This paper was prepared upon request from the organizers of the XVIII St. Petersburg conference "Ultrasonic Flaw Detection in Metal Structures. UZDM 2004." The progress made in the theoretical issues of ultrasonic flaw detection over the past 20 years is briefly considered, and some practical issues are discussed. Specific problems that are waiting to be solved are formulated, and the author's opinions about the prospects of developments in ultrasonic flaw detection are presented. The preparation of the paper was much facilitated by book [1], which was published recently.RUSSIAN JOURNAL OF NONDESTRUCTIVE TESTING Vol. 40 No. 10 2004 ERMOLOV L.V. Yuozonene [5] reported that the existence of surface-longitudinal waves follows from the characteristic Rayleigh equation, which is known to be used to prove the existence of Rayleigh-type surface waves. However, V.N. Danilov [6] showed this interpretation of the complex roots of the characteristic equation to be wrong. If the Poisson's coefficient is >0.26, the equation has a single root that corresponds to the Rayleigh wave. The root found by Yuozonene is a root of the characteristic equation after it has been squared (which has to be done when solving the equation), but not a root of the initial equation.Shear head waves. In [7, paper no. 1.28], M.V. Asadchaya et al. report that subsurface vertically polarized transverse waves exist and can be used. Their velocity is almost twice as high as that of subsurface longitudinal waves; hence, the depth of the layer that is subject to inspection decreases accordingly. The most efficient method for exciting waves when inspecting metals is to use piezoelectric probes with wedges made of Plexiglas arranged according to the duet scheme. The directional diagram of these waves is analyzed experimentally. Rayleigh SH-waves. The authors of [4, p. 3160] reported that they developed piezoelectric probes for radiating and receiving angular horizontally polarized transverse waves, including ones with a refraction angle of 90 ° . It should be noted that a surface horizontally polarized transverse wave is not a Rayleigh wave, since the latter is a combination of a vertically polarized transverse wave and a longitudinal wave, which together ensure that the stresses at the surface of a solid are equal to zero. In the case of the surface SHwaves under consideration, the longitudinal wave cannot interact with the transverse wave, since the oscillations occur in different planes.
Measurement of the Attenuation CoefficientWhen measuring the attenuation of waves, it is necessary to take into account the diffraction attenuation of ultrasonic rays in the probe's acoustic field and the incomplete reflection of ultrasound from the TOprobe boundary upon repeated reflections in the test object. In many cases, these corrections are not taken into account in studies on the measurement of the attenuation coefficient. A detailed procedure for the measurement of the attenuation coefficient including illustrative examples is presented in manual [8]. It is sta...
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