Abstract
Nickel–titanium shape memory alloys (NiTi SMA) working in superelastic regime have been applied in several fields, such as health (medicine and dentistry) and engineering, in a static or dynamic way. The aim of this paper is to study the behavior of these smart metals when subjected to dynamic mechanical stresses (fatigue). Cyclic stress-controlled tensile tests were performed to evaluate the functional and structural superelastic fatigue properties of NiTi SMA wires. The functional parameters were defined as energy dissipation, transformation stresses, residual strain, and superelastic strain, for peak stresses between 500 and 800 MPa, at frequencies of 1, 2, and 3 Hz. These frequencies were determined after a preliminary evaluation of self-heating of the NiTi wires. The number of cycles until failure (Nf) was plotted as a function of peak stresses (S) in an S–Nf fatigue curve, for each studied frequency. It was verified that both frequency and peak stress affected the functional behavior of the NiTi wires. However, the fatigue life was between 5.0 × 103 and 1.6 × 104 cycles, with a faster degradation in this range as higher is the applied peak stress, irrespective of the loading frequency.
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