TRANSVERSE FATIGUE RESPONSE OF A METAL-MATRIX COMPOSITE UNDER STRAIN-CONTROLLED MODE AT ELEVATED-TEMPERATURE .1. EXPERIMENTS

The transverse fatigue characteristics of a unidirectional titanium-ba sed metal matrix composite (MMC) (SCS-6/Ti-15-3) were investigated und er an isothermal condition. Fatigue tests were performed using a hybri d strain-controlled loading mode. In this hybrid control mode, the spe cimen was always in a tension-tension state of stress perpendicular to the fiber direction. This prevented any possible buckling effects. A systematic approach that involved fatigue tests, microscopic evaluatio n, and micromechanical analysis, was taken to characterize the fatigue response (that is, fatigue life, stress-strain response, and so forth ) and identify the damage and deformation mechanisms. The analysis inv olved a unique method to model the fiber-matrix interfacial damage. It was found that the fatigue response was initially dominated by the am ount of fiber-matrix interfacial damage that occurred during the first loading cycle. The subsequent response was dependent on the rate at w hich this interfacial damage progressed, the development and propagati on of matrix cracks, and matrix inelastic deformation (plasticity and creep). The chronology and accumulation of these damage mechanisms wer e dependent on the applied strain level. Using the combined approach i nvolving experiments, microscopy, and analysis, the correlation among applied strain levels, fatigue life, damage mechanisms, and macroscopi c response (stress and stiffness) were established in this paper. In P art II, the details and results of the micromechanical analysis are pr esented.