Showing papers on "Magnetorheological fluid published in 1994"

Shear stresses in magnetorheological fluids: Role of magnetic saturation

Abstract: The interparticle forces and resulting shear stresses in a magnetorheological fluid are calculated. The field due to a linear chain of particles in a fixed average magnetic induction Bave is determined from a finite element analysis in which the nonlinearity and saturation of the particle magnetization are incorporated. The shear stresses are then computed from the field using Maxwell’s stress tensor. The stresses obtained for all but the lowest magnetic inductions are controlled by the saturation of the magnetization in the contact regions of each particle. Identifying the maximum shear stress as a function of shear strain with the yield stress gives values in agreement with results reported for typical fluids. For high magnetic inductions the yield stress plateaus due to the complete saturation of the particle magnetization; the stress scales as the square of the saturation magnetization in this regime.

Controller valve device and method

Abstract: Device and method for regulating fluid flow within the human body includes small electromagnetic devices embedded in an inner housing of the present device that function under the control of a programmable control unit to create small magnetic fields which cause an artificial increase in the viscosity and apparent density of a magnetorheological fluid located in a compartment surrounding the structure through which fluid flow is to be controlled.

Magnetorheological polishing devices and methods

Abstract: A method of polishing an object is disclosed In one embodiment, as shown in the figure, the method comprises the steps of creating a polishing zone (10) within a magnetorheological fluid (2); determining the characteristics of the contact between the object and the polishing zone necessary to polish the object (4); controlling the consistency of the fluid (2) in the polishing zone (10); bringing the object (4) into contact with the polishing zone (10) of the fluid (2); and moving at least one of said object (4) and said fluid (2) with respect to the other Also disclosed is a polishing device (1) In one embodiment, the device comprises a magnetorheological fluid (2), a means (6) for inducing a magnetic field, and a means for displacing the object (4) to be polished or the means (6) for inducing a magnetic field relative to one another

Magnetorheological fluid composite structures

Abstract: Controllable composite structure or structural elements enclose magnetotheological fluids as a structural component between opposing containment layers to form at least a portion of any variety of extended mechanical systems, such as plates, panels, beams and bars or structures including these elements. The control of the stiffness and damping properties of the structure or structural elements is accomplished by changing the shear and compression/tension moduli of the magnetorheological fluid by varying the applied magnetic field. The composite structures of the present invention may be incorporated into a wide variety of mechanical systems for control of vibration and other properties.

Magnetic fluid-based magnetorheological fluids

Abstract: A magnetorheological fluid composition having a magnetizable carrier medium loaded with magnetizable particles to provide a magnetorheological fluid exhibiting enhanced rheological properties. Also disclosed is a magnetic-particle damper utilizing the magnetorheological fluid composition.

Controllable Fluids:. the Temperature Dependence of Post-Yield Properties

Abstract: This paper represents the first detailed description of the affect of temperature on the properties exhibited by state-of-the-art electrorheological (ER) and magnetorheological (MR) fluids. In particular, shear stress versus shear strain rate curves, dynamic and static yield stress values, zero-field viscosity data, and current density measurements are discussed. Specific comments concerning the stability of both mechanical and electrical properties over broad temperature ranges are provided. Finally, insight into the advantages associated with using electrorheological and magnetorheological fluids in a controllable device is provided.

Temperature independent magnetorheological materials

Abstract: A magnetorheological material containing a particle component and a carrier fluid or mixture of carrier fluids having a change in viscosity per degree temperature (Δη/ΔT ratio) less than or equal to about 160 centipoise/°C over the temperature range of about 25° C to -40° C The magnetorheological material exhibits a substantial magnetorheological effect and excellent lubricating properties with a minimal variation in mechanical properties with respect to changes in temperature The magnetorheological material is advantageous in that it provides for the design of devices that are smaller, more efficient and consume less power

Structure induced in suspensions by a magnetic field

Abstract: Magnetorheological as well as electrorheological fluids exhibit a phase separation when a field is applied to the suspension. We observe the formation of aggregates elongated in the direction of the field and whose length L is fixed by the thickness of the cell. The average radius b of these aggregates has been measured for L between 100 μm and 700 μm for two volume fractions Φ=5% and Φ=10%. In this range we find for a magnetorheological fluid composed of micronic superparamagnetic particles an experimental law b ∞ a(L/a) n with an exponent n=0.67±0.04. We can recover this experimental law and predict the characteristic size of the aggregates from the knowledge of the magnetic permeability of the particles with a model based on the hypothesis of close packed aggregates. The agreement with the experiments is good especially at the lower volume fraction. Actually on a larger range of thicknesses our model predicts a continuous increase of this exponent towards a final value of one for large values of L/a

Automobile shock absorber using magnetorheological fluid

Abstract: The shock absorber (1) has a cylinder divided into 2 working chambers via a sliding piston (3), pref. incorporating a number of flow channels of variable flow cross-section. Each chamber is filled with a magnetorheological fluid, acted on by an electrical coil for varying the spring characteristics of the shock absorber. The magnetorheological fluid lies in the magnetic field of at least one permanent magnet, providing a magnetic field ensuring a min. spring characteristic for safe driving of the vehicle upon failure of the coil system. The magnetic field provided by the permanent magnet may be partially compensated, or amplified, via an electric coil.

Magnetorheological properties of some ferrofluids

Abstract: The effect of an external magnetic field, velocity of flow and concentration of the magnetite on the rheological properties of some mineral oil based ferrofluids have been investigated. It has been shown that the increase of viscosity in magnetic field depends upon the velocity flow of ferrofluid and concentration of magnetite. >