Tensile deformation and rotating-bending fatigue properties of a highelastic thin wire, a superelastic thin wire, and a superelastic thin tube of NiTi alloys

The tensile deformation and rotating-bending fatigue properties of a highelastic thin wire, a superelastic thin wire and a superelastic thin tube, all made of NiTi alloys, were investigated experimentally. The results obtained are summarized as follows: (1) The stress-strain curve of the highelastic thin wire is approximately linear up to a strain of 4 percent with a stress of 1400 MPa and shows little dependency on temperature and strain rate; (2) The modulus of elasticity for the initial loading stage of both the highelastic wire and the superelastic tube is low, showing superior bending flexibility as is necessary for medical applications; (3) The slopes of the strain-life curves of the alloys are steep in the low-cycle fatigue region (the strain amplitude of the fatigue limit is in the region of 0.6-0.8 percent); and (4) In the tube, fatigue cracking initiates on the rougher inner surface, resulting in a shorter fatigue life than in the case of the wire.