PSI - Issue 57

J. Torggler et al. / Procedia Structural Integrity 57 (2024) 152–160 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Initial situation As part of the secondary spring stage, the air spring bellows form the connection between the running gear and the car body in the rail vehicle. Air spring bellows are used for increased comfort applications, for level control and high payloads. The spring effect due to the compressibility of the air is utilised in the air spring bellows. The advantages of this system are the possibility of level control, the controllable spring characteristics, the possible reduction of stiffness by means of an additional volume and the existing self-damping of the material. In addition to pure vertical suspension, lateral and, if necessary, longitudinal suspension and torsion must also be provided. Figure 1 (left) shows the loads on the air spring in vertical (red, dashed line), torsional (green, dotted line) and lateral (blue, solid line) direction and the internal pressure in the bellow characterised by p i . The lateral deflection amplitude U represents the dominant load and is considered in the following.

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ello tests

P s 50

50 ateral d s la ement am l t de n mm 5 100

p i

U

p i

Driving direction

10 3

10 4

10 5

10

N m ero load y lesN

Figure 1: Load situation in the air spring bellow (left) and S/N-curve for the tested air spring bellows (right)

Service life tests for an air spring bellow are available on a small scale. These tests were carried out by a cooperation partner with different internal pressures p i and lateral deflection amplitudes U . The results revealed that various types of damage can occur in the air spring bellows, such as bursting, cracking in the elastomer or the detachment of different layers from each other, referred to as delamination in the following. The evaluation of the test series and the operating experience of cooperation partners clearly highlight that the main damage type is delamination (in both cases over 60% of all testes). Figure 1 (right) shows the evaluation of the tests on the air spring bellows. Different load situations were tested and presented together utilizing the lateral displacement amplitude U . As observable, the scattering at the different load levels is significantly high. This indicates that this parameter is inconclusive and therefore not suitable as a failure-relevant parameter. In order to be able to investigate the fatigue strength more precisely and to assess the damage behaviour, a material sample was developed. 3. Experimental methodology The focus of this study is on fibre composite material, which consists of reinforcing fibres made of polyamide (PA) embedded in a matrix of a rubber compound (natural rubber). Figure 2 shows the developed sample geometry, designed for fatigue testing of the composite material. The flat specimen was developed using the finite element modelling method, see Torggler et al. (2023). The production and vulcanisation of the sample was performed with comparable manufacturing conditions as for the air spring bellow. The fibre angle of the sample can be varied from 0 to 35 degrees in respect to the longitudinal axis Y and there are up to eight layers of fibres possible. The investigated confections have fibre angles φ f of ±15, ±25 and ±35 degrees and consist of four layers.