@inproceedings{ThumannSwidergalWagner, author = {Thumann, Philipp and Swidergal, Krzysztof and Wagner, Marcus}, title = {Calculation and validation of material tests with specimens made out of filled elastomers}, series = {10th European LS-DYNA Conference 2015, W{\"u}rzburg}, booktitle = {10th European LS-DYNA Conference 2015, W{\"u}rzburg}, abstract = {In deep-drawing dies for steel sheet parts of car bodies huge masses are moved. To prevent vibrations, which occur by sudden acceleration or stopping of those masses, elastomeric tubular dampers [1] are used. The dampers are made out of carbon filled elastomers. A good knowledge about the material behaviour of metals is available. But for the numerical investigation of complete deep-drawing dies the elastomeric dampers must be taken into account, too. To characterize the material behaviour of the elastomers tensile tests and pressure tests were carried out. The received material data from the tests were read into LS-DYNA [2]. Simulation models of the tensile test and the pressure test were created for LS-DYNA according to the real dimensions and boundary conditions. For validation purposes, calculations of loading cycles were done to enable a comparison between test data and simulation results. For the calculations the implemented material model *MAT_SIMPLIFIED_RUBBER_WITH_DAMAGE (*MAT_183) was used. The comparison shows a good fitting between the test data and the calculation results with respect to the mechanical material behaviour by using this material model in single loading cases. The settings from the simulations of material tests were transferred to simulations of dampers, which are used in deep-drawing dies.}, language = {en} } @article{SittlMarburgWagner, author = {Sittl, Christopher and Marburg, Steffen and Wagner, Marcus}, title = {Application of a Krylov subspace method for an efficient solution of acoustic transfer functions}, series = {Mechanical Systems and Signal Processing}, volume = {148}, journal = {Mechanical Systems and Signal Processing}, publisher = {Elsevier}, doi = {10.1016/j.ymssp.2020.107135}, abstract = {Solving acoustic radiation problems, arising from systems including fluid-structure interaction, is of interest in many engineering applications. Computing frequency response functions over a large frequency range is a concern in such applications. A method which solves the Helmholtz equation for multiple frequencies in one step is the matrix-Pad{\´e}-via-Lanczos connection for unsymmetric systems, as presented by Wagner et al. [1]. The present work is based on Ref. [1] and presents a method for efficiently computing frequency responses over a frequency range for coupled structural-acoustic problems, where the structure and the acoustic near field are discretized with finite elements and an analytical Dirichlet-to-Neumann map approximates the far field. The method is based on a Krylov-subspace projection technique which derives a matrix-valued Pad{\´e} approximation for a restricted area in the near field and the pressure field on a spherical boundary. On the spherical boundary, where the finite domain is truncated, the non-local modified Dirichlet-to-Neumann operator is applied as a low-rank update matrix. The present contribution extends this method and incorporates new techniques for a more stable model reduction through the Lanczos algorithm and a novel weighted adaptive windowing technique. Further, structural damping is incorporated, for computing the acoustic radiation of a harmonically excited plate. These computed results are compared with acoustic measurements in an anechoic chamber and verified with computational results obtained with a commercial code that uses the perfectly matched layer method.}, language = {en} } @inproceedings{SwidergalWagnerLubesederetal., author = {Swidergal, Krzysztof and Wagner, Marcus and Lubeseder, Christian and Wurmb, Ingo von and Meinhardt, Josef and Marburg, Steffen}, title = {Finite element simulation of blankholder's lift-off in a deep drawing tool using Abaqus/Standard}, series = {SIMULIA Community Conference, 19 - 21 May 2015, Berlin, Germany}, booktitle = {SIMULIA Community Conference, 19 - 21 May 2015, Berlin, Germany}, abstract = {In the deep drawing tools for forming car body parts, heavy blankholders are used to prevent buckling and wrinkling of the blank. During each press cycle, those large masses need to be lifted, raising thereby the structural dynamic load on the deep drawing tool and on the press. Therefore a detailed knowledge about the blankholder's lift-off event is essential for an accurate and robust design of forming tools. In this paper, a dynamic finite element method (FEM) simulation of a blankholder's lift-off in a selected automotive deep drawing tool is presented enabling identification of regions of critical stresses. The FEM model is built within the Abaqus/CAE environment and solved with Abaqus/Standard. Each dynamic analysis is preceded by a static analysis where the gravity load is applied and the lifting bolts are pre-stressed. A special emphasis is put on modeling the elastomer dampers, which are installed between lifting bolts and the blankholder to avoid hard impacts during the lift-off event. Those dampers are modelled using a hyperelastic material with hysteresis. In addition, an experimental validation of a blankholder's vibration under operating loading was carried out. The simulation results are in good agreement with the measurements.}, language = {en} } @inproceedings{SwidergalThumannLubesederetal., author = {Swidergal, Krzysztof and Thumann, Philipp and Lubeseder, Christian and Wurmb, Ingo von and Meinhardt, Josef and Wagner, Marcus and Marburg, Steffen}, title = {Modeling and simulation of carbon black filled elastomer damper using LS-DYNA}, series = {LS-DYNA Forum 2014, Bamberg}, booktitle = {LS-DYNA Forum 2014, Bamberg}, language = {en} } @article{ThumannMarburgMeinhardtetal., author = {Thumann, Philipp and Marburg, Steffen and Meinhardt, Josef and Saubiez, Jean-Marc and Hoogen, Michael and Suck, Bertram and Wagner, Marcus}, title = {Frequency Dependent Fatigue Strength Investigations on Tempered Steel and Nodular Cast Iron}, series = {steel research international}, volume = {90}, journal = {steel research international}, number = {7}, publisher = {Wiley}, doi = {10.1002/srin.201800620}, abstract = {This paper presents experimental fatigue tests on specially shaped specimens made from quenched and tempered steel 42CrMoS4 and nodular cast iron EN-GJS-600-3. The specimens are geometrically designed to resemble actual subcomponents of forming and cutting dies for sheet metal manufacturing. These subcomponents have failed in the past.Experiments are carried out using a fictive load-time function, which is a modification of an actually measured load curve and has variable mean and amplitude values. This first test series serves as a general validation of a subsequent fatigue analysis. A second test series is carried out with constant mean and amplitude values with a load ratio 𝑅≈0. Here, the load frequencies in the individual test runs are varied between f = 5 Hz and f = 45 Hz in order to investigate the influence of the frequency. Both series are performed on a servo-hydraulic testing machine.The experimental data is then statistically evaluated. The values for the scatter correlate with data from the literature. The data from the test series with the fictive load-time function can thus be used for subsequent validation of a fatigue calculation, which will be addressed in a future publication. Most significant are the findings from the second series of experiments with varied load frequencies, as a significant frequency influence could be detected. Furthermore, the hardening and softening behavior under cyclic loading and the fracture behavior of the materials are analyzed and compared with data from the literature.}, language = {en} } @article{SwidergalLubesederWurmbetal., author = {Swidergal, Krzysztof and Lubeseder, Christian and Wurmb, Ingo von and Lipp, Arnulf and Meinhardt, Josef and Wagner, Marcus and Marburg, Steffen}, title = {Experimental and numerical investigation of blankholder's vibration in a forming tool}, series = {Production Engineering - Research and Development}, volume = {9}, journal = {Production Engineering - Research and Development}, number = {5-6}, publisher = {Springer}, issn = {0944-6524}, doi = {10.1007/s11740-015-0640-9}, pages = {634}, abstract = {In order to achieve the energy and efficiency goals in modern automotive press shops, press systems with increasingly high stroke rates are being implemented (Meinhardt in proceedings of ACI forming in car body engineering. Bad Nauheim, Germany 2012). As a side effect, the structural dynamic loads on the press and especially on the forming tool increase. Hence, to design reliable and withstanding forming tools, a detailed knowledge of the vibrations and resulting critical loads is essential. In this paper, the main focus is put on the vibration of the blankholder—the heaviest moving component in the forming tool. To predict those vibrations, a coupled multibody-finite element simulation (MBS-FEM) is conducted, which combines rigid and elastic modeling approaches. Also, an experimental validation of the blankholder vibration under operational load is carried out. To compare the numerical and experimental results—both in time and frequency domain—an 1/3-octave analysis of a blankholder's vibrational speed is performed. The test measurements agree well with the MBS-FEM simulation.