Characterization of surface-breaking defects in metals with the use of laser-generated ultrasound

Abstract
The interaction of ultrasound with surface-breaking slots has been used to characterize the slots, with laser generation of ultrasound providing the short-duration Rayleigh pulses used as the probe. Defect depth has been measured in the range 0.3-5.0 mm. Analysis has shown that surface echoes reflected from the defect have two major components. The first arises from direct reflection of a Rayleigh pulse from the top of the defect, whereas the second arises from a shear pulse originating from the bottom of the defect which mode-converts to a Rayleigh pulse on reaching the metal’s surface at the critical angle. This interpretation offers a diagnostic technique for measuring defect depths.
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