Backscatter from a spherical inclusion with compliant interphase characteristics

ND T Abstracts concentration or porosity at the optimum azimuthal angle for interrogation of a specific ply lay-up. 43385 Kitahara,M.; Nakagawa, K.; Achenbach, J.D. Ba~tter from a spherical inclusion with compliant i n t e r p h m e characteristics Review of Progress in Quantitative Nondestructive Evaluation, Vol. 8A. Edited by D.C. Thompson and D.E. Chimenti, pp. 47-54. Plenum Press (1989), ISBN 0 306 43209 9 In this paper it is investigated to what extent an interphase affects the scattered field geuerated by an incident ultrasonic wave. Both a completely intact but compliant interphase, and an interphase which does not transmit tractions over pan of the area between the inclusion and the matrix, have been considered. 43384 Kechter,G.E.; Achenbach, J.D. The extraction of single-void characteristics from ultrasonic backscatter from void d u s t e r s Review of Progress in Quantitative Nondestructive Evaluation, Vol. 8A. Edited by D.C. Thompson and D.E. Chimenti, pp. 55-62. Plenum Press (1989), ISBN 0 306 43209 9 Using ultrasonic backacatter from a specimen containing a cluster of cavities, the size of a single cavity in the cluster has been extracted. A time-domain response obtained by the extraction procedure compares favorably with the analytically calculated response for a single cavity. The procedure removes distortions of the measured response caused by the measuring system, by the specimen, and by other cavities in the cluster. This method should be useful for obtaining similar results from different types of flaw clusters in various types of materials. 43119 Roberts,RA.; Qu, J.; Achenbach, J.D. Experimental a n d theoretical analysis of backscattering mechanisms in fiber-reinforced composites Acousto-Ultrasonies, Theory and Application. Edited by J.C. Duke, Jr., pp. 151-164, Plenum Press, 353pp (1989). ISBN 0306430134 This paper examines experimental measurements of polar hackscatter following the techniques first employed by Bar-Cohen and Crane, and later by others. Experimental meusurements of the angular dependence of ultrasonic hackscatter are presented for fiber reinforced composite specimens containing various levels of porosity. This data demonstrates how hack~a~__~ed signals from porosity are inseparably intertwined with signals _sc~_~_.~lby the intemul fiber-related structures of the composite. The transmission characteristics at the water/composite interface are of fundamental importance to the tl~o~tical analysis of the backscaeu~ experiment. The transmission characteristics of the composite specimens were measured experimentally, and a comparison is made with theoretically evaluated transmission coefficients for a fiuld-lcuded transversely isotmpic halfspace. The close agreement observed in this comparison demonslrates the validity of the transverse isotropy assumption used in modeling the buckscatter from the fiberous microstructore. 42384 Kawano, K.; Birring,A.S. Hydrogen damage detection by a nondestructive testing technique Materials Performance, Vol. 28, No. 8, pp. 71-74 (Aug. 1989) This article discusses three ultrasonic testing techniques based on velocity change, attenuation,and beckacatter that can be applied to detect hydrogen a~a_ckin steel components in petroleum and petrochemical plants. Actual hydrogen-damaged samples were examined from vessels and piping. It was found that ultrasonic velocity change and backscatter techniques could detect early stages of hydrogen attack.

42044 Xin-long, W.; Ruo, F. Diffraction correction in backseattering measurement Ultrasonic Imaging, Voi. 27, No. 4, pp. 239-244 (Jul. 1989) In this paper, the meaning of the beckacatter coefficient of biological tissue is explained in detail, using statistical concepts, and the influence of the diffraction effect of the sound field on hackscatter coefficient measurement is analysed theoretically. For correcting the diffraction effect on the hackacatter coefficient measured in the near field, a quantity defined as the diffraction correction coefficient, [3, is introduced and an experimental method for determining the value of ~ is proposed, based on the theoretical analysis of the backscatter signs]. Using the method, the value of ~ for a transducer with nominal frequency 2.5 MHz has been measured in the frequency range 1.7-3.2 MHz. For demouslrating the validity oftbe method, the average hack~tfer coefficient of pigheart is determiued in beth the far field and near field, and the data measured in the near field have been corrected with [3. It is shown that the corrected backacatter coefficient for the near field agrees with that for the far field quite well.

