A constitutive model of continuous carbon fiber reinforced thermoplastic polyether ether ketone composites in a wide temperature range

As preferred high-temperature structural materials for the next generation aerospace craft, carbon fiber reinforced thermoplastic polyether ether ketone composite (CF/PEEK) has excellent properties, such as high impact resistance, repairability, high temperature resistance and so forth. Because of the crystallization characteristics, the PEEK matrix still has a high load-carrying capacity above the glass transition temperature (around 143℃), and therefore CF/PEEK composite can be used under long term operation at 200℃. However, due to the wide forming temperature range and service temperature range of CF/PEEK composites, PEEK resin will gradually relax at high temperature. Consequently, CF/PEEK composites will show obvious time-, temperature-, and loading history-dependent anisotropic viscoelasticity, which make it very hard to accurately design the forming history and service history of the composite structures. Currently, the existing high temperature prediction model of composites is usually based on the elastic-plastic constitutive stiffness reduction method, which does not fully consider the anisotropic relaxation behavior of the composites. In this paper, an anisotropic viscoelastic constitutive model was developed to describe the time- and temperature- dependent properties of composites. The generalized Maxwell viscoelastic parameters of the PEEK resin were obtained by characterizing the relaxation modulus main curve in a wide temperature range (25~200℃). Then, by semi-empirical solution for equivalent mechanical properties of composite materials, a three-dimensional anisotropic constitutive model was developed. Finally, the developed model has been verified by comparing with the high temperature relaxation experiments and the finite element simulation by the representative volume unit (RVE) along the transverse direction. Overall, the developed model can be used to simulate the forming process and design the high temperature mechanical properties of CF/PEEK composites.