@inproceedings{UngerKoenke, author = {Unger, J{\"o}rg F. and K{\"o}nke, Carsten}, title = {DISCRETE CRACK SIMULATION OF CONCRETE USING THE EXTENDED FINITE ELEMENTMETHOD}, editor = {G{\"u}rlebeck, Klaus and K{\"o}nke, Carsten}, organization = {Bauhaus-Universit{\"a}t Weimar}, doi = {10.25643/bauhaus-universitaet.3030}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170327-30303}, pages = {12}, abstract = {The extended finite element method (XFEM) offers an elegant tool to model material discontinuities and cracks within a regular mesh, so that the element edges do not necessarily coincide with the discontinuities. This allows the modeling of propagating cracks without the requirement to adapt the mesh incrementally. Using a regular mesh offers the advantage, that simple refinement strategies based on the quadtree data structure can be used to refine the mesh in regions, that require a high mesh density. An additional benefit of the XFEM is, that the transmission of cohesive forces through a crack can be modeled in a straightforward way without introducing additional interface elements. Finally different criteria for the determination of the crack propagation angle are investigated and applied to numerical tests of cracked concrete specimens, which are compared with experimental results.}, subject = {Architektur }, language = {en} } @article{UngerEckardtKoenke, author = {Unger, J{\"o}rg F. and Eckardt, Stefan and K{\"o}nke, Carsten}, title = {Modelling of cohesive crack growth in concrete structures with the extended finite element method}, series = {Computer Methods in Applied Mechanics and Engineering}, journal = {Computer Methods in Applied Mechanics and Engineering}, pages = {4087 -- 4100}, abstract = {Modelling of cohesive crack growth in concrete structures with the extended finite element method}, subject = {Angewandte Mathematik}, language = {en} } @article{UngerKoenke, author = {Unger, J{\"o}rg F. and K{\"o}nke, Carsten}, title = {Coupling of scales in a multiscale simulation using neural networks}, series = {Computers \& Structures}, journal = {Computers \& Structures}, abstract = {Coupling of scales in a multiscale simulation using neural networks}, subject = {Angewandte Mathematik}, language = {en} } @inproceedings{UngerKoenke, author = {Unger, J{\"o}rg F. and K{\"o}nke, Carsten}, title = {PARAMETER IDENTIFICATION OF MESOSCALE MODELS FROM MACROSCOPIC TESTS USING BAYESIAN NEURAL NETWORKS}, editor = {G{\"u}rlebeck, Klaus and K{\"o}nke, Carsten}, organization = {Bauhaus-Universit{\"a}t Weimar}, issn = {1611-4086}, doi = {10.25643/bauhaus-universitaet.2898}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170314-28984}, pages = {5}, abstract = {In this paper, a parameter identification procedure using Bayesian neural networks is proposed. Based on a training set of numerical simulations, where the material parameters are simulated in a predefined range using Latin Hypercube sampling, a Bayesian neural network, which has been extended to describe the noise of multiple outputs using a full covariance matrix, is trained to approximate the inverse relation from the experiment (displacements, forces etc.) to the material parameters. The method offers not only the possibility to determine the parameters itself, but also the accuracy of the estimate and the correlation between these parameters. As a result, a set of experiments can be designed to calibrate a numerical model.}, subject = {Angewandte Informatik}, language = {en} } @article{KoenkeEckardtHaefneretal., author = {K{\"o}nke, Carsten and Eckardt, Stefan and H{\"a}fner, Stefan and Luther, Torsten and Unger, J{\"o}rg F.}, title = {Multiscale simulation methods in damage prediction of brittle and ductile materials}, series = {International Journal for Multiscale Computational Engineering}, journal = {International Journal for Multiscale Computational Engineering}, pages = {17 -- 36}, abstract = {Multiscale simulation methods in damage prediction of brittle and ductile materials}, subject = {Angewandte Mathematik}, language = {en} } @article{BruhinStockDrueckeretal., author = {Bruhin, R. and Stock, U.A. and Dr{\"u}cker, J.-P. and Azhari, T. and Wippermann, J. and Albes, J.M. and Hintze, D. and Eckardt, Stefan and K{\"o}nke, Carsten and Wahlers, T.}, title = {Numerical simulation techniques to study the structural response of the human chest following median sternotomy}, series = {The Annals of Thoracic Surgery}, journal = {The Annals of Thoracic Surgery}, pages = {623 -- 630}, abstract = {Numerical simulation techniques to study the structural response of the human chest following median sternotomy}, subject = {Angewandte Mathematik}, language = {en} } @article{SchraderKoenke, author = {Schrader, Kai and K{\"o}nke, Carsten}, title = {Hybrid computing models for large-scale heterogeneous 3d microstructures}, series = {International Journal for Multiscale Computational Engineering}, journal = {International Journal for Multiscale Computational Engineering}, pages = {365 -- 377}, abstract = {Hybrid computing models for large-scale heterogeneous 3d microstructures}, subject = {Angewandte Mathematik}, language = {en} } @inproceedings{LutherKoenke, author = {Luther, Torsten and K{\"o}nke, Carsten}, title = {INVESTIGATION OF CRACK GROWTH IN POLYCRYSTALLINE MESOSTRUCTURES}, editor = {G{\"u}rlebeck, Klaus and K{\"o}nke, Carsten}, organization = {Bauhaus-Universit{\"a}t Weimar}, doi = {10.25643/bauhaus-universitaet.2988}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170327-29886}, pages = {11}, abstract = {The design and application of high performance materials demands extensive knowledge of the materials damage behavior, which significantly depends on the meso- and microstructural complexity. Numerical simulations of crack growth on multiple length scales are promising tools to understand the damage phenomena in complex materials. In polycrystalline materials it has been observed that the grain boundary decohesion is one important mechanism that leads to micro crack initiation. Following this observation the paper presents a polycrystal mesoscale model consisting of grains with orthotropic material behavior and cohesive interfaces along grain boundaries, which is able to reproduce the crack initiation and propagation along grain boundaries in polycrystalline materials. With respect to the importance of modeling the geometry of the grain structure an advanced Voronoi algorithm is proposed to generate realistic polycrystalline material structures based on measured grain size distribution. The polycrystal model is applied to investigate the crack initiation and propagation in statically loaded representative volume elements of aluminum on the mesoscale without the necessity of initial damage definition. Future research work is planned to include the mesoscale model into a multiscale model for the damage analysis in polycrystalline materials.}, subject = {Architektur }, language = {en} } @inproceedings{SchraderKoenke, author = {Schrader, Kai and K{\"o}nke, Carsten}, title = {SPARSE APPROXIMATE COMPUTATION OF SADDLE POINT PROBLEMS ARISING FROM FETI-DP DISCRETIZATION}, editor = {G{\"u}rlebeck, Klaus and K{\"o}nke, Carsten}, organization = {Bauhaus-Universit{\"a}t Weimar}, issn = {1611-4086}, doi = {10.25643/bauhaus-universitaet.2887}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170314-28874}, pages = {12}, abstract = {The numerical simulation of microstructure models in 3D requires, due to enormous d.o.f., significant resources of memory as well as parallel computational power. Compared to homogeneous materials, the material hetrogeneity on microscale induced by different material phases demand for adequate computational methods for discretization and solution process of the resulting highly nonlinear problem. To enable an efficient/scalable solution process of the linearized equation systems the heterogeneous FE problem will be described by a FETI-DP (Finite Element Tearing and Interconnecting - Dual Primal) discretization. The fundamental FETI-DP equation can be solved by a number of different approaches. In our approach the FETI-DP problem will be reformulated as Saddle Point system, by eliminating the primal and Lagrangian variables. For the reduced Saddle Point system, only defined by interior and dual variables, special Uzawa algorithms can be adapted for iteratively solving the FETI-DP saddle-point equation system (FETI-DP SPE). A conjugate gradient version of the Uzawa algorithm will be shown as well as some numerical tests regarding to FETI-DP discretization of small examples using the presented solution technique. Furthermore the inversion of the interior-dual Schur complement operator can be approximated using different techniques building an adequate preconditioning matrix and therewith leading to substantial gains in computing time efficiency.}, subject = {Angewandte Informatik}, language = {en} } @inproceedings{HaefnerKoenke, author = {H{\"a}fner, Stefan and K{\"o}nke, Carsten}, title = {DAMAGE SIMULATION OF HETEROGENEOUS SOLIDS BY NONLOCAL FORMULATIONS ON ORTHOGONAL GRIDS}, editor = {G{\"u}rlebeck, Klaus and K{\"o}nke, Carsten}, organization = {Bauhaus-Universit{\"a}t Weimar}, doi = {10.25643/bauhaus-universitaet.2963}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170327-29638}, pages = {15}, abstract = {The present paper is part of a comprehensive approach of grid-based modelling. This approach includes geometrical modelling by pixel or voxel models, advanced multiphase B-spline finite elements of variable order and fast iterative solver methods based on the multigrid method. So far, we have only presented these grid-based methods in connection with linear elastic analysis of heterogeneous materials. Damage simulation demands further considerations. The direct stress solution of standard bilinear finite elements is severly defective, especially along material interfaces. Besides achieving objective constitutive modelling, various nonlocal formulations are applied to improve the stress solution. Such a corrective data processing can either refer to input data in terms of Young's modulus or to the attained finite element stress solution, as well as to a combination of both. A damage-controlled sequentially linear analysis is applied in connection with an isotropic damage law. Essentially by a high resolution of the heterogeneous solid, local isotropic damage on the material subscale allows to simulate complex damage topologies such as cracks. Therefore anisotropic degradation of a material sample can be simulated. Based on an effectively secantial global stiffness the analysis is numerically stable. The iteration step size is controlled for an adequate simulation of the damage path. This requires many steps, but in the iterative solution process each new step starts with the solution of the prior step. Therefore this method is quite effective. The present paper provides an introduction of the proposed concept for a stable simulation of damage in heterogeneous solids.}, subject = {Architektur }, language = {en} }