Quasi-zero-stiffness vibration isolation via a double-layer compliant mechanism

Compliant mechanisms exhibit nonlinear restoring forces due to large deformations, and can be used in quasi-zero-stiffness (QZS) vibration isolators for broadband vibration isolations. The nonlinear stiffness of compliant mechanisms at buckling states is sensitive to the boundary conditions. Motivated by the parameter sensitivity, a novel double-layer compliant vibration isolator is proposed. Unlike traditional double/multi-layer isolators with a series arrangement of elastic components, the proposed isolator is with a perpendicular arrangement of two layers, and the cross layer provides nonlinear elastic boundary conditions for the vertical layer. Large-stroke QZS is achieved with an elaborate design of the compliant mechanisms, and subharmonic resonances are exhibited on some conditions. For a comprehensive investigation of the proposed isolator, a beam constraint model is adopted to characterize the deformations and the coupling of the two compliant layers. A harmonic balance method including half-order harmonics is developed to obtain the frequency responses. Both numerical simulations and experiments are performed to validate the theoretical results. The double-layer compliant vibration isolator exhibits stiffness-softening and QZS under compression, and the QZS region reaches 74.29 % of the effective stroke. The isolator achieves broadband isolations for different payload mass with the resonant frequencies lower than 3 Hz. The isolator demonstrates various nonlinear phenomena, including resonance shift, jump phenomena, asymmetric responses, and subharmonic resonances. The subharmonic resonance tends to occur under a light payload and a large excitation, where the corresponding restoring force is highly asymmetric about the equilibrium point.