Navigation

Prof. Dr.-Ing. habil. Paul Steinmann

 

 

  • Teilprojekt P10 - Configurational Fracture/Surface Mechanics
    (Third Party Funds Group – Sub project)
    Overall project: Fracture across Scales: Integrating Mechanics, Materials Science, Mathematics, Chemistry, and Physics (FRASCAL)
    Term: 2. January 2019 - 30. June 2023
    Funding source: DFG / Graduiertenkolleg (GRK)
    URL: https://www.frascal.research.fau.eu/home/research/p-10-configurational-fracture-surface-mechanics/
    In a continuum the tendency of pre-existing cracks to propagate through
    the ambient material is assessed based on the established concept of
    configurational forces. In practise crack propagation is
    however prominently affected by the presence and properties of either
    surfaces and/or interfaces in the material. Here materials exposed to
    various surface treatments are mentioned, whereby effects of surface
    tension and crack extension can compete. Likewise, surface tension in
    inclusion-matrix interfaces can often not be neglected. In a continuum
    setting the energetics of surfaces/interfaces is captured by separate
    thermodynamic potentials. Surface potentials in general result in
    noticeable additions to configurational mechanics. This is
    particularly true in the realm of fracture mechanics, however its
    comprehensive theoretical/computational analysis is still lacking.The project aims in a systematic account of the pertinent
    surface/interface thermodynamics within the framework of geometrically
    nonlinear configurational fracture mechanics. The focus is especially on
    a finite element treatment, i.e. the Material Force Method [6]. The
    computational consideration of thermodynamic potentials, such as the
    free energy, that are distributed within surfaces/interfaces is at the
    same time scientifically challenging and technologically relevant when
    cracks and their kinetics are studied.
  • Teilprojekt P5 - Compressive Failure in Porous Materials
    (Third Party Funds Group – Sub project)
    Overall project: Skalenübergreifende Bruchvorgänge: Integration von Mechanik, Materialwissenschaften, Mathematik, Chemie und Physik (FRASCAL)
    Term: 2. January 2019 - 30. June 2023
    Funding source: DFG / Graduiertenkolleg (GRK)
    URL: https://www.frascal.research.fau.eu/home/research/p-5-compressive-failure-in-porous-materials/
    Materials such as solid foams, highly-porous cohesive granulates, for
    aerogels possess a mode of failure not available to other solids. cracks
    may form and propagate even under compressive loads (‘anticracks’,
    ‘compaction bands’). This can lead to counter-intuitive
    modes of failure – for instance, brittle solid foams under compressive
    loading may deform in a quasi-plastic manner by gradual accumulation of
    damage (uncorrelated cell wall failure), but fail catastrophically under
    the same loading conditions once stress concentrations trigger
    anticrack propagation which destroys cohesion along a continuous
    fracture plane. Even more complex failure patterns may be observed in
    cohesive granulates if cohesion is restored over time by
    thermodynamically driven processes (sintering, adhesive aging of newly
    formed contacts), leading to repeated formation and propagation of zones
    of localized damage and complex spatio-temporal patterns as observed in
    sandstone, cereal packs, or snow.We study failure processes associated with volumetric compaction in
    porous materials and develop micromechanical models of deformation and
    failure in the discrete, porous microstructures. We then make a scale
    transition to a continuum model which we parameterise using the discrete
    simulation results.
  • Fractures across Scales: Integrating Mechanics, Materials Science, Mathematics, Chemistry, and Physics/ Skalenübergreifende Bruchvorgänge: Integration von Mechanik, Materialwissenschaften, Mathematik, Chemie und Physik
    (Third Party Funds Single)
    Term: 1. January 2019 - 30. June 2023
    Funding source: Deutsche Forschungsgemeinschaft (DFG)
    URL: https://www.frascal.research.fau.eu/
  • Fracture across Scales: Integrating Mechanics, Materials Science, Mathematics, Chemistry, and Physics (FRASCAL)
    (Third Party Funds Group – Overall project)
    Term: 1. January 2019 - 30. June 2023
    Funding source: DFG / Sonderforschungsbereich / Integriertes Graduiertenkolleg (SFB / GRK)
    URL: https://www.frascal.research.fau.eu/
    The RTG aims to improve understanding of fracture in brittle heterogeneous materials by developing simulation methods able to capture the multiscale nature of failure. With i) its rooting in different scientific disciplines, ii) its focus on the influence of heterogeneities on fracture at different length and time scales as well as iii) its integration of highly specialised approaches into a “holistic” concept, the RTG addresses a truly challenging cross-sectional topic in mechanics of materials. Although various simulation approaches describing fracture exist for particular types of materials and specific time and length scales, an integrated and overarching approach that is able to capture fracture processes in different – and in particular heterogeneous – materials at various length and time resolutions is still lacking. Thus, we propose an RTG consisting of interdisciplinary experts from mechanics, materials science, mathematics, chemistry, and physics that will develop the necessary methodology to investigate the mechanisms underlying brittle fracture and how they are influenced by heterogeneities in various materials. The insights obtained together with the methodological framework will allow tailoring and optimising materials against fracture. The RTG will cover a representative spectrum of brittle materials and their composites, together with granular and porous materials. We will study these at length and time scales relevant to science and engineering, ranging from sub-atomic via atomic and molecular over mesoscale to macroscopic dimensions. Our modelling approaches and simulation tools are based on concepts from quantum mechanics, molecular mechanics, mesoscopic approaches, and continuum mechanics. These will be integrated into an overall framework which will represent an important step towards a virtual laboratory eventually complementing and minimising extensive and expensive experimental testing of materials and components. Within the RTG, young researchers under the supervision of experienced PAs will perform cutting-edge research on challenging scientific aspects of fracture. The RTG will foster synergies in research and advanced education and is intended to become a key element in FAU‘s interdisciplinary research areas “New Materials and Processes” and “Modelling–Simulation–Optimisation”.
