Scattering Analysis and Simulation for Lamb Wave Ultrasonic Testing

Abstract

Lamb wave ultrasonic testing has been practically used as a nondestructive method to detect flaws in a thin plate. Accuracy of the ultrasonic testing has, however, not been evaluated quantitatively since propagation and scattering processes of Lamb waves depend on various experimental conditions such as the frequency, the plate thickness, the wave mode and the flaw's properties. As shown in Fig. 1, the Lamb wave ultrasonic testing includes three wave phenomena: 1) conversion of ultrasonic waves driven by a transducer into Lamb waves and vice versa, 2) Lamb wave propagation between a transducer and a flaw, and 3) scattering of Lamb waves by a flaw. The relatively classical elastodynamic theories have been applied to understand the former two wave phenomena, 1) and 2). The conversion process of ultrasonic waves to Lamb waves can be interpreted as the reflection and transmission of acoustic-elastic waves at the interface of dissimilar materials. Also, the propagation of Lamb waves in a plate is one of the fundamental problems in the classical elastodynamics. On the other hand, there are few studies on the scattering of Lamb waves, although the Lamb wave scattering is of importance to establish a quantitative Lamb wave ultrasonic method. Coen et al. [1] showed that the symmetric Lamb wave is more sensitive to flaws around the center plane of the plate, while the antisymmetric Lamb wave has better responses to flaws in the vicinity of the top and bottom surfaces of the plate. In order to investigate such interaction of the Lamb wave with a flaw, it is necessary to analyze the scattering problem of Lamb waves.