@inproceedings{StadtausDoynovMichailov, author = {Stadtaus, Marc and Doynov, Nikolay and Michailov, Vesselin}, title = {Investigation of the Modified CTS-Test for the Prediction of Cold Cracking Susceptibility by Numerical Models}, series = {Mathematical modelling of weld phenomena 8}, booktitle = {Mathematical modelling of weld phenomena 8}, editor = {Cerjak, Horst-Hannes}, publisher = {Verl. der Techn. Univ. Graz}, address = {Graz}, isbn = {978-3-902465-69-6}, language = {en} } @inproceedings{StapelfeldDoynovAtanasovaetal., author = {Stapelfeld, Christoph and Doynov, Nikolay and Atanasova, D. and Michailov, Vesselin}, title = {Calculation of Welding Distortions in Large Structures Using the Maximum Temperature Model and the Coupled Analytic-Numerical Shrinkage Force Model}, series = {ESI Global Forum 2010, 19. - 20. Mai 2010, M{\"u}nchen}, booktitle = {ESI Global Forum 2010, 19. - 20. Mai 2010, M{\"u}nchen}, language = {en} } @inproceedings{MichailovStapelfeldDoynov, author = {Michailov, Vesselin and Stapelfeld, Christoph and Doynov, Nikolay}, title = {Verzugsberechnung einer komplexen Struktur mittels eines analytisch-numerischen Hybridmodells}, series = {DVS Congress 2010, Große Schweißtechnische Tagung, Studentenkongress, Statusseminar "Schneidtechnik" - Abschlusskolloquium zum AiF-Forschungscluster "Integration des R{\"u}hrreibschweißens in Fertigungsprozessketten, N{\"u}rnberg 27./28. September 2010}, booktitle = {DVS Congress 2010, Große Schweißtechnische Tagung, Studentenkongress, Statusseminar "Schneidtechnik" - Abschlusskolloquium zum AiF-Forschungscluster "Integration des R{\"u}hrreibschweißens in Fertigungsprozessketten, N{\"u}rnberg 27./28. September 2010}, publisher = {DVS Media GmbH}, address = {D{\"u}sseldorf}, isbn = {978-3-87155-592-3}, pages = {128 -- 132}, language = {de} } @inproceedings{GenchevDoynovMichailov, author = {Genchev, Gancho Vladimirov and Doynov, Nikolay and Michailov, Vesselin}, title = {Kennlinien zur Festlegung der erforderlichen r{\"a}umlichen und zeitlichen Diskretisierung bei der thermomechanischen Schweißsimulation}, language = {de} } @incollection{MichailovKloshekDoynov, author = {Michailov, Vesselin and Kloshek, Alexander and Doynov, Nikolay}, title = {Thermomechanische Simulation geschweißter Mischverbindungen aus Aluminium- und Stahlwerkstoffen}, series = {Jahrbuch Schweißtechnik 2012}, booktitle = {Jahrbuch Schweißtechnik 2012}, publisher = {DVS Media GmbH}, address = {D{\"u}sseldorf}, isbn = {978-3-87155-606-7}, pages = {173 -- 184}, language = {de} } @misc{MichailovDoynovStapelfeldetal., author = {Michailov, Vesselin and Doynov, Nikolay and Stapelfeld, Christoph and Ossenbrink, Ralf}, title = {Hybrid Model for Prediction of Welding Distortions in Large Structures}, series = {Journal of Frontiers of Materials Science}, volume = {5}, journal = {Journal of Frontiers of Materials Science}, number = {2}, issn = {2095-025X}, pages = {209 -- 215}, language = {en} } @misc{DreibatiOssenbrinkDoynovetal., author = {Dreibati, Ossama and Ossenbrink, Ralf and Doynov, Nikolay and Michailov, Vesselin}, title = {Physical and numerical simulation of thermo-mechanical properties in the weld heat affected zone of an AlMgSi-alloy}, series = {Materials Science Forum}, volume = {706-709}, journal = {Materials Science Forum}, issn = {0255-5476}, pages = {1491 -- 1496}, language = {en} } @book{MichailovDoynovOssenbrink, author = {Michailov, Vesselin and Doynov, Nikolay and Ossenbrink, Ralf}, title = {Sensibilit{\"a}tsanalyse der thermomechanischen FE-Schweißsimulation}, publisher = {Shaker}, address = {Aachen}, isbn = {978-3-8440-1016-9}, pages = {137}, language = {de} } @misc{GenchevDreibatiOssenbrinketal., author = {Genchev, Gancho Vladimirov and Dreibati, Ossama and Ossenbrink, Ralf and Doynov, Nikolay and Michailov, Vesselin}, title = {Physical and Numerical Simulation of the Heat-affected Zone of Multi-pass Welds}, series = {Materials Science Forum}, journal = {Materials Science Forum}, number = {Vol. 762}, issn = {0255-5476}, pages = {544 -- 550}, abstract = {The paper presents a numerical and experimental approach for the quantification of the thermo-mechanical properties in multi-pass weld's heat affected zone (HAZ) of low alloy steel "S355J2+N". First, the characteristic temperature cycles for multi-pass welds were identified by FE temperature field simulations of welding. Based on the identified temperature cycles, the microstructure in the HAZ has been physically simulated with the simulation and testing system Gleeble 3500 to investigate the influence of multi thermal exposure on the thermo-mechanical properties. Thus, the thermo-mechanical material properties including thermal strain and temperature dependent stress strain behaviour as function of peak temperatures and cooling rates have been determined. These material properties were used to calibrate a developed model for numerical prediction of the material properties of multi-pass weld HAZ.