TY - GEN A1 - Genchev, Gancho Vladimirov A1 - Doynov, Nikolay A1 - Ossenbrink, Ralf A1 - Michailov, Vesselin T1 - Modelling the Local Microstructure Properties due to Multi-Pass Welding T2 - Materials Science Forum Y1 - 2017 U6 - https://doi.org/10.4028/www.scientific.net/MSF.879.595 SN - 0255-5476 SN - 1662-9752 N1 - International Conference on Processing & Manufacturing of Advanced Materials Processing, Fabrication, Properties, Applications, May 29 - June 3, 2016 Graz, Austria VL - Vol. 879 SP - 595 EP - 600 ER - TY - GEN A1 - Michailov, Vesselin A1 - Doynov, Nikolay T1 - Analytical-Numerical Modeling Approach for Calculation of the Structural Distortions after Welding and Thermal Straightening T2 - Journal of Mechanics Engineering and Automation Y1 - 2016 U6 - https://doi.org/10.17265/2159-5275/2016.05.004 SN - 2159-5283 SN - 2159-5275 VL - 6 IS - 5 SP - 246 EP - 253 ER - TY - CHAP A1 - Doynov, Nikolay T1 - Anwendungsnahe Simulation des thermischen Richtens T2 - Schweißen in der Maritimen Technik und im Ingenieurbau, 16. Tagung, 20./21. April 2016 in Hamburg Y1 - 2016 SP - 78 EP - 88 PB - GSI SLV Nord CY - Hamburg ER - TY - CHAP A1 - Genchev, Gancho Vladimirov A1 - Doynov, Nikolay A1 - Ossenbrink, Ralf A1 - Michailov, Vesselin T1 - Schweißtechnische Simulation der lokalen Eigenschaften in der Wärmeeinflusszone von Mehrlagenschweißungen T2 - ANSYS Conference & 33rd CADFEM Users' Meeting, 24. - 26. Juni, Bremen, conference proceedings Y1 - 2015 PB - CADFEM GmbH CY - Grafing ER - TY - CHAP A1 - Doynov, Nikolay A1 - Kuke, Felix A1 - Michailov, Vesselin T1 - Thermal straightening simulation of welded structures T2 - Proceedings, METEC & 2nd ESTAD 2015, European Steel Technology and Application Days, Düsseldorf, Germany, CCD Congress Center Düsseldorf, 15 - 19 June 2015 Y1 - 2015 SN - 978-3-00-049542-7 SP - P 709, 1 EP - 6 PB - TEMA Technologie Marketing AG CY - Aachen ER - TY - GEN A1 - Genchev, Gancho Vladimirov A1 - Doynov, Nikolay A1 - Ossenbrink, Ralf A1 - Bokuchava, Gizo A1 - Petrov, Peter A1 - Michailov, Vesselin T1 - Numerical and Experimental Study of Residual Stress Distribution in Laser Beam Welded Joint Y1 - 2016 UR - https://www.tugraz.at/fileadmin/user_upload/Events/Seggau/Dokumente/Dokumente_THERMEC/Program_Book_April_2016.pdf N1 - THERMEC 2016, 9th International Conference on Processing & Manufacturing of Advanced Materials, May 29-June 03, 2016, Graz, Austria SP - S. 20 ER - TY - CHAP A1 - Petrov, Peter A1 - Bokuchava, Gizo A1 - Papushkin, Igor A1 - Genchev, Gancho Vladimirov A1 - Doynov, Nikolay A1 - Michailov, Vesselin A1 - Ormanova, Maria T1 - Neutron diffraction studies of laser welding residual stresses T2 - 19th International Conference and School on Quantum Electronics: Laser Physics and Applications, 26–30 September 2016 Sozopol, Bulgaria Y1 - 2017 UR - http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2597355 SN - 978-1-5106-0953-2 SN - 978-1-5106-0954-9 U6 - https://doi.org/10.1117/12.2261802 PB - SPIE CY - Bellingham, Wash. ER - TY - CHAP A1 - Krawczynski, Damian A1 - Doynov, Nikolay A1 - Michailov, Vesselin T1 - Minimization of Residual Welding Stress and Distortins in Aluminium-Steel Hybrid Structure T2 - Innowacje w procesach produkcyjnych, technologicznych i bezpieczeństwie : XXXVIII Studencka Sesja Naukowa, Częstochowa, 29 maj 2014 : praca zbiorowa Y1 - 2014 SN - 879-83-63989-02-6 SP - 59 EP - 63 PB - Wydawnictwo Wydziału Inżynierii Produkcji i Technologii Materiałów Politechniki Częstochowskie CY - Częstochowa ER - TY - GEN A1 - Genchev, Gancho Vladimirov A1 - Doynov, Nikolay A1 - Ossenbrink, Ralf A1 - Michailov, Vesselin A1 - Bokuchava, Gizo A1 - Petrov, Peter T1 - Residual stresses formation in multi-pass weldment: A numerical and experimental study T2 - Journal of Constructional Steel Research N2 - In this