Arc welding

Résumé

Arc welding is a welding process that is used to join metal to metal by using electricity to create enough heat to melt metal, and the melted metals, when cool, result in a binding of the metals. It is a type of welding that uses a welding power supply to create an electric arc between a metal stick ("electrode") and the base material to melt the metals at the point of contact. Arc welding power supplies can deliver either direct (DC) or alternating (AC) current to the work, while consumable or non-consumable electrodes are used. The welding area is usually protected by some type of shielding gas (e.g. an inert gas), vapor, or slag. Arc welding processes may be manual, semi-automatic, or fully automated. First developed in the late part of the 19th century, arc welding became commercially important in shipbuilding during the Second World War. Today it remains an important process for the fabrication of steel structures and vehicles. Power supplies To supply the electric

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https://en.wikipedia.org/wiki/Arc_welding

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Welding is an important joining method for the work with metals. During the welding process, the material is heated and deforms plastically which leads a change in microstructure in the heat affected zone, to complex residual stress distributions, and distortions. The residual stresses can have a major impact, among other phenomena, on the fatigue resistance of a welded structure. The aim of this work was to develop a model with the finite element software Abaqus for the simulation of a welding process for butt welded tubes and the calculation of the resulting welding residual stress field. The residual stress field depends on several input parameters, like the geometry, the heat input, the welding speed, the material data, and the number of weld passes. The chosen dimensions of the tubes are realistic for tubular steel bridge constructions. Since, no experimental welding procedures were conducted, the welding parameters like the heat input and the welding speed were estimated in order to obtain a realistic temperature distribution in the weld and the heat affected zone. The assignment asked to place a main focus on the influence of the material data and the number of weld passes. Within the framework of this work, tensile tests at three different temperatures were conducted in order to find the deformational behavior of the two different steel grades S355 and S690. The results show generally good agreement with the data given by the European Standard for the structural fire design of steel structures [11], that is noted Eurocode 3 (EC3) in the course of this work. According to the test results, the yield strength at room temperature are underestimated by the Eurocode 3. Based on the experiments and the data given in the Eurocode 3, the influence of the mechanical properties were studied in several Abaqus models. For the description of the temperature dependent material behavior, a bilinear stress-strain curve was implemented. The resulting stress distributions show a similar trend, but the offset values between the stress curves of two models are dependent on the position in circumferential direction and the distance in axial direction. During the literature study, different welding simulation programs were compared. With specific welding simulation programs, mostly two-dimensional models can be realised. A major advantage of these programs is, that phase transformations can easily be considered and therefore a more realistic material model can be implemented provided that the temperature dependant behavior of the different microstructural phases are known. The influence of the number of weld passes was studied by comparing a single- and a multi-pass model with the material data from the Eurocode 3. The total heat input and the welding speed was the same for all the models. The tendency of the resulting stress distributions varied greatly and therefore implies that a multi-pass model cannot be approximated by a single-pass model.

2011

Chargement

Multiscale, Multiphysics Numerical Modeling of Fusion Welding with Experimental Characterization and Validation

Jonathan Dantzig, Jun Liu, Yu Xie

Various physical interfacial phenomena occur during the process of welding and influence the final properties of welded structures. As the features of such interfaces depend on physics that resolve at different spatial scales, a multiscale and multiphysics numerical modeling approach is necessary. In a collaborative research project Modeling of Interface Evolution in Advanced Welding, a novel strategy of model linking is employed in a multiscale, multiphysics computational framework for fusion welding. We only directly link numerical models that are on neighboring spatial scales instead of trying to link all submodels directly together through all available spatial scales. This strategy ensures that the numerical models assist one another via smooth data transfer, avoiding the huge difficulty raised by forcing models to attempt communication over many spatial scales. Experimental activities contribute to the modeling work by providing valuable input parameters and validation data. Representative examples of the results of modeling, linking and characterization are presented.

Springer Verlag2013

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This paper presents a 3D thermo-mechanical model of arc-welding applied to tubular K-joints susceptible to fatigue cracking. The 3D torch trajectory is reproduced to simulate both temperatures and stresses during welding and ultimately the 3D residual stress distribution after cooling. The influence of latent heat, of the increase of thermal conductivity to simulate the fluid convection within the weld pool, the activation of finite elements to simulate the use of filler wire and the number of passes on as-welded residual stresses is assessed using ABAQUS. Actions taken to simplify the problem and reduce the computation time are presented and discussed. Comparisons of fusion zones obtained numerically and using optical macrographs as well as comparisons between calculated and measured residual stresses are presented. This numerical analysis highlights high tensile residual stresses occurring at the gap zone which is the most critical location where fatigue cracks initiate and propagate in tubular bridge K-joints.

TU-Graz2013

Chargement

2011