TY - JOUR A1 - Huo, Wenjie A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael A1 - Wolter, Katinka T1 - Detection of solidification crack formation in laser beam welding videos of sheet metal using neural networks N2 - AbstractLaser beam welding has become widely applied in many industrial fields in recent years. Solidification cracks remain one of the most common welding faults that can prevent a safe welded joint. In civil engineering, convolutional neural networks (CNNs) have been successfully used to detect cracks in roads and buildings by analysing images of the constructed objects. These cracks are found in static objects, whereas the generation of a welding crack is a dynamic process. Detecting the formation of cracks as early as possible is greatly important to ensure high welding quality. In this study, two end-to-end models based on long short-term memory and three-dimensional convolutional networks (3D-CNN) are proposed for automatic crack formation detection. To achieve maximum accuracy with minimal computational complexity, we progressively modify the model to find the optimal structure. The controlled tensile weldability test is conducted to generate long videos used for training and testing. The performance of the proposed models is compared with the classical neural network ResNet-18, which has been proven to be a good transfer learning model for crack detection. The results show that our models can detect the start time of crack formation earlier, while ResNet-18 only detects cracks during the propagation stage. KW - Artificial Intelligence KW - Software PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-586116 DO - https://doi.org/10.1007/s00521-023-09004-y SN - 0941-0643 VL - 35 IS - 34 SP - 24315 EP - 24332 PB - Springer Science and Business Media LLC AN - OPUS4-58611 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hartwig, Philipp A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Scheunemann, Lisa A1 - Schröder, Jörg A1 - Rethmeier, Michael T1 - A Physically Motivated Heat Source Model for Laser Beam Welding N2 - In this contribution, we present a physically motivated heat source model for the numerical modeling of laser beam welding processes. Since the calibration of existing heat source models, such as the conic or Goldak model, is difficult, the representation of the heat source using so-called Lamé curves has been established, relying on prior Computational Fluid Dynamics (CFD) simulations. Lamé curves, which describe the melting isotherm, are used in a subsequent finite-element (FE) simulation to define a moving Dirichlet boundary condition, which prescribes a constant temperature in the melt pool. As an alternative to this approach, we developed a physically motivated heat source model, which prescribes the heat input as a body load directly. The new model also relies on prior CFD simulations to identify the melting isotherm. We demonstrate numerical results of the new heat source model on boundary-value problems from the field of laser beam welding and compare it with the prior CFD simulation and the results of the Lamé curve model and experimental data. KW - Welding simulation KW - Heat source models KW - Laser beam welding KW - Thermal analysis PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-600899 DO - https://doi.org/10.3390/met14040430 VL - 14 IS - 4 SP - 1 EP - 26 PB - MDPI CY - Basel AN - OPUS4-60089 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Artinov, Antoni A1 - Karkhin, V. A1 - Bakir, Nasim A1 - Meng, Xiangmeng A1 - Bachmann, Marcel A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Lamé curve approximation for the assessment of the 3D temperature distribution in keyhole mode welding processes N2 - A novel approach for the reconstruction of an equivalent volumetric heat source from a known weld pool shape is proposed. It is based on previously obtained weld pool geometries from a steady-state thermo-fluid dynamics simulation. Hereby, the weld pool dimensions are obtained under consideration of the most crucial physical phenomena, such as phase transformations, thermo-capillary convection, natural convection, and temperature-dependent material properties. The algorithm provides a time and calibration efficient way for the reproduction of the weld pool shape by local Lamé curves. By adjusting their parameters, the identification of the finite elements located within the weld pool is enabled. The heat input due to the equivalent heat source is assured by replacing the detected nodes’ temperature by the melting temperature. The model offers variable parameters making it flexible and adaptable for a wide range of workpiece thicknesses and materials and allows for the investigation of transient thermal effects, e.g., the cooling stage of the workpiece. The calculation times remain acceptably short especially when compared to a fully coupled process simulation. The computational results are in good agreement with performed complete-penetration laser beam welding experiments. KW - Lamé curves approximation KW - Equivalent heat source KW - Thermal cycles KW - Numerical modeling KW - Keyhole mode welding PY - 2020 DO - https://doi.org/10.2351/7.0000076 VL - 32 IS - 2 SP - 022042-1 EP - 022042-8 PB - AIP