backscattered wave in the time domain were found to provide a parameter for detection and characterization of various types of defects. Some unexplained phenomena were observed that cannot be predicted by any of the documented theories. The experimental results and their potential application to nondestructive evaluation are considered in this paper.

38414 Humphrey, V.F.; Murphy, C.; Mou~tafa, A,H.A. Wideband backseat ter ing measurements using a parametr ic a r r ay U~trasonics International 87, Conference Proceedings, London (United Kingdom), 6-9 Jul. 1987. pp. 265-270. Butterworth and Co. (Publishers) Ltd., Guildford, Surrey (1987)

A method of measuring the backscattering from a solid sphere over a wide f r e q u ~ range using a paramelric array as an acoustic source is desc~ihed and illustrated with experimental results for the frequency range 10-175kHz. The measurements were made using a a'uncated parameWic array to produce short low-frequency response of the sphere. Results are presented for the form function of a stainless steel sphere 38 mm in diameter for wavenumher-radius products (ka) from 0.8 to I0. The experimental results are in good agreement with theoretical predictions and show the effects of the creeping wave and elastic resonances. Measurements are also presented for a smaller tungsten carbide sphere 25.4mm in diameter.

38388 Varadan, V.V.; Tsao, S.L: Varadan, V.K. Image reconstruction of flaws using r amp response signatures An International Symposium on Pattern Recognition and Acoustical Imaging, Newport Beach, California (United States), 4-6 Feb. 1987. pp. 293-300. Proceedings of the SPlE - The International Society for Optical Engineering, Vol. 768 (1987)

A new method for generating three dimensional images of flaws in elastic solids from hackscattered data at a finite number of look angles (usually 2 to 3) is .presented. The procedure is based on the physical elastodynamics approximation "which leads to a relationship between the backscattered ramp response to an incident ultrasonic ramp pulse and the area of cross section of the object along the "line of sight."

38385 Se&gie, D.A.; Hoddinott, J.C.; Leeman, S.; Costa, E.T. Mapping u l t rasound pulse-echo non-stat ionari ty An International Symposium on Pattern Recognition and Acoustical Imaging, Newport Beach, California (United States), 4-6 Feb. 1987. pp. 241-247. Proceedings of the SPIE - The International Society for Optical Engineering, Vol. 768 (1987)

The use of ultrasound pulse-echo signals to produce quantitative parameter mappings (or images) of an inhomogeneous medium is complicated by the presence of echo interference and transducer field effects. This. paper discusses how the use of appropriate measurement techniques can counter the latter problem, leaving the speckle due to interference as the major source of artefact. Fluctuations in the, instantaneous frequency of the received signals may be used to pin- point the location of the destructive interference in the pulse-echo signals. When assessing bulk attenuation values by a backscattering technique, this allows the data to he selectively edited to exclude interference-con-apted segments, considerably reducing the need for gross averaging over large amounts of data, The approach also points towards a technique for reducing the (artefactual) speckle-like appearance of attenuation images obtained via a backscattering technique.

38372 Leviston, D.; Bridge, B. Evaluat ion of the subsurface microstructure of quenched and tempered carbon steel by ultrasonic backscatter NDT International, Vol. 21, No. 1, pp. 17-25 (Feb. 1988)

The behaviour of 5 MHz ultrasound hackscattet~ at the Rayleigh angle from water-immersed specimens of En3A, En9 and En25 steel has been related to microstructural features induced by heat IrentmenL The range of phase structures considered is a substantial extension on what has been described in the previous literature. In the case of the En25 samples, which all had the same mean grain size, the backscattered energy decreased systematically with increasing hardness, within the standard deviation of the energy backscattered from different regions of the same sample. When all samples of the three types of steel were compared at constant grain size in the Rayleigh scattering region, the backscattered energy was found to vary systematically with phase structure in the decreasing sequence: 80% peariite-20% ferrite > balnite > tempered martensite > 80% ferrite-20% pearlite > acicular ferrite > martensite. The intensity of backscattering can be changed by up to 20 dB by heat treatment, with a standard deviation of about 1.5 dB for repeat measurements at the same sample point, while the standard deviation for the signal intensity arising from different regions of the same specimen surface varied between 2 and 4 dB. It appears that the backscatter technique can readily distinguish between different phase

ND T Abstracts

structures as produced, for example, by oven cooling and air cooling, and it is worth noting that the data were obtained using a standard, relatively inexpensive, ultrasonic flaw detector.

