Study on the interaction mechanism of laser-generated Rayleigh waves and subsurface inclined cracks

Abstract

In this paper, the finite element method (FEM) was used to study the reflected and transmitted waves of laser-generated Rayleigh waves from subsurface inclined cracks, the propagation paths and mode conversion mechanisms of different characteristic waves are determined. The Rayleigh wave will interact with the crack top tip and propagate back and forth along the crack surface, and be converted to shear waves at the crack top tip. The shear waves will mode-convert to Rayleigh waves at the free surface when the incidence angle of the shear wave is larger than 60°. Moreover, for the Rayleigh wave interacting with the crack bottom tip, when the crack inclined angle is less than 60°, some Rayleigh waves will travel along the crack surface to the crack top tip. When the crack inclination angle is greater than 60°, in addition to the Rayleigh waves propagating upwards along the crack surface, some Rayleigh waves convert to shear waves at the crack bottom tip and then incident on the free surface of the workpiece. Experiments were carried out to validate some of the Rayleigh wave propagation paths. The experimental results matched the theoretical arrival time well, thus verifying the reliability of the analytical wave path. The results are helpful for the quantitative detection of subsurface inclined cracks using laser ultrasonic techniques.