Forschung
Liste aller Forschungsprojekte

Liste aller Forschungsprojekte

  • Physics-Informed Data-Driven Simulation
    This project investigates to what extent simulation with neural networks on the one hand and data-based empirical modeling on the other hand can be combined in a symbiotic manner. The ultimate goal is the generation of reliable models for complex dynamical systems known as digital twins.
    Leitung: H. Wessels, P. Wriggers
    Team: H. Wessels
    Jahr: 2020
  • Water-induced damage mechanisms of cyclic loaded high-performance concretes
    The use of offshore wind energy is expanding and fatigue-loaded concrete structures are built that are submerged in water. This currently already applies to so-called grouted joints, where high-strength fine-grained concrete (grout) is used in the steel support structures of offshore wind turbines. Such constructions are subjected to several hundred million load cycles within their service life. An increased water content in the concrete results from the offshore exposure which is principally different to onshore constructions,. Comparatively few investigations of fatigue-tested concrete specimens immersed in water are documented in the literature. Despite the fact, that considerably scatterings occur in these results a clear tendency can be observed. Specimens that are immersed in water have a significantly lower fatigue resistance compared with specimens tested in air. Some investigations also show that fatigue-loaded concrete specimens immersed in water have a significant change in their fracture behaviour compared with specimens tested in air. This can be seen, in tests, for example, by ascending air bubbles, wash-outs of fine particles and premature crack initiation.Water-induced damage mechanisms in fatigue-loaded concrete have indeed been recognised in the past, but they were not identified and described with sufficient precision. Consequently, they cannot be quantified reliably. Based on the existing knowledge gap, the vast majority of these mechanisms have currently escaped numerical modelling and simulation.The aim of this research project is to understand, analyse and quantify macroscopically water-induced damage mechanisms of fatigue-loaded high-performance concretes in the Experimental-Virtual-Lab (EVL) with complementary very latest state-of-the-art experimental methods. At the same time, models will be created and numerically implemented on a micromechanical basis that enables proving of hypotheses that will be derived from the experimental investigations. The structural data serve for the validation of these models; the data will be determined by µCT scans, NMR measurements and mercury intrusion porosimetry.After a first clarification of the origin of mechanisms by the EVL, modelling at the macroscopic level will be attempted on the basis of the micromechanical investigations. In this way it will be verified, how the water influences the degradation behaviour of fatigue-loaded high-performance concretes and which additional active, water-induced damage mechanisms are decisively involved in the degradation process. It will be possible for the first time to carry out a prediction of the degradation behaviour of fatigue-loaded high-performance concretes immersed in water based on microstructurally orientated parameters.
    Leitung: Fadi Aldakheel, Peter Wriggers
    Jahr: 2020
    Förderung: DFG SPP 2020, zweite Förderperiode
    Laufzeit: 3 Jahre
  • Numerical simulation of pile installation in a hypoplastic framework using an SPH based Method
    In this project, a 3D computational tool using smoothed particle hydrodynamics (SPH) is developed which based on a hypoplastic constitutive approach for the mechanical behavior of the soil. The numerical code is firstly validated against a benchmark problem. Then several test cases are simulated including monotonic and vibratory penetration of piles into the soil. A good agreement with the experimental observation is found. Additionally, the impact of pile running in the presence of sheetpiles (retainers) are investigated to see how pile running can alter the applied forces on the sheet piles. The simulation of such complex geotechnical problems which involve large deformation, material nonlinearity and moving boundary conditions demonstrates the applicability and versatility of the proposed numerical tool in this field.
    Leitung: Peter Wriggers
    Team: Meisam Soleimani, Christian Weißenfels
    Jahr: 2020
  • Virtual Element Method for 3D Contact
    Contact plays a very important role in engineering problems, where two or more bodies interact with each other through their surfaces. Many techniques were developed in the past, to formulate the contact constraint at the contact interface between two bodies. Nevertheless, VEM provides efficient and robust properties to enforce the contact constraint through the contact interface. Investigations in 2D have been done so far. This work aims an extensions of VEM to 3D contact problems.
    Leitung: F. Aldakheel, B. Hudobivnik, P. Wriggers
    Team: M. Cihan
    Jahr: 2020
  • Peridynamic Petrov-Galerkin Method
    A Generalization of the Peridyamic Theory of Correspondenc Materials
    Leitung: Christian Weißenfels, Peter Wriggers
    Team: M.Sc. Tobias Bode
    Jahr: 2019
  • Modelling and simulation of the joining zone during the tailored forming process
    In this project, micromechanically motivated thermo-chemo-mechanical material models are developed on a microscopic length scale and transformed to an effective macroscopic material model. In order to achieve a high mechanical strength of the hybrid solid component, these material models are used to evaluate the sensitivity of different process parameters after joining and during forming and heat treatment. Moreover, with aid of the the evaluation results the material behaviour of the joining zone can be accurately adjusted during the Tailored Forming process.
    Leitung: F. Aldakheel, P. Wriggers
    Team: C. Böhm, F. Töller
    Jahr: 2019
    Förderung: DFG im Rahmen des SFB 1153
  • Virtual Element Method for Dynamic Applications
    The Virtual Element Method is a recent developed discretization method, which can be seen as an extension of the classical Galerkin finite element method. It has been applied to various engineering fields, such as elasto-plasticity, multiphysics, damage and fracture mechanics. This project focuses on the extension of VEM towards dynamic applications. In the first part the appropriate computation of the Massmatrix regarding the vitual element ansatzspace will be done. In future works, VEM will be applied to engineering problems, considering the dynamic behavior.
    Leitung: F. Aldakheel, B. Hudobivnik, P. Wriggers
    Team: M. Cihan
    Jahr: 2019
  • Effective Characterization and Modelling of Elastomeric Materials for FE-Applications
    Finite-Element simulations are in wide use for the development and design of industrial products. The calculation of rubber parts faces special problems due to the highly nonlinear and time dependent nature of the material. For good prediction of the final product these effects have to be captured by the underlying material models. Although there is a vast amount of different models, most of them do not offer a sufficient description of the materials behaviour or are numerically inefficient. The latter class, containing more advanced models, suffers from a large amount of parameters. Parameter identification is usually carried out by doing mechanical experiments dependent on the use case of the simulation. There is no guideline regarding the choice, parameters and amount of these experiments. In many cases there has to be a trade-off between numerical cost, effort of characterization and accuracy of the resulting simulation, but the impact of each contribution is not precisely known. The proposed project aims to benchmark both established and emerging models for filled and unfilled elastomers in the context of usability. In more detail, the following indicators shall be investigated -Numerical properties of the models. This includes numerical cost and speed, mesh size dependency and ease of implementation. -Stability and robustness, especially in complex deformation states. -Predictability and plausibility of the models response. Moreover, the relation between fitting parameters and aspects of the materials behaviour is investigated. This question is closely related to the effort of model parameterization. -Physical basis and possibility of physical interpretation of fitting parameters. -Quality of the model fit, which is related to the amount of effects (e.g. relaxation/creep, temperature, volume changes etc.), modelled. -Modularity and extensibility. Based on the benchmarking a scheme for efficient parameter identification shall be drawn, dependent on the specific use case. This includes -Choice of samples and measurement setup. Here, the effort for the different tests is taken into account for different materials. -Measurement protocol including speed and relaxation/creep, if appropriate. -Possibilities to characterize the temperature dependent response.
    Leitung: N.H. Kröger
    Jahr: 2019
    Förderung: Joint Industry Project
    Laufzeit: 3 years
  • Smart hydrogels for drug-delivery and bioprinting applications
    Leitung: Meisam Soleimani
    Team: Aidin Hajikhani
    Jahr: 2018
  • 2D VEM for crack-propagation
    Leitung: F. Aldakheel, B. Hudobivnik, P. Wriggers
    Team: A. Hussein
    Jahr: 2018
    Förderung: IRTG 1627
  • Virtual element method (VEM) for phase-field modeling of brittle and ductile fracture
    Leitung: F. Aldakheel, B. Hudobivnik, P. Wriggers
    Jahr: 2018
    Förderung: DFG SPP 1748
  • In-stent restenosis
    Leitung: Michele Marino, Peter Wriggers
    Team: Meike Gierig
    Jahr: 2018
  • Multiscale Modeling of Buckling of Fiber-Reinforced Polymers
    This project is about multiscale modeling of fiber kinking in unidirectional fiber reinforced composites.