}, language = {en} } @inproceedings{ThumannWagnerSucketal., author = {Thumann, Philipp and Wagner, Marcus and Suck, Bertram and Meinhardt, Josef and Marburg, Steffen}, title = {Explicit and Implicit FE Simulations of Material Tests for Subsequent Durability Analyses}, series = {11th European LS-DYNA Conference, Salzburg}, booktitle = {11th European LS-DYNA Conference, Salzburg}, abstract = {Because of increased stroke rates the loads on forming tools increase too. To ensure a save design of components, durability analyses are intended. For this, simulation results from FE analyses are necessary. Therefore, it is desirable to use elements with quadratic function, because of a good stress approximation.The goal of the described investigation is to show if calculation results created by LS-DYNA [1] can be used for durability analyses. Especially the use of quadratic elements is investigated. For the evaluation, on the one hand explicit FE analyses of a special durability test are carried out. These analyses are validated by available test data. To create results for later durability analyses further FE analyses with implicit time discretisation are carried out. In this paper results of the investigations are presented and evaluated critically.}, language = {en} } @inproceedings{WeghWagnerGaudlitzetal., author = {Wegh, Niels and Wagner, Marcus and Gaudlitz, Daniel and Finckh, Hermann and Klein, Markus}, title = {Numerical Simulation of Filling Process in Resin Transfer Molding}, series = {13th International Conference on Flow Processes in Composites Materials (FPCM-13), Kyoto, Japan}, booktitle = {13th International Conference on Flow Processes in Composites Materials (FPCM-13), Kyoto, Japan}, language = {en} } @techreport{HedererWagner, author = {Hederer, Sebastian and Wagner, Marcus}, title = {Entwicklung und Implementierung eines konstitutiven Modells zur Beschreibung der Plastizit{\"a}t von Dualphasenst{\"a}hle bei großen plastischen Deformationen}, series = {Forschungsbericht 2018 / Ostbayerische Technische Hochschule Regensburg}, journal = {Forschungsbericht 2018 / Ostbayerische Technische Hochschule Regensburg}, editor = {Baier, Wolfgang}, organization = {Ostbayerische Technische Hochschule Regensburg}, isbn = {9783981820911}, pages = {68 -- 69}, language = {de} } @inproceedings{MecklLubesederZausingeretal., author = {Meckl, D. and Lubeseder, Christian and Zausinger, C. and Wurmb, Ingo von and Meinhardt, Josef and Swidergal, Krzysztof and Wagner, Marcus}, title = {Simulation of press dies for large presses using the flexible multibody dynamics in Recurdyn}, series = {4th RecurDyn TechnologyDays 2014, M{\"u}nchen}, booktitle = {4th RecurDyn TechnologyDays 2014, M{\"u}nchen}, language = {en} } @inproceedings{SwidergalLubesederWurmbetal., author = {Swidergal, Krzysztof and Lubeseder, Christian and Wurmb, Ingo von and Meinhardt, Josef and Wagner, Marcus and Marburg, Steffen}, title = {Effiziente Methode zur Bestimmung von dynamischen strukturellen Belastungen in Großpresswerkzeugen}, series = {36. EFB-Kolloquium Blechverarbeitung 2016, Fellbach}, booktitle = {36. EFB-Kolloquium Blechverarbeitung 2016, Fellbach}, language = {de} } @inproceedings{MartinsWagnerWagnerHaufeetal., author = {Martins-Wagner, Magda and Wagner, Marcus and Haufe, Andr{\´e} and Liebold, Christian}, title = {A Graphical User Interface for Simulating Resin-Transfer-Molding Combining LS-DYNA and OpenFOAM}, series = {10th European LS-DYNA Conference 2015, W{\"u}rzburg, Germany}, booktitle = {10th European LS-DYNA Conference 2015, W{\"u}rzburg, Germany}, abstract = {The paper describes parts of the joint research project Swim-RTM including several industrial and academic partners. Its goal is to combine LS-DYNA and the open-source CFD solver OpenFOAM to simulate the production process of continuous fiber-reinforced plastics, particularly the resin-transfer-molding (RTM) process, in which the layers of dry fabric (unidirectional or woven) are formed in the mold (draping) and then filled with liquid resin with high pressure at injection points. Through a combined analysis of both the structural mechanical and the fluid dynamical phases, a better prediction and thereby optimization of the textile components properties as well as injection points can be achieved, improving the manufacturing process. The draping simulation of the fabric layers is carried out with LS-DYNA, while the injection simulation of the matrix material is performed in full 3D with OpenFOAM. A key question