PSI - Issue 57

Boris Spak et al. / Procedia Structural Integrity 57 (2024) 445–451 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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4. Conclusions In the paper at hand, the impact of the forming by automated, robot-assisted roll forming for different tool paths is extensively studied through finite element analysis. The process simulation is carried out using commercial finite element solver LS-Dyna®. Fatigue life estimation is performed using the LSA with damage parameter P SWT , considering the initial residual stress state. From the results obtained, the following conclusion are reached: 1. The tool path can lead to a significantly different residual stresses distribution. As shown, variants 1 and 2 appear to result in a more favorable residual stress state, i. e. compressive stresses, compared to variant 3. 2. The residual stress state by itself is not sufficient to determine which of the tool paths results in a component exhibiting higher number of reversals up to failure. A subsequent loading simulation provides information to what degree residual stress relaxation occurs and how the fatigue life is affected. 3. In case of a different loading scenario, i. e. along the angled sheet in the z direction instead of a force applied perpendicularly, the variants 1 and 2 might potentially endure a higher number on reversal to failure due to greater compressive residual stresses. This implies the possibility to adapt a tool path that suits the actual loading conditions, thus improving the performance of the roll formed structural component. 4. The cold working during the forming operation can affect the local material properties in the expected failure location. At the same time, the degree of cold working near the failure location can alter the fatigue life and therefore should be taken into account at the stage of tool path selection. 5. Cold working is known to affect the cyclic materialproperties, therefore potentially altering the strain Wöhler curve. The fatigue life estimation in the present study was carried out with cyclic materialproperties obtained from aluminum sheet in the as received state. Further experimentalwork is required to validate the fatigue life estimation and to assess the impact of cold working on the performance under different loading conditions. Acknowledgements The research is being suported by Federal Ministry for Economic Affairs and Climate Action on the basis of a decision by the German Bundestag, within the aerospace program LuFo- VI of the project “Untersuchung der Prozess Struktur-Eigenschaftsbeziehungen des Rollprofilierens auf die Performanceverbesserung für Blechbauteile aus Aluminium“ (Funding ID: 20W2102D) . References Fiedler, M., Wächter, M., Varfolomeev, I., Vormwald, M., Esderts, A., 2019. FKM Richtlinie Nichtlinear - Rechnerischer Festigkeitsnachweis unter expliziter Erfassung nichtlinearen Werkstoffverformungsverhaltens für Bauteile aus Stahl, Stahlguss und Aluminiumknetlegierung. Halmos, G. T., 2006. Roll Forming Handbook. Kühne, D., Guilleaume, C., Seiler, M., Hantschke, P., Ellmer, F., Linse, T., Brosius, A., Kaestner, M., 2019. Fatigue analysis of rolled components considering transient cyclic material behaviour and residual stresses. Kühne, D., Spak, B., Kästner, M., Brosius, A. & Fiedler, M., 2021. Consideration of cyclic hardening and residual stresses in fatigue life calculations with the local strain approach. Masing, G., 1926. Proceedings of the 2nd International Congress for Applied Mechanics, 332-335. Neuber, H., 1961. Theory of Stress Concentration for Shear-Strained Prismatical Bodies With Arbitrary Nonlinear Stress-Strain Law. Radaj, D., Sonsino, C. M., Fricke, W., 2006. Fatigue assessment of welded joints by local approaches. Radaj, D., Vormwald, M., 2007. Ermüdungsfestigkeit: Grundlagen für Ingenieure. Ramberg, W., Osgood, W. R., 1943. Description of stress-strain curves by three parameters. Schijve, J., 2009. Fatigue of Structures and Materials. Smith, K. N., Watson, P.; Topper, T. H., 1970. A stress – strain function for the fatigue of metals. Journal of Materials 5, 767-778. Spak, B., Schlicht, M., Nowak, K., Kästner, M., Froitzheim, P., Flügge, W. & Fiedler, M., 2022. Estimation of fatigue life for clinched joints with the Local Strain Approach. Zaroog, O. S., Ali, A., Sahari, B. B., Zahari, R., 2011. Modeling of residual stress relaxation of fatigue in 2024-T351 aluminum alloy. Abvabi, A., Rolfe, B., Hodgson, P. D., Weiss, M., 2015. The influence of residual stress on a roll forming process. DIN 50125, 2016. Testing of metallic materials - Tensile test pieces. DIN EN ISO 6892-1, 2020. Metallic materials - Tensile testing - Part 1: Method of test at room temperature (ISO 6892-1:2019). SEP 1240, 2006. Testing and Documentation Guideline for the Experimental Determination of Mechanical Properties of Steel Sheets for CAE Calculations.