An acoustic-optical fiber NDE technique for interfacial debonding detection in FRP-retrofitted structures

•An acoustic-optical NDE tech. for interfacial damage detection in FRP-retrofitted structures.•Detect the existence of interfacial debonding based on free vibration theory of a thin plate.•Significant high velocity measurements at the debonding location is observed at resonant freq.•The influences of different debonding damage parameters have been studied.•The point-by-point excitation method is more precisely than the fixed excitation location method.

Based on the theory of free vibration of a thin plate, the acoustic-optical fiber NDE technique is proposed for the detection of interfacial debonding in FRP-retrofitted structures. A focused sound beam generated from a variable frequency loudspeaker source can be controlled to form a local vibration field at the surface of an FRP-retrofitted structure. Local vibration anomalies caused by interfacial debonding in the structure can be measured by the surface-mounted optical fiber interferometer, and thus, interfacial debonding can be detected, mapped, and quantified. Based on the results from both numerical and experimental studies, the feasibility of interfacial debonding detection in FRP-retrofitted structures with the proposed technique is demonstrated.