The way in which heat propagates through objects can be used to detect sub-surface features and some types of failures without needing to cross-section the objects under study. The object can be heated in a variety of ways, steady state through conduction or radiation, or pulsed with flash lamps. An infra-red camera is used to image the heat distribution and is propagation in to the surface. One of the features that makes this technique so attractive is that it can operate close to room temperature and is totally non-contact, so it is entirely non-destructive.
NPL is developing a predictive tool to assess the onset of failure of thermal barrier coatings used on turbine blades in the Power generation and Aero industries. Initially steady state thermography was being used, employing conductive and radiative heating techniques. More recently the application of pulsed thermography is being investigated in order to enhance the sensitivity to early signs of failure. Thermography has also been applied to the detection of air inclusions in rubber belts and to study adhesion strength in coatings.
Standard procedures used or applicable
No standards are applied to this type of detection technique at present. The approach is tailored to each application to obtain best results.