TY - JOUR A1 - Perret, William A1 - Thater, R. A1 - Alber, U. A1 - Schwenk, Christopher A1 - Rethmeier, Michael T1 - Approach to assess a fast welding simulation in an industrial envrionment - application for an automotive welded part N2 - Fusion welding processes are widely used for joining metal structures, such as pipes, ships, and cars. In general, these joining processes offer a very good compromise between reliability, safety, cost and maintenance which are important issues in the current economical context. The negative heat effects of welding, i.e. distortions and residual stresses of the welded parts, are well known and many researches in this field have already been done in the last decades in order to minimize them. On the experimental side, many sophisticated procedures have become state of the art to deal with this problem. On the computational side, the improvement of the simulation algorithms and the computing power enables the simulations of many physical phenomena occurring during the welding process. The implementation of welding simulation techniques is nevertheless not an easy task and often associated with expert knowledge which hinders their global application in an industrial environment. This paper is focused on the industrial requirements of a welding simulation software with special respect to the needs of the automotive industry. The necessary information to run a welding simulation and the expectations of a weld specialist without deep knowledge in numerical methods are investigated. These expectations are tested on an automotive welded assembly with a commercially available welding simulation software designed especially for the needs of the automotive industry. A welding experiment is done and the measured temperature distributions and distortions serve as reference to validate the simulation results. The result quality of the simulations of temperature fields and distortions is in best agreement with experimental data. The workflow is well adapted for the considered industrial requirements and the time-tosolution as well as the computational costs are acceptable, whereas the efficient calibration of the heat input model is still a point which will be further investigated in current and future research works. KW - Welding simulation KW - Distortion KW - Automotive industry KW - Work-flow KW - Time-to-solution KW - Simufact.welding PY - 2011 DO - https://doi.org/10.1007/s12239-011-0102-0 SN - 1229-9138 VL - 12 IS - 6 SP - 895 EP - 901 PB - KSAE / Springer CY - Seoul / Berlin ; Heidelberg AN - OPUS4-25139 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pittner, Andreas A1 - Weiß, D. A1 - Schwenk, Christopher A1 - Rethmeier, Michael T1 - Fast temperature field generation for welding simulation and reduction of experimental effort N2 - The quality of welding processes is governed by the occurring induced distortions yielding an increase in production costs due to necessary reworking. Especially for more complex specimens, it is difficult to evaluate the optimal configuration of welding sequences in order to minimize the distortion. Even experienced welding operators can solve this task only by trial and error which is time and cost consuming. In modern engineering the application of welding simulation is already known to be able to analyse the heat effects of welding virtually. However, the welding process is governed by complex physical interactions. Thus, recent weld thermal models are based on many simplifications. The state of the art is to apply numerical methods in order to solve the transient heat conduction equation. Therefore, it is not possible to use the real process parameters as input for the mathematical model. The model parameters which allow calculating a temperature field that is in best agreement with the experiments cannot be defined directly but inversely by multiple simulations runs. In case of numerical simulation software based on finite discretization schemes this approach is very time consuming and requires expert users. The weld thermal model contains an initial weakness which has to be adapted by finding an optimal set of model parameters. This process of calibration is often done against few experiments. The range of model validity is limited. An extension can be obtained by performing a calibration against multiple experiments. The focus of the paper is to show a combined modelling technique which provides an efficient solution of the inverse heat conduction problem mentioned above. On the one hand the inverse problem is solved by application of fast weld thermal models which are closed form solutions of the heat conduction equation. In addition, a global optimization algorithm allows an automated calibration of the weld thermal model. This technique is able to provide a temperature field automatically that fits the experimental one with high accuracy within minutes on ordinary office computers. This fast paradigm permits