Early detection of metal fatigue with a coherent optical cross-correlation process专利检索-统计变换视听技术与设备专利检索查询-专利查询网

Early detection of metal fatigue with a coherent optical cross-correlation process

阅读：431发布：2024-02-16

专利汇可以提供Early detection of metal fatigue with a coherent optical cross-correlation process专利检索，专利查询，专利分析的服务。并且A process for early detection of metal fatigue by coherent optical cross correlation of light from a test surface at time tk with a holographic filter of the same test surface made at an earlier point in time to. Early indication of fatigue is evidenced by minute translational displacement of the test surface''s microstructure at time tk with respect to the hologram of the same test surface made at an earlier time to. The setup includes a spherical lens to produce the Fourier transform of the image of the test surface both for making the holographic reference filter and for the subsequent cross-correlation test. Light passing through the holographic reference filter during cross correlation is converted to a substantially DC voltage by conventional photoelectrical techniques. A decrease in correlation, indicating the beginning of fatigue, is read out directly as a decrease in the DC voltage. The method is one shot noncontacting technique which is statistical in nature and can thus test relatively large surfaces, like an area of an airframe 2 feet square, in a single test.，下面是Early detection of metal fatigue with a coherent optical cross-correlation process专利的具体信息内容。

权利要求

1. The method of noncontacting detection of fatigue in a test surface by a coherent cross-correlation process to determine an impending fatigue failure prior to the occurrence of any such failure comprising the steps of: a. producing a reference hologram representing the test surface at an earlier time to; b. thereafter subjecting said surface to stress for a period of time; c. directing coherent radiation to strike and be modulated by said surface at a later time tk after said period of subjected stress; d. measuring the correlation between the pattern of said modulated radiation and said hologram; e. repeating the steps of lettered paragraphs (b through d) of this claim a plurality of times; and f. comparing a correlation measurement obtained by said repetition with previously obtained correlation measurements to detect any change in the rate of change of the correlation between said modulated radiation and said hologram, a sharp increase in said rate of change indicating an impending fatigue failure.

2. The method according to claim 1 wherein said measuring step includes cross correlation by superimposition of the modulated coherent radiation representing said test surface at a later time tk onto the recorded hologram to directly produce the cross correlation of the two patterns.

3. The method according to claim 2 wherein said coherent radiation comprises beams of laser light, wherein said hologram comprises an optic interference pattern recorded on otherwise transparent photographic film, and wherein said cross-correlation measurement is made by measuring the intensity of the light passing through said recorded hologram.

4. The method according to claim 3 wherein said correlation measuring step includes the step of converting said light intensity to a substantially DC voltage and measuring the magnitude of said voltage.

5. The method of noncontacting detection of fatigue in a test surface by a coherent cross-correlation process to determine an impending fatigue failure prior to the occurrence of any failure comprising the steps of: a. producing a reference hologram comprising a signal pattern representing the interference of the Fourier transform of coherent radiation representing the test surface at one point in time and a reference coherent radiation signal capable of interferring with said coherent radiation representing the test surface; b. thereafter subjecting Said surface to stress for a period of time; c. directing coherent radiation to strike and be modulated by the test surface at a time later than said one point after said period of subjected stress; d. generating the Fourier transform of the modulated radiation signal; e. measuring the correlation between said test surface at said one point in time and said test surface at said later time by multiplying said hologram and said Fourier transformed modulated radiation, forming the Fourier transform of the product of said hologram and said Fourier transformed modulated radiation, and measuring the intensity of said product; f. repeating the steps of lettered paragraphs (b through e) of this claim a plurality of times; and g. comparing a correlation measurement obtained by said repetition with previously obtained correlation measurements to detect any change in the rate of change of the correlation between said test surface and said hologram, a sharp increase in said rate of change indicating an impending fatigue failure.

6. The method according to claim 5 wherein said measuring step includes cross correlation by superimposition of the Fourier transform radiation representing said surface at said later time onto said hologram to produce a direct readout of the cross correlation between said surface and said hologram.

7. The method according to claim 6 wherein: said coherent radiation comprises beams of laser light; wherein: said hologram is produced by: directing a beam of laser light to strike and be modulated by said surface; forming the Fourier transform of the modulated coherent radiation; directing a reference beam of laser light to intersect and interfere with said Fourier transform laser light; and recording the holographic interference pattern on otherwise transparent photographic film; and wherein: said cross-correlation measurement is made by measuring the intensity of the laser light passing through said recorded hologram.

8. The method according to claim 7 wherein said cross correlation is accomplished by aligning a photoelectrical sensing device at a viewing angle with respect to the normal to the rear surface of said recorded hologram, substantially as shown so that said photoelectrical sensing device is aligned with the projection of a line that strikes the recorded hologram at an angle equal to the angle at which the reference beam struck the photographic film during recording of the hologram.

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Early detection of metal fatigue with a coherent optical cross-correlation process

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