Inspecting epoxy layer defect in steel-epoxy-steel sandwich structures using guided waves

Steel-epoxy sleeves are widely used in the repair of pipelines. The integrity of the epoxy layer between the sleeve and pipeline directly determines the repair quality. However, there is a lack of effective nondestructive testing methods for inspecting the integrity of the epoxy layer. In this work, a guided wave-based inspection method is developed to detect the defects of the epoxy layer in the steel-epoxy-steel sandwich structure. Firstly, the dispersion characteristics of guided waves in the sandwich are analyzed. Two wave modes (ASH1 and SSH0) are selected for defect detection. Then, piezoelectric transducers are designed to excite and receive ASH1 and SSH0 waves. The sensitivities of the two waves to defects are further explored by simulations and experiments. Results indicate that the SSH0 wave can detect defects in the adhesive layer, while the ASH1 wave presents difficulties. The work can provide a feasible way to detect epoxy defects in steel-epoxy-steel sandwich structures.