in this research project is how local porosities can be derived from the structural computation in the draping step. The purpose of the presented subproject is to develop a graphical user interface (GUI) to enable the simulation of the entire RTM process of long-fiber-reinforced components including the transfer of results between the draping and injection phases. The complete simulation task is relatively complex and involves several software packages, meaning a high effort for the user to get familiarized with. To circumvent this, the GUI aims at requiring from the user only the minimum necessary input data, creating and running the simulation and mapping tasks in the background, and showing graphically all demanded intermediate and final results. For the draping step several current fabric materials such as *MAT_034, *MAT_234, *MAT_235, *MAT_249 are available. Several modelling techniques for the composite setup are also conceivable, including a workflow similar to metal forming applications. In the injection step the fabric is modelled as a porous medium and different transport models and liquid resin types are at hand. For the data transfer between the draping and injection models, i.e. the mapping of data between shell and volume meshes within the developed GUI, first the OpenFOAM volume mesh is converted to LS-DYNA format and the necessary passing parameters are extracted from the output files, then the mapping tool DYNAmap [3] from DYNAmore GmbH is invoked, and finally the OpenFOAM command files are created. After the injection simulation is started and successfully terminated, information, such as the distribution of air inclusions or the shear stress distribution to analyze the reorientation of component fibers, is available and can be transferred from the 3D fluid mesh to an LS-DYNA shell mesh for further computations, for instance a crash simulation. This backward data mapping between volume and shell meshes can then be performed inside the GUI.}, language = {en} } @inproceedings{SwidergalLubesederWurmbetal., author = {Swidergal, Krzysztof and Lubeseder, Christian and Wurmb, Ingo von and Meinhardt, Josef and Wagner, Marcus and Marburg, Steffen}, title = {Vibration analysis of an automotive forming tool using coupled MBS-FEM simulation and experimental validation}, series = {Proceedings of the 26th International Conference on Noise and Vibration Engineering (ISMA2014), Leuven, Belgium}, booktitle = {Proceedings of the 26th International Conference on Noise and Vibration Engineering (ISMA2014), Leuven, Belgium}, pages = {2931 -- 2942}, abstract = {To improve efficiency in automotive press shops, press systems with increasingly high stroke rates are beingimplemented, raising thereby the structural dynamic load on the press and especially on the forming tool. Adetailed knowledge of the vibrations and resulting critical loads is thus essential for accurate and reliable de-signs of forming tools. In this paper, multibody simulation (MBS) of a selected automotive tool is presentedenabling the identification of the vibration of its components. Starting from a pure rigid modelling approach,the MBS model is extended by adding finite element (FE) component to allow extra flexibility in the sys-tem. As an example, a detailed vibrational analysis - both in time and frequency domain - is performed ona blankholder. Also an experimental validation of a blankholder vibration under operational load is carriedout, with test signal data gained by piezoelectric accelerometers.}, language = {en} } @techreport{ThumannSwidergalWagner, author = {Thumann, Philipp and Swidergal, Krzysztof and Wagner, Marcus}, title = {Experimentelle Ermittlung von Materialkennwerten und numerische Untersuchungen an einem gef{\"u}llten Elastomer}, series = {Forschungsbericht 2015 / Ostbayerische Technische Hochschule Regensburg}, journal = {Forschungsbericht 2015 / Ostbayerische Technische Hochschule Regensburg}, editor = {Baier, Wolfgang}, organization = {Ostbayerische Technische Hochschule Regensburg}, isbn = {978-3-00-048589-3}, pages = {49 -- 50}, language = {de} } @inproceedings{SwidergalLubesederWurmbetal., author = {Swidergal, Krzysztof and Lubeseder, Christian and Wurmb, Ingo von and Lipp, A. and Meinhardt, Josef and Wagner, Marcus and Marburg, Steffen}, title = {Structural analysis of an automotive forming tool for large presses using LS-DYNA}, series = {10th European LS-DYNA Conference, W{\"u}rzburg}, booktitle = {10th European LS-DYNA Conference, W{\"u}rzburg}, language = {en} } @inproceedings{KochThumannWagner, author = {Koch, F. and Thumann, Philipp and Wagner, Marcus}, title = {Simulation with implicit time integration of high loaded areas of a forming tool for large presses using LS-DYNA}, series = {13. LS-DYNA Forum 2014, 6.