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  • Artikel  (7)
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  • ultrasonics  (7)
  • 1980-1984  (7)
  • 1950-1954
  • Mathematik  (7)
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  • Artikel  (7)
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  • 1
    Digitale Medien
    Digitale Medien
    Interior imaging using spatial frequency sampling (1981)
    Springer
    Journal of nondestructive evaluation 2 (1981), S. 203-207 
    Details
    ISSN: 1573-4862
    Schlagwort(e): ultrasonics ; synthetic aperture ; spatial frequency ; interior imaging ; acoustic microscopy ; defect detection ; NDE
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik
    Notizen: Abstract A new acoustic synthetic aperture geometry is demonstrated in which the image field is sampled in the spatial frequency domain. This means the sampled field is recorded in a particularly convenient form for presentation to the back propagation algorithms used to reconstruct the field at the object plane. The method has applications in interior visualization. It is difficult to image the interior of solid objects using lens based imaging systems because a different lens geometry must be used for each distinct object material. The system presented here overcomes such problems since both the angular variation of the transmission coefficient at the object-water interface and the aberrations introduced by the velocity mismatch at the object surface may be readily compensated for in the back propagation routine. Experimental results are presented illustrating the detection of four half wavelength diameter defects, spaced by three wavelengths, at a depth of eight wavelengths below the surface of an aluminum block.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00570732
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Ill-posed and well-posed problems in inverse elastodynamic scattering for nondestructive evaluation (1981)
    Springer
    Journal of nondestructive evaluation 2 (1981), S. 161-172 
    Details
    ISSN: 1573-4862
    Schlagwort(e): elastodynamic inverse scattering ; ultrasonics ; data reduction ; ill-posed problems ; NDE
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik
    Notizen: Abstract The practical significance of ill-posedness in a data reduction problem is reviewed. Inverse elastodynamic scattering is shown to be ill-posed in general, although suitably restricted problems may be well-posed. These results underscore the need to analyze carefully the errors of data reduction problems in NDE, and to focus attention on final results of an NDE exercise, rather than on intermediate steps.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00570728
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Effects of sinusoidal crack-face perturbations on scattering of elastic waves (1981)
    Springer
    Journal of nondestructive evaluation 2 (1981), S. 153-159 
    Details
    ISSN: 1573-4862
    Schlagwort(e): ultrasonics ; scattering ; cracks ; periodic surface perturbation ; NDE
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik
    Notizen: Abstract The scattering of a plane longitudinal wave from a two-dimensional crack, with a sinusoidal surface perturbation whose amplitude and wavelength are much smaller than the length of the crack, is investigated. The amplitude of the cylindrical body waves in the far field are calculated from a Kirchhoff approximation that utilizes the solution to the reflection from the sinusoidal surface profile of a semiinfinite solid. The results are compared to those for a flat crack, and conditions for significant differences of the amplitude as a function of the angle of observation are discussed. Characteristic changes in the scattered field produced by profiles with different amplitudes and periods are explained.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00570727
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Elastic wave diffraction by elliptical cracks: Theory and experiment (1980)
    Springer
    Journal of nondestructive evaluation 1 (1980), S. 87-99 
    Details
    ISSN: 1573-4862
    Schlagwort(e): ultrasonics ; diffraction ; cracks ; titanium ; spectrum analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik
    Notizen: Abstract Analytical solutions to the diffraction of elastic waves by elliptical cracks in titanium are compared with experimental results. The analysis is based on physical elastodynamic theory and is valid forka≫1 and in the far field. A digitized ultrasonic spectrum analysis system is used to measure the frequency components of broadband waves diffracted from elliptical cracks with aspect ratios (ratio of major to minor axes) ranging from 1 to 8. The amplitude spectra show good agreement between experiment and theory.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00566117
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Separation and characterization of stress levels and texture in metal sheet and plate: I. Principles and preliminary experiment (1984)
    Springer
    Journal of nondestructive evaluation 4 (1984), S. 157-163 
    Details
    ISSN: 1573-4862
    Schlagwort(e): Residual Stress ; ultrasonics ; metals ; EMATs ; NDE
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik
    Notizen: Abstract An approach is proposed for obtaining separate measures of stress anisotropy and texture in metal sheet or plate. The approach is based on the propagation characteristics ofSH n modes of ultrasonic waves. Experimental work has established that differences betweenSH 0 modes with orthogonal directions of propagation provide a measure of stress anisotropy that is insensitive to texture, with the restriction that the pseudosymmetry of the polycrystalline matrix of the sheet or plate is orthorhombic or higher. In the present work, it is argued that the differences between elastic constants associated with orthogonal directions of propagation of higher order modes should provide a meaningful measure of texture. The only requirement is that the texture be sufficiently well developed so that the following inequality is obeyed: ∣C′44−C′55∣〉0.002 $$\bar C$$ with $$\bar C$$ =1/2 (C′44+C′55). HereC′44 andC′55 are the effective shear moduli for planes normal to the sheet or plate surface and at right angles to each other. They are measurable by observing the differences between the phase velocities of theSH 0 and theSH n〉0 modes in the principal directions. By using Electromagnetic Acoustic Transducers (EMATs), the phase velocities can be deduced from the frequencies at which an SH mode of fixed wavelength is optimally excited. This approach has the advantage of being independent of specimen geometry and dimensions other than thickness.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00566221
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Loss of specular reflection due to nonlinear crack-face interaction (1982)
    Springer
    Journal of nondestructive evaluation 3 (1982), S. 229-239 
    Details
    ISSN: 1573-4862
    Schlagwort(e): Crack-opening displacement ; crack closure ; ultrasonics ; Kirchoff approximation ; NDE
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik
    Notizen: Abstract The interaction between rough crack faces is modeled by nonlinear relations between the crack-face tractions and the crack-opening displacements. These relations account for crack closure and for the related resistance to crack-face sliding. The relations are used to investigate reflection and transmission of an incident pulse by an infinite flaw plane. The problem statement is reduced to a set of inhomogeneous nonlinear ordinary differential equations for the displacement discontinuities, [u] and [v], across the flaw plane. These equations have been solved numerically. The reflection and transmission of an incident pulse by a crack with interacting crack faces. Both incident longitudinal and transverse waves have been considered. The loss of specular reflection as compared to a perfect (traction-free) crack is exhibited by specific examples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00565867
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Computerized evaluation of acoustic images utilizing a method of averaging (1981)
    Springer
    Journal of nondestructive evaluation 2 (1981), S. 173-188 
    Details
    ISSN: 1573-4862
    Schlagwort(e): ultrasonics ; acoustic imaging ; computer image analysis ; failure prediction ; inhomogeneous materials ; accept/reject criteria ; NDE
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik
    Notizen: Abstract A computerized technique is presented which has been developed for analyzing acoustic images of an inhomogeneous material. The acoustic imaging system is briefly described with emphasis on its adaptation to billets of graphite for atmospheric reentry body use. Ultrasonic images of such inhomogeneous material contain a nonuniform distribution of anomalies and few, if any, geometrically regular features which can be assessed to establish material integrity. Results obtained with our new algorithms show, for certain discriminants, a high degree of correlation between the numerical accept/reject values obtained from acoustic image processing and the time-to-failure of the graphitic material in simulated atmospheric reentry tests.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00570729
    Standort Signatur Erwartet Verfügbarkeit
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