HIGH-TEMPERATURE MECHANICAL-BEHAVIOR OF MULTIDIRECTIONAL NICALON CAS-II COMPOSITE/

High-temperature mechanical behaviour of Nicalon/CAS-II composite has been investigated. Oxidation of the exposed interfaces along matrix cr acks at 1000 degrees C lowered the longitudinal unidirectional strengt h to the stress level at which matrix cracking began to occur. The str ength of cross-plied composites was also severely reduced in 800 degre es C air. Transverse plies cracked prior to 0 degrees ply matrix crack ing. However, embrittlement did not occur until the matrix in the 0 de grees plies cracked. It was established that oxidation does not take p art in crack growth parallel to the fibres, except adjacent to exposed edges. Neither does oxygen enter 90 degrees ply cracks in cross-plied composites in sufficient quantity to produce oxidation embrittlement, at least up to the 0 degrees matrix cracking strain.