An investigation of the effects of microstructure on fatigue damage in a symmetric [090]2s silicon carbide (SCS6) fiber-reinforced titanium matrix composite

The results of a systematic study of the effects of microstructure on the mechanisms of fatigue damage in a symmetric eight ply [090]2s Ti15Al3Cr3Al3Sn/SiC (SCS6) composite are presented. Damage mechanisms are elucidated using optical/scanning electron microscopy and acoustic emission techniques. Damage initiation under cyclic loading is shown to occur early in life, and is dominated by longitudinal and transverse interfacial cracking. Subsequent damage occurs by matrix and fiber cracking, slip band formation and crack coalescence prior to the onset of catastrophic failure. However, the sequence of the damage is sensitive to changes in the metastable β matrix and interfacial microstructure. Based on the experimental evidence, a micromechanics model is developed for the prediction of fatigue life. This model involves the use of crack-tip shielding concepts in the assessment of crack bridging phenomena during fatigue crack growth.