TY - JOUR A1 - Vöse, Markus A1 - Otto, F. A1 - Fedelich, Bernard A1 - Eggeler, G. T1 - Micromechanical investigations and modelling of a copper-antimony-alloy under creep conditions N2 - In many practical applications, creep damage is the limiting factor of a component’s lifetime. A micromechanical model of creep induced grain boundary damage is proposed, which allows for the simulation of creep damage in a polycrystal within the framework of finite element analysis. The model considers grain boundary cavitation and sliding according to a micromechanically motivated cohesive zone model while creep deformation of the grains is described following the slip system theory. The model can be applied to idealised polycrystalline structures, such as a Voronoi tessellation or, like demonstrated here, to real grain structures of miniature creep specimens. Creep tests with pure Cu single crystals and with a coarse-grained polycrystalline Cu-1 wt.% Sb alloy at 823 K have been performed and used to calibrate the polycrystal model. The grain structure of the polycrystalline Cu–Sb specimens has been revealed by the EBSD method. Extensive grain boundary sliding and cavitation has been observed in the crept specimens. Grain boundary sliding has been found to promote wedge-type damage at grain boundary triple junctions and to contribute significantly to the total creep strain. Furthermore, the assumed stress sensitivity of the models grain boundary cavity nucleation rate strongly influences the development of wedge-type damage. KW - Creep KW - Damage KW - Copper–Antimony-Alloy KW - Grain boundary cavitation KW - Grain boundary sliding KW - Micromechanical model PY - 2014 U6 - https://doi.org/10.1016/j.mechmat.2013.09.013 SN - 0167-6636 SN - 1872-7743 VL - 69 IS - 1 SP - 41 EP - 62 PB - Elsevier Ltd. CY - Amsterdam AN - OPUS4-29396 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Vöse, Markus A1 - Fedelich, Bernard A1 - Owen, J. T1 - A simplified model for creep induced grain boundary cavitation validated by multiple cavity growth simulations N2 - Simulations of cavitation processes on a grain boundary under creep conditions have been carried out, taking into account nucleation, growth, coalescence and sintering of multiple cavities. Cavity growth rates have been calculated through a resolution procedure based on the use of holomorphic complex functions. Three dimensionless parameters have been identified that are responsible for the cavitation development. Parameter studies have been carried out in order to characterise the mechanisms that are responsible for the cavitation development. These studies have been used to develop a physically motivated, simplified model in order to describe the cavitation development of the simulations in terms of global state variables. The simplified model is able to reproduce the cavitation development for all considered combinations of the dimensionless parameters and allows the description of the thickening behaviour of a cavitating grain boundary. KW - Creep damage KW - Grain boundary diffusion KW - Cavitation KW - Simulation PY - 2012 U6 - https://doi.org/10.1016/j.commatsci.2012.01.033 SN - 0927-0256 VL - 58 SP - 201 EP - 213 PB - Elsevier CY - Amsterdam AN - OPUS4-25630 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Vöse, Markus A1 - Fedelich, Bernard A1 - Otto, F. A1 - Eggeler, G. T1 - Micromechanical modeling of creep damage in a copper-antimony alloy N2 - A micromechanical model of creep induced grain boundary damage is proposed, which allows for the simulation of creep damage in a polycrystal with the finite element method. Grain boundary cavitation and sliding are considered via a micromechanically motivated cohesive zone model, while the grains creep following the slip system theory. The model has been calibrated with creep test data from pure Cu single crystals and a coarse-grained polycrystalline Cu-Sb alloy. The test data includes porosity measurements and estimates of grain boundary sliding. Finally, the model has been applied to Voronoi models of polycrystalline structures. In particular the influence of grain boundary sliding on the