Diagnostic imaging of debonding in FRP-strengthened reinforced concrete structures using combinational harmonics generated by Rayleigh waves

Abstract

A debonding location imaging technique (DLIT) utilising mixed-frequency Rayleigh waves is reported in this paper to predict the location of debonding in fibre-reinforced polymer (FRP) composite strengthened concrete structures. In the proposed methodology, a piezoceramic transducer network is employed to sequentially scan the FRP-concrete interface. One of the transducers serves as an actuator while the remainder serve as sensors. The incident waves which are sent by the actuator consist of two different fundamental frequencies. After the incident waves interact with debonding, additional signals are generated that coincide with the sum of the fundamental frequencies (i.e., sum frequency). The received wave component at the sum frequency is in accordance with theoretical predictions. In order to apply the DLIT, a time-frequency analysis is then applied to process the data collected by each actuator-sensor transducer pair in order to determine the signal energy density amplitudes (i.e., signal envelopes) at the fundamental frequencies and the sum frequency. Based on cross-correlation analysis between the signal envelopes of the fundamental frequencies and the sum frequency, an image can be constructed that reveals the centroid of the debonding region. Following the presentation of the proposed DLIT, numerical and experimental studies are then reported that compare the predicted centroid of debonding with the actual centroid of debonding as incorporated into the numerical model and the experimental specimens, respectively. The results demonstrate that the proposed DLIT based on the Rayleigh wave features at sum frequency can satisfactorily predict the location of debonding.