The Effect of Strain Rate on Detwinning and Superelastic Behavior of Ni Ti Shape Memory Alloys

Abstract

The effect of strain rate on the superelastic and detwinning behavior of shape memory alloys was studied in a series of experiments. The strain rate was tested in a range from 10-4 to 10-2/s. To ensure a stable and uniform temperature throughout the testing process, fine wire samples were used, and all tests were conducted in a liquid environment. Under these conditions, test results showed that the strain rate had no influence on the superelastic behavior and martensite detwinning of the Ni Ti alloys. In the superelastic deformation process, the austenite martensite transformation produced rather high latent heat as part of the transformation process within the specimen. As the strain rate increased, and as conditions became more adiabatic, a significant temperature change due to the release and absorption of latent heat occurred. The temperature rises upon loading and drops upon unloading. This phenomenon manifests itself, as the diameter of the specimens becomes progressively larger, or as test conditions become more adiabatic.