Evaluation of early-stage corrosion damage using quasi-static component pulse generated by longitudinal critically...

The nonlinear ultrasonic technique is an effective method for characterizing early-stage damage, such as initial corrosion, plastic deformation, and creep. However, the nonlinear response signal induced by micro-damage is typically one or two orders of magnitude weaker than the fundamental wave. This low signal-to-noise ratio is one of the main factors limiting the broader application of nonlinear ultrasonic technology. To address this issue, this study systematically investigates the quasi-static component pulse (QSCP) generated during the propagation of the longitudinal critically refracted (LCR) wave. The feasibility of assessing early corrosion damage in 7075 aluminum alloy was evaluated using the QSCP, a signal feature resulting from the interaction between corrosion-induced microcrack and LCR wave. Both numerical simulation and experimental results demonstrate a positive correlation between the QSCP-based acoustic nonlinearity parameter (ANP) and the extent of corrosion-induced microcrack, which is attributed to the increase in microcrack. Simulation results show that the ANP increases monotonically with the number of microcrack. This trend is experimentally validated, with the ANP showing a significant increase of approximately 54.8% by the fourth stage of corrosion compared to the baseline. These findings confirm the effectiveness and feasibility of the QSCP-based ANP method for detecting early-stage corrosion damage, offering a promising nondestructive approach with high sensitivity for assessing incipient corrosion in critical metallic structures.