  • Bridging scales - from Quantum Mechanics to Continuum Mechanics. A Finite Element approach.
    (Third Party Funds Single)
    Term: 1. January 2016 - 30. September 2018
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    The concurrently coupled Quantum Mechanics (QM) - Continuum Mechanics (CM) approach for electro-elastic problems is considered in this proposal. Despite the fact that efforts have been made to bridge different description of matter, many questions are yet to be answered. First, an efficient Finite Element (FE)-based solution approach to the Kohn-Sham (KS) equations of Density Functional Theory (DFT) will be further developed. The h-adaptivity in the FE-based solution with non-local pseudo-potentials, as well as the mesh transformation during the structural optimization and formulation of the deformation map are the main topics to be studied. It should be noted that until now there exists no open-source implementation of the DFT approach which uses a FE basis and provides hp-refinement capabilities. A FE basis is very attractive in the context of the DFT theory because of its completeness, refinement possibility as well as good polarization properties based on domain decomposition. Second, QM quantities will be related to their CM counterparts (e.g. displacements, deformation gradient, the Piola stress, polarization, etc). This will be achieved using averaging in the Lagrangian configuration. To that end the full control over a FE-based solution of the KS equations is required. The procedure is then to be tested on a representative numerical example - bending of a single wall carbon nanotube. On the CM side, the surface-enhanced continuum theory will be utilized to properly capture surface effects. It should be noted that although several theoretical works exist on this matter, no numerical attempts have been made to check their validity on test examples. Lastly, based on the correspondence between different formulations, a concurrently coupled QM-CM method will be proposed. Coupling will be achieved in a staggered way, i.e. QM and CM problems will be solved iteratively with a proper exchange of information between them. A test-problem of crack propagation in a graphene sheet will be considered. As a long term goal of the project, coupling strategies for electro-elastic problems will be developed. To the best of my knowledge, non of the QM-CM coupling method is capable to handle electro-elastic problems.
  • A hybrid Sampling-Stochastic-Finite-Element-Method for polymorphic, microstructural uncertainties in heterogeneous materials
    (Third Party Funds Group – Sub project)
    Overall project: SPP 1886: Polymorphic uncertainty modelling for the numerical design of structures
    Term: 1. January 2016 - 31. March 2020
    Funding source: DFG / Schwerpunktprogramm (SPP)
    The overarching goal of the proposed project at the methodological side is to establish a computationally tractable numerical method that is suited to capture polymorphic uncertainties in large-scale problems (as arising from the numerical analysis of heterogeneous materials microstructures). On the one hand the method will allow for fuzzy probability distributions of the random parameters (describing a microstructures geometry) and on the other hand the method will be based on only a few reduced basis modes. These ingredients will enable to capture epistemic uncertainties in addition to aleatoric uncertainties in a computationally accessible manner. The overarching goal of the proposed project at the application side is to establish a non-deterministic macroscopic material model. On the one hand the model accounts for the heterogeneity of the underlying material's microstructure by computational homogenization, and on the other hand it captures polymorphic uncertainties in the geometry description of the microstructure. The non-deterministic macroscopic material model then represents the necessary input for the mechanical design of macroscopic (engineering) structures under due consideration of polymorphic uncertainties in the heterogeneous materials microstructure.
  • Meso- and Macroscopic Modelling, Simulation and Numerical Homogenization of the Behaviour of Metallic Materials in Additive Manufacturing
    (Third Party Funds Group – Sub project)
    Overall project: Additive Manufacturing
    Term: 1. July 2015 - 30. June 2019
    Funding source: DFG - Sonderforschungsbereiche
    URL: http://www.sfb814.forschung.uni-erlangen.de/projekte/c-bauteile/teilprojekt-c5.shtml
    If metallic powders are used as base materials in selective beam melting processes, the resulting mesostructure of the solidified material, i.e. the geometry (shape, size) of the crystal grains and their orientation (texture), strongly dependent on the direction and magnitude of the temperature gradient at the solidification front. The objective of this project is the continuum-thermo-mechanical modelling and simulation of the material behaviour, taking into account the process-induced mesostructure. For this purpose, a gradient-enhanced crystal plasticity formulation is used on the mesoscale and the mesoscopic variables are transferred by the help of numerical homogenization to the macroscale, both for the isothermal behaviour after the process as well as for the cooling period during the process, which results in residual strains and accompanying residual stresses.
