Nonlinear vibration isolation via a compliant mechanism and wire ropes

Nonlinear vibration isolation systems with both stiffness and damping nonlinearities are promising for a broad-band and high-efficient isolation performance. In this research, a novel nonlinear isolator is proposed via a compliant mechanism with negative stiffness and wire ropes with hysteretic damping. The compliant mechanism consists of two pairs of tilted flexure beams, and the nonlinear restoring force is modelled based on a beam constraint model. The hysteretic restoring force of the wire ropes is characterized by a Bouc–Wen model. A dynamic model of the nonlinear isolator is established, and a semi-analytical method is adopted to analyze the model. Generalized equivalent stiffness and a generalized equivalent damping ratio are defined, respectively, for dynamic systems with multiple nonlinearities. The compliant mechanism exhibits negative stiffness in a limited stroke and endows the isolator with a lower resonant frequency and a smaller resonant amplitude. The complaint mechanism with a symmetric restoring force is more preferred for a broader band of vibration isolation and fewer harmonics in the responses. The wire ropes improve the high-frequency isolation efficiency at the cost of a higher resonant frequency. The incorporation of the compliant mechanism and the wire ropes is beneficial for vibration isolation. Furthermore, the influences of the dimensions of the complaint mechanism on the negative-stiffness stroke, load capacity and vibration isolation performances of the nonlinear isolator are revealed.