Publishing AN - OPUS4-50768 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim T1 - Numerical simulation of solidification crack formation during laser beam welding of austenitic stainless steels under external load T2 - The 3rd South-East European Welding Congress Welding and Joining Technologies for a Sustainable Development and Environment CY - Timisoara, Romania DA - 2015-06-03 PY - 2015 AN - OPUS4-34400 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Determination of critical local straining conditions for solidification cracking at laser beam welding by experimental and numerical methods N2 - AbstractThe phenomenon of solidification cracking has been the subject of numerous research projects over the years. Great efforts have been made to understand the fundamentals of hot cracking. It is generally agreed that solidification cracks form in the solidification range between the liquidus and solidus temperatures under the combination of thermal, metallurgical and mechanical factors. There is still a need to determine the time‐resolved strain distribution in the crack‐sensitive region in order to analyse the local critical conditions for solidification cracking phenomena. This was a strong motivation for the development of a measurement system used in this study to estimate the local strains and strain rates in the zone where the solidification crack is expected to occur. The laser beam welding experiments were conducted using the Controlled‐Tensile‐Weldability test (CTW test) to apply an external strain condition during welding to generate solidification cracks. The CTW test is a test method for investigating the susceptibility of laser‐welded joints to solidification cracking, in which the sample can be subjected to a defined strain at a defined strain rate during welding.In combination with experimental investigations, numerical simulations provide spatially detailed and time‐dependent information about the strain development during the welding process, especially regarding the critical conditions for solidification cracking. Therefore, this tool was also used in the present study to evaluate the accuracy of measurement methods and to estimate experimentally derived values and their concrete influence on the formation of solidification cracks. By integrating experimental methods and numerical simulations, this study investigates the spatially resolved and temporally changing development of strain during welding, with a particular focus on the critical conditions that lead to the formation of solidification cracks. The use of numerical simulations serves a dual purpose by validating the accuracy of measurement methods and examining experimentally determined values for their actual influence on the formation of solidification cracks. A three‐dimensional finite element (FE) model implemented with ANSYS is used to simulate strains and stresses during welding. The credibility of the model was first established by validation using experimental temperature measurements. Subsequently, structural simulations were carried out under external load. The results of the simulations showed commendable agreement with the strain measurements performed using the developed technique. KW - Laser beam welding KW - Solidification cracking KW - FEM simulation PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-612044 DO - https://doi.org/10.1002/pamm.202400020 SN - 1617-7061 VL - 24 IS - 2 SP - 1 EP - 16 PB - Wiley AN - OPUS4-61204 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gumenyuk, Andrey A1 - Üstündağ, Ömer A1 - Pelz, Till A1 - Bakir, Nasim A1 - Gerhards, Benjamin A1 - Schleser, Markus A1 - Rethmeier, Michael T1 - Single pass laser vacuum welding of thick steel plates using electromagnetic support N2 - The increasing demand for renewable energy produced by offshore wind turbines goes along with an increased demand in the production of offshore wind turbine foundations, so called “monopiles”, which are made by joining thick metal sheets. The industrial standard of multi-layer submerged arc welding (SAW) for joining of thick metal sheets is the current bottleneck in the production of monopiles. A possible increase in productivity by the implementation of high-power laser welding in a newly developed mobile vacuum chamber (MoVac) and an electromagnetic root support is the subject of this study. Single run butt welds are performed in flat position on S355 mild steel of thicknesses up to 80 mm using a disc laser system with 1030 nm wavelength and a maximum output of 60 kW. The laser optic is fixed on the MoVac-System which is held and manipulated by an articulated robot. KW - Laser beam welding KW - Laser welding with mobile vacuum PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-612068 DO - https://doi.org/10.1016/j.procir.2024.08.145 VL - 124 SP - 418 EP - 423 PB - Elsevier BV AN - OPUS4-61206 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gumenyuk, Andrey A1 - Bakir, Nasim A1 - Rethmeier, Michael T1 - Two-colour thermography for measurement of temperature distribution in laser beam welding N2 - Solidification cracking is a frequently observed phenomenon in laser beam welding of austenitic stainless steels and other metallic alloys. Characterisation of