Control of fatigue crack propagation in the TiNi shape memory fiber reinforced smart composite

Shape memory alloy (SMA) TiNi fiber reinforced /epoxy matrix composite was fabricated to demonstrate the active enhancement of mechanical properties, especially, fatigue resistance in our proposed new type of smart composite. Fatigue crack propagation behaviors were investigated by using the originally developed fine-grids method. Fatigue crack propagation was arrested or retarded immediately after heating the specimen above Af temperature. It depended on the increase of the pre-strain value for embedded TiNi fibers. Therefore, it seems to be attributed mainly to the introduced compressive stress field in the matrix due to the shrinkage of the pre-strained TiNi fibers. The local retardation phenomena of a fatigue crack approaching to the embedded fiber was also recognized especially very near the fiber. From a measurement of the crack-tip opening displacement (CTOD) in one loading cycle, the macroscopic compressive stress induced in the matrix and following crack closure phenomena play a key role to suppress the crack-tip stress intensity and fatigue crack propagation. These experimental results with suppression of fatigue crack propagation in this smart composite are discussed by comparing with theoretical analysis which are based on the elastically equivalent inclusion modeling and linear fracture mechanics approach.