-8. Oktober, Bamberg}, booktitle = {13. LS-DYNA Forum 2014, 6.-8. Oktober, Bamberg}, language = {en} } @inproceedings{GeithWagner, author = {Geith, Markus A. and Wagner, Marcus}, title = {Numerical Analysis Of Stent Delivery Systems During Pre- And Intraoperative Processes}, series = {Deutsches LS-DYNA Forum 2018, Bamberg}, booktitle = {Deutsches LS-DYNA Forum 2018, Bamberg}, language = {en} } @article{GeithSwidergalHochholdingeretal., author = {Geith, Markus A. and Swidergal, Krzysztof and Hochholdinger, Bernd and Schratzenstaller, Thomas and Wagner, Marcus and Holzapfel, Gerhard A.}, title = {On the importance of modeling balloon folding, pleating, and stent crimping: An FE study comparing experimental inflation tests}, series = {International Journal for Numerical Methods in Biomedical Engineering}, volume = {35}, journal = {International Journal for Numerical Methods in Biomedical Engineering}, number = {11}, publisher = {Wiley}, doi = {10.1002/cnm.3249}, abstract = {Finite element (FE)-based studies of preoperative processes such as folding,pleating, and stent crimping with a comparison with experimental inflation tests are not yet available. Therefore, a novel workflow is presented in which residual stresses of balloon folding and pleating, as well as stent crimping, and the geometries of all contact partners were ultimately implemented in an FE code to simulate stent expansion by using an implicit solver. The numerical results demonstrate that the incorporation of residual stresses and strains experienced during the production step significantly increased the accuracy of the subsequent simulations, especially of the stent expansion model. During the preoperative processes, stresses inside the membrane and the stent material also reached a rather high level. Hence, there can be no presumption that balloon catheters or stents are undamaged before the actual surgery. The implementation of the realistic geometry, in particular the balloon tapers, and the blades of the process devices improved the simulation of the expansion mech-anisms, such as dogboning, concave bending, or overexpansion of stent cells. This study shows that implicit solvers are able to precisely simulate the mentioned preoperative processes and the stent expansion procedure without a preceding manipulation of the simulation time or physical mass.}, subject = {Stent}, language = {en} } @article{StichelFrickLaumeretal., author = {Stichel, Thomas and Frick, Thomas and Laumer, Tobias and Tenner, Felix and Hausotte, Tino and Merklein, Marion and Schmidt, Michael}, title = {A Round Robin study for selective laser sintering of polymers: Back tracing of the pore morphology to the process parameters}, series = {Journal of Materials Processing Technology}, volume = {252}, journal = {Journal of Materials Processing Technology}, number = {February}, publisher = {Elsevier}, doi = {10.1016/j.jmatprotec.2017.10.013}, pages = {537 -- 545}, abstract = {The mechanical properties of polymer parts built by Selective Laser Sintering are strongly related to the internal microstructure which differs with the applied production parameters. The paper focuses on the back tracing of the pore morphology of laser sintered polyamide-12 samples to the process parameters. Therefore, a data base is used which is supplied by a Round Robin initiative and includes mechanical tensile tests and the microstructural analysis of the pore morphology of several different sample charges built with different machines. The pore morphologies (porosity, pore density, pore shape and pore arrangement) measured by X-ray computed tomography are compared and discussed regarding the employed parameters and the resulting mechanical properties. The investigations point out that pore density is a superior indicator than porosity for mechanical issues. This is especially valid along the build direction since pore morphology has shown to be strongly anisotropic. Moreover, the analysis revealed that pore density is strongly affected by the process temperature, which is proved to be essential for the fabrication of mechanical robust parts using Selective Laser Sintering.}, language = {en} } @misc{GeithSwidergalSchratzenstalleretal., author = {Geith, Markus A. and Swidergal, Krzysztof and Schratzenstaller, Thomas and Holzapfel, Gerhard A. and Wagner, Marcus}, title = {Numerical analysis of stent delivery systems during pre- and intraoperative processes}, series = {15. Deutsches LS-DYNA Forum, 15.-17.10.2018, Bamberg}, journal = {15. Deutsches LS-DYNA Forum, 15.-17.10.2018, Bamberg}, language = {en} } @inproceedings{OttawaRomanoEhrlichetal., author = {Ottawa, Patrycja and Romano, Marco and Ehrlich, Ingo and Wagner, Marcus and Gebbeken, Norbert}, title = {The influence of ondulation in fabric reinforced composites on dynamic properties in a mesoscopic scale}, series = {11. LS-DYNA Forum, 9. - 10. Oktober 2012, Ulm}, booktitle = {11. LS-DYNA Forum, 9. - 10. Oktober 2012, Ulm}, pages = {171 -- 172}, abstract = {Structural mechanic properties of fiber reinforced plastics depend on the single components' properties, namely matrix and fiber [5]. Simple micromechanic homogenization theories reach a limit when a laminate consists of fabric reinforced layers instead of unidirectional layers. The ondulations of warp and fill yarn caused by the textile semi-finished product are the reason why the mesoscopic scale, which is in between the microscopic and the macroscopic scale, has to be taken into account when mechanically characterizing fabric reinforced composites [3]. In this scale a mesomechanic kinematic can be derived analytically. Especially, when considering free damped vibrations of structures the repeated acting of the kinematic correlation significantly affects the damping behaviour to higher values compared to theoretically predicted damping ratios. The model is investigated using Finite-Element-Analyses and basically validated experimentally.}, language = {en} } @article{LedentsovDuesterVolketal., author = {Ledentsov, Dmitry and D{\"u}ster, Alexander and Volk, Wolfram and Wagner, Marcus and Heinle, Ingo and Rank, Ernst}, title = {Model adaptivity for industrial application of sheet metal forming simulation}, series = {Finite Elements in Analysis and Design}, volume = {46}, journal = {Finite Elements in Analysis and Design}, number = {7}, doi = {10.1016/j.finel.2010.02.006}, pages = {585 -- 600}, abstract = {finite element simulation of sheet metal forming, shell elements are widely used. The limits of applicability of the shell elements are sometimes disregarded, which leads to an error in predictions of important values such as springback geometry. The underlying kinematic assumptions of the shell elements do not hold where the thickness of In the metal sheet approaches the value of the radius of curvature. Complex three-dimensional material behavior effects cannot be represented precisely as the result of the simplified kinematics. Here we present a model adaptivity scheme based on a model error indicator. The model-adaptive technique presented in this paper aides to resolve only the critical areas of the structure with a three-dimensional discretization while keeping reasonable computational cost by utilizing shell elements for the rest of the structure. The model error indicator serves as a guide for subsequent automatic adaptive re-meshing of the work-piece followed by a model-adaptive finite element analysis. The accuracy of the approximation obtained by the model-adaptive technique coincides well with that of a more expensive solution obtained with solid elements only.}, language = {en} } @article{WagnerPinskyMalhotra, author = {Wagner, Marcus and Pinsky, Peter M. and Malhotra, Manish}, title = {Application of Pad{\´e} via Lanczos approximations for efficient multifrequency solution of Helmholtz problems}, series = {Journal of the Acoustical Society of America}, volume = {113}, journal = {Journal of the Acoustical Society of America}, number = {1}, publisher = {American Inst. of Physics}, issn = {1520-8524}, doi = {10.1121/1.1514932}, pages = {313 -- 319}, abstract = {This paper addresses the efficient solution of acoustic problems in which the primary interest is obtaining the solution only on restricted portions of the domain but over a wide range of frequencies. The exterior acoustics boundary value problem is approximated using the finite element method in combination with the Dirichlet-to-Neumann (DtN) map. The restriction domain problem is formally posed in transfer function form based on the finite element solution. In order to obtain the solution over a range of frequencies, a matrix-valued Pad{\´e} approximation of the transfer function is employed, using a two-sided block Lanczos algorithm. This approach provides a stable and efficient representation of the Pad{\´e} approximation. In order to apply the algorithm, it is necessary to reformulate the transfer function due to the frequency dependency in the nonreflecting boundary condition. This is illustrated for the case of the DtN boundary condition, but there is no restriction on the approach which can also be applied to other radiation boundary conditions. Numerical tests confirm that the approach offers significant computational speed-up.}, language = {en} }