}, language = {en} } @incollection{GenchevOssenbrinkDoynovetal., author = {Genchev, Gancho Vladimirov and Ossenbrink, Ralf and Doynov, Nikolay and Michailov, Vesselin}, title = {Gef{\"u}geeigenschaften in der W{\"a}rmeeinflusszone von Mehrlagenschweißungen aus S355J2+N}, series = {Fortschritte in der Metallographie}, booktitle = {Fortschritte in der Metallographie}, editor = {Keßler, Olaf}, publisher = {Inventum}, address = {Bonn}, isbn = {978-3-88355-392-4}, pages = {167 -- 172}, language = {de} } @misc{ZhangDoynovWolfetal., author = {Zhang, Wei and Doynov, Nikolay and Wolf, Matthias and Dreibati, Ossama and Ossenbrink, Ralf and Michailov, Vesselin}, title = {Investigation of the Thermal Shock Behavior of Ceramic Using a Combination of Experimental Testing and FE-Simulation Methods}, series = {Advanced engineering materials}, volume = {15}, journal = {Advanced engineering materials}, number = {6}, issn = {1527-2648}, doi = {10.1002/adem.201200241}, pages = {480 -- 484}, abstract = {Thermal shock behavior of ceramics plays a decisive role in their broad industrial applications. For enhanced understanding of damage and failure mechanism under thermal shock loading, in the present work, a combination of experimental testing and numerical simulation methods has been used. The thermal shock behavior of the alumina (99.7\%) disk samples has been investigated by using a plasma test stand: the bottom of the ceramic disks were locally heated in the center by plasma beam; during the heat treatment the temperature distribution at the top of the sample was recorded with a thermographic system. To characterize the thermal shock resistance, a thermomechanical simulation was subsequently carried out. It calculates the temperature and stress distribution within the ceramic disks. The calculated critical thermal tension stresses are reported, which led to the failure of the ceramic disks under thermal shock loading. The effect of the sample thickness on the temperature and stress distribution is presented. Compared with the experimental results the simulated results show excellent agreement. As conclusion, it is possible to determine the thermal shock behavior of ceramic materials by the combination of experimental testing and numerical simulation.}, language = {en} } @incollection{DoynovChristovMichailovetal., author = {Doynov, Nikolay and Christov, St. and Michailov, Vesselin and Wohlfahrt, Helmut}, title = {Finite Elements Simulation of Multipass Submerged Arc Welding}, series = {Mathematical Modelling of Weld Phenomena 6}, booktitle = {Mathematical Modelling of Weld Phenomena 6}, publisher = {Maney - IOM}, address = {London}, isbn = {978-1-902653-56-3}, pages = {651 -- 669}, language = {en} } @incollection{OssenbrinkGenchevDoynov, author = {Ossenbrink, Ralf and Genchev, Gancho Vladimirov and Doynov, Nikolay}, title = {Simulation der Schweißeigenspannungen und des -verzuges unter Ber{\"u}cksichtigung der Gef{\"u}geumwandlungen mit dem STAAZ-Modell}, series = {Internationales Symposium Schweißtechnik - Verfahren, Werkstoffe, Simulation, Cottbus, 6. November 2013}, booktitle = {Internationales Symposium Schweißtechnik - Verfahren, Werkstoffe, Simulation, Cottbus, 6. November 2013}, editor = {Michailov, Vesselin}, publisher = {Shaker Verlag}, address = {Aachen}, isbn = {978-3-8440-2319-0}, pages = {149 -- 167}, abstract = {Die vorliegende Arbeit stellt das von Professor Michailov vorgeschlagene Spitzentemperatur-Austenitisierungs- Abk{\"u}hlzeit-Modell f{\"u}r die thermomechanische Schweißsimulation unter Ber{\"u}cksichtigung der Gef{\"u}geumwandlungen vor. Das Modell erfasst die f{\"u}r die Gef{\"u}geausbildung maßgebenden Temperaturzyklen durch seine drei so genannten STAAZ-Parameter: Spitzentemperatur, Austenitisierungs- und Abk{\"u}hlzeit. Die Korrelation dieser Temperaturzyklusparameter mit den thermomechanischen gef{\"u}geabh{\"a}ngigen Werkstoffeigenschaften erfolgt auf Grundlage einer empirischen Datenbasis. Mit der vorgenommenen Erweiterung zu Mehrmalig-(M-)STAAZ l{\"a}sst sich das aus einem vorgelagerten Temperaturzyklus entstandene Zwischengef{\"u}ge ber{\"u}cksichtigen.