A fatigue experiment is carried out on filled natural rubber specimens with two different Shore hardnesses (45 and 50) and three different temperatures (23°C, 60°C and 90°C) under uniaxial tension loads. The measured fatigue life data obtained under different displacement loads are used to formulate fatigue life prediction models corresponding to different operating temperatures for the two hardnesses using the peak engineering strain as the damage parameter. The influences of the temperature, the stress softening at high temperatures and the hardness on the fatigue life of rubbers are measured and discussed. The proposed models are used to predict the fatigue life of a rubber mount for a powertrain mounting system. The validity of the prediction model is demonstrated by comparisons with the measured fatigue life data of the rubber mount at 90°C. A method for determining the damage parameters required for predicting the fatigue life is presented on the basis of the finite element model of the rubber mount. The Mooney-Rivlin constitutive constants of the hyperelastic rubber material are identified on the basis of the measured data on the specimens. Comparisons of the measured and the estimated fatigue lives of the rubber mount at 90°C revealed reasonably good agreement. The ratio of the predicted fatigue life to the measured fatigue life was within a factor of 2 under the range of loading conditions considered.

Prediction of fatigue lives of a rubber mount necessitate formulation of models for estimating fatigue life of the rubber materials used in the mount. Moreover, the prediction accuracy of the model is strongly dependent upon the choice of damage index that are based on different strain, energy or stress measures in the vicinity of critical locations of the rubber mount. In this study, relative performance of models employing different damage indices are evaluated for prediction of fatigue lives of rubber material and a drive-train rubber mount. A combined stress and an effective stress function are proposed as a damage index for predicting fatigue lives of rubber materials and the mounts. Different damage indices, identified from the finite element models of the rubber dumbbell cylindrical specimen are applied for formulations of fatigue life prediction models. The model parameters are identified from the measured data acquired for the rubber dumbbell cylindrical specimen under 31 different uniaxial displacement loads, using least squared error minimization technique. The identified models employing different damage indices are subsequently applied for predicting fatigue lives of rubber mounts under different magnitudes of loads applied along two different directions. The correlations of the predicted lives of the rubber mount from the models employing different damage indices with measured fatigue life data were subsequently investigated for the rubber mount subject to different load conditions. It is shown that the models identified for the rubber material could be effectively used for predicting fatigue lives of the mounts, which are made of same material. The fatigue lives predicted by the models considering either effective stress or combined stress as the damage index correlated with the measured data within a factor of two for the two, suggesting that stress-based damage indices could yield more accurate predictions of fatigue lives of typical mounts.

Hydraulically damped rubber bushings (HDBs) are important for vehicle noise, vibration, and harshness (NVH) performance as they are able to decay the vehicle’s oscillation induced by engine and road. The dynamic stiffness and loss angle of an HDB are crucial and it is significant to investigate the relations between the design parameters with the dynamic stiffness and loss angle. Therefore, the force-deflection relation of the HDB is measured statically and the dynamic stiffness and loss angle are measured dynamically and the test data are analyzed with a view to examine how the measurement results are influenced by the design parameters (the number of the fluid tracks). Compared with the results predicted by a nonlinear lumped parameter model whose parameters are extracted by a parameter identification technique, using the model, the effect of the main rubber and the fluid track on the dynamic stiffness and the loss angle is investigated. A unified analytical model of HDB is also developed with the purpose of predicting the static and dynamic characteristics, and the predictions are shown to be well correlated with the measurement data. The good correlation suggests the validity of the model and the parameter identification implementation.