Modeling the effect of pitting on the tensile behavior of amorphous carbon and carbon fiber

Abstract

FiberForm, the substrate of the Phenolic Impregnated Carbon Ablator (PICA), contains various fundamental forms of carbon, including vitreous or highly ordered graphitic regions in the carbon fiber core and amorphous or turbostratic carbon in the binder material, which provides stiffness to the material. In this study, we use the AIREBO potential to investigate the effect of pitting on the elastic properties of carbon fiber (CF) and amorphous carbon (AC). The generation, structural characterization, and loading of pristine AC and CF are compared with their pitted counterparts over a range of densities (1.27 g/cm³ to 2.93 g/cm³) and porosities. Results show a reduction of up to 18.7% in elastic modulus for AC and a reduction of 13.7% in modulus for CF. We also observe AC to have weaker tensile behavior for both oxidized and pristine states, supporting the hypothesis that FiberForm is likely to fail at the binder. The present work advances fundamental understanding of the coupling between oxidation and mechanical behavior of carbon-based TPS materials and serves as a basis for larger-scale simulations.