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Microstructural fracture behavior of a ceramic matrix composite (CMC) with nonuniformly distributed fibers is studied in the presentation. A comprehensive numerical analysis package to study the effect of nonuniform fiber dimensions and locations on the microstructural fracture behavior is developed. The package starts with an optimization algorithm for generating representative volume element (RVE) models that are statistically equivalent to experimental measurements. Experimentally measured statistical data are used as constraints while the optimization algorithm is running. Virtual springs are utilized between any adjacent fibers to nonuniformly distribute the coated fibers in the RVE model. The virtual spring with the optimization algorithm can efficiently generate multiple RVEs that are statistically identical to each other. Smeared crack approach (SCA) is implemented to consider the fracture behavior of the CMC material in a mesh-objective manner. The RVEs are subjected to tension as well as the shear loading conditions. SCA is capable of predicting different fracture patterns, uniquely defined by not only the fiber arrangement but also the specific loading type. In addition, global stress-strain curves show that the microstructural fracture behavior of the RVEs is highly dependent on the fiber distributions.

Evaluating thE Durability of SiC-CoatED Carbon CompoSitES unDEr thErmal ShoCk ConDitionSoxidation and indentation properties of silicon carbide-coated carbon composites were investigated to analyze its durability under atmospheric thermal shock conditions. The silicon carbide-coated samples were prepared either with chemical vapor deposition or chemical vapor reaction/chemical vapor deposition hybrid coating. The remnant weight of uncoated and coated samples was investigated after each thermal shock cycle. The surface and cross-section of coated samples were then analyzed to confirm morphological changes of the coating layers. The spherical indentation test for uncoated and coated samples were also performed. As a result, silicon carbide coating improved the oxidation resistance, elastic modulus, and hardness of carbon composites. hybrid coating drastically enhanced the durability of samples at high temperature in atmospheric conditions.