Self‐Powered Sensing of Mode I Delamination in Carbon Fiber Reinforced Polymer Laminates Enabled by a Lead‐Free Piezoelectric Interlayer

Carbon fiber reinforced polymers (CFRPs) are widely employed in load‐bearing structures. However, Mode I delamination is difficult to monitor using conventional externally powered structural health monitoring. In this study, a multifunctional CFRP/KNN–EP laminate was developed by embedding a lead‐free potassium sodium niobate–epoxy (KNN–EP) piezoelectric interlayer in a CFRP lay‐up, where the carbon fiber plies serve as both load‐bearing reinforcement and in‐plane electrodes. Mode I fracture is investigated in double cantilever beam (DCB) tests on baseline CFRP and CFRP/KNN–EP laminates. During delamination, the KNN–EP interlayer generates real‐time open‐circuit voltage outputs (up to ±0.5 V) with burst‐type transients that identify crack initiation and track stage‐dependent propagation activity. A crack‐length‐domain analysis has revealed that voltage‐spike activity decays with crack development, providing a mechanics‐consistent electrical signature of the evolving fracture. Multiscale finite‐element simulations support this interpretation by capturing crack‐tip stress/strain and electric‐field localization and by rationalizing the stage‐dependent attenuation of voltage activity. These findings demonstrate a scalable route toward self‐powered in situ monitoring of Mode I delamination in multifunctional CFRP laminates.