The behaviour of Nitinol Wire Bundles for Structural Applications

Abstract

Shape memory alloys (SMA) belong to a family of smart materials, which undergo diffusionless phase transformations when subjected to thermo-mechanical changes making them ideally suitable for utilization in several structural engineering applications. Within this class of materials, Ni-Ti (Nickel-Titanium) alloys are predominantly used due to their non-linear behaviour. Nitinol, one of the Ni-Ti alloys, possesses unique properties such as super-elasticity and shape- memory effect, which makes it suitable for damping vibrations transmitted to structures like buildings and bridges during high wind and seismic events. This paper presents selected results obtained from a series of tests conducted on Nitinol 55 wires and bundles made from wires having diameters of 0.25, 0.5, 0.55, and 1 mm. The tests conducted include microstructure analyses, static tensile tests, hysteresis tests, and cyclic dynamic tests performed on wire bundles of various diameters. It is demonstrated that wires having small diameters (0.25 and 0.5 mm) exhibit greater ultimate strength compared with the ones having a larger diameter (1 mm). The bundles produced from these wires displayed hysteretic behaviour under cyclic-dynamic testing conditions confirming their suitability in structural engineering applications.