Ultrasonic microstructural monitoring

factors governing fracture processes and associated stress wave interactions. Analysis of the empirical correlations indicates that, in addition to grain size and shape, grain boundary reflections, elastic anisotropy, and dislocation damping are factors that underly both fracture toughness and ultrasonic attenuation. 37341 Pao, Y-H. Theory of aconstoelasticity and aconst~plasticity Solid Mechanics Research for Quantitative Nondestructive Evaluation, Proceedings of the O N R Symposium on Solid Mechanics Research for Q N D E , Northwestern University, Evanston, Illinois (United States), 18-20 Sep. 1985. pp. 257-274. Martinus Nijhoff Publishers (1987) The theory of acoustoelasticity and several recently developed theories of acoustoplasticity are reviewed in this article. For a body with plastic deformation, the acoustoelastic birefringence is affected by the initial stress and the texture, and the latter is related to plastic strains and inherent anisotropy of the body. The bireftingence formula may be applied to measure residual stresses by ultrasonic techniques. 37340 Sayers, C.M. Ultrasonic determination of texture and residual stress in polycrystalline metals Solid Mechanics Research for Quantitative Nondestructive Evaluation, Proceedings of the O N R Symposium on Solid Mechanics Research for O N D E , Northwestern University, Evanston, Illinois (United States), 18-20 Sep. 1985. pp. 319-336. Martinus Nijhoff Publishers (1987) In a polycrystalline aggregate the elastic constants in the specimen reference frame vary from grain to grain due to the random orientation oi the grains. Polycrystalline metals are therefore elastically inhomogeneous, and the elastic constant mismatch at the grain boundaries leads to scattering of the ultrasonic wave. In the long wavelength limit, however, the metal can be modelled as an elastic continuum with elastic constants determined by the elastic constants of the grains and the crystallite orientation distribution function (CODF). This function gives the probability of a crystallite having a given orientation with respect to the specimen frame, and gives a quantitative description of the texture, or crystallographic alignment, of the material. In a strongly textured metal the yield stress varies as a function of direction and this can lead to non-uniform flow in deep drawing for example. As a result there is a need for a non- destructive measurement of texture in process control, and there is considerable interest in the use of ultrasonics for this purpose. Information on the CODF can be obtained from ultrasonic velocity measurements. 37333 UnitedKingdom Atomic Energy Authority Ultrasonic microstructural monitoring British Patent No. 2,172,106 (10 Sep. 1986) A method and apparatus use forward scatter for monitoring the microstructural features, such as grain size, of an object. A point- source broad-band ultrasonic wave transmitter (laser generates a sharp pulse of ultrasound at a point, which propagates through the object), and ultrasonic waves in the object are detected at a second point by a point broad-band detector (laser interferometer). Small signals detected after the arrival of a straight-through compression wave and before the arrival of a straight-through shear wave correspond to forward-scattered waves and are indicative of microstructural features lying substantially on the straight line between the generation point and the detection point. Much of the scattered energy is modeconverted. 37082 Bridge, B.; Bollini, G.J. 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, backscattered from oil-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 backscatter caused by surface roughness and other (incidental) effects of machining, could be distinguished from backscatter from flat uumachined specimens relating to features such as grain size, nature of the grain boundary and phase structure etc., in the subsurface. 37079 Taylor, J.J. Ultrasonic inspection of cast stainless steel (CCSS) E P R I Journal, Vol. 12, No. 4, pp. 54-55 (Jun. 1987) Centrifugally cast stainless steel (CCSS) is often used for main coolant piping in PWRs. Unfortunately, the characteristics of CCSS that account for its structural strength and durability also make it difficult to inspect with standard ultrasonic techniques. The manufacturing process-centrifugal casting-creates an anisotropic and inhomogeneous material that scatters ultrasonic pulses in unpredictable ways. In addition, ultrasonic pulses are severely attenuated before reaching the inner depths of a pipe wall, both because of the grain structure and because of the wall thickness, which in PWR applications is typically 2-3 in (5.1-7.6 cm) with pipe diameters on the order of 30 in (76 cm). EPRI is funding research to develop improved techniques for inspecting CCSS piping.

