A one-dimensional strain-rate-dependent constitutive model for superelastic shape memory alloys

Recently, there is increasing interest in using superelastic shape memory alloys (SMAs) in civil, mechanical and aerospace engineering, attributed to their large recoverable strain range (up to 6-8%), high damping capacity, and excellent fatigue property. In this research, an improved Graesser's model is proposed to model the strain-rate-dependent hysteretic behavior of superelastic SMA wires. Cyclic loading tests of superelastic SMA wires are first performed to determine their hysteresis properties. The effects of the strain amplitude and the loading rate on the mechanical properties are studied and formulated using the least-square method. Based on Graesser's model, an improved model is developed. The improved model divides the full loop into three parts: the loading branch, the unloading branch before the completion of the reverse transformation and the elastic unloading branch after the completion of reverse transformation, where each part adopts its respective parameters. Numerical simulations are conducted using both the original and the improved Graesser's models. Comparisons indicate that the improved Graesser's model accurately reflects the hysteresis characteristics and provides a better prediction of the SMAs' actual hysteresis behavior than the original Graesser's model at varying levels of strain and loading rate.