Self-centering and damping devices using SMA dual rings

Cyclic tests have been conducted on five shape memory alloy (SMA) rings, i.e. single superelastic ring (SE), single martensitic SMA ring (MA), two superelastic SMA rings (SE-SE), two martensitic SMA rings (MA-MA), and martensitic-superelastic SMA rings (MA-SE). Experimental results show that while the single SMA ring systems in this study showed better symmetrical behaviors than those in a previous study, the dual ring systems show perfectly symmetrical behaviors. The use of martensitic SMA could increase the damping ratios of the ring systems while the use of superelastic SMA could enhance the self-centering capacity. In addition to experimental studies, a numerical model of the superelastic SMA ring systems was also developed using ANSYS software. The verification of experimental results showed that the analytical results are acceptable. Furthermore, to examine the effect of SMA ring thickness on the symmetrical behavior of the single SMA systems, a thickness ratio and a hardening stiffness ratio (HSR) are introduced. The thickness ratio is the ratio between the thickness and outer diameter of the rings, while the HSR is the ratio between the stiffnesses in hardening phase of the ring in pulling action and that in pushing action. The analysis results obtained through ANSYS demonstrate that an increase in the thickness ratio leads to a decrease in the stiffness ratio. Therefore, the ring could behave symmetrically when the thickness of the ring reaches a critical value. However, due to the p-delta effect when large displacement is applied, unsymmetrical behavior still occurs. Thus, to ensure symmetrical behavior, it is recommended to use dual SMA ring systems or 2 rings in symmetrical structures.