Diffusion and separation mechanism of transient electromagnetic and thermal fields

Electromagnetic mechanism of Joule heating and thermal diffusion has considerable impacts on eddy current pulsed thermography (ECPT). Since ECPT is a multi-physics non-destructive testing (NDT) method depended on both transient electromagnetic and thermal fields, it is crucial to analyze the characteristic of heat propagation mechanism, characteristic time of diffusion as well as the separation of electromagnetic-thermal field for improving detection sensitivity and quantitative analysis. Deep inside to electromagnetic energy, this research constructs a physical-mathematical time-dependent partition model to analyze the whole thermal transient process and consider characteristic times for separating Joule heating and thermal diffusion into four different stage. This study sheds light not only on the deeper understanding of physical mechanism of inductive heating propagation but also on the better modeling and mining of mathematical time-spatial pattern in quantitative defects detection for NDT. Finally, numerical modeling and experiments have been conducted on both artificial slot of steel sample and natural edge crack on the turbine blade sample to validate the proposed study.