Impact of strain rate on thermomechanical coupling effects in TiNi SMA subjected to compression

Abstract

In this study, the thermomechanical coupling effects accompanying stress-induced martensitic transformation in TiNi shape memory alloy subjected to compression test were investigated. The mechanical characteristics were elaborated and the temperature changes related to the exothermic martensitic forward transformation and the endothermic reverse one were measured in a contactless manner by a fast and sensitive infrared camera. The obtained temperature changes of the specimen depend on the strain rate applied. At higher strain rate, greater temperature changes were observed, because the heat flow to the surroundings was lower and the process was closer to adiabatic conditions. The temperature changes of the shape memory alloy significantly influence its stress-strain characteristics. Moreover, the energy dissipated during a compression cycle was calculated for various strain rates. The study revealed that both the loading work and recoverable strain energy increase with increasing strain rate, while the dissipated energy fraction decreases. © 2012 The Japan Institute of Metals.