Fatigue behaviour of cross-ply Nicalon/CAS-II glass-ceramic matrix composite at room and elevated temperatures

An experimental study was carried out on cross-ply Nicalon/CAS-II glass-ceramic matrix composite under monotonic, static, cyclic and a combination of static and cyclic loadings. Tests were carried out at room temperature (20 degreesC) and 800 degreesC in air with varying levels of peak stress, stress ratio and loading history. At room temperature and 800 degreesC, the composite exhibited fatigue limit (10(6) cycles) at 40 and 20% of the room temperature flexural strength, respectively. Therefore, the fatigue limit of the composite at 800 degreesC reduced to half of its room temperature value. The composite also exhibited a shorter lifetime under cyclic loading than under static loading at 800 degreesC. Although the residual strength of the specimens those survived 10(6) cycles at 20 degreesC was similar to15% lower than the original flexural strength, the residual strength of the specimens those survived 10(6) cycles at 800 degreesC was similar to20% higher than the corresponding flexural strength. It indicates that the fatigue damage mechanisms at 20 degreesC is different from that at 800 degreesC. Parameters such as peak stress, stress ratio and loading history were also found to play strong role on the fatigue damage mechanisms of this composite. (C) 2004 Published by Elsevier Ltd.