Modeling the Environmental Effects on Carbon Fibers in a Ceramic Matrix at Oxidizing Conditions

摘要

Carbon fiber/silicon carbide matrix composites (C/SiC) are promising materials for space applications such as nozzles, thrusters, and bladed disks. However the as-fabricated, cracked nature of the material makes it susceptible to environmental degradation due to fiber oxidation. Theoretical models can be used to gain a better understanding of how certain variables (i.e. temperature, environment, diffusion coefficient and reaction rate constant) are related to a specific process and to supplement or analyze experimental results. Methods for predicting the distribution of local oxygen concentration from the edge to the interior of an open column in a matrix bounded by carbon fiber tows will be discussed. The amounts and distribution of oxygen in a matrix and the gradients in oxygen concentration convey information regarding the oxidation kinetics. The models consider the case of a crack in a ceramic matrix that is bridged by carbon fiber tows. Two analytical solutions and differing finite difference models will be used to predict oxygen concentrations. Results from each prediction method will be presented and compared. The results and their relation towards oxidation kinetics will be discussed. Several geometries for the composite (square and rectangular) are considered in the finite difference models.