Infrared Thermal Wave Studies of Coated Surfaces

In this paper we discuss the recent results of our infrared thermal wave studies of plasma-sprayed coatings, coatings on automotive metal panels, and metal to polymer adhesive joints. The purpose of this study is to develop a reliable NDE technique to assess the quality and test the integrity of these coatings and bonding. The experimental method is a pulsed heating and synchronous infrared thermal wave detection technique commonly referred to as box-car thermal wave video imaging. [1–3] The thermal wave propagation times for plasma-sprayed coatings and adhesive bonds are usually long enough for many NDE applications that the method used here can be considered to be a real time technique. In the IR thermal wave imaging method (Fig. 1) the sample surface is pulse-heated by a bank of flash lamps, and the thermal response of the surface is monitored as a function of time and space by means of an infrared video camera. The resulting video signal is sent to a fast signal processing system and averaged synchronously on a pixel-by-pixel basis. The final data are displayed in the form of 2-dimensional or 3-dimensional gray scale or pseudocolor images of subsurface thermal features