PSI - Issue 57

Tobias Pertoll et al. / Procedia Structural Integrity 57 (2024) 250–261 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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b

Figure 2. Introduced in-depth residual stress distribution for different applied deep rolling forces in the (a) circumferential and (b) longitudinal directions

2.3. Press fit stresses

As stated previously, the highly-stressed transition areas to the press seats are typically deep rolled. The attached components usually cause tensile residual stresses in the longitudinal direction in the investigated cross section, as demonstrated in (Lütkepohl et al. 2009; Rieger et al. 2020). For a conservative consideration, typical tensile residual stresses with a maximum magnitude value of 35 MPa at the surface are considered at the surface in the longitudinal direction. These tensile stresses are superimposed to the residual stresses of the deep rolling process application and further with the load-induced load stresses. The analytical software tool INARA (INARA 2022) is used to assess the crack growth behaviour. The software was developed within the framework of the research project "Eisenbahnfahrwerke 3" for the calculation of semi elliptical crack propagation and residual life estimation of railway axles. Crack closure, load interaction and, for this investigation of particular importance, residual stresses are considerable. Further details are provided in (MCL 2023, 2020; Maierhofer 2014; Gänser et al. 2021). For the calculation of the crack propagation behaviour, the cross-section of the railway axle has to be defined, whereas the dimensions are shown in Figure 3 (a). The outer radius R of the railway axle and the inner radius R i are selected as the dimensions of the full-scale railway axle and held constant for all presented investigations. The starting crack is defined semi-elliptically in INARA and is defined by the initial crack depth a 0 and the starting surface crack length 2 c 0 . For the investigations, initial cracks are defined using the a 0 / c 0 ratio. a 0 / c 0 ratios of 1.0, 0.8, 0.6 and 0.4 are considered for the investigation and thus the influence of starting crack geometry on crack propagation behaviour is investigated. Further, the maximum crack depth a max is set to 8 mm and the specified tolerable number of load-cycles always refer to the permissible number of load-cycles up to a crack depth of 8 mm. At this comparably increased crack depth, a reduced remaining service life due to cyclic loading of the railway axle and thus component failure can be expected. The cross-section involving the starting crack is cyclically loaded with rotational bending, which acts as main load during in-service. The loaded cross-section area is shown in Figure 3 (a). The coloured stress is scaled to the nominal stress of the railway axle. Due to the basket arch, an increased stress must be assumed, considered as a stress concentration factor of 1.2. The crack propagation behaviour of the material 34CrNiMo6 is considered using a multi-linear crack propagation curve. The crack propagation curve is taken from measurement data of the research project "Eisenbahnfahrwerke 2". Details and results are published in (Lütkepohl et al. 2009). The fracture mechanical parameters were determined by using samples taken from railway axles with R -ratios of 0.1 and -1.0. The results of these tests and thus the multi-linear approximation of the crack propagation curves are shown in 2.4. Crack propagation model