Influence of strain rate on deformation properties of TiNi shape memory alloy

Abstract

Tensile tests with loading and unloading under various strain rates ε̇ were performed for TiNi shape memory alloy wires at various constant temperatures. The influence of strain rate on the stress-strain-temperature relationship was investigated. The main results are summarized as follows. (1) For ε̇ <10%/min, the martensitic transformation stress and its reverse transformation stress did not depend on ε̇. These stresses were almost constant in the transformation regions. (2) For ε̇ ≧10%/ min, the martensitic transformation stress increased and its reverse transformation stress decreased with an increase in ε̇. These stresses fluctuated in the transformation regions. (3) The influence of ε̇ on the transformation stress due to R-phase transformation was slight. (4) The recoverable strain energy density depended slightly on ε̇ but increased significantly in proportion to temperature. The dissipated strain energy density depended slightly on temperature but increased in proportion to ε̇ for ε̇ ≧1%/ min. (5) The influence of ε̇ on deformation properties is important in the evaluation of mechanical properties of shape memory alloy elements.