study, the residual stresses distribution induced by multi-pass arc welding of the steel S355J2+N are investigated experimentally and numerically. An extended approach is used for the simulations, which considers the change of the local microstructure properties due to multiple reheating. Experimental material data obtained from physical welding simulations with Gleeble® are used for the model calibration. The experimental stress study is performed using a neutron diffraction method on a fourier stress diffractometer. Numerical analysis of the welding stresses formation in the weldment is performed and compared to the experimental study. The results explain the influence of the welding thermal history on the resulting local thermo-mechanical properties in the heat-affected zone and, thus, on the residual stress distribution. The consideration of the local microstructure properties in the welding simulation leads to a significant increase in accuracy of the numerical results. The major influence factor on the residual stress formation is the change in the interpass microstructure yield strength. When a root pass with short cooling times is subjected to re-austenitisation in the fine-grained zone, the yield strength increases in this area and affects consequently the residual stress distribution. The influence of the reheating is detectable in the depth of the weldment, but it is less significant for the residual stress formation near the surface of the welded joint. KW - Multi-pass weldment KW - Steel S355 KW - Thermo-mechanical properties KW - Stress distribution KW - Welding simulation KW - Neutron diffraction Y1 - 2017 UR - http://www.sciencedirect.com/science/article/pii/S0143974X17303358 U6 - https://doi.org/10.1016/j.jcsr.2017.08.017 SN - 0143-974X VL - 138 SP - 633 EP - 641 ER - TY - GEN A1 - Doynov, Nikolay A1 - Michailov, Vesselin T1 - Distortion analysis of heat spot straightening thin-walled welded structures: part 2: analytical-numerical approach T2 - International Journal of Advanced Manufacturing Technology N2 - An analytical model based on a theoretical model established in the previous work (part 1) is developed. The analytical model considers the particular case of an instantaneous high-density heat source acting on a thin pre-stressed plate. It calculates the plastic strain and the area of the zone of plastic deformation. A theoretical study is performed in order to quantify the major factors that influence the plastic strain formation. Furthermore, the work presents a calculation procedure for distortion analysis of lar ge and complex structures, intended to be used for solving industrial tasks. The calculation procedure consists of a combination of the analytical solution and an elastic finite element analysis with the aid of the inherent strain approach. Various aspects of its application are also discussed. The calculation procedure is finally explained using a simple example. Its reliability and practicability are demonstrated through verification and validation studies. The work is dedicated to the thermal straightening of thin-walled welded structures; however, it can also be related to other processes. KW - Thermal straightening KW - Distortion analysis KW - Computational welding mechanics KW - Finite element analysis KW - Inherent strain method KW - Virtual manufacturing Y1 - 2018 UR - https://link.springer.com/article/10.1007%2Fs00170-017-1214-0 U6 - https://doi.org/10.1007/s00170-017-1214-0 SN - 0268-3768 SN - 1433-3015 VL - 95 IS - 1-4 SP - 469 EP - 478 ER - TY - BOOK A1 - Michailov, Vesselin A1 - Doynov, Nikolay A1 - Kuke, Felix T1 - Anwendungsnahe Simulation des thermischen Richtens : Forschungsvorhaben P 1008/IGF-Nr. 17970 BR Y1 - 2016 SN - 978-3-946885-03-0 PB - Verlag und Vertriebsgesellschaft mbH CY - Düsseldorf ER - TY - GEN A1 - Doynov, Nikolay A1 - Michailov, Vesselin T1 - Distortion analysis of heat spot straightening thin-walled welded structures: part 1: analytical-numerical approach T2 - The International Journal of Advanced Manufacturing Technology N2 - The work deals with the elastic-plastic thermo-mechanical deformation process after spot heating of large thin plates. It promotes a new theoretical model of the process. The main target is to clarify the kinetics of the plastic strain formation during thermal straightening and to explore the main interactions. For this purpose, a simplified mechanical problem is formulated and applied. As a result, definite thermo-mechanical relations between temperature, initial strain, and accumulated plastic strain are obtained. Finally, a verification study is presented and discussed. The results contribute to extending the knowledge about the process and to establishing a theoretical background for development of applied analytical or analytical-numerical approaches for practical use in the designing and planning phases in welding production. An application to a particular case is described in an accompanying paper (part 2). KW - Straightening KW - Elastic-plastic analysis KW - Distortion analysis KW - Computational welding mechanics KW - Virtual manufacturing Y1 - 2018 UR - https://link.springer.com/article/10.1007%2Fs00170-017-0911-z U6 - https://doi.org/10.1007/s00170-017-0911-z SN - 0268-3768 SN - 1433-3015 VL - 94 IS - 1-4 SP - 667 EP - 676 ER - TY - CHAP A1 - Golubev, Iurii A1 - Doynov, Nikolay A1 - Hantelmann, Cord A1 - Michailov, Vesselin T1 - Wärmequellemodell und FE-Temperaturfeldsimulation für das Rührreibschweißen T2 - DVS Congress 2017 : Große Schweißtechnische Tagung : DVS-Studentenkongress : Vorträge der Veranstaltungen in Düsseldorf vom 26. bis 29. September 2017 KW - Wärmequellemodell KW - FE-Temperaturfeldsimulation KW - Rührreibschweißen Y1 - 2017 SN - 978-3-96144-008-5 SP - 112 PB - DVS Media CY - Düsseldorf ER - TY - GEN A1 - Evdokimov, Anton A1 - Springer, Katrin A1 - Doynov, Nikolay A1 - Ossenbrink, Ralf A1 - Michailov, Vesselin T1 - Heat source model for laser beam welding of steel-aluminum lap joints T2 - International Journal of Advanced Manufacturing Technology N2 - In this study, a three-dimensional thermal conduction model based on the finite element analysis was established to predict a heat distribution during laser welding in overlap configuration of austenitic stainless steel 1.4301 and hardenable aluminum alloy 6016. A hybrid model based on two expanded curve-rotated volumetric heat sources is suggested to capture the complex weld geometry. Since thermal flow in the overlap area is a crucial part of the model, an analytic calculation of a thermal contact conductance between the plates and its subsequent implementation in the FE model through a superposition of two contact surfaces are described in details in this paper. Full thermal cycles, weld shapes, and thus mixing grades were successfully predicted by means of the developed model for different parameter combinations. KW - Laser welding Dissimilar joint Heat source model Finite element analysis Thermal simulation Weld shape KW - Dissimilar joint KW - Heat source model KW - Finite element analysis KW - Thermal simulation KW - Weld shape Y1 - 2017 UR - https://link.springer.com/article/10.1007/s00170-017-0569-6 U6 - https://doi.org/10.1007/s00170-017-0569-6 SN - 0268-3768 SN - 1433-3015 VL - 93 IS - 1-4 SP - 709 EP - 716 ER - TY - CHAP A1 - Golubev, Iurii A1 - Morozova, Iuliia A1 - Naumov, Anton A1 - Hantelmann, Cord A1 - Doynov, Nikolay A1 - Michailov, Vesselin T1 - Numerical simulation and experimental investigation on Numerical simulation of 6082-T6 aluminum alloy T2 - Materials Science and Technology 2017, (MS&T17), Pittsburgh, Pennsylvania, USA, October 