Mechanical behaviour predictions for viscoelastic polymer matrix composites under high temperature and multi-axial conditions and experimental validation

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Composite materials are increasingly used in high performance applications, like in aircraft engines and fuselage. The materials are subjected to complex multi-axial stress states and to time-varying temperatures. These service conditions make accurate prediction of their mechanical behaviour a challenging task. Accurate predictive models are of considerable interest to the aerospace industry since they can reduce the number of iterations required for obtaining the final component. In addition, having precise tools allows reducing the design safety factors, which leads to lighter structures. Lighter structures require less energy for being moved, which has a direct impact on the environment. The research program aims at developing tools that will predict the mechanical behavior of polymers and polymer composites under multi-axial stress states and transient temperature histories. One part of the program is devoted to the development of nonlinearly viscoelastic constitutive theories for the polymer matrix when it is subjected to multi-axial loadings and elevated temperatures. In addition, an important experimental campaign is planned in order to generate data for various stress states under controlled conditions for a single material. The other part of the program is devoted to the development of homogenization models for predicting the mechanical response of composites based on the knowledge of the microstructure (shapes, orientations, volume fractions of reinforcements, etc.). The key issue to be addressed is to take into account the fact that the matrix is viscoelastic. Both analytical and numerical models will be built and validated by experimental results. The two parts of the research program will be developed in parallel since the constitutive theories developed for the matrix will be directly used into the homogenization models.