Nonlinear Dyn (2007) 47:83–104 DOI 10.1007/s11071-006-9060-x ORIGINAL ARTICLE Influence of excitation amplitude on the characteristics of nonlinear butyl rubber isolators K. Shaska · R. A. Ibrahim · R. F. Gibson Received: 31 March 2005 / Accepted: 24 October 2005 / Published online: 8 November 2006 C  Springer Science + Business Media B.V. 2006 Abstract The purpose of this study is to explore the ad- vantages 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. Nonlin- ear characteristics in shear deformation are reflected in mechanical properties such as stiffness and damp- ing. Furthermore, even when the excitation amplitude is small the response amplitude may often be large enough that nonlinearities cannot be ignored. The treat- ment involves developing phenomenological models of the effective storage modulus and effective loss fac- tor of a rubber isolator material as a function of ex- citation 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 mea- sure the normalized transmissibility. It is found that as the excitation amplitude of the nonlinear viscoelas- tic isolator increases, the response amplitude decreases K. Shaska Visteon Corporation, 45000 Helm Street, Plymouth, MI 48170 R. A. Ibrahim () · R. F. Gibson Department of Mechanical Engineering, Wayne State University, Detroit, MI 48202 e-mail: ibrahim@eng.wayne.edu and the transmissibility is improved over that of the linear isolator for excitation frequency that exceeds a particular value governed by the temperature and ex- citation amplitude. The method of multiple scales and numerical simulations are used to predict the response characteristics of the isolator based on the phenomeno- logical modeling under different values of system parameters. Keywords Nonlinear rubber isolator . Phenomenological modeling . Storage modulus . Loss factor . Transmissibility 1. Introduction Viscoelastic materials such as rubber are widely uti- lized in vibration damping mounts. Examples of vibra- tion damping mounts in the automobile industry are engine, front end cooling system, and body-frame rub- ber mounts. It is well known that the shear modulus and loss factor of rubber materials depend on frequency as well as temperature [1–4]. At the so-called rubber-to- glass transition, the loss factor passes through a max- imum value that lies approximately in the frequency or temperature range through which the shear modu- lus changes rapidly. The frequency at which the shear modulus increases rapidly as the excitation frequency increases is called the transition frequency. On the other hand, the temperature at which the shear mod- ulus decreases rapidly as the temperature increases is Springer