Showing papers on "Magnetorheological fluid published in 1995"

Influence of the particle size on the rheology of magnetorheological fluids

Abstract: The rheogram, shear stress versus shear rate of magnetic suspensions composed either of monodisperse or polydisperse spherical particles, has been measured for different particle sizes. For small particles, where the ratio λ of magnetostatic energy to thermal energy is already much larger than unity (λ≊102–103), we find that the apparent yield stress is still strongly increasing with the size of the particles. It is only for very high values of λ (λ≊109) that we find experimental results which show no dependence on the size of the particles. These results are discussed with the help of a structural model based on the deformation of simple chains of particles, with an interparticle distance which depends on λ. It is shown that the experimental results can be explained by taking into account the fluctuations of the positions of the particles in a chain.

Exercise apparatus and associated method including rheological fluid brake

Abstract: An exercise apparatus includes a frame, user actuation components connected to the frame for being engaged and moved by a user during an exercise, and a rheological fluid brake operatively connected to the user actuation components for applying a controllable resistance to movement thereof. The rheological fluid brake includes a rheological fluid having a controllable viscosity, a housing connected to the frame and containing the rheological fluid, and a rotatable shaft extending outwardly from the housing and connected between the rheological fluid and the user actuation components. A flywheel is also preferably connected to the rotatable shaft to further smooth action of the brake. A controller, such as a microprocessor operating under stored program control, is preferably operatively connected to the rheological fluid brake for causing a predetermined field strength to be applied to the rheological fluid based upon a user-selected resistance value. In one embodiment, the rheological fluid is a magnetorheological fluid and in another embodiment, the fluid is a electrorheological fluid. A stair stepper, exercise bicycle and treadmill incorporating the rheological brake are disclosed.

Magnetorheological fluid devices and process of controlling force in exercise equipment utilizing same

Abstract: The invention relates to magnetorheological (MR) fluid devices (20) and the process of controlling the force in exercise equipment by utilizing the MR fluid devices. The MR fluid devices include rotary and linear acting varieties and are useful for controlled forces in exercise bicycles, recumbent exercisers, ski machines, rowing machines, and stair stepper machines. The rotary MR fluid device is comprised of a rotor (26) supported by bearings (44) and received within a housing (22). An MR fluid is received adjacent the rotor (26) and within a cavity (28) in the housing (22) and the MR fluid is controlled by an applied magnetic field to vary the operating torque resistance. Spring (43) biasing the rotor (26) allows for relaxed tolerances. Optimization of the Ri/Ro ratio is described which reduces the size and weight of the device (20). The linear acting version utilizes simple extensible pumps and an external MR fluid valve to provide a modularized system.

On magnetorheology and electrorheology as states of unsymmetric stress

Abstract: General expressions for the yield stress of a magnetorheological substance are derived in this work from consideration of unsymmetric elastic and magnetic stress states of a continuum. Geometrical models of composites illustrate use of the general expressions to obtain closed‐form analytical formulas exhibiting the dependence of the shear stress on shear strain, magnetic susceptibility and volumetric loading of the composite materials, demagnetization coefficient, and the applied field intensity over the full range of composition and shear strain. The model prediction recovers scaling behavior known from laboratory experiments, and values of shear modulus that compare in order of magnitude and trend with existing values determined from dipole–dipole and finite element analyses. Duality of electro‐ and magnetopolarized systems permits the results to be applied to the polarization component of the electrorheological response.

Magnetorheological fluid coupling device and torque load simulator system

Abstract: A fluid coupling device for coupling torque between two members and utilizing a magnetorheological fluid having a controllable yield strength in shear in response to a magnetic field and having a determinable viscosity in the absence of a magnetic field and with the coupling device having a rotor, rotatably supported in a cavity in a housing with the cavity filled with the magnetorheological fluid and with the cavity and rotor having similarly shaped contours and constructed to concentrate the magnetic coupling effect through the fluid at the radially outer end of the rotor and a torque load simulator system utilizing the fluid coupling for determining the performance of a torque tool or other torque related apparatus relative to a predetermined standard of performance.

Vibration damper, in particular for motor vehicles

Abstract: Vibration damper, in particular for motor vehicles, including a work cylinder, a work piston fastened to a piston rod and dividing the work cylinder into two work chambers, possibly an equalization chamber and a piston rod guide which seals the piston rod against the atmosphere, whereby the work chambers are filled with a magnetorheological fluid to which an electric coil can be applied. In the event of a failure or malfunction of the electric coil, it must be possible to achieve a safe damping force, by having at least one permanent magnetic field which acts on the magnetorheological fluid.

Fifth International Conference on Electrorheological Fluids, Magnetorheological Suspensions, and Associated Technology

Abstract: (1995). Fifth International Conference on Electrorheological Fluids, Magnetorheological Suspensions, and Associated Technology. Materials Technology: Vol. 10, No. 7-8, pp. 156-158.