Brakes – Internal-resistance motion retarder – Magnetic fluid or material
Patent
1996-07-22
1998-09-22
Oberleitner, Robert J.
Brakes
Internal-resistance motion retarder
Magnetic fluid or material
1883225, 252570, 26714014, F16F 1503
Patent
active
058101268
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a composite structure having two or a plurality of layers and containing an electrorheological fluid and, more particularly, to an improved composite structure element which allows the complex shear modulus of the composite element to differ for different sections of the composite element.
BACKGROUND OF THE INVENTION
In electrorheological fluid composite structures, creating an electric field in each layer of the electrorheological fluid can change the mechanical properties of the composite structure as a whole. In the presence of an electric field the flexibility and stiffness of an electrorheological fluid composite system, such as a plate, panel, or beam, are changed; the amplitude of flexibility or bending is decreased, and the damping properties are altered.
In electrorheological fluid composite structures, the foundation of the laminated composite structure is a composite element which consists of two metal flexible laminae or two non-metal layers having an electrically conducting coating and serving as electrodes. A spacing between these layers is filled with an electrorheological fluid. When an electric potential is created between the electrodes, the dispersed phase of electrorheological fluid forms a bridge structure which connects the electrodes. In the presence of an electric field, the cohesive strength between particles in the electrorheological fluid and between the fluid particles and the electrode surfaces is increased, as compared with the cohesive strength with no electric field. In the presence of an electric field, the rheological properties of the electrorheological fluid layer between the electrodes change; its viscosity and yield stress are increased, visco-elastic properties appear, and the cohesive force between the particles and electrodes grows. When voltage is supplied to the electrodes of a deformed composite element, the complex shear modulus, G*=G'+iG", is varied, including its real part G' (elasticity modulus), imaginary part G" (loss modulus) and loss factor G"/G'. As a result, the energized composite structure exhibits improved damping properties over a frequency range which is dependent on the design of the composite element and its bending stiffness.
In the composite element described, it is difficult to maintain a relatively constant spacing between the electrode surfaces when the composite element is deformed. If the spacing is decreased too much, a short circuit of the electrodes may occur. This inability to avoid short circuits causes relatively low reliability in prior composite elements. The fluid in prior systems may also escape from the interspace of the composite element unless the fluid layer is confined by a barrier.
Carlson, U.S. Pat. No. 4,923,057, discloses an electrorheological composite structure consisting of an electrorheological fluid layer confined by a barrier and located between two electrically conductive flexible layers. Carlson attempts to maintain the uniformity of the electrorheological fluid layer thickness, and corresponding separation of the electrodes, by pasting insulating pads between the electrodes at designated positions, such as around the perimeter of the element. In an effort to prevent a short circuit of the electrodes, Carlson discloses that a layer of a fabric or other porous or mesh material is placed between the electrodes.
In a composite element according to the Carlson patent, the spacing between the flexible laminae must be increased by the fabric thickness, and the voltage must therefore be elevated in order to maintain a required field strength. In addition, optimal properties of such a pad are unknown; for example, use of an insulating fabric reduces the area of the bridge structures formed by the electrorheological fluid that connect the electrodes, and the effect of the electric field on the mechanical properties of the electrorheological fluid will be diminished.
The Carlson patent also describes the use of an electrorheological fluid which tends to migrate fr
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Demchuk Svetlana Antonovna
Kordonsky William Ilyitch
Makatun Victor Nesterovich
Matsepuro Alina Danilovna
Novicova Zoja Anatoljevna
Byelocorp Scientific, Inc.
Lipka Pamela J.
Oberleitner Robert J.
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