Quantitative assessment for the identification and characterisation of buried defects using electromagnetic induction thermal diffusion

This study presents a systematic methodology for the quantitative evaluation of buried defects through the heat conduction characteristics induced by electromagnetic induction. Theoretical foundations are developed through analytical solutions for transient temperature distributions under both reflection and transmission modes. Development of mathematical models correlating thermal response parameters with defect characteristics, where deviation time in reflection mode and thermal contrast emergence time in transmission mode demonstrate strong dependence on burial depth. Implementation of a comprehensive detection methodology utilising two-dimensional thermal response curves for evaluating defect depth, width, and spatial position. Advanced three-dimensional thermographic analysis for spatial defect characterisation. Experimental validation using 45 steel specimens with artificial cylindrical defects confirms that defect detectability varies significantly with burial depth. In reflection mode, 3 mm height defect showed earliest detectable thermal contrast due to its proximity to the defect-free surface, while deeper defects exhibited delayed deviation times. Transmission mode experiments revealed that defects with smaller burial depths produced more pronounced thermal anomalies and earlier peak times during cooling stages. The research demonstrates that complementary use of both inspection modes enables optimised detection performance, providing reliable quantification of defect parameters including depth, position, and geometric characteristics.