LONGITUDINAL FATIGUE RESPONSE OF A METAL-MATRIX COMPOSITE UNDER STRAIN CONTROLLED MODE AT ELEVATED-TEMPERATURE

The fatigue characteristics of a unidirectional titanium-based metal m atrix composite (MMC) (SCS-6/Ti-15-3) were investigated at elevated te mperature (427 degrees C). A hybrid strain controlled loading mode was employed for this purpose. This hybrid control mode did not allow the specimen to experience compressive stress in order to prevent any pos sible buckling effects. To fully understand the fatigue behavior of th e MMC under this control mode, fatigue tests, microscopic evaluation, and micromechanical analysis were performed. Based on this combination of activities, the damage and deformation mechanisms were systematica lly identified. It was found that the fatigue behavior was initially d ominated by creep deformation of the matrix. This was accompanied by p lastic deformation in those specimens that were subjected to a maximum strain level of 0.55% or higher. Depending on the maximum strain leve l, the specimen failure was a result of either fiber fracture or matri x cracking. Using the combined approach involving experiments, microsc opy, and analysis, the interrelationships among applied strain levels, fatigue life, damage mechanisms, and macroscopic response were establ ished to characterize the longitudinal fatigue characteristics of the tested MMC.