Fatigue life prediction of titanium matrix composites under mission spectrum loading

Fatigue life predictions are conducted for a high temperature composite for hypersonic vehicle structural applications. A SCS-6/Timetal(R)21S [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. Spectrum loading is decomposed into a series of in-phase and out-of-phase TMF segments whose lives are predicted from a life fraction model which was developed for isothermal and TMF data. Analytical predictions for the mission spectrum and the simple mission profiles are compared with experimental data obtained here as well as in a previous study. The model is demonstrated to be able to predict fatigue life under mission spectrum loading based solely on calibration under simple isothermal fatigue and TMF conditions.