Comparison of several techniques of ultrasonic Lamb waves velocities measurements

Abstract

In ultrasonic NDT the important question is how precisely the velocity of ultrasonic waves propagating in the object under investigation is known. Accurate measurements of the ultrasound velocity are necessary for estimation of the elastic properties of the object material. These properties are used in numerical modelling of propagation of ultrasonic waves and determination of the object response. In the presented study a few different ultrasonic techniques for measurement of the phase velocity of Lamb waves in metal plates are presented. The immersion measurement technique was used for estimation of the S₀ mode phase velocity in the case of contact type excitation. The air-coupled measurement technique was used for estimation of the A₀ mode phase velocity which posses high leakage losses in the case of the plate loaded by liquid. The air-coupled investigations have been carried out using both through-transmission and one-side access configurations. The measured values of the phase velocities were compared with theoretically predicted and the good correspondence has been obtained.