Fatigue crack propagation and local crack-tip strain behavior in TiNi shape memory fiber reinforced composite

Active enhancement of fatigue resistance of shape memory alloy TiNi fiber reinforced epoxy matrix composite was studied in this paper. Fatigue crack propagation behaviors were investigated by using fine-grid method, which was engraved on the epoxy surface by photo-etching. The effects of prestrain in TiNi fiber on fatigue crack development and suppression in the local domain region around the embedded TiNi fibers were investigated in detail. The retardation of fatigue crack propagation is attributed mainly to the compressive stress in the matrix caused by shrinkage of the pre-strained TiNi fibers above Af temperature. The local crack-retardation at the interface region very near the TiNi fiber is experimentally 0 confirmed by the change of local crack-tip strain behavior. Crack-tip strain hysteresis in one load cycle indicates that the compressive stress induced in the matrix and the following crack closure play key roles to suppress the crack-tip stress intensity and fatigue crack propagation. Fractographic study verified that suppression by shape memory alloy (SMA) fiber improves fatigue fracture toughness.