Q. Sun, Y. He, Hong Kong University of Science and Technology, Hong Kong, China
Recent experiments showed that the pseudoelastic hysteresis of shape memory alloys (SMA) varied non-monotonically with the external driving rate, i.e., the maximum hysteresis occurs at an intermediate strain rate. A simple thermo-mechanical coupling model is developed in this paper to explain the observed rate-dependency, incorporating the effects of the released/absorbed heat during phase transition and the associated heat transfer on the pseudoelastic hysteresis. An analytical expression for the rate-dependent hysteresis is derived. The theoretical calculations agree quantitatively well with the experimental data.
Summary: We present our recent modelling and experiment on the role of loading time or strain rate in the stress hysteresis in tensile loading of superelastic NiTi SMA strip. The strong effects of loading time or strain rate on the stress hysteresis will be modelled and analyzed. It is shown that the coupling between the material’s mechanical phase transition process and transfer of heat is the key underlying mechanism for the observed rate-dependent hysteresis. The model prediction agrees well with the available experimental hysteresis data. The important roles of heat transfer time and loading time in governing the observed rate-dependent phenomenon is demonstrated.
