J. Vinolas

Torsion stiffness of a rubber bushing : a simple engineering design formula including amplitude dependence

An engineering design formula for the torsion stiffness of a filled rubber bushing in the frequency domain, including the amplitude dependence, is presented. It is developed by applying a novel separable elastic, viscoelastic, and friction material model to an equivalent strain of the strain state inside the bushing, thus leading to an equivalent shear modulus that is inserted into an analytical formula for the torsion stiffness. The rubber model is the result of extending the force-displacement relation established in a sound rubber component model to the stress-strain level. Unlike other simplified methods, this procedure takes into account the variation in the properties inside the bushing owing to non-homogeneous strain states. Moreover, as this formula depends on the bushing geometry in addition to the material properties, it is a fast engineering tool to design the most suitable rubber bushing to fulfil user requirements. Furthermore, it is shown - by dividing the considered bushing into several slices, consequently each equivalent shear modulus is closer to the true value - that the approach of working with only one equivalent shear modulus for the whole bushing is accurate enough.

Viscoelastic models for rubber mounts: influence on the dynamic behaviour of an elastomeric isolated system

The influence of the viscoelastic model employed to represent the stiffness of rubber mounts on the dynamic response of an elastomeric isolated system is investigated. A steel block supported on four rubber mounts is analysed. Each mount is characterised by its axial stiffness and two shear stiffness. Three viscoelastic models are proposed to fit the experimental stiffness of the mounts over a frequency range from 0 Hz to 50 Hz, defined by two, three and five parameters respectively. Simulations in IDEAS® are compared to dynamic measurements performed on the supporting system, showing that the Generalised-2 Maxwell model provides the best agreement.