Surface Acoustic Wave Interactions with Cracks and Slots: A Noncontacting Study Using Lasers

Abstract

Abstruct-The interaction of surface acoustic Rayleigh pulses with surface-breaking defects has been experimentally studied. The pulses were generated using a Q-switched Nd:YAG laser, and were detected by either a ball capacitance transducer or a laser interferometer. It is shown that reflected waveforms from a defect possess two major components. The first arises from direct reflection of a Rayleigh pulse from the top of the defect, while the second appears to arise from a shear pulse originating from the base of the defect, which is then mode-converted to a Rayleigh pulse on reaching the metal's surface. This model is supported by further experiments which examined interaction with 90 and 270 corners, as well as down-steps. The results offer a new laser technique for measuring defect depths in the range 0.1 to 5 mm.