8-12, 2017, volume 2 N2 - The series of impulse friction stir welding (IFSW) experiments for aluminum alloy 6082-T6 butt joints was performed to obtain micrographs, tensile and hardness test samples and to receive the validation data for a numerical model of the process. Impulse force and frequency were varied to determine the effect of individual process parameters on microstructure evolution and mechanical properties of the welded butt joints. A three-dimensional model was established to simulate temperature distribution, heat generation and contact state between the tool and the workpiece during IFSW. Based on the numerical simulation, the influence of the impulses on heat input, maximum weld temperatures and contact state was found. The combination of impulse force and frequency effected the grain refinement. The influence of impulses on the elongation and hardness of the welded joints during IFSW were determined. KW - Aluminum alloy KW - Numerical simulation Y1 - 2017 SN - 978-1-5108-5058-3 SP - 987 EP - 994 PB - Curran Associates, Inc. CY - Red Hook, NY ER - TY - CHAP A1 - Stapelfeld, Christoph A1 - Launert, Benjamin A1 - Pasternak, Hartmut A1 - Doynov, Nikolay A1 - Michailov, Vesselin T1 - Numerische Festigkeitsberechnung einer versteiften Struktur unter Berücksichtigung realitätsnaher geometrischer und struktureller Imperfektionen T2 - 110 Jahre DASt und 21. DASt-Forschungskolloquium an der Technischen Universität Kaiserslautern, 6./7. März 2018 N2 - Die Festigkeitsberechnung von Strukturen, zum Beispiel Platten oder Schalen, mittels der Finite-Elemente-Methode gehört schon seit längerem zum Stand der Technik. Berücksichtigt werden bei der Berechnung sowohl geometrische Nichtlinearitäten als auch das nichtlineare Verhalten des Werkstoffs. Die geometrischen und strukturellen Imperfektionen werden bei der Ermittlung der Festigkeit zumeist in ausschließlich geometrischen Imperfektionen, wie bspw. Kombinationen aus Fertigungstoleranzen und den Ergebnissen von Beulanalysen zusammengefasst. Zur Rechtfertigung dieser Vorgehensweise werden die geometrischen Imperfektionen gemäß DIN EN 1993-1-5 erhöht. In einem Kommentar zur selben Norm findet sich ebenfalls eine Empfehlung zur Berücksichtigung von Schweißimperfektionen in Form von vereinfachten Längseigenspannungsverläufen. Diese werden in Abhängigkeit der Fließgrenzspannung des Werkstoffs bei Raumtemperatur und der Dicken der Fügepartner angenommen. Sowohl die Annahme rein geometrischer Imperfektionen als auch die Berücksichtigung vereinfachter Eigenspannungszustände, sind mit Sicherheitszuschlägen behaftet. Durch eine realitätsnähere Berücksichtigung von strukturellen und geometrischen Imperfektionen, hervorgerufen durch Schweißprozesse, kann die tatsächliche Tragfähigkeit einer Struktur wesentlich exakter bestimmt werden. Inhalt dieses Artikels ist die Anwendung eines analytisch-numerischen Hybridmodells zur Schweißimperfektionsberechnung an einer doppelt versteiften Platte und einer anschließenden Festigkeitsanalyse. Eingangs wird das analytische Modell vorgestellt und auf die grundlegenden physikalischen Zusammenhänge eingegangen. Es folgt die Erläuterung des Kopplungsalgorithmus zwischen analytischem Modell und der numerischen Berechnung. Angewendet an der doppelt versteiften Platte, wird ein realitätsnaher geometrischer und struktureller Imperfektionszustand berechnet. Eine anschließende Traglastanalyse gibt Aufschluss über das Verformungsverhalten unter achsialer Krafteinwirkung. Zur Bewertung der Ergebnisse wird ein Modell gleicher geometrischer Abmessungen und Werkstoffkennwerte aus der Literatur herangezogen. Berechnet wurden die ersten 6 Eigenformen mittels analytischer und numerischer Modelle sowie die Last-Verformungskurven unter der Annahme unterschiedlicher