    Leitung: S. Löhnert, P. Wriggers
    Team: S. Hosseini
    Jahr: 2018
    Förderung: DFG (Graduiertenkolleg 1627)
  • Creep deformation of nickel based superalloys
    Modeling of nickel based superalloys on two scales using crystal plasticity and XFEM methods.
    Leitung: P. Wriggers
    Team: L. Munk
    Jahr: 2018
  • Using Machine Learning to Improve the Modelling of Machining and Cutting Processes
    Metal cutting is a fundamental process in industrial production. The fast and accurate on-line prediction of metal cutting processes is crucial for the Intelligent Manufacturing (IM). With the advent of high-speed computing, robust numerical algorithms and machine learning technology, computational modelling serves as a tool for not only accurate but also fast predicting the complex machining processes and understanding the complex physics. In this work, the machine learning based numerical model is developed for simulation of metal cutting processes.
    Leitung: C. Weißenfels, P. Wriggers
    Team: M.Sc. Dengpeng Huang
    Jahr: 2018
    Förderung: China Scholarship Council (CSC)
  • The stress and fatigue analysis of the transportation line
    The conveyor of the production line in Salzgitter Flachstahl GmbH which carries the steel coils is going to be subjected to an extra load due to the bigger coil size. The objective is to do a structural analysis of the conveyor to see if the safety factor of structure is still in the allowable region. Since, the loading condition is naturally variable due to continuously feeding the moving conveyor with steel coils, a fatigue analysis is required in addition to an ordinary static analysis.
    Leitung: Peter Wriggers
    Team: Meisam Soleimani
    Jahr: 2018
  • Charakterisierung sowie Modellbildung zur Beschreibung von Kompressionsmoduli technischer Gummiwerkstoffe
    In der Auslegung von Elastomerbauteilen steht zu Beginn ein aufwendiger Entwicklungsprozess. Dieser Prozess wird oftmals mit Finite-Elemente-Analysen (FEA) zur Vorhersage der mechanischen und dynamischen Eigenschaften begleitet. Insbesondere für Dichtungsanwendungen sind vorab Aussagen über die Verformungen im Bauteil sowie Anpressdrücke, somit Aussagen zur Beständigkeit, von großem Interesse. Im Gegensatz zur Reifenindustrie, die fast ausschließlich sehr große Unternehmen umfasst, sind in der Herstellung von technischen Gummiwaren wie z.B. Feder-Dämpfer-Elementen, Dichtungen, Profilen und Schläuchen zahlreiche kleinere und mittlere Unternehmen tätig, für die die Projektergebnisse und deren Umsetzung auf Grund zu meist relativ geringer Entwicklungskapazitäten besonders wichtig sind. Zur Vorabberechnung per FEA sind Materialmodelle für die technischen Gummiwerkstoffe von Nöten. In Vereinfachung wird für die eingesetzten Elastomere Inkompressibilität angenommen. Diese Annahme ist korrekt für einfache Zugzustände. Überlagern sich einfache Zugzustände mit hydrostatischem Druck können deutliche Abweichungen zwischen der Annahme idealer Inkompressibilität sowie Kompressibilität vorkommen. In realen Bauteilbelastungen wird das Elastomer zudem zyklisch belastet und Teilbereiche im Bauteil erfahren unterschiedliche Belastungshistorien. Die aus der Belastung resultierende Inelastizität und Materialerweichung zum einem und Effekte eines nichtlinearen Kompressionsmoduls zum anderen führen in der Validierung bestehender Materialmodelle zu unbefriedigenden Resultaten. Im Rahmen dieses Projektes soll insbesondere ein Augenmerk auf die Quantifizierung des Kompressionsmoduls auf zyklische hydrostatischer Drücke, vgl. Dichtungen, gelegt werden. Diese Betrachtung findet bisher in der Literatur kaum Beachtung. Auf Grundlage der experimentellen Versuche wird ein geeignetes Materialmodell zur Beschreibung der Effekte erweitert und in der FEA validiert. In der Herstellung von technischen Gummiwaren wie z.B. Feder-Dämpfer-Elementen, Dichtungen, Profilen und Schläuchen sind zahlreiche KMU tätig, für die die Projektergebnisse und deren Umsetzung auf Grund zu meist relativ geringer Entwicklungskapazitäten besonders wichtig sind.
    Leitung: N.H. Kröger
    Jahr: 2018
    Laufzeit: 2 Jahre
  • Water-induced damage mechanisms of cyclic loaded high-performance concretes
    Leitung: P. Wriggers
    Team: F. Aldakheel
    Jahr: 2017
    Förderung: DFG SPP 2020, erste Förderperiode
    Laufzeit: 3 Jahre
  • Environmentally best practices and optmisation in hydraulic fracturing for shale gas/oil development
    Collaborative Research Project funded in the "MSCA-RISE-2016 - Research and Innovation Staff Exchange" Program and the "Horizon2020-EU.1.3.3. - Stimulating innovation by means of cross-fertilisation of knowledge" Program.
    Leitung: Prof. Dr.-Ing. Timon Rabczuk
    Jahr: 2017
    Förderung: : H2020-EU.1.3.3. - Stimulating innovation by means of cross-fertilisation of knowledge
    Laufzeit: 01.01.2017-31.12.2020
  • Computational modeling of in-stent restenosis
    This project aims to develop a computational tool for the modeling of the long-term behaviour of stent deployment, with a special focus on both current and prospective approaches. A multiscale description of arterial constitutive behaviour will be employed, including possible damage due to the stenting procedure. Moreover, the chemo-biological mechanisms underlying the growth and remodelling due to wound healing in tissues will be introduced. Therefore, a multiphysics computational framework will be developed and applied for the analysis of both metal and drug-eluting stents. The project will allow to identify the dominant mechanisms driving in-stent restenosis, deciphering the role of the different molecular species in the pathological remodeling of arteries. The final target is to optimise the clinical outcome of current approaches and propose targeted therapeutic approaches.
    Leitung: M. Marino
    Jahr: 2017
    Förderung: Masterplan SmartBiotecs, MWK (Lower Saxony, Germany)
  • In silico morphogenesis of collagen tissues for targeted drugs and bio-printing
    This project targets to understand the mechanisms behind the morphogenesis and the development of living tissues. To this aim, mechanical and biological actions that contribute to confer tissue desired topology and functionality will be modelled and analysed in silico. A computational framework for the modeling of tissue morphogenesis in natural and bio-printed systems will be developed. In particular, the project will address: the multiscale hierarchical and organized arrangement of tissue constituents; the chemo-mechanical interaction among tissue constituents and among cells; the chemo-mechano-biological mechanisms driving growth and remodeling; the extrusion and the curing of multicellular aggregates blended with bio-inks. Obtained results will target to elucidate mechanisms behind tissue functional/dysfunctional structure; conceive targeted drug systems for stimulating optimal molecular pathways promoting tissue healing; develop novel or optimize existing 3D bio-printing technologies.
    Leitung: M. Marino
    Jahr: 2017
    Förderung: Masterplan SmartBiotecs, MWK (Lower Saxony, Germany)
  • ISPH-based Simulation of the Selective Laser Melting Process
    Development of a thermo-mechanical model for the simulation of the SLM process.
