Carsten Könke - Profile on Academia.edu (original) (raw)

Papers by Carsten Könke

Computers & Structures, Feb 1, 2006

Mesoscale analysis is a promising discipline for concrete mix design and damage prediction. Besid... more Mesoscale analysis is a promising discipline for concrete mix design and damage prediction. Besides many other aspects, its success crucially depends on accurate modeling of the mesoscale geometry and efficient numerical analysis of high resolution, to both of which this article contributes. Mesoscale models of concrete include aggregates, cement stone and, optionally, interfacial transition zones. The present paper establishes transparent formulas for consistent numerical generation of aggregate sizes. Fast separation checks are applied to place ellipsoidal and in particular arbitrary shaped particles. The multigrid method enables efficient computation of very large heterogeneous mesoscale models. This is exemplified by linear finite element analysis of two-dimensional models. Corresponding results are confirmed by experiments and analytical models from literature. The influence of concrete mix parameters on effective elastic properties is studied.

Investigation of different types of damping effects for automotive components –preliminary work

Materials Today: Proceedings, 2021

Abstract Automotive components are excited dynamically by interior (engine, gear system) and exte... more Abstract Automotive components are excited dynamically by interior (engine, gear system) and exterior effects (rough street surfaces, aerodynamics). This leads to dynamically induced vibrations which can end in fatigue cracking of components and/or undesirable acoustic emissions. With recent trends in optimizing/minimizing mass of vehicles, vibration problems are becoming an even more pronounced problem. In this research, a way has been investigated to reduce structural vibrations for a simple aluminium cantilever beam object, which is deduced from a cantilever beam of an automotive engine-transmission system. For this academic example the vibration has been reduced by attaching friction strips. The goal is to minimize the overall mass of the structure (cantilever beam plus friction strips) and simultaneously control the vibration amplitude. The energy lost due to the friction between the friction strips and the body of the vibrating beam will reduce the overall mechanical energy of the vibrating system and hence the vibrations will be controlled.

Dynamische Berechnungen für eine aufgeständerte Hochgeschwindigkeitsbahnstrecke in einem Erdbebengebiet

Advances in Engineering Software, Aug 1, 2013

Modern digital material approaches for the simulation and visualization of heterogeneous material... more Modern digital material approaches for the simulation and visualization of heterogeneous materials allow to investigate the behavior of complex multiphase materials with their physical nonlinear material response at various scales. However, these computational techniques require extensive hardware resources with respect to computing power and main memory to solve numerically large-scale discretized models in 3D. Due to a very high number of degrees of freedom, which may rapidly be increased to several 10 million degrees of freedom, the limited hardware resources are to be utilized in a most efficient way to enable an execution of the numerical algorithms in minimal computation time. The computational efficiency and the distribution among available hardware resources (often based on a parallel hardware architecture) can significantly be improved. In the past years, high-performance computing (HPC) based computation techniques were established for the investigation of scientific objectives. Their application results in the modification of existing and the development of new computational methods for the numerical implementation, which enables to take advantage of massively clustered computer hardware resources. Due to the high numerical effort for such simulations, an alternative approach for the nonlinear finite element analysis, based on the sequential linear analysis, was implemented in respect to scalable HPC. The incremental-iterative procedure in finite element analysis (FEA) during the nonlinear step was then replaced by a sequence of linear FE analysis, known in literature as saw-tooth approach. As a result, qualitative (smeared) crack initiation in 3D multiphase specimens has efficiently been simulated.

Computers & Structures, Feb 1, 2018

In this paper, location and degree of damages in massive masonry structures are identified by a m... more In this paper, location and degree of damages in massive masonry structures are identified by a multifield based inverse analysis which relies on a series of measurements such as transient displacements, temperatures and water pressures. As it is typical for the multi-field problems, the existence of damage leads to local changes in parameters of the different physical fields. The degree of the damage is defined by one primary variable, from which other quantities are derived. For fluid-flow problems in deformable porous media under non-isothermal boundary conditions such a quantity is the porosity of the material. The inverse analysis bases on a global search method, in which a dual-level parallel-computation is applied to improve computational cost. The effects of uncertainties in measurements and the size of the damage on the accuracy of the solutions are also discussed in the paper.

International Journal for Numerical and Analytical Methods in Geomechanics, Aug 30, 2017

Multiscale Simulation Methods in Damage Prediction of Brittle and Ductile Materials

International Journal for Multiscale Computational Engineering, 2010

... Carsten Konke Bauhaus-Universität Weimar, Institute of Structural Mechanics, Germany.Stefan E... more ... Carsten Konke Bauhaus-Universität Weimar, Institute of Structural Mechanics, Germany.Stefan Eckardt Institute of Structural Mechanics, Bauhaus-Universitat, Weimar, Germany.Stefan Hafner inuTech GmbH, Nurnberg, Germany. ...

arXiv (Cornell University), Oct 25, 2020

Sch�digungs- und Verbundmodellierung f�r Stahlbetontragwerke

Numerical models for the simulation of concrete on the mesoscale

Numerical Models for the simulation of concrete on the mesoscal

With the help of modern CAE-based simulation processes, it is possible to predict the dynamic beh... more With the help of modern CAE-based simulation processes, it is possible to predict the dynamic behavior of fatigue strength problems in order to improve products of many industries, e.g. the building, the machine construction or the automotive industry. Amongst others, it can be used to improve the acoustic design of automobiles in an early development stage. Nowadays, the acoustics of automobiles plays a crucial role in the process of vehicle development. Because of the advanced demand of comfort and due to statutory rules the manufacturers are faced with the challenge of optimizing their car's sound emissions. The optimization includes not only the reduction of noises. Lately with the trend to hybrid and electric cars, it has been shown that vehicles can become too quiet. Thus, the prediction of structural and acoustic properties based on FE-simulations is becoming increasingly important before any experimental prototype is examined. With the state of the art, qualitative comparisons between different implementations are possible. However, an accurate and reliable quantitative prediction is still a challenge. One aspect in the context of increasing the prediction quality of acoustic (or general oscillating) problemsespecially in power-trains of automobiles-is the more accurate implementation of damping in joint structures. While material damping occurs globally and homogenous in a structural system, the damping due to joints is a very local problem, since energy is especially dissipated in the vicinity of joints. This paper focusses on experimental and numerical studies performed on a single (extracted) screw connection. Starting with experimental studies that are used to identify the underlying physical model of the energy loss, the locally influencing parameters (e.g. the damping factor) should be identified. In contrast to similar research projects, the approach tends to a more local consideration within the joint interface. Tangential stiffness and energy loss within the interface are spatially distributed and interactions between the influencing parameters are regarded. As a result, the damping matrix is no longer proportional to mass or stiffness matrix, since it is composed of the global material damping and the local joint damping. With this new approach, the prediction quality can be increased, since the local distribution of the physical parameters within the joint interface corresponds much closer to the reality.

Computational Mechanics, Mar 1, 1995

This research presents a new simulation concept of damage evolution for metallic materials under ... more This research presents a new simulation concept of damage evolution for metallic materials under large displacements and deformations. The complete damage range is subdivided into both the micro-damage and the macro-damage range. The micro-damage phase is described by the Cocks/Ashby void-growth model for isotropic, ductile materials under isothermal conditions. After having reached a critical void-volume fraction, a macro-crack is introduced into the model. With such a concept the damage evolution from nucleation and growth of first micro-voids to initiation of macro-cracks and complete failure of the material can be simulated. Applying the Finite Element Method for the numerical formulation, at every incremental macro-crack step the Finite Element mesh is adapted such that the crack path remains independent of the initial mesh.

Coupling of scales in a multiscale simulation using neural networks

Computers & Structures, Nov 1, 2008

Multiscale approaches require the coupling of models on different spatial scales. In this paper, ... more Multiscale approaches require the coupling of models on different spatial scales. In this paper, a coupling using neural networks is proposed. Based on a set of mesoscale simulations of concrete a system of neural networks is trained to approximate the response. A macroscale constitutive model is obtained by homogenizing the mesoscale response. Special focus is put on the mesh sensitivity,

Polycrystal models for the analysis of intergranular crack growth in metallic materials

Engineering Fracture Mechanics, Oct 1, 2009

In polycrystal materials the intergranular decohesion is one important damage phenomena that lead... more In polycrystal materials the intergranular decohesion is one important damage phenomena that leads to microcrack initiation. The paper presents a mesoscale model, which is focused on the brittle intergranular damage process in metallic polycrystals. The model reproduces the crack initiation and propagation along cohesive grain boundaries between brittle grains. An advanced Voronoi algorithm is applied to generate polycrystal material structures based on arbitrary distribution functions of grain size. Therewith, the authors are more flexible to represent realistic grain size distributions. The polycrystal model is applied to analyze the crack initiation and propagation in statically loaded samples of aluminium on the mesoscale without the necessity of initial damage definition.