cracking susceptibility requires knowledge of the precise and spatially resolved temperature distribution near the solidification front in the welding process. Thermography is a standard tool that provides a qualitative estimate of the 2D temperature field. The general disadvantage of this method is its dependence on the emission characteristics of the measured object. For welding applications, these can vary significantly in the temperature range above and below the melting temperature. For this purpose, we have developed a thermography-based measurement technique using a SWIR camera system in combination with two narrow bandpass filters that use the principle of two-wavelength pyrometry to estimate absolute temperature values. This technique was used to determine the temperature distributions and gradients near the solidification front of laser-welded austenitic steel. The results were validated by other measurements. KW - Laser beam welding KW - Two-colour thermography KW - Solidification cracking PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-612070 DO - https://doi.org/10.1016/j.procir.2024.08.155 VL - 124 SP - 468 EP - 471 PB - Elsevier BV AN - OPUS4-61207 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Akyel, Fatma A1 - Üstündag, Ömer A1 - Bakir, Nasim A1 - Brunner-Schwer, Christian A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Influence of heat input on cooling rates and mechanical properties of laser hybrid welded thick structural steels N2 - Laser hybrid welding presents several challenges when used to weld thick steels. A typical weld is divided into the arcdominated and laser-dominated zone. These zones lead to variations in the mechanical properties of the weld. The laserdominated zone is of particular importance regarding mechanical properties, notably Charpy impact toughness, due to the high cooling rates and the absence of filler wire. The low heat input of the laser can lead to martensitic microstructure causing hardening and deterioration of impact toughness. The high heat input of the arc can lead to grain coarsening and even loss of impact toughness. This study examines the influence of heat input on the cooling rates, microstructure and mechanical properties of single-pass laser hybrid welded steels of S355J2 and EH36 with thicknesses up to 30 mm. The experiments were performed with a 20-kW fibre laser and a contactless electromagnetic weld backing in the butt-joint configuration in 1G welding position. The cooling time was measured in three different locations near the fusion lines corresponding to different heights of the seam using a special configuration with pyrometers, collimators and optical fibres. The test specimens for the Charpy impact testing and tensile testing were extracted in three different depths. The experiments indicated that a heat input of 1.6 kJ/mm–2 kJ/mm, 2 kJ/mm–2.4 kJ/mm and 3.7 kJ/mm were recommended when single-pass laser hybrid welding of 20-, 25-, and 30-mm-thick structural steels regarding the minimum requirements of the mechanical properties, respectively. KW - Laser hybrid welding KW - Heat input KW - Mechanical properties KW - Charpy impact toughness KW - Cooling rate PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-625282 DO - https://doi.org/10.1007/s40194-025-01924-8 SN - 1878-6669 SP - 1 EP - 15 PB - Springer CY - United Kingdom AN - OPUS4-62528 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Investigation of solidification cracking susceptibility of laser welded joints of austenitic stainless steels N2 - Laser welding is a widely established manufacturing process in many industry sectors. Solidification cracking represents one of the most inadequately solved problems in welding and has major economic implications. The avoidance of hot crack forms for most fusion welding processes poses a key challenge for an important range of metallic construction materials and affects not only the manufacturers of welding equipment and material manufacturers, but also a large number of customers using welding technologies, as well as welding technical standardization and research. Solidification cracking susceptibility was examined with the help of the Controlled Tensile Weldability Test (CTW) developed by Federal Institute for Materials Research and Testing (BAM), Berlin. The test is based on the fact that hot crack formation depends on a critical strain that emerges within a critical temperature range, the so called brittle temperature range (BTR). Using this test and defined investigation programme a centreline solidification crack was generated. By controlling the applied strain during the laser beam welding process, it was possible to determine the critical strain and strain rate that led to solidification cracking formation. The hot cracking susceptibility of the tested stainless steels was qualified and quantified. The results demonstrate that the crack length increases with increasing applied strain. Furthermore, the strain rate has a significant influence on the formation of the solidification crack. T2 - 3rd International conference in Africa and Asia CY - Luxor, Egypt DA - 02.11.2015 KW - Laser beam welding KW - Hot cracking KW - Solidification cracking KW - Hot cracking test PY - 2015 