A bidirectional-controllable magnetorheological elastomer-based quasi-zero-stiffness isolator

To enhance the low-frequency vibration isolation bandwidth of quasi-zero stiffness (QZS) isolators under variable amplitude excitations, this paper proposes an adaptive bidirectional-controllable QZS isolator (Bi-QZS) based on magnetic-controlled smart material named magnetorheological elastomer (MRE) as positive element and tilting spring as negative element. Firstly, the positive element of isolator is composed of laminated MRE and permanent magnet to realize bidirectional stiffness adjustment. Then the magnetic circuit of vibration isolator is designed and the specific parameters are obtained by taking the magnetic field and energy consumption as the optimization objectives. Secondly, a static theoretical model is established to calculate the achievable range of stiffness variation, and match the parameters of the negative element. Static analysis shows that bidirectional stiffness control is beneficial to achieve stiffness matching. Additionally, the adjustment of bidirectional stiffness variation on the dynamic response of the system is deduced by harmonic balance method. Numerical simulation results indicate that adjusting stiffness in reverse can increase the vibration isolation bandwidth when the excitation amplitude increases, and adjusting in forward can reduce the peak value of jump region. Also, increasing the damping ratio under reverse conditions has a certain contribution to reducing the response peak. Finally, static and dynamic tests are carried out, results reveal a bidirectional stiffness adjustment capability, with a 36.4% adjustment in reverse stiffness and a 70% adjustment in forward stiffness. The resonance frequency can be reduced from 14.4 Hz to 5.8 Hz by stiffness bidirectional-controllable.