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

摘要

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 t_p and stress Δσ.