An experimental study of specimen size and type effects on cyclic behavior of superelastic NiTi

Abstract The remarkable ability of shape memory alloys (SMAs) to dissipate energy during cyclic loading, combined with their outstanding superelasticity, make them a highly suitable material for passive vibration control systems. Both experimental observations and theoretical insights in previous studies showed that the mechanical behavior of SMA could be influenced by the size and type of specimens. Despite its importance, studies dedicated to evaluating the effect of specimen size and type on the cyclic behavior of SMA are scarce. This paper addresses the gap by experimentally evaluating the mechanical behavior of SMA specimens of different sizes and types under various cyclic loading conditions. The specimens include single-strand wires with a 0.5 mm and 1.2 mm diameter, and a 1.2 mm diameter multi-strand rope. The evolution of the hysteresis loop, energy dissipation, residual strain, and effective modulus of these specimens are investigated systematically. The results indicate that as loading frequency gradually increases, the cyclic behavior of different size SMA wires consistently exhibit four distinct patterns. The frequency thresholds that distinguish these patterns decrease as wire diameter increases. The mechanical behavior of a SMA rope appears to be influenced by both the size of the constituent strand and the overall diameter of the rope. It was found that while the behavior of a rope closely resembles that of a single-strand wire of the same component size in the low frequency range, as loading frequency increases, it quickly transitions to a behavior more similar to that of a single-strand wire having the same diameter as the rope.