Nondestructive Testing for Multi-Layer Metal-Metal Bonded Structure by Using Inductive Lock-In Thermograhy

Multilayer materials with metal-metal bonded structure have been widely applied in aviation, aerospace and nuclear industrial fields. The presence of inner defects such as debonding, air gaps leads to significant degradation of the load capacity and mechanical behaviors. Due to their complex structure, debonding detection in metal-metal structure inherently remains challenge. This paper proposes a feasibility study of non-destructive inspection of debonding defect in lead-steel sample by using inductive lock-in thermography (ILT). The detectability validation is carried out based on experimental studies. Theoretical analysis, excitation source and system design as well as various influence parameters of ILT are discussed and optimized. Fourier-transform based post-processing has been investigated to analyze both magnitude and phase images for defects identification. The obtained results have been promising validated and it indicated the ability to improve the signal-to-noise ratio. The comparative experiment using different methods (ILT, ECPT, and OLT) has been carried out. The results have revealed that the ILT has advantages and could be served as a strong candidate for practical adoption in debonding defect inspection in metal-metal bonded sample.