Accession Number : ADA565962


Title :   Calculation of Growth Stress in SiO2 Scales Formed by Oxidation of SiC Fibers (PREPRINT)


Descriptive Note : Technical paper 1 Jun-1 Jul 2012


Corporate Author : AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH STRUCTURAL MATERIALS DIV


Personal Author(s) : Hay, Randall S


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a565962.pdf


Report Date : Jul 2012


Pagination or Media Count : 11


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.


Descriptors :   *OXIDATION , *SILICON CARBIDES , CERAMIC MATRIX COMPOSITES , CRYSTAL CHEMISTRY , FIBERS , SHEAR STRESSES , SILICON DIOXIDE


Subject Categories : Physical Chemistry
      Ceramics, Refractories and Glass
      Crystallography


Distribution Statement : APPROVED FOR PUBLIC RELEASE