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Logo: Institute of Continuum Mechanics/Leibniz Universität Hannover
Logo Leibniz Universität Hannover
Logo: Institute of Continuum Mechanics/Leibniz Universität Hannover
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Constitutive Modelling of Materials

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

 

Supervisor:

M. Marino

Funded by:

Masterplan SmartBiotecs, MWK (Lower Saxony, Germany)

Brief description:

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.

 

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Micro- and meso-scale modeling of dental composite materials

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

Supervisor:

P. Wriggers, P. Behrens

Researcher:

M. Shahbaz

Brief description:

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.

 

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Hypoplastic material models for soil-structure interaction problems

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

Supervisor:

P. Wriggers, C. Weissenfels

Researcher:

A. B. Harish

Brief description:

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

 

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Nanoindentation for material property characterization

Bild zum Projekt Nanoindentation for material property characterization

Supervisor:

P. Wriggers, S. Löhnert

Researcher:

A. B. Harish, V. Kruppernikova

Brief description:

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.

 

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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

Supervisor:

P. Wriggers, J. J. Rimoli

Researcher:

A. B. Harish, A. B. Shah

Brief description:

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.

 

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Thermal conductivity study of two – phase nano composite material

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

Supervisor:

X. Zhuang

Researcher:

Bo He

Brief description:

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.

 

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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

Supervisor:

X. Zhuang

Researcher:

Yiming Zhang

Brief description:

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.

 

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Constitutive modeling of large deformation behavior of filled elastomers

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

Supervisor:

P.. Wriggers

Researcher:

A. B. Harish

Brief description:

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.

 

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Mesoscale constitutive modeling of filled elastomers

Bild zum Projekt Mesoscale constitutive modeling of filled elastomers

Supervisor:

P. Wriggers

Researcher:

A. B. Harish

Brief description:

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.

 

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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

Supervisor:

P. Wriggers, S. Löhnert

Researcher:

M. Baldrich, F. Töller

Funded by:

DFG im Rahmen des SFB 1153

Brief description:

[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.

 

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3D Dynamic Fracture in Heterogeneous Media

Bild zum Projekt 3D Dynamic Fracture in Heterogeneous Media

Supervisor:

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

Researcher:

Mahmoud Pezeshki

Funded by:

DFG (Graduiertenkolleg 1627)

Brief description:

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.

 

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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

Supervisor:

S. Löhnert, P. Wriggers

Researcher:

S. Beese, S. Zeller

Brief description:

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.

 

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Computational multiscale modelling of localized ductile failure

Bild zum Projekt Mehrskalenmodellierung von lokalisiertem duktilen Versagen

Supervisor:

P. Wriggers

Researcher:

H. Clasen

Funded by:

DFG im Normalverfahren

Brief description:

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.

 

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Computational homogenisation of elasto plastic material

Bild zum Projekt Computational homogenisation of elasto
plastic material

Supervisor:

P.Wriggers

Researcher:

Chao Zhang

Brief description:

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.

 

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Multiscale Methods for Fracturing Solids

Bild zum Projekt Multiscale Methods for Fracturing Solids

Supervisor:

P. Wriggers, S. Löhnert

Researcher:

D. Müller-Hoeppe

Brief description:

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.

 

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Crack propagation and crack coalescence in a multiscale framework

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

Supervisor:

S. Löhnert, P. Wriggers

Researcher:

M. Holl

Brief description:

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.

 

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Multiscale modeling and extended finite element analysis of fracture processes in ceramics

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

Supervisor:

P. Wriggers, S. Löhnert

Researcher:

C. Prange

Brief description:

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.

 

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Micromechanics of Nanoindentation

Bild zum Projekt Micromechanics of Nanoindentation

Supervisor:

P. Wriggers, C.B. Hirschberger

Researcher:

D. Gottschalk

Funded by:

DFG IRTG 1627

Brief description:

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.

 

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Design and Control of Additive Manufacturing Processes for Medical Silicone

 

Researcher:

M.Sc. Philipp Hartmann

 

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High Performance Computing of Stereolithography Processes

 

Researcher:

M.Sc. Sandeep Kumar

 

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Improved Frictional Models for Pile Installations

 

Researcher:

M.Sc. Ajay Harish

 

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