Microscale Thermal–Structural Modeling for Carbon Fibers Subjected to a Hypersonic Boundary Layer

With regard to the thermal protection system, the thermal–structural responses of modern ablative materials are of primary importance in many aspects, including material selection and sizing. Due to the intricate nature of their porous structure and complicated thermal conditions they are subjected to, ablative materials may exhibit unexpected behavior, which can potentially lead to material failure. In this study, two solvers—a direct simulation Monte Carlo solver and a finite-volume-based material response solver—are coupled together to predict the microscale thermal– structural performance of a thermal protection system material like phenolic impregnated carbon ablator. In this approach, individual fibers are modeled at the microscale, which provides valuable knowledge of porous media behavior. Nonuniform boundary conditions, including the heat flux and external force, are captured by the direct simulation Monte Carlo solver, and the detailed thermal and structural performance of the fiber is captured by the material response solver. The results show that individual fibers do not fail based on the temperature gradient and applied aerodynamic forces. However, it is shown that the attachment points of the fibers are the most vulnerable. This vulnerability can potentially lead to a breakdown of the binders, which would separate fibers and cause material failure.