Chapter 43. Thermostructural Behavior of Sic Fiber Fabrics and Implications for Cmc

Summary

In order to better understand SiC fiber behavior within CMC microstructures, mechanical tests were performed on different types of as-produced and CVI BN coated single-ply 0/90° woven fabrics. Tensile strength and creep-rupture properties were measured on single-ply fabrics at various temperatures in air for the following types of polymer-derived SiC fibers: Hi-Nicalon, Hi-Nicalon Type-S, Tyranno SA, Sylramic, and a developmental Sylramic. For each fiber type, room temperature tensile strength for resin-impregnated as-produced fabrics and for dry BN-coated fabrics were found to be in agreement with each other and with bundle theory based on previously measured results for single fibers and tows. Exposures of the fabrics to simulated CMC process conditions typically degraded fabric room-temperature strengths, particularly for those that were initially BN coated. High temperature creep properties for as-produced fabrics were also in general agreement with single fiber and single tow data, However, high-temperature fast-fracture and rupture properties were typically worse than those of single fibers and tows tested under the same conditions. The underlying mechanisms and CMC implications of the SiC-fiber fabric results are discussed, as well as the benefits of the fabric test over single fiber and tow testing.