A Multi-Physics-Based Approach to Active Microwave Thermography
[Thesis]
Mirala, Seyed Ali
Donnell, Kristen M.
Missouri University of Science and Technology
2020
116
Ph.D.
Missouri University of Science and Technology
2020
The goal of this work is to advance a novel nondestructive testing (NDT) method for controlled, rapid, and effective inspection of a structure through the integration of microwave NDT and thermography, referred to as Active Microwave Thermography (AMT). In AMT, the structure under test is exposed to microwave radiation and the thermal profile of the structure is monitored via a thermal camera in order to obtain desired information regarding the structure. This new technique is applicable across a wide range of NDT needs including detection of voids, delamination, water ingress, debonding, and cracks in numerous structures such as carbon fiber and glass fiber reinforced polymers (CFRP and GFRP, respectively), cement-based materials, corroded metals, and structures coated with radio-frequency absorbing materials (RAM). This research is dedicated to three special cases among these applications of AMT; detection of voids in CFRP, evaluation of water ingress, and detection of delamination in RAM-coated structures. The effect of the structures' properties, excitation parameters, and defect size and location on the thermal response are investigated through analyses of technical outputs such as thermal contrast and signal-to-noise ratio. The main contributions of this research are first, enabling defect quantification through a formulation of the microwave heating and subsequently calculating the temperature's temporal and spatial variation. This formulation is validated through commercial simulation software and measurement. Second, it is shown (through simulation and measurement) that AMT is a reliable NDT technique that may be superior to other techniques for specific applications such as water ingress detection and inspection of RAM-coated structures.