overall creep rate is demonstrated. T2 - ECF20 - 20th European conference on fracture CY - Trondheim, Norway DA - 28.06.2014 KW - Creep damage KW - Grain boundary sliding KW - Cohesive zone KW - Micromechanical model KW - Polycrystal PY - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-309914 SN - 2211-8128 VL - 3 SP - 21 EP - 26 PB - Curran CY - Red Hook, NY, USA AN - OPUS4-30991 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vöse, Markus A1 - Fedelich, Bernard ED - Maruyama, K. ED - Abe, F. ED - Igarashi, M. ED - Kishida, K. ED - Suzuki, M. ED - Yoshimi, K. T1 - Grain boundary cavitation under time-varying normal stresses T2 - 12th International conference on creep and fracture of engineering materials and structures CY - Kyoto, Japan DA - 2012-05-27 KW - Creep damage KW - Grain boundary diffusion KW - Cavitation KW - Simulation KW - Evolution equations PY - 2012 SP - 1 EP - 4(?) AN - OPUS4-27544 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vöse, Markus A1 - Fedelich, Bernard T1 - Simulation of creep damage in a Cu polycrystal under multiaxial loading N2 - The stress States of components under Service conditions differ in general from the loading conditions that are routinely applied during material testing. When data that results, e.g., from uniaxial testing should be used for lifetime assessment, a good understanding of the failure behaviour in dependence of the stress state is necessary. For polycrystalline materials under high temperature loading, the development of creep damage is one important factor that limits a component’s lifetime. For cases where creep damage is related to the nucleation and growth of grain boundary cavities, the local normal stress acting on a grain boundary has been found to have a strong influence on the damage development. Hence, creep damage is usually localized along planes that lie perpendicular to the maximum principal tensile stress. T2 - CREEP 2015 - 13th International conference on creep and fracture of engineering materials and structures CY - Toulouse, France DA - 31.05.2015 PY - 2015 SP - 175 EP - 176 AN - OPUS4-33455 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Vöse, Markus T1 - Mikromechanische Modellierung der Korngrenzenschädigung in einer Kupferlegierung unter Kriechbeanspruchung N2 - Mit dem Ziel, die auf der Ebene der Kornstruktur ablaufenden Prozesse mit in die Beschreibung des Kriechverhaltens polykristalliner Werkstoffe einzubeziehen, wurde in der vorliegenden Arbeit zunächst die Schädigungsentwicklung einer einzelnen Korngrenze untersucht. Hierfür wurde eine spezielle Simulationsmethode verwendet, deren Lösungsansatz auf holomorphen Funktionen basiert. Die für die Simulationen berücksichtigten Mechanismen umfassten insbesondere Nukleation, Wachstum durch Korngrenzendiffusion, Zusammenwachsen und Schrumpfen bis zum vollständigen Sintern von Korngrenzenporen. Auf Grundlage der Simulationsergebnisse konnte ein vereinfachtes Porositätsmodell entwickelt werden, welches die Korngrenzenschädigung durch zwei Zustandsvariablen und die zeitliche Entwicklung durch eine Mechanismen-orientierte Ratenformulierung beschreibt. Um den Einfluss von Korngrenzen in kontinuumsmechanischen Betrachtungen von Polykristallen berücksichtigen zu können, wurde ein Grenzflächenmodell erarbeitet, welches sowohl Schädigung entsprechend dem vereinfachten Porositätsmodell als auch Korngrenzengleiten in Abhängigkeit von einer phänomenologischen Korngrenzenviskosität umfasst. Darüber hinaus wurde ein mikromechanisches Polykristallmodell entwickelt, welches es im Rahmen von Finite-Elemente-Simulationen erlaubt, das Kriechverhalten unter Einbeziehung der Gefügestruktur eines polykristallinen Werkstoffes zu simulieren. Dabei werden die Deformationen einzelner Körner durch ein viskoplastisches Einkristallmodell und die Korngrenzen durch das entwickelte Grenzflächenmodell beschrieben. Die Gefügestruktur wird durch ein Finite-Elemente-Modell abgebildet, wobei die Korngrenzen durch kohäsive Elemente modelliert werden. Durch Auswertung experimenteller Kriechdaten konnte das Polykristallmodell für eine Kupfer-Antimon-Legierung bei einer Temperatur