Tensile Behavior of Glass/Ceramic Composite Materials at Elevated Temperatures

This paper describes the tensile behavior of high-temperature composite materials containing continuous Nicalon ceramic fiber reinforcement and glass and glass/ceramic matrices. The longitudinal properties of these materials can approach theoretical expectations for brittle matrix composites, failing at a strength and ultimate strain level consistent with those of the fibers. The brittle, high-modulus matrices result in a nonlinear stress-strain curve due to the onset of stable matrix cracking at 10 to 30 percent of the fiber strain to failure, and at strains below this range in off-axis plies. Current fibers and matrices can provide attractive properties well above 1000°C, but composites experience embrittlement in oxidizing atmospheres at 800 to 1000°C due to oxidation of a carbon interface reaction layer. The oxidation effect greatly increases the interface bond strength, causing composite embrittlement.