Effect of spring index on the energy absorption capacity of Nitinol springs

Abstract:

Shape memory alloy (SMAs) springs have the ability to perform giant reversible strain, which is of great importance to the energy absorption buffer and vibration control applications. In this paper, the influence of structure design on the performance of NiTi SMAs springs is studied. Ti-52.5at.%Ni alloy wires with diameters of 1.2mm were prepared by cold drawing and subsequent annealing, and springs with spring index C of 6.0, 7.7, and 9.3 were prepared by mandrel wound molding and subsequent high temperature annealing, respectively. The energy absorption performances of the springs were studied by testing the superelastic curves of the alloy wires and springs. The results show that, based on the superelastic processes, the energy absorption capacity per unit volume of the three types of springs at room temperature (298K) is 4618, 2225 and 1143kJ/m3 at a maximum displacement amplitude of 120mm, respectively, where the spring with spring index C of 6.0 has the best energy absorption capacity. Furthermore, the energy absorption per unit volume of spring with spring index C of 6.0 reaches 6662kJ/m3 at 318K due to its full austenite state, which is 192 times higher than that of the alloy wire (34.7kJ/m3) under the same load (47N), meaning that under same condition, the spring structure has better energy absorption capacity than that of the alloy wire. Therefore, superelastic SMAs springs may show great potential in the future application of damping structures.

Key words:Shape memory alloys; spring; superelaticity; energy absorption; Ni-Ti alloys