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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-4862
    Keywords: Ultrasonics ; wavy composites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The through-thickness waviness in a sublamina in a composite laminate is the subject of study for the purposes of nondestructive evaluation by ultrasound. The model consists of a flat composite laminate with one sublamina which has sinusoidal waviness. The theoretical analysis of a longitudinal wave propagating through such a laminate is presented and the reflection coefficients at various locations on the plate are calculated. The results are validated by experimental ultrasonic C-scan.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4862
    Keywords: Nondestructive evaluation ; ultrasonic spectroscopy ; attenuation coefficients ; porosity characterization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In conventional material evaluation and attenuation measurement, methods employing multiple ultrasonic echoes in the thickness direction of the samples are often used to calculate the reflection and attenuation coefficients. The successive echoes must be well resolved, and there is consequently a minimum thickness of material which can be tested for a given frequency transducer. For thin specimens, a high frequency probe may be used, but this may be problematic for composite laminates since the reflections from the individual plies can cause interference. In this paper, an alternative method based on the amplitude spectrum of the reflections from the specimen is presented. The technique deduces the attenuation coefficients by using the spectral amplitudes at the anti-resonance (or resonance) frequencies of the normalized amplitude spectrum, and has the advantage that it does not require that the successive echoes be separated in time. Measurements made on glass, epoxy, and composite laminate specimens are used to compare our attenuation measurement technique with the standard method.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-4862
    Keywords: Ultrasonic velocity measurements ; bar velocity ; single crystal α-Al2O3 (saphire) fibers ; Young's modulus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Single crystal α-Al2O3, (sapphire) fibers of ∼ 100 μm diameter have recently emerged as candidates for stiffening and strengthening high temperature composites. The Young's modulus of these fibers depends upon their crystallographic orientation, ranging from a high of 461 GPa for thec-orientation to a low of ∼373 GPa for orientations 45° off thec-axis. A deviation of the fibers' axial orientation from the c-axis and thus a reduction in the fibers' axial modulus can sometimes occur during the fiber growth process, and so a simple reliable method is needed to characterize the modulus and/or orientation of the fibers. A laser generated-piezoelectric transducer detected ultrasonic method has been used for this purpose. It has been found that a clear correlation exists between the velocity of the first arriving ultrasonic signal and the deviation of the fiber's axis from thec-axis. The measured velocity is found to be in reasonably good agreement with the calculated bar velocity,ν b =√E/ρ, for the fiber, providing an estimate of the fiber's orientation dependent Young's modulus. The small differences between the measured and the calculated velocities are believed to be caused by a combination of measurement errors, uncertainties in the reference elastic compliance constants of α-Al2O3 and the presence of small volume fractions of pores and other (low modulus) aluminum oxide phases in the fibers.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-4862
    Keywords: Digital speckle pattern interferometry ; nondestructive inspection ; digital speckle shearing interferometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In this paper, a digital speckle pattern interferometer configuration for the enhanced nondestructive inspection of components in the production line is presented. The setup used is adapted from the original design employed for digital speckle shearing interferometry. The theoretical principle behind the technique is outlined and its application in the detection of poor bolting in plates is demonstrated.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 14 (1995), S. 47-47 
    ISSN: 1573-4862
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-4862
    Keywords: Rayleigh waves ; surface crack ; reflection coefficient ; weight function estimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A numerical evaluation model of the reflection coefficient of Rayleigh waves for a linear distribution of surface cracks is developed using the weight function estimation method. The numerical evaluation of the reflection coefficients varying with respect to the crack depth ratios, frequencies, and the number of the cracks for several commonly used engineering materials is performed. The results show that the model can effectively be used to evaluate the reflection coefficient for a linear distribution of the cracks. The crack depth which can be evaluated has been extended substantially and the evaluation results have been improved.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-4862
    Keywords: Coherent scattering ; incoherent scattering ; rough interface ; imperfect interface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A theoretical model for ultrasonic wave scattering for geometrically irregular and imperfectly bonded interfaces is presented. Part I presents the stochastic interface characterization and a model for its mechanical response based on a micromechanics model of asperity contact. Part II uses this interface representation to write the well used “quasi-static” boundary conditions for scattering from a.flat imperfect interface1 directly on the irregular interface profile. The boundary conditions are then expanded in an asymptotic series in the roughness parameter (standard deviation of the surface height) which is small compared to wavelength. The slope of the profile must also be everywhere small. These equations are solved exactly for the zero-th and second order terms, which are the flat coherent solution and its' first coherent correction, and the first order term, which is the first term in the expansion for the incoherently scattered solution. Results for obliquely incident longitudinal and shear waves show a strong dependence on the roughness in both the coherent and incoherent reflected fields, but little if any dependence on the roughness in the transmitted fields. In particular, the reflected coherent fields show markedly increasing attenuation compared to the flat compliant interface with increasing roughness and increasing ultrasonic frequency, the latter result being in qualitative agreement with results for scattering from an inhomogeneous array of individual scatterers.2 There is evidence in the incoherent reflected fields for the existence of an incoherent leaky interface disturbance which manifests itself as a bulk incoherent shear wave at a scattering angle equal to the critical longitudinal angle. A coherent true interface wave is also supported by the rough interface which is shown to further attenuate the coherent reflected fields compared to the flat compliant interface solution.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-4862
    Keywords: Self-focusing ; arrays ; ultrasonics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A self-focusing technique and its application to a linear array system are presented in this paper. By application of the technique the system is capable of both sonification and reception focusing. The array is first excited as an unfocused array. Next a cross-correlation technique is used to determine time delays of reception of the largest amplitude backscattered signals at the elements of the array. The original transducer signal is then reemitted with the appropriate time delays to achieve sonification focusing on the scatterer producing the largest signal. This process is repeated in an iterative mode to focus energy on the strongest scatterer. Once insonification focusing has been achieved the last time-delay calculations are used once more for reception focusing, i.e., to correct the signals received by the individual elements for differences in arrival times. A low cost linear array has been constructed to implement the self-focusing technique. Examples demonstrate the capability of the technique to focus on the largest hole of sets of three holes in an aluminum specimen.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-4862
    Keywords: Eddy-current NDE ; defect sizing ; benchmark problems ; inverse problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A set of four benchmark problems is presented for verification of theoretical calculations of defect size and shape in eddy-current nondestructive evaluation. The benchmark problems are based on careful measurements of the change in coil impedance as a function of frequency for a circular air-cored coil which is scanned along the axis of an electrodischarge machined slot in a thick aluminum alloy plate. Slots of (i) semi-elliptical, and (ii) double-peaked profiles are considered. Deviations from ideal coil behavior are identified and corrected so that the final impedance data and experimental parameters can be directly used to verify theoretical inversion algorithms.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 15 (1996), S. 43-43 
    ISSN: 1573-4862
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Type of Medium: Electronic Resource
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