DAMAGE MECHANISMS OF SCS-6/TI-6AL-4V COMPOSITES UNDER THERMAL-MECHANICAL FATIGUE

The damage mechanisms of the unidirectional SCS-6/Ti-6Al-4V composites under thermal-mechanical fatigue loading and high temperature isothermal fatigue were studied. The maximum cyclic temperature varied from 370 to 650-degrees-C and maximum applied stresses ranged from 828 to 1180 MPa. The resulting thermal-mechanical fatigue life for each condition was plotted against the maximum stress in the matrix. The crack initiation and propagation mechanisms were identified. It was found that matrix cracking with unbroken fiber bridging is the major damage mode for the composites under thermal-mechanical fatigue and isothermal fatigue loading. Furthermore, oxidation-assisted matrix cracking and oxidation pitting on the fiber surface are the major damage mechanisms for high temperature oxidizing environments.