H. Kimura, Y. Akiniwa, T. Fujii, Nagoya University, Nagoya, Japan; K. Tanaka, Meijo University, Meijo, Japan
TiNi is most widely used shape memory alloy because of the large recovery strain and superelasticity as well as the excellent resistance against corrosion and wear. In addition to the conventional use such as pipe couplings and the frames of glasses, TiNi has attracted attention as structural components of medical devices and actuators of intelligent structures in recent years. Therefore, the fatigue reliability over long-term use has been recognized as an increasingly important subject in the utilization. It has been reported that the fatigue crack propagation behavior is different in austenite and martensite of TiNi. Though the stress-induced martensitic transformation at a fatigue crack tip is considered to play an important role in the propagation behavior, the effect and mechanism is not fully clarified. In this research, shape memory alloy TiNi was fatigued under tension-compression loading and the stress-induced martensitic transformation was observed by SEM and high-resolution X-ray diffraction technique that can measure the distribution of the phase change around the fatigue crack. The effect of the stress-induced martensite at the crack tip on the fatigue crack propagation behavior was investigated.
Summary: TiNi is most widely used shape memory alloy because of the large
recovery strain and superelasticity as well as the excellent
resistance against corrosion and wear. In addition to the conventional
use such as pipe couplings and the frames of glasses, TiNi has
attracted attention as structural components of medical devices and
actuators of intelligent structures in recent years. Therefore, the
fatigue reliability over long-term use has been recognized as an
increasingly important subject in the utilization. It has been
reported that the fatigue crack propagation behavior is different in
austenite and martensite of TiNi. Though the stress-induced
martensitic transformation at a fatigue crack tip is considered to
play an important role in the propagation behavior, the effect and
mechanism is not fully clarified. In this research, shape memory alloy
TiNi was fatigued under tension-compression loading and the
stress-induced martensitic transformation was observed by SEM and
high-resolution X-ray diffraction technique that can measure the
distribution of the phase change around the fatigue crack. The effect
of the stress-induced martensite at the crack tip on the fatigue crack
propagation behavior was investigated.
