Frequency and amplitude dependence of the axial and radial stiffness of carbon-black filled rubber bushings

The frequency and amplitude dependent dynamic behavior of carbon-black filled rubber bushings is experimentally investigated for a commercially available bushing in the axial and radial directions. Based on measurement observations, models for the axial and radial dynamic stiffness of rubber bushings are developed. The amplitude dependence-referred to as the Fletcher-Gent effect and mainly caused by the presence of carbon-black fillers in the rubber-is included in the analytical models by means of equivalent shear moduli, which result from applying a separable elastic, viscoelastic and friction material model to equivalent strains of the non-homogeneous strain states inside the bushing when subjected to axial or radial deflections. Good correlations between measurements and the axial and radial models at amplitudes of 0.1, 0.2 and 0.5 mm from 5 to 155 Hz-when the material parameters are achieved from axial measurements at 0.1 mm-prove the accuracy of both stiffness models.