13 Zentrale Universitätseinrichtungen

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/14

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    A new approach to modelling friction stir welding using the CEL method
    (2013) Hoßfeld, Max; Roos, Eberhard
    Although 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. This lack of understanding mainly arises from the adverse observability of the actual process with phenomena like material flow and deposition, large material deformations and thermomechanical interactions determining the mechanical properties of the weld. To close this gap an appropriate numerical model validated by experiments may be helpful. But because of the issues mentioned above most numerical techniques are not capable of modelling the FSW process. Therefore in this study a Coupled Eulerian-Lagrangian (CEL) approach is used for modelling the whole FSW process. A coupled thermomechanical 3D FE model is developed with the CEL formulation given in the FE code ABAQUS® V6.12. Results for temperature fields, weld formation and the possibility of void formation are shown and validated.
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    A fully coupled thermomechanical 3D model for all phases of friction stir welding
    (2016) Hoßfeld, Max
    Although 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.
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    Liquation cracking and chromium depletion in austenitic welds of light water reactors
    (1999) Blind, Dieter; Weber, Georg; Kussmaul, Karl
    Different types of austenitic stainless CrNi-steels were tested in hot tensile and weld simula-tion tests including two melts of niobium stabilized austenitic steel, three melts of titanium stabilized austenitic steel and one melt of an unstabilized austenite. The stabilized austenites were tested in conventional versions and in optimized nuclear grade versions. The unstabi-lized austenite was tested in a conventional version. The hot tensile tests revealed the conventional Nb-stabilized austenites to have the strongest susceptibility to intergranular liquation cracking followed by the unstabilized material A 304. The titanium stabilized qualities (conventional and optimized ones) exhibited no relevant susceptibility to intergranular liquation cracking. The optimized Nb-stabilized austenite showed no relevant susceptibility to intergranular liquation cracking. The weld simulation tests revealed with respect to the heat affected zone (HAZ) close to the fusion line the unstabilized austenite A 304 to be most sensitive to intergranular stress cor-rosion cracking (IGSCC) under Boiling Water Reactor (BWR) conditions. The titanium stabilized austenites (conventional and optimized ones) showed a significantly lower suscep-tibility to IGSCC. Furthermore, the conventional Nb-stabilized austenites proved to be less sensitive to IGSCC than the Ti-stabilized ones. According to the actual state presented here, the optimized Nb-stabilized austenite shows no susceptibility to IGSCC.
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    High speed friction stir welding of thick copper plates
    (2015) Hoßfeld, Max
    When welding large copper parts, the process is strongly limited by the high thermal conductivity and capacity as well as the high temperature strength of copper. These slow down the welding process and require a large heat input. By this the process forces are high and probe failure is a severe issue. Typical welding speeds of thick copper plates today are around 50 to 150 mm/min under laboratory like conditions, requiring a spindle torque up to 1000 Nm, excluding usual multipurpose FSW-machines from this application. This study shows the process and tool development including the verification of a robust tool design. The process is carried out on a multipurpose machine reaching welding speeds up to 500 mm/min in 20 mm rolled Cu-OF. A significant reduction of the process forces, especially traverse force and spindle moment is reached. Due to the relatively low heat input good mechanical properties could be achieved. Tool design, parameters, microstructure, hardness profiles and tensile properties are shown.