Logo Leibniz Universität Hannover
Logo: Institut für Kontinuumsmechanik/Leibniz Universität Hannover
Logo Leibniz Universität Hannover
Logo: Institut für Kontinuumsmechanik/Leibniz Universität Hannover
  • Zielgruppen
  • Suche
 

Materialmodellierung

In silico morphogenesis of collagen tissues for targeted drugs and bio-printing

 

Leitung:

M. Marino

Förderung durch:

Masterplan SmartBiotecs, MWK (Lower Saxony, Germany)

Kurzbeschreibung:

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.

 

| details |

 

Micro- and meso-scale modeling of dental composite materials

Bild zum Projekt Micro- and meso-scale modeling of dental composite materials

Leitung:

P. Wriggers, P. Behrens

Bearbeitung:

M. Shahbaz

Kurzbeschreibung:

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.

 

| details |

 

Hypoplastic material models for soil-structure interaction problems

Bild zum Projekt Hypoplastic material models for soil-structure interaction problems

Leitung:

P. Wriggers, C. Weissenfels

Bearbeitung:

A. B. Harish

Kurzbeschreibung:

In this work, a hypoplastic material model is implemented using AceGen with an eventual goal to model soil-structure interaction.

 

| details |

 

Nanoindentation for material property characterization

Bild zum Projekt Nanoindentation for material property characterization

Leitung:

P. Wriggers, S. Löhnert

Bearbeitung:

A. B. Harish, V. Kruppernikova

Kurzbeschreibung:

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.

 

| details |

 

Entropic approach to modeling Mullins effect in non-crystallizing filled elastomers

Bild zum Projekt Entropic approach to modeling Mullins effect in non-crystallizing filled elastomers

Leitung:

P. Wriggers, J. J. Rimoli

Bearbeitung:

A. B. Harish, A. B. Shah

Kurzbeschreibung:

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.

 

| details |

 

Thermal conductivity study of two – phase nano composite material

Bild zum Projekt Thermal conductivity study of two – phase nano composite material

Leitung:

X. Zhuang

Bearbeitung:

Bo He

Kurzbeschreibung:

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.

 

| details |

 

Durability analysis of composite materials by strong discontinuity embedded multifield framework

Bild zum Projekt Durability analysis of composite materials by strong discontinuity embedded multifield framework

Leitung:

X. Zhuang

Bearbeitung:

Yiming Zhang

Kurzbeschreibung:

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.

 

| details |

 

Mesoscale modeling of large deformation behavior of nanoparticle-reinforced elastomers

Bild zum Projekt Mesoscale modeling of large deformation behavior of nanoparticle-reinforced elastomers

Leitung:

P.. Wriggers

Bearbeitung:

A. B. Harish

Kurzbeschreibung:

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.

 

| details |

 

Mesoscale constitutive modeling of filled elastomers

Bild zum Projekt Mesoscale constitutive modeling of filled elastomers

Leitung:

P. Wriggers

Bearbeitung:

A. B. Harish

Kurzbeschreibung:

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.

 

| details |

 

Modelling and simulation of the joining zone during the tailored forming process

Bild zum Projekt Modelling and simulation of the joining zone during the tailored forming process

Leitung:

P. Wriggers, S. Löhnert

Bearbeitung:

M. Baldrich, F. Töller

Förderung durch:

DFG im Rahmen des SFB 1153

Kurzbeschreibung:

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.

 

| details |

 

3D Dynamic Fracture in Heterogeneous Media

Bild zum Projekt 3D Dynamic Fracture in Heterogeneous Media

Leitung:

Principal Investigator: Dr.-Ing. Stefan Löhnert - French Co-Advisor in Cachan: Prof. Pierre-Alain Guidault

Bearbeitung:

Mahmoud Pezeshki

Förderung durch:

DFG (Graduiertenkolleg 1627)

Kurzbeschreibung:

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.

 

| details |

 

Modelling the temperature development and crack propagation during sheet-bulk metal forming

Bild zum Projekt Modelling the temperature development and crack propagation during sheet-bulk metal forming

Leitung:

S. Löhnert, P. Wriggers

Bearbeitung:

S. Beese, S. Zeller

Kurzbeschreibung:

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.

 

| details |

 

Mehrskalenmodellierung von lokalisiertem duktilen Versagen

Bild zum Projekt Mehrskalenmodellierung von lokalisiertem duktilen Versagen

Leitung:

P. Wriggers

Bearbeitung:

H. Clasen

Förderung durch:

DFG im Normalverfahren

Kurzbeschreibung:

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.

 

| details |

 

Computational homogenisation of elasto plastic material

Bild zum Projekt Computational homogenisation of elasto
plastic material

Leitung:

P.Wriggers

Bearbeitung:

Chao Zhang

Kurzbeschreibung:

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.

 

| details |

 

Multiscale Methods for Fracturing Solids

Bild zum Projekt Multiscale Methods for Fracturing Solids

Leitung:

P. Wriggers, S. Löhnert

Bearbeitung:

D. Müller-Hoeppe

Kurzbeschreibung:

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.

 

| details |

 

Crack propagation and crack coalescence in a multiscale framework

Bild zum Projekt Crack propagation and crack coalescence in a multiscale framework

Leitung:

S. Löhnert, P. Wriggers

Bearbeitung:

M. Holl

Kurzbeschreibung:

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.

 

| details |

 

Multiskalenmodellierung und erweiterte finite Elmente Analyse von Bruchprozessen in Keramik

Bild zum Projekt Multiskalenmodellierung und erweiterte finite Elmente Analyse von Bruchprozessen in Keramik

Leitung:

P. Wriggers, S. Löhnert

Bearbeitung:

C. Prange

Kurzbeschreibung:

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.

 

| details |

 

Micromechanics of Nanoindentation

Bild zum Projekt Micromechanics of Nanoindentation

Leitung:

P. Wriggers, C.B. Hirschberger

Bearbeitung:

D. Gottschalk

Förderung durch:

DFG IRTG 1627

Kurzbeschreibung:

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.

 

| details |

 

Design and Control of Additive Manufacturing Processes for Medical Silicone

 

Bearbeitung:

M.Sc. Philipp Hartmann

 

| details |

 

High Performance Computing of Stereolithography Processes

 

Bearbeitung:

M.Sc. Sandeep Kumar

 

| details |

 

Improved Frictional Models for Pile Installations

 

Bearbeitung:

M.Sc. Ajay Harish

 

| details |

 

A 3D CAD/CAE integration using isogeometric symmetric Galerkin boundary element method