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Nondestructive characterization of defects using ultrasonic backscattering
ND T Abstracts 39046 Shankar, P.M.; Bencharit, U.; Bilgutay, N.M.; SAM&, J. G r a i n noise suppression through bandpass filtering Materials Evaluation, Vol. 46, No. 8, pp. 1100-1104 (Jul. 1988) Ultrasonic nondestructive evaluation (NDE) of materials is limited by the presence of the backscattered echoes from the grain boundaries (i.e., grain noise).This noise often masks the signal leading.todifficultiesin its detection and identification.Itis shown that in NDE applicationswhere the received noise is primarily due to Rayleigh scattering (from the grain boundaries) and the flaw echo can be represented by a delta function,flaw visibilitycan be improved significantly(without the need for sophisticated signal-processingalgorithms) by merely ban@ass filtering(BPF) the lower edge of the received echo spectrum. Both theoretical analysis and experimental results are presented to support this conclusion. The limitationsof thistechnique are also discussed. 39028 Saniie,J.; Wang, T.; Bilgutay,N.M. Statistical evaluation of backscattered ultrasonic grain signals Journal of the Acoustical Society of America, Vol. 84, No. I, pp. 400- 408 (Jul. 1988) Insonification of the microstmcturo of materials results in a backscattered signal consisting of multiple interfering echoes with random amplitudes and phases. Information pertaining to grain scattering cross section and grain size distribution is an inherent property of the backscattered signal. A statistical model of grain signals is developed that describes the spatial and time averaged data, and their relationship to signal attenuation caused by scattering and absorption. Both spatial and temporal averaging permits the estimation of the attenuation coefficient, which has been found to be position dependent. Furthermore, it has been shown experimentally and theoretically that the performance of spatial and time averaging is governed by correlation properties of the grain signal.
38935 Peters, K3.; Wang, R.C. Compensation for receiver bandpass effects on ultrasonic backscatter power spectra using a r a n d o m medium reference Journal of the Acoustical Society of America, Vol. 84, No. 1, pp. 392- 399 (Jul. 1988) A linear model of an ultrasonic pulse-echo system is used to express the measured power spectrum as the product of a scattering medium power spectrum and a transfer function accounting for system effects. Transfer functions are experimentally determined for multiple ranges using a random medium reference. Measured pQwer spectra normalized by these functions are shown to be in close agreanmnt with theoretical power spectra both in shape and absolute magnitude. The results indicate that the model allows scattering media to be distinguished when the media hackscatter characteristics differ in the bandwidth of the measurement system. 38719 Anon. Porosity characterization in fiber-reinforced composites using ultrasonic backscatter Argonne National Laboratory, Illinois (United States), CONF860856-10, DE87-001484, 23 pp. (Sep. 1986) The use of ultrasonic backscatter to characterize anomolous states in fiber-reinforced composites has received considerable attention in recent years. Unlike monolithic materials, ultrasonic back-scatter from composites with oriented fiber reinforcement displays a strong angular dependence. Hence, three independent variables are available over which to analyze the hackscatter, i.e. time, asimuthai angle, and elevation angle. In this paper, specific questions are addressed concerning the angular dependence of backscatter, and the subsequent use of the angular dependence to assess porosity levels. Additionally, problems inherent in the analysis of the temporal behavior of backscatmr are discussed, and an approach to the spectral analysis of backscattexof porosity assnssr:~entis demonstrated. 38504 Qu Jianmin Baekscatter from flaws in fiber-reinforced composites Dissertation Abstracts International, Vol. 48, No. 8, pp. 2377-2378 (Feb. 1988) This thesis consists of two parts. The first part deals with wave scattering by cracks in anisotropic elastic media. A slit, as well as a penny-sbaped crack in a transversely isotropic solid, are considered. A new method of asymptotic analysis based on the integral representation for the scattered field is formulated to solve scattering by a planar crack in materials with a more general kind of anisotropy. The second part of this thesis is concerned with detection and characterizationof flaws in composite plates by ullrasonicmeans. A range of wavelengths is selected so that the mechanical behavior of the inhomogeneons fiber-:'ei;fforcedcompositescan be represented by that of a homogeneous but ani~,:a:.opicelastic solid. It is anticipated that the hackscatter analysis will p.ove useful in the nondestructive characterization of flaw sizes, attenu~ioi coefficients and the density of porosity of composite materials.
