Simultaneous and direct identification of thermophysical properties for orthotropic materials

Elissa El Rassy , Yann Billaud (1, 2) , Didier Saury (1, 2)

1 PPrime [Poitiers] - Institut Pprime [UPR 3346]
2 COST - Convection, Optimisation, Systèmes Thermiques [Institut Pprime]

A direct and simultaneous estimation method of the main three dimensional thermal diffusivity tensor(ax;ay;az) of orthotropic opaque materials, is presented in this paper. This method consists in couplinga non-intrusive and unique 3D flash experiment with a transient nonlinear inverse heat transfer tech-nique. A short and non-uniform excitation is applied on the surface of an orthotropic material using aCO2laser, while the front face temperature cartography is measured over time by an IR camera. Theinverse problem developed in the present study is based on the minimization of the least-squares crite-rion between the outputs of a 3D thermal quadrupoles model, and the experimental measurements. Inorder to properly estimate the thermal diffusivities, parameters related to the thermal excitation, interms of shape and intensity, should be also estimated. In addition to that increase in the number ofunknown parameters, the discontinuity nature of the excitation justify the choice of an analytical model.Considering the large number of parameters to estimate, as well as the non-linear nature of the problem,a hybrid optimization algorithm combining a stochastic method and deterministic one, is applied. Theidentification method proposed in this work, named as DSEH (Direct and Simultaneous Estimation usingHarmonics), is validated using an isotropic opaque material of known properties. Finally, the method isused on an orthotropic carbon fiber composite, commonly used in industries, thanks to its thermal andmechanical characteristics. The results are compared to other methods and shown to be in a good agree-ment with the literature values. The parameters identification is then completed by a sensitivity analysis,and evaluated in terms of robustness, accuracy, and time consumption

Mots clés: IR thermography; Thermophysical properties; Thermal quadrupolesIntegral transforms; Flash methodInverse problems; thermal quadrupoles; integral transforms; orthotropic materials; flash method; inverse problems; parameters estimation

Domaines: Thermique [physics.class-ph]

Elissa El Rassy, Yann Billaud, Didier Saury. Simultaneous and direct identification of thermophysical properties for orthotropic materials. Measurement - Journal of the International Measurement Confederation (IMEKO), 2019, 135, pp.199-212. ⟨10.1016/j.measurement.2018.11.048⟩. ⟨hal-02134971⟩