FATIGUE BEHAVIOR OF A CROSS-PLY TITANIUM MATRIX COMPOSITE WITH TENSILE AND ZERO MEAN LOAD AT ELEVATED-TEMPERATURE

The fatigue response of a cross-ply [0/90](2S) titanium (Ti-15-3) matr ix composite reinforced with silicon carbide fibers (SCS-6) was invest igated at 427 degrees C. Tension-tension (tensile mean stress) and ten sion-compression (zero mean stress) loadings were applied. For the sam e stress range, tension-tension loading caused much lower fatigue live s and greater strain ratchetting than those under tension-compression loading. Despite the longer fatigue lives under tension-compression lo ading, additional plasticity sites and fatigue damage mechanisms were observed. Fatigue damage mechanisms could be classified into two disti nct regimes, independent of mean load, fiber-dominated (fibers fractur e prior to matrix cracking) at high-stresses and low-cyclic lives, and matrix dominated (matrix fatigue cracks prior to fiber fracture) at l onger lives. Comparisons of the 427 degrees C results are made with pr eviously reported results at room temperature. Deformation mechanisms and fatigue lives were influenced by the testing temperature.