Experimental Study on Damage Detection of CFRP-Steel Interface Based on PMN-PT Piezoelectric Single Crystal

CFRP–steel composite strengthening systems are widely used in engineering; however, interface debonding and internal material defects easily lead to overall structural failure, requiring high-precision and quantitative detection methods. In this paper, lead magnesium niobate–lead titanate (PMN–PT) piezoelectric single crystals are used as sensing elements to develop high-sensitivity externally bonded piezoelectric sensors. Combined with ultrasonic guided-wave active detection technology, identification and quantitative evaluation of CFRP–steel interface debonding and CFRP groove defects are systematically carried out. Disperse software is used to analyze the dispersion characteristics of CFRP and steel plates, and 150 kHz is determined as the optimal excitation frequency to effectively suppress multi-mode interference. Specimens with gradient debonding lengths (0–40 mm) and CFRP groove specimens with different geometric parameters are designed. A “pitch–catch” PMN–PT sensing scheme is adopted to collect ultrasonic time-domain signals, extract the first-arrival wave amplitude, and construct a damage index (DI). The experimental results show that the first-arrival wave amplitude changes monotonically with increasing debonding length, and the damage index exhibits a good linear correlation with debonding length. For CFRP groove defects, the first-arrival wave amplitude increases with groove length and decreases with groove depth, enabling effective differentiation of geometric differences. The study confirms that PMN–PT piezoelectric sensing combined with ultrasonic guided-wave technology can sensitively identify CFRP–steel interface damage and achieve quantitative assessment, providing reliable technical support for the health monitoring of CFRP-strengthened steel structures.