TiNi形状記憶合金の曲げ疲労特性

Abstract

Tensile deformation properties and pulsating-plane bending, alternating-plane bending and rotating-bending fatigue properties of a superelastic thin tube (SE-tube) and a highelastic thin wire (FHP-wire) of TiNi alloy were investigated experimentally. The main results obtained are as follows. (1) The stress-strain curve of SE-tube in tension draws a large hysteresis loop and elastic modulus is 35GPa. Therefore, SE-tube is superior as a medical catheter tube with flexibility and shape recovery. The stress-strain curve of FHP-wire is close to a straight line up to strain of 4% and stress of 1500MPa and elastic modulus is 50GPa. Therefore, FHP-wire is superior as a medical guide wire with flexibility, high pushability and torque transmission performance. (2) With respect to fatigue properties of NT-tube and FHP-wire, the fatigue life in pulsating-plane bending is longer than those in alternating-plane bending and rotating bending. The difference in the fatigue life between alternating-plane bending and rotating bending is small. The relationship between maximum bending strain and the number of cycles to failure in low-cycle fatigue can be expressed by a power function in every bending fatigue. (3) The maximum bending strain at the fatigue limit of SE-tube is 0.8%-1.0% which is close to a starting strain of stress-induced martensitic transformation. The maximum bending strain at the fatigue limit of FHP-wire is 0.7%-0.8%.