FATIGUE LIFE PREDICTION OF TITANIUM MATRIX COMPOSITES UNDER MISSION SPECTRUM LOADING

Fatigue life predictions are conducted for a high temperature composit e for hypersonic vehicle structural applications. A SCS-6/Timetal(R)21 S [0/90](S) composite is evaluated under thermomechanical fatigue (TMF ) as well as under typical hypersonic mission profiles and segments of those missions. The fatigue life analysis is based on micromechanical stresses which, in turn, are input into a damage summation model. Spe ctrum loading is decomposed into a series of in-phase and out-of-phase TMF segments whose lives are predicted from a life fraction model whi ch was developed for isothermal and TMF data. Analytical predictions f or the mission spectrum and the simple mission profiles are compared w ith experimental data obtained here as well as in a previous study. Th e model is demonstrated to be able to predict fatigue life under missi on spectrum loading based solely on calibration under simple isotherma l fatigue and TMF conditions.