PSI - Issue 68

Lars A. Lingnau et al. / Procedia Structural Integrity 68 (2025) 303–309 L. A. Lingnau et al. / Structural Integrity Procedia 00 (2025) 000–000

309

7

performance was also demonstrated. Specimens with a shoulder opening angle of 2α = 30° had number of cycles to failure N f that was approximately 14% higher than specimens with a shoulder opening angle of 2α = 90°. Metallographic studies showed the influence of forming-induced ductile damage in the form of voids and MnS inclusions on crack initiation and propagation. Furthermore, combination of FIB-SEM, deep learning AI image segmentation and CAD was used to generate high-resolution 3D models of MnS inclusions and void distribution in a full forward rod extruded case-hardened steel 16MnCrS5. It was found that the voids are distributed throughout the entire representative volume and not, as previously assumed, only in the MnS inclusions. The visualization of the distribution of MnS inclusions also allowed their influence on crack initiation and propagation to be considered separately from that of the voids, since a significant influence of these inclusions was found in the fractographic studies. The platelet-shaped MnS inclusions also show a notch effect microstructure, as the brittle phases cannot compensate for the deformation of the matrix. The combination of the two 3D models showed that the largest voids are located in and around the MnS inclusions. The investigation of the void distribution in the existing phases showed that about 2% of the voids are located in MnS inclusions. Further investigations on short term crack growth, defect evolution or damage accumulation under different fatigue conditions are the next logical steps. These will help to deepen the understanding of the influence of forming-induced ductile damage using 3D models. In the future, in-situ tests will be performed in the SEM to evaluate the evolution of microstructural damage. Acknowledgements The authors gratefully acknowledge the funding by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) for the subproject C01 within the Collaborative Research Center CRC/Transregio 188 “Damage Controlled Forming Processes” (project no. 278868966). The authors further thank the German Research Foundation and the Ministry of Culture and Science of North Rhine-Westphalia (Ministerium fuer Kultur und Wissenschaft des Landes Nordrhein-Westfalen, NRW) for their financial support within the Major Research Instrumentation Program for the FIB-SEM (project no. 386509496). References Beretta, S., Foletti, S., Valiullin, K., 2011. Fatigue strength for small shallow defects/cracks in torsion. Int. J. Fatigue 33, 287–299. https://doi.org/10.1016/j.ijfatigue.2010.08.014. Callaghan, M.D., Humphries, S.R., Law, M., Ho, M., Bendeich, P., Li, H.; Yeung, W.Y., 2010. Energy-based approach for the evaluation of low cycle fatigue behaviour of 2.25Cr–1Mo steel at elevated temperature. Mater. Sci. Eng. A 527, 5619–5623. https://doi.org/10.1016/j.msea.2010.05.011. Hering, O., Tekkaya, A.E., 2020. Damage-induced performance variations of cold forged parts. J. Mater. Process. Technol. 279, 116556. https://doi.org/10.1016/j.jmatprotec.2019.116556. Langenfeld, K., Lingnau, L., Gerlach, J., Kurzeja, P., Gitschel, R., Walther, F., Kaiser, T., Clausmeyer, T., 2023. Low cycle fatigue of components manufactured by rod extrusion: Experiments and modeling. Adv. Ind. Manuf. Eng. 7, 100130. https://doi.org/10.1016/j.aime.2023.100130. Lingnau, L.A., Walther, F., 2023. Characterization and separation of damage mechanisms of extruded case-hardening steel AISI 5115 under cyclic axial-torsional loading. Trans Tech Publications Ltd.: Bäch, Switzerland; ISBN 978-3-0364-1104-0. Lingnau, L.A., Heermant, J., Otto, J.L., Donnerbauer, K., Sauer, L.M., Lücker, L., Macias Barrientos, M., Walther, F., 2024. Separation of damage mechanisms in full forward rod extruded case-hardening steel 16MnCrS5 using 3D image segmentation. Materials 17, 3023. https://doi.org/10.3390/ma17123023 Moehring, K., Walther, F., 2020. Performance-related characterization of forming-induced initial damage in 16MnCrS5 steel under a torsional forward-reverse loading path at LCF regime. Materials 13, 2463. https://doi.org/10.3390/ma13112463. Shankar, V., Mariappan, K., Sandhya, R., Laha, K., 2016. Understanding low cycle fatigue and creep–fatigue interaction behavior of 316 L(N) stainless steel weld joint. Int. J. Fatigue 82, 487–496. https://doi.org/10.1016/j.ijfatigue.2015.09.003. Tekkaya, A.E., Bouchard, P.-O., Bruschi, S., Tasan, C.C., 2020. Damage in metal forming. CIRP Ann. 69, 600–623. https://doi.org/10.1016/j.cirp.2020.05.005. Zapara, M., Augenstein, E., Helm, D., 2014. Prediction of damage in cold bulk forming processes. PAMM Proc. Appl. Math. Mech. 14, 1037– 1040.