}, language = {de} } @misc{GenchevDoynovOssenbrinketal., author = {Genchev, Gancho Vladimirov and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin}, title = {Modelling the Local Microstructure Properties due to Multi-Pass Welding}, series = {Materials Science Forum}, volume = {Vol. 879}, journal = {Materials Science Forum}, issn = {0255-5476}, doi = {10.4028/www.scientific.net/MSF.879.595}, pages = {595 -- 600}, language = {en} } @misc{MichailovDoynov, author = {Michailov, Vesselin and Doynov, Nikolay}, title = {Analytical-Numerical Modeling Approach for Calculation of the Structural Distortions after Welding and Thermal Straightening}, series = {Journal of Mechanics Engineering and Automation}, volume = {6}, journal = {Journal of Mechanics Engineering and Automation}, number = {5}, issn = {2159-5283}, doi = {10.17265/2159-5275/2016.05.004}, pages = {246 -- 253}, language = {en} } @misc{JakobsenZhangDoynovetal., author = {Jakobsen, Daniel and Zhang, Wei and Doynov, Nikolay and B{\"o}hm, Anna and Malzbender, J{\"u}rgen and Michailov, Vesselin and Roosen, Andreas}, title = {Thermal shock behaviour of laminated multilayer refractories for steel casting applications reinforced by residual stresses}, series = {Ceramics International}, volume = {42}, journal = {Ceramics International}, number = {12}, issn = {0272-8842}, doi = {10.1016/j.ceramint.2016.05.149}, pages = {13562 -- 13571}, language = {en} } @misc{ZhangDoynovOssenbrinketal., author = {Zhang, Wei and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin}, title = {Physical and FE-Simulation of Thermal Shock Behaviour of Refractory Ceramics}, series = {refractories WORLDFORUM}, volume = {8}, journal = {refractories WORLDFORUM}, number = {2}, issn = {1868-2405}, pages = {110 -- 117}, language = {en} } @misc{AtangaZhangDreibatietal., author = {Atanga, Valetine Kubong and Zhang, Wei and Dreibati, Ossama and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin and Scheffler, Michael}, title = {Alumina-mullite Materials for Refractory Applications: Microstructure, Physical and Finite Element Simulation of Thermal Shock Behaviour}, series = {refractories WORLDFORUM}, volume = {4}, journal = {refractories WORLDFORUM}, number = {1}, issn = {1868-2405}, pages = {159 -- 164}, 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} } @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} } @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{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} } @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} } @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} } @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{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} } @misc{KaishevaBokuchavaPapushkinetal., author = {Kaisheva, Darina and Bokuchava, Gizo and Papushkin, Igor and Genchev, Gancho Vladimirov and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin and Petrov, Peter}, title = {Determination of residual stresses in fiber laser welded stainless steel joints by neutron diffraction method}, series = {Proc. SPIE 11047, 20th International Conference and School on Quantum Electronics: Laser Physics and Applications}, journal = {Proc. SPIE 11047, 20th International Conference and School on Quantum Electronics: Laser Physics and Applications}, address = {Nessebar}, doi = {10.1117/12.2516421}, pages = {7}, abstract = {This study presents an experimental results of residual stress states in stainless steel plate samples with size 100 x 50 x 10 mm welded using a high-power fiber laser. The technological parameters of the welding process were: laser power Q = 15 kW; laser spot size = 0.65 mm; welding speed V = 3 m/min; 4 m/min; 5 m/min, using 30 L/min of protective Ar gas. The neutron diffraction method was used to determine the residual stresses in the bulk of the material. The neutron experiments were performed on the FSD diffractometer at the IBR-2 pulsed reactor in the Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research - Dubna, Russian Federation. The measured residual stress distributions exhibit maxima at weld seam centers. As expected, for all specimens the residual stress is falling down in regions distant from the weld zone. Maximal residual stress value of 492 MPa was observed for sample welded with speed of V = 5 m/min.