Rubber is excellent at isolating shock and vibrations and reducing noise. Its damping properties make it particularly useful in engine mounts and suspension bushings. However, many factors affect the rubber’s damping characteristics and performance, for example, the heat generated during damping, repeated stretching which reduces stiffness, etc. Fillers in the rubber also influence its damping behavior.
Rubber is viscoelastic and is usually analyzed using quasi-static methods. The usual design goal is to prolong the component’s service life, which ultimately means keeping stress levels as low as possible. Sometimes, this means designing a rubber shock mount to buckle in order to absorb a large amount of energy, followed by eventual stiffening.
This bushing example assumes a Mooney-Rivlin strain energy function. As with the other case studies, the analysis is static. Automated contact analysis is used, where the top rigid surface moves downwards, causing the rubber to contact itself. Mesh distortion is usually a problem in such analyses.
The figures show the deformed geometry and equivalent Cauchy stress distributions after various increments (panels a and b). The FEA code must be able to handle such variable contact automatically. This analysis was performed both with and without adaptive meshing. When using local adaptive meshing techniques, additional elements are automatically located in regions of stress concentrations and high stress gradients (panel c). This improves the accuracy of the solution.
One also has to take into account several real-life phenomena beyond those explored in the above example: material damage; viscoelastic behavior—to account for creep and relaxation effects; actual service environments—which typically include combined axial, radial, and torsional loadings, and very often, a metallic sleeve around the rubber insert; bushing preload (if any); dynamic (inertial) effects; and fracture and tearing effects.