On Dynamic Properties of Rubber Isolators

This work aims at enhancing the understanding and to provide improved models of the dynamic behavior of rubber vibration isolators which are widely used in mechanical systems. Initially, a time domain model relating compressions to component forces accounting for preload effects, frequency and dynamic amplitude dependence is presented. The problem of simultaneously modelling the elastic, viscoelastic and friction forces are removed by additively splitting them, where the elastic force response is modelled either by a fully linear or a nonlinear shape factor based approach, displaying results that agree with those of a neo-Hookean hyperelastic isolator under a long term precompression. The viscoelastic force is modelled by a fractional derivative element, while the friction force governs from a generalized friction element displaying a smoothed Coulomb force. This is a versatile one-dimensional component model effectively using a small number of parameters while exhibiting a good resemblance to measured isolator characteristics. Additionally, the nonlinear excitation effects on dynamic stiffness and damping of a filled rubber isolator are investigated through measurements. It is shown that the well-known Payne effect ? where stiffness is high for small excitation amplitudes and low for large amplitudes while damping displays a maximum at intermediate amplitudes ? evaluated at a certain frequency, is to a large extent influenced by the existence of additional frequency components in the signal. Finally, a frequency, temperature and preload dependent dynamic stiffness model is presented covering the ranges from 20 to 20 000 Hz, ?50 to +50 ?C at 0 to 20 % precompression. A nearly incompressible, thermo -rheologically simple material model is adopted displaying viscoelasticity through a time ? strain separable relaxation tensor with a single Mittag? Leffler function embodying its time dependence. This fractional derivative based function successfully fits material properties throughout the whole audible frequency range. An extended neo-Hookean strain energy function, being directly proportional to the temperature and density, is applied for the finite deformation response with component properties solved by a nonlinear finite element procedure. The presented work is thus believed to enlighten working conditions’ impact on the dynamic properties of rubber vibration isolators, while additionally taking some of these most important features into account in the presented models.