Thermomechanical coupling in cyclic phase transition of shape memory material under periodic stressing—experiment and modeling

Abstract

Experiment and modeling analysis are performed to study the evolution dynamics due to thermomechanical coupling in cyclic phase transformation responses of a superelastic NiTi shape memory alloy rod under periodic tensile stress. Synchronized acquisition of time evolutions in temperature and stress-strain curve of the rod were realized in the frequency range of 0.0004 ~ 4 Hz (average stress rate from 0.42 MPa/s to 4200 MPa/s). Significant frequency dependent oscillations, drifts and stabilizations in the strain, temperature and stress-strain curves are quantified and the roles of thermomechanical coupling in the observed evolution dynamics of the responses are revealed. It is found that the stress-strain responses are non-isothermal over the tested frequency range and that the evolution dynamics is quite distinct from that of displacement-controlled cyclic phase transition (Yin et al., JMPS, 2014) due to the non-prescribed heat sources and the implicit nature of the response. The evolution dynamics are modelled by two coupled non-linear governing equations to obtain numerical and approximate analytical expressions of the transient and steady-state stress-strain and temperature oscillations. It is shown that, for given material and ambient properties, the thermomechanical responses under cyclic-stressing can be divided into three regions and are essentially governed by the non-dimensional time scale tp¯ and stress Δσ¯.