Development of experimental, theoretical and numerical tools for studying thermo-oxidation of CFRP composites

In our laboratory, recent studies concerning damage mechanisms of continuous carbon/epoxy composites induced by isothermal ageing or thermal cycling have shown interactions between mechanical loading and oxidation process. The objectives of the research program named COMEDI, initiated at LMPM-ENSMA, in collaboration with CCR-EADS, LIM ENSAM and supported by the – French – Research National Agency ANR, are to better understand these couplings and to develop a numerical tool capable to predict the evolution of the mechanical behavior of a composite laminate subjected to a thermal ageing. In this paper, on one hand the expression of the interactions between mechanics, oxygen diffusion and chemical reaction will be deduced from thermodynamics concepts for a neat resin material. On the other hand, interest will be put on the development of a ‘user’ finite element involving the first disposable couplings: matrix shrinkage and evolution of the elastic modulus with oxidation. An application will be presented in the case of a unidirectional CFRP composite model, which gives the stress field around carbon fibers induced by the oxidation of the matrix. At last, a specific experimental device developed at the laboratory will be presented. This heated and pressurized vessel will allow performing accelerated thermal aging tests of samples submitted to constant deformation in order to put coupling effects under evidence, as well as to improve and validate the modeling approach.