Sizing Wedge Delaminations Using Lock-in Thermography

Abstract Sizing hidden defects is a major challenge in many industries. In the last years we have successfully used optically excited lock-in infrared thermography to size the geometrical parameters of both infinite and semi-infinite uniform delaminations. In this work, we study more realistic flaws, by dealing with wedge delaminations of continuously varying width, depth, thickness and combination of two of them. As these parameters vary slowly, the previously developed analytical model for semi-infinite delamination remains valid. We present experimental data taken by applying lock-in infrared thermography on stainless steel samples containing calibrated wedge delaminations. The resulting amplitude and phase thermograms are fitted to the analytical model to obtain the parameters describing the geometry of the delaminations. The agreement found between the retrieved geometry and the true varying parameters strengthens lock-in infrared thermography as a powerful tool to size hidden defects.