Fatigue crack growth in Ti-matrix composites with spatially varied interfaces

Spatially varied interfaces (SVIs) is a design concept for composite materi als where the interface mechanical properties are varied along the length a nd circumference of the fiber/matrix interface. These engineered interfaces can be used to modify critical titanium matrix composite properties such a s transverse tensile strength and fatigue crack growth resistance in ways t hat produce a balanced set of properties. The SVI approach may also be used to probe interface failure mechanisms for the purpose of understanding com plex mechanical phenomena. Single lamina Ti-6Al-4V matrix composites contai ning strongly bonded SiC fibers were fabricated both in the as-received con dition and with a weak longitudinal stripe along the sides of the fibers. T he striped SVI composites exhibited an increase in the overall fatigue crac k growth life of the specimens compared to the unmodified specimens. This i mprovement was caused by an increased extent of debonding and crack bridgin g in SVI composites.