Limb-inspired quasi-zero stiffness structure for ultralow-frequency vibration attenuation

A bio-inspired limb-like vibration isolation structure is systematically studied by emulating the hexagonal skeletal configuration of animal legs under external loads and impact, which demonstrates a wide range of quasi-zero stiffness (QZS) characteristics. The dynamic model of the limb-like structure is established using Lagrange's equations to analyze the dynamical responses with QZS characteristics. The transmissibility of the system subject to periodic excitations is obtained by the Harmonic Balance Method and verified using the numerical integration method. In addition to the typical QZS, a unique configuration allows for a zero-stiffness feature throughout the entire stroke, enabling almost full-band frequency vibration isolation as the experimentally verified. Comparative analyses with a conventional QZS isolator prove the superior performance of the proposed structure, particularly in achieving full-band vibration isolation under zero-stiffness conditions. Furthermore, a novel QZS metamaterial, consisting of limb-like units, is modeled as a lumped-mass-spring chain. The linear and nonlinear analyses of the QZS metamaterial reveal that the QZS attribute lowers the cut-off frequency of the band structure. The diatomic QZS model generates a band gap in the ultralow frequency range attributed to the QZS and inertial amplification. Notably, this band gap can be tuned in real-time through pre-pressure adjustments, offering adaptability to variable engineering requirements.