  • A numerical model of translational and rotational momentum transfer of small on-spherical rigid particles in fluid dominated two-phase flows
    (Third Party Funds Single)
    Term: 1. December 2014 - 31. January 2020
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    The overarching goal of the proposed Mercator project is to establish a numerical model of translational and rotational momentum transfer of small non-spherical rigid particles in fluid dominated two-phase flows. Thereby the main aims are threefold:The first aim is to establish an accurate numerical model for particle-fluid interaction. It will in particular take into account the translational and rotational effects in the fluid flow field, and will put a special focus on the resulting particle rotational motion in terms of the accurate determination of its orientation and angular velocity. Here, the development of an advanced Lagrangian particle tracking algorithm for the tracking of non-spherical particles in a velocity-vorticity resolved fluid flow field and the development of a two-way coupling algorithmwithin a suited BEM framework, based on an advanced source distribution modelwithin the fluid phase, are planned.The second aim is to incorporate non-spherical particle force and torque models to capture the momentum transfer between particles and the fluid flow field. Here special attention will be paid to particle shapes in terms of generic ellipsoidal geometries. In the context of the envisioned rigid body modelling for the particles this will be accompanied by the development of a particle preprocessor in order to provide particle inertia properties.The third aim is to devise accelerated parallel numerical algorithms which will enable accurate and fast computations of the vortical part of the fluid flow field within the previously established BEM framework as well as the efficient solution of the set of DAEs related to the particle motion.The developed algorithms will be validated by comparison with independent computational results and will eventually be applied to the experimentally verified test case of sludge flocsedimentation.
  • Mikroskalige Charakterisierungsmethoden zur Kalibrierung von Stoffgesetzen für Biomaterialien und Kunststoffe
    (Own Funds)
    Term: 1. August 2014 - 31. December 2025
    Aussagefähige Bauteilsimulationen erfordern eine quantitativ exakte Kenntnis der Materialeigenschaften. Dabei sind klassische Charakterisierungsmethoden
    teilweise aufwendig, in der Variation und Kontrolle der Umgebungsbedingungen anspruchsvoll oder in der räumlichen Auflösung begrenzt. Das Projekt beschäftigt sich
    deshalb mit der Ertüchtigung hochauflösender Meßmethoden wie Nanoindentation oder Rastkraftmikroskopie und der komplementierenden Entwicklung numerischer
    Verfahren zur Kalibrierung (Parameteridentifikation) inelastischer Stoffgesetze aus den Meßdaten. Inhärent anspruchsvoll sind dabei die geeignete Gestaltung der
    Probekörper und ihrer Fixierung, die den gesuchten Eigenschaften angepaßte Versuchsführung und die hinreichend genaue Reproduktion derselben im Rahmen der zur
    Parameteridentifikation erforderlichen Finite-Elemente-Simulationen.
     
  • Experimentell basierte Modellierung, Simulation und Kompensation thermischer Einflüsse beim Drehen mesoheterogener Werkstoffe aus Al-MMC. Phase 2
    (Third Party Funds Group – Sub project)
    Overall project: SPP 1480: Modellierung, Simulation und Kompensation von thermischen Bearbeitungseinflüssen für komplexe Zerspanprozesse
    Term: 1. July 2014 - 1. July 2017
    Funding source: DFG / Schwerpunktprogramm (SPP)
    Aluminium-Metall-Matrix-Composltes (Al-MMC) zählen zu einer Gruppe komplexer zweiphasiger Hochleistungswerkstoffe, für die aufgrund Ihrer hervorragenden Funktionseigenschaften zukünftig stark ansteigende Verwendung prognostiziert wird. Bei der Bearbeitung von Werkstücken aus Al-MMC treten prozessbedingt hohe Temperaturen auf. Abhängig von der Höhe der eingebrachten Temperatur können diese zu Werkstückverformungen sowie zu Änderungen im Werkstoffgefüge führen. Um Prozessparameter zu finden, die diese Veränderungen im Werkstück vermeiden, sind heute zeit- und materialintensive experimentelle Untersuchungen notwendig. Aufgrund der hohen Herstellkosten von Al-MMC ist die Reduzierung der Zahl experimenteller Untersuchungen für diese Werkstoffgruppe von besonderer Relevanz. Im Rahmen des hier beantragten Forschungsvorhabens soll daher ein Modell für das thermomechanische Materialverhalten von Al-MMC entwickelt werden, welches eine FE-Simulation des thermischen Einflusses auf das Werkstück bei der Drehbearbeitung ermöglicht. Anhand der Simulationsergebnisse wird eine Kompensation thermischer Einflüsse durch gezielte Prozessführung vorgenommen. In der ersten Antragsphase dieses Vorhabens wird grundlegend die Auswirkung des Temperatureintrags bei der Drehbearbeitung von homogenen Werkstoffen untersucht. Aufbauend auf diesen Untersuchungen erfolgt dann in der zweiten und dritten Antragsphase die Betrachtung mehrphasiger Al-MMC. Dabei wird auch der Einfluss einer variierenden Partikelverteilung auf das thermische Verhalten berücksichtigt werden.
