@misc{GenchevDoynovOssenbrinketal., author = {Genchev, Gancho Vladimirov and Doynov, Nikolay and Ossenbrink, Ralf and Bokuchava, Gizo and Petrov, Peter and Michailov, Vesselin}, title = {Numerical and Experimental Study of Residual Stress Distribution in Laser Beam Welded Joint}, pages = {S. 20}, language = {en} } @inproceedings{PetrovBokuchavaPapushkinetal., author = {Petrov, Peter and Bokuchava, Gizo and Papushkin, Igor and Genchev, Gancho Vladimirov and Doynov, Nikolay and Michailov, Vesselin and Ormanova, Maria}, title = {Neutron diffraction studies of laser welding residual stresses}, series = {19th International Conference and School on Quantum Electronics: Laser Physics and Applications, 26-30 September 2016 Sozopol, Bulgaria}, booktitle = {19th International Conference and School on Quantum Electronics: Laser Physics and Applications, 26-30 September 2016 Sozopol, Bulgaria}, publisher = {SPIE}, address = {Bellingham, Wash.}, isbn = {978-1-5106-0953-2}, doi = {10.1117/12.2261802}, language = {en} } @inproceedings{KrawczynskiDoynovMichailov, author = {Krawczynski, Damian and Doynov, Nikolay and Michailov, Vesselin}, title = {Minimization of Residual Welding Stress and Distortins in Aluminium-Steel Hybrid Structure}, series = {Innowacje w procesach produkcyjnych, technologicznych i bezpieczeństwie : XXXVIII Studencka Sesja Naukowa, Częstochowa, 29 maj 2014 : praca zbiorowa}, booktitle = {Innowacje w procesach produkcyjnych, technologicznych i bezpieczeństwie : XXXVIII Studencka Sesja Naukowa, Częstochowa, 29 maj 2014 : praca zbiorowa}, publisher = {Wydawnictwo Wydziału Inżynierii Produkcji i Technologii Materiał{\´o}w Politechniki Częstochowskie}, address = {Częstochowa}, isbn = {879-83-63989-02-6}, pages = {59 -- 63}, language = {en} } @misc{GenchevDoynovOssenbrinketal., author = {Genchev, Gancho Vladimirov and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin and Bokuchava, Gizo and Petrov, Peter}, title = {Residual stresses formation in multi-pass weldment: A numerical and experimental study}, series = {Journal of Constructional Steel Research}, volume = {138}, journal = {Journal of Constructional Steel Research}, issn = {0143-974X}, doi = {10.1016/j.jcsr.2017.08.017}, pages = {633 -- 641}, abstract = {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.}, language = {en} } @misc{DoynovMichailov, author = {Doynov, Nikolay and Michailov, Vesselin}, title = {Distortion analysis of heat spot straightening thin-walled welded structures: part 2: analytical-numerical approach}, series = {International Journal of Advanced Manufacturing Technology}, volume = {95}, journal = {International Journal of Advanced Manufacturing Technology}, number = {1-4}, issn = {0268-3768}, doi = {10.1007/s00170-017-1214-0}, pages = {469 -- 478}, abstract = {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.}, language = {en} } @book{MichailovDoynovKuke, author = {Michailov, Vesselin and Doynov, Nikolay and Kuke, Felix}, title = {Anwendungsnahe Simulation des thermischen Richtens : Forschungsvorhaben P 1008/IGF-Nr. 17970 BR}, publisher = {Verlag und Vertriebsgesellschaft mbH}, address = {D{\"u}sseldorf}, isbn = {978-3-946885-03-0}, pages = {XV, 122}, language = {de} } @misc{DoynovMichailov, author = {Doynov, Nikolay and Michailov, Vesselin}, title = {Distortion analysis of heat spot straightening thin-walled welded structures: part 1: analytical-numerical approach}, series = {The International Journal of Advanced Manufacturing Technology}, volume = {94}, journal = {The International Journal of Advanced Manufacturing Technology}, number = {1-4}, issn = {0268-3768}, doi = {10.1007/s00170-017-0911-z}, pages = {667 -- 676}, abstract = {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).