Thermophysical characterization of anisotropic composite materials is extremely important in the control of today fabrication processes and in the prediction of structure failure due to thermal stresses. Accuracy in the estimation of the thermal properties can be improved if the experiments are designed carefully. However, on one hand, the typically used parametric study for the design optimization is tedious and time intensive. On the other hand, commonly used gradient-based estimation methods show instabilities resulting in nonconvergence when used with models that contain correlated or nearly correlated parameters. The objectives of this research were to develop systematic and reliable methodologies for both Experimental Design Optimization (EDO) used for the determination of thermal properties, and Simultaneous Parameter Estimation (SPE). Because of their advantageous features, Genetic Algorithms (GAs) were investigated for use as a strategy for both EDO and SPE. The EDO and SPE approaches used involved the maximization of an optimality criterion associated with the sensitivity matrix of the unknown parameters, and the minimization of the ordinary least squares error, respectively. Two versions of a general-purpose genetic-based program were developed: one is designed for the analysis of any EDO / SPE problems for which a mathematical model can be provided, while the other incorporates a control-volume finite difference scheme allowing for the practical analysis of complex problems. The former version was used to illustrate the genetic performance on the optimization of a difficult mathematical test function. Two test cases previously solved in the literature were first analyzed to demonstrate and assess the GA-based {EDO/SPE} methodology. These problems included the optimization of one and two dimensional designs for the estimation at ambient temperature of two and three thermal properties, respectively (effective thermal conductivity parallel and perpendicular to the fibers plane and effective volumetric heat capacity), of anisotropic carbon/epoxy composite materials. The two dimensional case was further investigated to evaluate the effects of the optimality criterion used for the experimental design on the accuracy of the estimated properties. The general-purpose GA-based program was then successively applied to three advanced studies involving the thermal characterization of carbon/epoxy anisotropic composites. These studies included the SPE of successively three, seven and nine thermophysical parameters, with for the latter case, a two dimensional EDO with seven experimental key parameters. In two of the three studies, the parameters were defined to represent the dependence of the thermal properties with temperature. Finally, the kinetic characterization of the curing of three thermosetting materials (an epoxy, a polyester and a rubber compound) was accomplished resulting in the SPE of six kinetic parameters. Overall, the GA method was found to perform extremely well despite the high degree of correlation and low sensitivity of many parameters in all cases studied. This work therefore validates the use of GAs for the thermophysical characterization of anisotropic composite materials. The significance in using such algorithms is not only the solution to ill-conditioned problems but also, a drastically cost savings in both experimental and time expenses as they allow for the EDO and SPE of several parameters at once. / Ph. D.

Les matériaux thermodurcissables sont naturellement des isolants électriques, limitant leurs applications dans certains domaines comme l’électronique ou l'aéronautique. Ce travail de thèse consiste à développer un nouveau matériau composite thermodurcissable en présence de charges inorganiques conductrices pour apporter des propriétés électriques sans pour autant changer notablement la viscosité du système avant la polymérisation afin de permettre l'utilisation des technologies d'infusion de résine de l'aéronautique. La stratégie des travaux est basée sur la génération d'une séparation de phase au sein du matériau et la localisation des charges conductrices aux interfaces.Cette étude est scindée deux objectifs principaux. Le premier objectif consiste à étudier un système TP/TD (thermoplastique/thermodurcissable) afin d’obtenir et contrôler une morphologie interpénétrée, selon le processus de séparation de phase induite par la polymérisation. Le second objectif consiste à étudier la localisation des charges conductrices dans un système TP/TD. Deux procédés de mise en œuvre ont été développés. Le premier procédé dit « one shot » permet de localiser les charges préférentiellement et de manière homogène dans la phase thermodurcissable et apporte une conductivité uniquement à forte concentration en particules conductrices.Une seconde méthodologie a été élaborée permettant d’obtenir un matériau biphasique dans lequel les charges sont localisées préférentiellement à l’interface du système Epoxy/thermoplastique. Des conductivités, à faible taux de charges (5 % massique), de l’ordre 10-1 S/m ont pu être atteintes avec cette méthodologie. / Thermosetting materials suffer from a lack of electrical conductivity. In order to overcome this barrier, a natural strategy is to introduce conductive fillers above the percolation threshold. However, addition of fillers usually leads to an increase of viscosity of the formulation which precludes infusing the resin through the porous bed of carbon fibers. In order to solve this problem, we aim at creating a two phase material and locate the fillers at the interface in order to decrease the percolation at very low values.With this view, this study is divided into two parts. The first one concerns the control of multiphase composites in order to get a co-continuous morphology by a strategy called Reaction Induced Phase Separation (RIPS). Phase diagram and influence of parameters have been studied.The second part is the formulation of a composite material (thermoplastic/thermoset) in presence of inorganic fillers. We developed two differents processes which allowed us to control fillers localisation in the blend. A process called “one shot” allows to locate homogeneously inorganic particles in epoxy phase. A second process called “premix” would preferentially locate conductive fillers at the interface of the interpenetrating system.Diffusion of particles at the interface was observed in situ during the curing of a biphasic thermoset material permitting to open the road of conducting materials and a conductivity around 10-1 S/m has been reached using as low as 5 wt% carbon black. The concept of localization of filler has been valided on several systems.