheffield, 1995, edited by W Bullough (World Scientific, Singapore, 1996), p 140] We have also used this model to study the interaction of two chains The results of this study help in the understanding of the connection between the thickness of the sample and the increased complexity of the observed lateral pattern \textcopyright{} 1996 The American Physical Society

Method and apparatus for varying the stiffness of a suspension bushing

Abstract: A variable stiffness suspension bushing (18) for use in a suspension of a motor vehicle comprises a shaft or rod (40) connected to a suspension member (12), an inner cylinder (42) fixedly connected to the shaft or rod (40), and an outer cylinder (44) fixedly connected to a chassis member (16). A magnetorheological (MR) elastomer (48), having iron particles embedded therein, is interposed between the inner (42) and outer (44) cylinders, and a coil (54) is disposed about the inner cylinder (42). When the coil (54) is energized by electrical current provided from a suspension control module (20), a variable magnetic field is generated so as to influence the magnetorheological (MR) elastomer (48) whereby variable stiffness values of the elastomer (48) are obtained to provide the bushing (18) with variable stiffness characteristics in order to eliminate compromises heretofore necessary when using single, fixed rate bushings.

Rheology of a Magnetorheological Fluid

Abstract: We report on experimental investigations of the rheological behavior of aqueous magnetic suspensions. The suspended particles are monodisperse colloidal polystyrene spheres which contain magnetic Fe203-grains. In the absence of a magnetic field these suspensions behave as Newtonian fluids, whereas under the influence of a magnetic field due to the formation of an ordered structure the apparent viscosity of the suspension increases up to three orders of magnitude and they clearly exhibit non-Newtonian properties, such as shear thinning and yield stress. The apparent viscosity depends on the magnetic field according to aq - H2". Increasing the volume fraction of the particles in the range of 0.014 < 0 < 0.12 results in a linear increase in apparent viscosity and yield stress. Both apparent viscosity and yield stress depend also on the particle size as first measurements on particles with diameters ranging from 0.5 Am to 1.0,Am clearly show. All measurements were carried out with a rotation viscometer using ...

A method and magnetorheological fluid formulations for increasing the output of a magnetorheological fluid device

Abstract: A magnetorheological fluid that includes a carrier component and a magnetizable particle component wherein the magnetizable particle component has a fraction packing density of at least 0.50 prior to formulation into the magnetorheological fluid. Use of this magnetorheological fluid can increase the force output of a magnetorheological device without increasing the viscosity of the fluid because the particle volume concentration in a working gap of the device increases when a magnetic field is applied.

Torque transfer apparatus using magnetorheological fluids

Abstract: A fluid-based torque transfer device modulates the amount of torque which is transmitted from an input shaft to an output shaft. The torque transfer device includes a first plate connected to the input shaft. A second plate is connected to the output shaft and spaced from the first plate. A magnetorheological fluid is provided between the first and second plates. A magnetic circuit, including a coil wound around a core material defining a gap, applies a magnetic field to the magnetorheological fluid to variably control the rotation of the second plate in response to the rotation of the first plate. A controller adjusts the current to the coil to vary the magnetic field. Sensors detect at least one of the rotational speed and the torque of the input shaft, the output shaft, vehicle speed, steering direction, throttle position, gear position and brake position. The controller varies the current provided to the coil based thereon. Exemplary applications for the fluid-based torque transfer device include a fuse, a clutch between an engine and a transmission, and a transfer case for four wheel drive powertrains.

