Active thermography signal processing techniques for defect detection and characterization on composite materials

Active thermography has been extensively investigated in the past few years for the nondestructive evaluation of different types of materials. Composites in particular have received considerable attention given that active thermography has shown to be well suited for the detection and characterization of most kinds of defects typically found in these materials such as impact damage, delaminations, disbonds and inclusions. Signal processing is a necessary step of the inspection process, especially if defect characterization is required. A wide variety of techniques have been developed from the classical thermal-based techniques to signal transformation algorithms (adapted from the area of machine vision) on which temporal data is transformed to a different domain (frequency, Hough, principal components, Laplace, high-order moments, etc.) with the purpose of simplifying data analysis. In this paper, a review of some of these processing techniques is presented and exemplified using a Kevlar® panel and a GLARE specimen.