High speed thin plate fatigue crack monitor
First Claim
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1. An apparatus for high speed monitoring of fatigue cracks in a thin plate, comprising:
- means for vibrating to apply a sinusoidal driving function to produce resonant vibrations in said thin plate; and
means for detecting acoustic emissions from cracks in said thin plate and correlating said acoustic emissions with crack geometry, wherein said acoustic emissions are produced by interactions of crack faces during resonant vibration of said thin plate.
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Abstract
A device and method are provided which non-destructively detect crack length and crack geometry in thin metallic plates. A non-contacting vibration apparatus produces resonant vibrations without introducing extraneous noise. Resulting resonant vibration shifts in cracked plates are correlated to known crack length in plates with similar resonant vibration shifts. In addition, acoustic emissions of cracks at resonance frequencies are correlated to acoustic emissions from known crack geometries.
42 Citations
25 Claims
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1. An apparatus for high speed monitoring of fatigue cracks in a thin plate, comprising:
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means for vibrating to apply a sinusoidal driving function to produce resonant vibrations in said thin plate; and means for detecting acoustic emissions from cracks in said thin plate and correlating said acoustic emissions with crack geometry, wherein said acoustic emissions are produced by interactions of crack faces during resonant vibration of said thin plate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An apparatus for vibrating a thin metal plate, comprising an electromagnet having a first and a second end, to be disposed a distance from the surface of said thin metal plate, the ends of said electromagnet having a concave surface;
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a pair of rare earth permanent magnets, each of said permanent magnets fixedly disposed at each concave end of said electromagnet; means for supplying a driving current to said electromagnet; and means for controlling the frequency and amplitude of said driving current.
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15. A method for high speed monitoring of fatigue cracks in a thin plate, comprising the steps of:
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(a) producing resonant vibrations in said thin plate by actuating a non-contacting vibrating source which generates a sinusoidal driving function; (b) detecting the resonance frequency of said thin plate; and (c) determining fatigue crack size in said thin plate by correlating the resonance frequency of said thin plate to resonance frequencies associated with known crack sizes of a thin plate of similar dimensions and composition. - View Dependent Claims (16, 17)
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18. A method for high speed monitoring of fatigue cracks in a thin plate, comprising the steps of:
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(a) producing resonant vibrations in said thin plate by actuating vibrating source which generates a sinusoidal driving function; (b) detecting acoustic emissions produced by the interactions of crack faces resulting from resonant vibration of said thin plate; and (c) characterizing the geometry of a crack in said thin plate by correlating detected acoustic emissions from said thin plate to acoustic emissions obtained from cracks with known geometries in thin plates of similar dimensions and composition. - View Dependent Claims (19, 20)
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21. A method -for high speed monitoring of fatigue cracks in a thin plate, comprising the steps of:
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(a) producing resonant vibrations in said thin plate by actuating a non-contacting vibrating source which generates a sinusoidal driving function; (b) detecting the resonance frequency of said thin plate; and (c) determining fatigue crack size in said thin plate by correlating the resonance frequency of said thin plate to resonance frequencies associated with known crack sizes calculated by finite element modeling of a thin plate of similar dimensions and composition. (d) detecting acoustic emissions produced by the interactions of crack faces resulting from resonant vibrations of said thin plate; and (e) characterizing the geometry of a crack in said thin plate by correlating acoustic emissions from said thin plate to acoustic emissions obtained from cracks with known geometries in thin plates of similar dimensions and composition. - View Dependent Claims (22, 23, 24)
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25. An apparatus for high speed monitoring of fatigue cracks in a thin plate, comprising:
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a vibrator for vibrating said thin plate to produce resonant vibrations by generating a sinusoidal driving function, wherein said vibrator does not contact said thin plate, the vibrator having; an electromagnet having a first and a second end, to be disposed a distance from the surface of said thin plate, the ends of said electromagnet having a concave surface; a pair of rare earth permanent magnets, each of said permanent magnets fixedly disposed at each concave end of said electromagnet; means for supplying a driving current to said electromagnet; means for controlling the frequency and amplitude of said driving current; and means for detecting resonance frequency shifts resulting from cracks in said thin plate, wherein said resonance frequency shifts are correlated to crack length.
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Specification