Temperature variation of a NiTi wire considering the effects of test machine grips

Abstract

Recent experiments showed that the specimen temperature variations caused by latent heat release/absorption place an important role on the mechanical responses of NiTi SMAs like the propagation stress and the damping capacity due to the dependence of phase transformation stress on temperature. This paper studies the temperature variation of a NiTi wire considering the effects of the test machine grips. In addition to the heat convection with the ambient condition, the existence of strong heat exchange between the specimen ends and the test machine grips highly affects the temperature evolution. To investigate this effect on temperature variation, a simplified model is proposed and the closed-form solution of the axial temperature variation is obtained. The validity of the model is verified by two common cases. In the case of sufficiently long specimen, it reduces to the Dirichlet boundary condition. In the case of relatively short specimen, the temperature variation obtained in this model is similar to that under the Neumann boundary condition usually used in the previous work. The results presented in this paper that have clear physical interpretations can give useful advice in the design and simulation of SMA devices in practice.