38169 Chu Weikom; Botros, N.; Cheung, J.Y. In-vivo determinat ion of hum an liver acoustic characteristics Ultrasonic Technology 1987. Proceedings of the Toyohashi International Conference on Ultrasonic Technology, Toyohashi (Japan), 20-22 Apr. 1987. pp. I-6. Edited by K. Toda. MYU (1987)

The goal of our project was to study the feasibility of pursuing in- vivo ultrasound tissue differentiation through a microcomputer-besed digitizing and analysis system. The tissue of interest was the human liver. Differentiation was done by comparing the average acoustic attenuation coefficients and backscanering coefficients of twenty-four normal livers with that of four abnormal livers. To measure the attenuation and backscattering coefficients, we designed and constructed a comprehensive data acquisition system that would digitize the hackscattering ultrasound signals from liver tissues.

38154 Nagy, P.B.; Jungman, A.; Adler, L. Measurements of backseattered leaky Lamb waves in composite plates Materials Evaluation, Vol. 46, No. l , pp. 97-100 (Jan. 1988)

Experiments to observe backscattered leaky Lamb waves from a fiber- reinforced composite plate immersed in water have been carried out by using a broadband pulse-echo technique. Extensive spatial averaging was used to recover the backscattered power spectrum from the detected incoherent signal. Sharp peaks were observed at frequencies corresponding to backward-propagating leaky lamb waves caused by scattering inhomogeneities in the plate.

37763 Stockman, A.; Nicholson, P.S.; van den Andel, J. Detection and characterization of spherical particles in glass and glass-ceramic matrices Fifth Pan Pacific Conference on Nondestructive Testing, Vancouver (Canada), Apr. 1987, pp. 173-183. Atomic Energy of Canada Limited, AF.CI.,-9394 (Mar. 1987)

In order to characterize inhomogeneities in monolithic ceramics, signal characterization of back-scattered 25 MHz focussed, pulsed ultrasound has been applied in a step by step approach. The first step was to examine voids in glass. These were optically characterized as spheres with diameters of 30 to 120 microns. Correlations were made with the ultrasonic signals returned. A mathematical model for ultrasound scattering from spheres in an elastic medium was used to predict the f~luency response characteristics for voids. The next step involved the manufacture of spherical particles of zircouia in the size range of 20 to 200 microns diameter which were also imbedded in glass. The model was modified to calculate the heckscattering of ultrasound from inhomogeneities of known elastic constants. The most recent step was the inU'oduction of spherical inclusions into crystallizable glass. Optical characterization was made. then the glass was crystallized to introduce a host matrix structure similar to that of a ceramic. Using appropriate values for elastic constants, experimental and theoretical results are found to be well correlated. This presentation reviews the work done on inhomogeneities in glasses and its application to defect characterization in ceramics.

37082 Bridge, B.; Bollini, GJ. The effect of surface roughness on ultrasonic backscatter monitoring of intrinsic (subsurface) s t ructure British Journal of Nondestructive Testing, Vol. 29, No. 4, pp. 228-237 (Jul. 1987)

The angular dependence of the amplitude of ultrasound pulses, backscatternd from oH-immersed machined bars of bright steel, has been obtained in the frequency range 5-40 MHz. The scattering surfaces had a wide spread of roughness, 0.1-14 microns, encompassing the range ordinarily encountered after very fine to very coarse machining by grinding, milling or shaping. The prime aim of the work was to establish whether the contributions to hackscatter caused by surface roughness and other (incidental) effects of machining, could be distinguished from backscatter from fiat unmachined specimens relating to features such as grain size, nature of the grain boundary and phase structure etc., in the subsurface.

36816 Tittmann, L.A.; Ahlberg, and K. Fertig. Ultrasonic characterizat ion of microstructure in powder metal alloy Analytical Ultrasonics in Materials Research and Testing. Proceedings of a conference, NASA Lewis Research Center, Ohio (United States), 13- 14 Nov. 1984. pp. 1-29. NASA Conference Publication 2383 (1986)

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