Experimental study on temperature evolution and strain rate effect on phase transformation of TiNi shape memory alloy under shock loading

Abstract

Thermo-mechanical coupling is the intrinsic property of the phase transition in TiNi alloy. In this paper, we study the temperature evolution and the strain rate effect in pseudoelastic and the shape memory TiNi alloy under shock loading conditions. Synchronized measurements of temperature evolution and the associated with the macro stress–strain cure in the strain rate range of 500–1500/s. It was shown that, temperature evolution is consistent with phase transformation deformation, and the main difference of temperature evolution between pseudoelastic and shape memory behavior is reflected in unloading process. The corresponding mechanical behavior mainly is mainly manifested in the strain rate hardening and strain hardening characteristic for pseudoelastic and shape memory behavior, respectively. In the stress-temperature space, the strain rate dependence of the transformation path is due to the coupling between the local uniform released/absorbed heat and the temperature dependence of the transformation stress. A simple one-dimensional theoretical model is proposed to explain this effect of thermal-mechanical coupling on the measured temperature evolution. Analytical relationship between the temperature evolution rate, externally applied strain rate and thermal-mechanical coupling properties of the materials is established. It was found that the effect of the dissipated energy on the temperature evolution can not be ignored. Moreover, it is further revealed that the mechanism of macro strain rate hardening and strain hardening of materials lies in the temperature. The results of this investigation provide insight into intriguing strain rate-dependent phenomena intrinsic of TiNi alloys and elucidate complex phase transformations due to thermal and strain rate effects.