Baseline-Free Detection of Progressive Fatigue Damage Using Nonlinear Ultrasonic Guided Waves

Abstract Detecting fatigue-induced progressive damage under varying environmental conditions remains a major challenge in structural health monitoring (SHM). This study investigates a baseline-free nonlinear guided wave method, which extracts nonlinear parameters to detect fatigue cracks without requiring baseline signals from the pristine state. The method demonstrates reliable detection of cracks around 3 mm in size, with the nonlinear parameter serving as a sensitive indicator of damage initiation and growth. Its independence from baseline signals enhances practicality for in-service monitoring applications. However, experimental results reveal that the method’s performance is sensitive to temperature variations, with irregular responses observed at different temperatures, which may affect detection consistency. These findings highlight both the potential and the limitations of nonlinear guided wave methods, underscoring the need for temperature compensation strategies to improve their robustness under variable environmental conditions. Overall, the proposed approach contributes to advancing baseline-free SHM techniques by offering a viable solution for progressive crack detection in realistic service environment.