Calculation of Growth Stress in SiO2 Scales Formed by Oxidation of SiC Fibers (PREPRINT)
Abstract
A numerical method to calculate growth stress in SiO2 scales formed during SiC fiber oxidation is described. Calculations were done for SiC fibers between 700 degrees and 1300 degrees C using previously measured Deal-Grove parameters for oxidation kinetics and an Eyring viscoplastic model for SiO2 scale viscosity. Initial compressive stresses in SiO2 of approximately 25 GPa from the 2.2 x oxidation volume expansion are rapidly relaxed to lower levels by flow of silica with a shear stress-dependent viscosity. At 700 degrees - 900 degrees C, axial and hoop stress at the GPa level persist. Radial expansion of the outer scale causes hoop stress to become tensile; axial stress becomes tensile by the Poisson effect. Tensile hoop stresses can be >2 GPa for thick scales formed at <1000 degrees C. Effects of different fiber radii on growth stresses are examined. Limitations of the method and analytical approximations are discussed.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 2012
- Accession Number
- ADA565962
Entities
People
- Randall S. Hay
Organizations
- Air Force Research Laboratory