Thermal expansion of unidirectional and cross-ply fibrous monoliths

An investigation of the thermal expansion behavior of ceramic fibrous monoliths (FMs) is presented. The emphasis is on the development and validation of material models applicable to Si3N4/BN FMs in both unidirectional and cross-ply architectures. Approximate analytical models are developed for the coefficient of thermal expansion (CTE) based on the analysis of representative unit cells of the Si3N4 fibers and the surrounding BN interphase. The pertinent cell shapes are identified from quantitative measurements on real Si3N4/BN FMs. Corresponding finite element analyses are performed on the same unit cells for the purpose of validating the analytical models. Good agreement is obtained between the model predictions and experimental measurements of CTE. A rudimentary modification to the analytical model to account for texturing and anisotropy of the BN appears to yield adequate results.