Fatigue behavior of a cross-ply titanium matrix composite under tension-tension and tension-compression cycling

The fatigue behavior of a titanium-based metal-matrix composite reinforced with silicon carbide fibers, SCS-6/Ti-15-3, with the cross-ply lay-up of [090]2S, was investigated at room temperature for two conditions; tension-tension and tension-compression. On the maximum applied stress basis, the tension-tension condition had longer fatigue lives than the tension-compression condition. On the stress-range basis, however, the tension-tension condition had shorter fatigue lives than the tension-compression condition. For both conditions, three distinct regimes of fatigue behavior were present. These were fiber-dominated, matrix-dominated, and mixed fiber/matrix-dominated regions. In these regimes, fatigue damage mechanisms and the stress-strain response during cycling were, in general, similar for both fatigue conditions. However, additional damage mechanisms and plasticity sites were present in tension-compression cycling which resulted in different fatigue lives in comparison with tension-tension cycling.