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  • 1
    Electronic Resource
    Electronic Resource
    Directionally sensitive photorefractive interferometric line receiver for ultrasound detection on rough surfaces (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2236-2238 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An adaptive heterodyne interferometer is configured as a line receiver using wave mixing in photorefractive bismuth silicate crystal. The line receiver is directionally most sensitive to ultrasound impinging normal to the line, and is significantly less sensitive to ultrasound impinging in other directions. Such a system is attractive in situations where the ultrasonic scatter from a specific direction is to be selectively pulled out in the presence of scatter from other "noise" sources. It is also demonstrated that the line probe system can be used to bridge the sensitivity gap that optical detection thus far has suffered vis-à-vis piezoelectric detection. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121687
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  • 2
    Electronic Resource
    Electronic Resource
    Photoacoustic characterization of the mechanical properties of thin films (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 691-693 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Narrow band photoacoustics (laser ultrasonics) are used to characterize the properties of free-standing nanometer-sized thin films. Photoacoustic generation is achieved by use of a microchip laser which deposits pulsed laser energy in the form of a spatially periodic source on the structure. The resulting narrow band ultrasonic modes are monitored using a Michelson interferometer. By varying the geometry of the spatially periodic source, a wide range of acoustic wave numbers is probed. Results are presented for two-layer thin film aluminum/silicon-nitride (Al/Si3N4) membranes. For such thin films, only the two lowest order guided modes are generated and these in turn can be related to sheet and flexural modes in plates. The mechanical properties and residual stress in the thin films are evaluated from measured acoustic dispersion curves for these two lowest order modes. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1434303
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  • 3
    Electronic Resource
    Electronic Resource
    Heterodyne interferometer with two-wave mixing in photorefractive crystals for ultrasound detection on rough surfaces (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3782-3784 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Heterodyne interferometers using two-wave mixing in photorefractive cubic crystals for ultrasound detection on rough surfaces are demonstrated. The speckled scattered beam from a rough surface sample interferes with a planar coherent pump beam inside a photorefractive crystal. A third frequency-shifted beam is used to read the grating. The diffracted readout beam and the transmitted signal beam are wavefront matched, resulting in an optimal heterodyne interference signal. The signal to noise ratio for the two commonly used crystallographic configurations with cubic crystals, G(parallel)〈110〉(parallel) and G(parallel)〈001〉, where G is the grating wave vector, are investigated. Very good sensitivity is demonstrated for the detection of small amplitude ultrasonic surface displacements. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116997
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  • 4
    Electronic Resource
    Electronic Resource
    Synchronized reference updating technique for electronic speckle interferometry (1993)
    Springer
    Journal of nondestructive evaluation 12 (1993), S. 133-138 
    Details
    ISSN: 1573-4862
    Keywords: Electronic speckle interferometry ; nondestructive evaluation of disbonds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In this paper, a video-based speckle interferometric method using a continuous reference updating technique is presented. Unlike conventional ESPI techniques, this methodsynchronizes the optical interferometric detection system with the acoustic stressing of the test object, and includes continuous renewal of the reference image. It is shown that the susceptibility of the method to environmental noise caused by vibration, temperature gradients, or thermal currents is substantially lower than that of conventional techniques. The application of this technique to the detection of defects in adhesively bonded structures is demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00567569
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  • 5
    Electronic Resource
    Electronic Resource
    Advanced Image-Processing Techniques for Automatic Nondestructive Evaluation of Adhesively-Bonded Structures Using Speckle Interferometry (1997)
    Springer
    Journal of nondestructive evaluation 16 (1997), S. 215-227 
    Details
    ISSN: 1573-4862
