Acoustic nonlinearity of narrowband laser-generated surface waves in the bending fatigue of Al6061 alloy

The present study describes the acoustic nonlinearity phenomenon of a narrowband lasergenerated surface wave for the characterization of an aluminum alloy subjected to bending fatigue. The surface wave is very attractive for field applications because it does not require both sides of the test materials to access the transducers and has strong acoustic nonlinear effects on the surface. The intrinsic higher-order harmonic components generated by a line-arrayed laser beam have been analyzed theoretically, and a relative acoustic nonlinear parameter has been successfully measured on the surface of a fatigue-damaged aluminum 6061 alloy. The results show that the acoustic nonlinear parameter increased after fatigue damage with respect to dislocation evolution. Consequently, this study suggests that the new acoustic nonlinearity technique of a laser-generated surface wave can be potentially used to characterize surface damage resulting from bending fatigue prior to the formation of fatigue cracks.