TENSION-TENSION FATIGUE BEHAVIOUR OF NEXTEL 720/ALUMINA UNDER COMBUSTION ENVIRONMENT

The fatigue behaviour of Nextel 720/alumina composites was investigated under a combustion environment, and compared with that in a laboratory environment. The fatigue strength for 90000 cycles was equal to 150 MPa under combustion conditions, and 170 MPa in laboratory environment. However, the normalised fatigue strength (ratio of fatigue strength and ultimate tensile strength) was equal in combustion and laboratory environments. The difference in fatigue strength was due to thermal stresses from impingement of the combustion flame on one side of the specimen. Fractographic analysis showed that combustion had little effect on fibre/matrix bonding in only the flame impingement region. A combustion environment was not, therefore, damaging to Nextel 720/alumina.