    Leitung: Christian Weißenfels, Peter Wriggers
    Team: M.Sc. Jan-Philipp Fürstenau
    Jahr: 2017
  • Fatigue lifetime prediction using Wavelet transformation induced multi-time scaling (WATMUS)
    A fast and accurate numerical method for fatigue lifetime prediction using eXtended Finite Element Method(XFEM) and WATMUS
    Leitung: S. Löhnert, P. Wriggers
    Team: Tengfei Lyu
    Jahr: 2017
  • Red blood cell simulation using a coupled shell-fluid analysis purely based on the SPH method
    If the rheological behavior of a Red-Blood-Cell (RBC) changes, for example due to some infection, it is reflected in its deformability when it passes through the microvessels. It can severely affect its proper function which is providing the oxygen and nutrient to the living cells. In this research project, a novel 3D numerical method has been developed to simulate RBCs based on the interaction between a shell-like solid structure and a fluid. RBC is assumed to be a thin shell encapsulating an internal fluid (Cytoplasm) which is submerged in an external fluid (blood plasma). The approach is entirely based on the smoothed particle hydrodynamics (SPH) method for both fluid and the shell structure. The method was motivated by the goal to benefit from the Lagrangian and meshless features of SPH in order to handle several complexities in the problem due to the coupling between the RBC membrane as a deformable elastic shell and interior/exterior fluids.
    Leitung: Peter Wriggers
    Team: Meisam Soleimani
    Jahr: 2017
    Laufzeit: 3 Jahre
  • Improved Frictional Models for Pile Installations
    Team: M.Sc. Ajay Harish
    Jahr: 2016
  • Patient-Specific FSI Analysis of the Blood Flow in the Thoracic Aorta
    The complexity of numerical modeling and simulation of blood flow in patient-specific thoracic aorta geometries leads to a number of major computational challenging issues. For instance, for an adequate simulation of the flow and pressure field, the incompressible Navier-Stokes equations have to be solved with the assumption that the relatively thin blood vessels suffer large displacements and undergo large elastic or visco-elastic deformations caused by the pulsatile blood flow. Subsequently, inaccurate predictions would be obtained for the hemodynamic quantities with the very simplifying rigid-wall assumption (CFD modeling). Moreover, when applying only the CFD modeling approach the essential phenomena of pressure wave propagation in cardiovascular systems are disregarded, however these phenomena are of major relevance for clinical practice. Accordingly, strongly coupled FSI schemes are inevitable for comprehensive blood flow simulations in arterial systems, and as blood and vascular walls have comparable densities, monolithic or at least partitioned strongly coupled FSI schemes are required for solving the multi-physics problem with its inherent significant added-mass effects.
    Leitung: P. Wriggers, B. Avci
    Team: B. Avci
    Jahr: 2016
  • Process Simulation for Selective Laser Melting
    A phase change model for solution with the meshfree Galerkin OTM method is developed.
    Leitung: Christian Weißenfels, Peter Wriggers
    Team: M.Sc. Henning Wessels
    Jahr: 2016
  • A Novel Design Approach for Safety at Ship Collision
    Team: M.Sc. Mohsin Ali Chaudry
    Jahr: 2016
  • 3D-Printing of Curing Polymers
    3D-Printing simulations of curing polymers within the concept of Peridynamics are developed.
    Leitung: Christian Weißenfels, Peter Wriggers
    Team: M.Sc. Philipp Hartmann
    Jahr: 2016
    Förderung: DFG (Graduiertenkolleg 1627)
  • Micro-Mechanically Based Modeling of Degradation of Composite Materials with Random Microstructure
    High-performance composite materials, such as carbon-fiber-reinforced polymers, serve as construction materials in various lightweight structures, subjected to high loads. Severe environmental conditions, such as oxidative atmosphere, affect the material microstructure and properties and thus induce material degradation which can lead to premature failure under mechanical loads. There is experimental evidence of a microstructure dependency of the material degradation. The goal of the work in progress is to develop a framework for analysis of the degradation of CFRP upon oxidation which accounts for the random distribution of the phases.
    Leitung: Prof. P. Wriggers, Dr. F. Daghia
    Team: Dipl.-Ing. V. Krupennikova
    Jahr: 2016
    Förderung: DFG (Graduiertenkolleg 1627)
  • Micro- and meso-scale modeling of dental composite materials
    Homogenization techniques can help to optimize composite materials. In this special PhD topic dental composite materials will be investigated. The main goal is, to optimize and improve the mechanical properties of these materials that consist of acrylate polymers and nanoparticles as fillers. One possibility is to change shape and geometric distribution of the fillers. This can be investigated at micro-scale by using homogenization to obtain the effective material parameters and direct computations to investigate material damage. The micro structure of the composite will be obtained by up-scaling of results obtained by the group of P. Behrens and M.A. Schneider who investigate the molecular structure composite. The results are then validated by means of experiments performed in the group of Dr. L. Borchers/Prof. M Stiesch.
    Leitung: P. Wriggers, P. Behrens
    Team: M. Shahbaz
    Jahr: 2016
  • Topology optimization of nano piezo/flexoelectric structures for energy harvesting applications
    Energy harvesters convert the ambient vibration into useful electrical energy. The energy harvesting ability of a structure is characterised by the energy conversion factor, which is the ratio of electrical energy and mechanical energy under external mechanical vibrations. The developments in nanotechnology has lead to the field of Nano Electro Mechanical Systems (NEMS). Nano scale energy harvesting devices with nano sized piezoelectric layers have also become a possibility, where the surface elastic and surface piezoelectric effects become dominant.
    Leitung: X. Zhuang
    Team: Nanthakumar Srivilliputtur Subbiah
    Jahr: 2016
  • Nanoindentation for material property characterization
    In this work, techniques are developed for nanoindentation of soft polymers and brittle powdery materials and measurement of properties like modulus, hardness and fracture toughness.
    Leitung: P. Wriggers, S. Löhnert
    Team: A. B. Harish, V. Kruppernikova
    Jahr: 2016
  • Hypoplastic material models for soil-structure interaction problems
    In this work, a hypoplastic material model is implemented using AceGen with an eventual goal to model soil-structure interaction.
    Leitung: P. Wriggers, C. Weissenfels
    Team: A. B. Harish
    Jahr: 2016
  • Thermal conductivity study of two – phase nano composite material
    This project focues on the thermal conductivity of polymer-matrix nano composites accounting for the interface conductance. The influence of the scale effect and different fillers, i.e. spherical, cylindrical and plate-like fillers (fullerene, carbon nanotubes and graphene sheets) with different ratios (plate diameter to plate thickness and length to diameter ratios for plate-like and cylindrical fillers, respectively) on the thermal conductivity is studied. The representative volume elements (RVEs) possess periodical fillers. The computational homogenization is performed to extract the thermal conductivity of polymer-matrix composites.
    Leitung: X. Zhuang
    Team: Bo He
    Jahr: 2016
  • A 3D CAD/CAE integration using isogeometric symmetric Galerkin boundary element method
    A seamless communication of computer aided design (CAD) and computer aided engineering (CAE) has always been the ultimate goal in product lifecycle management. The forward in- tegration CAD/CAE, in which the simulation tasks are operated directly on CAD model, can be achieved by the isogeometric analysis (IGA) within the conventional finite element method (FEM). Despite of this successful implementation that covers many engineering aspects, the crucial challenge in this CAD/CAE integration is the incompatible geometric representation, namely the volumetric representation of CAE versus the boundary representation of CAD in three-dimensional problems.
    Leitung: X. Zhuang
    Team: Binh H. Nguyen
    Jahr: 2016
  • Micro-structure Topology Optimization of Auxetic Materials
    Auxetic materials with negative Poisson’s ratio can lead to dramatic enhancements in mechanical properties of structures. Such materials are created by modifying periodic unit cells so that the micro-mechanical structure of the unit cells contain hinge-like features. One of the implication of auxetic materials is their resistance to fracture since the lateral expand of material close up potential cracks. Auxetic materials flow toward the point of applied force in the impact problem and result in increase of dense at the impact zone. This show the indentation properties of auxetic materials and are adopted for various needs in military, automotive industries.
    Leitung: X. Zhuang
    Team: Thanh Chuong Nguyen
    Jahr: 2016
  • Higher-order stress-based gradient-enhanced damage model using isogeometric analysis for shell delamination analysis
    The micro-damage associated with diffuse fracture processes in quasi-brittle materials can be described by continuum damage mechanics. In order to overcome the mesh dependence of local damage formulations, non-local and gradient-enhanced approaches are often employed.
