Bending Fatigue Properties of a Superelastic Thin Tube and a High-Elastic Thin Wire of TiNi Alloy

Experiments were conducted to investigate the deformation behaviors and fatigue properties of a superelastic thin tube (SE-tube) and a high-elastic thin wire (HE-wire) of TiNi alloy under conditions of pulsating-plane, alternating-plane and rotating bending. The main results obtained are summarized as follows. (1) The stress-strain curve of the SE-tube in tension describes a superelastic hysteresis loop with an elastic modulus of 35 GPa. It is thus suited for use as a medical catheter tube with flexibility and shape recovery. The stress-strain curve of the HE-wire stays close to a straight line up to a strain of 4% and a stress of 1500 MPa with an elastic modulus of 50 GPa, and is suited for use as a medical guide wire with flexibility, high pushability and a good torque transmission performance. (2) With respect to fatigue, the SE-tube and the HEwire in air both have a longer life in pulsating-plane than in alternating-plane and rotating bending, whereas the difference in fatigue life between alternating-plane and rotating bending is small. The relationship between the maximum bending strain and the number of cycles to failure in the region of low-cycle fatigue can be expressed by a power function for each kind of bending fatigue. The fatigue life in the body is longer than that obtained in air. (3) The maximum bending strain at the fatigue limit of the SE-tube is 0.8%–1.0% which is close to the starting strain of the stressinduced martensitic transformation. The maximum bending strain at the fatigue limit of the HE-wire is 0.7%–0.8%. [doi:10.2320/matertrans.M2009073]