Micromechanical Modeling of Oxidation Induced Stresses in SiC/SiC Composites

Abstract

Silicon Carbide fiber reinforced composites are used in high temperature aerospace and propulsion applications due to their light weight, increased toughness and high thermal stability. However, their durability is limited due to environmental degradation. This paper focuses on the oxidation of SiC fibers and SiC/SiC composites at high temperature. The constrained volume expansion accompanying oxidation leads to development of large residual volumetric growth stresses. A micromechanical model was used to study the effect of oxidation induced stresses in a SiC fiber and in a unitcell of a SiC/SiC lamina. The oxidation induced strains are estimated by using Pilling- Bedworth expansion ratio and applied to the oxide layer as volumetric strains. The evolution of the oxide layer and stresses during isothermal aging was simulated using finite element methods. Two studies have been conducted considering with intact PyC and eroded PyC interphase regions. Paper describes the stresses developing during oxide growth with linear elastic and visco-elastic oxide layer behaviors. Simulations results are compared with experimental data and predictions from other models obtained from published literature.