Modeling the two-way coupling of stress, diffusion, and oxidation in heterogeneous CMC microstructures

Abstract

A multiphysics methodology and a corresponding numerical scheme are proposed for modeling the complex interactions between oxygen diffusion, matrix cracking, oxidation, and the state of stress in carbon silicon carbide (C/SiC) ceramic matrix composites (CMCs) at the microstructural scale. The model is derived from the governing equations for force equilibrium and conservation of mass for oxygen and carbon, which are coupled through reaction terms, oxygen diffusivities and solubilities, and damage in the matrix. The Galerkin method of weighted residuals is used to derive the finite element method (FEM) equations, and the model is demonstrated on a representative stochastic heterogeneous microstructure to investigate the creep-like strain acceleration of stressed oxidation experiments and analyze the fundamental differences between the reaction-limited and diffusion-limited temperature regimes.