Multiphysics model of thermomechanical oxidative degradation in SiC/SiC ceramic matrix composite microstructures

Abstract

A coupled thermomechanical-oxidation damage formulation, based on governing multiphysics constitutive relations and stochastic microstructure representation, is developed to provide fundamental insights into the life-limiting oxidative degradation mechanisms in ceramic matrix composites (CMCs) with a silicon carbide (SiC)-based matrix reinforced by SiC fibers. The methodology includes passive oxidation of the fibers governed by reaction kinetics and diffusion-limited degradation. Conservation of mass equations, incorporating a modified Fick’s law, govern the evolution of oxygen and silica concentrations in CMC constituents. The effective oxygen diffusivities in the matrix and fibers are modeled as functions of matrix damage and normalized silica concentration, respectively. The model is numerically implemented using the finite element method and tested on stochastic representative volume elements, accounting for the inherent flaws in the CMC microstructure. The fundamental differences between oxidation regimes, the time-dependent deformation mechanisms, and the influence of matrix damage on oxidation kinetics at the microscale are analyzed.