confirming the application of welding simulation in an industrial environment as automotive industry. On the other hand, the initial model weakness is compensated by calibrating the model against multiple experiments. The unknown relationship between model and process parameters is approximated by a neural network. The validity of the model is increased successively and enables to decrease experimental effort, For a test case, it is shown that this approach yields accurate temperature fields within very short amount of time for unknown process parameters as input data to the model contributing to the requirement to construct a substitute system of the real welding process. KW - Heat flow KW - Neural networks KW - Simulating KW - Temperature KW - Welding PY - 2011 SN - 0043-2288 SN - 1878-6669 VL - 55 IS - 09-10 SP - 83 EP - 90 PB - Springer CY - Oxford AN - OPUS4-24603 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kromm, Arne A1 - Brauser, Stephan A1 - Kannengießer, Thomas A1 - Rethmeier, Michael T1 - High-energy synchrotron diffraction study of a transformation induced plasticity steel during tensile deformation N2 - Energy-dispersive x-ray diffraction offers the possibility for measurement and evaluation of diffraction spectra containing information of various diffraction lines of all contributing crystalline phases of a material. Combined strain imaging and diffraction analysis was conducted during the tensile test of a low alloyed transformation-induced plasticity (TRIP) steel in order to investigate the transformation induced plasticity, strain hardening, and load partitioning effects. Optical strain imaging allowed for determination of localized true strains from three-dimensional deformations measured in situ. High-energy synchrotron radiation has permitted diffraction analysis in transmission mode to gather information from the material interior. Phase-specific stress evolution during loading could be observed applying the sin2ψ technique during certain load steps. The strains of the individual lattice planes were determined in different locations under varying angles between loading and perpendicular direction. Using energy-dispersive methods it was also possible to determine the transformation behaviour during elastic and plastic regime taking into account a large number of diffraction lines. The results show that the approach practised here enables one to pull together macroscopic and phase-specific microscopic material behaviour in order to improve existing models for prediction of complex load situations. KW - EDXRD KW - Transformation-induced plasticity (TRIP) KW - Residual stress KW - Synchrotron KW - Martensite transformation PY - 2011 DO - https://doi.org/10.1177/0309324711403969 SN - 0309-3247 SN - 2041-3130 VL - 46 IS - 7 SP - 581 EP - 591 PB - Sage CY - London AN - OPUS4-24604 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schempp, Philipp A1 - Schwenk, Christopher A1 - Rethmeier, Michael A1 - Cross, C.E. T1 - Weld metal grain refinement of aluminium alloy 5083 through controlled additions of Ti and B N2 - Kornfeinung im Schweißgut kann die mechanischen Eigenschaften der Schweißnaht und die Schweißeignung des Grundwerkstoffs deutlich verbessern. Eine Möglichkeit korngefeintes Schweißgut zu erreichen, ist das Versetzen des Schmelzbades mit kornfeinenden Mitteln. In dieser Studie wird gezeigt wie Titan- und Borzusätze Korngröße und -struktur von WIG-Schweißnähten der Al-Legierung 5083 (Al Mg4,5Mn0,7) beeinflussen. Dazu wurden in einem Gießprozess stäbchenförmige Einlagen hergestellt, die aus Grundwerkstoff und definierten Zusätzen der Kornfeinungslegierung Al Ti5B1 bestanden. Sie wurden als Ersatz für einen Schweißzusatzwerkstoff in einer Nut im Grundwerkstoff untergebracht und im WIG-Verfahren überschweißt. Durch die Steigerung des Titan- und Borgehalts im Schweißgut konnte dessen mittlere Korngröße deutlich verringert werden. Außerdem wurde eine Änderung der Kornstruktur beobachtet. Die Ergebnisse können als Grundlage genutzt werden, um die empfohlene chemische Zusammensetzung von Schweißzusätzen für Lichtbogenschweißen von Aluminium anzupassen. KW - Aluminium-Legierung 5083 KW - Kornfeinung KW - WIG-Schweißen PY - 2011 DO - https://doi.org/10.3139/120.110265 SN - 0025-5300 VL - 53 IS - 10 SP - 604 EP - 609 PB - Hanser CY - München AN - OPUS4-24654 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schwenk, Christopher A1 - Rethmeier, Michael T1 - Standards and guidelines for numerical welding simulation PY - 2011 SN - 1001-1382 VL - 459 IS - 9 SP - 5 EP - 8 PB - Jixie Dianzi Gongye Bu * Harbin Hanjie Yanjiusuo AN - OPUS4-24644 LA - zho AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Avilov, Vjaceslav A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Numerical simulation of full-penetration laser beam welding of thick aluminium plates with inductive support N2 - A three-dimensional laminar steady-state numerical model was developed to investigate the influence of an alternating current (ac) magnetic field during high-power full-penetration laser welding on the weld pool dynamics and weld cross section of a 20 mm thick aluminium plate in flat position. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential equations were solved iteratively with the commercial finite element software COMSOL Multiphysics using temperature-dependent material properties up to evaporation temperature. Thermocapillary convection at the weld pool surfaces, natural convection and latent heat of solid–liquid phase transition were taken into account in this model. Solidification was modelled by the Carman–Kozeny equation for porous media morphology. The ac magnet was mounted on the root side of the weld specimen. The magnetic field was aligned perpendicular to the welding direction. The flow pattern in the melt and thus also the temperature distribution were significantly changed by the application of oscillating magnetic fields. It was shown that the application of an ac magnetic field to laser beam welding allows for a prevention of the gravity drop-out. The simulation results are in good qualitative agreement with the experimental observations. KW - Electromagnetic weld pool support KW - Laser beam welding KW - Lorentz force KW - Marangoni stresses KW - Natural convection PY - 2012 DO - https://doi.org/10.1088/0022-3727/45/3/035201 SN - 0022-3727 SN - 1361-6463 VL - 45 IS - 3 SP - 035201-1 - EP - 035201-13 PB - IOP Publ. CY - Bristol AN - OPUS4-25286 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ullner, Christian A1 - Brauser, Stephan A1 - Subaric-Leitis, Andreas A1 - Weber, Gert A1 - Rethmeier, Michael T1 - Determination of local stress-strain properties of resistance spot-welded joints of advanced high-strength steels using the instrumented indentation test N2 - For spot-welded joints, the resistance to mechanical stress depends on the local strength properties and gradients in the weld area. The commonly used methods for investigating the stress–strain behaviour across the weld area are connected with a high level of sample preparation and with considerable limitations in local resolution. A promising method for determining locally resolved stress–strain curves is the instrumented indentation test in connection with the method of representative stress and strain (RS) and the method of artificial neural networks (NNs). The stress–strain properties of the weld nugget and the base metal determined by these two methods are compared and discussed, additionally in relation to the stress–strain curves obtained from the tensile test. The measured Vickers hardness across the weld area is compared with the evaluated local stress–strain properties. Three steels used in automobile manufacturing are investigated: mild steel DC04 and two advanced high-strength steels (TRIP steel HCT690T and martensitic steel HDT 1200M). The results of the two methods (RS and NN) show good correspondence for the base metal area but some significant differences for the weld nugget. Comparing the data across the weld area, no evidence of the presence of residual stress (which would influence the results) was found. KW - Ortsaufgelöst KW - Lokale Spannungs-Dehnungskurven KW - Punktschweißverbindung KW - Instrumentierte Eindringprüfung PY - 2012 DO - https://doi.org/10.1007/s10853-011-5936-3 SN - 0022-2461 SN - 1573-4803 VL - 47 IS - 3 SP - 1504 EP - 1513 PB - Springer Science + Business Media B.V. CY - Norwell, Mass. AN - OPUS4-25276 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Petrovskii, V.N. A1 - Uspenskii, S.A. A1 - Shcheglov, Pavel A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Investigation of a vapor-plasma welding torch induced by a high-power ytterbium fiber laser KW - Laser welding KW - Condensation KW - Diagnostic of the torch PY - 2011 SN - 2079-5629 VL - 2 IS - 2 SP - 159 EP - 165 PB - MAIK Nauka AN - OPUS4-24811 LA - rus AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Shcheglov, Pavel A1 - Uspenskii, S.A. A1 - Gumenyuk, Andrey A1 - Petrovskii, V.N. A1 - Rethmeier, Michael A1 - Yermachenko, V. M. T1 - Plume attenuation of laser radiation during high power fiber laser welding N2 - The results of an in-situ plume-laser interaction measurement during welding of mild steel with a 5 kW ytterbium fiber laser are reported. A measurement of the attenuation of probe laser beam passing through the plume has allowed to estimate the plume characteristics like the size of the extinction area and the spatial distribution of the extinction coefficient. The power loss of the fiber laser radiation propagating through the whole plume length was calculated. Together with a measured temporal characteristics of extinction the result indicates a significant decreasing of the laser radiation stability, which can lead to the formation of the macroscopic welding defects. KW - Laser welding KW - Plume KW - Beam attenuation KW - Particles PY - 2011 DO - https://doi.org/10.1002/lapl.201110010 SN - 1612-2011 VL - 8 IS - 6 SP - 475 EP - 480 PB - Wiley-VCH CY - Berlin AN - OPUS4-24812 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Tölle, Florian A1 - Gumenyuk, Andrey A1 - Backhaus, A. A1 - Olschok, S. A1 - Rethmeier, Michael A1 - Reisgen, U. T1 - Welding residual stress reduction by scanning of a defocused beam N2 - The residual stresses in narrow electron or laser beam welds with high stress gradients are decreased without any contact surfaces or additional equipment by applying the welding beam after welding in a defocused mode for heating the material regions in a certain distance from the weld on both sides. In case of electron beam application, the beam is positioned and focused by the electromagnetic coil with high frequency. In case of laser beam application a laser scanner optics enables fast positioning by an optomechanic beam deflection, while defocusing of the laser beam is obtained by increasing the distance between scanner optics and workpiece. Dependent on the component geometry and on the beam power different process parameters are used. The adjustable process parameters are the radius and the power of the defocused beam and the transversal and longitudinal distances between the welding and the defocused beam. The mechanism and the influence of the process parameters are investigated by FEM-simulation and a number of experiments on a ferritic steel S355J2+N with 5 mm thickness. FEM-simulation is used to reduce the matrix of process parameters for the experiments. The best experimental result shows a stress reduction of about 70%. KW - Residual stresses KW - Stress reduction KW - High energy beam welding KW - Post-weld heat treatment KW - Laser scanner optics PY - 2012 DO - https://doi.org/10.1016/j.jmatprotec.2011.07.019 SN - 0924-0136 SN - 1873-4774 VL - 212 IS - 1 SP - 19 EP - 26 PB - Elsevier CY - Amsterdam AN - OPUS4-24787 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Heinze, Christoph A1 - Schwenk, Christopher A1 - Rethmeier, Michael T1 - The effect of tack welding on numerically calculated welding-induced distortion N2 - A single-layer pulsed gas metal arc weld of structural steel S355J2+N with a thickness of 5 mm is experimentally and numerically investigated. Two tack welds are considered in the numerical simulation into two different ways. First, the tack welds are represented by elements belonging to the initial material. This implies that the 'tack weld material' was not exposed to any thermal load or phase transformation before actual welding was performed. The weld seam is shortened and there is an influence on the stiffness of the whole structure affecting the calculation result. Secondly, the tack welds were simulated as conducted in the experimental welding procedure. The cases considering tack welding are compared to a simulation neglecting tack welding and to the experimental results. The influence of tack welds on the calculated welding-induced distortion is clarified and a contribution to an improved simulation-based prediction of welding-induced distortion is possible by modeling tack welding according to the realistic fabrication procedure. KW - Welding simulation KW - Welding-induced distortion KW - Gas metal arc welding KW - Tack welding PY - 2012 DO - https://doi.org/10.1016/j.jmatprotec.2011.09.016 SN - 0924-0136 SN - 1873-4774 VL - 212 IS - 1 SP - 308 EP - 314 PB - Elsevier CY - Amsterdam AN - OPUS4-24820 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gaul, Holger A1 - Brauser, Stephan A1 - Weber, Gert A1 - Rethmeier, Michael T1 - Methods to obtain weld discontinuities in spot-welded joints made of advanced high-strength steels N2 - Resistance spot welding is the major joining technique in mass car production. This applies in particular to high-strength steel and advanced high-strength steel (AHSS) joining of thin sheet steel components for lightweight body shell structures. Joining of AHSS in mass production might lead to weld discontinuities under certain circumstances. Those discontinuities in form of cracks might be an initial start of cracking in the spot-welded joints regarding fatigue loads. It is of great interest to figure out, if, in comparison to specimens without weld discontinuities, the crack initiating point changes and if the fatigue resistance might be reduced by the discontinuities. In this contribution, an overview of potential discontinuities is given. Their possible causes are discussed and means for their detection are highlighted. Among the possible causes of weld discontinuities, two major groups are distinguished: the welding parameters as primary influences in the welding process, and the production-specific influences as secondary ones. With emphasis on major cracks penetrating the weld nugget, these influences are analysed. Finally, a combination of extreme welding parameters with production-specific influences is chosen in order to establish a method which enables