  • Modeling and computation of growth in soft biological matter
    (Third Party Funds Single)
    Term: 1. February 2014 - 30. April 2018
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
  • Multi-scale modeling of nano-structured polymeric materials: from chemistry to materials performance
    (Third Party Funds Group – Sub project)
    Overall project: Multi-scale modeling of nano-structured polymeric materials: from chemistry to materials performance
    Term: 1. January 2014 - 31. December 2016
    Funding source: EU - 7. RP / Cooperation / Verbundprojekt (CP)
  • Modelling and simulation of nonlinear electro-thermo-visco-elastic EAPs(Electronic Electro-Active Polymers)
    (Third Party Funds Single)
    Term: 1. January 2014 - 1. January 2017
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    The numerical modeling and simulation of the behavior of EEAPs (Electronic Electro-Active Polymers) under electric loading is considered in this proposal. Despite the fact that efforts have been made to simulate the behavior of EEAPs, work still needs to be done to model the electro-thermo-mechanical interaction in a body undergoing large deformation and being subjected to the influence of the free space surrounding the material body. First of all, until now there exists no thermo-dynamically consistent model that at the same time accounts for large deformations, nonlinear electric polarization, visco-elasticity and the temperature-dependent electro-mechanical properties of EEAPs. At the moment, there exists no software that is capable of simulating these effects simultaneously. In addition, almost all works in the literature related to EEAPs did not consider the effect of the free space surrounding a body of interest and as a consequence can only be used in the case of simulating condensator-like structures whose thickness is very small in comparison with other dimensions. In this proposal, the behavior of EEAPs will be modeled using the theory of electro-thermo-visco-elasticity and will be simulated by using the finite element method (FEM) coupled with the boundary element method (BEM). The FEM will be used to model the material body and the BEM will be used to model the surrounding free space. Besides the numerical simulation of the electro-thermo-mechanical interaction in EEAPs, the numerical evaluation of material forces in structures with defects made of EEAPs, taking into account the electro-thermo-visco-elastic effect, is also considered. These forces can be used, for example, in the prediction of the propagation of cracks, which can take place in EEAP-based structures under electric loads.
  • Structural optimization of shape and topology using an embedding domain discretization technique
    (Own Funds)
    Term: 1. January 2013 - 31. December 2018
    This project targets the formulation and implementation of a method for structural shape and topology optimization within an embedding domain setting. Thereby, the main consideration is to embed the evolving structural component into a uniform finite element mesh which is then used for the structural analyses throughout the course of the optimization. A boundary tracking procedure based on adaptive (or hierarchical) mesh refinement is used to identify interior and exterior elements, as well as such elements that are intersected by the physical domain boundary of the structural component. By this mechanism, we avoid the need to provide an updated finite element mesh that conforms to the boundary of the structural component for every single design iteration. Further, when considering domain variations of the structural component, its material points are not attached to finite element nodal points but rather move through the stationary finite element mesh of the embedding domain such that no mesh distortion is observed. Hence, one circumvents the incorporation of time consuming mesh smoothing operations within the domain update procedure. In order to account for the geometric mismatch between the boundary of the structural component and its non-conforming finite element representation within the embedding domain setting, a selective domain integration procedure is employed for all elements that are intersected by the physical domain boundary. This is to distinguish the respective element area fractions interior and exterior to the structural component. We rely on an explicit geometry description for the structural component, and an adjoint formulation is used for the derivation of the design sensitivities in the continuous setting.
