ULTRASONIC LAMB-WAVE PROPAGATION MODELS FOR NONDESTRUCTIVE TESTING APPLICATIONS

摘要

Basic Lamb wave propagation formulae are presented. The propaga-tion equations leading to the type of Lamb mode vibration explained in terms of net particle vibrations in, and perpendicular to, the direction of Lamb wave travel are repeated after Worlton. The elliptical particle move¬ment which results from the net particle vibration is shown to be contin¬uously distributed throughout the wave carrying specimen. Interpretation of practical Lamb wave tests in terms of net particle movements is helpful is some instances. However, the treatment of the propagation in terms of separate waves has offered further insight. Accordingly, a technique for separating Lamb waves into longitudinal and shear wave components was developed and formulas for amplitude ratios are presented. The net particle movement for Lamb wave phase velocities, V, greater than the Zircaloy longitudinal velocity, V1, is shown to be the combined effects of a pair of longitudinal and a pair of shear waves. For phase velocities between V1, and the shear velocity, Vs , the situation is not clear since the longitudinal waves convert to boundary layer waves which are not easily explained physically.nIn order to demonstrate the existence of the four waves for V>V1, Zircaloy plates vibrating in the Lamb wave domain were observed using the Schlieren image technique which is briefly described. Sound leakage from the end of plates immersed in water is demonstrated to be the result of the expected pairs of longitudinal and shear waves. An attempt to obtain a mathematical model describing the observed end leakage in terms of the ratio of longitudinal and shear wave amplitudes within the plate was only partially successful. Wave phenomena in the range of V