Geschweißte Kranbahnträger mit größeren Steghöhen werden in der Praxis üblicherweise mit zusätzlichen Quersteifen zwischen den Auflagern ausgeführt. Dadurch wird die Beultragfähigkeit des Stegs ...erhöht und die Verdrehung des Obergurts zufolge exzentrischer Radlasteinleitung begrenzt. Allerdings werden dadurch in Hinblick auf eine möglichst kerbarme Radlasteinleitung in den Trägersteg zusätzliche kritische Konstruktionsdetails im Bereich der an den Obergurt angeschweißten Quersteifen erzeugt, die im Nachweis gegen Ermüdungsversagen zu berücksichtigen sind. Darüber hinaus finden sich in DIN EN 1993‐6 derzeit keine Regeln zur Berechnung der lokalen Spannungen im Steg und in den Quersteifen für Radlasteinleitung im Nahbereich der Quersteifen. Daher werden in diesem Beitrag sowohl Laborversuche als auch FE‐Berechnungen präsentiert, welche die lokalen Spannungen in unmittelbarer Nähe von Quersteifen im Detail untersuchen. Die ermittelten Spannungen werden anschließend für vergleichende Ermüdungsnachweise an den nun maßgebenden Konstruktionsdetails im Verhältnis zu entsprechenden Nachweisen ohne Berücksichtigung des Quersteifeneinflusses verwendet. Auf Basis der gewonnenen Ergebnisse werden Defizite der aktuellen Vorgehensweise aufgezeigt und Empfehlungen für die Bemessungspraxis abgeleitet.
Keyhole gas tungsten arc welding (K-TIG) was used to weld AISI 316L stainless steel of mid-thickness (thickness ranging 6–13mm). 316L plates of 10-mm thickness were jointed using an I-groove in a ...single pass without filler metal. The effects of welding parameters on the fusion zone profile were investigated. The weld properties, including mechanical properties, microstructure, and corrosion resistance, were analyzed. The primary weld microstructures were austenite and δ-ferrite. The tensile strength and impact property of the weld were almost the same as those of the base metal, while the corrosion resistance of the weld was even better than that of the base metal. High-quality 316L stainless steel joints can be realized through K-TIG welding with high productivity and low processing cost. The practical application of K-TIG welding to join mid-thickness workpieces in industry is well demonstrated and an ideal process for welding AISI 316L of mid-thickness with high efficiency and low cost is presented.
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•10mm-thick AISI 316L stainless steels can be welded by single-pass K-TIG process.•High-quality joints can be realized with high productivity and low cost.•The practical application of the K-TIG process in industry is well demonstrated.•An ideal process to weld mid-thickness 316L (thickness from 6–13mm) is presented.
•Physical models containing flaws and tubes are made by high-strength gypsum.•Fracturing characteristic of physical models are obtained from experimental tests.•The cracking mechanism of lining ...structure around tunnel is proposed.•Stress distribution and displacement field explain failure characteristic of model.
The diverse joint distributions in natural layered rock masses bring a great difficulty to the study on fracturing characteristics of surrounding rock in the process of tunnel excavation. The joint angle plays a vital role in the fracturing behaviors of tunnels. In this paper, taking the shallow-buried tunnel in layered rock masses as the background, a series of uniaxial compression tests were performed on the physical models containing joints and tubes made of high-strength gypsum. The fracturing characteristics of models with joints of different combinations are obtained, and the cracking mechanism of lining structure is further explored. Furthermore, the influences of linings on the stress distribution in surrounding rock and lining around tunnel and the displacement field in the model are investigated by a particle-based discrete element method. The supporting effect of lining on the stability of tunnels is finally evaluated.
A unified fluid flow and heat transfer model is developed by taking into account the coupled transport mechanisms of the plasma arc, weld pool and keyhole in stationary plasma arc welding. The local ...thermodynamic equilibrium-diffusion approximation method is used to treat the interface between the arc plasma and the weld pool. The volume-of-fluid method is employed to track the keyhole boundary, and the underlying physics in the whole domain are self-consistent. The whole welding process from arc ignition to penetrated keyhole formation, including the weld pool surface depression, blind keyhole expansion, dynamic coupling between the arc plasma and keyhole, interaction of keyhole and weld pool, and the transient behaviors of temperature, fluid flow and electromagnetic fields in the arc column, keyhole and weld pool, are numerically simulated. The dynamic variations of the current density, plasma arc pressure and heat flux at the weld pool surface with the evolution of keyhole boundary are quantitatively analyzed. It is found that as the keyhole depth increases the plasma arc shape, temperature profile and current density distribution undergo dynamic evolution so that the heat flux on the keyhole wall (plasma arc–weld pool interface) changes continuously. However, the plasma jet velocity is insensitive to the keyhole depth so that the plasma arc pressure at the keyhole wall is almost stable. The stationary plasma arc welding experiments are performed, and the macrographs of welds are made to validate the model.
•Strain fields on the surface of a transverse flat specimen are obtained with a DIC system (ARAMIS).•Experimental strain fields obtained from ARAMIS are compared to the Rousselier simulation ...results.•The Rousselier model is used to predict stress-strain curve and crack propagation of different specimens from welded joints.
In this paper, the fracture behavior of an aluminum laser welded butt joint was studied numerically and experimentally. With the assistance of a digital image correlation (DIC) system, the strain variation of the flat specimen under deformation is obtained. Void sheeting mechanism and shear bands are found on the surface of the specimen to precede rupture. Although initial pores are found in the fusion zone, good predictions are obtained with respect to stress-strain, F-COD as well as fracture resistance JR curves for flat and compact tension (C(T)) specimens, confirming the Rousselier model can predict the fracture behavior of aluminum laser welded joint well, with the Rousselier parameters calibrated from simulation of fracture behavior of notched round specimens.