}, language = {en} } @incollection{GolubevDoynovHantelmannetal., author = {Golubev, Iurii and Doynov, Nikolay and Hantelmann, Cord and Michailov, Vesselin}, title = {W{\"a}rmequellemodell und FE-Temperaturfeldsimulation f{\"u}r das R{\"u}hrreibschweißen}, series = {DVS Congress 2017 : Große Schweißtechnische Tagung : DVS-Studentenkongress : Vortr{\"a}ge der Veranstaltungen in D{\"u}sseldorf vom 26. bis 29. September 2017}, booktitle = {DVS Congress 2017 : Große Schweißtechnische Tagung : DVS-Studentenkongress : Vortr{\"a}ge der Veranstaltungen in D{\"u}sseldorf vom 26. bis 29. September 2017}, publisher = {DVS Media}, address = {D{\"u}sseldorf}, isbn = {978-3-96144-008-5}, pages = {112}, language = {de} } @misc{EvdokimovSpringerDoynovetal., author = {Evdokimov, Anton and Springer, Katrin and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin}, title = {Heat source model for laser beam welding of steel-aluminum lap joints}, series = {International Journal of Advanced Manufacturing Technology}, volume = {93}, journal = {International Journal of Advanced Manufacturing Technology}, number = {1-4}, issn = {0268-3768}, doi = {10.1007/s00170-017-0569-6}, pages = {709 -- 716}, abstract = {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.}, language = {en} } @inproceedings{GolubevMorozovaNaumovetal., author = {Golubev, Iurii and Morozova, Iuliia and Naumov, Anton and Hantelmann, Cord and Doynov, Nikolay and Michailov, Vesselin}, title = {Numerical simulation and experimental investigation on Numerical simulation of 6082-T6 aluminum alloy}, series = {Materials Science and Technology 2017, (MS\&T17), Pittsburgh, Pennsylvania, USA, October 8-12, 2017, volume 2}, booktitle = {Materials Science and Technology 2017, (MS\&T17), Pittsburgh, Pennsylvania, USA, October 8-12, 2017, volume 2}, publisher = {Curran Associates, Inc.}, address = {Red Hook, NY}, isbn = {978-1-5108-5058-3}, pages = {987 -- 994}, abstract = {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.}, language = {en} } @inproceedings{StapelfeldLaunertPasternaketal., author = {Stapelfeld, Christoph and Launert, Benjamin and Pasternak, Hartmut and Doynov, Nikolay and Michailov, Vesselin}, title = {Numerische Festigkeitsberechnung einer versteiften Struktur unter Ber{\"u}cksichtigung realit{\"a}tsnaher geometrischer und struktureller Imperfektionen}, series = {110 Jahre DASt und 21. DASt-Forschungskolloquium an der Technischen Universit{\"a}t Kaiserslautern, 6./7. M{\"a}rz 2018}, booktitle = {110 Jahre DASt und 21. DASt-Forschungskolloquium an der Technischen Universit{\"a}t Kaiserslautern, 6./7. M{\"a}rz 2018}, publisher = {Deutscher Ausschuß f{\"u}r Stahlbau DASt}, address = {D{\"u}sseldorf}, isbn = {978-3-941687-27-1}, pages = {245 -- 249}, abstract = {Die Festigkeitsberechnung von Strukturen, zum Beispiel Platten oder Schalen, mittels der Finite-Elemente-Methode geh{\"o}rt schon seit l{\"a}ngerem zum Stand der Technik. Ber{\"u}cksichtigt werden bei der Berechnung sowohl geometrische Nichtlinearit{\"a}ten 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 gem{\"a}ß DIN EN 1993-1-5 erh{\"o}ht. In einem Kommentar zur selben Norm findet sich ebenfalls eine Empfehlung zur Ber{\"u}cksichtigung von Schweißimperfektionen in Form von vereinfachten L{\"a}ngseigenspannungsverl{\"a}ufen. Diese werden in Abh{\"a}ngigkeit der Fließgrenzspannung des Werkstoffs bei Raumtemperatur und der Dicken der F{\"u}gepartner angenommen. Sowohl die Annahme rein geometrischer Imperfektionen als auch die Ber{\"u}cksichtigung vereinfachter Eigenspannungszust{\"a}nde, sind mit Sicherheitszuschl{\"a}gen behaftet. Durch eine realit{\"a}tsn{\"a}here Ber{\"u}cksichtigung von strukturellen und geometrischen Imperfektionen, hervorgerufen durch Schweißprozesse, kann die tats{\"a}chliche Tragf{\"a}higkeit 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 Zusammenh{\"a}nge eingegangen. Es folgt die Erl{\"a}uterung des Kopplungsalgorithmus zwischen analytischem Modell und der numerischen Berechnung. Angewendet