Nonlinear Laser-generated Surface Wave Technique for Evaluation of Surface Damage

Abstract

This study presents the nonlinear narrowband laser-generated surface wave technique as a non-contact method to evaluate the surface micro-damage of aluminum alloy specimens subjected to tensile deformation. The basis of narrowband surface wave generation principles by line-arrayed laser beam and second harmonic generation by acoustic nonlinearity were analyzed theoretically. For the experimental generation of the narrowband surface wave, the system consisted of pulsed laser, beam expander and slit mask was used. The acoustic nonlinearity of surface wave is evaluated by measuring the magnitude of second harmonic in the received wave signal. This process is applied to several specimens with different level of surface micro damage. Experimental results showed good correlation between the acoustic nonlinear parameter of a laser-generated surface wave and tensile deformation.