Yb–YAG laser offset welding of AA5754 and T40 butt joint Casalino, Giuseppe; Mortello, Michelangelo; Peyre, Patrice
Journal of materials processing technology,
September 2015, 2015-09-00, 20150901, Letnik:
223
Journal Article
Recenzirano
Odprti dostop
In this work, a 5754 Al alloy and T40 were joined in butt configuration by focusing a fiber laser onto the titanium side, close to the weld centerline (offset). The keyhole was made entirely of ...titanium, and the fusion of the aluminum was achieved by heat conduction. Neither filler metal nor chamfering was necessary to produce a sound, dissimilar weld. The assembly was free from porosity and spatter defects. The mechanical properties were satisfactory. The energy input, the laser offset, and their interaction had statistically significant effects on the ultimate tensile strength. The findings of this investigation prove the robustness and suitability of fiber laser offset welding for Al–Ti weld fabrication.
During Friction Stir Welding (FSW) of aluminum (Al 2024) to titanium (Ti-6Al-4V), it is observed that titanium fragments at the interface get distributed in the weld nugget. These particles are both ...coarse and fine in size. Such a particle distribution, particularly due to presence of coarse particles, is expected to negatively impact the mechanical properties of the welds. In an effort to further fragment the coarse Ti particles, FSW was performed with an additional pass in the weld nugget region. Characterization was done using X-ray Micro-Computed Tomography (XCT), Scanning Electron Microscope (SEM) equipped with an Energy Dispersive Spectrometer (EDS), X-ray Diffraction and Electron Back-scattered Diffraction (EBSD) method. Tensile tests were performed to determine the mechanical properties of the weld. The Ti particles of various shapes and sizes were seen to be inhomogeneously distributed in the weld nugget even after the second pass. A detailed observation revealed that the larger particles (as flakes) were inhomogeneously distributed but the finer particles (more spherical) were homogeneously distributed in the weld nugget. It is observed that the weld after second pass contains a higher number of finer Ti particles. The variation in particles size and number fraction is due to the continuous fragmentation that occurs during the processing. Phase analysis reveals the formation of intermetallic compounds such as Al3Ti and AlTi in the welds. A detailed analysis discloses that the fraction of intermetallics in the weld nugget increases in the second pass when compared to the first pass. Aluminum in the weld nugget was substantially refined and recrystallized with grains consisting of mixed types of grain boundaries, which points to the mechanism of Continuous Dynamic Recrystallization (CDRX) through Dynamic Recovery (DRV). The EBSD analysis also reveals that the weld after second pass promotes the development of a high fraction of recrystallized grains (87%) when compared to that of first pass (78%). The second pass resulted in a significant improvement in the ultimate tensile strength (from 231 ± 8 MPa to 271 ± 6 MPa) and ductility (from 7.4 ± 0.3% to 9 ± 1.0%) of the weld. Such improvement in joint properties is analyzed considering the relative mechanical properties of the different zones across the weld nugget. A spring model has been employed to characterize the fracture behavior of the welds. This method and mechanism may be used to produce composite and dissimilar welds with unique mechanical properties by employing multi-pass processing and welding methodology.
The article studies the change in the content of alloying elements in multi-pass welded joints formed by manual arc welding with TsL-11, TsT-15, and OZL-8 coated electrodes at different currents ...during welding of tubes made of 12Kh18N10T austenitic steel with a thickness of 6 mm. Based on the results of layer-by-layer chemical analysis of the welded joint metal and base metal, the most efficient welding modes and the sequence of bead surfacing are proposed. Practical recommendations for soft and rigid manual arc welding modes with different TsL-11 electrodes in order to form one- and two-pass welded joints with a uniform distribution of alloying elements are given.
In the last decade, the friction stir welding of polymers has been increasingly investigated by the means of more and more sophisticated approaches. Since the early studies, which were aimed at ...proving the feasibility of the process for polymers and identifying suitable processing windows, great improvements have been achieved. This owes to the increasing care of academic researchers and industrial demands. These improvements have their roots in the promising results from pioneer studies; however, they are also the fruits of the adoption of more comprehensive approaches and the multidisciplinary analyses of results. The introduction of instrumented machines has enabled the online measurement of processing loads and temperature, and critical understanding of the principal aspects affecting the material flow and welds quality. Such improvements are also clearly demonstrated by the increase of the strength of recent joints (up to 99% of joining efficiency) as compared to those reached in early researches (almost 47%). This article provides a comprehensive review of the recent progresses on the process fundamentals, quality assessment and the influence of process parameters on the mechanical behavior. In addition, emphasis is given to new developments and future perspectives.
The corrosion-fatigue behavior of X65 welded joints, processed by cold metal transfer (CMT) and gas metal arc welding (GMAW) backing, was examined. The application of the CMT backing process led to a ...22% increase in the corrosion-fatigue performance, which was attributed to the optimization of the microstructure (synergistic cracking-arrest ability of acicular ferrite (AF) and grain boundary ferrite (GBF)) and the reduction in the stress concentration at the weld root. Nonetheless, a lower heat input contributed to a consequent decrease in corrosion-fatigue performance. In addition, H2S corrosion fatigue was governed by the combined effect of anodic dissolution and hydrogen embrittlement.
•The corrosion-fatigue behavior of the cold metal transfer (CMT) and gas metal arc welding (GMAW) backing were compared.•The CMT backing process improves the corrosion fatigue performance by about 22% compared to the GMAW backing process.•CMT backing process improves corrosion fatigue performance by optimizing microstructure and reducing stress concentration.•The H2S corrosion-fatigue failure is governed by the combined effect of anodic dissolution and hydrogen embrittlement.
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