the preparation of fatigue test specimens with reproducible major cracks in different locations of the spot-welded joints. This method is than applied in order to prepare spot weld specimens for fatigue tests. KW - Cracking KW - Defects KW - Fatigue loading KW - High strength steels KW - Resistance spot welding PY - 2011 SN - 0043-2288 SN - 1878-6669 VL - 55 IS - 11/12 SP - 99 EP - 106 PB - Springer CY - Oxford AN - OPUS4-25026 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schwenk, Christopher A1 - Rethmeier, Michael T1 - Material properties for welding simulation - measurement, analysis, and exemplary data N2 - Welding is a key technology in the area of industrial production due to its flexibility and efficiency. However, new materials and welding techniques necessitate permanent research activities in order to keep up with the demands. A detailed knowledge about the process itself and the heat effects of welding, e.g., temperatures, distortions, and stresses, is the basis for a target-oriented optimization instead of a trial-and-error approach. Numerical welding simulation is a powerful tool to meet these demands. Complementary to an experimental investigation, it enables the analysis of the specimen during the welding process, commonly known as computational welding mechanics (CWM). Whereas simulation is nowadays a common tool in different development processes, the modeling of welding still remains difficult because of the multiple physical effects taking place. One of the most important problems for the user is the lack of knowledge about the material properties as input data for the simulation. Furthermore, any scattering of the data causes uncertainties that can have major effects on the calculations. The objective of this paper is to give an overview about the experimental determination and analysis of the material properties needed as input data for a welding simulation. The measurement techniques and the occurring deviations of the results are discussed. Additionally, the collected data for three representative alloys (dual-phase steel, austenitic steel, precipitation-hardenable aluminum alloy) are analyzed. Finally, the temperature-dependent thermophysical and thermomechanical material properties for these three alloys are given in a ready-to-use format for a numerical welding simulation. KW - Thermophysical material properties KW - Thermomechanical material properties KW - Experimental determination KW - Numerical welding simulation PY - 2011 SN - 0043-2296 SN - 0096-7629 VL - 90 SP - 220-s EP - 227-s PB - American Welding Society CY - New York, NY AN - OPUS4-25028 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Perret, William A1 - Thater, Raphael A1 - Alber, U. A1 - Schwenk, Christopher A1 - Rethmeier, Michael T1 - Case study for welding simulation in the automotive industry N2 - Welding is one of the most widely used joining processes in structural applications, like in car body production in the automotive industry. It is well-known that distortions and residual stresses occur during and after the welding process. Many procedures exist to decrease these negative heat effects of welding, but are often coupled with highly cost intensive experiments. For several decades, simulation models have been developed to understand and predict the heat effects of welding and to reduce experimental effort. In the production planning of various Original Equipment Manufacturers (OEM), some simulation tools are already well established, e.g. for crash test, forming or casting simulations. For welding, the demand is high but the implementation of welding simulation software is still not established yet. Welding is a complex process and the development of a flexible simulation tool, which produces good simulation results without expert knowledge in simulation, is not an easy task. In this paper, a welded assembly from the automotive industry has been simulated and compared to experimental data. Temperature fields and transient distortion distributions have been measured with thermocouples and with an optical 3D deformations analysis tool, respectively. The simulation has been run with a commercially available welding simulation software. The simulated temperature fields match the numerical ones perfectly. The simulated distortions are also qualitatively in best agreement with the experimental ones. Quantitatively, a difference of approximately 20 % between the simulated and the measured distortions is visible; this is acceptable considering the simplifications and assumptions of the simulation model. The global time to solution to get these results without expert knowledge in welding simulation was between 4 and 6 weeks, which is a reasonable time frame for an industrial application of welding simulation. KW - Automobiles KW - Distortion KW - Simulating KW - Temperature KW - Welding KW - Aluminium alloys KW - Al Mg Si alloys KW - Automobile engineering KW - Finite elements