All-optical probing of laser-induced modulation of crack parameters by surface Rayleigh and surface skimming longitudinal bulk acoustic pulses

Abstract

All-optical monitoring of the nonlinear motion of surface-breaking cracks is reported. Crack closing is induced by quasi-continuous laser heating, while Rayleigh acoustic pulses and skimming longitudinal surface acoustic pulses are also generated and detected by lasers. By exploiting the strong dependence of the acoustic pulses reflection and transmission efficiency on the state – open or closed – of the contacts between crack faces, the parametric modulation of ultrasonic pulses is achieved. It is demonstrated that detection of the parametric modulation of the reflected and transmitted skimming longitudinal waves and Rayleigh waves mode converted by the crack from skimming longitudinal waves is a sensitive technique for the evaluation of crack modifications and local closure. It is observed that skimming longitudinal waves can be more sensitive to crack motion than Rayleigh waves, which are probing the crack motion without mode-conversion. In comparison with an all-optical frequency-domain technique, 1 the time-domain technique is potentially faster for the imaging applications. This research is supported by the grant ANR-10-BLAN-092302 and a post-doctoral fellowship from the Région des Pays de la Loire for Dr. C. Ni. Also, the support for travelling and participation to the conference from China Postdoctoral Science Foundation (No. 20110491409) is acknowledged. 1 S. Mezil, N. Chigarev, V. Tournat, V. Gusev, “All-optical probing of the nonlinear acoustic of a crack”, Opt. Lett. 36, 3449-3451 (2011).