Dynamic Thermal Tomography of Composites: A Comparison of Reference and Reference-Free Approaches

Dynamic thermal tomography is a technique that allows the display of “slices” of solids by analyzing the evolution of surface temperature as a function of time. This paper presents the principles of one-sided thermal tomography using reference points and also introduces a technique of thermal tomography that does not require the use of reference point. The diffusion nature of heat conduction in solids causes lateral diffusion, which modifies and complicates the heat flow that is needed to detect defects. In the case of anisotropic composite materials the heat will diffuse more readily in one direction than another. Lateral diffusion can make it difficult to detect (visualize) deep defects, especially those located under shallower ones. Artifacts can be reduced by thresholding timegrams but this may hide small defects. The effectiveness of thermal tomography in detecting impact damage (cracks/delaminations) in composites has been confirmed by numerous experiments.