Magnetorheological Materials Based on Iron Alloy Particles

Abstract: A magnetorheological material containing iron alloy particles demonstrates magnetorheological strength dependent upon the elements of the alloy and relative concentration of the alloy elements Selected iron/cobalt alloys demonstrate improved yield strength over traditional carbonyl iron based MR materials when the iron-cobalt alloy has an iron-cobalt ratio ranging from about 30:70 to 95:5 The iron-nickel alloys which have an iron-nickel ratio ranging from about 90:10 to 99:1 maintains superior strength over iron-nickel alloys outside that range

Magnetorheological fluid composites

Abstract: An interesting extension in the use of magnetic fluids has resulted from the development of magnetic fluid composites obtained by dispersing micrometre-sized non-magnetic particles in a magnetic fluid. The composites possess a yield stress in a magnetic field which can be described at sufficiently high strain rates by the Bingham relation , where is the shear stress perpendicular to the applied field, the extrapolated yield stress, the strain rate and the plastic viscosity. Thus, a composite, particle concentration , in a field 0.036 T with has a yield stress of 26 Pa. The yield stresses obtained experimentally for different and correspond well to values predicted theoretically by Rosensweig using a determination of based on a continuum concept of unsymmetric stress that develops in the deformed but unyielded anisotropic medium.

Mr fluids with nano-sized magnetic particles

Abstract: Recently magnetorheological fluids with nanosized magnetic ferrite particles have become available. Their composition, rheological and magnetic properties are described. A comparison with conventional MR fluids based on micron-sized particles is given. The yield stress of nano-MR fluids can be increased by a moderate magnetic field (0,2 T) by 4000 Pa. It can be modulated by the magnetic field with a response time of less than 5 ms. Details are given on the long term thermal stability at 150 °C, on flow properties at elevated temperatures and at high shear rates. Design principles for MR fluid actuator design are outlined.

Aqueous magnetorheological materials

Abstract: A magnetorheological material that includes magnetic particles; at least one water-soluble suspending agent selected from the group consisting of cellulose ether and biosynthetic gum; and water. The material can have a high particle loading, minimizes waste disposal problems, and can be produced at a lower cost relative to magnetorheological materials that include hydrophobic-oil type fluids as a carrier fluid.

Method and apparatus for reducing brake shudder

Abstract: A variable stiffness suspension bushing (18) that is useful in a suspension of a motor vehicle to reduce brake shudder includes a shaft or rod (40) connected to a suspension member (12), an inner cylinder (42) fixedly connected to the shaft or rod (40), and an outer cylinder (44) fixedly connected to a chassis member (16). A magnetorheological (MR) elastomer (48), having iron particles embedded therein, is interposed between the inner (42) and outer (44) cylinders, and a coil (54) is disposed about the inner cylinder (42). When the coil (54) is energized by electrical current provided from a suspension control module (20), a variable magnetic field is generated so as to influence the magnetorheological (MR) elastomer (48) whereby variable stiffness values of the elastomer (48) are obtained to provide the bushing (18) with variable stiffness characteristics in order to eliminate compromises heretofore necessary when using single, fixed rate bushings.

Deterministic magnetorheological finishing

Abstract: Method and apparatus (10) for finishing a workpiece surface using magnetorheological fluid (16) wherein the workpiece (26) is positioned near a carrier surface (14) such that a converging gap (22) is defined between the workpiece surface and the carrier surface (14); a magnetic field is applied at the gap (22); a flow of magnetorheological fluid (16) is introduced into the gap (22) creatign a work zone in the fluid (16) to form a transient finishing tool for engaging and causing material removal at the workpiece surface.

Rheometry on magnetorheological (MR) fluids I. steady shear flow in stationary magnetic fields

