Quantitative study of buried heat sources by lock-in vibrothermography: an approach to crack characterization

摘要

Vibrothermography has proven to be a useful technique for the detection of cracks, which reveal themselves as heat sources when mechanically excited in vibrothermography experiments. In this work we present a method to evaluate the size and depth of buried heat sources in metallic samples, from lock-in vibrothermography measurements. We have developed a theoretical model allowing us to calculate the surface temperature produced by modulated buried heat sources of arbitrary shape and power distribution by integrating the contribution of point-like heat sources over the entire heat source extension. In order to test the validity of the model, we have chosen homogeneous and rectangular heat sources, perpendicular to the sample surface. We have prepared calibrated heat sources by attaching two flat pieces of stainless steel and controlling the tightness with screws. Measurements of the surface temperature by an infrared video camera have been compared with the predictions of the theoretical model. The agreement between experimental and theoretical results confirms that lock-in vibrothermography is an efficient tool not only to detect but also to characterize the geometrical parameters of inner heat sources.