Numerical simulation of phase images and depth reconstruction in pulsed phase thermography

摘要

In this work we apply the finite element (FE) method to simulate the results of pulsed phase thermography experiments on laminated composite plates. Specifically, the goal is to simulate the phase component of reflected thermal waves and therefore verify the calculation of defect depth through the identification of the defect blind frequency. The calculation of phase components requires a higher spatial and temporal resolution than that of the calculation of the reflected temperature. An FE modeling strategy is presented, including the estimation of the defect thermal properties, which in this case is represented as a foam insert impregnated with epoxy resin. A comparison of meshing strategies using tetrahedral and hexahedral elements reveals that temperature errors in the tetrahedral results are amplified in the calculation of phase images and blind frequencies. Finally, we investigate the linearity of the measured diffusion length (based on the blind frequency) as a function of defect depth. The simulations demonstrate a nonlinear relationship between the defect depth and diffusion length, calculated from the blind frequency, consistent with previous experimental observations.