  • On the Formulation and the Micromechanical Origin of Non-Classical Models of Diffusion
    (Third Party Funds Single)
    Term: 1. July 2012 - 31. July 2019
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    Diffusionsprozesse, insbesondere deren Kopplung mit Verformungen, sind von großer wissenschaftlicher und technologischer Bedeutung in verschiedensten Feldern der Ingenieur-, Material- und Naturwissenschaften und deren Schnittmengen. Hervorstechende Beispiele sind etwa die Modellierung und Simulation von Lötverbindungen, die Entwicklung von Mikrostrukturen in modernen Materialien, wie sie z.B in hochentwickelten sowie zukünftigen einkristallinen Turbinenblättern verwendet werden, mineralische Entmischungen in der Geologie, Schadstoffausbreitung im Umweltbereich, sowie der Arzneimitteltransport in biologischem Gewebe. In vielen dieser Fälle werden die beobachteten Phänomene jedoch durch ein klassisches Ficksches Diffusionsmodell nicht ausreichend genau beschrieben, sondern erfordern die Modellierung als nichtklassische Diffusion. Typische Beispiele für nichtklassische Diffusionsmodelle sind die Cahn-Hillard Gleichung sowie die sogenannte Mikrokräftebilanz von Gurtin. Die übergreifenden Ziele dieses Vorhabens sind daher (i) die Formulierung und die Simulation einer generischen Klasse von nichtklassischen Diffusionsmodellen, (ii) die Ermittlung ihres mikromechanischen Ursprungs, und (iii) ihre Kopplung mit der Deformation. Es sei dabei daran erinnert, dass höhere Gradienten- sowie mikromorphe Formulierungen als Paradigmen erweiterter Kontinuums-modelle eng miteinander verbunden und mit unterschiedlichen Vor- und Nachteilen verknüpft sind. Es ergibt sich daher die Erforschung von Gradienten- und mikromorphen Diffusionsformulierungen als unmittelbares Ziel der Phase I. Um dabei deren mikromechanischen Ursprung zu ergründen, sollen dann die relevanten Antwortgrößen, die in die zugrundeliegenden Feldgleichungen auf der Makroebene eingehen, aus den entsprechenden Größen auf der Mikroebene durch numerische Homogenisierung zweiter Ordnung bestimmt werden. Das erwartete Ergebnis dieses Vorhabens in Phase I ist somit die Klärung des zugrundeliegenden mikromechanischen Ursprungs einer generischen Klasse von nichtklassichen Diffusionsmodellen. Phase II wird sich dann hauptsächlich auf die Kopplung von Diffusion und Verformungen konzentrieren. Insgesamt wird erwartet, dass die Ergebnisse dieses Vorhabens für unterschiedliche Gebiete der Ingenieur-, Material- und Naturwissenschaften aus wissenschaftlicher und technologischer Sicht von großer Bedeutung sein werden. Insbesondere sollen die Entwicklung und das Verständnis im Bereich neuartiger Materialien durch die erwarteten Erkenntnisse dieses Vorhabens unterstützt werden.
  • Multi-scale, Multi-physics Modelling and Computation of magneto-sensitive POLYmeric materials
    (Third Party Funds Single)
    Term: 1. April 2012 - 31. March 2017
    Funding source: EU - 7. RP / Ideas / ERC Advanced Investigator Grant (AdG)
    MOCOPOLY is a careful revision of an AdG2010-proposal that was evaluated above the quality threshold in steps1&2. In the meantime the applicant has made further considerable progress related to the topics of MOCOPOLY. Magneto-sensitive polymers (elastomers) are novel smart materials composed of a rubber-like matrix filled with magneto-active particles. The non-linear elastic characteristics of the matrix combined with the magnetic properties of the particles allow these compounds to deform dramatically in response to relatively low external magnetic fields. The rapid response, the high level of deformations achievable, and the possibility to control these deformations by adjusting the external magnetic field, make these materials of special interest for the novel design of actuators for a fascinating variety of technological applications. It is the overall objective of this proposal to uncover the process-microstructure-properties relations of the emerging novel multi-scale, multi-physics material class of magneto-sensitive polymers with the aim to better exploit its promising potential for future, currently unimagined technological applications. This objective will only be achieved by performing integrated multi-disciplinary research in fabrication, characterisation, modelling, simulation, testing and parameter identification. This proposal therefore sets up a work programme consisting of nine strongly interconnected work packages that are devoted to:1) Fabrication of magneto-sensitive polymers2) microstructure characterisation by modelling and simulation3) microstructure characterisation by CT-scanning4) continuum physics modelling at the micro-scale5) computational multi-physics homogenisation6) continuum physics modelling at the macro-scale7) testing at the macro-scale8) multi-scale parameter identification9) macro-scale parameter identification.The work programme is therefore characterised by various feedback loops between the work packages.
  • Adaptive finite elements based on sensitivities for topological mesh changes
    (Own Funds)
    Term: 16. March 2012 - 15. March 2018
    We consider local refinements of finite element triangulations as continuous graph operations, for instance by splitting nodes and inflating edges to elements. This approach allows for the derivation of sensitivities for functionals depending on the finite element solution, which may in turn be used to define local refinement indicators. Thereby, we develop adaptive algorithms exploiting sensitivities for both hierarchical and non-hierarchical mesh changes, and analyze their properties and performance in comparison with established methods.
  • Macroscopic modeling, simulation, and optimization of the selective beam melting process (C03)
    (Third Party Funds Group – Sub project)
    Overall project: SFB 814: Additive Fertigung
    Term: 1. July 2011 - 30. June 2015
    Funding source: DFG / Sonderforschungsbereich (SFB)
    Das Ziel des Teilprojekts ist die makroskopische Modellierung und Simulation strahlbasierter Ferti-gungsprozesse unter simultaner Berücksichtigung des Materialauftrags, thermischer Effekte und inelastischen Materialverhaltens. Kontinuumsmechanische Methoden und Finite-Elemente Simulationen werden eingesetzt, um prozessinduzierte Eigenspannungen, Schädigungen und Bauteilverzug zuverlässig vorherzusagen.
