Influence of excitation amplitude on the characteristics of nonlinear butyl rubber isolators

Abstract

The purpose of this study is to explore the advantages and characteristics of nonlinear butyl rubber (type IIR) isolators in vibratory shear by comparison with linear isolators. It is known that the mechanical properties of viscoelastic materials exhibit significant frequency and temperature dependence, and in some cases, nonlinear dynamic behavior as well. Nonlinear characteristics in shear deformation are reflected in mechanical properties such as stiffness and damping. Furthermore, even when the excitation amplitude is small the response amplitude may often be large enough that nonlinearities cannot be ignored. The treatment involves developing phenomenological models of the effective storage modulus and effective loss factor of a rubber isolator material as a function of excitation amplitude. The transmissibility of a nonlinear viscoelastic isolator is compared with that of a linear isolator using an equivalent linear damping coefficient. Forced resonance vibration and impedance tests are used to characterize nonlinear parameters and to measure the normalized transmissibility. It is found that as the excitation amplitude of the nonlinear viscoelastic isolator increases, the response amplitude decreases and the transmissibility is improved over that of the linear isolator for excitation frequency that exceeds a particular value governed by the temperature and excitation amplitude. The method of multiple scales and numerical simulations are used to predict the response characteristics of the isolator based on the phenomenological modeling under different values of system parameters.

Multi-Degree-of-Freedom Modeling of Mechanical Snubbing Systems

“…As a result the arithmetic mean of these parameters can be used without a significant loss of accuracy, these values are listed in Table 1. This observation about non-linear parameters of elastomeric isolators has been made in relevant literature as well [5]. The damping constant, however, is seen to reduce with the increasing excitation frequency, and is replaced by the hysteresis damping constant as explained in Section 2.…”

“…In order to simplify the EOM formulated in Eqs. (2), (5) and 7, the reaction forces resulting from the spring elements are used to replace the corresponding terms in the EOM by making the following substitutions: 7, can be re-written using the substitutions from Eq. (11) as:…”

“…This model, however, did not account for non-linear behavior. Shaska et al [5] presented experimental results in order to demonstrate non-linear behavior of isolators made from butyl rubber using excitation amplitude, excitation frequency and ambient temperature as input variables. Ni et al [6] used the general Bouc-Wen element for modeling hysteretic behavior of isolators.…”

Perturbation methods in evolutionary spectral analysis for linear dynamics and equivalent statistical linearization

“…After recasting (63) into a state space formalism, the time evolution of the covariance matrix Σ z is described with a Lyapunov equation by invoking Itô's lemma [47], such that The application of the multiple scales technique [32,43], widely used for decades in mechanics [40,21,57,17], and in random dynamics [53,3], looks perfectly appropriate, since an analysis of the different regimes is mandatory at this step. A convenient way to sort the timescales is to introduce a distinction between the fast timescale t f and the slow timescale t s .…”

Dynamics of a Upright Pole Coupled with Nonlinear Hysteretic Isolators under Harmonic Base Excitation

“…Wang and Zheng [22] studied the coupling vibration of nonlinear isolators and two flexible beams by experimental and analytical methods. Shaska et al [23] explored the advantages and characteristics of nonlinear butyl rubber isolators in vibratory shear by comparison with linear isolators. Nonlinear characteristics in shear deformation, which was dependent on frequency and temperature, were reflected on stiffness and damping.…”