analysis KW - Mathematical models KW - MIG welding KW - Residual stresses KW - Vehicle bodies PY - 2011 DO - https://doi.org/10.1007/BF03321546 SN - 0043-2288 SN - 1878-6669 VL - 55 IS - 11/12 SP - 89 EP - 98 PB - Springer CY - Oxford AN - OPUS4-25029 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Heinze, Christoph A1 - Schwenk, Christopher A1 - Rethmeier, Michael T1 - Numerical calculation of residual stress development of multi-pass gas metal arc welding under high restraint conditions N2 - During welding, residual stresses build-up created by the steep thermal gradient that occurs in the weld zone from localized heating and cooling, and phase transformations appearing in low-alloyed structural steel is inevitable. Welding of rather simple test plates do not cover the actual structural effects, which have to be considered during real component welding. However, the resulting welding-induced residual stress state is highly influenced by the structural characteristics, i.e. restraint conditions, of the welded construction. Therefore, a unique large-scale testing facility providing a specific shrinkage restraint while welding and subsequent cooling was used for the present investigations. Hereby, a six bead multi-pass gas metal arc weld of 20 mm thick structural steel S355J2 + N was welded under shrinkage restraint. The residual stresses were experimentally and numerically investigated, and compared to an analysis of plates welded under force-free support and free shrinkage conditions. The experimentally determined and calculated residual stresses using both 2D and 3D numerical models are in a good agreement. Furthermore, the influence of a shrinkage restraint on the residual stress distribution is both experimentally and numerically shown for the present test set-up. KW - Welding KW - Shrinkage KW - Ferrous metals and alloys PY - 2011 DO - https://doi.org/10.1016/j.matdes.2011.09.021 SN - 0261-3069 SN - 0264-1275 VL - 35 SP - 201 EP - 209 PB - Elsevier Science CY - Oxford AN - OPUS4-25036 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weber, Gert A1 - Brauser, Stephan A1 - Gaul, Holger A1 - Rethmeier, Michael T1 - Study of fatigue behavior for spot welded tensile shear specimens of advanced high strength steels N2 - For automotive body-in-white applications the influence of manufacture-related gaps between the steel sheets and also of manufacture-related surface cracks on the fatigue behavior of tensile shear specimens for spot welded TRIP steel was analyzed. It was shown that gaps between the steel sheets reduce the fatigue strength, whereas the fatigue behavior is neither influenced by cracks in the electrode indentation area nor in the heat effected zone. PY - 2012 DO - https://doi.org/10.1002/srin.201100286 SN - 1611-3683 SN - 0177-4832 VL - 83 IS - 10 SP - 988 EP - 994 PB - Verl. Stahleisen CY - Düsseldorf AN - OPUS4-27632 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Heinze, Christoph A1 - Pittner, Andreas A1 - Rethmeier, Michael A1 - Babu, S. S. T1 - Dependency of martensite start temperature on prior austenite grain size and its influence on welding-induced residual stresses N2 - Austenite grain growth during welding is a critical factor for controlling weld microstructure in addition to nominal composition and thermal cycles. Recently, experimental data suggesting a decrease in martensite start temperature with a decrease in prior austenite grain size has been published. However, the actual sensitivity of this phenomenon on residual stresses evolution in the heat-affected zone has not been investigated, yet. Therefore, a numerical model was modified to consider this phenomenon. Numerical simulations were performed for welding of a low-alloy structural steel with minimum yield strength of 355 MPa (S355J2+N) and a heat-resistant steel P91 or 9Cr–1Mo, respectively. The results clarify the influence of prior austenite grain size on the residual stress development and show the importance martensite transformation temperatures and final martensite fraction. Consequently, the residual stress evolution of P91, which completely transforms to martensite while cooling, based on the enhanced model leads to maximum stress differences of 200 MPa in the heat-affected zone. KW - Prior austenite grain size KW - Martensite start temperature KW - Welding-induced residual stress KW - Numerical simulation KW - Gas metal arc welding PY - 2013 DO - https://doi.org/10.1016/j.commatsci.2012.11.058 SN - 0927-0256 VL - 69 SP - 251 EP - 260 PB - Elsevier CY - Amsterdam AN - OPUS4-27633 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brauser, Stephan A1 - Rethmeier, Michael A1 - Pepke, Lutz-Alexander A1 - Weber, Gert T1 - Influence of production-related gaps on strength properties and deformation behaviour of spot welded trip steel HCT690T N2 - In this study, the influence of production-related gaps on the shear tension strength and fatigue performance was investigated for resistance