  • A coupled MD-FE simulation method accounting for interphases in nanoparticle filled thermoplastics.
    (Third Party Funds Group – Sub project)
    Overall project: SPP 1369: Polymer-Festkörper-Kontakte: Grenzflächen und Interphasen
    Term: 1. February 2011 - 28. February 2014
    Funding source: DFG / Schwerpunktprogramm (SPP)
    This proposal aims at an extension of a recently developed, hybrid MD-FE simulation scheme towards its application to materials dominated by polymer-solid interphases. Only particle-based methods are able to intrinsically resolve microstructure and mechanical behavior of interphases. Therefore, we proceed with the following setup: A coarse-grained MD domain, which contains a single nanoparticle and as much polymer as necessary to ensure bulk behavior at the boundary, is included into a FE do-main. The FE boundary is used to apply various types of deformations and to record the overall stress responses of particle, surrounding interphase and bulk. With these data, the parameters of a purely continuous counterpart to the hybrid setup are iteratively adjusted until it behaves identically. As its main feature, the continuous ersatz-model substitutes the interphase between particle and polymer by an interface governed by a surface energy in the sense of Gibbs. This can be understood as a condensation of micro-scale property profiles within the 3-D interphase into a 2-D continuum mechanical model. Ultimately, after homogenizing the continuous ersatzmodel, macroscopic structure simulations allowing for a due consideration of interphase effects as occurring around nanoparticles are to be realized.
  • Experimentell basierte Modellierung, Simulation und Kompensation thermischer Einflüsse beim Drehen mesoheterogener Werkstoffe aus Al-MMC.
    (Third Party Funds Group – Sub project)
    Overall project: SPP 1480: Modellierung, Simulation und Kompensation von thermischen Bearbeitungseinflüssen für komplexe Zerspanprozesse
    Term: 1. August 2010 - 30. August 2012
    Funding source: DFG / Schwerpunktprogramm (SPP)
    Aluminium-Metall-Matrix-Composltes (Al-MMC) zählen zu einer Gruppe komplexer zweiphasiger Hochleistungswerkstoffe, für die aufgrund Ihrer hervorragenden Funktionseigenschaften zukünftig stark ansteigende Verwendung prognostiziert wird. Bei der Bearbeitung von Werkstücken aus Al-MMC treten prozessbedingt hohe Temperaturen auf. Abhängig von der Höhe der eingebrachten Temperatur können diese zu Werkstückverformungen sowie zu Änderungen im Werkstoffgefüge führen. Um Prozessparameter zu finden, die diese Veränderungen im Werkstück vermeiden, sind heute zeit- und materialintensive experimentelle Untersuchungen notwendig. Aufgrund der hohen Herstellkosten von Al-MMC ist die Reduzierung der Zahl experimenteller Untersuchungen für diese Werkstoffgruppe von besonderer Relevanz. Im Rahmen des hier beantragten Forschungsvorhabens soll daher ein Modell für das thermomechanische Materialverhalten von Al-MMC entwickelt werden, welches eine FE-Simulation des thermischen Einflusses auf das Werkstück bei der Drehbearbeitung ermöglicht. Anhand der Simulationsergebnisse wird eine Kompensation thermischer Einflüsse durch gezielte Prozessführung vorgenommen. In der ersten Antragsphase dieses Vorhabens wird grundlegend die Auswirkung des Temperatureintrags bei der Drehbearbeitung von homogenen Werkstoffen untersucht. Aufbauend auf diesen Untersuchungen erfolgt dann in der zweiten und dritten Antragsphase die Betrachtung mehrphasiger Al-MMC. Dabei wird auch der Einfluss einer variierenden Partikelverteilung auf das thermische Verhalten berücksichtigt werden.
