A 3D-printed quasi-zero-stiffness isolator for low-frequency vibration isolation: modelling and experiments

Quasi-zero-stiffness (QZS) isolators have shown great promise for low-frequency vibration isolation, thus outperforming conventional linear isolators. However, the hardening behavior typically exhibited in QZS isolators can deteriorate the isolation performance at high excitation amplitudes. To tackle this problem, utilizations of inherent material damping in soft resin offer a feasible way to counteract the hardening effect. This paper proposes a continuous QZS isolator, which can be readily fabricated by three-dimensional (3D) printing using soft resin. QZS properties are achieved by combining the snap-through behavior of inclined beams and the support of folded beams, acting as negative-stiffness (NS) and positive-stiffness (PS) elements, respectively. Analytical methods are developed for predicting the stiffness of the NS and PS elements of the design, whose efficacy is demonstrated numerically and experimentally through examining the static behavior. To evaluate the vibration isolation performance of the QZS isolator, a nonlinear single-degree-of-freedom (SDOF) model is proposed. The model incorporates cubic nonlinear damping in addition to classical viscous damping. The harmonic balance method (HBM) and the Runge-Kutta algorithm are employed to solve the equation of motion and to predict the velocity transmissibility. Parametric analyses are conducted to assess the effect of the excitation amplitude on isolation performance. The results show that an increased excitation level entails a down-shifting of the peak frequency in the transmissibility curve and that of the starting frequency of the effective isolation zone, resulting in enhanced isolation performance at large amplitudes. Numerical findings are further supported by dynamic experiments with varying excitation levels, demonstrating the validity of the proposed numerical model.