Characterization of semi-infinite delaminations using lock-in thermography: Theory and numerical experiments

Delaminations are buried defects parallel to the sample surface. In the last decades infrared thermography with optical excitation has been used to detect and size the depth of this kind of defects. However, sizing the delamination thickness has been usually disregarded. In a recent paper we proposed a method to size both depth and thickness of ideal delaminations (infinite area) using modulated excitation. Here, we extend the previous work to approach more realistic situations, tackling the case of semi-infinite delaminations. First, we calculate analytically the surface temperature oscillation of a sample containing a semi-infinite delamination using the thermal quadrupoles formalism. Then, we corroborate the analytical results by solving the same problem numerically. Finally, we perform an inverse parametric estimation of synthetic temperature amplitude and phase data with added Gaussian noise to retrieve the three geometrical parameters characterizing the delamination: length, depth and thickness.