A Novel Computational Framework for the Oxidation of C/C Composites under Thermal Shock

In this paper, the influence of thermal shock conditions on both, the extent of carbon materials decomposition and the through-thickness compressive mechanical response of 2D woven C/C composites is investigated by computational efforts using ABAQUS. First, C/C composite specimens and carbon fibers are exposed to thermogravimetric (TG) experiments under isothermal conditions at 400 degrees C, 600 degrees C and 800 degrees C. The weight loss with time is recorded and TG curves are obtained for the C/C composite specimens and carbon fibers, which are utilized to predict the degree of decomposition of the carbon fiber tow and carbon matrix by using rule of mixtures. Finally, these TG curves are related to the Arrhenius equation to determine the corresponding kinetic parameters, which are the inputs to the proposed computational scheme. A novel computational framework consisting of two main steps is proposed. In the first step, a finite element radiation heat transfer analysis is developed on a meso-scale representative model of a C/C composite specimen exposed to thermal shock conditions with peak temperatures in the range of 400 degrees C to 800 degrees C. The radiation heat transfer analysis is coupled to a HETVAL subroutine to account for the degree of decomposition at every integration point and time within the meso-scale model. In the second step, a UMAT subroutine is added to the computational framework to account for the carbon materials stiffness degradation with temperature and time. Following this, a static analysis is performed by applying a through-thickness compressive load on the meso-scale model to determine its compressive stiffness. Finally, the predicted compressive responses of the meso-scale model under various thermal shock conditions are compared with experimental results provided in the literature, resulting in good agreement. In conclusion, this computational model can also be extended to other composites by changing individual material properties, fiber architecture, weave pattern and/or fiber volume fraction.