13 Zentrale Universitätseinrichtungen
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/14
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Item Open Access A fully coupled thermomechanical 3D model for all phases of friction stir welding(2016) Hoßfeld, MaxAlthough friction stir welding (FSW) has made its way to industrial application particularly in the last years, the FSW process, its influences and their strong interactions among themselves are still not thoroughly understood. The lack of understanding mainly arises from the adverse observability of the actual process with phenomena like material ow and deposition, large material deformations plus their complex thermo-mechanical interactions determining the weld formation and its mechanical properties. A validated numerical process model may be helpful for closing this gap as well as for an isolated assessment of individual influences and phenomena. Hereby such a model will be a valuable assistance for process and especially tool development. In this study a Coupled Eulerian-Lagrangian (CEL) approach with Abaqus V6.14 is used for modeling the whole FSW process within one continuous model. The resolution reached allows not only simulating the joining of two sheets into one and real tooling geometries but also burr and internal void formation. Results for temperature fields, surface and weld formation as well as process forces are shown and validated.Item Open Access Testing and evaluation of anchor channels under fatigue loading(2020) Fröhlich, Thilo; Lotze, DieterCast-in anchor channels are used to connect steel components to concrete structures e.g., for elevators, cranes or machines, where repeated load cycles require verification against fatigue failure. The fatigue resistance of anchor channels may be determined by tests according to the interactive method, which provides a complete description of the S/N curve from one to infinite load cycles according to the current assessment document. This procedure differs from conventional fatigue concepts, which do not consider loads that are part of low cycle fatigue, but also question the general existence of an endurance limit. An alternative approach presented in this paper is based on the assumption that the S/N curve can be approximated by a bilinear function. The procedure for the evaluation of fatigue tests on anchor channels embedded in concrete is described. A comparison with the current qualification criteria is given by a test example to discuss the applicability of the proposed method.Item Open Access Effect of weld length on strength, fatigue behaviour and microstructure of intersecting stitch-friction stir welded AA 6016-T4 sheets(2023) Walz, Dominik; Göbel, Robin; Werz, Martin; Weihe, StefanFriction stir welding is a promising joining process for boosting lightweight construction in the industrial and automotive sector by enabling the weldability of high-strength aluminum alloys. However, the high process forces usually result in large and heavy equipment for this joining method, which conflicts with flexible application. In order to circumvent this issue, a friction stir welding gun has been developed which is capable of producing short stitch welds-either stand-alone as an alternative to spot welds or merging into each other appearing like a conventional friction stir weld. In this study, the influence of the stitch seam length on the strength properties of intersecting friction stir welds is investigated, and the weld is characterized. For this purpose, EN AW-6016 T4 sheets were welded in butt joint configuration with varying stitch lengths between 2 and 15 mm. Both the static and dynamic strength properties were investigated, and hardness and temperature measurements were carried out. The results show a scalability of the tensile strength as well as the fatigue strength over the stitch seam length, while the substitute proof strength is not affected. Hereby, the tensile strength reached up 80% of the base materials tensile strength with the chosen parameter setup. Likewise, the stitch weld length influences the hardness characteristics of the welds in the transition area.Item Open Access Untersuchung über den Einfluß des Restaustenitzerfalls auf die Bildung von Kaltrissen beim Schweißen(1980) Makarov, E. L.; Gospodarevskij, V. I.; Frieß-Ehlers, Ulrike (Übersetzerin); Pertschi, Ottmar (Übersetzer)In der vorliegenden Arbeit wurden niedriglegierte Stahlproben untersucht, auf die eine Schweißraupe aufgeschweißt wurde. Nach dem Schweißen wurden die Proben mit Wasserstoff elektrolytisch gesättigt. Durch eine solche Behandlung bilden sich Unternahtrisse sowie Risse an der Oberfläche der Proben, wo die erhabene Schweißraupe in den Grundwerkstoff übergeht.Item Open Access Ein- und zweiseitiges Fließpressen von Werkstücken mit Flansch aus Rohrabschnitten(1983) Kirsanov, K. A.; Zimin, V. A.; Revtova, E. A.; Abramenko, V. Ju.; Pertschi, Ottmar (Übersetzer)Anhand der Untersuchungen wurde von den Verfassern ein technischer Vorgang erarbeitet und ein Werkzeug erstellt, mit dem man Fertigteile aus Rohrabschnitten mit hohem und massivem Flansch in einem Arbeitsgang herstellen kann. Damit können Werkstoffverbrauch und Arbeitsaufwand bei der Herstellung beträchtlich gesenkt werden.Item Open Access Investigation of tool degradation during friction stir welding of hybrid aluminum-steel sheets in a combined butt and overlap joint(2024) Göbel, Robin; Schwertel, Stefanie; Weihe, Stefan; Werz, MartinFriction stir welding, as a solid-state welding technique, is especially suitable for effectively joining high-strength aluminum alloys, as well as for multi-material welds. This research investigates the friction stir welding of thin aluminum and steel sheets, an essential process in the production of hybrid tailor-welded blanks employed in deep drawing applications. Despite its proven advantages, the welding process exhibits variable outcomes concerning formability and joint strength when utilizing an H13 welding tool. To better understand these inconsistencies, multiple welds were performed in this study, joining 1 mm thick steel to 2 mm thick aluminum sheets, with a