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38452 Herment, A.; Demoment, G.; Peronneau, P. High definition backscatter imaging: A different approach Ultrasonics International 87, Conference Proc.eedings, London (United Kingdom), 6-9 Jul. 1987. pp. 537-542. Butterworth and Co. (Publishers) Ltd., Guildford, Surrey (1987) A method for acquisition and processing of echographic B scans was developed. It affords high definition images and a number of advantages with respect to 2D deconvolution. The process works as follows: a) acquisition of radio-frequency B-scans, b) flue-by-line deconvolution of each scan in the axial direction, c) video detection, d) reconstruction of the image using a •tered hackprojection process. A study on simulated data and on phantoms will be discussed. For a typical image obtained from 16 scans, the comparison with 2D deconvolution indicates: a) a gain in definition of about five, b) a four time improvement of the S/N ratio, c) a processing time reduced by a ratio of 12.
38450 Li, X.; Bilgutay, N.M.; Tartono, S.; SAM&, J. Grain size estimation using a statistical scattering model Ultrasonics International 87, Conference Proceedings, London (United Kingdom), 6-9 Jul. 1987. pp. 526-531. Butterworth and Co. (Publishers) Ltd., Guildford, Surrey (1987) Grain size estimation in polycrystalline materials using ultrasonic backscattered echoes has significant practical implications in evaluating the integrity of materials during their manufacture and use. In addition, it has been shown that certainmaterial characteristics can be evaluated based on grain size analysis. Therefore, reliable methods for nondestructively evaluating the grain size are highly desirable in industrial applications. However, the complexity of the ultrasonic backscattered signal, which consists of interfering multiple echoes with random positions and amplitudes, makes accurate grain size evaluation difficult with conventional signal processing techniques. In this paper, analytical calculations based on a statistical scattering model are presented which show that the average grain size can be extracted from the power spectrum of the backscatte~ echoes obtained by deconvolution. The simulation results presented here show the potential feasibility of the proposed method in practical applications. 38449 Gaunaurd, G.C. Inverse scattering techniques for material characterization Ultrasonics International 87, Conference Proceedings, London (United Kingdom), 6-9 Jul. 1987. pp. 520-525. Butterworth and Co. (Publishers) Ltd., Guildford, Surrey (1987) We study inverse scattering techniques useful for the extraction of composition and shape information from the resonances in the echoes returned by elastic targets within elastic or fluid media. All the information required to characterizean elastic scatterer is contained in the p a l m of poles of its ~_~e_~g amplitude in the (complex) frequency plane. Two easily distinguishable sets of poles characterize shape and composition. separately. These pole positions arc related to tim locations and widths of the resonances in the inclusion's backscattering cross section, or its partial waves. The asymptotic spacings between any two consecutive dilatafional (broad) and any two shear (narrow) resonances, and the width of any dilatational one, uniquely determine the composition of an elastic spherical targeL 38426 Pederseno P.C. Inverse methods in ultrasonics Ultrasonics International 87, Conference Proceedings, London (United Kingdom), 6-9 Jul. 1987. pp. 372-380. Buttetworth and Co. (Publishers) Ltd., Guildford, Surrey (1987) As the understanding of the interaction betvama ultrasound and scattering media is deepened, and as compu~ional systemsbecomemore powerful, the ability to extract quantitative information by means of invene methods from transmitted and/or backscau~ ~and has improved. This paper examines inverse methods in ullmsound, such as tomngn~bic techniques and impediography, the~ applications, advantages and drawbacks. In addition, ultrasound inverse methods in non-destructive evaluation is reviewed. 38422 Bar-Cohen, Y. Nondestructive characterization of defeem ruing ultrasonic backscattering Ultrasonics International 87, Conference Proceedings, London (United Kingdom), 6-9 Jul. 1987. pp. 345-352. Buttexwor~ and Co. (Publishers) Ltd., Guildford, Surrey (1987) Ultrasonic back_~a~ering measurements were made for discon.finuities having a wavenumber-langth smaller than 1. These tests were conducted for multilayered materials consisting of metals, composites, and their combination as an ARALL material. Amplitude meusmements of the
ND T Abstracts 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. W i d e b a n d backseattering measurements using a parametric array 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 sphereover 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 a m p 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. M a p p i n g ultrasound pulse-echo non-stationarity 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. Evaluation of the subsurface microstructure of quenched and tempered c a r b o n 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 caseof the En25 samples,which all had the same mean grain size, the backscattered energy decreased systematically with increasinghardness, 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 backscatteredenergy 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
