37061 Clarke, L.R.; Chou, C-H.; Khuri-Yakub, B.T.; Marshall, D.B. Acoustic evaluation of grinding damage to ceramic materials Ceramic Materials and Components for Engines, Proceedings of the 2nd International Symposium, Lubeck-Travemunde (FRG) 14-17 Apr. 1986. pp. 790-797. Edited by W. Bunk and H. Hausner, Verlag Deutsche Keramische GeseUschaft (FRG), 1205 pp. (1986)

Two complementary acoustic techniques, a 50 MHz broadband pulse-echo technique and a defocused variable frequency scanning acoustic microscope technique, have been used to nondestructively evaluate grinding damage in ceramic materials. The operating theory, relative merits, and typical data for each technique are presented. In addition, some recent improvements over previous implementations of these methods are described.

37045 Kushibiki, J.; Chubachi, N. Application of LFB acoustic microscope to film thickness measure- ments Electronics Letters, Vol. 23, No. 12, pp. 652-654 (4 Jun. 1987)

The line-focus-beam (LFB) acoustic microscope is applied to measure the precise thickness of thin films using the velocity dispersion of leaky waves in layered samples. The measurement principle and accuracy are investigated theoretically and experimentally, taking a configuration of Au-film on fused quartz. It is demonstrated at 225 MHz that the thickness resolution better than 2 angstroms is achieved for a 3000 angstroms sample using leaky pseudosurface acoustic waves.

37026 Goebbels, K.; Reiter, H.; Arnold, W.; Hirsekorn, S. A concept for the quality assurance of components of the ceramic gas turbine by Nondestructive Testing (In German) Fraunhofer-Institut, Saarbrucken (Federal Republic of Germany), N86- 17773, 55 pp. (Aug. 1985)

This work to develop nondestructive testing (NDT) methods for components made from high temperature and high strength ceramics was sponsored during the years 1977-1983 by the BMFT in a ceramic gas turbine program. The central task was to make available NDT methods for the detection of defects with linear dimensions between 10 and 100 microns. The presented final report demonstrates the elaborated concept for quality assurance.

37016 Klima, S.J.; Baaklini, G.Y.; Roth, D.J. Factors that affect reliability of nondestructive detection of flaws in structural ceramics Ceramic Materials and Components for Engines, Proceedings of the 2nd International Symposium, Lubeck-Travemunde (FRG) 14-17 Apr. 1986. pp. 833-840. Edited by W. Bunk and H. Hausner, Verlag Deutsche Keramische Gesellschaft (FRG), 1205 pp. (1986)

The purpose of this paper is to re-examine some of the factors that influence the detectability qf minute flaws in ceramics, and focus attention on requirements for assuring adequate detection sensitivity and reliability. The reliability of microfocus radiography and scanning laser acoustic microscopy (SLAM) for detection of seeded voids was evaluated.

37015 Goebbels, K. Nan-Destructive evaluation of ceramic components for engines Ceramic Materials and Components for Engines, Proceedings of the 2nd International Symposium, Lubeck-Travemunde (FRG) 14-17 Apr. 1986. pp. 779-787. Edited by W. Bunk and H. Hausner, Verlag Deutsche Keramische Gesellschaft (FRG), 1205 pp. (1986)

Surface defects in ceramics are more critical than internal defects and cracklike defects are much more severe then volumetric flaws such as inclusions. Therefore, NDE methods not only have to detect and to locate the defects, they also have to characterize them in terms of location, type, size and orientation. Microstructural features which need to be characterized by NDE include inhomogeneity and anisotropy; residual stresses can reduce the materials ability to withstand the design load and therefore require quantitative determination. NDE methods considered in this paper for surface inspection include visual inspection, dye penetrants, dye-enhanced radiography and ultrasonic testing with surface waves. In the future acoustic microscopy as well as photoacoustic microscopy will provide the highest sensitivity and resolution for surface inspection problems. Finally, from the point of view of mass production, vibration analysis will provide an attractive quality control method prior to more sophisticated NDE techniques.

36998 Baaklini, G. Y. NDE reliability and process control for structural ceramics National Aeronautics and Space Administration, Cleveland, Ohio (United States), N87-12910, 17 pp. (1986)

The reliability of microfocus x-radiography and scanning laser acoustic microscopy for detecting microvoids in silicon nitride and silicon carbide was statistically evaluated. Materials-and process-related parameters that influenced the statistical findings in research samples are discussed. The use of conventional x-radiography in controlling and optimizing the processing and sintering of a silicon nitride composition is described. Radiographic evaluation and guidance helped develop uniform high-density modulus-of-rupture bars with improved four-point flexural strength (857,544, and 462 MPa at room temperature, 1200 C, and 1370 C, respectively) and reduced strength scatter.