    Leitung: X. Zhuang
    Team: Thai Q. Tran
    Jahr: 2016
  • Virtual Element Method for modeling crack propagation
    The virtual element method (VEM) is a very recent numerical technique for solving partial differential equations. It can be seen as a generalization of the Finite Element Method to arbitrary polygons and polyhedra. What makes VEM become special is that the explicit calculation of integral shape functions is not required. It is possible through introduced polynomial functions and defined degrees of freedom. Due to the fact that VEM is able to generate flexible element mesh type even convex elements or concave elements, it allows us to arbitrarily add more nodes to the large stress concentration areas such as crack tips in crack simulation. In this study, we aim to develop an approach utilizing VEM to model crack growth with minimal remeshing or without remeshing. Nevertheless, the final formulation should fulfill the consistency and stability term in our approach to guarantee the accuracy and the convergence.
    Leitung: X. Zhuang
    Team: Minh T.V Nguyen
    Jahr: 2016
  • Durability analysis of composite materials by strong discontinuity embedded multifield framework
    Composite materials experience energy mass transport, potential phase change, chemical degradation and mechanical deformation when subjected to high temperature loading or long term chemical interaction with the surrounding environments, with is a coupled multi-physical-chemical process. Moreover, the evolving micro/macro cracks in the materials will cause extra mass transport and accelerate the degradation of materials, jeopardizing the durability of the structure.
    Leitung: X. Zhuang
    Team: Yiming Zhang
    Jahr: 2016
  • Entropic approach to modeling Mullins effect in non-crystallizing filled elastomers
    The work was done in collaboration with Mrs. Aarohi B. Shah and Dr. Julian J Rimoli of School of Aerospace Engineering, Georgia Tech, USA. In this work, we investigate non-crystallizing nanoparticle-reinforced polymers. The effects of the interface rubber between elastomeric matrix and filler particles and its alteration are investigated as a primary cause of Mullins and Payne effect.
    Leitung: P. Wriggers, J. J. Rimoli
    Team: A. B. Harish, A. B. Shah
    Jahr: 2016
  • Advanced multiscale computational mechanics for physiopathological behavior analysis of tissues and organs
    The physiological functionalities of large biological structures are highly affected by the mechanics of living tissues which is, in turn, related to microstructural arrangement of histological constituents and biochemical environment at nanoscale. Present research activity aims to develop a novel tissue multiscale description, including also inelastic mechanisms, coupled with an advanced computational formulation under finite strain and large-displacement assumptions. As a result, an innovative in-silico tool for simulation of organs and large biological structures will be developed, allowing to predict pathology-related damage or pharmacological-related healing and providing novel diagnostic and clinical indications for highly patient-specific medical treatments.
    Leitung: P. Wriggers, M. Marino
    Jahr: 2015
    Förderung: Alexander von Humboldt-Stiftung
  • Towards multiscale modeling of Abrasive wear
    The work is motivated towards understanding wear as a multiscale-multiphysics approach. A 3D framework is developed to simulate cracks propagation in a microstructure due to contact loading to eventually predict wear trends in filled elastomeric compounds.
    Leitung: P. Wriggers
    Team: A. B. Harish
    Jahr: 2015
  • Mesoscale constitutive modeling of filled elastomers
    In this work, we develop a heterogeneous (or multiphase) constitutive model at the mesoscale model explicitly considering filler particle aggregates, elastomeric matrix and their mechanical interaction through an approximate interface layer. The developed constitutive model is used to demonstrate cluster breakage, also, as one of the possible sources for Mullins observed in non-crystallizing filled elastomers. This work considers the large deformation behavior of the filled elastomers.
    Leitung: P. Wriggers
    Team: A. B. Harish
    Jahr: 2015
  • Numerical Simulation and Experimental Validation of Biofilm Growth
    Biofilms are bacterial colonies growing on solid-fluid interfaces, wherever enough dissolved nutrients are available. Their formation is a complex process in the sense that several Physical phenomena (Reaction-Diffusion-Advection, Sedimentation, Erosion, Fluid-Solid-Interaction) are coupled and consequently different time-scales are involved. In this project, the focus is on the biofilm formation in a flow chamber which resembles the mouth cavity in the vicinity of dental implants. The goal is to develop a computational tool capable of simulating the biofilm growth. Numerical solution of the Navier–Stokes equation in domains with complex boundaries that dynamically change as a result of biological diffusion-reaction, detachment and sedimentation in biofilm growth presents a very serious challenge to grid-based methods. In this project, a fully Lagrangian particle approach(mesh-less method) based on smoothed particle hydrodynamics (SPH) is developed.
    Leitung: P. Wriggers , M. Stiesch
    Team: M. Soleimani
    Jahr: 2015
  • Mesoscale modeling of large deformation behavior of nanoparticle-reinforced elastomers
    Elastomeric materials exhibit distinct fracture behavior compared to several other materials. The fracture process involves extensive chain scission (similar to crazing) in rubbery elastomers. Upon loading, the chains start to align along the direction of loading forming a zone just ahead of the crack tip. Upon further loading, more chains are drawn in from the bulk to eventually fail and leading to formation of crack front. Additionally, due to the viscoelastic nature of these polymers, there is a viscoelastic dissipation of energy just ahead of the crack tip leading to phenomena like crack tip blunting etc. A 3D finite thickness cohesive zone mode, alongside directional node release is used for modeling fracture in filled elastomeric materials.
    Leitung: P.. Wriggers
    Team: A. B. Harish
    Jahr: 2015
  • Large Deformation Cohesive-Zone Element for Fracture in Rubbery Polymers
    In this work, a 3D cohesive zone element is developed considering material and geometric nonlinearities and suitable for modeling large deformations and rotations.
    Leitung: P. Wriggers
    Team: A. B. Harish
    Jahr: 2015
  • Experimental and Numerical investigation of collision of particle-filled double hull vessel
    A novel design approach for safety of double hull vessel is presently being investigated, which involves usage of granular materials between the hull of ship. This strategy provides a medium between the hull which can absorb impact energy and transfer the load to the inner hull. Therefore, impact energy is shared between two hulls, in contrast to localized impact on outer hull only.
    Leitung: P. Wriggers, C. Weißenfels
    Jahr: 2015
  • Simulation of atherosclerotic plaque impact on the red blood cells dynamics in arteries
    Atherosclerosis, a coronary disease, is one of the main cause of mortality in the many countries. Atherosclerosis emerges as a results of hardening and narrowing of the blood vessels , caused by the gradual accumulation of deposits on the inside of arteries walls. This finally leads to atherosclerotic plaque. In this work, The impact of atherosclerotic plaque on red blood cells (RBC) dynamics in the blood vessels is studied. A fluid-solid interaction (FSI) analysis is developed. For the fluid phase, a mesh-less Lagrangian method is adopted which is called smoothed particle hydrodynamics (SPH). RBCs are considered to be the solid phase and are assumed to behave like deformable solid floated in the blood. A strong two way coupling is developed in the context of immersed boundary method (IBM) to capture the accurate fluid-solid interaction.
    Leitung: P. Wriggers
    Team: M.R.Hojjati
    Jahr: 2015
    Förderung: DAAD
  • Gekoppelte Simulation von Aerosolströmungen in asthmatischen Bronchien
    Das Ziel dieses Projektvorhabens ist es, auf Basis eines gekoppelten 3D Mehrfeldmodells die partikelbeladene Luftströmung in gesunden sowie in asthmatisch verengten Bronchien anhand von numerischen Simulationen zu studieren.
    Leitung: P. Wriggers, B. Avci
    Team: J. Stasch, J.-P. Fürstenau
    Jahr: 2014
    Förderung: Leibniz Universität Hannover, Wege in die Forschung
  • In many cases, massive parallel large-scale computations are indispensable for solving problems of practical interest. The numerical treatment of such class problems requires not only highly efficient scalable parallel solvers, moreover, efficient parallel algorithms covering the whole simulation pipeline – also including pre- and post-processing, mesh generation and design solvers considering uncertainties – are essential to model and to simulate large-scale or exascale class problems. The specific goal of this project is therefore the development and implementation of new parallel algorithms and methods that will allow to solve large-scale class problems with high efficiency.
