Optical method for fatigue crack detection

Pernick, B. J.; Kennedy, J. R.

doi:10.1364/ao.19.003224

Cited by 10 publications

(5 citation statements)

References 5 publications

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“…11, p. 93) the object pupil function (which can also specify a limited illumination field), the illumination and observation directions, the surface microtopography -i.e., the height h(x o , y o ) of the surface points with respect to a reference plane-, multiple scattering, and shadowing. In a first approach, under normal incidence and observation, the following expression applies in many cases of practical interest: 2,4,5,8,11 [ ]…”

Section: Spectrum Analyzermentioning

confidence: 99%

“…Since the invention of laser, many attempts have been made to extract surface roughness and defect features by exploiting different optical configurations, usually contrived to render the spectrum of the scattered radiation [1][2][3][4][5][6][7][8] . In most cases, speckle is present in the whole space downstream from the scatterer, and it sometimes constitutes a kind of noise which must be filtered, but other times speckle is precisely the desired signal.…”

Section: Introductionmentioning

confidence: 99%

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Episcopic coaxial illumination device for the simultaneous recording of the speckle signature in the spectrum and in the image of scattering reflective surfaces

et al. 2012

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Inspection of optically rough surfaces in search of defects or other surface features with deterministic reflectance distributions is a subject well suited to optical techniques. We present a device with episcopic coaxial illumination, specifically developed for such kind of inspection tasks, which simultaneously renders both a coherent image and the spatial spectrum of a portion of the surface, precisely defined by the illuminating laser spot. It is based on the wellknown single-lens coherent image processing system, with beamsplitters added to insert the illuminating laser beam and to allow simultaneous access to the Fourier transform and the image planes. The device allows inspecting the speckle signature of surface features in both planes, thus allowing different defect recognition approaches. By selecting the size of the illuminated area of the object or the lens aperture, different speckle sizes can be obtained. If the speckle size is made large enough, identification of individual features can be made on the basis of their particular speckle signatures. Some envisaged applications are the characterization of defects or structures in rough surfaces, the evaluation of speckle statistics in precisely defined zones of surfaces or the identification of authentication marks.

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Section: Spectrum Analyzermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Episcopic coaxial illumination device for the simultaneous recording of the speckle signature in the spectrum and in the image of scattering reflective surfaces

et al. 2012

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“…In the references found, the particular configuration of collimated illumination is the most commonly used. [16][17][18][19][20][21][22] b.…”

Section: Introductionmentioning

confidence: 99%

Episcopic coaxial illumination instrument for the simultaneous recording of the speckle signature in the energy spectrum and in the image of scattering reflective surfaces

et al. 2013

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Abstract. The inspection of optically rough surfaces searching for defects or other macroscopic features, or with the aim of characterizing roughness, are tasks well suited to optical techniques. We present the concept, the architecture, the mathematical modeling, the calibration, and some results of a device with episcopic coaxial illumination, specifically developed for surface inspections, which simultaneously renders both a coherent image and the energy spectrum of the complex reflection coefficient of a portion of the surface, precisely delimited by the illuminating laser spot. This concept is based on the well-known, singlelens, coherent image processing setup with beamsplitters added to insert the illuminating beam and to allow simultaneous access to the Fourier transform plane and to the image plane. Information about the resolved macroscopic features and the nonresolved surface microstructure (through the corresponding speckle signature) is obtained in both planes which enables different surface analysis strategies. The speckle sizes in the spectrum, and in the image, can be controlled by selecting the size of the illuminated area of the object and the lens aperture, respectively. Some envisaged applications are the detection and characterization of defects or macroscopic structures in rough surfaces, identification of authentication marks, evaluation of roughness parameters, and of speckle statistics.

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“…However, the structural response under impact wave has been recognized as a global damage detection method [2]. As early as 1980, 1-D optical Fourier spectrum analyzer system is used to detect fatigue cracks, as small as 0.5mm fatigue cracks can be tested [3]. Since 1989, the Bragg grating has become the dominant sensor to monitor strains and deformation [4][5].…”

Section: Introductionmentioning

confidence: 99%

Pencil-lead-break transient detecting by phase- optical time domain reflectometer based on coherent detecting

2013

2013 International Conference on Optoelectronics and Microelectronics (ICOM)

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Pencil-lead-break transient detecting is demonstrated by phase-optical time domain reflectometer based on coherent detecting and data processing. By using coherent detecting technology, combined with Erbium-doped Optical Fiber Amplifier and high power load Acousto-optical Modulators (AOM), we improves signal detecting sensitive and Signal-noise-ratio by 2~3dB coherent detection advantage over direct detection of phase-OTDR. Location of pencil-lead-break transient signal was detected with higher spatial resolution in time domain by averaged traces transiently. Using varying power with time of the location, frequency information can be obtained by fast Fourier transforms (FFT) analyzer. With loop geometry fiber, as short as 0.25cm fiber can give effective signal over 12km long single-mode fiber and as high as 50 kHz frequency component can be detected.

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Optical method for fatigue crack detection

Cited by 10 publications

References 5 publications

Episcopic coaxial illumination device for the simultaneous recording of the speckle signature in the spectrum and in the image of scattering reflective surfaces

Episcopic coaxial illumination device for the simultaneous recording of the speckle signature in the spectrum and in the image of scattering reflective surfaces

Episcopic coaxial illumination instrument for the simultaneous recording of the speckle signature in the energy spectrum and in the image of scattering reflective surfaces

Pencil-lead-break transient detecting by phase- optical time domain reflectometer based on coherent detecting

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