Depth evaluation of surface-breaking cracks using laser-generated transmitted Rayleigh waves

Abstract

A theoretical and experimental study of nondestructive evaluation of surface-breaking cracks with linear surface acoustic wave (SAW) pulses is presented. Schwarz–Christoffel conformal mapping was used to introduce a special orthogonal coordinate system that conserves the profile of the cracked surface. The inverse problem for two dimensions has been solved by means of conformal mapping. Thermoelastically generated broadband SAW pulses were employed to study the scattering of linear SAW pulses by a single crack. The surface wave component transmitted through the isolated microcrack was recorded as a function of distance by the cw laser probe-beam-deflection method. The Fourier transform of the transmitted SAW waveforms provides a stationary solution for any frequency. With this procedure the depth of the crack, produced in a separate experiment with a strongly nonlinear SAW pulse in a silica sample, was evaluated.