Development of UAV-aided laser thermography system for visualizing invisible coating defects in steel structures

Abstract

This dissertation proposes an unmanned aerial vehicle (UAV) aided laser thermography system for visualizing invisible coating defects in steel structures. Once the UAV-aided laser thermography system moves over the steel structure, the heat energies are generated on the coating surface, which is the exterior layer of the steel structure. Then, the resultant heat responses are measured by an infrared (IR) camera, and through the heat analysis and image processing process, the coating defects, such as coating delamination and thickness uncertainty, are classified and visualized. Note that, the whole parameters used for the coating defect visualization are decided based on the 3-dimensional numerical heat transfer simulation. The uniqueness of this study lies in (1) world-first deployment of laser thermography with UAV overcoming the spatial constraints involved in inspecting the structural hard-to-access areas, (2) development of the portable laser thermography system for an automated visualization as well as classification of invisible coating defects, and (3) automated evaluation of steel structure coatings through the convergence of the smart sensing and data processing technology. The performance of the proposed UAV-aided laser thermography system was verified through the lab-scale tests and field deployment on real steel bridges, and the test results reveal that the coating delamination area and coating thickness can be successfully visualized and quantified within 10% uncertainties.