Research
List of all research projects

List of all research projects

  • Modelling and simulation of the joining zone during the tailored forming process
    [Translate to Englisch:] The topic of project C4 is the multiphysical modelling and simulation of the microstructural behaviour of the joining zone during the tailored forming process. The goal is the determination of the macroscopic, effective, thermomechanical properties of joining zones during and after forming.The model will be able to capture the contact and diffusion processes during joining, the thermal and mechanical properties during forming as well as the material behaviour during heat treatment which is responsible for calibrating material properties.
    Led by: F. Aldakheel, P. Wriggers
    Team: C. Böhm, F. Töller
    Year: 2019
    Funding: DFG im Rahmen des SFB 1153
  • In-stent restenosis
    Led by: Michele Marino, Peter Wriggers
    Team: Meike Gierig
    Year: 2018
  • Creep deformation of nickel based superalloys
    Modeling of nickel based superalloys on two scales using crystal plasticity and XFEM methods.
    Led by: P. Wriggers
    Team: Lukas Munk
    Year: 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.
    Led by: C. Weißenfels, P. Wriggers
    Team: M.Sc. Dengpeng Huang
    Year: 2018
    Funding: China Scholarship Council (CSC)
  • Process Simulation for Selective Laser Melting
    A phase change model for solution with the meshfree Galerkin OTM method is developed.
    Led by: Christian Weißenfels, Peter Wriggers
    Team: M.Sc. Henning Wessels
    Year: 2016
  • Micro-structure Topology Optimization of Auxetic Materials
    [Translate to Englisch:] 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.
    Led by: X. Zhuang
    Team: Thanh Chuong Nguyen
    Year: 2016
  • Micro-Mechanically Based Modeling of Degradation of Composite Materials with Random Microstructure
    Materials undergo degradation in different situations that are characterized by the environmental conditions. Here a thermo-chemo-mechanical investigation using knowledge of the microstructure will be performed. However usually the microstructures have a random distribution of the phases. For such microstructures a continuum damage mechanics framework has to be developed at micro-level that depends on thermal but also chemical reactions. The associated coupled problem includes partial differential equations of different type and thus robust numerical schemes have to be designed for the solution of the problem. Validation at micro level will be needed to calibrate the continuum modeling. This will be achieved in collaboration with the Institute for Material Science.
    Led by: Prof. P. Wriggers
    Team: Dipl.-Ing. V. Krupennikova
    Year: 2015
    Funding: DFG (Graduiertenkolleg 1627)
  • Constitutive modeling of large deformation behavior of filled elastomers
    In this work, a finite thickness cohesive zone model is used to study the large deformation & fracture behavior of filled elastomeric materials at the mesoscale. The study includes and has implications on filler cluster breakage, Mullins softening etc.
    Led by: P.. Wriggers
    Team: A. B. Harish
    Year: 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.
    Led by: P. Wriggers
    Team: M.R.Hojjati
    Year: 2015
    Funding: DAAD
  • 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.
    Led by: Principal Investigator: Dr.-Ing. Stefan Löhnert - French Co-Advisor in Cachan: Prof. Pierre-Alain Guidault
    Team: Mahmoud Pezeshki
    Year: 2014
    Funding: 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.
    Led by: P. Wriggers
    Team: W. Rust
    Year: 2014
  • Modeling 3D crack coalescence and percolation with the XFEM and level sets
    [Translate to Englisch:] 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.
    Led by: S. Löhnert, E. Budyn
    Team: H. Attar
    Year: 2014
  • Non-convex particle shape and parallelization
    Many materials found in nature or technical processes have a granulated structure. Examples are sand and ores, fruits and grain, (dry) pharmaceutical and chemical products. Compared to other materials, granular materials are difficult to handle: Different particle shapes result in different material behaviour. To have a simulation with realistic particle properties, more complex and more realistic particle shapes are needed. This means, in addition to the often used purely convex particles (spheres and ellipsoids), a description for more complex and non-convex shaped particles is essential. The higher computational costs can be handled by a parallelization.
    Led by: P. Wriggers
    Team: M. Hothan
    Year: 2014
    Funding: DFG (Project: IRTG 1627)
  • SFB 599 TP D1 – Functionalized middle ear prostheses
    The participating institutions in the sub-project D1 of the SFB 599 (Institute of Inorganic Chemistry, LUH, Helmholtz Centre for Infection Research, Ear, Nose and Throat Clinic, Hannover Medical School, IKM) have the aim to develop an optimized middle ear prosthesis. This is done through the use of newly developed biomaterials on the one hand and by using simulation techniques to optimize the design on the other hand. During the last funding period, the focus of the simulation was on the healthy ossicular chain. In the third period the contact between the implant and the tympanic membrane should be simulated. Polymer cushions will be used to create a tissue-friendly interface that enables a uniform loading of the eardrum.
    Led by: P. Wriggers
    Team: S. Besdo, D. Doniga-Crivat
    Year: 2012
    Funding: DFG im Rahmen des SFB 599
  • Investigation of the behavior of the crystalline lens accommodation by introducing femtosecond laser-induced (fs-laser) cut surfaces
    This project is conducted in cooperation with the Laser Zentrum Hannover eV. With age, the ability of the human eye lens to adjust from the distant view of the near vision increases. There is still no satisfactory method of treatment for the so called pres-byopie. However, it was shown that it is possible to influence the flexibility of the lens by introducing micro-cuts with a femtosecond laser (fs-Lentotomie). The aim of this project is to develop a method which makes it possible to predict the changes of accommodation behavior of ophthalmic lenses after cutting using finite element analyses.
    Led by: S. Besdo
    Year: 2012
    Funding: DFG im Normalverfahren
  • SFB 599 TP R6 – Degradable Osteosynthese
    Within the framework of SFB 599 osteosynthesis systems for fracture stabilization out of magnesium alloys are being developed. The advantage of magnesium is that the body needs it for its metabolism and it degrades over time. Due to the mechanical properties and the degradation of magnesium alloys, it is necessary to adjust the implant design. First, the primary stability of implant-bone composite is investigated using finite element analysis, before the implants are tested on animals. In a second step, the degradation has to be integrated into the simulation. Therefore, different simulation methods have been developed and should be adapted to results from in vitro experiments. Furthermore, the magnesium degradation will be considered in the simulation of bone healing.
    Led by: P. Wriggers
    Team: S. Besdo
    Year: 2012
    Funding: DFG im Rahmen des SFB 599
  • Computational multiscale modelling of localized ductile failure
    Many phenomenological material models capture ductile damage. However, to flexibly incorporate the underlying the governing microstructural properties and damage mechanisms, a multiscale framework is needed. The few recent numerical multiscale works on localized failure are limited to brittle microdamage. Therefore, the goal of this project is to provide a computational multiscale framework for the modelling of localized failure stemming from a microstructure undergoing ductile damage.
    Led by: P. Wriggers
    Team: H. Clasen
    Year: 2012
    Funding: DFG im Normalverfahren
  • Improvement of cardiovascular Implants and a FE-Framework for Degradation of Mg-Alloys
    A surgical option is to replace damaged myocardial tissue, e. g. after a heart attack, with tissue transplants. Problematic is the minor initial strength of these biological grafts to resist loads of the high pressure system. Therefore, scaffolds are developed to mechanically support these grafts. Until now, developed scaffolds do not achieve the required durability. With use of the finite element method, simulations are performed where the scaffolds are deformed according to the heart movement. This allows identifying highly strained regions within the implant that need design changes. Another approach to reduce stresses is preforming scaffolds according to the heart curvature preoperatively. Further, new scaffold designs are developed and tested.&nbsp;<br /> Scaffolds are made from magnesium alloys, which can be resorbed by the body. This degradation affects the mechanical behavior of the implants under load. There are FE simulations developed in which the magnesium degradation is considered.
    Led by: P. Wriggers, J. Lamon, S. Besdo
    Team: M. Weidling
    Year: 2011
    Funding: DFG within IRTG 1627
  • Micromechanical Modelling of inelastic grain boundary effects in polycrystalline materials
    The research project focuses on the computational materials modelling of metals microstructure. Within the project, polycrystalline materials shall be micromechanically investigated by means of dislocation-based crystal plasticity. The goal is to gain a clearer understanding in the nonlocal behaviour and to obtain useful models for the prediction of the inelastic response, which become relevant in applications such as micro-manufactured structures.
    Led by: Britta Hirschberger
    Team: H. Clasen
    Year: 2010
    Funding: Leibniz Universität Hannover via programme "Wege in die Forschung II"
    Duration: 1 year
  • 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.
    Led by: S. Löhnert, P. Wriggers
    Team: M. Holl
    Year: 2010
  • DEVELOPMENT OF A MATERIAL MODEL FOR METAL SHEETS AT FINITE DEFORMATION
    [Translate to Englisch:] 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.
    Led by: P. Wriggers, S. Löhnert
    Team: E. Lehmann, S. Zeller
    Year: 2009
  • Multiscale modeling and extended finite element analysis of fracture processes in ceramics
    The extended finite element method (XFEM) enables the modelling and calculation of cracks independent of mesh topologies. Due to this advantage it has become the most widely used method for computations of fracture processes. In the vicinity of a macrocrack front the microstructure of the material can have a significant influence and needs to be considered in detail. Especially microcracks can affect crack propagation drastically. This leads to the necessity of multiscale methods like the multiscale projection method to capture microstructural details where necessary. Even though the XFEM is known to be a comparably accurate method to calculate cracks, discretisation errors occur. Therefore, the discretisation error on the finescale is estimated via a stress smoothing technique. The realtive error of stresses enables adaptive mesh refinement on the microscale leading to more accurate results also on the macroscale. The computational model is validated by comparison of the results to experimental data.
    Led by: P. Wriggers, S. Löhnert
    Team: C. Prange
    Year: 2009
  • Coupled Contact of Lubricated Contact
    [Translate to Englisch:] 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.
    Led by: P. Wriggers
    Team: M. Budt
    Year: 2009
  • Micromechanics of Nanoindentation
    The properties of many modern metallic materials are obtained through a defined micro structural treatment. The grain size of a steel influences its macroscopic material behavior to a considerable extent. Nanoindentation technics are a possibility to examine the micro mechanical coherences. The goal of this project is a proper simulation of a nanoindentation test into a poly crystalline metal. In order to model the occurring size effects, it is necessary to implement a model for gradient crystal plasticity and grain boundary behavior.
    Led by: P. Wriggers, C.B. Hirschberger
    Team: D. Gottschalk
    Funding: DFG IRTG 1627