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

Spatially varied interfaces (SVIs) is a design concept for composite materials where the interface mechanical properties are varied along the length and circumference of the fiber/matrix interface. These engineered interfaces can be used to modify critical titanium matrix composite properties such as transverse tensile strength and fatigue crack growth resistance in ways that produce a balanced set of properties. The SVI approach may also be used to probe interface failure mechanisms for the purpose of understanding complex mechanical phenomena. Single lamina Ti-6Al-4V matrix composites containing strongly bonded SiC fibers were fabricated both in the as-received condition and with a weak longitudinal stripe along the sides of the fibers. The striped SVI composites exhibited an increase in the overall fatigue crack growth life of the specimens compared to the unmodified specimens. This improvement was caused by an increased extent of debonding and crack bridging in SVI composites.