Analytical and experimental investigation on a NiTiNOL circular ring-type vibration isolator with both stiffness and damping nonlinearities

Vibration isolators with both stiffness and damping nonlinearities are expected to exhibit the advantages of broad-band and high-efficiency vibration isolation. A NiTiNOL circular ring is used to implement a novel type of high-static-low-dynamic-stiffness vibration isolator with nonlinear damping. The nonlinear restoring and damping force of the NiTiNOL circular ring is fitted by a restoring force surface method, and the dynamic equation of the isolator under a harmonic base excitation is established. A harmonic balance method is applied to determine the steady-state responses and the displacement transmissibility. The analytical outcomes are numerically confirmed by the direct integration of the dynamic equation. The restoring and damping force measurement experiment and the vibration isolation experiment on both the NiTiNOL and the spring steel circular ring-type isolators are performed, and the experimental results validate the analytical results. For the NiTiNOL circular ring with an obvious material nonlinearity, the restoring force surface model achieves higher accuracy than the elliptical integral method with a linear damping assumption. The errors in predicting the restoring and damping force and the displacement transmissibility are below 0.89% and 1.78%, respectively. Compared with the spring steel circular ring with the same dimensions and preload, the NiTiNOL circular ring-type isolator exhibits a stronger high-static-low-dynamic-stiffness characteristic, together with a larger damping ratio due to the energy consumption of the phase transition. Thus, the NiTiNOL circular ring-type isolator demonstrates a better vibration isolation performance with a broader frequency band and a higher dissipation efficiency.