Estimation of defect depth in steel plate using lock-in IR thermography

The paper deals with the application of lock-in active infrared thermography as one of the non-contact and nondestructive techniques used for defect depth estimation. Preliminary research was done by testing a specimen made of austenitic steel plate with artificially created defects, i.e. flat-bottom holes. The obtained dependence between defect depth and phase shift was presented for different frequencies of “thermal waves” generated inside the sample. The experiment was carried out to determine the application of the lock-in thermography approach in testing materials with a high thermal diffusivity.