}, language = {en} } @misc{MorozovaObrosovNaumovetal., author = {Morozova, Iuliia and Obrosov, Aleksei and Naumov, Anton and Kr{\´o}licka, Aleksandra and Golubev, Iurii and Bokov, Dmitry O. and Doynov, Nikolay and Weiß, Sabine and Michailov, Vesselin}, title = {Impact of Impulses on Microstructural Evolution and Mechanical Performance of Al-Mg-Si Alloy Joined by Impulse Friction Stir Welding}, series = {Materials}, volume = {14}, journal = {Materials}, number = {2}, issn = {1996-1944}, doi = {https://doi.org/10.3390/ma14020347}, abstract = {Impulse Friction Stir Welding (IFSW) was utilized to join 6082-T6 alloy plates at various impulse frequencies. A distinctive feature of IFSW is the generation of mechanical impulses that enhances the forging action of the tool, and thereby, alters the weld microstructure. The microstructural evolution in the Stir Zone (SZ) with special focus on the strengthening precipitation behavior, and overall mechanical properties of the IFSW joints have been investigated. It was demonstrated that the strengthening β″ precipitates reprecipitated in the SZ of the IFSW joints during natural aging. In contrast, no precipitates were found in the SZ of the Friction Stir Welding (FSW) weld. Partial reversion of β″ after IFSW is supposed to occur due to more developed subgrain network and higher dislocation density introduced by impulses that accelerated precipitation kinetics. Dynamic recrystallisation was facilitated by impulses resulting in a fine, homogeneous structure. There was no significant difference between the microhardness in the SZ, tensile and yield strength of the FSW and IFSW joints. However, the application of impulses demonstrated the smoothing of the hardness reduction in the transition region at the advancing side. The shift of the fracture location from the Heat-Affected Zone (HAZ) by FSW to the SZ as well as higher elongation of the joints by IFSW of lower frequencies could be related to the grain refinement and the change of the grain orientation.}, language = {en} } @misc{JokischDoynovOssenbrinketal., author = {Jokisch, Torsten and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin}, title = {Heat source model for electron beam welding of nickel-based superalloys}, series = {Materials testing : Materialpr{\"u}fung}, volume = {63}, journal = {Materials testing : Materialpr{\"u}fung}, number = {1}, issn = {2195-8572}, doi = {10.1515/mt-2020-0002}, pages = {17 -- 28}, language = {en} } @misc{ValkovKotlarskiOrmanovaetal., author = {Valkov, Stefan and Kotlarski, Georgi and Ormanova, Maria and Doynov, Nikolay and Ossenbrink, Ralf and Petrov, Peter and Michailov, Vesselin}, title = {Crystallography and Mechanical Properties of Wire Arc Additively Manufactured Al5356 Components}, series = {Comptes Rendus de L'Academie Bulgare des Sciences}, volume = {74}, journal = {Comptes Rendus de L'Academie Bulgare des Sciences}, number = {No. 6}, issn = {1310-1331}, doi = {10.7546/CRABS.2021.06.03}, pages = {820 -- 827}, abstract = {In this study, we present results of the evolution of the crystallographic texture and imperfections, as well as the corresponding mechanical properties of wire and arc additively manufactured (WAAM) Al5356 specimens, studied by X-ray diffraction (XRD) and tensile testing, respectively. The results show that the phase composition is in the form of a face-centred cubic (fcc) crystal structure, corresponding to the base material, as well as some traces of oxide phase Al2O3. The WAAM specimen growing is accompanied by a slight change in the preferred crystallographic orientation, from (111) to (200) and a decrease in the imperfections concentration. Also, it was found that the ultimate tensile strength (UTS), yield strength (YS), and elongation slightly decrease from the initial to the more advanced stages of growth.