Damper

Details Damper Damper

1996-04-22

2001-04-24

Oberleitner, Robert J. (Department: 3613)

Brakes

Plastic deformation or breakage of retarder element

C052S167100, C052S167800

Reexamination Certificate

active

06220410

ABSTRACT:

This invention relates to dampers of the type commonly referred to as extrusion dampers, used for reducing the effects of induced motion or displacement in a variety of structures and equipment.
The dampers of the invention may be used in large structures such as bridges or buildings to reduce the effects of motion induced during earthquakes or from strong winds. They may also be used to damp motion of large or small moving objects. They may be used to damp motion in industrial machinery or engines or the like or from domestic appliances such as washing machines for example, or in any other application where it is desired to damp any motion, vibrations or similar. They may be used to damp displacement arising from thermal expansion. The extrusion dampers of the invention have various applications.
BACKGROUND OF THE INTENTION
Devices known as extrusion dampers which employ elastic or plastic deformation of certain materials to absorb energy are well known. U.S. Pat. No. 3,833,093 describes a form of extrusion damper consisting of an energy absorber material confined between an elongate outer jacket which is typically a cylinder, and a shaft which moves longitudinally within the jacket. The absorber material is typically lead while the jacket and shaft are typically formed of steel. Opposite ends of the jacket and shaft are connected between two members in a structure which are expected to move relative to one another during an earthquake or other induced motion. A general discussion of these and related devices is given in “An Introduction to Seismic Isolation”, R I Skinner, W H Robinson and G H McVerry, Wiley, 1993.
Lead is the preferred deformable energy absorbing material for several reasons. First it yields at a room temperature shear stress of around 10.5 MPa which is low compared with other metals and equivalent plastic materials. Second it restores its mechanical properties through recrystallisation and associated processes relatively rapidly following yield deformations, which provides outstanding resistance to work hardening under cyclic shear at ordinary temperatures. Third lead is readily available at the purity required to exhibit these properties.
In practice such dampers are individually designed to protect a particular structure against damage by damping certain motions imparted to it. Their behaviour is quite closely approximated by that of an ideal Coulomb damper in having a force-displacement hysteresis loop which is nearly rectangular and practically rate independent over a wide range of frequencies. Research into performance of these devices is ongoing.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide for improved performance of such dampers for seismic isolation and other applications.
The invention broadly comprises a damper for interposing between two members to damp motion which may be induced between the two, comprising an elongate outer jacket means, a shaft passing through the outer jacket which is forced to move through the outer jacket during induced motion and a body of a plastically deformable energy absorbing material filling the space between the outer jacket and the shaft, wherein the body of energy absorbing material is fixed relative to the outer jacket and the shaft comprises a portion of reduced diameter which is forced through the energy absorbing material during said induced motion and/or the body of energy absorbing material is fixed to the shaft and the outer jacket comprises a portion of enlarged diameter through which the body of energy absorbing material is forced during said induced motion.
Preferably the body of energy absorbing material is subjected to approximately hydrostatic pressure at least approaching the shear yield stress of the material. Preferably the hydrostatic pressure applied to the energy absorbing material exceeds the shear yield stress of the energy absorbing material. Preferably the hydrostatic pressure is 5 MPa or more and most preferably in the range 10-100 MPa.
Preferably the energy absorbing material is lead, but other energy absorbing materials which may be used include alloys of lead, aluminium at elevated temperature e.g. about 200° C., tin, zinc, brass, iron, super plastic alloys, or any other material having a low rate of work hardening, including also densely packed granular materials such as steel shot, glass beads, alumina, silica, silicon carbide or any other very hard granular material.
Dampers of the invention may be used in seismic isolation applications to damp seismic motion in large structures such as bridges or buildings or motion from very strong wind buffeting or similar. They may also be used in any other application where it is desired to damp any motion, vibrations, or similar. For example, dampers of the invention may be used to damp motion of engines or other industrial machinery. In domestic applications, dampers of the invention may be used in washing machines or spin dryers or dish washers to isolate vibrations. Small size dampers of the invention may be used as “microisolators” for sensitive electronic equipment such as the mechanism of a video recorder etc or in other similar applications. Numerous applications of the extrusion dampers of the invention are envisaged and the invention is not limited only to seismic isolation dampers.


REFERENCES:
patent: 3721320 (1973-03-01), Hirsch
patent: 3833093 (1974-09-01), Robinson
patent: 3938625 (1976-02-01), Radermacher et al.
patent: 5458221 (1995-10-01), Flux et al.
patent: 0266841 (1986-11-01), None

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