SP - A-29, 1 EP - A-29, 9 AN - OPUS4-36522 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Anwendung der digitalen Bildkorrelationstechnik zur Untersuchung der Heißrissanfälligkeit laserstrahlgeschweißter Verbindungen mit dem CTW-Test N2 - In dieser Studie wurde die Heißrissanfälligkeit beim Laserstrahlschweißen für die Werkstoffe 1.4376, 1.4301 und 1.4828 mit Hilfe des CTW­ Test quantifiziert. Bei den Versuchen konnten Erstarrungsrisse in den Proben generiert werden. Zusätzlich können mit der Bildkorrelations-Technik die lokalen Dehnungen und Dehnungs­raten während des Heißrisstests gemessen wer­ den. In Verbindung mit einem externen Dioden­laser zum Beleuchten der zu messende Oberflä­che und lnterferenzfiltern an den Kameras konn­ten die DIC Messungen ohne optische Störungen durchgeführt werden. Die Ergebnisse zeigen, dass die Heißrissbildung bei einer externen Belastung von 3 % für die Stahlsorte 1.4376 zu erwarten ist. Für die Stahls­ orte 1.4301 beträgt dieser Grenzwert 2 % und 1,5 % für die Stahlgüte 1.4828. Außerdem ist zu beobachten, dass die Gesamtrisslänge mit zu­ nehmender äußerer Zugbeanspruchung steigt T2 - 35. Assistentenseminar Füge- und Schweißtechnik CY - Institut für Werkstoff- und Fügetechnik der Otto-von­ Guericke-Universität Magdeburg DA - 01.12.2014 KW - Digitale Bildkorrelationstechnik KW - Heißrissanfälligkeit KW - Untersuchung laserstrahlgeschweißter Verbindungen KW - CTW-Test PY - 2016 SN - 978-3-945023-55-6 VL - 2016/34 SP - 50 EP - 54 PB - DVS Media GmbH CY - Düsseldorf AN - OPUS4-38065 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael ED - Wieland, H.-J. ED - Brockmann, S. T1 - Investigation of solidification cracking susceptibility in laser welded H400 austenitic stainless steel using digital image correlation technique N2 - One trend in today’s structural design for automobiles is towards application of stainless Steel in addition to traditional carbon Steel. This is mainly due to the advantages offered by stainless steel to the designer, i.e. its high corrosion resistance, heat resistance, strength and formability. Welding of austenitic stainless steel involves a high risk of solidification cracking due to low melting eutectics containing different kinds of impurities and to accumulated strain behind the weld pooi in the mushy zone. As a result, the quality of stainless steel welded joints will greatly be affected which may give cause for safety concerns. The intention of this study was to investigate the hot cracking sensitivity of laser welded fully austenitic stainless steels and to determine the critical local strain and strain rate from the formation of solidification cracks. C02-laser welding experiments were conducted using the steel X8CrMnNi19-6-3 (Nirosta H400). Solidification cracking susceptibility was examined with the help of the Controlled Tensile Weldability (CTW) Test developed by BAM Federal Institute for Materials Research and Testing in Berlin. The critical strain and strain rate of solidification cracking was measured at the surface of the workpiece directed to the laser beam in the close vicinity of the weld pool by using the Digital Image Correlation (DIC) technique and diode laser as the illuminating source. T2 - SCT2014 - 4th International conference on steels in cars and trucks CY - Braunschweig, Germany DA - 15.06.2014 KW - Hot cracking KW - Stainless steels KW - Critical strains KW - Strain rates KW - Hot cracking test KW - CTW test KW - Digital image correlation PY - 2014 SN - 978-3-514-00813-7 SP - 299 EP - 307 PB - Verl. Stahleisen GmbH CY - Düsseldorf AN - OPUS4-31166 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bakir, Nasim A1 - Üstündag, Ömer A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Experimental and numerical study on the influence of the laser hybrid parameters in partial penetration welding on the solidification cracking in the weld root N2 - In this study, the influence of the welding speed, the arc power, and the laser focal position on the solidification crack formation for partial penetration laser hybrid–welded thick-walled plates was investigated. The solidification cracking in the weld root is a result of interaction between metallurgical and geometrical and thermomechanical factors. Experimentally, a direct correlation between the welding speed and the crack number was observed. That is by reducing the welding velocity, the crack number was decreased. The focal position shows also a significant influence on the crack number. By focusing the laser on the specimen surface, the crack number has been significantly diminished. The wire feed speed showed a very slight influence on the crack formation. That is due to the large distance between the critical region for cracking and the arc region. The numerical model shows a high stress concentration in the weld root for both components (vertical and transversal). Numerically, the reduced welding speed showed a strong impact on stress, as the model demonstrated a lower stress amount by decreasing the welding speed. The metallurgical factors, such as the assumed accumulation of the low-melting eutectics in the weld root, should be a contribution for solidification cracking, where the tensile stress is acting. KW - Laser hybrid