A quasi-zero stiffness isolator based on the second-order antisymmetric buckling mode of beams

Compared with conventional linear isolators, quasi-zero stiffness (QZS) isolators offer superior load-bearing capacity and low-frequency vibration isolation performance. This study proposes a QZS isolator based on a continuous structure, in which negative stiffness is achieved through the second-order antisymmetric buckling behavior of inclined beams in an X-shaped structure, while a folded beam serves as the positive stiffness component to realize QZS characteristics. The static behavior of the proposed QZS isolator, formed by combining the negative and positive stiffness components, is thoroughly investigated via numerical simulations and experimental tests. Particular attention is given to the influence of the geometric parameters of the X-shaped structure. A nonlinear single-degree-of-freedom (SDOF) model incorporating quadratic and cubic stiffness terms is established, and the harmonic balance method (HBM) is employed to calculate the transmissibility and assess the isolation performance. Results demonstrate that the QZS isolator can effectively reduce both the resonance frequency and the onset frequency of isolation. Nonlinear phenomena such as stiffness softening and harmonic resonance are also examined, revealing that increased excitation amplitude and reduced damping ratio intensify the system’s nonlinearity.