Inspection of Materials and Structures by Infrared Thermography: SignalProcessing Techniques for Defect Enhancement and Characterization

摘要

Active infrared thermography is a nondestructive evaluation technique wherebyheat perturbation is used to stimulate the thermal response of a given part. Appropriate signal processing techniques must be developed in order to detect subsurface defects or to obtain quantitative information from the raw data. Because of the limited heating temperatures (of the order of 10 C) and other diffusion-based propagation of thermal waves, the constrast of thermal features in a thermographic image is relatively low. Image proccessing must be based on blurred feature recognition rather than on the detection of edges and contours as is usually the case for video images. In this paper some recent developments on thermographic inspection at the Industrial Materials Research Institute (IMRI) are described. A substantial amount of effort has been devoted to image processing and thermal modelling as required for rapid image analysis, signal enhancement, and noise removal from the thermograph, as well as for a quantitative sizing of defects. Examples are presented concerning the inspection of graphite-epoxy structures and of aluminum bonded panels with foam or honeycomb core.