INTEGRAL METHODS AND NONDESTRUCTIVE TESTI NG THROUGH STIMULATED INFRARED THERMOGRAPHY

Integral methods and non-destructive testing through stimulated infrar ed thermography. integral methods (Fourier, Laplace, Hankel, Mellin,.. .) constitute classical tools for solving diffusion problems in simple geometries. Recently these methods have been applied to heat transfer in multilayer materials in electronics or in the composite industry. Solution of a multidimensional diffusion problem within a slab that co ntains one or several defects (delamination, bad sticking, etc.) const itutes an interesting application. These techniques provide a solution of the inverse problem under an explicit form, which brings some adva ntages when compared to numerical methods (finite elements, finite dif ferences, etc.) low computation time, simple error analysis, filtering . An application to non-destructive testing through active thermograph y is presented here. It deals with the problem of detecting defects of resistive nature in planar materials and of estimating their characte ristics on a quantitative basis. Two inverse methods are presented. Th e first one is based on a one-dimensional transfer model that is appli ed locally (Laplace transforms with respect to the time variable), whi le the second one takes into account the two-dimensional character of the transfer (same time Laplace transformation followed by a Fourier c osine transformation with respect to space). An experiment allows the validation of these two inversion methods.