Effects of stiffness and load imperfection on the isolation performance of a high-static-low-dynamic-stiffness non-linear isolator under base displacement excitation

The dynamic characteristics of a high-static-low-dynamic-stiffness (HSLDS) non-linear isolator, built by combining an Euler beams formed negative stiffness corrector and a traditional linear isolator are investigated. The system imperfection caused by detuning of the stiffness and the load are considered. The frequency response curves (FRCs) for the non-linear isolator with load and stiffness imperfection under base displacement excitation are calculated by using Harmonic Balance Method (HBM). The stability is studied by the Floquet theory. The effect of the imperfection on the dynamic response as well as the displacement transmissibility of the non-linear isolator is explored and discussed. The results show that both the stiffness and load imperfection can affect the performance of the non-linear isolator significantly. The HSLDS isolator with load and stiffness imperfection for different base excitation amplitudes can demonstrate pure softening, softening-to-hardening and pure hardening characteristics with multi-valued solutions. The occurrence of jump phenomena is observed and explained by the stiffness variation. When the isolator is subjected to load imperfection, keeping a small positive stiffness, rather than making the minimum dynamic stiffness as zero, is preferred in order to obtain the best isolation performance. The performance of the non-linear isolator can outperform the linear one provided that the base displacement excitation is not too large. The non-linear system may undergo unbounded responses for very large base displacement excitation.