Damage mechanisms and life prediction in high temperature fatigue of a unidirectional SiC–Ti composite

Isothermal fatigue tests are performed in the longitudinal direction at 450°C on a unidirectional SiC/Ti composite. Three major damage mechanisms are identified: the matrix cyclic softening which overloads fibers leading to their progressive rupture; the interfacial degradation of these broken fibers and their oxidation by the environment. Damage kinetics are estimated using microscopic observations and acoustic emission. Finally, a micromechanical model is used in order to understand the respective influence of these damage mechanisms. It is shown that, at a sufficient load level, fatigue fracture of the composite strongly depends on the interfacial degradation kinetics and that fiber oxidation by the environment generates more progressive damage and considerably reduces the composite fatigue life compared to loading under vacuum.