Modeling stress evolution during fiber oxidation

Abstract

The paper examines stress evolution in oxidizing ceramic fibers, specifically focusing on silica scales growing on silicon carbide (SiC) fibers. Oxidation leads to the formation of oxide scales that induce significant stresses due to the molar volume expansion during oxidation. These stresses can lead to cracking of the oxide scale and reduction in fiber strength. To model these phenomena, an analytical framework is developed to describe stress evolution in cylindrical fibers. The elastic-creep behavior of the oxide is represented by a viscoelastic Maxwell model. By solving the governing ordinary differential equations (ODEs) and applying material properties relevant to the oxidation of SiC fibers, the study provides insights into the interplay between oxide growth, stress relaxation, and fiber geometry. The findings show that a single material parameter—encompassing fiber radius, oxidation rate, and oxide viscosity—dominates the stress evolution. The study also reveals approximate closed-form solutions for hoop and axial stresses, which match well with results from finite element analyses. These stresses are found to depend strongly on environmental conditions, with higher stress developing in steam compared to dry air. The results provide new insights into potential stress-induced fracture in oxidizing SiC fibers, with implications for high-temperature applications of ceramic materials.