    Leitung: P. Wriggers, B. Avci
    Team: B. Avci
    Jahr: 2014
    Förderung: FP7 of the EU
  • 3D Dynamic Fracture in Heterogeneous Media
    In this project crack growth in brittle media is being investigated by means of the eXtended Finite Element Method (XFEM) and damage mechanics. XFEM is a numerical method, based on the Finite Element Method (FEM), which is especially designed for treating non-smooth problems such as cracks. An essential advantage of the XFEM is that the finite element mesh does not require updating to be able to track the crack path. Enrichments added to classical FE models take into account the effects of a crack or discontinuity. In fiber reinforced materials a fracture process often starts with the delamination between the matrix material and the fibers. At some point these crack propagation processes may lead to an abrupt rupture of the entire structure. A gradient enhanced damage model is being utilized to evaluate degradation of the material at each point of the domain. In gradient enhanced damage models, a chosen length scale behaves as a localization limiter and describes the influence of the microstructure on the damage process. Moreover, such a model smoothes the deformation of the structure and avoids energy dissipation in a narrow band (surface). Damage values obtained based on this approach are used as the crack propagation criterion.
    Leitung: Principal Investigator: Dr.-Ing. Stefan Löhnert - French Co-Advisor in Cachan: Prof. Pierre-Alain Guidault
    Team: Mahmoud Pezeshki
    Jahr: 2014
    Förderung: DFG (Graduiertenkolleg 1627)
  • Application of the Virtual Element Method to Non-Conforming Contact Interfaces
    When using standard Finite Elements the discretization is subject to limitations depending on the element geometry. In contrast to this the Virtual Element Method offers the possibility for elements with an arbitrary number of nodes and special geometries like non-convex polygons or hanging nodes. In this Project the application of the Virtual Elements to different problems is investigated. Here it is used to create an efficient contact discretization.
    Leitung: P. Wriggers
    Team: W.T. Rust
    Jahr: 2014
  • Modeling 3D crack coalescence and percolation with the XFEM and level sets
    In three dimensions the accurate geometrical and mechanical modeling of crack coalescence, crack percolation and the splitting of cracks due to dynamic processes is a severe challenge. Using the XFEM in combination with level sets, new enrichment patterns as well as multiple level set functions need to be defined to account for the complex crack geometries and discontinuities within elements. In addition the definition of accurate fracture criteria for more complex material models remains a challenge. In this project crack coalescence and percolation in three dimensions is investigated in detail and accurate fracture criteria for elastoplastic material behavior within the fracture process zone are developed.
    Leitung: S. Löhnert, E. Budyn
    Team: H. Attar
    Jahr: 2014
  • Multi-Fluid Simulations for High Density Ratios
    Although the contact between fluids or gases of different densities is a common event in nature, like the interaction of water and air, the simulation of multiple fluids often comes along with numerous problems. With the Lagrangian description of continuous fluids in terms of the Smoothed Particle Hydrodynamics (SPH) method multi-fluid interactions within the particle scale can simulated. Nevertheless with the standard SPH algorithms multi-fluid problems can not be solved because of the density jumps at the interfaces. Within the project the state of the art of current multi-fluid approaches are compared and evaluated to develop appropriate methods for the simulation of multi-fluid systems with high density ratios.
    Leitung: P. Wriggers, B. Avci
    Team: J.-P. Fürstenau
    Jahr: 2014
  • Non-konvexe Partikel und parallelisierte Berechnung
    In der Natur und technischen Prozessen sind viele Materialien Granulate. Als Beispiele sind Sand und Erze, Früchte und Getreibe oder auch (trockene) pharmazeutische und chemische Produkte zu nennen. Im Vergleich zu anderen Materialien, wie Stückgut, sind Granulate kompliziert in der Handhabung: Je nach Form und Oberflächenbeschaffenheit ergibt sich ein komplett anderes Materialverhalten. Um das Materialverhalten mit realitätsnahen Ergebnissen simulieren zu können, ist ein besseres Modell der Partikel notwendig. Die bisher häufig verwendeten rein konvexen Partikel (wie Kugeln oder Ellipsoide) reichen hierfür nicht aus, so dass eine komplexere Partikelbeschreibung und nicht-konvexe Formbeschreibung erforderlich ist. Die hierdurch verursachten höheren rechentechnischen Anforderungen können über Parallelisierung der Berechnung kompensiert werden.
    Leitung: P. Wriggers
    Team: M. Hothan
    Jahr: 2014
    Förderung: DFG (Graduiertenkolleg 1627)
  • Homogenization procedures for coupled thermo-chemo-mechanical problems
    In order to understand processes of continuum damage mechanics it is necessary to investigate thermo-chemo-mechanical coupled processes at micro scale. However for engineering purposes it is still necessary to be able to model these processes at macro scale, especially when large structures have to be designed. Thus a homogenization procedure or a FE^2 framework is necessary to transform the relation, describing the coupled thermo-chemo-mechanical response at micro scale to the macro scale. The related equations and procedures have to be developed and implemented in a finite element software system.
    Leitung: P. Wriggers, E. Baranger
    Team: Jin Man Mok
    Jahr: 2013
  • Modelling the temperature development and crack propagation during sheet-bulk metal forming
    n metal forming processes a large amount of mechanical work is dissipated due to large plastic deformations. The accompanying temperature rise leads to thermal strains and a change in the material behaviour which can influence the mechanical behaviour during the forming process and the final shape of the part. For this reason it is important to consider temperature effects and heat conduction in the material modelling of the polycrystalline microstructure. The resulting thermomechanical problem exhibits a strong coupling since on the one hand through mechanical deformation heat sources are introduced and on the other hand material parameters may depend on the temperature and also large thermal strains can emerge. Experimentally the temperature influence can be analysed by performing experiments at IW, IFUM, LFT or IUL with material specimens at different temperatures. The results can be used to develop a thermomechanical material model for the microstructure. By using homogenization techniques the macroscopic effective material model developed in period 1 of the SFB/TR73 will be extended by temperature effects. Another critical effect occurring during the forming process is the initiation and propagation of microcracks. This effect will lead to a stiffness reduction or even to failure of the entire structure. Therefore it is essential to study the degradation mechanisms of the crystallographic microstructure. A nonlocal damage model will be used to induce microcracks. For propagating the crack existing models have to be extended to nonlinear anisotropic and inelastic materials. Especially a criterion has to be found when cracks collide with grain boundaries. For the case of stable crack growth with a statistical simulation series a representative volume element can be found. This is used to produce a micromechanically motivated stress strain relationship by a homogenization procedure. With this material response the effective material model of period 1 of the SFB/TR73 will be extended. Here it is important to capture the softening effects with a nonlocal damage model which is for example used and developed at the IUL. In a last step the two approaches will be combined for the construction of a material model capturing thermomechanical effects and cracks on the microstructural level.
