Seahorse-exoskeleton-inspired structure with linear-to-torsion transition property for low-frequency vibration isolation.

The square exoskeleton of seahorses can transit linear motion into torsion to dissipate energy and protect the vertebrate when subjected to external disturbances. Inspired by the self-protection mechanism of the linear-to-torsion transition of the square exoskeleton of seahorses, a novel seahorse-exoskeleton-inspired structure (SES) is designed, which consists of two oblique rods and springs, and a rotational disc. The geometric relationship and dynamic model are established to reveal the corresponding nonlinear stiffness, adjustable high carrying capacity and large working range characteristics. The dynamic equation of the SES is derived according to the Lagrange equation and the frequency response relationship is obtained with the harmonic balance method. Then the effects of structural parameters on the nonlinear restoring force, nonlinear inertia, nonlinear quadratic force, nonlinear damping and the vibration isolation performance are studied comprehensively to achieve the low-frequency isolation characteristics. A SES prototype was manufactured and the corresponding experiment was carried out to verify the low-frequency vibration isolation performance of SES. The tested peak frequency of the unloaded SES can be lower to 1.48 Hz due to the linear-to-torsion property, which can generate torsional inertia and anti-resonance phenomenon. Furthermore, the nonlinear damping is positively correlated with input displacement. SES has a better vibration isolation performance under large excitation amplitude. This paper provides a guideline for the design of low-frequency bio-inspired vibration isolators with the linear-to-torsion transition mechanism.