Abstract: Test fixtures of a commercial concentric cylinder rheometer (Physica Rheolab MC 20) were modified to enable measurements under magnetic inductions up to 0.5 Tesla in a shear rate range of 0.1 up to 1000 s −1 and temperatures 0° to 150°C. In the 2 x90°-cups only two 90° sectors of the stationary part of the double concentric cylinder arrangement are submitted to the magnetic field which is created outside the test tools by an electromagnet. A prototype of a 360°-cup contains the electromagnet within the cup and avoids the correction necessary for the sector geometry. Measurements are shown for a carbonyl iron MR fluid and two nano MR fluids. An encouraging comparison of the viscosity function and MR effect (shear stress changes due to the field) measured by using the various cups is presented. The detailed investigation of the magnetic field distribution in the tools yields a distinct radial field gradient and also stray fields that make the quantification of the effective field in the gap difficult. The change of the field when the gap is filled with MR fluid is addressed. MR effects up to 13 000 Pa have been found, the limited torque range of the rheometer making it necessary to use relatively small gap dimensions which introduce errors due to edge effects. Shear rates up to 40000 s−1 as typical for the application in dampers were investigated by a piston-driven capillary rheometer making use of a thermostated rectangular slit with superimposed magnetic field. A satisfactory agreement of the magnetorheological data with the concentric cylinder results is found in the overlapping shear rate range.

Quasistatic measurements on a magnetorheological fluid

Abstract: The shear stress τ–shear strain γ behavior of suspensions of carbonyl iron particles in silicone oil was determined at a shear rate γ=0.042 s−1 as a function of applied magnetic induction B0 (0.5–6.0 kG), volume fraction of particles φ(0.05–0.30), and roughness of the shearing surfaces. At low fields, the steady‐state shear stress τS was significantly higher for a roughened surface compared to a smooth surface, but became only slightly dependent on roughness at high fields. In accord with theoretical considerations, the ratio τS/φ was proportional to the square of the calculated magnetic field H0 inside the suspension at low fields, but its dependence on H0 became smaller as the field increased. The smaller dependence may result from the magnetic saturation of the particles or the slipping boundary condition.

Controllable fluid rehabilitation device including a reservoir of fluid

Abstract: A controllable fluid device (20) for rehabilitation of injured or weakened complex appendages such as the hands and feet. The controllable fluid device (20)includes a reservoir (34)which contains a sufficient amount of controllable fluid (52)such as a Magnetorheological (MR) fluid. A magnetic field generator (36)provides the magnetic field (H) which is applied to the controllable fluid (52) by a magnetic circuit (60). In one aspect, an electromagnet including a coil (58) and core (54) provides the magnetic field (H). The intensity of the magnetic field is controlled via a controller (38). In another aspect, the magnetic field (H) is provided by a permanent magnet (44) and a mechanical shunt mechanism (42) is used to vary the magnetic field intensity. Other embodiments include a heater unit (66) with optional thermostat (74).

Variable stiffness bushing using magnetorheological elastomers

Abstract: A variable stiffness automotive vehicle suspension bushing (10) comprises a shaft or rod (12) connected to the vehicle subframe, an inner cylinder (14) fixedly connected to the shaft or rod (12), and an outer cylinder (16) fixedly connected to a vehicle suspension control arm. A magnetorheological (MR) elastomer (20), having iron particles embedded therein, is interposed between the inner (14) and outer (16) cylinders, and a coil (24) is disposed about the inner cylinder (14). When the coil (24) is energised by electrical power from the vehicle battery, a variable magnetic field is generated so as to influence the magnetorheological (MR) elastomer (20) whereby variable stiffness and modulus values or, characteristics of the elastomer (20) are derived so as to provide the bushing (10) with variable spring rate or stiffness characteristics in order to, in turn, provide the vehicle with optimal ride characteristics. Energisation of the coil (24) may be controlled by means of a suitable computer mounted upon the vehicle and which is responsive to various vehicle input data, such as, for example, engine speed, vehicle speed, vehicle acceleration, wheel height, and the like.

Magnetorheological fluid composition

Abstract: A magnetorheological fluid comprises non-colloidal magnetic particles, an abrasive, water, glycerol, and an alkaline buffer. The abrasive may be CeO 2 , the non-colloidal magnetic particles may be carbonyl iron, and the alkaline buffer may be Na 2 CO 3 . The fluid is useful for magnetorheological finishing.

