Optics: measuring and testing – Inspection of flaws or impurities – Having predetermined light transmission regions
Patent
1982-10-22
1986-12-16
Willis, Davis L.
Optics: measuring and testing
Inspection of flaws or impurities
Having predetermined light transmission regions
250227, G01B 1116
Patent
active
046293183
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a measuring device for determining cracks in test objects by means of a crack detector which is comprised of light conductive fibers to be applied upon test objects which crack detector produces a signal for indicating a crack in the case of occurence of cracks.
It is customary in aircraft and other structure components to use measuring devices for determining cracks. There is a pronounced demand for such measuring devices which are also called crack sensors because an early recognition (of such cracks) in operating aircraft and other structure components as well as during tests make possible a suppression of interference at a sufficiently early time.
It is known for determining cracks to paste a wire upon the component, the wire being provided with an insulated jacket coating, and to use the fracture of the wire resulting from a crack for purposes of indicating the crack. Pursuant to this method, an electrical current is run through the wire which collapses when the wire fractures and triggers the crack indication in an evaluating electronic circuit. In accordance with another method for determining cracks, the respective component is provided in its entirety with an insulating layer and subsequently conductor strips are sprayed on which, just as aforedescribed trigger a crack indication upon fracture. Both methods have some drawbacks. First of all, the required insulating layer between the component and the crack identifying conductors reduce the detection sensitivity. Moreover in the case of outdoor use and particularly upon employing silver conducting lacquer, one has to expect corrosion problems which renders impossible for practical reasons any long lasting monitoring. Moreover, silver conducting lacquer is very expensive and furthermore, the depositing of conductor strips is rather expensive and troublesome. Finally, only a temporary interruption may occur upon a fracture of the conductor strips or wires, for example, because the load has abated which leads to a reclosing of the electric circuit. Moreover, the strips or wires are subject to electromagnetic interferences in the environment. This way a crack indication may be extinguished again and a non-existing freedom from cracks may be simulated.
Therefore it is an object of the invention to provide a measuring device for determining cracks in accordance with the kind mentioned in the beginning which however, guarantees always a reliable and irreversible crack indication. This object is obtained in accordance with the invention through the characterizing features of the main claim.
Further developments and advantageous embodiments of the invention can be taken from the dependent claims.
The invention is more fully explained with reference to the appended drawings. There is shown in:
FIG. 1, the principle of a measuring device for determining cracks,
FIG. 2, a light coupler,
FIG. 3, a construction part provided with light conducting fibers, and
FIG. 4, a structure connection with attached light conducting fibers,
FIG. 5, a perforated adhesive foil ribbon,
FIG. 6, a device for placing light conducting fibers upon a adhesive foil ribbon,
FIG. 6a, an adhesive foil ribbon provided with light conducting fiber,
FIG. 7, an adhesive foil ribbon with light conducting fibers placed in a meander pattern,
FIG. 8, two templates for placing light conducting fibers in a special configuration,
FIGS. 9a and 9b, the principle for producing an indication of the progression of a crack,
FIG. 10, a construction part provided with numerous light conducting fibers,
FIGS. 11a and 11b, two signal diagrams,
FIG. 12, a construction part which is periodically inspected by means of a light deflector, and
FIG. 13, a diagram showing crack progression.
The principle of a measuring device for determining cracks is illustrated in FIG. 1 wherein a light conducting fiber 2 is pasted to a construction part 1 by means of a suitable adhesive. The light conducting fiber 2 which may be comprised of glass, quartz or synthetic material, is applied to the construction
REFERENCES:
patent: 3910105 (1975-10-01), Hoffstedt
Korth, "Integrated Optical Force and Stress Sensor", IBM Tech. Disclos. Bull, vol. 24, No. 2, pp. 893-894, 7/81.
Hofer Bernd
Malek Samir
Koren Matthew W.
Siegemund Ralf H.
VFW GmbH
Willis Davis L.
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