Experimental Investigations of Mechanical Behavior of Superelastic NiTi Shape Memory Alloy (SMA) Wires

摘要

This study evaluates the mechanical behaviors of super-elastic shape memory alloys (SMAs) for civil engineering applications. Superelastic Ni-Ti SMA wires, which include the uncycled and the pre-cycled wires, are tested to investigate the effects of temperature, strain rate and strain amplitude on its mechanical behaviors such as the phase transformation stresses, the secant stiffness, the dissipated energy and the loss factor. The experimental results as follow: (1) The pre-cycled training reduce the forward transformation starting stress and the dissipated energy, but almost no effect on the secant stiffness. (2) After the pre-cycled training, the pre-cycled wire's dissipated energy decreases greater with temperature increasing than the uncycled wire's. Temperature's effect on the secant stiffness depends on the strain amplitude. (3) The inverse transformation starting stress increase obviously with strain rate. Above 0.5 mm/s, the dissipated energy decreases and the decreasing degree of the pre-cycled wires' is less than of the uncycled wires'. But after strain rate increasing above 3 mm/s, both the dissipated energy and the loss factor reduce slightly. (4) Increased strain amplitudes lead to linear increase in both the dissipated energy and the loss factor. In the scope of the maximum phase transformation strain, the secant stiffness decreases with strain amplitude increasing.