    Keywords: Quantitative nondestructive evaluation (QNDE) ; shearography ; electronic speckle pattern interferometry ; fringe pattern analysis and interpretation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In conventional optical nondestructive evaluation (NDE) of structures using shearography or electronic speckle pattern interferometry (ESPI), results are typically provided in the form of fringe patterns or deformation contour plots. However, in order to fully automate the process of defect detection, it is desirable to obtain simpler results which are easier to interpret. We present here one such optical system based on additive–subtractive shearography/ESPI. This system processes additive–subtractive fringe patterns and provides the sizes and locations of defects such as disbonds in adhesively-bonded composite structures. This is achieved by exciting the structure under inspection using an acoustic stressing mechanism which sweeps a range of vibration frequencies of the structure. Since the defective areas of the structure have different mechanical properties from their neighboring regions, varying and complex fringe patterns are obtained at different stressing frequencies. We propose an algorithm which enables the automatic identification and selection of relevant additive–subtractive fringe patterns that pertain only to localized deformations associated with defects, and which excludes images that pertain to any overall modes of the entire structure. The algorithm also includes a pixel-by-pixel adjustable thresholding scheme which compensates for intensity variations due to nonuniform reflectivity from unpainted and dirty test objects. Morphological processing is then performed to extract the shapes of the defect from the processed fringe clusters. Various structures, from simple aluminum specimens with simulated defects to a complex honeycomb-based aviation repair patch specimen, have been successfully evaluated using this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021848031529
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  • 6
    Electronic Resource
    Electronic Resource
    Application of Scanning Laser Source Technique for Nondestructive Flaw Detection (2004)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 270-273 (Aug. 2004), p. 787-792 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/48/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.270-273.787.pdf
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamic measurement of the J integral in ductile metals: Comparison of experimental and numerical techniques (1990)
    Springer
    International journal of fracture 42 (1990), S. 209-230 
    Details
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Experiments and analyses designed to develop an extension of the method of caustics to applications in dynamic, elastic-plastic fracture mechanics are described. A relation between the caustic diameter, D, and the value of the J integral was obtained experimentally and numerically for a particular statically loaded specimen geometry (three point bend) and material (4340 steel). Specimens of the same geometry and material were then loaded dynamically in impact. The resulting caustics, recorded using high speed photography, were analyzed on the basis of the J versus D relation to determine the time history of the dynamic value of J, J d (t). The history of J d thus obtained is compared with good agreement to an independent determination of J d (t) based on a two-dimensional, dynamic, elastic-plastic finite element analysis, which used the experimentally measured loads as traction boundary conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00013214
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  • 8
    Electronic Resource
    Electronic Resource
    A coherent gradient sensor for crack tip deformation measurements: analysis and experimental results (1991)
    Springer
    International journal of fracture 48 (1991), S. 193-204 
    Details
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A first order diffraction analysis of an optical interferometer, Coherent Gradient Sensor (CGS), for measuring surface gradients is presented. Its applicability in the field of fracture mechanics is demonstrated by quantitatively measuring the gradients of out-of-plane displacements around a crack tip in a three point bent fracture specimen under static loading. This method has potential for the study of deformation fields near a quasi-statically or dynamically growing crack.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00036631
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  • 9
    Electronic Resource
    Electronic Resource
    Optical mapping of crack tip deformations using the methods of transmission and reflection coherent gradient sensing: a study of crack tip K-dominance (1991)
    Springer
    International journal of fracture 52 (1991), S. 91-117 
    Details
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A new full field optical technique-‘Coherent Gradient Sensing’ (CGS)-is developed and used to study crack tip deformations in transparent as well as opaque solids. A first order diffraction analysis is provided for the technique and its feasibility is demonstrated both in transmission and reflection modes. Preliminary results from the dynamic crack growth experiment clearly demonstrate the capability of CGS to be an effective experimental alternative to other optical methods used in dynamic fracture studies. Notably, it is a full field technique which works with optically isotropic materials. The static fringe patterns obtained from the experiments are analyzed in regions outside the 3-D zone. For geometries where the region outside the 3-D zone is K-dominant, the fringes provide an accurate value of 2-D stress intensity factor. For geometries where the region outside the 3-D zone is not K-dominant, Williams' expansion is used in conjunction with a least squares procedure to obtain the stress intensity factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00032372
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