an der doppelt versteiften Platte, wird ein realit{\"a}tsnaher geometrischer und struktureller Imperfektionszustand berechnet. Eine anschließende Traglastanalyse gibt Aufschluss {\"u}ber 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 L{\"a}ngsrichtung invers, durch den Vergleich der ersten 6 Beulformen sowie der Last-Verformungskurven dreier Imperfektionen, bestimmt. Darauf aufbauen wird die Last-Verformungskurve f{\"u}r einen {\"u}berlagerten Imperfektionszustand berechnet, wobei die geometrischen Imperfektionen aus den Fertigungstoleranzen abgeleitet und die strukturellen idealisiert, gem{\"a}ß DIN EN 1993-1-5, gew{\"a}hlt werden. Abschließend werden alle Last-Verformungskurven einander gegen{\"u}bergestellt. Anhand des Vergleichs kann quantifiziert werden, wie konservativ die einzelnen angenommenen Imperfektionen sind und wie sich der Verformungsverlauf darstellt, berechnet man diesen unter Verwendung realit{\"a}tsnaher geometrischer und struktureller Imperfektionen.}, language = {de} } @inproceedings{StapelfeldLaunertPasternaketal., author = {Stapelfeld, Christoph and Launert, Benjamin and Pasternak, Hartmut and Doynov, Nikolay and Michailov, Vesselin}, title = {Strength Calculation of Stiffened Structures Taking Into Consideration Realistic Weld Imperfections}, series = {European Conference on Residual Stresses 2018, ECRS-10, Leuven, Belgium, 11-14th September, 2018}, booktitle = {European Conference on Residual Stresses 2018, ECRS-10, Leuven, Belgium, 11-14th September, 2018}, editor = {Seefeldt, Marc}, publisher = {Materials Research Forum LLC}, address = {Millersville, PA}, isbn = {978-1-945291-88-3}, doi = {10.21741/9781945291890-39}, pages = {245 -- 250}, abstract = {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.}, language = {en} } @misc{StapelfeldLaunertPasternaketal., author = {Stapelfeld, Christoph and Launert, Benjamin and Pasternak, Hartmut and Doynov, Nikolay and Michailov, Vesselin}, title = {Traglastberechnung versteifter Platten und Schalen unter Ber{\"u}cksichtigung realer Schweißimperfektionen}, series = {Bauingenieur}, volume = {93}, journal = {Bauingenieur}, number = {10}, issn = {0005-6650}, pages = {403 -- 411}, abstract = {Imperfektionen, die bei Traglastberechnungen Ber{\"u}cksichtigung finden m{\"u}ssen, haben ihre Ursachen in Herstellungs- und Fertigungstoleranzen oder werden durch das Schweißen und den damit zumeist einhergehenden Nachbehandlungen in den Bauteilen hervorgerufen. Durch die W{\"a}rmewirkung 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 Schweißn{\"a}hte sowie den Schweißparametern bestimmt. F{\"u}r die Ber{\"u}cksichtigung in Traglastberechnungen ist ein physikalisch fundiertes Modell erforderlich, welches die Schweißimperfektionen schnell und pr{\"a}zise berechnet. Das gekoppelte analytisch numerische Hybridmodell erf{\"u}llt 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 Verz{\"u}gen an einer Schiffsektion demonstriert. Darauffolgend wird das Hybridmodell an einer eben und einer gekr{\"u}mmten 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 dar{\"u}ber, welches Potenzial die realit{\"a}tsnahe direkte Ber{\"u}cksichtigung von Schweißimperfektionen birgt.}, language = {de} } @inproceedings{StapelfeldLaunertPasternaketal., author = {Stapelfeld, Christoph and Launert, Benjamin and Pasternak, Hartmut and Doynov, Nikolay and Michailov, Vesselin}, title = {The Influence of Geometrical and Welding Imperfections on the Strength of Stiffened Structures}, series = {High Performance Steel Structures Research Council (HPSSRC), Delft, Netherlands, 2018}, booktitle = {High Performance Steel Structures Research Council (HPSSRC), Delft, Netherlands, 2018}, pages = {191 -- 201}, abstract = {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.