    Leitung: S. Löhnert, P. Wriggers
    Team: S. Beese, S. Zeller
    Jahr: 2013
  • Numerical simulation and experimental validation of biofilm formation
    In this Reserch , a state-of-the-art 3D computational model has been developed to investigate biofilms in a multi-physics framework using smoothed particle hydrodynamics (SPH) based on a continuum approach. Biofilms are in fact aggregation of microorganisms such as bacteria. Biofilm formation is a complex process in the sense that several physical phenomena are coupled and consequently different time-scales are involved. On one hand, biofilm growth is driven by biological reaction and nutrient diffusion and on the other hand, it is influenced by the fluid flow causing biofilm deformation and interface erosion in the context of fluid and deformable solid interaction (FSI). The geometrical and numerical complexity arising from these phenomena poses serious complications and challenges in grid-based techniques such as finite element (FE). Such issues are generally referred to as mesh distortion. Here the solution is based on SPH as one of the powerful meshless methods. SPH based computational modeling is quite new in the biological community and the method is uniquely robust in capturing the interface-related processes of biofilm formation especially erosion. The fact is that SPH is a versatile tool owing to its adaptive Lagrangian nature in the problems whose geometry is temporarily varying (dynamic). Moreover, its mesh-less feature is considered to be favorable in interpreting the method as a particle based one. Hence, it is quite straight forward to incorporate complex interactions and ad-hoc rules at the particle level into the method. This is the case for the problems with coupled governing equations with different time and length scale. In this thesis all different physics which account for biofilm formation have been implemented in the framework of SPH and one can say that this tool is purely SPH based. Besides the numerical simulation, experiments were conducted by our partners in the medical school of Hannover. The obtained numerical results show a good agreement with experimental and published data which demonstrates that the model is capable of predicting overall spatial and temporal evolution of the biofilms. The developed tool can be employed in either controlling the detrimental biofilms or harnessing the beneficial ones.
    Leitung: Peter Wriggers
    Team: Meisam Soleimani, Peter Wriggers, Meike Stiesch
    Jahr: 2013
  • Numerical simulations of delamination in FRP shell structures using XFEM
    When using Fiber Reinforced Plastics (FRP) delamination can occur leading to significant reduction of the load carrying capacity of a structure. Here the focus is on structural stability (buckling and snap-through). Furthermore, the propagation of delamination in pre- and postbuckling regime is of interest. A standard model for such simulations consists either of two shell elements with nodes at a given location of delamination or of a stack of shell-like solids, one per layer. The former has limits in its application while the latter leads to enormous computational effort. In this project eXtended FEM is applied to structural delamination problems. This allows the description of delamination at arbitrary through-the-thickness locations by means of shape functions enriched for discontinuities. Criteria for starting and propagating delamination should be integrated, if applicable combined with cohesive zone models. Contact in a delaminated zone must be accounted for. The new element must be suitable for large rotations and buckling.
    Leitung: Prof. Wilhelm J.H. Rust, Prof. P. Wriggers
    Team: Saleh Yazdani
    Jahr: 2013
  • Dynamic crack propagation using the XFEM
    Imperfections in composite materials can occur at interfaces but also within the matrix material, particles or fibers. These imperfections often lead to cracks and thus are responsible for degradation and failure of these heterogeneous materials. In this project the attention turns to the dynamic crack propagation. Therefore a numerical approach by using the eXtended Finite Element Method (XFEM) to describe the problem within heterogeneous materials will be developed. The XFEM has proven to be adequate to handle cracks and heterogeneities in a precise geometrical and numerical framework.
    Leitung: P. Wriggers, S. Löhnert
    Team: D. Nolte
    Jahr: 2012
  • SFB 599 TP D1 – Funktionalisierte Mittelohrprothesen
    Im Teilprojekt D1 des SFB 599 haben es sich die beteiligten Institutionen (Institut für Anorganische Chemie, LUH; Helmholtz-Zentrum für Infektionsforschung; Hals-Nasen-Ohrenklinik, MHH; IKM) zum Ziel gesetzt, eine optimierte Mittelohrprothese zu entwickeln. Dies soll durch den Einsatz neu entwickelter Biomaterialien einerseits und durch die mittels Simulationsverfahren optimierte Gestaltung andererseits geschehen. Nachdem in der letzten Förderperiode der Schwerpunkt der Simulation auf der Untersuchung der gesunden Gehörknöchelchenkette lag, steht in der dritten Förderperiode besonders der Kontakt zwischen Implantat und Trommelfell im Mittelpunkt. Hierbei soll mit Hilfe von Polymerpolstern eine gewebefreundliche Oberfläche geschaffen werden, die eine gleichmäßige Belastung des Trommelfells ermöglicht.
    Leitung: P. Wriggers
    Team: S. Besdo, D. Doniga-Crivat
    Jahr: 2012
    Förderung: DFG im Rahmen des SFB 599
  • Weiterentwicklung von kardiovaskulären Implantaten und finite Element Modellierung der Degradation von Mg-Legierungen
    Ein Ansatz der kardiovaskulären Forschung ist es geschädigtes Herzmuskelgewebe, z. B. in Folge eines Herzinfarkts, mit einem Gewebetransplantat zu ersetzen. Diese Gewebe besitzen anfänglich eine geringe Festigkeit. Daher werden Strukturen entwickelt, welche die Gewebetransplantate mechanisch unterstützen, um den Belastungen im Hochdrucksystem standzuhalten. Die bisher entwickelten Strukturen erreichen noch nicht die erforderliche Standzeit. Mit Hilfe der Finite Element Methode werden Simulationen erstellt, in denen Stützstrukturen entsprechend der Herzbewegung verformt werden. Hierdurch können hochbelastete Bereiche des Implantats identifiziert und konstruktiv verändert werden. Eine weitere Möglichkeit um Spannungen zu reduzieren besteht darin die Strukturen bereits bei der Fertigung gemäß der Herzgeometrie vorzuformen. Zusätzlich werden neue Strukturdesigns entwickelt und getestet. Die Stützstrukturen werden aus Magnesiumlegierungen gefertigt, welche vom Körper resorbiert werden können. Diese Degradation beeinflusst das mechanische Verhalten der Implantate unter Belastung. Es werden FE-Simulationen entwickelt bei denen die Magnesiumdegradation berücksichtigt wird.
    Leitung: P. Wriggers, J. Lamon, S. Besdo
    Team: M. Weidling
    Jahr: 2012
    Förderung: DFG im Rahmen des IRTG 1627
  • Untersuchung des Akkommodationsverhaltens der Augenlinse nach Einbringung Femtosekun-den-Laser-induzierter (fs-Laser) Schnittflächen
    Dieses Projekt wird in Kooperation mit dem Laserzentrum Hannover e.V. durchgeführt. Mit zunehmendem Alter lässt die Fähigkeit der menschlichen Augenlinse nach, sich von der Fernsicht auf die Nahsicht einzustellen. Für die dadurch verursachte Altersweitsichtigkeit (Pres-byopie) gibt es noch keine befriedigende Behandlungsmethode. Es wurde allerdings gezeigt, dass es möglich ist, die Verformbarkeit der Linse durch das Einbringen von Mikroschnitten mit-tels fs-Laser zu beeinflussen (fs-Lentotomie). Ziel dieses Projektes ist es, eine Methode zu ent-wickeln, die es ermöglicht, das veränderte Akkommodationsverhalten von Augenlinsen nach fs-Lentotomie mittels eines Finite-Elemente (FE)-Modells vorherzusagen.
    Leitung: S. Besdo
    Jahr: 2012
    Förderung: DFG im Normalverfahren
  • SFB 599 TP R6 – Degradable Osteosynthese-Systeme
    Im Rahmen des SFB 599 werden Osteosynthese-Systeme zur Frakturstabilisierung aus Magnesiumlegierungen entwickelt. Der Vorteil von Magnesium ist, dass der Körper es für seinen Stoffwechsel benötigt und es mit der Zeit abgebaut wird. Aufgrund der mechanischen Eigenschaften und der Degradation der Magnesiumlegierungen ist es notwendig das Implantat-Design anzupassen. Zunächst wird die Primärstabilität des Implantat-Knochen-Verbundes mit Hilfe von FE-Analysen untersucht, bevor die Implantate im Tierversuch getestet werden. In einem zweiten Schritt soll die Degradation der Implantate bei der Simulation berücksichtigt werden. Hierfür wurden bereits verschiedene Simulationsmethoden entwickelt, die an die Ergebnisse aus in vitro Versuchen angepasst werden. Des Weiteren wird die Knochenheilung bei der Simulation der Magnesiumdegradation berücksichtigt.
