Cyclic Deformation and Fatigue of a TiNi Shape-Memory Alloy Wire Subjected to Rotating-Bending

The cyclic deformation and fatigue of a TiNi shape-memory alloy wire was studied by carrying out rotating-bending fatigue tests at various strain amplitudes, temperatures and rotational speeds in air and in water. The results were summarized as follows: (1) for strain amplitudes in the rhombohedral-phase transformation region, the fatigue life was longer than 10⁷ cycles and the deformation properties did not change under cyclic deformation; (2) for the strain amplitudes in the martensitic transformation region, the fatigue life was shorter than 10⁵ cycles and the higher the temperature, the shorter was the fatigue life; (3) the rotational speed did not affect the fatigue life in water but a higher rotational speed led to a shorter fatigue life in air.