geometrischer Imperfektionen. Um die Vergleichbarkeit der Ergebnisse zu sichern, wird eingangs die Lagerung des Modells sowie der Kraftangriffspunkt in Längsrichtung invers, durch den Vergleich der ersten 6 Beulformen sowie der Last-Verformungskurven dreier Imperfektionen, bestimmt. Darauf aufbauen wird die Last-Verformungskurve für einen überlagerten Imperfektionszustand berechnet, wobei die geometrischen Imperfektionen aus den Fertigungstoleranzen abgeleitet und die strukturellen idealisiert, gemäß DIN EN 1993-1-5, gewählt werden. Abschließend werden alle Last-Verformungskurven einander gegenübergestellt. Anhand des Vergleichs kann quantifiziert werden, wie konservativ die einzelnen angenommenen Imperfektionen sind und wie sich der Verformungsverlauf darstellt, berechnet man diesen unter Verwendung realitätsnaher geometrischer und struktureller Imperfektionen. Y1 - 2018 SN - 978-3-941687-27-1 SP - 245 EP - 249 PB - Deutscher Ausschuß für Stahlbau DASt CY - Düsseldorf ER - TY - CHAP A1 - Stapelfeld, Christoph A1 - Launert, Benjamin A1 - Pasternak, Hartmut A1 - Doynov, Nikolay A1 - Michailov, Vesselin ED - Seefeldt, Marc T1 - Strength Calculation of Stiffened Structures Taking Into Consideration Realistic Weld Imperfections T2 - European Conference on Residual Stresses 2018, ECRS-10, Leuven, Belgium, 11-14th September, 2018 N2 - The topic of this article is the application of an analytical numerical hybrid model for a realistic prediction of imperfections induced by welds. At the beginning, the analytical model, its physical basis as well as the physical interrelationships are explained. This is followed by the explanation of the coupling procedure between the analytical model and the numerical calculation. Afterwards, the coupled hybrid model is applied on the investigated stiffened curved structure for the determination of the weld imperfections. An ultimate load analysis gives information about the load carrying behavior under axial loading. The results are compared against the traditional approach using eigenmode-based imperfections. The comparison underlines the potential additional utilization of load bearing capacity by this new approach. Y1 - 2018 SN - 978-1-945291-88-3 SN - 978-1-945291-89-0 U6 - https://doi.org/10.21741/9781945291890-39 SP - 245 EP - 250 PB - Materials Research Forum LLC CY - Millersville, PA ER - TY - GEN A1 - Stapelfeld, Christoph A1 - Launert, Benjamin A1 - Pasternak, Hartmut A1 - Doynov, Nikolay A1 - Michailov, Vesselin T1 - Traglastberechnung versteifter Platten und Schalen unter Berücksichtigung realer Schweißimperfektionen T2 - Bauingenieur N2 - Imperfektionen, die bei Traglastberechnungen Berücksichtigung finden müssen, haben ihre Ursachen in Herstellungs- und Fertigungstoleranzen oder werden durch das Schweißen und den damit zumeist einhergehenden Nachbehandlungen in den Bauteilen hervorgerufen. Durch die Wärmewirkung des Schweißens entstehen sowohl sehr große Verformungen als auch signifikante Zug und Druckspannungen. Der strukturelle und geometrische Imperfektionsgrad wird somit maßgeblich von der Anzahl und der Lage der Schweißnähte sowie den Schweißparametern bestimmt. Für die Berücksichtigung in Traglastberechnungen ist ein physikalisch fundiertes Modell erforderlich, welches die Schweißimperfektionen schnell und präzise berechnet. Das gekoppelte analytisch numerische Hybridmodell erfüllt diese Kriterien. Die mathematischen Grundlagen des analytischen Modells sowie die Kopplung mit der numerischen Finite-Elemente-Berechnung werden eingangs vorgestellt und die Anwendung zur Berechnung von Verzügen an einer Schiffsektion demonstriert. Darauffolgend wird das Hybridmodell an einer eben und einer gekrümmten versteiften Platte zur Berechnung der Schweißimperfektionen angewendet. Anschließende Traglastberechnungen sowie