Determination of the Mechanical Properties of Shape Memory Alloys

Abstract

Shape memory alloys are materials which can be deformed by cooling below a certain critical temperature and then regain their original shape after heating above this critical transition temperature.. Shape memory alloys (SMAs) are a class of functional materials that possess unique thermo mechanical properties, such as shape memory effect (SME), super elasticity (SE), damping, and good fatigue and corrosion resistance, which enable them to become ideal materials for applications in earthquake engineering. Numerous studies have shown that the mechanical properties of Superelastic SMAs mainly depend on the wire form or the relationship between the microstructure and thermally induced phase transitions. However, extremely few studies have elucidated the effects of the heat-treatment strategy, size effect of large diameters, and cyclic loading. Here in, the mechanical properties of SMA bars, such as residual strain, energy dissipation, and equivalent damping ratio, were studied with different heat-treatment strategies, cyclic loadings, and strain amplitudes; this was achieved by conducting cyclic tensile tests on SMA bars with four different diameters. In this research work, two types of methods i.e. tensile testing and cantilever deflection method is used to determine the mechanical properties of NiTi alloy. In the first part of the experiment, mechanical properties of two NiTi samples of different composition are determined by tensile test. Both of the wire-shaped samples have the same diameter of 300µm but differ in the transformation temperature Cantilever deflection method (CDM) is used to characterize the shape memory alloy film deposited on the Mo substrate. The sample is placed on the holder which lies close to the thermoelement.