}, language = {en} } @inproceedings{DoynovOssenbrinkMichailov, author = {Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin}, title = {Unterst{\"u}tzung beim thermischen Richten von geschweißten Großstrukturen durch praktikable Computersimulationen}, series = {DVS Congress 2018 : Große Schweißtechnische Tagung, DVS-Studentenkongress, Vortr{\"a}ge der Veranstaltungen in Friedrichshafen am 17. und 18. September 2018}, booktitle = {DVS Congress 2018 : Große Schweißtechnische Tagung, DVS-Studentenkongress, Vortr{\"a}ge der Veranstaltungen in Friedrichshafen am 17. und 18. September 2018}, publisher = {DVS Media GmbH}, address = {D{\"u}sseldorf}, isbn = {978-3-96144-036-8}, pages = {364 -- 369}, abstract = {Unterst{\"u}tzung beim thermischen Richten von geschweißten Großstrukturen durch praktikable Computersimulationen}, language = {de} } @misc{BokuchavaPetrovGenchevetal., author = {Bokuchava, Gizo and Petrov, Peter and Genchev, Gancho Vladimirov and Michailov, Vesselin and Doynov, Nikolay and Ossenbrink, Ralf}, title = {Residual stress analysis in welded joints by neutron difffraction and comouter modeling}, series = {Romanian Journal of Physics}, volume = {Vol. 63}, journal = {Romanian Journal of Physics}, number = {7-8}, issn = {1221-146X}, pages = {16}, abstract = {Numerical models for thermo-mechanical simulation of the welding residual stresses in laser beam and multi-pass arc welded joints are developed. The models describe the resulting microstructure as a function of the peak temperature, austenization time, cooling time and take into account the microstructure formed after single or multiple thermal cycles. The results of simulations are validated by neutron diffraction experiments performed on FSD diffractometer at the IBR-2 pulsed reactor in FLNP JINR (Dubna, Russia). The elaborated numerical models are in good agreement with obtained neutron diffraction data, which enable to study the influence of different conditions and process parameters on the distribution of residual welding stresses.}, language = {en} } @misc{DoynovStapelfeldMichailovetal., author = {Doynov, Nikolay and Stapelfeld, Christoph and Michailov, Vesselin and Pasternak, Hartmut and Launert, Benjamin}, title = {Distortion analysis of large scaled welded structures}, series = {Mathematical Modelling of Weld Phenomena 12 : selected peer reviewed papers from the 12th International Seminar Numerical Analysis of Weldability : September 23-26, 2018, Graz, Schloss Seggau - Austria}, journal = {Mathematical Modelling of Weld Phenomena 12 : selected peer reviewed papers from the 12th International Seminar Numerical Analysis of Weldability : September 23-26, 2018, Graz, Schloss Seggau - Austria}, editor = {Sommitsch, Christof and Enzinger, Norbert and Mayr, Peter}, publisher = {Verlag der Technischen Universit{\"a}t Graz}, address = {Graz}, isbn = {978-3-85125-615-4}, doi = {10.3217/978-3-85125-615-4}, pages = {254 -- 280}, abstract = {The work presents an innovative approach for simulation of welding induced distortions, which allows taking into consideration the local effects of the welding process as well as the global interactions in the structure. The approach bases on an integration of analytical and numerical calculation's procedures in a hybrid model, realized with the aid of the inherent strain concept. The analytical procedure calculates the shrinkage strain components and area of the plastic deformed zone, caused by welding. The calculated strains are then transferred to the global finite element model in order to predict the distortions and stresses in the structure after every welding stage, as well as their final state. The consideration of welding scenarios, weld sequence, clamping conditions and the assembling stages is done by taking into account the intermediate variation of the strain state during the manufacturing steps. The article gives the theoretical basis of the analytical model. The consideration of the essential physical relations is put into discussion. The application of the model is illustrated on complex structures. Its reliability and practicability are demonstrated by means of a validation study.