    Leitung: P. Wriggers
    Team: S. Besdo
    Jahr: 2012
    Förderung: DFG im Rahmen des SFB 599
  • Mutiscale FEM approach for rubber friction on rough surfaces
    Understanding the frictional behaviour of elastomers on rough surfaces is of high practical importance in many industrial applications. For example the traction of a tire is directly linked to the material properties of the considered elastomer and the surface conditions of the road track. One goal of our studies is to gain a deeper understanding of the underlying contact physics at all length scales. Another aim is to determine a macroscopic coefficient of friction for varying material and surface properties and to validate the results with experimental data.
    Leitung: P. Wriggers
    Team: P. Wagner
    Jahr: 2012
  • Mehrskalenmodellierung von lokalisiertem duktilen Versagen
    Es existieren viele phänomenologische Materialmodelle, die duktile Schädigung vorhersagen. Um jedoch die Materialeigenschaften und Schädigungsmechanismen der vorliegenden Mikrostrukturen flexibel einzubinden, ist eine Mehrskalenformulierung notwendig. Die existierenden Multiskalenmodelle beschränken sich jedoch zumeist auf spröde Mikroschädigung. Aus diesem Grund soll in diesem Projekt eine Mehrskalenmethode entwickelt werden, die lokalisiertes plastisches Versagen aufgrund einer duktil schädigenden Mikrostruktur vorhersagen kann.
    Leitung: P. Wriggers
    Team: H. Clasen
    Jahr: 2012
    Förderung: DFG im Normalverfahren
  • Computational homogenisation of elasto plastic material
    Particle-matrix materials are commonly used in different fields(aerospace components, bicycle frames and racing car bodies) for its mechanical and economical advantages,such as high strength, low weight and less expense.However,Because of the microstructural complexities,it is very time and labor consuming to determin the mechanical properties of composite materials. Hence,in order to reduce laboratory expense, numerical simulations via Homogenized techniques are performed on RVE to predict mechanical behavior of composite material.
    Leitung: P.Wriggers
    Team: Chao Zhang
    Jahr: 2012
  • Contact models for soil mechanics
    The installation of foundations influences strongly the load bearing capacity of the soil. The large discrepancy between experimental and numerical results, using Coulomb friction law for modeling the soil structure interaction, points out that new strategies to solve this kind of problems are necessary. Experimental observations show that for rough surfaces of the structure the friction angle at the contact zone corresponds to the friction angle of the soil. This leads to the conclusion that the contact zone lies completely within the soil. A way to improve the friction laws for soil structure interactions is to project the soil models onto the contact surface which is the motivation of this work. </a></p>
    Leitung: P. Wriggers
    Team: C. Weißenfels
    Jahr: 2012
  • Discrete Element Method
    This project is concerned with the development of a discrete element method (DEM) code for the simulation of large particle systems in 3-D, where also complex moving boundary geometries can be taken into account. The DEM is a well established numerical method to simulate systems consisting of granular matter. Granular mixing, tumbling mills, transport of particles via conveyor belts or screw conveyors are just some examples of important particulate processes in industry sectors like mining, pharmaceutical and food industries. For such systems, the optimization of the design variables as well as the appropriate choice of the operating parameters is still a difficult and a challenging task.
    Leitung: P. Wriggers
    Team: B. Avci
    Jahr: 2011
  • Multiscale Methods for Fracturing Solids
    In this project multiscale methods and homogenization techniques for the numerical simulation of three dimensional fracture processes are developed. These methods are important in aerospace and automotive industries and many other fields of mechanical and civil engineering as well as in bio-mechanics and material science. They will improve the prediction of the failure of structures.
    Leitung: P. Wriggers, S. Löhnert
    Team: D. Müller-Hoeppe
    Jahr: 2011
  • Interaction between tire and vulcanizing mold during extraction
    One sub-step of tire production is the vulcanization of a green tire under pressure inside a mold. Adherence of the rubber to this mold leads to problems during the subsequent extraction phase. Within this project the extraction of a vulcanized tire from a mold will be simulated, to obtain a better understanding of the mechanisms leading to the problems and to develop solution strategies.
    Leitung: P. Wriggers
    Team: J.-H. Dobberstein
    Jahr: 2011
  • Mikromechanische Modellierung von inelastischen Korngrenzeneffekten in polykristallinen Materialien
    In diesem Projekt soll das Verhalten polykristalliner Materialien mittels versetzungsbasierter Kristallplastizität untersucht und vorhergesagt werden. Ziel der Arbeit ist es, ein besseres Verständnis mikroskopisch nichtlokalen Verhaltens zu erlangen und geeignete Modelle für die Vorhersage der inelastischen Materialantwort zu entwickeln, die beispielsweise bei Strukturen in der Mikrosystemtechnik besonders relevant werden.
    Leitung: B. Hirschberger
    Team: H. Clasen
    Jahr: 2010
    Förderung: Leibniz Universität Hannover im Programm "Wege in die Forschung II"
    Laufzeit: 1 Jahr
  • Crack propagation and crack coalescence in a multiscale framework
    In this project a numerical framework for propagating and intersecting cracks on micro and macro scales is set up. Modeling cracks using the eXtended Finite Element Method (XFEM) provides an accurate and efficient numerical framework to model propagating and intersecting cracks. Since cracks of different length scales are assumed, a multiscale method is applied in order to be numerical efficient.
    Leitung: S. Löhnert, P. Wriggers
    Team: M. Holl
    Jahr: 2010
  • Multiscale Method for Hydro-Chemo-Thermo-Mechanics Coupling due to Alkali Silica Reaction in Concrete
    Alkali Silica Reaction(ASR) is one of most determinant reasons leading to the deterioration of concrete structures, which can be ascribed to the expansion of gel produced by ASR in the microstructural level of concrete. The challenge in the modeling of ASR is due to the necessity to take into account the presence of heterogeneities and physical processes distributed over multiple length scales. With increasing computation power and the tomography scan technology, it can be implemented by numerical simulation . In this contribution, 3D multiscale hydro-chemo-thermal-mechanical coupling based on a staggered method is demonstrated, which explicitly describes the damage evolution originating from the chemical reaction in the microscale and the dependence on environmental factors.
    Leitung: P. Wriggers
    Team: T. Wu
    Jahr: 2009
  • DEVELOPMENT OF A MATERIAL MODEL FOR METAL SHEETS AT FINITE DEFORMATION
    Technical procedures claim an improved material model for the simulation of metal forming processes. An effective, anisotropic elastoplastic material model for the macroscopic material behaviour for sheet metals is developed for further usage in commercial finite element programs.
    Leitung: P. Wriggers, S. Löhnert
    Team: E. Lehmann, S. Zeller
    Jahr: 2009
  • Contiuum Mechanical Modelling of Self-Cleaning Surface Mechanisms
    Some biological surfaces, like several plant leaves, exhibit remarkable self cleaning mechanism. These are called hydrophobic surfaces, where the water does not coat the surface but rather forms small droplets which then roll-off easily on inclined surfaces and sweep foreign pollutants, like dirt or germ particles, away from the surface. A continuum mechanical model suitable for computational multiscale analysis is therefore required for describing the interaction between the water droplet, the pollutant particle and the substrate surface. This model provides better understanding of basic droplet-substrate interaction characteristics such as contact angle, roll off angle and droplet deformation due to the microstructure of the substrate. The surface self-cleaning capabilities can be therefore improved by optimizing the artificial surface microstructure.
    Leitung: R. A. Sauer
    Team: M.Osman
    Jahr: 2009
  • Multiskalenmodellierung und erweiterte finite Elmente Analyse von Bruchprozessen in Keramik
    Die erweiterte finite Elemente Methode (XFEM) ermöglicht die Modellierung von Rissen unabhängig von der Vernetzung. Dadurch hat sich die XFEM für Rissberechnungen durchgesetzt. Vor allem in der Nähe von Makrorissspitzen muss die Mikrostruktur des Materials berücksichtigt werden, da Mikrorisse das Risswachstum verstärken oder abschwächen können. Mikrorisse entstehen unter Belastung in der Nähe des fortschreitenden Makrorisses. Dies motiviert eine Mehrskalenmodellierung z.B. mit der Multiskalenprojektionsmethode, die in der Lage ist, Feinskaleneffekte dort genau aufzulösen, wo es notwendig ist. Auch wenn die Modellierung von Rissen mit der XFEM unabhängig von der Vernetzung ist, hat das Netz einen Einfluss auf die Genauigkeit der Spannungen. Spannungssingularitäten können mit feineren Netzen besser erfasst werden. Die Berechnung eines Diskretisierungsfehlers für den Mikrobereich ermöglicht eine adaptive Verfeinerung des Netzes, so dass genaue Ergebnisse erzielt werden können. Die verwendeten Modelle werden durch einen Vergleich mit experimentellen Daten validiert.
