Unconventional flash technique for the identification of multilayer thermal diffusivity tensors
Résumé
This paper presents a novel non-intrusive technique for the thermal characterization of
opaque multilayer materials that consists in the simultaneous estimation of the thermal
diffusivities tensors of each constituting layers that may be isotropic or orthotropic. The
present identification method is based on the resolution of an inverse heat conduction problem
consisting in the minimization of the least square objective function constructed with the
temperature measurements and the prediction of a pseudo-analytical model. The pseudo-
analytical model relies on the quadrupoles formalism that proves its capability to treat multi-
layered materials and to mimic the experimental method investigated in this work. This
latter, inspired from the flash method, relies on a unique and non-intrusive experiment,
in terms of excitation and measurements. One of the sample surfaces is locally and shortly
heated by means of a CO2 laser, while the resulting transient temperature field is continuously
recorded during the cooling period by an IR camera. The minimization procedure invokes
a PSO algorithm that has been proved to be convenient for such complex problems that
deal with a non-linearity and a large number of unknown parameters, including those related
to the excitation. The overall identification method is validated using an isotropic opaque
monolayer material of known properties. The identification method is then performed on an
actual two layers sample. The accuracy and robustness is discussed depending on the face of
excitation and measurement leading to two distinct experimental configurations. A strong
emphasis is placed on the sensitivity analysis in order to test the feasibility of the estimation
for both configurations