von 823 K kalibriert werden. Die Anpassung des Einkristallmodells erfolgte dabei anhand der Kriechraten von reinen Kupfereinkristallproben. Die experimentelle Erfassung der Korngrenzenabgleitung und der Korngrenzenporosität für grobkörnige Kupfer-Antimon-Proben konnten hingegen zur Anpassung des Grenzflächenmodells genutzt werden. Das kalibrierte Polykristallmodell wurde abschließend in Kombination mit künstlich erzeugten Kornstrukturen genutzt, um zum einen numerische und modellierungstechnische Einflüsse auf die Simulationsergebnisse zu untersuchen. Dabei zeigte sich, dass die Vernetzungsfeinheit nur zu einer vergleichsweise geringen Beeinflussung des makroskopischen Kriechverhaltens führt. Aufgrund des nahezu inkompressiblen Deformationsverhaltens des Einkristallmodells war aber die Nutzung spezieller Kontinuumselementtypen notwendig, um das Auftreten von Volumenlocking zu verhindern. Zum anderen konnte das Kriechverhalten polykristalliner Werkstoffe, zu welchem insbesondere die versagensrelevante Schädigungsentwicklung zählt, für verschiedene Material- und Belastungsparameter analysiert werden. Speziell für die betrachtete Kupfer-Antimon-Legierung zeigte sich, dass das Kriechverhalten durch Korngrenzengleiten geprägt war. Insbesondere die Spannungsumlagerungen an den Korngrenzen waren vergleichbar mit dem Verhalten für ungehindertes Korngrenzengleiten. Darüber hinaus deuteten Simulationen für mehrachsige Belastungszustände darauf hin, dass die Schädigungsentwicklungmaßgeblich durch die maximale Hauptspannung und die von Mises-Spannung beeinflusst wird. N2 - In order to include the processes on the scale of the grain structure into the description of the creep behaviour of polycrystalline materials, the damage development of a single grain boundary has been initially investigated in the present work. For this purpose, a special simulationmethod has been used, whose resolution procedure based on holomorphic functions. The mechanisms taken into account for the simulations include nucleation, growth by grain boundary diffusion, coalescence and shrinkage until complete sintering of grain boundary cavities. These studies have then been used to develop a simplified cavitation model, which describes the grain boundary damage by two state variables and the time-dependent development by a mechanism-oriented rate formulation. To include the influence of grain boundaries within continuum mechanical considerations of polycrystals, an interface model has been developed, that incorporates both damage according to the simplified cavitation model and grain boundary sliding in dependence of a phenomenological grain boundary viscosity. Furthermore a micromechanical model of a polycrystal has been developed that allows to include a material’s grain structure into the simulation of the creep behaviour by means of finite element simulations. Thereby, the deformations of individual grains are expressed by a viscoplastic single crystal model and the grain boundaries are described by the proposed interface model. The grain structure is represented by a finite element model, in which the grain boundaries are modelled by cohesive elements. From the evaluation of experimental creep data, the micromechanical model of a polycrystal has been calibrated for a copper-antimony alloy at a temperature of 823 K. Thereby, the adjustment of the single crystal model has been carried out on the basis of creep rates of pure copper single crystal specimens. The experimental determination of grain boundary sliding and grain boundary porosity for coarse-grained copper-antimony specimens, on the other hand, have been used for the adjustment of the interface model. The calibrated model has finally been used in combination with artificially generated grain structures to investigate influences resulting from numerical and modelling issues. It was found that the mesh size has only a relatively small influence on the macroscopic creep behaviour. But because of the nearly incompressible deformation behaviour of the single crystal model, the use of special purpose continuum element types was necessary to avoid the occurrence