Characterization of semi-infinite inhomogeneous delaminations using lock-in thermography

Abstract

Delaminations are buried defects parallel to the surface. Beyond detection, the challenge is to size the geometrical parameters of the delamination. For detection and characterization purposes, we propose using optically excited lock-in infrared thermography. In previous papers we dealt with infinite and semi-infinite delaminations featuring homogeneous thickness, i.e. constant thermal resistance. In this work, with the aim of approaching real life flaws, we propose to characterize semi-infinite heterogeneous delaminations, i.e. of varying thickness. We calculate the surface temperature oscillation analytically. Then, we perform experiments on calibrated delaminations of triangular cross-section. By fitting the analytical model to the experiments, we obtain the morphological parameters of the delamination. The quality of the fittings allows us to unambiguously distinguish between homogeneous and heterogeneous delaminations.