  • Mehrskalenmodellierung und -simulation der Mechanik von Materialien mit Faserstruktur
    (Third Party Funds Single)
    Term: 1. March 2010 - 30. March 2012
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    Im Fokus dieses Vorhabens steht die mechanische Mehrskalenmodellierung und -simulation von Materialien mit heterogener Faserstruktur (z.B. schaumartige Filterstrukturen oder Dämmungs-materialien aus der Automobilindustrie) unter besonderer Berücksichtigung des Kontakts zwi-schen den einzelnen Fasern. Das Problem wird dabei durch die Berücksichtigung der verschie-denen geometrischen Längenskalen so komplex, dass eine direkte numerische Simulation nicht mehr möglich ist. Für eine effektive Berechnung ist daher ein Mehrskalenzugang erforderlich. Das Vorhaben soll daher zum einen die Anwendungsgrenzen der asymptotischen Homogenisie-rung auf die mechanische Analyse von Kontaktproblemen in der Mikrostruktur von Fasermate-rialien erweitern und damit ein geeignetes effektives phänomenologisches Konstitutivgesetz herleiten. Aufgrund des Kontaktes zwischen den Fasern ist das resultierende effektive phäno-menologische Konstitutivgesetz nichtlinear. Das effektive phänomenologische Konstitutivgesetz soll dabei insbesondere für verschiedene Kontaktgesetze in der Mikrostruktur hergeleitet und umfassend analysiert werden. Zum anderen soll das Mehrskalenproblem inklusive Kontakt in der Mikrostruktur basierend auf dem Konzept eines Repräsentativen-Volumen-Elementes (RVE) direkt berechnet und die nume-rischen Ergebnisse nach einer Volumenmittelung mit dem vorgeschlagenen effektiven phäno-menologischen Konstitutivgesetz gefittet werden. Als Werkzeug zur Simulation eines RVEs (bzw. einer Periodizitätszelle) dient hierbei die Finite-Element-Methode, die sowohl mit 3D Vo-lumenelementen als auch mit Balkenelementen umgesetzt und auf die Behandlung des Kon-takts zwischen den Fasern erweitert werden soll. Das Gesamtvorhaben soll in einer engen Kooperation zwischen den beteiligten Antragstellern mit den jeweiligen Kernkompetenzen im Bereich der asymptotischen Homogenisierung und der Kontinuumsmechanik bzw. Numerischen Mechanik bearbeitet werden.
  • Modeling and computation of solvent penetration in glassy polymers
    (Third Party Funds Single)
    Term: 1. July 2009 - 30. July 2011
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    The main goal of this proposal is the computational modeling of solvent penetration in glassy polymers. For most engineering applications, Fick s law accurately describes diffusive processes, but one of the applications where it miserably fails is in glassy polymers near the glass transition temperature. In the vicinity of the glass transition temperature, when a low molecular weight solvent diffuses into a glassy polymer, the latter is caused to undergo a rubber-glass phase transition. The diffsive process follows non-Fickian behavior. Whereas the classical Fickian diffusion is referred to as case I diffusion, diffusion in glassy polymers is known as non-Fickian „case II diffusion“. A typical system undergoing case II diffusion is polymethylmethacrylate (PMMA) and methanol, for example.Modeling polymers which undergo case II diffusion is of particular interest in pharmaceutical and automotive industries, for example. Due to the importance of diffusion in many industrial and biological processes, a complete examination from a variety of perspectives and techniques is necessary. One tool at hand is the computational modeling at which this project aims. Hereby, an all-embracing theoretical model is to be set up extending existing approaches. Thus the very challenging modeling of non-Fickian behavior is one main task of this project. The numerical implementation of this ambitious theory is to be done subsequently in order to computationally model distinct typical applications from engineering or biomechanics.
  • C3: Parameter and shape optimization in finite elastoplasticity
    (Third Party Funds Group – Sub project)
    Overall project: TRR 73: Umformtechnische Herstellung von komplexen Funktionsbauteilen mit Nebenformelementen aus Feinblechen - Blechmassivumformung
    Term: 1. January 2009 - 31. December 2012
    Funding source: DFG / Sonderforschungsbereich / Transregio (SFB / TRR)
    URL: http://www.tr-73.de
  • Kontinuumsmechanische Modellierung und Simulation der Aushärtung und Inelastizität von Polymeren sowie Interphasen in Klebverbunden
    (Own Funds)
    Term: 1. August 2008 - 31. December 2025
    Die mechanischen Eigenschaften von Polymerwerkstoffen hängen nicht nur von der chemischen Komposition und den Umgebungsbedingungen (Temperatur, Feuchte,...) ab,
    sondern sie variieren teilweise erheblich mit dem verwendeten Aushärteregime und der Temperaturhistorie. Sie sind darüber hinaus vor allem in Verbundsituationen
    u.U. sogar ortsabhängig von den Eigenschaften der Kontaktpartner beeinflußt, bilden also Eigenschaftgradienten (sog. Interphasen) aus.
    Um diese Effekte bei der Simulation von Bauteilen korrekt abbilden zu können werden im Rahmen des Projektes Modelle entwickelt und erweitert,
    die zeit-, orts- und umgebungsabhängige Materialeigenschaften wie Steifigkeitsevolutionen und -gradienten, Aushärteschrumpf und verschiedene Arten von
    Inelastizität (Viskoelastizität, Elastoplastizität, Viskoplastizität, Schädigung) berücksichtigen können.
  • Discrete and Continuous Methods for Modelling and Simulation of Polymeric Materials
    (Own Funds)
    Term: 1. May 2008 - 1. May 2011
    Classical continuum approaches do not explicitly consider the specific atomistic or molecular structure of materials. Thus, they are not well suited to describe properly highly multiscale phenomena as for instance crack propagation or interphase effects in polymer materials. To integrate the atomistic level of resolution, the “Capriccio” method has been developed as a novel multiscale technique and is employed to study e.g. the impact of nano-scaled filler particles on the mechanical properties of polymer-nanocomposites. Further research activities focus on adaptive particle-based regions moving within the continuum, which is essential for multiscale simulation of crack propagation.