of volumetric locking. Also the creep behaviour of polycrystalline materials, which includes the damage development leading to failure, has been analysed for different material and loading parameters. Especially for the copper-antimony alloy under consideration, it becomes evident that the creep behaviour was affected by grain boundary sliding. In particular, stress redistributions at the grain boundaries were comparable to the behaviour of free grain boundary sliding. Furthermore, simulations for multiaxial loading conditions indicated that the damage development is significantly influenced by the maximum principal stress and the von Mises stress. T3 - BAM Dissertationsreihe - 130 KW - Finite-Elemente-Simulationen KW - Kriechen KW - Polykristall KW - Korngrenzenschädigung KW - Kupfer-Antimon-Legierung PY - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-5053 SN - 978-3-9817149-0-6 VL - 130 SP - 1 EP - 205 PB - Bundesanstalt für Materialforschung und -prüfung (BAM) CY - Berlin AN - OPUS4-505 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vöse, Markus A1 - Fedelich, Bernard T1 - Development of a cohesive model for grain boundary damage under creep T2 - 7th Meeting of the TC2 on Micromechanisms of the European Structural Integrity Society CY - Berlin, Germany DA - 2011-11-24 PY - 2011 AN - OPUS4-25303 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vöse, Markus A1 - Fedelich, Bernard T1 - Grain boundary cavitation under time-varying normal stresses T2 - 12th International Conference on Creep and Fracture of Engineering Materials and Structures CY - Kyoto, Japan DA - 2012-05-27 PY - 2012 AN - OPUS4-26301 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vöse, Markus A1 - Otto, F. A1 - Fedelich, Bernard A1 - Eggeler, G. T1 - Micromechanical modelling of a Copper-Antimony-Alloy under creep conditions T2 - 23rd International Workshop on Computational Mechanics of Materials CY - Singapore DA - 2013-10-02 PY - 2013 AN - OPUS4-29264 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vöse, Markus A1 - Fedelich, Bernard T1 - A simplified model for multiple cavity growth controlled by boundary diffusion under creep loading T2 - 2nd International Conference on Material Modelling CY - Paris, France DA - 2011-08-31 PY - 2011 AN - OPUS4-23180 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vöse, Markus A1 - Otto, F. A1 - Kianinejad, Kaveh A1 - Eggeler, G. A1 - Hartmeier, A. T1 - Modellierung des Kriechschädigungsverhaltens einer Kupfer-Antimon-Legierung durh ein mikromechanisches Polykristallmodell T2 - DGM Arbeitskreis Sitzung "Mechanisches Werkstoffverhalten bei hoher Temperatur" CY - Berlin, Germany DA - 2012-09-21 PY - 2012 AN - OPUS4-26625 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vöse, Markus A1 - Fedelich, Bernard T1 - Creep deformation and damage in a polycrystalline Copper-Antimony-Alloy T2 - Colloquium Materials Modelling CY - Stuttgart, Germany DA - 2014-06-05 PY - 2014 AN - OPUS4-30995 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vöse, Markus A1 - Fedelich, Bernard T1 - Simulation of creep damage in a Cu polycrystal under multiaxial loading T2 - 13th International Conference on Creep and Fracture of Engineering Materials and Structures (CREEP 2015) CY - Toulouse, France DA - 2015-05-31 PY - 2015 AN - OPUS4-33387 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Vöse, Markus A1 - Fedelich, Bernard T1 - Creep deformation and damage in a polycrystalline Copper-Antimony-Alloy T2 - 5th European Conference on Computational Mechanics CY - Barcelona, Spain DA - 2014-07-21 PY - 2014 AN - OPUS4-31119 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Fedelich, Bernard A1 - Vöse, Markus ED - Klingbeil, D. ED - Vormwald, M. ED - Eulitz, K.-G. T1 - Modeling of creep damage by multiple cavity growth on grain boundaries T2 - 18th European conference on fracture (ECF 18) - Fracture of materials and structures from micro to macro scale CY - Dresden, Germany DA - 2010-08-30 KW - Creep KW - Cavities KW - Grain boundary KW - Damage PY - 2010 SN - 978-3-00-031802-3 SP - 1 EP - 8 AN - OPUS4-22269 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -