On the lifetime prediction of rolling lobe air springs

In this paper, the fatigue life of rolling lobe air springs made from cord-rubber composites is investigated with particular focus on the crack nucleation approach. Commonly used test specimens like the simple tension test specimen or the dumbbell specimen fail in the fatigue analysis of rolling lobe air springs because the fatigue characteristic of the cord-rubber interface is represented insufficiently. Therefore a new cord-rubber specimen is developed. The fatigue characteristic of the new specimen is discussed and Wöhler curves for two different predictors based on Cauchy stress and configurational stress are determined. Using FEA with a two-scale model of the air spring, the cycles-to-failure with respect to piston diameter and different inner pressures are determined and compared to test results taken from the literature. The results from the literature were derived at elevated temperature. Therefore, the Arrhenius approach is used to take into account different temperatures. In addition the crack growth approach using the cracking energy density is applied. The results show an improvement in the prediction of rolling lobe air springs fatigue life with respect to the crack initiation plane orientation and the cycles-to-failure using the new specimen. Compared to the crack nucleation approach, the crack growth approach seems to slightly overpredict the fatigue lives.