Use of high-speed camera for defect detection in FRP bonded system under different excitation methods

Fiber reinforced polymers (FRP) strengthening has been demonstrated as an effective method to reinforce or repair the structural elements in the application of civil engineering. One issue that affects the effectiveness of FRP bonded system is the interfacial integrity between FRP and bonded substrate. The interfacial defect can cause the deterioration of the performance of strengthened/repaired structures, which should be identified as early as possible. Compared with conventional non-destructive techniques (NDTs), image acquisition method, such as high-speed camera, has received increasing attention due to the advantages of its non-sensor/wiring requirements. Coupled with proper video processing techniques, the high-speed camera has been reported as an effective tool in the interfacial defect detection for FRP bonded system. Moreover, the accuracy of results from high-speed camera is sensitive to the excitation resources applied on the FRP bonded system, since the vibration response of FRP varies under different excitation methods. In this research, three typical excitation methods for FRP bonded system, i.e. mechanical impact excitation, air pressure excitation and acoustic excitation, were tested to evaluate their effects on the detection accuracy using high-speed camera in FRP bonded system. The findings provide practical recommendations on the selection of proper excitation methods for the applications of high-speed cameras in the defect detection of FRP bonded system.