}, language = {en} } @misc{JokischDoynovOssenbrinketal., author = {Jokisch, Torsten and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin and B{\"o}ttger, Bernd and Senger, Aleksej}, title = {Analysis of temperature field during electron beam welding of hot crack sensitive nickel base alloy}, series = {IEBW International Electron Beam Welding Conference: lectures of the 6th International Conference taking place online on 9 to 10 March 2021}, journal = {IEBW International Electron Beam Welding Conference: lectures of the 6th International Conference taking place online on 9 to 10 March 2021}, publisher = {DVS Media GmbH}, address = {D{\"u}sseldorf}, isbn = {978-3-96144-133-4}, pages = {81 -- 87}, abstract = {The use of temperature-resistant nickel-based superalloys in the field of industrial gas turbines is increasing due to constantly rising operating temperatures. Among different joining methods the electron beam welding is commonly used for manufacturing of turbine components because it provides a reduced heat input. However, the highly localized beam impact causes high temperature gradients and leads to the formation of hot cracks. Welding of such material with a high brittle temperature range is challenging and needs an increasing effort of process adaption. Experiments indicate a significant improvement of hot crack susceptibility when welding outside the common welding parameter range. To understand these observations a study of the temperature field in the specimens using numerical simulations was carried out. For this purpose, a validated simulation model was used. Special attention was paid to the domain in close vicinity of the weld pool. The results illustrate the velocity of solidification isotherm as well as the temperature rates when crossing the melting point. Finally, the relations between thermal fields, crack types and distributions in the different specimens are discussed.}, language = {en} } @misc{PiottWerberSchleussetal., author = {Piott, Michael and Werber, Alexandra and Schleuss, Leander and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin}, title = {A study of the heat transfermechanism in resistance spot welding of aluminum alloys AA5182 and AA6014}, series = {International Journal of Advanced Manufacturing Technology}, volume = {Vol. 111}, journal = {International Journal of Advanced Manufacturing Technology}, issn = {0268-3768}, doi = {10.1007/s00170-020-05650-x}, pages = {263 -- 271}, abstract = {This work investigates heat transfer mechanism of aluminum resistance spot welding process. The main target is to determine thermal contact conductance and heat transfer coefficients for natural convection and thermal radiation at ambient air and forced convection inside the water-cooled electrodes. For this purpose, the heat transfer of hot sheets in a welding gun for aluminum alloys AA5182 and AA6014 is analyzed experimentally and numerically. The transient temperature field is measured by several thermocouples in a simplified experimental setup. Subsequent thermal-mechanical coupled finite element simulations of the experiments were used to calibrate the heat transfer coefficients. The heat transfer coefficient for natural convection and thermal radiation to ambient air is 13 W m2 K and the heat transfer coefficient for forced convection of electrode water-cooling is 25,000 W m2 K. The results indicate that the thermal contact conductance can be assumed ideal for welding process. Additionally, the finite element model is validated by the measured and calculated dissipated heat due to forced convection. Finally, a sensitivity analysis is performed to compare the influence of maximum and minimum heat transfer coefficients of forced convection (water-cooling) on transient temperature field and dissipated heat of sample AA5182.}, language = {en} } @misc{JokischDoynovOssenbrinketal., author = {Jokisch, Torsten and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin}, title = {Analysis of Local Strain Evolution during Electron Beam Welding of Hot Crack Sensitive Nickel Base Conventionally Cast Alloy 247 LC CC}, series = {Journal of Materials Engineering and Performance}, volume = {31}, journal = {Journal of Materials Engineering and Performance}, number = {9}, issn = {1544-1024}, doi = {10.1007/s11665-022-06660-4}, pages = {7009 -- 7017}, abstract = {Among different joining methods, the electron beam welding is recently applied for manufacturing of turbine components from temperature-resistant nickel-based conventionally cast Alloy 247 LC CC. However, the high tendency to hot cracking, in particular the formation of solidification cracks, remains a major challenge. Experiments indicate a significant reduction in hot cracks if the welding is performed outside the common welding parameter range. To understand these observations, a study of local thermo-mechanical conditions