Thermography is cool: Defect detection using liquid nitrogen as a stimulus

This paper explores cooling instead of heating for external stimulation in infrared thermography for NDT & E. Liquid nitrogen is poured on the surface of a steel sample with flat-bottom holes and a thermal camera captures the whole process. Pulsed thermography and lock-in thermography are also employed to obtain a good comparison. In image processing procedure, the principal component thermography method is performed on all thermal images. Moreover, the corresponding receiver operating characteristic curves are established and discussed. A comparison of the results indicates that the liquid nitrogen technique could be considered as a valid option for NDT & E.