Spatial and Temporal Multiscale Simulations of Damage Processes for Concrete

Computational science, engineering and technology series, May 22, 2009

Spatial and temporal multiscale simulations of damage processes for concret

Welding in The World, Jun 24, 2020

The possibilities and challenges of using fiber optical sensors to monitor the laser-assisted joi... more The possibilities and challenges of using fiber optical sensors to monitor the laser-assisted joining of metal-polymer joints have been described in this article. Fundamental investigation proves the basic suitability of the measuring method for this application and studies the effect of essential influencing variables of the joining process-e.g., the clamping force-on the resulting sensor signals. In addition, the strain state (because of the process temperature and shrinkage of the polymer) of the parts to be joined can be traced as a function of the joining partners, the process parameters, and the material thicknesses. It is shown that the fiber optical method is suitable for process monitoring directly in the joining zone of metal-polymer hybrids and providing a tool for detailed strain measurements in the joint zone during subsequent component testing.

The Annals of Thoracic Surgery, Aug 1, 2005

Background. The optimal closure technique of median sternotomy remains controversial. The objecti... more Background. The optimal closure technique of median sternotomy remains controversial. The objective of this study was to analyze the structural response of the separated sternum using computer-based numerical discretization techniques, such as finite element methods. Methods. Thoracic computer tomographic scans (2.5-mm slices) were segmented, analyzed by image processing techniques, and transferred into a three-dimensional finite element model. In a first approach a linear elastic material model was used; neglecting nonlinear and damage effects of the bones. The influence of muscles and tendons was disregarded. Nonlinear contact conditions were applied between the two sternal parts and between fixation wires and sternum. The structural response of this model was investigated under normal breathing and asymmetric leaning on one side of the chest. Displacement and stress response of the segmented sternum were compared regarding two different closure techniques (single loop, figure-of-eight). Results. The obtained results revealed that for the normal breathing load case the single loop technique is capable of clamping the sternum sufficiently, assuming that the wires are prestressed. For asymmetric loading conditions, such as leaning on one side of the chest, the figure-of-eight loop can substantially reduce the relative longitudinal displacement between the two parts compared with the single loop. Conclusions. The application of numerical simulation techniques using complex computer models enabled the determination of structural behavior of the chest regarding the influence of different closure techniques. They allowed easy and fast modifications and therefore, in contrast to a real physical model, in-depth parameter studies.

A mesoscale model for concrete to simulate mechanical failure

Computers and Concrete, Aug 25, 2011

ABSTRACT In this paper, a mesoscale model of concrete is presented, which considers particles, ma... more ABSTRACT In this paper, a mesoscale model of concrete is presented, which considers particles, matrix material and the interfacial transition zone (ITZ) as separate constituents. Particles are represented as ellipsoides, generated according to a prescribed grading curve and placed randomly into the specimen. In this context, an efficient separation procedure is used. The nonlinear behavior is simulated with a cohesive interface model for the ITZ and a combined damage/plasticity model for the matrix material. The mesoscale model is used to simulate a compression and a tensile test. Furthermore, the influence of the particle distribution on the loaddisplacement curve is investigated.

Modelling of cohesive crack growth in concrete structures with the extended finite element method

Computer Methods in Applied Mechanics and Engineering, Sep 1, 2007

... In this paper, the extended finite element method (XFEM) is used for a discrete crack simulat... more ... In this paper, the extended finite element method (XFEM) is used for a discrete crack simulation of concrete using an adaptive crack growth algorithm. Different criteria for predicting the direction of the extension of a cohesive crack are investigated in the context of the XFEM. ...

Distributed FE Analysis of Multiphase Composites Regarding 3D Elasticity Problems

Springer eBooks, Oct 22, 2012

Today the numerical simulation of damage effects in heterogeneous materials is done by adaption o... more Today the numerical simulation of damage effects in heterogeneous materials is done by adaption of multiscale approaches. A consistent modeling in three dimensions with a high discretization resolution on each scale based on a hierarchical or concurrent multiscale model still has issues. The algorithms have to be optimized in regards to the computational efficiency and the distribution among available hardware resources often based on parallel hardware architectures. In the last 5 years high performance computing (HPC) as well as GPU computation techniques were established for investigation of scientific aims. Consequently, in this work substructuring methods for partitioning of FE meshed specimens were implemented, tested and adapted to the HPC computing framework using several hundred CPU nodes. An memory-efficient iterative and parallelized equation solver combined with a special preconditioning technique for solving the underlying equation system was modified and adapted to the consideration of combined CPU and GPU based computations.