during electron beam welding of Alloy 247 samples was carried out using numerical simulations. The results were subsequently compared with reference test welds. For this purpose, a finite element model for coupled transient thermal and mechanical analysis was created and used. The work presents a comparative analysis of the evolution of strain components in brittle temperature range during cooling, considering the distribution and orientation of the cracks. Various relations between local strain kinetics and crack appearance, with notable influence of the plastic strain vector, were observed. Finally, the aspects of assessment of hot crack susceptibility with aid of thermo-mechanical welding simulation are discussed.}, language = {en} } @misc{MorozovaKrolickaObrosovetal., author = {Morozova, Iuliia and Kr{\´o}licka, Aleksandra and Obrosov, Aleksei and Yang, Yitong and Doynov, Nikolay and Weiß, Sabine and Michailov, Vesselin}, title = {Precipitation phenomena in impulse friction stir welded 2024 aluminium alloy}, series = {Materials Science and Engineering: A}, journal = {Materials Science and Engineering: A}, issn = {0921-5093}, doi = {10.1016/j.msea.2022.143617}, pages = {1 -- 11}, abstract = {Microhardness variations across the friction stir welded (FSW) and impulse friction stir welded (IFSW) AA2024-T351 joints have been elucidated by the transformations of the S-Al2CuMg phase with a special focus on a distinguished hardness peak within the heat-affected zone (HAZ) of the impulse welds. The increase in hardness within the stir zone (SZ) originated from the partial re-precipitation of the initial Guinier-Preston-Bagaryatsky zones (GPB) and metastable S needles, previously dissolved.) Formation and growth of stable S precipitates via coalescence accounted for the softening through the thermo-mechanically affected zone (TMAZ). The peak strengthening within the HAZ of the IFSW joints was mainly caused by the dense needle-shaped S particles, which can be explained by a mutual influence of the process specific temperature and strain cycles. Dislocations and subgrain boundaries introduced to the material due to plastic deformation facilitated the nucleation of strengthening S precipitates in the HAZ. It demonstrates that the impact of deformation should be considered by the characterization of the precipitation development in the HAZ.}, 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} } @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{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{EvdokimovDoynovOssenbrinketal., author = {Evdokimov, Anton and Doynov, Nikolay and Ossenbrink, Ralf and Obrosov, Aleksei and Weiß, Sabine and Michailov, Vesselin}, title = {Thermomechanical laser welding simulation of dissimilar steel-aluminum overlap joints}, series = {International Journal of Mechanical Sciences}, volume = {190}, journal = {International Journal of Mechanical Sciences}, issn = {1879-2162}, doi = {10.1016/j.ijmecsci.2020.106019}, pages = {18}, abstract = {Mixing of steel and aluminum within the weld pool during keyhole laser welding results in a complex dissimilar microstructure, which in turn, initiates a shift in weld metal mechanical properties. In this study, a numerical model for computation of distortions in laser-welded dissimilar overlap joints (austenitic stainless steel 304 - 6082-T6 aluminum alloy), which considers properties of the mixed steel-aluminum weld metal was developed. The required yield strength, Young's modulus, and strain hardening exponent of the weld metal were experimentally determined using the indentation technique coupled with energy-dispersive X-ray spectroscopy. The designed material model calculates the weld elastic-plastic properties as a function of the aluminum concentration. The softening of the alloys in the heat-affected zone was determined by physical simulations and considered as a function of maximum temperature. Computed and measured distortions showed good agreement for various welding regimes with an average deviation of 18.4\%. The sensitivity analyses indicated that the application of the developed weld material model significantly improves the accuracy of the thermomechanical simulations.