Feasibility study on time-domain extraction method for zero-frequency pulse signal of nonlinear Lamb waves and early fatigue damage detection

The early damage can be effectively and sensitively characterized by zero-frequency component of nonlinear Lamb waves, which exhibits some more favorable properties than higher harmonics. However, in the process of extracting zero-frequency component, it is challenging to determine the time period that needs to be analyzed. In this study, the residual component obtained from the empirical mode decomposition of nonlinear Lamb waves was compared with the zero-frequency pulse signal after low-pass filtering. The results showed consistency between the two. Furthermore, a method for extracting the zero-frequency pulse signal in the time domain is developed, which is without signal decomposition. Furthermore, a time-domain index is established by zero-frequency pulse signal to indicate the severity of early damage in mechanical parts. Finite element simulation validates the accuracy of zero-frequency pulse signal extraction and evaluates nonlinear damage. Experimental validation is conducted by ultrasonic nonlinear testing on alloy-6061 plates with fatigue damage, affirming the effectiveness of early damage detection. This work proposes a method that allows for the intuitive analysis of the time domain zero-frequency pulse signal, providing a reference for determining the time duration in subsequent studies. Additionally, the established index provides a reference for early fatigue damage detection.