der Vergleich mit den Ergebnissen unter der Annahme einer geometrischen Ersatzimperfektion in Form des kritischsten Eigenwerts gibt Auskunft darüber, welches Potenzial die realitätsnahe direkte Berücksichtigung von Schweißimperfektionen birgt. Y1 - 2018 SN - 0005-6650 VL - 93 IS - 10 SP - 403 EP - 411 ER - TY - CHAP A1 - Stapelfeld, Christoph A1 - Launert, Benjamin A1 - Pasternak, Hartmut A1 - Doynov, Nikolay A1 - Michailov, Vesselin T1 - The Influence of Geometrical and Welding Imperfections on the Strength of Stiffened Structures T2 - High Performance Steel Structures Research Council (HPSSRC), Delft, Netherlands, 2018 N2 - The strength calculation of stiffened plates and shells via finite element simulation has been part of the state of the art for a long time. Geometrical nonlinearities as well as the nonlinear material behavior are considered within the calculation. To simplify, both types of imperfections, geometrical and structural ones, are mostly combined in these strength calculations being considered as equivalent geometrical imperfections. Values for standard cases are included in EN 1993-1-5 in case of plated structures or 1-6 in case of shells. A second possibility is the separate definition of fabrication tolerances and residual stresses, as far as they are known. With increasing complexity of the structure, less information are however available on geometrical and particularly structural imperfections. Nevertheless, by means of a more realistic consideration of these values, the actual ultimate load can be determined significantly more exactly and the performance of high performance steel structures is increased. In the investigated cases, deformations and stresses arise mainly due to welding. Therefore, the topic of this article is the application of an analytical numerical hybrid model for predicting imperfections induced by welds. This is presented on an example of a stiffened steel structure and a subsequent ultimate load calculation. At the beginning the analytical model, its physical basis as well as the physical interrelationships are introduced and explained. This is followed by the explanation of the coupling procedure between the analytical model and the numerical calculation for the calculation of weld-induced deformations and residual stresses. The significance of the hybrid model is proven by means of a few sample applications. For a realistic determination of the weld imperfections in the investigated stiffened structure, the coupled hybrid model is used afterwards. An ultimate load analysis gives information about the load carrying behavior under axial loading. The results are compared with the results of an ultimate load analysis from a literature example assuming different eigenvalues with different scaling. The results underline the potential additional utilization of load bearing capacity by this new approach. KW - Welding KW - Stresses KW - Strains KW - Imperfections KW - Stiffened Structures KW - Distortions Y1 - 2018 UR - https://www-docs.b-tu.de/fg-stahlbau/public/Fachgebiet_Stahlbau/publikationen/Workshop_Proceedings_of_HPSSRC-updated_cs.pdf SP - 191 EP - 201 ER - TY - CHAP A1 - Doynov, Nikolay A1 - Ossenbrink, Ralf A1 - Michailov, Vesselin T1 - Unterstützung beim thermischen Richten von geschweißten Großstrukturen durch praktikable Computersimulationen T2 - DVS Congress 2018 : Große Schweißtechnische Tagung, DVS-Studentenkongress, Vorträge der Veranstaltungen in Friedrichshafen am 17. und 18. September 2018 N2 - Unterstützung beim thermischen Richten von geschweißten Großstrukturen durch praktikable Computersimulationen KW - Thermisches Richten KW - Großstrukturen KW - Simulation KW - Umformen KW - Schiffbau KW - Richten Y1 - 2018 SN - 978-3-96144-036-8 SP - 364 EP - 369 PB - DVS Media GmbH CY - Düsseldorf ER -