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 determination of h u m a n 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 designedand 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 L a m b waves in composite plates Materials Evaluation, Vol. 46, No. l, pp. 97-100 (Jan. 1988) Experiments to observe backscattered leaky Lamb waves from a fiberreinforced 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 a n d 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 characterizeinhomogeneitiesin monolithic ceramics, signal characterizationof back-scattered25 MHz focussed,pulsed ultrasoundhas 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) structure 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 characterization 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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38935 Peters, K3.; Wang, R.C. Compensation for receiver bandpass effects on ultrasonic backscatter power spectra using a r a n d o m medium reference Journal of the Acoustical Society of America, Vol. 84, No. 1, pp. 392- 399 (Jul. 1988) A linear model of an ultrasonic pulse-echo system is used to express the measured power spectrum as the product of a scattering medium power spectrum and a transfer function accounting for system effects. Transfer functions are experimentally determined for multiple ranges using a random medium reference. Measured pQwer spectra normalized by these functions are shown to be in close agreanmnt with theoretical power spectra both in shape and absolute magnitude. The results indicate that the model allows scattering media to be distinguished when the media hackscatter characteristics differ in the bandwidth of the measurement system. 38719 Anon. Porosity characterization in fiber-reinforced composites using ultrasonic backscatter Argonne National Laboratory, Illinois (United States), CONF860856-10, DE87-001484, 23 pp. (Sep. 1986) The use of ultrasonic backscatter to characterize anomolous states in fiber-reinforced composites has received considerable attention in recent years. Unlike monolithic materials, ultrasonic back-scatter from composites with oriented fiber reinforcement displays a strong angular dependence. Hence, three independent variables are available over which to analyze the hackscatter, i.e. time, asimuthai angle, and elevation angle. In this paper, specific questions are addressed concerning the angular dependence of backscatter, and the subsequent use of the angular dependence to assess porosity levels. Additionally, problems inherent in the analysis of the temporal behavior of backscatmr are discussed, and an approach to the spectral analysis of backscattexof porosity assnssr:~entis demonstrated. 38504 Qu Jianmin Baekscatter from flaws in fiber-reinforced composites Dissertation Abstracts International, Vol. 48, No. 8, pp. 2377-2378 (Feb. 1988) This thesis consists of two parts. The first part deals with wave scattering by cracks in anisotropic elastic media. A slit, as well as a penny-sbaped crack in a transversely isotropic solid, are considered. A new method of asymptotic analysis based on the integral representation for the scattered field is formulated to solve scattering by a planar crack in materials with a more general kind of anisotropy. The second part of this thesis is concerned with detection and characterizationof flaws in composite plates by ullrasonicmeans. A range of wavelengths is selected so that the mechanical behavior of the inhomogeneons fiber-:'ei;fforcedcompositescan be represented by that of a homogeneous but ani~,:a:.opicelastic solid. It is anticipated that the hackscatter analysis will p.ove useful in the nondestructive characterization of flaw sizes, attenu~ioi coefficients and the density of porosity of composite materials.
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38452 Herment, A.; Demoment, G.; Peronneau, P. High definition backscatter imaging: A different approach Ultrasonics International 87, Conference Proc.eedings, London (United Kingdom), 6-9 Jul. 1987. pp. 537-542. Butterworth and Co. (Publishers) Ltd., Guildford, Surrey (1987) A method for acquisition and processing of echographic B scans was developed. It affords high definition images and a number of advantages with respect to 2D deconvolution. The process works as follows: a) acquisition of radio-frequency B-scans, b) flue-by-line deconvolution of each scan in the axial direction, c) video detection, d) reconstruction of the image using a •tered hackprojection process. A study on simulated data and on phantoms will be discussed. For a typical image obtained from 16 scans, the comparison with 2D deconvolution indicates: a) a gain in definition of about five, b) a four time improvement of the S/N ratio, c) a processing time reduced by a ratio of 12.