spot welded TRIP steel HCT690. Furthermore, the local strain distribution in shear tension test was calculated by the digital image correlation technique (DIC). The static shear tension strength was found to be almost independent of gaps up to 3 mm. The maximum local strain in the spot weld region however decreases depending on which sample side (deformed or undeformed) is considered. In addition, it has been ascertained that gaps of 3 mm lead to a significant drop in fatigue life compared to gap-free shear tension samples. This fact could be attributed to decreased stiffness, higher transverse vibration and higher rotation (θ) between the sheets as well as increased local stress calculated by 2 dimensional FE simulation. KW - Deformation KW - Fatigue life KW - Finite element analysis KW - Gap KW - Resistance spot welding KW - Shear strength PY - 2012 SN - 0043-2288 SN - 1878-6669 VL - 56 IS - 03-04 SP - 115 EP - 125 PB - Springer CY - Oxford AN - OPUS4-27590 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Avilov, Vjaceslav A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - About the influence of a steady magnetic field on weld pool dynamics in partial penetration high power laser beam welding of thick aluminium parts N2 - A multi-physics numerical model was developed to investigate the influence of a steady magnetic field aligned perpendicular to the welding direction during partial penetration high power laser beam welding of aluminium in downhand position. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential equations were successfully solved with the finite element differential equation solver COMSOL Multiphysics 4.2. The implemented material model used temperature-dependent properties up to evaporation temperature. Marangoni convection in the surface region of the weld pool, natural convection due to the gravitational field and latent heat of solid–liquid phase transition were taken into account. Solidification was modelled by the Carman–Kozeny equation for porous media morphology. The flow pattern in the melt as well as the weld bead geometry were significantly changed by the induced Lorentz force distribution in the liquid metal. It reveals that the application of a steady magnetic field to laser beam welding with corresponding Hartmann numbers Ha2 ≈ 104 allows for a suppression of the characteristic wineglass-shape of the weld cross section caused by thermocapillary flow. The numerical results are in good agreement with experimental results obtained with welding of AlMg3 with a 16 kW disc laser. The steady magnetic field was delivered by permanent magnets mounted on both lateral sides of the weld specimen. The maximum magnetic flux density was around 500 mT. It shows, that the applied magnetic field has a predominant dissipating effect on the weld pool dynamics independently of its polarity. KW - Electromagnetic weld pool control KW - Hartmann effect KW - Laser beam welding KW - Lorentz force KW - Marangoni flow KW - Natural convection PY - 2013 DO - https://doi.org/10.1016/j.ijheatmasstransfer.2013.01.015 SN - 0017-9310 VL - 60 SP - 309 EP - 321 PB - Elsevier CY - Amsterdam AN - OPUS4-27655 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Babu, N. K. A1 - Brauser, S. A1 - Rethmeier, Michael A1 - Cross, C.E. T1 - Characterization of microstructure and deformation behaviour of resistance spot welded AZ31 magnesium alloy N2 - Resistance spot welds were prepared on 3 mm thick sheets of continuous cast and rolled AZ31 magnesium alloy. The microstructure and composition analysis of weld nugget, heat affected zone (HAZ) and base metal were examined using optical and scanning electron microscopy (HR-SEM and EDS/X). The resistance spot welded magnesium alloy joints consist mainly of weld nugget and HAZ. The nugget contains two different structures, i.e. the cellular-dendritic structure at the edge of the nugget and the equiaxed dendritic structure in the centre of the nugget. The structure transition is attributed to the changes of solidification conditions. In the HAZ, grain boundary melting occurred and grain boundaries became coarse. It has been shown that hardness reduction in the weld nugget and HAZ compared with base metal is evident due to dendritic microstructure and grain growth, respectively. The results showed that spot welded joints have failed in interfacial mode under torsion and tensile–shear loading conditions. Digital image correlation during tensile–shear testing showed that low surface strains occur in the interfacial failure mode, because fracture and deformation happened primarily in the nugget area. KW - Resistance spot welding KW - AZ31 magnesium alloy KW - Microstructure KW - Hardness KW - Torsion KW - Tensile–shear PY - 2012 DO - https://doi.org/10.1016/j.msea.2012.04.021 SN - 0921-5093 SN - 1873-4936 VL - 549 SP - 149 EP - 156 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-25924 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -