Abstract
Shape memory alloys (SMAs) have unique properties of shape memory effect and superelasticity. These properties are based on the phase transformation between the martensite phases and the austenite phase. When a large load acts on the SMA, it deforms plastically and the above properties come not to appear fully due to accumulating dislocation, mismatches of grain boundaries, etc. To heal the properties and bring them back into the original ones, a heat treatment is applied after the plastic deformation. To verify the healing effect, a cycle composed of a tensile test and the heat treatment is repeated and stress-strain curves are obtained. The result shows that the shape of stress-strain curve to the strain at which the phase transformation to the stress-induced martensite phase finishes is restored after the heat treatment, but tangential stiffness of the stress-induced martensite phase increases with increase in cycle number.
