Dynamic and experimental analyses of QZS system with beneficial quadratic stiffness

A quasi-zero-stiffness (QZS) vibration-isolation system is assumed effective for low-frequency and ultra-low-frequency vibration isolation. However, owing to the existence of cubic stiffness nonlinearity, jump-through phenomenon may occur in a QZS system and affect its vibration isolation performance. In this study, an asymmetric QZS system is investigated to solve this problem by introducing a beneficial quadratic stiffness element. According to theoretical analysis, beneficial quadratic stiffness can suppress the nonlinear hardening characteristics in the primary response. Furthermore, it may lead to an isolated resonance curve and ‘Isola’ characteristics. Both theoretical and numerical results indicate that beneficial quadratic stiffness can weaken the jump-up phenomenon in the secondary resonance. The optimal design criteria for nonlinear stiffness are obtained by analysing the effect of quadratic stiffness on the 1/3 and 1/2 subharmonic resonances. This aids in quantitatively designing a vibration-isolation system. Based on our analyses, a prototype of the asymmetric QZS is manufactured to conduct vibration tests. By comparing the experimental results of the QZS system with and without quadratic stiffness, the effect of beneficial quadratic stiffness on the vibration-isolation performance is verified.