Structural Repair and Health Monitoring Techniques Using Piezoelectric Transducers: A Critical Review

Piezoelectric transducers have attracted considerable attention in structural repair and health monitoring because of their dual actuation and sensing capabilities. This review critically examines their application in repairing and monitoring damaged engineering structures, particularly those containing cracks, notches, delamination, and debonding. First, analytical, numerical, and experimental approaches for piezoelectric-based structural repair are evaluated, with emphasis on crack suppression, stress intensity factor reduction, stress concentration control, and structural response improvement. The effects of actuator location, applied voltage, patch geometry, adhesive prop-erties, loading conditions, and optimization techniques are also discussed. The review then examines piezoelec-tric-based structural health monitoring techniques, including guided Lamb waves, electromechanical impedance, vibration-based sensing, sensor placement, and machine-learning-assisted damage assessment. The critical analysis shows that numerical investigations dominate the existing literature, whereas experimental validation, mixed-mode fracture studies, and long-term performance assessments remain limited. Finally, current research gaps, challenges, and future opportunities for intelligent and adaptive engineering structures are identified.