    Leitung: P. Wriggers, S. Löhnert
    Team: C. Prange
    Jahr: 2009
  • Coupled Contact of Lubricated Contact
    In many engineering applications fluid lubricants are used to separate two solid bodies that rub against one another to minimize friction. Such devices are referred to as hydrodynamic bearings. There exist a large variety of bearings for translational and rotational movement. For engineers designing such bearing, computational methods can deliver useful information on its performance characteristics prior to its manufacturing. Within this project a three-dimensional finite element model is developed, that describes lubricated contact between two bodies with rough surfaces.
    Leitung: P. Wriggers
    Team: M. Budt
    Jahr: 2009
  • MULTIPHYSICS COMPUTATIONAL HOMOGENIZATION METHODOLOGIES
    Computational homogenization techniques that are amenable to a multiscale implementation are being developed for multiphysics problems at the finite deformation regime. Applications include the estimation of the contact conductance for rough interfaces and the modeling of the coupled thermomechanical response of heterogeneous materials.
    Leitung: P. Wriggers, I. Temizer
    Jahr: 2009
  • Direct Numerical Simulation of Multiphase Flows
    Multiphase flows consisting of a continuous fluid phase and a dispersed phase of macroscopic particles are present in many engineering applications. In general, a main task in the study of the particle-laden fluid flow of an application is to make predictions about the system's nature for various boundary conditions, since, depending on the volume fraction and mass concentration of the dispersed phase a fluid-particle system shows quite different flow properties. Unfortunately, often it is impossible to investigate such a system experimentally in detail or even at all. An option to capture and to predict its properties is performing a direct numerical simulation of the particulate fluid. For this purpose, an efficient approach is developed in this project by coupling the discrete element method and finite element method.
    Leitung: P. Wriggers
    Team: B. Avci
    Jahr: 2009
  • Numerical modeling of electrical contacts
    The focus of this work is the investigation of the behavior in electrical contacts, where electrical, thermal and mechanical fields are coupled. Specifically, theoretical constitutive models for the electrical conductance and electrical wear phenomena are developed and implemented in a three dimensional finite element setting. Also a new relation for wear is proposed, where the amount of wear is coupled to the dissipation arising at the contact interface. </a></p>
    Leitung: P. Wriggers
    Team: C. Weißenfels
    Jahr: 2009
  • FAILURE ANALYSIS - ERROR ESTIMATION FOR MULTISCALE METHODS
    This project is concerned with the development of tools for error-estimation based adaptive multiscale failure analysis. In order to enable a more accurate mechanical analysis of composite aircraft substructures, existing discretisation error estimators will be improved to be used as indicators for mesh refinement. Additionally, physical error estimators will be developed to identify regions where higher-order material modelling is required.
    Leitung: P. Wriggers
    Team: N. Hajibeik
    Jahr: 2009
  • MULTISCALE CONTACT HOMOGENIZATION OF GRANULAR INTERFACES
    Dry granular third bodies are frequently encountered at multiple scales of contact interfaces in contexts that range from mechanical problems of tire traction and semiconductor manufacturing to biological problems of wear debris generation and mobility in implant joints. The investigations that are envisaged within this proposal will provide further insight into the modeling and simulation of third body effects in a fully nonlinear three-dimensional virtual setting that accounts for inelastic phenomena.
    Leitung: P. Wriggers, I. Temizer
    Team: R. Weidlich
    Jahr: 2009
  • ADAPTIVE MULTISCALE MODELING AND ANALYSIS OF HETEROGENEOUS MATERIALS
    Accurate computational analyses of a composite structure requires multiple levels of resolution: (i) a region where effective elastic properties are employed, (ii) a region where embedded micro-macro problems are solved, and (iii) a region where explicit microstructural evaluation is required. Development of such computational schemes for the adaptive multiscale analysis of heterogeneous materials is the main purpose of this project.
    Leitung: P. Wriggers, I. Temizer
    Jahr: 2009
  • Analysis of local friction between rubber and dry and wet surfaces
    A prediction of the friction behavior of a rubber compound sliding over a road surface is an important topic in tire industry. Within this project the parameters which mainly influence the friction between a single tread block and a rough surface are investigated. The relevant physical mechanism of contact between a tread block and a rough surface, both wet or dry has to be understood. To validate the model a large number of test rigs is investigated at the Institute of Dynamics and Vibration Research (IDS).
    Leitung: P. Wriggers, R. A. Sauer
    Team: J. Dobberstein
    Jahr: 2009
  • RAMWASS - Integrated Decision Support System for Risk Assessment and Management
    The objective of the EU-project RAMWASS is to develop and validate a new decision support system (DSS) for the risk assessment and management for the prevention and/or reduction of the negative impacts caused by human activities on the water/sediment/soil system at river basin scale in fluvial ecosystems.
    Leitung: P. Wriggers
    Team: B. Avci
    Jahr: 2009
  • Einfluss inelastischer Effekte auf die Reibung in zyklischen Prozessen
    Bei der Modellierung der Polreibung von Reifen ist eine große Anzahl einzelner Effekte zu berücksichtigen, insbesondere, dass sich Gummi mit ursprünglich einheitlichem Ausgangszustand nach einiger Verformung von Ort zu Ort sehr unterschiedlich verhalten kann. Die Ursache ist, dass die so genannte Gummi-Elastizität sehr beträchtliche inelastische Anteile aufweist, die von den vorangegangenen Lastzyklen, insbesondere von früheren Verformungsmaxima signifikant abhängen (Mullins-Effekt). Somit ist bei einer genauen Modellierung des Rollkontaktes unbedingt die Heterogenität des Vor-Verformungszustandes und ihr Einfluss auf die inelastischen Effekte zu beachten.
    Leitung: D. Besdo
    Jahr: 2008
  • Frictional contact of elastomer materials on rough rigid surfaces
    The purpose of this work is the derivation of a friction law for rubber materials on rough tracks by numerical investigations. Rubber friction includes a number of influences like hysteresis due to material damping, adhesional effects or thermomechanical coupling.
    Leitung: P. Wriggers
    Team: J. Reinelt
    Jahr: 2008
  • Simulating the microstructure of cement-based construction materials
    In this thesis three-dimensional computational homogenization of hardened cement paste (HCP) including micro-structural damage due to frost is introduced. Based on a computer-tomography at a resolution of 1µm a finite-element model of HCP is developed with different elastic and inelastic constitutive equations for the three parts unhydrated residual clinker, pores, and hydration products.
    Leitung: P. Wriggers, S. Löhnert
    Team: N. Dabagh
    Jahr: 2008
  • Micromechanics of Nanoindentation
    Viele moderne metallische Werkstoffe erhalten ihre Eigenschaften durch gezielte Beeinflussung ihrer Mikrostruktur. Die Korngröße eines Stahls bestimmt zum großen Teil sein makroskopisches Materialverhalten. Für die Untersuchung dieser Zusammenhänge auf der Mikroskala eignen sich beispielsweise Nanoindentierungsversuche. Ziel dieses Projekts ist die Simulation eines Nanoindentationsversuchs in eine polykristalline Metallprobe. Um die auftretenden Größeneffekte abbilden zu können, werden Gradientenkristallplastizitätsmodelle und ein Modell für das Korngrenzenverhalten benötigt.
    Leitung: P. Wriggers, C.B. Hirschberger
    Team: D. Gottschalk
    Förderung: DFG IRTG 1627