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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Figure 7. Tolerable number of load-cycles in dependence of the deep rolling force at initial crack depths of (a) 3,0 mm; (b) 4,5 mm; (c) 5,5 mm and (d) 6,5 mm 4. Conclusion and outlook In this study, it succeeded to combine a previously developed crack propagation simulation tool for crack growth investigations on railway axles with a validated finite element deep rolling simulation model and thus to investigate the influence of the deep rolling treatment on the crack growth behaviour of a deep rolled railway axle. Based on the presented results, the following conclusions can be drawn: • The near-surface residual stress state introduced by the deep rolling process has a significant influence on the threshold crack depth a th and the tolerable number of load-cycles. • If the railway axle is not deep rolled, a th is less than 0.5 mm for the investigated start crack geometries. • In deep rolled conditions, a th increases up to nearly 3 mm with a deep rolling treatment of 5 kN deep rolling force and increases to more than 6 mm with an increased deep rolling force of 20 kN. • The behaviour of a th as a function of the deep rolling force can be well described with exponential equations. The value of a th significantly increases with higher deep rolling forces. • The starting crack geometry described by the a 0 / c 0 ratio shows a major influence on the propagation ability of cracks. While in the not deep rolled state the largest a 0 / c 0 ratio of 1.0 results in the largest threshold crack depth, the behaviour changes with deep rolled surface state and the smallest a 0 / c 0 ratio of 0.4 shows the largest a th . • The remaining service life evaluated based on a representative load spectrum is strongly dependent on the deep rolling condition. For a deep rolling application with 20 kN and a starting crack depth of 6.5 mm, still a number of load-cycles of 1.1 . 10 8 can be expected. • According to the results of the investigation, cracks with a reliably detectable depth of about 1-2 mm are capable to propagate in the not deep rolled surface condition. However, if the surface is deep rolled with a force of 5 kN or more, cyclic crack propagation is not expectable.