}, language = {en} } @misc{StapelfeldLaunertPasternaketal., author = {Stapelfeld, Christoph and Launert, Benjamin and Pasternak, Hartmut and Doynov, Nikolay and Michailov, Vesselin}, title = {Improve load capacity calculations by considering realistic imperfections induced by welding for plates and shells}, series = {Stability and ductility of steel structures 2019 : proceedings of the International Colloquia on Stability and Ductility of Steel Structures (SDSS 2019), September 11-13, 2019, Prague, Czech Republic}, journal = {Stability and ductility of steel structures 2019 : proceedings of the International Colloquia on Stability and Ductility of Steel Structures (SDSS 2019), September 11-13, 2019, Prague, Czech Republic}, publisher = {CRC Press}, address = {Boca Raton}, isbn = {978-0-367-33503-8}, pages = {1059 -- 1067}, language = {en} } @misc{GolubevMorozovaNaumovetal., author = {Golubev, Iurii and Morozova, Iuliia and Naumov, Anton and Hantelmann, Cord and Doynov, Nikolay and Michailov, Vesselin}, title = {Numerical Simulation and Experimental Investigation on Impulse Friction Stir Welding of 6082-T6 Aluminum Alloy}, series = {Papers from Materials Science and Technology 2017 (MS\&T17), October 8 - 12, 2017, David L. Lawrence Convention Center, Pittsburgh, Pennsylvania USA}, journal = {Papers from Materials Science and Technology 2017 (MS\&T17), October 8 - 12, 2017, David L. Lawrence Convention Center, Pittsburgh, Pennsylvania USA}, doi = {10.7449/2017/mst_2017_987_994}, pages = {987 -- 994}, abstract = {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.}, language = {en} } @misc{EvdokimovOssenbrinkDoynovetal., author = {Evdokimov, Anton and Ossenbrink, Ralf and Doynov, Nikolay and Michailov, Vesselin}, title = {Laser beam welding of steel-aluminum joints - influence of weld metal elastic-plastic properties on the distortions}, series = {Mathematical Modelling of Weld Phenomena 12 : selected peer reviewed papers from the 12th International Seminar Numerical Analysis of Weldability : September 23-26, 2018, Graz, Schloss Seggau - Austria}, journal = {Mathematical Modelling of Weld Phenomena 12 : selected peer reviewed papers from the 12th International Seminar Numerical Analysis of Weldability : September 23-26, 2018, Graz, Schloss Seggau - Austria}, editor = {Sommitsch, Christof and Enzinger, Norbert and Mayr, Peter}, publisher = {Verlag der Technischen Universit{\"a}t Graz}, address = {Graz}, isbn = {978-3-85125-615-4}, doi = {10.3217/978-3-85125-615-4}, pages = {431 -- 440}, abstract = {Great attention is focused nowadays on laser welding of dissimilar steel-aluminum joints in overlap configuration in key-hole mode. It was found that elastic-plastic properties of the weld metal exhibit strong difference to those of the base alloys and can be defined as a function of aluminum content in the weld metal. A developed Finite-Element simulation model allows prediction of the aluminum content as a function of welding parameters and subsequently the elastic-plastic properties of the weld metal as a function of the determined content. The main goal of the present study is to show the impact of the weld metal properties on welding distortions and residual stresses. For that purpose, a sensitivity analysis of the thermomechanical model was performed, where the distortions and residual stresses were computed as a function of welding parameters and therefore as a function of corresponding weld metal properties. The analysis showed that the influence of the weld metal is essential, and its properties should be taken into consideration in the models for better prediction accuracy.}, language = {en} }