  • Electronic electro-active polymers under electric loading: Experiment, modeling and simulation
    (Third Party Funds Single)
    Term: 1. February 2008 - 30. January 2013
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    The mechanical response of electronic electro-active polymers (EEAP) under electric loading is influenced both by mechanical and electric properties of the material. Understanding the behavior of EEAP is vital in the development and design of EEAP based actuators and artifical muscles. Despite the fact that applications of EEAP are very promising, until now only a handful of experimental works have been realized to characterize their material properties. Moreover, so far only one-sided coupled models were used to explain experimental data and there exist discrepancies between meausrement, modeling and simulation. In this proposal, first experimental work will be performed to determine the material characteristics of a typical EEAP material then the electro-mechanical coupling phenomenon exhibited by EEAP will be modeled within the frameof hyperelasticity and viscoelasticity. Finally, by using a variational approach, a formulation representing the fully coupled problem will be derived, discretized, linearized and solved by the Finite Element Method in order to simulate the behavior of EEAP. Benchmark simulations will be performed to validate the applicability of the coupled model. Efforts will also be directed to the study of defects of EEAP by the Material Force Method and with the help of some recent developments in the spatial and material setting of nonlinear electro-elasticity. Especially the Material Force Method will be applied in numerical studies of cracked structures made of EEAP.
  • On the Modelling and Computation of Magneto-Sensitive-Elastomers
    (Third Party Funds Single)
    Term: 1. November 2007 - 31. December 2012
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    Magneto-sensitive-elastomers are smart materials which are composed of a rubber-like basis matrix filled with magneto-active particles. Due to the highly elastic properties of the rubberlike material, these compounds are able to deform significantly, i.e. geometrically non-linearly by the application of external magnetic fields. The rapid response, the high level of deformations that may be achieved, and the possibility of controlling these deformations by varying an external magnetic field, make these materials of special interest; e.g., for vibration and noise suppression. Thus, there is an urgent need for research on this novel material class in terms of modelling within the framework of geometrically nonlinear continuum physics and in the area of suitable computational methods in order to simulate technologically relevant benchmark problems. In this proposal, three main objectives are pursued: (i) the discussion and formulation of appropriate boundary conditions for the coupled magneto-elastic problem, in particular the correct acknowledgement of the influence of the magnetic field on the mechanical boundary conditions; (ii) the development of simple and at the same time realistic forms for the constitutive equations, respecting the microstructural features and including a careful analysis of the ellipticity (or infinitesimal rank-one convexity) condition; and, finally, an objective of utmost importance is (iii) to solve relevant nonlinear boundary value problems by resorting to a newly developed finite element method.
  • Simulations- und versuchsbasierte Untersuchung der Wechselwirkung zwischen Zerspanprozess und Maschinenstruktur beim Hochleistungsflachschleifen
    (Third Party Funds Group – Sub project)
    Overall project: SPP 1180: Prognose und Beeinflussung der Wechselwirkungen von Strukturen und Prozessen
    Term: 1. February 2005 - 30. March 2011
    Funding source: DFG / Schwerpunktprogramm (SPP)
    Aufgrund des mikroskopischen Materialabtrags haben beim Schleifen bereits kleine Schwingungsamplituden und Strukturverlagerungen eine große Bedeutung für das Prozessverhalten und -ergebnis. Vor diesem Hintergrund werden in diesem Forschungsvorhaben Schleifprozess und Schleifmaschine gemeinsam simulativ und experimentell betrachtet, um auftretende Wechselwirkungen und deren Einflüsse auf Prozessverhalten und -ergebnis zu erfassen. In der dritten Projektphase sollen die entwickelten Strategien zur gekoppelten Simulation der Prozess- und Maschinenmodelle detailliert analysiert und optimiert werden. Des Weiteren wird das gekoppelte Simulationssystem an eine weitere Werkzeug-Werkstoff- Paarung angepasst, um dessen Adaptionsfähigkeit zu untersuchen. Dadurch sind weitere messtechnisch überwachte Schleifexperimente zur Verifikation und Kalibrierung notwendig, in denen sowohl Prozessgrößen zur Beschreibung des Maschinenverhaltens als auch Qualitätsmerkmale erfasst werden. Durch Einbeziehung thermischer Effekte sollen das Maschinenmodell verfeinert und die Ergebnisse der gekoppelten Simulation verbessert werden. Die Gesamtheit der durchgeführten experimentellen und numerischen Untersuchungen gewährleistet die Parametrierung und Verifikation der gekoppelten Simulation und ihrer Modelle und ermöglicht die Prognose von Stabilitätskarten zur Korrelation von Qualitätsmerkmalen und Prozessparametern. Diese bieten im Wesentlichen eine Unterstützung bei der Parameterauswahl in der vorbereitenden Prozessauslegung.

Vorlesung (VORL)