Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2002-02-27
2004-03-23
Porta, David (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S227110, C250S227180, C073S800000, C073S862324, C073S862624, C356S032000
Reexamination Certificate
active
06710328
ABSTRACT:
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
BACKGROUND OF THE INVENTION
The present invention relates to methods and apparatuses for sensing or detecting structural damage in objects, more particularly to methods and apparatuses for sensing or detecting fractures, delamination and other forms of mechanical damage in structures such as composites.
Presently there is no completely satisfactory method or mature sensing technology to detect composite damage in-situ and in real-time, or to remotely interrogate such occurrences. Sage et al. U.S. Pat. No. 5,905,260 issued May 18, 1999, incorporated herein by reference, disclose a sensing technology to make such measurements; however, the technology disclosed by Sage et al. has its limitations. The sensor proposed by Sage et al. is a discrete sensor (described by Sage et al. as including “a small piece of a triboluminescent material”) that will locate damage only when damage occurs within the sensor's triboluminescent material itself. This approach by Sage et al. is problematic for various reasons. Firstly, the area (areas) of interest is (are) very specifically targeted according to the Sage et al. methodology, which assumes that the user of the composite structure knows exactly where damage will occur. Secondly, the Sage et al. methodology assumes that any damage in the composite is transferred to cracking in the sensor's triboluminescent material. Thirdly, measurements made at or near the outside surface of the composite may be impossible to make in accordance with the Sage et al. methodology.
In addition to Sage et al., other United States patents disclose triboluminescence or triboluminescent material in some context or capacity, including the following which are incorporated herein by reference: Qiu et al. U.S. Pat. No. 6,281,617 B1 issued Aug. 18, 2001; Storey U.S. Pat. No. 6,270,117 B1 issued Aug. 7, 2001, Akiyama et al. U.S. Pat. No. 6,159,394 issued Dec. 12, 2000; Watanabe et al. U.S. Pat. No. 6,117,574 issued Sep. 12, 2000; Hall-Goulle U.S. Pat. No. 6,071,632 issued Jun. 6, 2000; Hansma et al. U.S. Pat. No. 5,581,082 issued Dec. 3, 1996; Pappalardo et al. U.S. Pat. No. 4,772,417 issued Sep. 20, 1988; Dante U.S. Pat. No. 4,372,211 issued Feb. 8, 1983; Glass, deceased et al. U.S. Pat. No. 4,020,765 issued May 3, 1977.
“Triboluminescent” (sometimes called “mechanoluminescent”) material is a substance (usually, a crystalline substance) that, when fractured or otherwise subjected to some form of mechanical action, releases optical radiation in the visible spectrum (about 400-700 nm). Although the consistency of some triboluminescent materials may be roughly compared to that of sand, this is not a valid comparison for many triboluminescent materials. There are numerous different triboluminescent substances which share certain attributes and thus exhibit triboluminescent properties. A triboluminescent substance can be comprised of any of various organic and inorganic materials. As used herein, the terms triboluminescence (or triboluminescent) and mechanoluminescence (or mechanoluminescent) are synonymous. Both terms refer to luminescence (light emission) resulting from mechanical action, such as friction (rubbing), pressure, fracturing, scratching, striking, sawing, crushing, pulverizing, smashing or tearing.
Derivationally, triboluminescence comes from “tribo” or the Greek term “tribein,” meaning “friction” or “rubbing.” Notwithstanding that the prefix “tribo” seems to connote a more specific meaning of “friction” or “rubbing,” the terms triboluminescence and triboluminescent are intended herein to denote luminescence resulting from any and all forms of mechanical action. The prefix “mechano” in “mechanoluminescence” and “mechanoluminescent” seems to have a broader connotation more in keeping with the broadest concept of luminescence resulting from any and all forms of mechanical action. Nevertheless, the terms triboluminescence and mechanoluminescence are used fairly interchangeably in conventional usage. Thus, the terms triboluminescence and mechanoluminescence are intended herein to have the same broadest meaning, viz., luminescence resulting from any and all forms of mechanical action. Consistent with conventional usage, the terms fractoluminescence and fractoluminescent are intended herein to more specifically denote luminescence resulting from fracturing, since the prefix “fracto” suggests the more specific meaning of “fracture.”
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide method and apparatus for remotely detecting mechanical damage (e.g., fracture or delamination) occurring in a structure of any kind, especially to provide such method and apparatus in relation to a structure which is a composite structure such as a matrix composite or a laminar composite.
It is another object of the present invention to provide method and apparatus for remotely monitoring the mechanical damage condition of a structure which is known to be susceptible to certain types of damage such as involving fracture or delamination.
In accordance with typical practice of the present invention, a combination is provided which is suitable for detecting damage in an object. The combination comprises fiber optic means and triboluminescent means. The fiber optic means and the triboluminescent means are each adaptable to association with the object so that a mechanical event attendant the damage is capable of causing the triboluminescent means to emit light at least some of which is transmissible by the fiber optic means.
According to many embodiments of the present invention, “damage-autosensitive” apparatus (e.g., apparatus which, in functional effect, is capable of automatically sensing damage to itself) is provided. The damage-autosensitive apparatus comprises a structure, at least one fiber optic line, and at least one triboluminescent element. Each fiber optic line is connectable to a photodetector and is situated so that a portion of the fiber optic line is in communication with the structure. Each triboluminescent element is integrated with the structure and is sufficiently proximate a fiber optic line so that, upon an occurrence of damage to the structure: (i) an accompanying mechanical action upon the triboluminescent element results in a luminescent emission of light by the triboluminescent element; and, (ii) at least a portion of the luminescently emitted light is transmissible to the photodetector via the fiber optic line.
According to frequent inventive practice, a method for sensing mechanical damage comprises triboluminescently radiating light in response to the damage, and fiber optically conveying at least some of the triboluminescently radiated light so as be informative about the mechanical damage.
Many inventive embodiments provide a method of sensing the damage condition of an object. The method comprises (a) integrating triboluminescent material with the object, and (b) associating at least one fiber optic line with the object and with a photosensitive device. The at least one fiber optic line is associated with the object and with a photosensitive device so that, following a damage-causing event accompanied by a mechanical action upon at least some of the integrated triboluminescent material, a quantity of a resultant triboluminescent light emanation is transmitted by at least one fiber optic line to the photosensitive device.
Featured by typical embodiments of the present invention is a sequence of events including a damage-related mechanical action with respect to triboluminescent material, followed by a triboluminescent emission of light, followed by a fiber optic admission of at least some of the emitted light, followed by a fiber optic transmission of at least some of the admitted light, followed by an electronic indication (e.g., including an identification, a registration
Jarrett Andrew W.
Mastro Stephen A.
Mathur Veerendra K.
Kaiser Howard
Meyer David C
Porta David
The United States of America as represented by the Secretary of
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