Magnetorheological Fluid-Based Seal:

Abstract: The present experimental work has been done to study the characteristics of the simplest one-step magnetofluid seal (MFS) of the rotary shaft in which the MR fluid (MRF) serves as a sealing medium.The experiments show that the characteristics of the MRF-based seal differ very much from those of the ferrofluid (FF)-based one. In the static regime (stationary shaft), all other things being equal, the MRF holds an approximately three-fold pressure drop. The distinguishing feature of the functioning of such a seal is revealed and lies both in sharply elevating the pressure drop in the dynamic regime (rotary shaft) as against the static one and in having a maximum on the dependence of the pressure drop on the shaft rotation speed. In this regime, the MRF efficiency grows almost by the order of magnitude. However, the seal under study has an increased friction torque due to the growth of the shear stress of the MRF volume subject to shearing in the magnetic field.

Model of Magnetorheological Finishing

Abstract: The technology of finishing for optics, ceramics, and semiconductors is one of the most promising uses of the magnetorheological effect. It perfectly coupled with computer control, allowing in quantity production the unique accuracy and quality of a polished surface to be achieved. The polishing process may appear as follows. A part rotating on the spindle is brought into contact with a magnetorheological polishing (MRP) fluid which is set in motion by the moving wall. In the region where the part and the MRP fluid are brought into contact, the applied magnetic field creates the conditions necessary for the material removal from the part surface. The material removal takes place in a certain region contacting the surface of the part which can be called the polishing spot or zone. The polishing process comes to the program-simulated movement of the polishing spot over the part surface. The mechanism of the material removal in the contact zone is considered as a process governed by the particularities of th...

Magnetorheological finishing of edges of optical elements

Abstract: Method and apparatus using magnetorheological fluid for finishing a non-image-forming edge of an optical element to a very high degree of smoothness and for removing microscopic fissures from such edges, the method comprising positioning an optical element near a continuous carrier surface such that a converging gap is defined between an edge of the optical element and the carrier surface, the element being disposed such that image-forming refractive and reflective surfaces thereof do not create a gap with the carrier surface; applying a magnetic field substantially at the gap; introducing a magnetorheological fluid onto the carrier surface; driving the magnetorheological fluid through the gap to cause a flow of magnetic field-stiffened magnetorheological fluid through this gap to create a work zone and to form a transient finishing tool for removing material from the edge of the optical element; and moving the optical element relative to the work zone to expose different portions of the edge to the fluid for predetermined time periods to finish the edge to a predetermined degree. The lateral extent of fluid may be broad enough to permit polishing of a plurality of optical elements simultaneously on a single carrier surface, or a plurality of finishing stations may be ganged to finish a plurality of optical elements on a plurality of carrier surfaces.

Additional Magnetic Dispersed Phase Improves the Mr-Fluid Properties

Abstract: The main characteristics of the MR-fluid are the stability and sensitivity of its effective viscosity to an applied magnetic field. Such systems must be well fluid outside the applied field, as the viscosity increases many times in the magnetic field. A method is proposed for improving the MR-fluid properties by adding an additional high-dispersed magnetosolid powder to it. A relatively small content of magnetosolid particles causes a more than 9-fold increase of the MR-fluid viscosity in the magnetic field.

Effects of Cell Confinement on the Evolution of Field-Induced Structures in a Magnetorheological Fluid

Abstract: The evolution of field-induced structure in ferrofluid emulsions is studied during the "gas-solid" phase transition. The chain formation and coarsening are measured by monitoring the average separation between aggregates d using static light scattering and optical microscopy. A powerlaw relation, d -tr, is obtained for all measured cell thicknesses ranging 10 c L c 700 jim along the field direction. The rate of chain coarsening strongly depends on the chain length, weakly depends on the particle volume fraction and is independent of the field strength at a finite cell thickness. A theoretical model based on thermal fluctuation induced coupling and nucleation theory has been developed to explain the data at large L successfully.