Abstract：Based on the anti-resonance characteristics of multi-degree-of-freedom systems, negative-stiffness structures containing nonlinear inclined springs are introduced into both the upper and lower layers of a traditional linear vibration isolation system to form a two-degree-of-freedom quasi-zero-stiffness vibration isolator. First, through the analysis of static characteristics, a set of relations between the parameters of a quasi-zero-stiffness isolation system is derived. The influences of mechanical and structural parameters on stiffness characteristics of the system are studied. Then, the nonlinear dynamic equations of the two-degree-of-freedom vibration isolation system with quasi-zero stiffness are established. Using the averaging method, the frequency-domain analytical solutions and the expression of force transmissibility are derived. The effects of upper damping ratio, lower damping ratio, vertical stiffness ratio and mass ratio on force transmissibility are numerically discussed. The vibration isolation performance of the two-degree-of-freedom quasi-zero-stiffness vibration isolation system with nonlinear inclined springs is compared with that of the single-degree-of-freedom quasi-zero-stiffness vibration isolation system. The results indicate that the smaller the structural parameter (i.e. the ratio of length when the nonlinear inclined springs are at static equilibrium and initial positions) is, or the softer the nonlinear inclined springs are, the smaller stiffness of the system and the larger low-stiffness interval near the equilibrium position can be obtained. Furthermore, by selecting suitable values of the upper damping ratio, lower damping ratio, vertical stiffness ratio and mass ratio, the initial vibration isolation frequency of the system can be reduced, the vibration isolation band width can be further expanded, the attenuation rate of the force transmissibility in a certain frequency region can be obviously accelerated, and the low-frequency vibration isolation performance of the system can be dramatically improved.
2021, Vol. 42 
