Evolving fatigue damage detection based on multi-component nonlinear modulation mechanism of tuned laser-generated Rayleigh waves

In this paper, we clarify the nonlinear interaction between tuned Rayleigh waves and evolving fatigue damage and achieve evolving fatigue damage detection. Firstly, the impact of laser parameters on Rayleigh waves is investigated to generate stronger Rayleigh waves. Secondly, the multi-component nonlinear modulation mechanism of Rayleigh waves is analyzed using the nonlinear model considering contact and friction. The simulation results indicate that during the plastic deformation stage, waveform distortion is minimal. As microcracks form, the longitudinal wave component becomes dominant in Rayleigh wave nonlinearity due to contact and friction behaviors between microcrack faces, resulting in waveform distortion, harmonic generation, and increased acoustic nonlinearity parameters. However, the shear wave component only exhibits high-frequency filterability without nonlinearity. As macrocracks develop, both longitudinal and shear wave component amplitudes decrease significantly. Finally, an experimental validation is carried out. The experimental results validate that the acoustic nonlinearity parameters first stabilize and then increase significantly from the pristine state to the microcrack propagation, and the indicator can be utilized for fatigue damage detection. The research can provide guidance for nonlinear laser-generated Rayleigh wave detection of fatigue damage.