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Logo: Institut für Kontinuumsmechanik/Leibniz Universität Hannover
Logo Leibniz Universität Hannover
Logo: Institut für Kontinuumsmechanik/Leibniz Universität Hannover
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Bruchmechanik/ XFEM

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.

 

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Higher-order stress-based gradient-enhanced damage model using isogeometric analysis for shell delamination analysis

Bild zum Projekt Higher-order stress-based gradient-enhanced damage model using isogeometric analysis for shell delamination analysis

Leitung:

X. Zhuang

Bearbeitung:

Thai Q. Tran

Kurzbeschreibung:

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.

 

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Virtual Element Method for modeling crack propagation

Bild zum Projekt Virtual Element Method for modeling crack propagation

Leitung:

X. Zhuang

Bearbeitung:

Minh T.V Nguyen

Kurzbeschreibung:

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.

 

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Large Deformation Cohesive-Zone Element for Fracture in Rubbery Polymers

Bild zum Projekt Large Deformation Cohesive-Zone Element for Fracture in Rubbery Polymers

Leitung:

P. Wriggers

Bearbeitung:

A. B. Harish

Kurzbeschreibung:

In this work, a 3D cohesive zone element is developed considering material and geometric nonlinearities and suitable for modeling large deformations and rotations.

 

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Modeling 3D crack coalescence and percolation with the XFEM and level sets

 

Leitung:

S. Löhnert, E. Budyn

Bearbeitung:

H. Attar

Kurzbeschreibung:

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.

 

 

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.

 

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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

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.

 

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Design and Control of Additive Manufacturing Processes for Medical Silicone

 

Bearbeitung:

M.Sc. Philipp Hartmann

 

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High Performance Computing of Stereolithography Processes

 

Bearbeitung:

M.Sc. Sandeep Kumar

 

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Improved Frictional Models for Pile Installations

 

Bearbeitung:

M.Sc. Ajay Harish

 

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