38450 Li, X.; Bilgutay, N.M.; Tartono, S.; SAM&, J. Grain size estimation using a statistical scattering model Ultrasonics International 87, Conference Proceedings, London (United Kingdom), 6-9 Jul. 1987. pp. 526-531. Butterworth and Co. (Publishers) Ltd., Guildford, Surrey (1987) Grain size estimation in polycrystalline materials using ultrasonic backscattered echoes has significant practical implications in evaluating the integrity of materials during their manufacture and use. In addition, it has been shown that certainmaterial characteristics can be evaluated based on grain size analysis. Therefore, reliable methods for nondestructively evaluating the grain size are highly desirable in industrial applications. However, the complexity of the ultrasonic backscattered signal, which consists of interfering multiple echoes with random positions and amplitudes, makes accurate grain size evaluation difficult with conventional signal processing techniques. In this paper, analytical calculations based on a statistical scattering model are presented which show that the average grain size can be extracted from the power spectrum of the backscatte~ echoes obtained by deconvolution. The simulation results presented here show the potential feasibility of the proposed method in practical applications. 38449 Gaunaurd, G.C. Inverse scattering techniques for material characterization Ultrasonics International 87, Conference Proceedings, London (United Kingdom), 6-9 Jul. 1987. pp. 520-525. Butterworth and Co. (Publishers) Ltd., Guildford, Surrey (1987) We study inverse scattering techniques useful for the extraction of composition and shape information from the resonances in the echoes returned by elastic targets within elastic or fluid media. All the information required to characterizean elastic scatterer is contained in the p a l m of poles of its ~_~e_~g amplitude in the (complex) frequency plane. Two easily distinguishable sets of poles characterize shape and composition. separately. These pole positions arc related to tim locations and widths of the resonances in the inclusion's backscattering cross section, or its partial waves. The asymptotic spacings between any two consecutive dilatafional (broad) and any two shear (narrow) resonances, and the width of any dilatational one, uniquely determine the composition of an elastic spherical targeL 38426 Pederseno P.C. Inverse methods in ultrasonics Ultrasonics International 87, Conference Proceedings, London (United Kingdom), 6-9 Jul. 1987. pp. 372-380. Buttetworth and Co. (Publishers) Ltd., Guildford, Surrey (1987) As the understanding of the interaction betvama ultrasound and scattering media is deepened, and as compu~ional systemsbecomemore powerful, the ability to extract quantitative information by means of invene methods from transmitted and/or backscau~ ~and has improved. This paper examines inverse methods in ullmsound, such as tomngn~bic techniques and impediography, the~ applications, advantages and drawbacks. In addition, ultrasound inverse methods in non-destructive evaluation is reviewed. 38422 Bar-Cohen, Y. Nondestructive characterization of defeem ruing ultrasonic backscattering Ultrasonics International 87, Conference Proceedings, London (United Kingdom), 6-9 Jul. 1987. pp. 345-352. Buttexwor~ and Co. (Publishers) Ltd., Guildford, Surrey (1987) Ultrasonic back_~a~ering measurements were made for discon.finuities having a wavenumber-langth smaller than 1. These tests were conducted for multilayered materials consisting of metals, composites, and their combination as an ARALL material. Amplitude meusmements of the
ND T Abstracts 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. W i d e b a n d backseattering measurements using a parametric array 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 sphereover 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 a m p 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. M a p p i n g ultrasound pulse-echo non-stationarity 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. Evaluation of the subsurface microstructure of quenched and tempered c a r b o n 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 caseof the En25 samples,which all had the same mean grain size, the backscattered energy decreased systematically with increasinghardness, 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 backscatteredenergy 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
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 determination of h u m a n 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 designedand 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 L a m b waves in composite plates Materials Evaluation, Vol. 46, No. l, pp. 97-100 (Jan. 1988) Experiments to observe backscattered leaky Lamb waves from a fiberreinforced 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 a n d 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 characterizeinhomogeneitiesin monolithic ceramics, signal characterizationof back-scattered25 MHz focussed,pulsed ultrasoundhas 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) structure 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 characterization 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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