Nodal and modal strategies for longitudinal thermal diffusivity profile estimation: Application to the non destructive evaluation of SiC/SiC composites under uniaxial tensile tests

In this paper, infrared image sequences of a SiC/SiC composite excited with a non uniform heat pulse (also known as Flash) are processed using two different strategies. In a first approach, a modal strategy based on the decomposition of infrared sequences in an orthogonal basis is applied. A discrete version of the heat equation is solved in the transformed space using only a very limited number of modes for which the sensitivity to diffusivity is optimal. In a second time, a nodal approach that consists in solving locally a finite difference scheme is performed at each pixel. A new sensitivity analysis based on a local correlation study of the partial derivatives of the experimental data (transformed or not) allows validating the relevance of each approach, and determining the optimal space where to perform estimations. As a result, effective local longitudinal diffusivity profiles of a SiC/SiC composite under mechanical testing are provided and analyzed to detect the presence of microcracks. (C) 2008 Published by Elsevier B.V