The roller straightening process is a common method for straightening long products like beams after rolling and cooling. This process often causes an adverse residual stress state. All previous investigations operate only with the roller adjustment as correcting variable. However, this cannot properly describe the consequences on the cross section of the beam during bending. The present paper presents a concept to consider the development of curvature during the straightening process. In finite element analyses using Abaqus/Standard a beam with a rectangular cross section and simplified material properties is modeled for a fundamental and clear demonstration. The theo-retically determined residual stress state depends on the development of curvature during straight-ening. Vice versa it is possible to design a trend of curvature with the goal of tailoring the final re-sidual stress distribution to the desired optimum. The necessary roller adjustment is found in a simulation using the Abaqus user subroutine UAMP, where the curvature is permanently tuned by controlling the roller adjustment. The residual stress state resulting from these 1D considerations (“the theoretical stress state”) is verified in a subsequent 2D analysis giving the “actual stress state”. A comparison of the theoretical and the actual residual stress state illustrates the influence of the roller contact. The concept presented in this work can be applied to complex cross sections in com-bination with realistic material properties. However, for this purpose a large amount of calculation resources due to an extensive 3D modeling are needed.
Residual stresses in railway rails have a significant influence on the rail functional properties and reliability in service life. Already during the production, the roller straightening as the final production step removing the rail curvature causes the formation of complex stress fields. In this work, a complementary experimental characterization of longitudinal, transversal and normal residual stresses in an uncut straightened rail with a length of 0.5 m is performed using neutron diffraction and contour method. Additionally, the residual stresses are predicted numerically by means of an extensive three-dimensional finite element simulation taking into account the cyclic elastic-plastic material behaviour of the rail including combined kinematic-isotropic hardening. The very good agreement between the experimental and numerical data provides a basis for the understanding and predicting how the straightening procedure, that is, the positioning of the individual rollers and forces applied by the rollers, influences the triaxial stress fields at the rail cross-section.
A conical slit cell for depth-resolved diffraction of high-energy X-rays was used for residual stress analysis at the high-energy materials science synchrotron beamline HEMS at PETRA III. With a conical slit width of 20 µm and beam cross-sections of 50 µm, a spatial resolution in beam direction of 0.8 mm was achieved. The setup was used for residual stress analysis in a drawn steel wire with 8.3 mm diameter. The residual stress results were in very good agreement with results of a FE simulation.
Schrauben aus hochfesten Stählen und deren wirtschaftliche Fertigung unterliegen hohen Qualitätsansprüchen und werden ständig weiter verbessert. Für hochfeste Schrauben werden üblicherweise MnB-und 1 %Cr-Stähle im vergüteten Zustand verwendet. Als kostengünstige Alternativen gelten thermomechanisch gewalzte Stähle, Dualphasenstähle und AFP-Stähle, die ohne zusätzliche Wärmebehandlung (Vergütung) hergestellt werden können. Ausgehend von der Beschreibung der metallurgischen und walzbedingten Einflüsse bei der Drahtherstellung und deren Auswirkungen auf die Umformbarkeit bei der Schraubenherstellung werden die alternativen Stahlgüten vergleichend dargestellt. Ergänzend dazu werden die verfahrenstechnischen Optimierungsmöglichkeiten bei der Schraubenfertigung betrachtet, wobei primär der Vorzug, die Eigenspannungsentwicklung und die Wärmebehandlung untersucht werden. Durch FE-Simulationen werden die Fertigungsschritte analysiert und mittels Schädigungsmodellen die Grenzen der Umformbarkeit aufgezeigt.
Materials and Processing Optimization for the Manufacturing of High Strength Fasteners.Fasteners made from high strength steels and their economical production are faced to high quality requirements and are improved continuously. High strength screws are usually made from MnB and 1 %Cr steels. Alternative cost-saving steel grades are thermomechanically rolled steels, dual phase steels and precipitation hardened ferritic-perlitic steels, which do not need an extra heat treatment (Q&T). Based on the description of the effect of metallurgical influences and the conditions during hot rolling of the wire on the formability, the alternative steel grades are compared. In addition, the measures to optimize the processing parameters during the manufacturing of fasteners are considered, taking into account pre-drawing, residual stresses and heat treatment. By finite element simulations, the fastener production steps and forming limits are analysed by damage models.
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