Damage‐Enhanced Creep in a Siliconized Silicon Carbide: Mechanics of Deformation

TLDR: In this article, three loading modes (tension, compression, and bending) are considered in the analysis of flexural deformation of silicon carbide at elevated temperatures: tension, cavitation at stresses in excess of a temperature-dependent threshold level, resulting in bilinear power-law creep, and compression, where greater applied stresses are required to achieve the same rate of strain.

Abstract: Continuum mechanics methods were employed to analyze creep deformation of a grade of siliconized silicon carbide at elevated temperatures. Three loading modes (tension, compression, and bending) are considered in this analysis. In tension, deformation is accompanied by cavitation at stresses in excess of a temperature-dependent threshold level, resulting in bilinear power-law creep. In compression, greater applied stresses are required to achieve the same rate of strain, and although bilinear creep behavior is also observed, a single power-law creep equation was assumed to simplify the mathematical analysis of the flexure problem. Asymmetrical creep in siliconized silicon carbide leads to a number of unique features in flexural creep. At steady state, a threshold bending moment exists below which no damage occurs. The neutral axis shifts from the geometric center toward the compressive side of the specimen by an amount that depends on the level of applied stress. Cavitation zone shapes, which are predicted to develop in a four-point bend specimen as a function of load, are found to be in qualitative agreement with those obtained experimentally. For transient creep under bending, the time-dependent neutral axes for stress and strain do not coincide, although they do converge toward a single axis at steady state. Quantitative predictions are given for relaxation of tensile stresses at the outer fiber, reverse loading in the midplane region, and the growth of the damage zone toward the compressive side of the flexural specimen. This load redistribution leads to a prolonged transient stage as compared to its counterpart in uniaxial creep.