36959 Centre National de Recherche Scientifique Acoustic microscope for analyzing an object in depth having ospherical lenses

U.S. Patent No. 4,641,530 (10 Feb, 1987) An acoustic microscope permitting the analysis of an object in depth

comprising two identical bars positioned in an extension of one another and provided at their facing ends with a cavity, said cavities defining at least one focussing lens and at least one objective lens, said two identical lenses having coinciding foci being linked by a liquid drop in which the object to be analysed can be immersed, the bars being provided at their other ends with a piezoelectric transducer, said transducers being able to produce ultrasonics focussed within the object by the focussing lens and to detect ultrasonics reflected or transmitted by the object via the objective lens, means for analysing the ultrasonics reflected or transmitted by the object and means for displacing the object in the focal plane of the two lenses.

36952 Olympus Optical KK Ultrasonic microscope with frequency changing system British Patent No. 2,175,395 (26 Nov. 1986)

In order to replace acoustic lenses respective frequency units are provided to operate at frequencies corresponding to the frequencies used by the acoustic lenses, and each having a pulse generator, circulator and receiving means. A change-over switch selectively connects the circulator via an attenuator to a transmitter at a frequency required for a particular lens. An integrated lens and matching box construction and a gate-timing control circuit are also disclosed.

36945 Tokyo Shibaura Denki Kabushiki Kaisha Ultrasonic microscope apparatus U.S. Patent No. 4,618,934 (21 Oct. 1986)

An ultrasonic microscope apparatus comprising: means for varying the operating conditions of an integrated circuit; means for obtaining ultrasonic images of said integrated circuit by scanning said circuit with an ultrasonic beam; memory means for individually storing said ultrasonic images; means for calculating difference values for corresponding portions of said stored ultrasonic images produced for different operating conditions of said circuit; and means for displaying said difference values to provide information regarding defects in said circuit.

36940 Leland Stanford Junior University Low frequency acoustic microscope U.S. Patent No. 4,620,443 (4 Nov. 1986)

The method of detecting and isolating near-surface flaws, inclusions or voids in a solid sample which comprises: directing a focused beam of acoustic energy at the sample with its focal plane at the subsurface flaw, inclusion or void location; scanning the sample with the beam; detecting acoustic energy specularly reflected and mode converted at the surface of the sample and acoustic energy reflected by subsurface flaws, inclusions or voids at the focal plane and generating an interference signal; and processing said signal and forming a signal indicative of the subsurface flaws, inclusions or voids.

36818 Roth, D.J.; Klima, S.J.; Kiser, J.D.; Baaklini, G.Y. Reliability of void detection in structural ceramics using scanning laser acoustic microscopy National Aeronautics and Space Administration, Cleveland, Ohio (United States), N85-32337, 54pp. (1985)

The reliability of scanning laser acoustic microscopy (SLAM) for detecting surface voids in structural ceramic test specimens was statistically evaluated. Specimens of sintered silicon nitride and sintered silicon carbide, seeded with surface voids, were examined by SLAM at an ultrasonic frequency of 1130 MHz in the as fired condition and after surface polishing. It was observed that polishing substantially increased void detectability.

36810 Klirna, S.J.; Baaklini G. Y. Ultrasonic characterization of structural ceramics Analytical Ultrasonics in Materials Research and Testing. Proceedings of a conference, NASA Lewis Research Center, Ohio (United States), 13- 14 Nov. 1984. pp. 117-126. NASA Conference Publication 2383 (1986).

Ultrasonic velocity and attenuation measurements were used to characterize density and microstructure in monolithic silicon nitride and silicon carbide. Research samples of these structural ceramics exhibited a wide range of density and microstructural variations. It was shown that bulk density variations correlate with and can be estimated by velocity measurements. Variations in microstructural features such as grain size or shape and pore morphology had a minor effect on velocity. However, these features had a pronounced effect on ultrasonic attenuation. The ultrasonic results are supplemented by low-energy radiography and scanning laser acoustic microscopy.

36798 Generazio, R.E.; Roth, D.J. Quantitative flaw characterization with scanning laser acoustic microscopy Analytical Ultrasonics in Materials Research and Testing. Proceedings of a conference, NASA Lewis Research Center, Ohio (United States), 13- 14 Nov. 1984. pp. 341-358. NASA Conference Publication 2383 (1986)

Surface roughness and diffraction are two factors that have been observed to affect the accuracy of flaw characterization with scanning laser acoustic microscopy. This paper investigates the relationship between the direction of sound propagation within a sample, the apparent flaw depth, and the sample's surface roughness. Diffraction effects can mask the acoustic images of minute flaws and make it difficult to establish their size, depth, and other characteristics. It is shown that for Frannhofer diffraction conditions the acoustic

48 NDT International February 1990