cumulative length of 7.65 m. The accumulation of material on the welding tool was documented through 3D scanning and weighing. The integrity of the resulting weld seam was analyzed through metallographic sections and X-ray imaging. It was found that the adhering material built up continuously around the tool pin over several welds totaling between 1.5 m and 2.5 m before ultimately detaching. This accretion of material notably affected the welding process, resulting in increased intermixing of steel particles within the aluminum matrix. This research provides detailed insights into the dynamics of friction stir welding in multi-material welds, particularly in the context of tool material interaction and its impact on weld quality.Item Open Access Experimental investigation on the fatigue design of anchor channels(2022) Fröhlich, Thilo; Lotze, DieterCast‐in anchor channels subjected to repeated cyclic actions need to be verified against fatigue failure. However, the fatigue behavior of these fasteners has rarely been investigated up to now. Consequently, the fatigue verification is not covered by the provisions of EN 1992‐4 and specific design rules apply for this product. This article gives a brief overview of the current design methods for anchor channels under fatigue loading and addresses its limitations. Results of experimental investigations within a recent research project are presented that focused on the fatigue resistance of fastenings under combined static and fatigue loading. Accompanying strain measurements provide insights about the distribution of cyclic tension loads through the channel profile to the anchors. In addition, tests under pulsating and alternating shear perpendicular to the channel axis were performed to outline the suitability under fatigue relevant shear loads. The test results obtained are discussed with respect to the existing state of knowledge. Finally, recommendations for the fatigue design of anchor channels are given.Item Open Access Spannungszustand im Rohlingflansch beim Tiefziehen eines komplizierten Werkstücks(1980) Rubenkova, L. A.; Kazakov, Ju. P.; Pertschi, Ottmar; Frieß-Ehlers, Ulrike (Übersetzer)A two-dimensional stress state occurs during stamping in the flange of a blank, a characteristic feature of which is that one of the main stresses is compression, the other tension. Under such conditions the equations which determine the stress state of an ideally plastic metal coincide with the equations relating to a two-dimensional deformed state. A system of equations of the hyperbolic type is obtained, which has two families of real characteristics, both of which coincide with the trajectories of the maxiumum tangential stresses and have the property of orthogonality. Using the method of characteristics, it is possible to construct the optimal contour of the blank which will ensure that there is no displacement along a contour of the die. The described method of determining the stress state in the flange of the blank during extrusion can also be used in cases when the shape of the clamping surface is not two-dimensional and the contour of the inside of the die has an arbitrary configuration. If the clamping surface is a complicated one, the surface must be developed onto a plane in order to construct the trajectories of the maximum tangential stresses.Item Open Access Untersuchung des Rollbiegens(1992) Renne, I. P.; Kartasov, A. F.; Pertschi, Ottmar (Übersetzer)Mechanik des Rollbiegeverfahrens von dem Streifen, welcher in eine halbrunde Biegematritze hineingedrückt wird. Theoretische Untersuchung des Verfahrens unter Berücksichtigung des Einflusses des Verfestigungsexponenten n = 0 - 0,3 und der Rückfederung. Ermittlung der geometrischen Parameter des Verfahrens, minimaler Biegeradius, notwendige Verbiegung des Streifenendes, andere Verfahrensparamter.Item Open Access Anisotropy of the tribological performance of periodically oxidated laser-induced periodic surface structures(2023) Onufrijevs, Pavels; Grase, Liga; Padgurskas, Juozas; Rukanskis, Mindaugas; Durena, Ramona; Willer, Dieter; Iesalnieks, Mairis; Lungevics, Janis; Kaupuzs, Jevgenijs; Rukuiža, Raimundas; Kriūkienė, Rita; Hanesch, Yuliya; Speicher, MagdalenaLaser-induced periodic surface structures (LIPSS) enable advanced surface functionalization with broad applications in various fields such as micro- and nanoelectronics, medicine, microbiology, tribology, anti-icing systems, and more. This study demonstrates the possibility of achieving anisotropy in the tribological behavior of C45-grade steel structured by nanosecond laser radiation using the LIPSS method. The lateral surface of the steel roller was irradiated with a pulsed Nd:YAG laser at an optimum intensity I = 870 MW/cm2 for the formation of LIPSS. Two sets of samples were formed with LIPSS that were perpendicular and parallel to the roller’s rotational motion direction. The Raman intensity maps revealed that the LIPSS structure consisted of periodically arranged oxides at the top of hills. At the same time, the valleys of the LIPSS structures were almost not oxidized. These results correlated well with scanning electron microscopy energy dispersive X-ray spectroscopy mapping and atomic force microscopy measurements. A comparison of Raman and X-ray photoelectron spectroscopy spectra revealed that both the magnetite phase and traces of the hematite phase were present on the surface of the samples. Tribological tests were performed in two cycles with periodic changes in the normal clamping force and sliding speed. It was found that the LIPSS structures which were formed perpendicularly to the sliding direction on the roller had a significantly greater impact on the friction processes. Structures oriented perpendicular to the direction of motion had a positive influence on reducing the energy consumption of a friction process as well as increasing the wear resistance compared to LIPSS formed parallel to the direction of motion or ones having a non-texturized surface. Laser texturing to produce LIPSS perpendicular to the direction of motion could be recommended for friction pairs operating under low-load conditions.