Debonding detection in CFRP-strengthened steel structures using guided wave nonlinear frequency mixing

Carbon fibre reinforced polymer (CFRP) composites are commonly used for repair and strengthening steel structures. To ensure the safety of CFRP-strengthened steel structures, a probabilistic inspection technique based on nonlinear frequency mixing of guided waves is proposed to predict the location of debonding in this paper. An acoustic emission transducer which has abroad operating frequency range is employed to collect guided waves in the sensing array. In the proposed methodology, each nonlinear mixing component is subjected to cross-correlation analysis with fundamental frequencies, and the results from the 12 sensing paths are superimposed to reconstruct damage localisation imaging. The damage localisation accuracy of each nonlinear component is compared and analysed. In addition, the localisation accuracy is further improved by fusing the results of the nonlinear mixing components. Within the monitoring area, the relative error of the localisation based on the fusion of the nonlinear mixing components does not exceed 4%. Finally, utlized the transducer’s flexibility to increase additional sensing paths, enhancing thelocalisation accuracy at the array edge and outside the array. The results indicate that the proposed approach based on guided wave nonlinear frequency mixing provides a reliable method of detecting and locating debonding in CFRP-strengthened steel structures.