Structural Health Monitoring of Composite Structures with Piezoelectric-Wafer Active Sensors

Piezoelectric wafer active sensors are lightweight and inexpensive enablers for a large class of structural health monitoring applications such as 1) embedded guided-wave ultrasonics, i.e., pitch-catch, pulse-echo, and phased arrays; 2) high-frequency modal sensing, i.e., the electromechanical impedance method; and 3) passive detection (acoustic emission and impact detection). The focus of this paper will be on the challenges and opportunities posed by use of piezoelectric-wafer active sensors for structural health monitoring of composite structures as different from that of the metallic structures on which this methodology was initially developed. After a brief introduction, the paper discusses damage modes in composites. Then it reviews the structural health monitoring principles based on piezoelectric-wafer active sensors. This is followed by a discussion of guided-wave propagation in composites and how piezoelectric-wafer active sensor tuning can be achieved. Finally, the paper presents some damage detection results in composites: I) hole damage in unidirectional and quasi-isotropic plates and 2) impact damage in quasi. isotropic plates. The paper ends with conclusions and suggestions for further work.