Unidirectional behavior of superelastic SMA rings incorporated with steel rings and their strain analysis

This study investigated the cyclic behavior of hybrid rings used as smart dampers composed of superelastic shape memory alloy (SMA) and steel rings. The aim of the SMA ring was to provide recentering capacity, while the steel ring was intended to enhance energy dissipation through interaction with the SMA ring. To this end, hybrid rings with various configurations were examined, considering the location of the steel ring (inner, outer, and combined inner–outer), different diametric differences, and varying steel-ring thicknesses. The experimental data from cyclic loading tests were compared with those of a pure SMA ring to evaluate the influence of these parameters. The results indicated that the pure SMA ring exhibited excellent self-centering with stable flag-shaped behavior, whereas hybrid rings showed similar responses during loading but significantly different behaviors during unloading. The influence of steel-ring location was minor when the total thickness was the same, whereas thickness governed energy dissipation and reduction in recentering capacity. Increasing diametric difference intensified interface interaction, leading to a damping-dominant response and loss of self-centering. The influence of steel rings on the loading path was minimal, whereas their effect on the unloading path was dominant due to interface interaction. Relative displacement between the SMA and steel rings during unloading induced frictional forces and additional resistance, which inhibited recovery of the SMA ring. Furthermore, finite element (FE) analysis was conducted to support the experimental observations and to provide insight into the interaction mechanisms. The findings suggest that interface behavior governed by diametric difference and contact conditions plays a critical role in balancing recentering capacity and energy dissipation.