42031 Cheung,A.T.~I.; Buchen, P.W.; Macaskill, C. Backscatter spectrum of a r a n d o m l y p e r t u r b e d regular a r r a y of discrete scatterers Journal of the Acoustical Society of America, Vol. 86, No. 1, pp. 407- 413 (Jul. 1989) This paper inve~igl~s the ~__k~t,,,r spectnnn of acoustic beams and plane waves from a particular distribution of discrete _s~_~__,~m~.The distribution is a random spatial perturbation ~om some underlying regular structure. Models of this type sre considered as crude ~esentations of biological tissue, such as the fiver. It is shown that, for plane waves, the random perturbations of the scatters act as a linear filter of the backscatter response. The analytic form of the filter function is directly related to the pmhability distribution of the spatial perturbations. It is further demonstrated that a similar result holds for acoustic beams, if the lateral scale of the beam variations is large compared with the mean scatterer separations. The impact of this result on ultrasonic tissue characterization studies using attenuation measurements is discussed. 42010 Saniie,J.; Bilgutay, N.M.; Wang, T. Signal processing of ultrasonic backscattered echoes for evaluating the microstructure of materials - a review Signal Processing and Pattern Recognition in Nondestructive Evaluation of Materials, Proceedings of the NATO Advanced Research Workshop, Lac Beauport, Quebec, Canada, 19-22 Aug. 1987. Edited by C.M. Chert, pp. 87-100. Springer-Verlag (1988) The microstructure evaluation of materials using ultrasonic hackscaucred echoes has significant practical implications. Ultrasonic bacl~,-~ered grain echoes are random signals which bear information related to the attenuation caused by scatteringand absorption. The variation of attenuation as a function of position and fzequency represents changes in the sc_~_~eringcrc~-section and absorption effects of grains. We present a statistical model of backacattered signals which is used for developing signal processing techniques in both time and frequency domain. The attenuation in the b a c k m m e ~ signal is evaluated by porfonning temporal and spatial average. The spectral shift in the backacaUe~ signal is characterized using moment analysis. Furthermore, frequency-dependent attenuation is estimated by applying spectral processing. Experimetal results using steel samples of different grain sizes are in close agreement with theoretical predictions. 42002 Amurwabumi,K.; Bridge, B. Non-contact method of monitoring stress n e a r the yield point Journal of Physics D, Vol. 22, No. 8, pp. 1062-1067 (Aug. 1989) The stress dependence of the intensity of 3 MHz ultrasound hacksc~e_ted at an oblique angle from a water-Duralumin interface is reported. Tensile test specimens of Duralumin were subjected to cyclic stresses of amplitude 200 MPa. The amplitodns of hackscatten~ signals having a well defined frequency were obtained by spectrum analysis. If the changes in backscaUer amplitude are assumed to have been related to dislocation clamping, it is shown that the damping must have inczeused by typically 0.6 dB ps before plastic deformation occurred. The possibilities of using the technique for practical non- contact monitoring of local plastic deformation and related effects are discussed. 41639 Kechter,G.E.: Achenbach, J.D. Void characterization using ultrasonic backscatter from void clusters Research in Non-destructive Evaluation, Vol. 1, No. 1, pp, 13-29 (1989) A technique to extract the deconvolved response of a single cavity from the backacattered ultrasonic signal received from a cluster of cavities is presented. Fu-st, a standard deconvolution removes noise and distortions of the signal caused either by the measuring system or the specimen. This is followed by homorphic deconvolution using the complex spectrum to extract the response of a single cavity when signals from adjacent cavities in the cluster are superimposed on each other. The technique is applied to backscatter from a cluster of spherical cavitins located in an epoxy specimen. The recovered signal compares favorably with the analytically calculated, back_~_~e~ time-domain response of a spherical cavity due to the incidence of a plane longitudinal wave on the single cavity. The radius of the cavity can be obtained from the extracted response using a simple formula derived from elastodynamic ray theory. 41631 Tao, W. Ultrasonic signal processing a n d pattern recognition in evaluating the microstructure of materials Dissertation Abstracts International, Vol. 49, No. 4, p. 1327 (Oct. 1988) This thesis focuses on the analysis and development of signal processing

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