welding KW - Solidification cracking KW - Partial penetration welding KW - Weld root KW - Numerical simulation PY - 2020 DO - https://doi.org/10.1007/s40194-020-00847-w VL - 64 SP - 501 EP - 511 PB - Springer AN - OPUS4-50625 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim T1 - In situ determination of the critical staining condition for solidification cracking during laser beam welding N2 - Using a novel optical measurement technique together with the OF algorithm, a two-dimensional deformation analysis during welding was conducted. The OF technique was the first of its kind to provide a measurement of the full strain field locally in the immediate vicinity of the solidification front. The local critical strain and strain rate in vicinity of the solidification front has observed 1.57%, 28 %/s, respectively. T2 - Lane 2020 CY - Online meeting DA - 07.09.2020 KW - Optical measurement technique KW - Laser beam welding KW - Solidification cracking PY - 2020 AN - OPUS4-51741 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Üstündag, Ömer A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Influence of oscillating magnetic field on the keyhole stability in deep penetration laser beam welding N2 - The stability of the keyhole decreases for deep penetrated high-power laser beam welding. The keyhole tends to collapse with increasing laser power and e.g. keyhole induced porosity can occur. This study deals with the observation of the keyhole during high-power laser beam welding in partial penetration mode by means of a high-speed camera. A butt configuration of 25 mm thick structural steel and transparent quartz glass was used for the experiments. An oscillating magnetic field was applied perpendicular to the welding direction on the root side of the steel plate. The keyhole was highlighted with a coaxial diode laser. It was ascertained that the stability of the keyhole and the weld penetration depth were increased by applying an oscillating magnetic field with an oscillating frequency of 1.2 kHz and a magnetic flux density of 50 mT. KW - Magnetic field KW - Laser beam welding KW - Keyhole stability PY - 2021 DO - https://doi.org/10.1016/j.optlastec.2020.106715 SN - 0030-3992 VL - 135 SP - 106715 PB - Elsevier Ltd. AN - OPUS4-52007 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim T1 - Investigation of hot cracking susceptibility of laser welded joints of four austenitic steels T2 - The METEC and 2nd European Steel Technology and Application Days (ESTAD) 2015 CY - Duesseldorf, Germany DA - 2015-06-15 PY - 2015 AN - OPUS4-34402 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Using the optical measuring techniques to investigate the hot cracking susceptibility laser welded joints N2 - The safety of components or constructions is of great importance in the manufacturing and processing of metallic materials. Solidification cracking as well as the weldability of materials remain still for many years a highly contentious issues, particularly with regard to the causes of the hot crack formation. Many of studies have been conducted to determine the critical condition of occurrence of the solidification cracking. In this study different digital image correlation measuring techniques in conjunction with laser diodes as the illuminating source have been employed to measure the arising strain field during the laser welding process at the surface of the workpiece directed to the laser beam in the close vicinity of the weld pool. The Controlled Tensile Weldability test (CTW) was used to apply an external tensile load during the laser beam welding in order to generate the solidification cracks. The results showed that by means of those techniques it is possible to measure the strain field without any disturbances from the intense welding light or the smoke. Additionally, the strain and the strain rate as a critical factor determining solidification crack formation can be measured and analyzed. T2 - LiM 2015 - Lasers in manufacturing conference 2015 CY - Munich, Germany DA - 22.06.2015 KW - Solidification cracking KW - Laser beam wlding KW - Optical measuring technique KW - Hot cracking test PY - 2015 SP - 1 EP - 7 AN - OPUS4-35100 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Investigation of hot crack susceptibility of laser welded joints of four austenitic steels N2 - Laser welding is a widely established manufacturing process in many industry sectors. Solidification cracking represents one of the most inadequately solved problems in welding and has major economic implications. The avoidance of hot crack is for most fusion welding processes a key challenge for an important range of metallic construction materials and affects not only the manufacturers of welding equipment and material manufacturers, but also a large number of customers using welding technologies, as well as welding standardization and research. In this study a new investigation programme has been developed to qualify the hot cracking susceptibility of a variety of austenitic stainless steels. The results show the possibility of using this technique to determinate the critical values that occur with initiation of solidification cracking during laser beam welding T2 - The METEC and 2nd European