Characterization and spatial resolution of cracks using lock-in vibrothermography

We present a method to characterize vertical cracks that combines lock-in vibrothermography experiments and a stabilized inversion algorithm. We analyze its capability to retrieve the shape and location of square flaws buried at increasing depths and its ability to resolve two square buried cracks by inverting synthetic data. The predictions on the reconstruction of single and double cracks are checked by inverting experimental data obtained from metallic samples containing calibrated cracks at low excitation powers. Experimental results confirm that the method is able to reconstruct square heat sources whose depth is twice the lateral dimension.