PSI - Issue 46

J. Bialowas et al. / Procedia Structural Integrity 46 (2023) 49–55 J. Bialowas et al. / Structural Integrity Procedia 00 (2021) 000–000

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Fig. 4 (a) Residual σ zz stress and (b) equivalent plastic strain ε p,eq distributions of the updated model with aperture angles 6° and 12° and the reference model with an aperture angle of 45°. The two curves for the updated models nearly coincide.

wheelset axles, at least 20 rollovers are required to reach a steady state in the region of interest, which leads to a total computation time of less than 20 hours. Fig. 4 shows the σ zz stress and the equivalent plastic strain ε p, eq distributions evaluated along the evaluation path of Fig. 3. The results labeled 45° correspond to the reference model in Fig. 3 (a) and those labeled 6° and 12° to the updated model in Fig. 3 (b). The good agreement between the results of the 6° and 12° model shows that a reduction to a 6° aperture angle is acceptable, since they were calculated with the same element size. The differing results between 6° and 45° in Fig. 4 (a) can be explained by the choice of a finer mesh in tangential and axial direction, since smaller elements can better resolve the high stress gradients towards the surface. The differing results in Fig. 4 (b) can be explained with the same argument, although the difference for the equivalent plastic strain ε p, eq is even more pronounced. Moreover, this indicates that the element size of the reference model does not lead to a complete convergence of the plastic deformations in the deep rolled zone. The simulation methodology with periodic boundary conditions is equivalent to as if several work rollers were deep rolling the axle simultaneously. This means that in the model with an aperture angle of 6°, there are 60 rollers distributed around the entire circumference one behind the other, each of which deep rolling an angle of 6°. By further reducing the opening angle, the stress fields of the individual work rollers could influence each other and thus falsify the results. Furthermore, it must be ensured that the size of the contact patch corresponds to a fraction of the surface of the cylinder sector in order to exclude the overlapping of the contact by the shadow elements. 4. Conclusion and Outlook A general method for finite element simulations of the deep rolling process has been developed. By combining the ideas of Meyer et al. (2021) with previous models of the deep rolling process, it is possible to reduce the computation time of such simulations by a factor of 25, generating results with an even higher accuracy. The proposed method not only predicts more detailed residual stress fields for a certain set of parameters significantly faster but also allows studying a wider range of these parameters. In future simulations, the uncoupled zone (cf. Fig. 2 (b)) between the coupled elements can be used to investigate the effects of additional features like cracks, notches, or other defects. Also preceding manufacturing steps such as heat treatment should be taken into account in order to consider the influence of already existing residual stresses on the deep rolling process.