Investigating Damage Mechanisms in Cord-Rubber Composite Air Spring Bellows of Rail Vehicles and Representative Specimen Design

Cord-rubber materials are used in crucial components of rail vehicles, such as air spring bellows in secondary suspension. A detailed understanding of the material behaviour of these components is thus of the utmost importance at an early stage of development. In general, a minor knowledge of the fatigue behaviour is currently all that is available today, while empirical methods involving designer experiences are in most cases essential requirements for this work. The design can be carried out more efficiently based on a representative cord-rubber composite specimen than on an entire air spring bellow. In this paper, the design of such representative specimens is shown taking different geometries and test conditions into consideration. It is found, that a flat specimen design is suitable for analysing the base material under different loading scenarios. The design and optimisation of the specimen geometry was carried out using finite element analysis, which was validated by means of optical strain measurement. The test procedure for the specimen was designed to provide a sound transferability to experimental testing of the components. A fracture pattern study was carried out using radiography and micro computed tomography. The results show, that the dominant damage mechanism is the separation of the layers from each other, denoted as delamination. In conclusion, the developed specimen is well suited for further investigations of the composite material. Furthermore, it will significantly accelerate the development of new air springs and new layups in particular. Future work will focus on a systematic investigation of the fatigue behaviour of the cord-rubber composite air-spring bellows based on the fatigue data of the representative specimens designed in this work.