Evolution of stress and deformations in high-temperature polymer matrix composites during thermo-oxidative aging

This paper presents a model-based analysis of thermo-oxidative behavior in high-temperature polymer matrix composite (HTPMC) materials. The thermo-oxidative behavior of the composite differs from that of the constituents as the composite microstructure, the fiber/matrix interphase/interface behavior and damage mechanisms introduce anisotropy in the diffusion and oxidation behavior. Three-dimensional Galerkin finite element methods (GFEM) that model the thermo-oxidative layer growth with time are used together with homogenization techniques to analyze lamina-scale behavior using representative volume elements (RVEs). Thermo-oxidation-induced shrinkage is characterized from dimensional changes observed during aging in inert (argon) and oxidative (air) environments. Temperature-dependent macro-scale (bulk) mechanical testing and nano-indentation techniques are used for characterizing the effect of oxidative aging on modulus evolution. The stress and deformation fields in a single ply unidirectional lamina are studied using coupled oxidation evolution and non-linear elastic deformation analyses. Deformation and stress states are shown as a function of the aging time. While the thermo-oxidative processes are controlled by diffusion phenomenon in neat resin, the onset and propagation of damage determines the oxidative response of an HTPMC.