NDT International October 1989

37051 Kupperman, D.S.; Reimann, K.J.; Abrego-Lopez, J. Ultrasonic NDE of cast stainless steel N D T International, Vol. 20, No. 3, pp. 145-152 (3 Jun. 1987) The microstructure of cast stainless steel can vary considerably, from elastically isotropic with an equiaxial, relatively small grain structure to elastically anisotropic with a columnar grain structure to a combination of the two. The ultrasonic inspection of this material may be optimized if the grain structure is known. Shear waves will be more effective with the isotrnpic material whereas longitudinal waves will be better for the anisotropic material because of beam-focusing effects. In this paper, the results of experiments to characterize the microstructure by use of ultrasonic waves are discussed. It is shown that velocity of sound and beam skewing can be measured accurately enough to characterize cast stainless steel even in thick-walled reactor components. The consequences for field inspections are discussed, along with some results obtained from preservice field tests. 37047 Williams, J.H. Jr.; Lee, S.S. Pattern recognition characterizations of micromechanical and morphological materials states via analytical quantitative ultrasonics International Advances in Nondestructive Testing, Vol. 12, pp. 193-212 (1986) An outline is provided for the pattern recognition characterizations of micromechanicai and morphological materials states via analytical quantitative ultrasonics. The concepts, terminology and techniques of statistical pattern recognition are reviewed. Via a program of ultrasonic data generation, feature extraction and classification, states of the structure can be determined. 36815 Green, R.E. Jr. Ultrasonic nondestructive materials characterization Analytical Ultrasonics in Materials Research and Testing. Proceedings of a conference, N A S A Lewis Research Center, Ohio (United States), 13- 14 Nov. 1984. pp. 31-47. N A S A Conference Publication 2383 (1986). A brief review of ultrasonic wave propagation in solid materials is presented with consideration of the altered behavior in anisotropic and non-linear elastic materials in comparison with isotropic and linear elastic materials. Some experimental results are described in which ultrasonic velocity and attenuation measurements give insight into materials microstructure and associated mechanical properties. Recent developments with laser beam non-contact generation and detection of ultrasound are presented. The ultrasound are discussed, which provide substantial evidence of the inability of presently accepted theories to fully explain the interaction of ultrasound with solid materials. Finally, a special synchrotron x-ray topographic system is described which affords the possibility of observing direct interaction of ultrasonic waves with the microstructural features of real crystalline solid materials for the first time. 36812 Rosen, M. Analytical ultrasonics for characterization of metallurgical microstructures and transformations Analytical Ultrasonics in Materials Research and Testing. Proceedings of a conference, N A S A Lewis Research Center, Ohio (United States), 13- 14 Nov. 1984. pp. 83-102. N A S A Conference Publication 2383 (1986). Application of contact (piezoelectric) and noncontact (laser generation and detection) ultrasonic techniques for dynamic investigation of precipitation hardening processes in aluminum alloys, as well as crystallization and phase transformation in rapidly solidified amorphous and microcrystalline alloys are discussed. 36806 Thompson, R.B.; Smith, J.F.; Lee, S.S. Inference of stress and texture from angular dependence of ultrasonic plate mode velocities Analytical Ultrasonics in Materials Research and Testing. Proceedings of a conference, N A S A Lewis Research Center, Ohio (United States), 13- 14 Nov. 1984. pp. 169-180. N A S A Conference Publication 2383 (1986). The theory for the angular dependence of the ultrasonic wave velocity in a symmetry plane of an orthorhombic, stressed material is presented. The two waves having polarizations in this plane are shown to have velocities which can be estimated from measurements of the SH/sub o/and S/sub o/guided modes of thin plate: the relationship being exact for the SH/sub o/mode and requiring a 10% correction for the S/sub o/mode at long wavelength. It is then shown how stress and texture can be independently inferred from various features of the angular dependence of these two velocities. From the SH/sub o/data, the ability to determine the directions and differences in magnitudes of principal stresses is described and supported by experimental data on several materials. From a combination of the SH/sub o/and S/sub o/data, a procedure is proposed for determining the coefficients W/sub 400/, W/sub 420/, and W/sub 440/ of an expansion of the crystallite orientation distribution function in terms of generalized Legendre functions. Possible applications in process control are indicated.

36804 Williams, J.H. Jr.; Lee, S.S. Pattern recognition characterizations of micromeehanical and morphological materials states via analytical quantitative ultrasonics Analytical Ultrasonics in Materials Research and Testing. Proceedings of a conference, N A S A Lewis Research Center, Ohio (United States),

309