Flying spot thermography: Quantitative assessment of thermal diffusivity and crack width

摘要

Flying spot thermography is an efficient thermographic non-destructive technique that has been widely applied to detect surface breaking cracks on large parts in a fast way. It consists in heating the sample surface with a laser spot that moves at a constant speed and recording the surface temperature with an infrared camera. The presence of a crack hinders heat propagation and produces a discontinuity in the temperature at the surface, that is, the signature of the crack. In this tutorial, we address two quantitative applications of flying spot thermography: the measurement of thermal diffusivity and the determination of the width of cracks. We present derivations of the analytical expressions of the surface temperature, from which specific methods for the quantitative assessment of thermal diffusivity and crack width are introduced. We show that the methodology is also valid for the complementary configuration, with a static laser spot exciting a moving specimen, as in industrial production chains. The methodology is illustrated with experimental data on sound and artificially cracked samples. We conclude the tutorial by discussing the limitations and future perspectives of this technique.