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

Abstract

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.

Design and analysis of computer experiments for efficient model-based active thermography in the agro-food sector

“…While most initial studies on AT adopted an empirical approach, in the last decade, focus has shifted towards modeling and fully understanding the underlying heat transfer processes [9][10][11]. There are several motivations to model the heat transfer processes occurring during an AT experiment, including to verify experimental observations, to optimize the experimental settings to inspect a certain sample, to determine a sample's thermo-physical properties, etc [11]. In general, heat transfer simulations provide a way to reduce the workload and costs associated with physical experimentation.…”

Quantification of the Effective Detectable Period for Concrete Voids of CLP by Lock-In Thermography

“…These basic equations can be solved for known initial and boundary conditions, where the initial conditions take the form of the initial temperature distribution, while the boundary and load conditions can take the form of a specific temperature, a specific heat flux, convective conditions, radiant temperatures, etc. In FEM, Equation ( 3) is discretized for each node, and a matrix equation that is solved for an unknown temperature at any time is generated [23].…”