FATIGUE-ENVIRONMENT INTERACTIONS IN A SIC/TI-15-3 COMPOSITE

Load-controlled isothermal and non-isothermal fatigue lives of a [0-degrees]8 SiC/Ti-15-3 were evaluated at temperatures between 150 and 550-degrees-C and a target strain range of about 0.45%. In non-isothermal fatigue tests, load was first cycled at minimum temperature and then temperature was cycled at zero load. For fatigue tests with peak temperatures at or above 300-degrees-C, fatigue life was dramatically reduced compared to that at 150-degrees-C. The shortest life was produced by the non-isothermal test with the greatest temperature range (DELTAT = 400-degrees-C) and highest peak temperature (T(max) = 550-degrees-C). Vacuum testing showed that much of the life reduction under isothermal and non-isothermal conditions was related to environmental effects, although the nature of the fatigue-environment interaction was decidedly different for the isothermal and non-isothermal test cycles which were studied.