}, language = {en} } @misc{PiottWerberSchleussetal., author = {Piott, Michael and Werber, Alexandra and Schleuss, Leander and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin}, title = {Numerical and experimental analysis of heat transfer in resistance spot welding process of aluminum alloy AA5182}, series = {International Journal of Advanced Manufacturing Technology}, volume = {Vol. 111}, journal = {International Journal of Advanced Manufacturing Technology}, number = {5-6}, issn = {0268-3768}, doi = {10.1007/s00170-020-06197-7}, pages = {1671 -- 1682}, abstract = {In this work, a numerical model and experiments are used to investigate heat transfer processes during resistance spot welding process of aluminum. For this purpose, calibrated heat transfer conditions and thermal contact conductance are transferred from a previous work to a coupled thermal-electrical-mechanical finite element model. First, all domains of the numerical model are validated by an experimental study. The experimental setup includes the measurement of current, voltage drops, electrode force, electrode displacement, and temperatures while two sheets of aluminum alloy AA5182 are joined. Computational results show that most of the generated Joule heat (78\%) is stored in the electrodes or transferred to cooling water until the end of weld time. Heat transfer by natural convection and thermal radiation is very small and can in general be neglected for complete process. Afterwards, the influence of electrode water-cooling on welding process is investigated numerically. The results indicate that the generation of Joule heat and thermal energy of the sheets during weld time is only slightly affected by electrode water-cooling. As a consequence, water-cooling conditions do not affect nugget formation. In contrast, electrode water-cooling highly influences cooling conditions during hold time.}, 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{GenchevDoynovOssenbrinketal., author = {Genchev, Gancho Vladimirov and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin}, title = {Schweißtechnische Simulation der lokalen Eigenschaften in der W{\"a}rmeeinflusszone von Mehrlagenschweißungen}, series = {ANSYS Conference \& 33rd CADFEM Users' Meeting, 24. - 26. Juni, Bremen, conference proceedings}, booktitle = {ANSYS Conference \& 33rd CADFEM Users' Meeting, 24. - 26. Juni, Bremen, conference proceedings}, publisher = {CADFEM GmbH}, address = {Grafing}, language = {de} } @inproceedings{Doynov, author = {Doynov, Nikolay}, title = {Anwendungsnahe Simulation des thermischen Richtens}, series = {Schweißen in der Maritimen Technik und im Ingenieurbau, 16. Tagung, 20./21. April 2016 in Hamburg}, booktitle = {Schweißen in der Maritimen Technik und im Ingenieurbau, 16. Tagung, 20./21. April 2016 in Hamburg}, publisher = {GSI SLV Nord}, address = {Hamburg}, pages = {78 -- 88}, language = {de} } @inproceedings{ZhangDoynovOssenbrinketal., author = {Zhang, Wei and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin and Scheithauer, Uwe and Michaelis, Alexander}, title = {Investigation of thermal shock behaviour of refractory ceramics based on the calcium-aluminate}, series = {14th Biennial Worldwide Congress Unified International Technical Conference on Refractories (UNITECR) 2015, Vienna, Austria, September 15-18, 2015}, booktitle = {14th Biennial Worldwide Congress Unified International Technical Conference on Refractories (UNITECR) 2015, Vienna, Austria, September 15-18, 2015}, address = {Hannover}, isbn = {978-3-9815813-1-7}, language = {en} } @book{PasternakStapelfeldLaunertetal., author = {Pasternak, Hartmut and Stapelfeld, Christoph and Launert, Benjamin and Michailov, Vesselin and Doynov, Nikolay}, title = {Ermittlung der Tragf{\"a}higkeit neuartiger st{\"a}hlerner Schalenbauwerke unter realit{\"a}tsnaher Ber{\"u}cksichtigung des Schweißverzugs}, publisher = {Forschungsvereinigung Stahlanwendung e. V.}, address = {D{\"u}sseldorf}, isbn = {978-3-946885-89-4}, pages = {227}, language = {de} } @misc{WasilewskiKaneneksDoynovetal., author = {Wasilewski, Eric and Kaneneks, Michael and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin}, title = {Laserstrahlschweißen - Verzugs- und Kaltrissminimierung durch simulationsbasierte Steuerung}, series = {DVD Congress 2020 : Große Schweißtechnische Tagung : DVS Campus : Vortr{\"a}ge der Online-Veranstaltungen vom 14. bis 18. September 2020}, journal = {DVD Congress 2020 : Große Schweißtechnische Tagung : DVS Campus : Vortr{\"a}ge der Online-Veranstaltungen vom 14. bis 18. September 2020}, publisher = {DVS Media GmbH}, address = {D{\"u}sseldorf}, isbn = {978-3-96144-098-6}, pages = {9}, abstract = {Leichtbau und das Streben nach Ressourcen- und Energieeffizienz f{\"o}rdern in den letzten Jahren vermehrt den Einsatz hochfester St{\"a}hle. Das Laserstrahlschweißen dieser Werkstoffe wird in der industriellen Großserienferti-gung zur effizienten Herstellung hochpr{\"a}ziser Bauteile und Komponenten mit h{\"o}chsten Qualit{\"a}tsanforderungen eingesetzt. Die Vermeidung schweißbedingter Fehler wie Schweißverzug und Kaltrissbildung sind dabei von ent-scheidender Bedeutung. Konventionelle Anwendungen erf{\"u}llen diesen Anspruch derzeit bedingt durch sehr enge Prozesstoleranzen und die Auswahl unkritischer Werkstoffe, was die Potentiale der F{\"u}geverbindung begrenzt. Auf Basis von FE-Schweißprozesssimulationen konnten Konzepte entwickelt werden, welche eine Verzugs- und Riss-minderung durch aktive Steuerung des Laserschweißprozesses erm{\"o}glichen. Die zugrundeliegenden Modelle be-r{\"u}cksichtigen zum einen das schweißbedingte Temperaturfeld, Gef{\"u}geumwandlungen und Eigenspannungen f{\"u}r die Berechnung des Verzugs. Zudem wird die lokale Wasserstoffkonzentration berechnet und die Ergebnisse der Schweißprozesssimulation mittels eines Kaltrisstools bewertet, welches werkstoffspezifische Risskriterien enth{\"a}lt. Die F{\"a}higkeit das Verzugs- und Kaltrissverhalten abzubilden, er{\"o}ffnet die M{\"o}glichkeit zur Parametervariation. Aus den erhobenen Daten wurden Konzepte der aktiven Krafteinleitung mit einer dynamischen Werkst{\"u}ckeinspannung abgeleitet, die zu Verzugs- und Kaltrissminimierung f{\"u}hren und die Schweißbarkeit hochfester Werkstoffe f{\"o}rdern.}, language = {de} } @inproceedings{OssenbrinkDoynovMichailov, author = {Ossenbrink, Ralf and Doynov, Nikolay and Michailov, Vesselin}, title = {Welding simulation of aluminium to steel joints by means of arc welding Processes}, series = {10th International Scientific and Technical Conference, Advanced metal materials and technologies (AMMT'2013), June 25-29, Saint Petersburg, 2013}, booktitle = {10th International Scientific and Technical Conference, Advanced metal materials and technologies (AMMT'2013), June 25-29, Saint Petersburg, 2013}, publisher = {Izdat. Polytechn. Univ.}, address = {Saint Petersburg, Russia}, pages = {523 -- 528}, abstract = {The object of the present work is the introduction of a welding simulation approach for aluminium to steel welded joints which are realised by short-arc welding. The study is carried out with special emphasis on the simulation of temperature field by means of conduction solution, on the applicability of different metallurgical models as well as the aspects of the mechanical simulation of the residual welding stresses and distortions. As result an approved heat source model is suggested and the calibration parameters are presented. For the modelling of the microstructure and corresponding thermomechanical material properties in the heat affected zone different material models are validated. They are used to simulate the welding residual stresses and distortions. Furthermore, the welding simulation of a real component as well as a simulation study of different welding scenarios is presented.}, language = {en} } @inproceedings{GenchevDoynovOssenbrinketal., author = {Genchev, Gancho Vladimirov and Doynov, Nikolay and Ossenbrink, Ralf and Michailov, Vesselin}, title = {Simulation des Mehrlagenschweißens unter Ber{\"u}cksichtigung der Gef{\"u}geumwandlungen}, series = {Conference proceedings, 2012 - ANSYS Conference \& 30. CADFEM Users' Meeting, 24. - 26. Oktober 2012, Kassel}, booktitle = {Conference proceedings, 2012 - ANSYS Conference \& 30. CADFEM Users' Meeting, 24. - 26. Oktober 2012, Kassel}, publisher = {CADFEM GmbH}, address = {Grafing}, pages = {Art. 2.2.9}, abstract = {Der Konferenzvortrag stellt das entwickelte M-STAAZ Modell vor. Mit dem M-STAAZ l{\"a}sst sich in der FE-Simulation die {\"A}nderung der Werkstoffkennwerte bei mehrmaliger Temperaturbelastung wie in der WEZ von Mehrlagenschweißungen ber{\"u}cksichtigen.}, language = {de} } @inproceedings{GenchevOssenbrinkDoynovetal., author = {Genchev, Gancho Vladimirov and Ossenbrink, Ralf and Doynov, Nikolay and Michailov, Vesselin}, title = {Material Properties of the HAZ of Multi-Pass Welded Joints from low alloyed Steel}, series = {Junior Euromat 2012, Paperlist}, booktitle = {Junior Euromat 2012, Paperlist}, pages = {A297}, language = {en} }