Acoustic emission monitoring and damage evaluation of bi-adhesive joint patch-repaired composites

Tensile behavior and failure modes of the bonding interface of the repaired composite were investigated in combination with nondestructive testing techniques. The carbon nanotube-modified two-sided adhesive repair method improved the repair effect, while different failure modes of patch fracture and patch debonding were observed. The condition monitoring and damage pattern identification of the composites were performed in a non-destructive manner using acoustic emission and digital image correlation techniques. Analysis of acoustic emission signals was used to discriminate between matrix/patch cracking and bonding layer failure. The clustering analysis of the characteristic parameters is corroborated with the time-frequency domain analysis of the signal waveform to discriminate the interfacial damage of the patch debonding damage behavior. It was found that the double adhesive repair with the modified adhesive layer placed at the edge showed better repair results. In contrast, the repair pattern with the modified adhesive layer in the middle is relatively poor, and the patch debonding behavior corresponding to the multimodal acoustic emission signal at the high peak frequency is observed.