Fast simulation approach dedicated to infrared thermographic inspection of delaminated planar pieces

Infrared thermography is a popular Non-Destructive Testing (NDT) technique that is typically used to detect delamination and volumetric flaws in composite materials, or to detect small cracks affecting metallic part near the piece surface. We propose a fast semi-analytical model based on Truncated Region Eigenfunction Expansion (TREE) method. The problem is thus solved in Laplace domain with respect to time and the temperature distribution is approximated by its expansion on a tensor product modal basis. This approach yields very fast and accurate results in tis domain of application. Configurations addressed by this model are inspections of stratified planar pieces containing thin delamination patches. Sources considered in this work are lamps providing an excitation at the surface of the inspected piece. The flaws are modelled as thin air gaps between the piece layers, which consist in an additional resistance to heat flow if the laminate is thermally stimulated. Hence, they are integrated in the modal approach and do not require additional discretization. This work complements a previous work aiming at treating 2D configurations involving induction coils as thermal sources . The principle of the theoretical approach will be exposed and quantitative comparisons with reference data from the literature will be presented.