A Lock-In thermography based post-processing scheme for the detection of sub-surface rivet-related defects in aircraft structures

This research is focused on developing a novel Lock-In Thermography-based scanning system to detect subsurface defects in aircraft rivets. The proposed system included a customized thermographic device consisting of a thermal camera, heating source, synchronized control circuitry, and post-processing software utilizing the Discrete Wavelet Transform technique, augmented by spatial gradient and mean filtering methods. To validate the developed system, a two-pronged hierarchical approach was adopted. The detection scheme for looseness and internal cracks in rivets was first developed and refined in a lab environment. After successful trials on lab samples, the scheme was further employed in different areas of actual aircraft. A total of 751 rivets were scanned for looseness and internal cracks, and a very promising detection rate was observed, confirmed through visual inspection and microscopic analysis. The developed setup can be further extended to other sub-surface defects such as corrosion and other structural non-homogeneities.