ND T Abstracts

The ultrasonic wave propagation characteristics were ~ u r o d for IN- 100, a powder metallurgy alloy used for aircraft engine components. This material was selected as a model system for testing the feasibility of characterizing the microslructure of a variety of inhomogeueous media including powder metals, ceramics, castings and composites. The data were obtained for a frequency range from about 2 to 20 MHz and were statistically averaged over numerous volume elements of the samples. Micrographical examination provided size and number dislributions for grain and pore structure. The results showed that the predominant source for the ultrasonic attenuation and backscatter was a dense (approx. 100/ram) disUibution of small micropores (approx. 10 microns radius). Two samples with different micropore densities were studied in detail to test the feasihility of calculating from observed microstrnctural parameters the frequency dependence of the microstrnctural hackscatter in the regime for which the wavelength is much larger than the size of the individual scattering centers.

36784 Telschow, K I..; Flinn, J.E. Ultrasonic backscat ter and at tenuat ion measurements for microstructure characterization: application to consolidated rapidly solidified type 304 stainless steel powder Idaho National Engineering Laboratory, Idaho (United States), EGG-SCM- 7198, DE86-014917, 41 pp. (Mar. 1986)

The results of this study show that ultrasonic measurements of attenuation and hackscatter energy can be correlated with microstructural features in the RSP consolidated materials utilized. In particular, attenuation and backscatter energy were shown to be consistent with each other and to yield approximately the same microstructurni information. This is important because the buckscatter technique can be implemented more easily than the attenuation measurement as it requires access to only one surface of the sample under study. More information is available in the backscatter signals, but as yet is not understood well enough to be utilized. The high degree of correlation between the microstructural examinations and the ultrasonic measurements allows the latter to be of use in evaluating the effectiveness of various consolidation methods.

36777 Miller, J.G. Quant i ta t ive non-destruct ive evaluat ion of damage in composite materials using t ransmit ted and reflected ultrasound Washington University, St. Louis, Missouri (United States), N85-21269, 40 pp. (1985)

The application of ultrasound for the nondestructive evaluation of advanced composite materials is summarized. Quantitative indices from fundamental acoustic parameters of the inhomogeneous malmials were derived. The investigations into the estimation of the average attcauation from backscattered ultrasound are described. The use of a centroid.shift

technique in inhomogeneons materials is reported and investigation into the use of the Wigner distribution for attenuation estimation is summarized.

36557 Bostrom, A.; Olsson, P. Scattering of elastic waves by non-planar cracks Wave Motion, Vol. 9, No. I, pp. 61-76 (Jan. 1987)

A modification of the null field approach is used to study the scattering of elastic waves by non-planar cracks. A fictitious surface is added to the crack so that a convenient closed surface is obtained and the surface fields on this dosed surface are expanded in vector spherical harmonics. The edge conditions are introduced into these expansions and this is shown to be essential for the numerical convergence. Total cross sections and b~kscattering amplitudes as functions of frequency are computed numerically for rotationally symmeaic cracks which are part of spherical or spheroidal surfaces. By integration in frequency backscattered pulses are also computed. Some cases with two cracks are also considered.

36522 Buoncn'stiani, A.M.; Smith, B.T. Backscatter of acoustic signals from inhomogeneities in composites IEEE 1985 Ultrasonics Symposium, San Francisco, California (United States), 16-18 Oct. 1985, pp. 1068-1071. Edited by B.R. McAvoy. IEEE, Piscataway, New Jersey 0985)

We have developed a simple, effective method for analyzing the transmission aad reflection of acoustic signals from the bulk of a composite material. Using a one-dimensional invariant embedding argument, we derive two coupled recorsion relations for the reflection and transmission coefficients and a non-linear identity between them.

36470 Saniie, J.; Bilgutay, N.M. Quanti tat ive grain size evaluation using ultrasonic backscattered echoes Journal of Acoustical Society of America, Vol. 80, No. 6, pp. 1816- 1824 (Dec. 1986)

Grain size characterization using ultrasonic hack~c~_!tezed signals is an important problem in nondestructive testing of materials. In this paper, a heuristic model which relates the statisticni clmrscamstics of the memured signal to the mean ultrasonic wavelet and atwamation coeffic~t in different regions of the sample is investigated. The losses in the t~_ t-~m.xed signal are examined using temporal averaging, correlation, and pmb~li ty distribution functions of the segmented data. Farthetmore, homom0rl~ic processing is used in a novel application to estimate the mean ultrasonic wavelet (as it propagates through the sample) and the ftexl~,,ncy-dependent attenuation. In the work presented, heat-treateA stainless steel samples with various grain sizes am examined. The processed experiment~ results support the feasibility of the grain size evaluation techniques presented here using the hackscattered grain signal.

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