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The main objective of this research is to develop experimental and analytical methodologies to predict the lifetimes for internally pressurized SiC tubes from the lifetimes of simple specimens subjected to similar delayed failure modes. In general, two different mechanisms are responsible for delayed failure behavior in ceramics, depending on the material, microstructure, size of inherent flaws, and the level af applied stress. These delayed failure mechanisms are slow crack growth (SCG) and creep rupture. In this paper, a methodology to predict the lifetimes for sintered alpha silicon carbide (SASC) tubes, expected to fail due to SCG mechanism, will be shown. This methodology involved experimental determination of the SCG parameters for the SASC material and the scaling analysis to project the stress rupture data for small specimens (O-rings and compressed C-rings) to large tubular components. Also included in this paper is a methodology to predict the lifetimes for internally pressurized reaction bonded silicon carbide (SCRB210) tubes, for which delayed failure behavior is expected to be controlled by creep rupture mechanism. Finite element analysis (FEM) in association with the Monkman-Grant creep rupture criterion, were used to predict the lifetimes for the SCRB210 tubes. The relationship between the two delayed failure mechanisms, specimen size and applied stress level will also be discussed.
Silicon carbide, slow crack growth, creep, Weibull statistics
Assistant Professor, College of Engineering, University of Wisconsin-Platteville, Platteville, WI