Evaluation of stress softening of the rubber suspension used on rail vehicles

In the rail industry, the important design parameters of rubber suspension systems are currently solely based on the loading part of the loading/unloading history, e.g. the load–deflection characteristics and fatigue requirement. Different energy levels and stress values are created for an identical load value during loading and unloading cycles in rubber-like materials. Hence, the performance of a rubber suspension can be substantially different during loading and unloading, which can lead to unexpected effects. An engineering approach is proposed to account for this so-called Mullins effect. Existing elastomeric models, widely used in rail vehicle design, can be modified to account for the unloading using this methodology. A typical rubber-to-metal bonded component, which is used in rail suspension systems, is selected for a verification study. It is shown that the predictions from the new approach are consistent with the results of the whole load/deflection history obtained in a laboratory experiment. In addition, if the unloading characteristics are not considered, results obtained from stress calculations can have a 20% margin of error. The proposed approach should be further verified using other types of rubber suspension systems.

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