Tension–Tension Fatigue Behavior of Nextel ^TM 720/Alumina under Combustion Environment

Fatigue behavior of Nextel720 ^™ /alumina was investigated under combustion environment, which was then compared with that in laboratory environment. Fatigue strength for 90,000 cycles was equal to 150 MPa under combustion condition, while 170 MPa in laboratory environment. However, normalized 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 combustion flame on one side of specimen. Fractographic analysis showed that combustion had little effect on fiber/matrix bonding in only flame impingement region. Combustion environment was not thus damaging to Nextel720 ^™ /alumina.