Strain self-sensing property and strain rate dependent constitutive model of austenitic shape memory alloy: Experiment and theory

By using both the pseudoelasticity and strain self-sensing ability of shape memory alloy (SMA) material, an innovative smart SMA-based damper can be developed. This damper has comprehensive energy dissipation and strain self-sensing abilities (i.e., electric resistance versus applied strain relationship) simultaneously. Before shaking table test on a building installed with such SMA-based dampers, the tests were conducted on the hysteresis stress-strain-electric resistance relationship of SMA wires (diameter 1.2 mm). These tests were carried out under sinusoidal excitations with different loading frequencies at different ambient temperatures, to investigate the energy dissipation ability and strain self-sensing property of SMA wires. The sensitivity coefficient of electric resistance versus applied strain of the SMA wires was identified to be 5.948 from the test results, which is larger than that of the conventional strain gage and is independent of loading frequency. The experimental results indicate that the pseudoelastic hysteresis loops of the SMA wires are dependent on loading frequencies, particularly in the case of lower frequency. Further tests aimed at revealing the mechanism of the strain rate dependence of pseudoelasticity of SMA wire were conducted. The results indicate that the phase transformation temperature is dependent on strain rate, i.e., both the martensitic phase transformation finish temperature and the austenitic phase transformation start temperature decrease with increasing of strain rate. Based on the results of these tests, a one-dimensional strain rate dependent constitutive model of SMA wires was developed. This model predicts pseudoelastic behavior of SMA under various loading frequencies. Finally, a numerical simulation using the proposed model was performed, and the simulated pseudoelastic hysteresis loops agree well with test results presented not only by writers but also by other researchers.