Thermal-mechanical-chemical coupling behaviors of carbon/carbon composites

Oxidation behavior significantly influences the mechanical properties of carbon/carbon (C/C) composites operating in high-temperature service environments. A thermal-mechanical-chemical coupling constitutive model is developed using a kinetic method for the gas-solid oxidation reaction. This model incorporates a four-phase representation of the carbon/carbon composite and derives the mass transfer rate for a first-order irreversible reaction. Component conversions and their nondimensional reaction times are predicted. By coupling the constitutive relations for oxidation and the mechanical behavior, transient mechanical properties are theoretically determined. This multi-scale model is integrated into Abaqus finite-element software to numerically simulate and the progressive oxidation and damage processes in needle-punched carbon/carbon composites that are experimentally validated. The obtained results showed that modulus and strength decreased by 15 % and 17.6 % due to oxidation, respectively. The matrix phase between punched bundles oxidized and damaged first, with the subsequent crack propagation accelerating the oxidation process by providing oxygen diffusion channels. This research contributes to a potential reuse of thermal protection structures in aerospace engineering.