Nondestructive evaluation of carbon fiber reinforced polymer (CFRP)-steel interfacial debonding using eddy current thermography

When carbon fiber reinforced polymer (CFRP) is used to strengthen steel structures, interfacial debonding between CFRP and steel can substantially compromise the composite action and trigger structural failure. This study investigates eddy current thermography (ECT) for nondestructive evaluation of CFRP-steel interface. Four CFRP-steel specimens with different shapes and sizes of interface defects were tested. With eddy current induced in steel plates, thermal profiles of CFRP were measured to detect and characterize interface defects. The results showed that the proposed ECT system was capable of detecting CFRP-steel interfacial defects within 80 s. ECT results were subjected to edge effects that compromised the evaluation resolution and precise determination of damage regions. The edge effect was prominent in the heating stage but alleviated in the cooling stage because of heat redistribution. The blurring effect caused by the heat diffusion from the internal defect to the external surface of CFRP also hindered precise determination of damage regions. It is recommended to perform ECT for shallow interfacial defect in the cooling stage of steel-CFRP structures to achieve desired results.