Steel Technology and Application Days CY - Düsseldorf, Germany DA - 15.06.2015 KW - Laser beam welding KW - Hot cracking KW - Solidification cracking KW - Hot cracking test PY - 2015 SP - 1 EP - 5 AN - OPUS4-36525 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Experimental study and numerical simulation of hot crack formation for novel laser weldability test. N2 - Laser beam welding is a widely established manufacturing process in several industries. The solidification cracking seriously effecting the safety of welded joints could arise during the beam welding of stainless steels caused by high solidification rates. In this study the controlled tensile weldability test (CTW) was used to investigate the solidification cracking susceptibility the fully austenitic stainless steels CrMnNi (1.4376), CrNi (1.4301), CrNiMo (1.4404) and CrNiSi (1.4828) during laser beam welding. The test facility allows welding of specimens with simultaneous application of tensile load along or cross to the welding direction while the speed of tensile force application is either constant or increases linearly. The tensile force increment and/or the displacement are set by means of a CNC controller. Trials were conducted by varying the ultimate tensile strain and cross-head speed while keeping the welding parameters constant. By observing the crack-no crack behaviour and estimating the generated crack length for each trail using a new optimized experimental procedure the influence of the two important conditions (the strain and the strain rate) for the formation of solidification cracks can be investigated, the critical values of strain and strain rate that are responsible for solidification cracking formation have been determined. In the present study a three-dimensional FEM using the contact element technique was developed to simulate the solidification cracking during laser full penetration welding under external load conditions for the steel 1.4376 in order to get a better understanding of the mechanisms of hot crack initiation and the theoretical results were compared to the experimental ones. By comparing the resulting solidification crack with simulated crack, it is possible to determine the critical condition of solidification crack formation in the region where the strains and the strain rates cannot be measured due to the high temperature. The results show a good agreement between numerical calculation and experiment. It is proposed that the solidification cracking susceptibility may be predicted by FEM analysis by using the correct mechanical and thermo-physical constants of the materials. T2 - BEAM TECHNOLOGIES & LASER APPLICATION CY - St. Petersburg, Russia DA - 21.09.2015 KW - Solidification cracking KW - Hot cracking test KW - FEM KW - Laser beam welding PY - 2015 SN - 978-5-7422-5150-7 SP - 55 EP - 68 AN - OPUS4-36615 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pavlov, V.A. A1 - Zavialov, S.V. A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Development of a measuring technology of strain field in welds N2 - In the article considered the problem of hot cracks occurrence during laser welding process. The main reason of their appearance is strain. The optical method for measuring full field strain locally near the solidification front during laser welding process is proposed. The proposed method of optical measurement allows to determine the real values of the critical strain for various materials characterizing the occurrence of hot cracks in laser welding process. T2 - 20th international conference "Digital signal processing and applications DSPA-2018" CY - Moskau, Russia DA - 28.03.2018 KW - Solidification cracking KW - Critical strain KW - Strain rate KW - Optical measurement KW - Laser welding KW - In situ strain PY - 2018 SN - 978-5-905278-33-4 SP - 749 EP - 754 AN - OPUS4-44910 LA - rus AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - RPRT A1 - Rethmeier, Michael A1 - Gumenyuk, Andrey A1 - Bakir, Nasim T1 - Entwicklung eines Verfahrens zur Untersuchung der Heißrissresistenz lasergeschweißter Verbindungen N2 - In den letzten Jahrzehnten hat sich die Strahlschweißtechnik signifikant weiterentwickelt und als effizientes und wirtschaftliches Werkzeug in der Industrie etabliert. Für die Untersuchung der Heißrissresistenz verschiedener Werkstoffe existieren zahlreiche eigen- und fremdbeanspruchende Tests. Diese wurden aber speziell für andere Schweißverfahren, insbesondere das Lichtbogenschweißen, konzipiert. Daher besteht die Notwendigkeit eines geeigneten Heißrisstests, bei dem Werkstoffe realen Strahlschweißbedingungen ausgesetzt werden können. Die Entwicklung sowie die Standardisierung einer aussagekräftigen experimentellen Methode stellen einen wichtigen Schritt auf dem Weg zur Vermeidung von Heißrissen und damit für die Gewährleistung der Sicherheit von gefügten Bauteilen dar. Ziel der Forschungsarbeiten ist es, einen geeigneten Test zur effektiven Untersuchung der Heißrissanfälligkeit von lasergeschweißten Verbindungen zu konzipieren und zu entwickeln. KW - Heißrissresistenz PY - 2016 SN - 978-3-942541-94-7 SP - 1 EP - 110 PB - Verlag und Vertriebsgesellschaft mbH CY - Düsseldorf AN - OPUS4-41846 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -