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@article{faucris.230059881,
abstract = {The spectral stochastic FEM with local basis functions in the stochastic domain (SL-FEM) is one of the most flexible and accurate stochastic methods, however, also the most computationally expensive. These expenses are traditionally associated with the extra large tangent stiffness matrix and a huge number of elements which need to be re-integrated in every iteration. In this work we incorporate the proper orthogonal decomposition (POD) into the SL-FEM, thus performing a drastic reduction of the stiffness matrix. In order to reduce the integration costs by hyperreduction, a novel element-based modification of the discrete empirical interpolation, the so-called element-based empirical approximation method (EDEAM), is developed and combined with the POD. Particular advantages of the SL-FEM for order reduction and hyperreduction compared to other stochastic techniques are discussed. The new reduced-order SL-FEM is applied to the computational homogenization of materials with random geometry of the microstructure, i.e. to a general class of problems exhibiting strongly nonlinear, non-smooth and sometimes discontinuous dependency of the solution on some random parameters. The reduced-order SL-FEM demonstrates a high accuracy and a high solution speed, whereby the solution time for the reduced-order SL-FEM is comparable to the solution time of only one single Monte-Carlo sample.},
author = {Pivovarov, Dmytro and Steinmann, Paul and Willner, Kai},
doi = {10.1016/j.cma.2019.112689},
faupublication = {yes},
journal = {Computer Methods in Applied Mechanics and Engineering},
keywords = {Computational homogenization; Hyperreduction; POD; Random geometry; Reduced order modeling; Stochastic FEM},
note = {CRIS-Team Scopus Importer:2019-12-03},
peerreviewed = {Yes},
title = {{Acceleration} of the spectral stochastic {FEM} using {POD} and element based discrete empirical approximation for a micromechanical model of heterogeneous materials with random geometry},
year = {2019}
}
@inproceedings{faucris.221146344,
address = {Cambridge, United Kingdom},
author = {Heling, Björn and Oberleiter, Thomas and Rohrmoser, Andreas and Kiener, Christoph and Schleich, Benjamin and Hagenah, Hinnerk and Merklein, Marion and Willner, Kai and Wartzack, Sandro},
booktitle = {Proceedings of the 22nd International Conference on Engineering Design (ICED19)},
date = {2019-08-05/2019-08-08},
doi = {10.1017/dsi.2019.351},
faupublication = {yes},
pages = {3441 - 3450},
peerreviewed = {Yes},
publisher = {Cambridge University Press},
title = {{A} concept for process-oriented interdisciplinary tolerance management considering production-specific deviations},
url = {https://www.cambridge.org/core/services/aop-cambridge-core/content/view/2DD6B2058F383E18C465C8731DBE9666/S2220434219003512a.pdf/concept{\_}for{\_}processoriented{\_}interdisciplinary{\_}tolerance{\_}management{\_}considering{\_}productionspecific{\_}deviations.pdf},
venue = {Delft},
year = {2019}
}
@article{faucris.122296504,
abstract = {Friction has a significant effect on metal forming both in economic and technical terms. This is especially true for sheet-bulk metal forming, which is a combination of bulk metal forming and sheet metal forming. Contact loads of sheet forming processes are typically low to moderate. In contrast, very high contact loads occur in bulk metal forming. Therefore, a friction law, which is applicable for a broad range of contact loads, is necessary, if such a process has to be modelled accurately with the finite element method. A friction law fulfilling this demand is identified with the use of an elastic-plastic half-space model. The half-space model is used to determine the normal contact of rough surfaces and it is validated with experiments. In order to highlight the impact of the identified friction law, a typical sheet-bulk metal forming process is taken into account in the framework of the finite element metho},
author = {Beyer, Florian and Willner, Kai},
doi = {10.2474/trol.11.614},
faupublication = {yes},
journal = {Journal of Japanese Society of Tribologists},
keywords = {constitutive friction law, simulation, half-space, sheet-bulk metal forming, finite element method, orbital forming},
pages = {614-622},
peerreviewed = {Yes},
title = {{A} constitutive friction law for sheet-bulk metal forming},
volume = {11},
year = {2016}
}
@article{faucris.112805924,
abstract = {The selective control of the frictional behavior (tailored friction) in metal forming processes is of high importance with regard to technical and economic aspects. This applies especially for the sheet-bulk-metal forming process. Milling with intentionally invoked regenerative tool vibrations can be applied in order to generate structured surfaces with tailored friction properties on the forming tool. These structures affect the formation of lubrication pockets during the forming process which determine the local frictional properties exceedingly. The full potential of this emerging technology can, however, only be revealed if the heuristic and design-relevant knowledge is acquired and provided to the tool-designer already in the early phases of process development. One thing the tool-designer has to specify is the local frictional behavior on the tool surface. But, however, he does not know which milling parameters lead to the necessary surface structures because in most cases he has no expert knowledge in milling, tribology and forming tools. In this paper data mining is used to determine the frictional behavior based on these parameters. The potential of this method in the described context is revealed by the application on data derived from simulation results, both from milling simulations and contact simulations. The latter are performed by using a Halfspace model for rough surface contact. Both approaches for these simulations, the data mining process and the results are explained to the reader.© (2012) Trans Tech Publications.},
author = {Breitsprecher, Thilo and Hense, R. and Hauer, Franz and Wartzack, Sandro and Biermann, Dirk and Willner, Kai},
doi = {10.4028/www.scientific.net/KEM.504-506.963},
faupublication = {yes},
journal = {Key Engineering Materials},
keywords = {Data mining; Halfspace model; Milling with vibrations; Self-learning system},
note = {UnivIS-Import:2015-03-09:Pub.2012.tech.FT.FT-KLMEFK.acquis},
pages = {963-968},
peerreviewed = {Yes},
title = {{Acquisition} of heuristic knowledge for the prediction of the frictional behavior of surface structures created by self-excited tool vibrations},
volume = {504-506},
year = {2012}
}
@inproceedings{faucris.106726004,
author = {Nowak, Alexander and Willner, Kai and Campanile, Lucio Flavio and Hasse, Alexander},
booktitle = {International Conference on Adaptive Structures and Technologies},
date = {2017-10-08/2017-10-11},
faupublication = {yes},
peerreviewed = {unknown},
title = {{Active} {Vibration} {Control} of {Excited} {Structures} by means of {Shape} {Adaption}},
venue = {Krakau},
year = {2017}
}
@inproceedings{faucris.108295924,
abstract = {One of the most challenging tasks in structural dynamics is given by analyzing and predicting the behavior of jointed structures. In order to perform numerical investigations the Harmonic Balance Method (HBM) is a very mature and efficient technique for estimating the response behavior of such systems in the frequency domain. A better approximation can be obtained by accounting for more harmonic parts and introducing the Multiharmonic Balance Method (MHBM). This leads to a simultaneous reduction of efficiency due to a huge growth of the system dimensions. The goal of this paper is to present an Adaptive Harmonic Balance Method joining together the advantages of both, HBM and MHBM. Therefore the number of harmonics accounted for is adaptively chosen as small as possible, in order to get an efficient procedure and as big as necessary, in order to obtain precise results. The selection is performed by various criteria estimating the most important harmonic parts from an user defined pool of harmonics.},
author = {Süß, Dominik and Jerschl, Martin and Willner, Kai},
booktitle = {34th IMAC, A Conference and Exposition on Structural Dynamics, 2016},
doi = {10.1007/978-3-319-29739-2{\_}36},
faupublication = {yes},
isbn = {9783319297385},
keywords = {Adaptive procedure; FEM; Harmonic balance; Jointed structure; Structural dynamics},
pages = {405-414},
peerreviewed = {Yes},
publisher = {Springer New York LLC},
title = {{Adaptive} harmonic balance analysis of dry friction damped systems},
volume = {1},
year = {2016}
}
@article{faucris.119892564,
abstract = {This paper presents an algorithm for solving quasi-static, non-linear elasticity contact problems without friction in the context of rough surfaces. Here, we want to model the transition from soft to hard contact in case of rough surfaces on the micro-scale. The popular dual mortar method is used to enforce the contact constraints in a variationally consistent way without increasing the algebraic system size. The algorithm is deduced from a perturbed Lagrange formulation and combined with mass-lumping techniques to exploit the full advantages of the duality pairing. This leads to a regularized saddle point problem, for which a non-linear complementary function and thus a semi-smooth Newton method can be derived. Numerical examples demonstrate the applicability to industrial problems and show a good agreement to experimentally obtained results.},
author = {Sitzmann, Saskia and Willner, Kai and Wohlmuth, B. I.},
doi = {10.1002/nme.4683},
faupublication = {yes},
journal = {International Journal for Numerical Methods in Engineering},
keywords = {Constitutive contact equations; Contact; Dual mortar methods; Perturbed lagrange; Rough surfaces; Semi-smooth Newton},
pages = {221-238},
peerreviewed = {Yes},
title = {{A} dual {Lagrange} method for contact problems with regularized contact conditions},
volume = {99},
year = {2014}
}
@article{faucris.107401844,
abstract = {This paper presents an algorithm for solving quasi-static, non-linear elasticity contact problems with friction in the context of rough surfaces. Here, we want to model the transition from sticking to slipping also called micro slip in a physically correct way in order to reproduce measured frictional damping. The popular dual Mortar method is used to enforce the contact constraints in a variationally consistent way without increasing the algebraic system size. The algorithm is deduced from a perturbed Lagrange formulation and combined with a serial-parallel Iwan model. This leads to a regularized saddle point problem, for which a non-linear complementary function and thus a semi-smooth Newton method can be derived. Numerical examples demonstrate the applicability to industrial problems and show good agreement to experimentally obtained results.},
author = {Sitzmann, Saskia and Willner, Kai and Wohlmuth, B. I.},
doi = {10.1016/j.cma.2014.11.022},
faupublication = {yes},
journal = {Computer Methods in Applied Mechanics and Engineering},
keywords = {Constitutive contact equations; Contact with friction; Dual Mortar methods; Iwan model; Micro slip; Rough surfaces},
pages = {468-487},
peerreviewed = {Yes},
title = {{A} dual {Lagrange} method for contact problems with regularized frictional contact conditions: {Modelling} micro slip},
volume = {285},
year = {2015}
}
@inproceedings{faucris.111724624,
abstract = {This contribution presents, how to identify a material model of a lamination stack. The contact behavior between the single sheets is nonlinear and influences the behavior of the whole stack. The Simulation of the contact behavior is performed with contact models for normal and tangential direction. Due to the fact that calculating all sheets with contact is computational very expensive, a FE2-method is presented. With this method the calculation of the stack's behavior is based on a representative volume element. Further it is possible to identify a material model for the whole stack, which has got a linear and a nonlinear part. The linear part is caused by the material of the sheet, whereas the nonlinear part is a result of the contact behavior.},
author = {Luchscheider, Vera and Willner, Kai and Maidorn, Mischa},
booktitle = {2014 4th International Electric Drives Production Conference, EDPC 2014},
doi = {10.1109/EDPC.2014.6984431},
faupublication = {yes},
isbn = {9781479950089},
keywords = {lamination stack; material model; multiscale homogenization; normal and tangential contact behavior},
peerreviewed = {Yes},
publisher = {Institute of Electrical and Electronics Engineers Inc.},
title = {{A} material model for lamination stacks based on rough contacts},
year = {2014}
}
@article{faucris.279719027,
abstract = {We consider a deformable body in frictionless unilateral contact with a moving rigid obstacle. The material is described by a viscoelastic law with short memory, and the contact is modeled by a Signorini condition with a time-dependent gap. The existence and uniqueness results for a weak formulation based on a Lagrange multipliers approach are provided. Furthermore, we discuss an efficient algorithm approximating the weak solution for the more general case of a two-body contact problem including friction. In order to illustrate the theory we present two numerical examples in 3D.},
author = {Matei, Andaluzia Cristina and Sitzmann, Saskia and Willner, Kai and Wohlmuth, B. I.},
doi = {10.1080/00036811.2017.1359569},
faupublication = {yes},
journal = {Applicable Analysis},
keywords = {3D numerical examples; Dual lagrange multipliers; Primal-dual active set strategy; Unilateral contact; Viscoelasticity},
note = {CRIS-Team Scopus Importer:2022-08-05},
pages = {1340-1356},
peerreviewed = {Yes},
title = {{A} mixed variational formulation for a class of contact problems in viscoelasticity},
volume = {97},
year = {2018}
}
@inproceedings{faucris.118244324,
author = {Luchscheider, Vera and Willner, Kai},
booktitle = {PAMM},
doi = {10.1002/pamm.201210091},
edition = {1},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2012.tech.FT.FT-TM.analys{\_}5},
peerreviewed = {unknown},
title = {{Analysis} of the lamination stack influence on the stiffness of stator active component},
venue = {Darmstadt, Germany},
volume = {12},
year = {2012}
}
@inproceedings{faucris.120525284,
author = {Willner, Kai and Gaul, L.},
booktitle = {Computational Methods in Contact Mechanics II},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.1995.tech.FT.FT-TM.apenal},
pages = {257264},
peerreviewed = {Yes},
title = {{A} {Penalty} {Approach} for {Contact} {Description} by {FEM} {Based} on {Interface} {Physics}},
venue = {Computational Mechanics Publications},
year = {1995}
}
@article{faucris.243727570,
abstract = {In civil engineering reduction methods are used for the mechanical design of buildings in order to avoid unnecessary complexity and computational effort especially in the seismic design of structures. The determination of vibration modes by earthquake excitation is carried out by using Ritz vectors instead of eigenvectors. Thus, only the modes of interest are obtained. Furthermore, the Fast Nonlinear Analysis (FNA) method was formulated to easily insert nonlinearities like concentrated damping in a construction model. The main idea is to take the nonlinear forces to the right hand side of the equation of motion. In the context of this work, the FNA method is applied on a finite element model of a clamped beam with a cubic spring that works at the free end of the beam. First, a harmonic excitement is applied and the vibration modes of the system are obtained by using Ritz vectors. Then, a piecewise exact integration method is implemented to iteratively determine the results for displacement, velocity and acceleration of the discretized beam.
frequency-energy plot (FEP). A NNM branch can be calculated by a numerical continuation method with starting at low energy level in a quasi linear regime and increasing the energy and reducing the period of the oscillation iteratively. Thereby a branch is a family of NNM oscillations with qualitatively equal motion properties [2]. In non-linear systems internal resonances and other phenomena can occur. Several tongues can bifurcate from a NNM branch. Therefore ordinary continuation methods may fail at such bifurcation points. Here a predictor-corrector-method is used and different corrector algorithms are discussed for the branch continuation.},
author = {Jerschl, Martin and Willner, Kai},
doi = {10.1002/pamm.201410131},
faupublication = {yes},
journal = {Proceedings in Applied Mathematics and Mechanics},
pages = {287--288},
peerreviewed = {Yes},
title = {{Arclength} {Continuation} {Methods} for the {Investigation} of {Non}-linear {Oscillating} {Systems} with the {Concept} of {Non}-linear {Normal} {Modes}},
volume = {14},
year = {2014}
}
@inproceedings{faucris.115945984,
author = {Selvadurai, A.P.S. and Willner, Kai and Gaul, L.},
booktitle = {Proceedings of the Seventh Pan American Congress of Applied Mechanics},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.2002.tech.FT.FT-TM.areced},
pages = {117120},
peerreviewed = {Yes},
title = {{A} {Receding} {Contact} {Problem} in {Elastostatics}},
venue = {American Academy of Mechanics},
year = {2002}
}
@inproceedings{faucris.119958564,
abstract = {In this paper the phenomenon of mode lock-in is investigated, which occurs in structures where vibrations are excited by frictional contact forces, as for example at disc brakes. In general "mode lock-in" denotes the coupling of substructure modes which form the vibratory response of the assembly, leading e.g. to brake squeal. For studying this effect an experimental beam-disk set-up was built and a corresponding FE model was generated. A presented normal and tangential contact law is based on the statistical distribution of contacting asperities derived from measured surface roughness profiles. The time-stepping solutions of the FE model were checked for system resonances and compared to the experimentally observed mode lock-i},
author = {Allgaier, R. and Gaul, L. and Keiper, W. and Willner, Kai and Hoffmann, N.},
booktitle = {IMAC-XX: A Conference on Structural Dynamics},
faupublication = {no},
pages = {528-534},
peerreviewed = {Yes},
title = {{A} study on brake squeal using a beam-on-disc model},
url = {https://www.scopus.com/inward/record.url?partnerID=HzOxMe3b&scp=0036420879∨igin=inward},
venue = {Los Angeles, CA},
year = {2002}
}
@article{faucris.111726604,
abstract = {The phenomenon of "mode lock-in" occurs in structures, where vibrations are excited by contact forces, as for example between disc and pads at disc brakes. In general, mode lock-in denotes the coupling of substructure modes which form the vibratory response of the assembly, leading to brake squeal.},
author = {Willner, Kai and Allgaier, R. and Gaul, L. and Keiper, W.},
faupublication = {no},
journal = {Konstruktion},
peerreviewed = {Yes},
title = {{A} study on brake squeal using a beam-on-disc model},
url = {https://www.scopus.com/inward/record.url?partnerID=HzOxMe3b&scp=33645420010&origin=inward},
year = {2005}
}
@inproceedings{faucris.115947744,
author = {Allgaier, R. and Gaul, L. and Willner, Kai and Hoffmann, N.},
booktitle = {Proceedings of IMAC-XX},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.2002.tech.FT.FT-TM.astudy},
pages = {CD-ROM},
peerreviewed = {Yes},
title = {{A} {Study} on {Brake} {Squeal} {Using} a {Beam}-{On}-{Disk} {Model}},
venue = {SEM, CD-ROM},
year = {2002}
}
@inproceedings{faucris.211308292,
address = {Stamsried},
author = {Heling, Björn and Oberleiter, Thomas and Rohrmoser, Andreas and Kiener, Christoph and Schleich, Benjamin and Hagenah, Hinnerk and Merklein, Marion and Willner, Kai and Wartzack, Sandro},
booktitle = {Industriekolloquium der Forschergruppe FOR 2271},
date = {2019-02-05/2019-02-05},
editor = {Wartzack},
faupublication = {yes},
isbn = {978-3-89650-477-7},
month = {Jan},
note = {LFT Import::2019-08-05 (2353)},
pages = {36-45},
peerreviewed = {No},
publisher = {Druck+Verlag Ernst Vögel GmbH},
title = {{Berücksichtigung} von produktionsspezifischen {Abweichungen} im interdisziplinären {Toleranzmanagement}},
url = {https://www.archiv.mfk.tf.fau.de?file=pubmfk{\_}5c6a7ad28207e},
venue = {Erlangen},
year = {2019}
}
@incollection{faucris.119777504,
abstract = {This chapter focuses on the presentation of zero thickness elements as a method to discretize the contact plane of a bolted joint in the framework of the finite element method (FEM). A constitutive law based on a Jenkins element is used to describe the dry friction within the zero thickness elements. The harmonic balance method (HBM) is applied to calculate the dynamic response of the system in the frequency domain. In this chapter, a three-dimensional constitutive law based on Jenkins elements is used in order to simulate the dynamic behavior of a jointed friction resonator. The calculation is performed in the frequency domain utilizing the adaptive harmonic balance method (AHBM). This new, adaptive tool combines the advantages of classical HBM and multi-harmonic balance method (MHBM). Two different approaches for the application of the adaptive harmonic balance are shown with both delivering different results. The combination of the general modeling approach via zero thickness elements and the efficient computation using the AHBM brings out a powerful methodology for the calculation of the dynamics of jointed structures in the framework of the FEM.},
address = {Cham},
author = {Süß, Dominik and Jerschl, Martin and Willner, Kai},
booktitle = {The Mechanics of Jointed Structures},
doi = {10.1007/978-3-319-56818-8{\_}27},
editor = {Matthew R.W. Brake},
faupublication = {yes},
isbn = {978-3-319-56818-8},
pages = {491-510},
peerreviewed = {No},
publisher = {Springer},
title = {{Calculating} the {Dynamic} {Response} of {Jointed} {Structures} in the {Frequency} {Domain} {Using} {Contact} {Interface} {Elements}},
year = {2018}
}
@article{faucris.216848456,
abstract = {Modeling of mechanical systems with uncertainties is extremely challenging and requires a careful analysis of a huge amount of data. Both, probabilistic modeling and nonprobabilistic modeling require either an extremely large ensemble of samples or the introduction of additional dimensions to the problem, thus, resulting also in an enormous computational cost growth. No matter whether the Monte-Carlo sampling or Smolyak's sparse grids are used, which may theoretically overcome the curse of dimensionality, the system evaluation must be performed at least hundreds of times. This becomes possible only by using reduced order modeling and surrogate modeling. Moreover, special approximation techniques are needed to analyze the input data and to produce a parametric model of the system's uncertainties. In this paper, we describe the main challenges of approximation of uncertain data, order reduction, and surrogate modeling specifically for problems involving polymorphic uncertainty. Thereby some examples are presented to illustrate the challenges and solution methods.},
author = {Pivovarov, Dmytro and Willner, Kai and Steinmann, Paul and Brumme, Stephan and Müller, Michael and Srisupattarawanit, Tarin and Ostermeyer, Georg Peter and Henning, Carla and Ricken, Tim and Kastian, Steffen and Reese, Stefanie and Moser, Dieter and Grasedyck, Lars and Biehler, Jonas and Pfaller, Martin and Wall, Wolfgang and Kohlsche, Thomas and Estorff, Otto von and Gruhlke, Robert and Eigel, Martin and Ehre, Max and Papaioannou, Iason and Straub, Daniel and Leyendecker, Sigrid},
doi = {10.1002/gamm.201900011},
faupublication = {yes},
journal = {GAMM-Mitteilungen},
keywords = {approximation of uncertain data; model order reduction; sensitivity analysis; surrogate modeling; uncertainty quantification},
note = {CRIS-Team Scopus Importer:2019-05-02},
peerreviewed = {Yes},
title = {{Challenges} of order reduction techniques for problems involving polymorphic uncertainty},
year = {2019}
}
@article{faucris.111727484,
abstract = {The aim of this work is to compare different biaxial specimen geometries and loading conditions concerning their applicability as experimental database for an inverse finite element model updating procedure to identify the material parameters of sheet steel. Therefore, the deformation of the specimens is recorded with an optical, three-dimensional full-field deformation measurement system, and the utilised displacement data at the surface of the specimens are calculated via digital image correlation. The numerical material model for the simulations is based on a three-dimensional, anisotropic elasto-plastic ansatz and is implemented into a commercial finite element software code. The material parameters that are identified with the different specimen geometries are the hardening variables and the anisotropic plastic values. Based on the identification results, a selection criterion for the evaluation of specimen geometries for the inverse parameter identification is presented.},
author = {Schmaltz, Stefan and Willner, Kai},
doi = {10.1111/str},
faupublication = {yes},
journal = {Strain},
keywords = {Anisotropy; Computational plasticity; FEMU; Parameter identification; Sheet steel},
pages = {389-403},
peerreviewed = {Yes},
title = {{Comparison} of different biaxial tests for the inverse identification of sheet steel material parameters},
volume = {50},
year = {2014}
}
@inproceedings{faucris.119829204,
abstract = {Although mass production parts look the same, every manufactured part is unique, at least on a closer inspection. The reason for this is that every manufactured part is inevitable subjected to different scattering influencing factors and variation in the manufacturing process, such as varying temperatures or tool wear. All these factors inevitably lead to parts, which deviate from their ideal shape. Products, which are built from these deviation-afflicted parts consequently show deviations from their ideal properties. To ensure that every single product nevertheless meets its technical requirements, it is necessary to specify the permitted deviations. Furthermore it is necessary to estimate the consequences of the permitted deviations, which is done via tolerance analysis. During this process the imperfect parts are assembled virtually and the effects of the geometric deviations can be calculated during a variation simulation.
Since the tolerance analysis is to enable engineers to identify weak points in an early design stage it is important to know which contribution every single tolerance has on a certain quality-relevant characteristic, to restrict or increase the correct tolerances. In this paper two different approaches are shown and compared to represent the statistical behavior and the strongly connected sensitivity analyses. In particular a newly developed approach, which is based on fuzzy arithmetic, is compared to the established EFAST-method. The exemplary application of both methods and the comparison of the results are illustrated on a case stud},
author = {Heling, Björn and Oberleiter, Thomas and Schleich, Benjamin and Willner, Kai and Wartzack, Sandro},
booktitle = {ASME 2017 International Mechanical Engineering Congress and Exposition, Volume 2: Advanced Manufacturing},
date = {2017-11-03/2017-11-09},
doi = {10.1115/IMECE2017-70550},
editor = {ASME},
faupublication = {yes},
isbn = {978-0-7918-5835-6},
peerreviewed = {Yes},
title = {{Comparison} of {Different} {Sensitivity} {Analysis} {Methods} in the {Context} of {Dimensional} {Management}},
url = {https://www.archiv.mfk.tf.fau.de?file=pubmfk{\_}5c37456fa5d56},
venue = {Tampa, Florida, USA},
year = {2017}
}
@inproceedings{faucris.111730344,
abstract = {The influence of the lamination stack on the mechanical behavior of an electrical machine is significant, especially for lightweight designs. Information about the stack's behavior is relevant for a proper calculation of the whole motor. This behavior is dependent on the contact between the single sheets. This paper aims to show that the normal contact behavior can be simulated with the elastic model of Bush, Gibson and Thomas, a plastic term depending on deformation of the highest peaks and a viscous term. The tangential slip is described through a micro-macro model. These models can be used in a representative volume element and consequently for a multi-scale homoge-nization. A material model of the whole lamination stack can be identified by loading the representative volume element with different deformations.},
author = {Luchscheider, Vera and Maidorn, Mischa and Willner, Kai},
booktitle = {Joint 11th World Congress on Computational Mechanics, WCCM 2014, the 5th European Conference on Computational Mechanics, ECCM 2014 and the 6th European Conference on Computational Fluid Dynamics, ECFD 2014},
faupublication = {yes},
isbn = {9788494284472},
keywords = {Contact mechanics; Homogenization; Lamination stack},
pages = {1950-1959},
peerreviewed = {Yes},
publisher = {International Center for Numerical Methods in Engineering},
title = {{Computation} of the effective lamination stack's behavior considering the contact simulation with a multi-scale homogenization},
url = {https://www.scopus.com/inward/record.url?partnerID=HzOxMe3b&scp=84923963712&origin=inward},
year = {2014}
}
@article{faucris.120673784,
abstract = {The dynamic behavior of structures with joints is strongly influenced by the constitutive behavior within the contact areas. In this paper the influence of an elaborate constitutive contact model based on a rough surface model is investigated. The contact model is able to describe several effects like pressure dependent contact stiffness in normal and tangential direction as well as microslip effects. The corresponding constitutive contact laws are implemented in a finite element code. Numerical simulations are compared to experimental results of a clamped double-beam experiment. Copyright © 2009 Tech Science Press.},
author = {Willner, Kai},
faupublication = {yes},
journal = {Cmes-Computer Modeling in Engineering & Sciences},
keywords = {Damping; Friction; Joints; Structural dynamics},
note = {UnivIS-Import:2015-03-09:Pub.2009.tech.FT.FT-TM.consti},
pages = {303-336},
peerreviewed = {Yes},
title = {{Constitutive} {Contact} {Laws} in {Structural} {Dynamics}},
volume = {48},
year = {2009}
}
@incollection{faucris.246011761,
address = {Cham},
author = {Henneberg, Johannes and Beyer, Florian and Löffler, Maria and Willner, Kai and Merklein, Marion},
booktitle = {Sheet Bulk Metal Forming},
doi = {10.1007/978-3-030-61902-2{\_}14},
editor = {Merklein, M.
Tekkaya, A. E.
Behrens, B.-A.},
faupublication = {yes},
isbn = {978-3-030-61901-5},
pages = {307 - 333},
peerreviewed = {Yes},
publisher = {Springer Nature Switzerland},
series = {Lecture Notes inProduction Engineering},
title = {{Constitutive} {Friction} {Law} for the {Description} and {Optimization} of {Tailored} {Surfaces}},
year = {2021}
}
@article{faucris.208936331,
abstract = {Sheet‐layered lamination stacks found in electric motors as rotor and stator are a challenging task in structural mechanics due to their special design. The manufacturing process determines the nature of the microstructure resulting in the presence of bonding varnish or frictional contact between the individual metal sheets. For the latter case, a penalty method in normal and tangential direction can be used to capture the contact interactions of single plates. In combination with homogenization techniques, a transversely isotropic surrogate material model with a corresponding strain energy density can be identified. In this paper, the focus lies on the influence of the penalty parameters on the elastic quantities of the constitutive equation.
The numerical simulation of sheet‐layered lamination stacks is a challenging task in structural mechanics due to the layout of these components. Depending on the manufacturing process, these sheets are either linked together with the help of a bonding varnish or are just packed up and basically free to slip inside of the stack, which can result in a nonlinear deformation behavior. To avoid a full FE‐simulation incorporating every layer, homogenization can be applied to identify a surrogate material model to achieve the desired accuracy by gaining performance. In this paper, a transversely isotropic material model is analytically formulated for a lamination stack with isotropic sheets in contact, which is captured with the help of a linear penalty method. The resulting stress‐strain relation is compared to results obtained by a numerical homogenization.},
author = {Baloglu, Maximilian Volkan and Willner, Kai},
doi = {10.1002/pamm.201710166},
faupublication = {yes},
journal = {Proceedings in Applied Mathematics and Mechanics},
keywords = {lamination stack; homogenization; material modelling; contact mechanics},
pages = {393-394},
peerreviewed = {Yes},
title = {{Determination} of material parameters for a sheet‐layered lamination stack},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/pamm.201710166},
volume = {17},
year = {2017}
}
@inproceedings{faucris.121587884,
abstract = {Fiber reinforced composites may have unknown non-isotropic properties due to the manufacturing process. Especially injection molded members tend to have orthotropic properties due to alignment of short fibers along streamlines. To obtain the stiffness parameters of such materials, a non-destructive testing method is developed. Electronic-Speckle-Pattern-Interferometry is used to determine the eigenfrequencies and eigenmodes of square sample plates and a simple analytical model of the free vibrating plate is used to identify dynamic stiffness parameters. The method is verified by testing plates with known orthotropy and by static bending tests.},
author = {Gaul, L. and Willner, Kai and Hurlebaus, S.},
booktitle = {Proceedings of the International Modal Analysis Conference},
date = {1999-02-08/1999-02-11},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.1999.tech.FT.FT-TM.determ},
pages = {17561762},
peerreviewed = {Yes},
publisher = {Society for Experimental Mechanics},
title = {{Determination} of {Material} {Properties} of {Plates} from {Modal} {ESPI} {Measurements}},
venue = {XVII},
year = {1999}
}
@article{faucris.111883244,
abstract = {Friction has a considerable impact in metal forming. This is in particular true for sheet-bulk metal-forming (SBMF) in which local highly varying contact loads occur. A constitutive friction law suited to the needs of SBMF is necessary, if numerical investigations in SBMF are performed. The identification of the friction due to adhesion and ploughing is carried out with an elasto-plastic half-space model. The normal contact is verified for a broad range of normal loads. In addition, the model is used for the characterization of the occurring shear stress. Ploughing is determined by the work which is necessary to plastically deform the surface asperities of the new area that gets into contact during sliding. Furthermore, the surface patches of common half-space models are aligned orthogonally to the direction in which the surfaces approach when normal contact occurs. For a better reflection of the original surfaces, the element patches become inclined. This leads to a geometric share of lateral forces which also contribute to friction. Based on these effects, a friction law is derived which is able to predict the contact conditions especially for SBMF.},
author = {Beyer, Florian and Hauer, Franz and Willner, Kai},
faupublication = {yes},
journal = {Tribology in Industry},
keywords = {half-space ,elasto-plastic contact, simulation, constitutive friction law, sheet-bulk metal forming},
pages = {400-412},
peerreviewed = {Yes},
title = {{Development} of a {Constitutive} {Friction} {Law} based on the {Frictional} {Interaction} of {Rough} {Surfaces}},
url = {http://www.tribology.fink.rs/journals/2016/2016-2/4.pdf},
volume = {37},
year = {2015}
}
@inproceedings{faucris.118644724,
abstract = {The paper presents measurements and simulations of the stiffness of lamination stacks, which is a relevant parameter for the construction of electric machines. Since the progressive stiffness behavior of a lamination stack is dominated by the contact between the single sheets, different contact models are presented, where the selection and combination of the contact models is based on experimental tests on simple stacks of typical sheet material. With the help of the contact models, a material model will be created using the method of multiscales. © 2013 IEEE.},
author = {Luchscheider, Vera and Willner, Kai and Maidorn, Mischa},
booktitle = {Proceeding 3rd International Electric Drives Production Conferenz},
date = {2013-10-29/2013-10-30},
doi = {10.1109/EDPC.2013.6689722},
faupublication = {yes},
isbn = {978-1-4799-1102-8},
keywords = {contact behavior; hysteresis; lamination stack},
note = {UnivIS-Import:2015-04-16:Pub.2013.tech.FT.FT-TM.develo{\_}5},
pages = {32-36},
peerreviewed = {unknown},
publisher = {IEEE Computer Society},
title = {{Development} of a contact and a material model of laminated stacks},
venue = {Nuremberg, Germany},
year = {2013}
}
@inproceedings{faucris.121884004,
abstract = {For electric motors light weight construction is becoming increasingly important, therefore the dynamical behavior of the lamination stack has to be known. The stacking of a lot of sheets has a relevant influence onto the behavior of the whole motor due to significant contact characteristics between the sheets. In this paper quasi-static tests are performed to identify this characteristic. At first a load representing the packaging process is applied onto the stack. Thereafter a cyclic load is superposed to show the forces during the motors life. With these quasi-static tests elastic and plastic effects and a hysteretic behavior are detected. These nonlinearities are referring to the sheet's roughness, the surface waviness and the existence of a coreplate varnish. In the modeling of the stiffness the roughness parameters are used. Based on the quasi-static model and with dynamic tests it is possible to identify the dynamic characteristic of the lamination stack.},
author = {Luchscheider, Vera and Willner, Kai},
booktitle = {ECCOMAS 2012 -- European Congress on Computational Methods in Applied Sciences and Engineering, e--Book Full Papers},
date = {2012-09-10/2012-09-14},
faupublication = {yes},
keywords = {Contact mechanics; Lamination stack; Roughness},
note = {UnivIS-Import:2015-04-16:Pub.2012.tech.FT.FT-TM.develo{\_}8},
pages = {1947-1955},
peerreviewed = {Yes},
title = {{Development} of a contact model for an electric motor lamination stack},
venue = {Vienna, Austria},
year = {2012}
}
@article{faucris.113434244,
abstract = {Friction has a significant effect on the metal forming. This is in particular true for the emerging sheet-bulk metal forming process. Therefore an adequate friction law is necessary for the accurate Finite-Element modelling of the process. This friction law has to incorporate a smooth transition from the Coulomb friction law for low contact pressures to a Tresca friction law for high contact pressures. Furthermore the plastic smoothing of surface roughness has to be taken into account. A friction law fulfilling these requirements is developed based on the results of an elastic-plastic halfspace contact model. This model is verified and calibrated experimentally. Its ability to model the changes in the roughness parameters as well as the Abbott curves in normal contact is demonstrated. Copyright © 2013 Trans Tech Publications Ltd.},
author = {Hauer, Franz and Willner, Kai},
doi = {10.4028/www.scientific.net/KEM.554-557.1471},
faupublication = {yes},
journal = {Key Engineering Materials},
keywords = {Contact; Friction; Halfspace; Sheet-bulk metal forming; Simulation},
note = {UnivIS-Import:2015-03-09:Pub.2013.tech.FT.FT-TM.develo},
pages = {1471-1477},
peerreviewed = {Yes},
title = {{Development} of a friction law respecting plastic surface smoothing},
volume = {554-557},
year = {2013}
}
@inproceedings{faucris.118523064,
abstract = {A light-weight design is becoming increasingly important for electric motors. As a consequence, adequate knowledge of the mechanical behavior of the lamination stack is of prime importance, since the lamination stack has a significant influence onto the behavior of the complete motor due to the significant contact characteristics between the single sheets. Quasi-static tests are performed to identify this stiffness behavior. A load representing the packaging process is first applied onto the stack. A cyclic load is then superposed to simulate the forces during the motor lifetime. With these quasi-static tests a progressive stiffness behavior with elastic and plastic effects is identified. This non-linearity can be attributed to the sheet's roughness and surface waviness. Based on the identified contact stiffness, an improved simulation of the quasi-static behavior of an electrical motor is possible. © 2012 IEEE.},
author = {Luchscheider, Vera and Willner, Kai and Maidorn, Mischa},
booktitle = {Proceedings, 2nd International Electric Drives Production Conference (EDPC 2012)},
date = {2012-10-15/2012-10-18},
doi = {10.1109/EDPC.2012.6425107},
faupublication = {yes},
isbn = {9781467330077},
keywords = {contact mechanics; lamination stack; roughness},
note = {UnivIS-Import:2015-04-16:Pub.2012.tech.FT.FT-TM.develo{\_}3},
pages = {142-146},
peerreviewed = {Yes},
title = {{Development} of a model to describe the stiffness of an electric motor lamination stack},
venue = {Nuremberg, Germany},
year = {2012}
}
@inproceedings{faucris.123479884,
abstract = {When bodies rotate they are subjected to velocity-dependent gyroscopic and inertia effects, which alter the dynamic behaviour of the structure. Analysing its eigenpairs consisting of eigenvalues and eigenvectors, these parameter-dependent changes can be tracked as eigenpaths by means of a continuation algorithm as in [1]. For rotationally symmetric structures an ALE approach (ALE = Arbitrary LAGRANGIAN-EULERIAN) for the finite element method as described in [2] can be employed. It allows simulating rotational influences on the body without actually having to rotate the mesh of the structure itself. This still-standing mesh facilitates further steps like coupling of other, static components with the rotating body. The combination of ALE with eigenpath analysis including an example is described in the following. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)},
address = {Weinheim},
author = {Weidauer, Tim and Willner, Kai},
booktitle = {PAMM, Volume 16, Issue 1},
date = {2016-03-07/2016-03-11},
doi = {10.1002/pamm.201610113},
faupublication = {yes},
keywords = {eigenpath; continuation; rotation; ALE},
pages = {249 - 250},
peerreviewed = {unknown},
publisher = {Wiley-VCH Verlag GmbH & Co. KGaA},
title = {{Eigenpath} analysis of rotating mechanical systems based on {ALE} formulation},
url = {http://onlinelibrary.wiley.com/doi/10.1002/pamm.201610113/abstract},
venue = {Braunschweig},
year = {2016}
}
@phdthesis{faucris.122553464,
author = {Willner, Kai},
faupublication = {no},
note = {UnivIS-Import:2016-07-26:Pub.1995.tech.FT.FT-TM.einsta{\_}6},
peerreviewed = {automatic},
school = {Friedrich-Alexander-Universität Erlangen-Nürnberg},
title = {{Ein} statistisches {Modell} für den {Kontakt} metallischer {Körper}},
year = {1995}
}
@inproceedings{faucris.106909044,
abstract = {
Due to the roughness of technical surfaces only the surface peaks are in contact for moderate contact pressures. Thus, the real contact area is smaller than the apparent contact area. Contact forces can only occur in the real contact area. Consequently it is necessary to determine the deformation of surface asperities in order to analyse the tribological properties of surfaces. The real contact area is usually small in initial contact. This leads to large contact pressures which in turn lead to the plastic deformation of surface roughness peaks. Therefore an elastic-plastic model is necessary. The halfspace model seems to be beneficial because there is only a system of equations on a surface mesh to be solved and not on a volume mesh like in the Finite-Element-Method. This leads to a much smaller system of equations which should allow reasonable calculation times even for large contact surfaces.
},
address = {Weinheim},
author = {Hauer, Franz and Willner, Kai},
booktitle = {PAMM 2011},
doi = {10.1002/pamm.201110101},
faupublication = {yes},
isbn = {978-3-902078-17-9},
note = {UnivIS-Import:2015-07-08:Pub.2011.tech.FT.FT-TM.elasti{\_}5},
pages = {219-220},
peerreviewed = {unknown},
publisher = {Wiley},
title = {{Elastic}-plastic halfspace simulation},
volume = {-},
year = {2011}
}
@inproceedings{faucris.118081964,
abstract = {The elasto-plastic normal contact of fractal surfaces is numerically investigated using a halfspace model. Artificial surface data are generated using the structure function, to study the influence of different surface parameters with respect to the load-area relationship and the load-gap relationship. The simulations show that for realistic surface parameters the deformation is always in the plastic range. © Springer 2006.},
address = {Berlin},
author = {Willner, Kai},
booktitle = {Analysis and Simulation of Contact Problems},
doi = {10.1007/3-540-31761-9{\_}34},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2006.tech.FT.FT-TM.elasto},
pages = {305-312},
peerreviewed = {Yes},
publisher = {Springer Verlag},
title = {{Elasto}-plastic contact of fractal surfaces},
volume = {27},
year = {2006}
}
@inproceedings{faucris.121499224,
abstract = {If two rough surfaces are brought into contact, asperities will deform either elastically or plastically. While the mode of initial deformation will depend on geometrical and material properties at any single asperity, the deformation upon unloading and reloading will be in the elastic regime. As it is not feasible to model the behaviour of each single asperity in a structural mechanics application, global contact laws are needed. In the present paper such contact laws are derived for several deformation models.},
author = {Willner, Kai},
booktitle = {Computational Methods in Contact Mechanics III},
date = {1997-07-01/1997-07-01},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.1997.tech.FT.FT-TM.elasto},
pages = {13-22},
peerreviewed = {Yes},
publisher = {Computational Mechanics Publ},
title = {{Elasto}-{Plastic} {Contact} of {Rough} {Surfaces}},
venue = {Computational Mechanics Publications},
year = {1997}
}
@article{faucris.116271364,
abstract = {The elasto-plastic normal contact of fractal surfaces is investigated. To study the influence of several surface parameters like fractal dimension and resolution, the surfaces are numerically generated using a special form of the structure function which is motivated by measurements of real rough surfaces. The contact simulation uses an iterative elastic halfspace solution based on a variational principle. A simple modification allows also the approximative solution of elasto-plastic contact problems. The influence of different surface parameters is studied with respect to the load-area relationship and the load-gap relationship. The simulations show that for realistic surface parameters the deformation is always in the plastic range. © 2004 by ASME.},
author = {Willner, Kai},
doi = {10.1115/1.1631019},
faupublication = {yes},
journal = {Journal of Tribology},
note = {UnivIS-Import:2015-03-09:Pub.2004.tech.FT.FT-TM.elstop},
pages = {28-33},
peerreviewed = {Yes},
title = {{Elasto}-{Plastic} {Normal} {Contact} of {Three}-{Dimensional} {Fractal} {Surfaces} {Using} {Halfspace} {Theory}},
volume = {126},
year = {2004}
}
@article{faucris.117606544,
abstract = {The aim of this work is the improvement of a constitutive friction law which has been identified for the specific demands of sheet-bulk metal-forming. The constitutive friction law determines the friction shear stress in dependency on the plastic smoothing of the surface roughness, which also affects the real contact area. An experimental setup is introduced to determine the change of the surface roughness, which is influenced by the tensile bulk stress in the workpiece. In order to model the experimental results, a well-established half-space model is presented and improved to consider strain hardening. The half-space model is used to determine the change of the contact area as a function of the tensile bulk stress. This interdependency is also reflected by the proposed constitutive friction law.},
author = {Beyer, Florian and Löffler, Maria and Willner, Kai and Engel, Ulf and Merklein, Marion},
faupublication = {yes},
journal = {Tribology in Industry},
keywords = {friction, constitutive friction law, half-space model, elasto-plastic contact, strain hardening, bulk stresses, sheet-bulk metal forming},
pages = {163-175},
peerreviewed = {Yes},
title = {{Enhancement} of a {Constitutive} {Friction} {Law} by {Considering} {Plastic} {Smoothing} of {Rough} {Surfaces} in {Dependency} on the {Bulk} {Stresses}},
url = {http://www.tribology.fink.rs/journals/2016/2016-2/4.pdf},
volume = {38},
year = {2016}
}
@article{faucris.247537509,
abstract = {Diamond-like carbon (DLC) coatings, frequently used to reduce wear and friction in machine components as well as on forming tools, are often subjected to cyclic loading. Doping of DLC coatings with metals or metal carbides as well as the usage of multilayer architectures represent promising approaches to enhance toughness, which is beneficial for the coatings’ behavior under cyclic loading. In this study, we utilized cyclic nanoindentation to characterize the tribologically induced surface fatigue behavior of single-layer tungsten-doped (a-C:H:W) and multilayer silicon oxide containing (a-C:H:Si:O/a-C:H)25 amorphous carbon coatings under cyclic loading. Columnar growth was observed for both coatings by focused ion beam microscopy and scanning electron microscopy, while the multilayer architecture of the (a-C:H:Si:O/a-C:H)25 coating was verified by the silicon content using glow-discharge optical emission spectroscopy. In cyclic nanoindentation of the (a-C:H:Si:O/a-C:H)25 multilayer coating, stepwise small changes in indentation depth were observed over several indentation cycles. The surface fatigue process of the single-layer a-C:H:W covered a smaller number of indentation cycles and was characterized by an early steep increase of the static displacement signal. Microscopical analyses hint at grain deformation, sliding at columnar boundaries, and grain detachment as underlying fatigue mechanisms of the a-C:H:W coating, while the (a-C:H:Si:O/a-C:H)25 multilayer coating showed transgranular crack propagation and gradual fracturing. In case of the (a-C:H:Si:O/a-C:H)25 multilayer coating, superior indentation hardness (HIT) and indentation modulus (EIT) as well as a higher HIT3/EIT2 ratio suggest a higher resistance to plastic deformation. A high HIT3/EIT2 ratio, being an indicator for hindered crack initiation, combined with the capability of stress relaxation in soft layers contributed to the favorable surface fatigue behavior of the (a-C:H:Si:O/a-C:H)25 multilayer coating observed in this cyclic nanoindentation studies.
},
author = {Weikert, Tim and Wartzack, Sandro and Baloglu, Maximilian Volkan and Willner, Kai and Gabel, Stefan and Merle, Benoit and Pineda, Fabiola and Walczak, Magdalena and Marian, Max and Rosenkranz, Andreas and Tremmel, Stephan},
doi = {10.1016/j.surfcoat.2020.126769},
faupublication = {yes},
journal = {Surface & Coatings Technology},
keywords = {Diamond-like carbon; Cyclic nanoindentation; Surface fatigue; Multilayer architecture},
peerreviewed = {Yes},
title = {{Evaluation} of the surface fatigue behavior of amorphous carbon coatings through cyclic nanoindentation},
url = {http://www.sciencedirect.com/science/article/pii/S0257897220314390},
volume = {407},
year = {2021}
}
@article{faucris.107430884,
abstract = {Sheet-Bulk Metal Forming (SBMF) allows the manufacture of complex parts with integrated functional form elements, such as teeth and thickened areas. Therefore, bulk forming operations are applied to sheets with initial thicknesses of 2 or 3 mm. The design and functionality of the tools are as important as the process itself. Therefore, the working group “Tools” of the Transregional Collaborative Research Centre on Sheet-Bulk Metal Forming (CRC/TR73) focuses on the optimization of the technical tool design. By varying topographies or applying tailored coatings, the friction behavior is changed to achieve a better form filling and to reduce process forces during the forming operations. In this paper, the potential of different tailored surfaces is validated by simulations and experimental studies. The tribological behavior of 14 surface microstructures is evaluated using a half-space model in order to select structures suitable for application. Those were characterized experimentally by ring-compression and pin-extrusion tests. The determined friction factors were used in a forming simulation to predict the form filling of small cavities in a flow forming operation. Furthermore, special attention is paid to the utilization of the anisotropic behavior of specific structures. The results were validated by an incremental gear forming process.},
author = {Kersting, Petra and Gröbel, Daniel and Merklein, Marion and Peter, Sieczkarek and Wernicke, Sebastian and Tekkaya, A. Erman and Krebs, Eugen and Freiburg, Dennis and Biermann, Dirk and Weikert, Tim and Tremmel, Stephan and Stangier, Dominic and Tillmann, Wolfgang and Matthias, Steffen and Reithmeier, Eduard and Löffler, Maria and Beyer, Florian and Willner, Kai},
doi = {10.1007/s11740-015-0651-6},
faupublication = {yes},
journal = {Production Engineering},
keywords = {Sheet-Bulk Metal Forming; Tailored surfaces; Milling technologies; Coating technologies; Forming simulations; Tribology simulation},
pages = {37-50},
peerreviewed = {unknown},
title = {{Experimental} and numerical analysis of tribological effective surfaces for forming tools in {Sheet}-{Bulk} {Metal} {Forming}},
url = {https://www.mfk.uni-erlangen.de?file=pubmfk{\_}5695fddc4e358},
volume = {10},
year = {2016}
}
@article{faucris.110377784,
abstract = {Friction has a considerable influence in metal forming both in economic and technical terms. This is especially true for sheet-bulk metal forming (SBMF). The contact pressure that occurs here can be low making Coulomb’s friction law advisable, but also very high so that Tresca’s friction law is preferable. By means of an elasto-plastic half-space model rough surfaces have been investigated, which are deformed in such contact states. The elasto-plastic half-space model has been verified and calibrated experimentally. The result is the development of a constitutive friction law, which can reproduce the frictional interactions for both low and high contact pressures. In addition, the law gives conclusion regarding plastic smoothening of rough surfaces. The law is implemented in the framework of the finite element method (FEM). However, compared to usual friction relations the tribological interplay presented here comes with the disadvantage of rising numerical effort. In order to minimise this drawback, a model adaptive finite element simulation is performed additionally. In this approach, contact regions are identified, where a conventional friction law is applicable, where the newly developed constitutive friction law should be used, or where frictional effects are negligible. The corresponding goal-oriented indicators are derived based on the “dual-weighted-residual” (DWR) method taking into account both the model and the discretisation error. This leads to an efficient simulation that applies the necessary friction law in dependence of contact complexity.},
author = {Beyer, Florian and Blum, Heribert and Kumor, Dustin and Rademacher, Andreas and Willner, Kai and Schneider, Thomas},
doi = {10.4028/www.scientific.net/KEM.639.283},
faupublication = {yes},
journal = {Key Engineering Materials},
keywords = {Friction, simulation, model adaptivity},
pages = {283-290},
peerreviewed = {Yes},
title = {{Experimental} and {Simulative} {Investigations} of {Tribology} in {Sheet}-{Bulk} {Metal} {Forming}},
url = {http://www.scientific.net/KEM.639.283},
volume = {639},
year = {2015}
}
@article{faucris.112097084,
abstract = {A normal contact test setup that is capable of measuring the elastoplastic deformation of a joint during loading and the elastic spring-back during unloading has been presented. The deformation is measured by two extensometers, which are clamped at the bottom and at the top specimen. The normal contact behavior of surfaces, which are made of different materials, sizes, and roughness parameters, is tested. The application of two extensometers is necessary to measure the bending, which can occur during the experiments. Finite element models with geometrical irregularities are applied to examine more closely the larger elastic spring-back of unloaded stainless steel surfaces. The determined pressure-approach relationships can, be used for simulations of bolted joints. Geometrical irregularities cause a large scattering of the elastic joint deflection if the contact surface has a small area or is made of a material with a high Young's modulus.},
author = {Görke, Daniel and Willner, Kai},
doi = {10.1111/j.1747-1567.2008.00448.x},
faupublication = {yes},
journal = {Experimental Techniques},
note = {UnivIS-Import:2015-03-09:Pub.2009.tech.FT.FT-TM.experi{\_}5},
pages = {46-52},
peerreviewed = {Yes},
title = {{Experimental} setup for normal contact stiffness measurement of technical surfaces with geometrical irregularities},
volume = {33},
year = {2009}
}
@article{faucris.117719404,
abstract = {Forming of near-net-shaped and load-adapted functional components, as it is developed in the Transregional Collaborative Research Centre on Sheet-Bulk Metal Forming SFB/TR 73, causes different problems, which lead to non-optimal manufacturing results. For these high complex processes the prediction of forming effects can only be realized by simulations. A stamping process of pressing eight punches into a circular blank is chosen for the considered investigations. This reference process is designed to reflect the main aspects, which strongly affect the final outcome of forming processes. These are the orthotropic material behaviour, the optimal design of the initial blank and the influences of different contact and friction laws. The aim of this work is to verify the results of finite element computations for the proposed forming process by experiments. Evaluation methods are presented to detect the influence of the anisotropy and also to quantify the optimal blank design, which is determined by inverse form finding. The manufacturing accuracy of the die plate and the corresponding roughness data of the milled surface are analysed, whereas metrological investigations are required. This is accomplished by the help of advanced measurement techniques like a multi-sensor fringe projection system and a white light interferometer. Regarding the geometry of the punches, micromilling of the die plate is also a real challenge, especially due to the hardness of the high-speed steel ASP 2023 (approx. 63 HRC). The surface roughness of the workpiece before and after the forming process is evaluated to gain auxiliary data for enhancing the friction modelling and to characterise the contact behaviou},
author = {Landkammer, Philipp and Loderer, Andreas and Krebs, Eugen and Söhngen, Benjamin and Steinmann, Paul and Hausotte, Tino and Kersting, Petra and Willner, Kai and Biermann, Dirk},
doi = {10.4028/www.scientific.net/KEM.639.251},
faupublication = {yes},
journal = {Key Engineering Materials},
keywords = {Evaluation; Metal Forming; Simulation},
note = {UnivIS-Import:2015-03-09:Pub.2015.tech.FT.lfmt.experi},
pages = {251-258},
peerreviewed = {Yes},
title = {{Experimental} verification of a benchmark forming simulation},
volume = {639},
year = {2015}
}
@book{faucris.117819724,
address = {Tönning},
author = {Willner, Kai and Hanss, M.},
faupublication = {no},
isbn = {3899595343},
note = {UnivIS-Import:2015-04-02:Pub.2006.tech.FT.FT-TM.experi},
peerreviewed = {No},
publisher = {Der Andere Verlag},
title = {{Experimentelle} und {Angewandte} {Mechanik} - {Ein} {Querschnitt}},
url = {http://buch.preisorakel.de/vergleich/9783899595345/},
year = {2006}
}
@inproceedings{faucris.118314724,
address = {Aachen},
author = {Landkammer, Philipp and Söhngen, Benjamin and Loderer, Andreas and Krebs, Eugen and Steinmann, Paul and Willner, Kai and Hausotte, Tino and Wiederkehr (geb. Kersting), Petra and Biermann, Dirk},
booktitle = {Tagungsband zum 18. Workshop Simulation in der Umformtechnik & 3. Industriekolloquium Blechmassivumformung 2015 - DFG Transregio 73},
faupublication = {yes},
note = {UnivIS-Import:2015-04-17:Pub.2015.tech.FT.lfmt.experi{\_}8},
pages = {91-110},
peerreviewed = {Yes},
publisher = {Shaker Verlag},
title = {{Experimentelle} {Verifizierung} eines {Benchmark}-{Umformprozesses}},
year = {2015}
}
@inproceedings{faucris.115600804,
author = {Willner, Kai and Hanss, M.},
booktitle = {Proceedings of the 6th Pan-American Congress of Applied Mechanics PACAM VI.},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.1999.tech.FT.FT-TM.finite{\_}7},
pages = {397400},
peerreviewed = {Yes},
title = {{Finite} {Element} {Problems} with {Uncertain} {Parameters}},
venue = {de Janeiro},
year = {1999}
}
@article{faucris.111916024,
abstract = {The effect of dry metallic friction can be attributed to two major mechanisms: adhesion and ploughing. While ploughing is related to severe wear and degradation, adhesion can be connected to pure elastic deformations of the contacting bodies and is thus the predominant mechanism in a stable friction pair. The transmitted friction force is then proportional to the real area of contact. Therefore, a lot of effort has been put into the determination of the fraction of real area of contact under a given load. A broad spectrum of analytical and numerical models has been employed. However, it is quite common to employ the so-called Mindlin assumptions, where the contact area is determined by the normal load only, disregarding the influence of friction. In the subsequent tangential loading, usually the contact pressure distribution is kept fixed such that the coupling between the tangential and normal solutions is neglected. Here, a numerical solution scheme based on elastic halfspace theory for frictional contact problems is presented where full coupling between the normal and tangential tractions and displacements is taken into account. Several examples show the influence of the coupling effects, but also the limitations for the analysis of rough contacts. Copyright © 2008 by ASME.},
author = {Willner, Kai},
doi = {10.1115/1.2913537},
faupublication = {yes},
journal = {Journal of Tribology},
keywords = {Elastic contact; Friction; Halfspace theory; Rough surfaces},
note = {UnivIS-Import:2015-03-09:Pub.2008.tech.FT.FT-TM.fullyc},
pages = {031405 1-6},
peerreviewed = {Yes},
title = {{Fully} {Coupled} {Frictional} {Contact} {Using} {Elastic} {Halfspace} {Theory}},
volume = {130},
year = {2008}
}
@inproceedings{faucris.206432718,
abstract = {In this contribution, we investigate the accuracy of surrogate models
for fuzzy systems. Within a virtual tolerance analysis, unknown
uncertainties are considered by fuzzy numbers. These fuzzy numbers
consist of higher‐dimensional intervals, where each interval is assigned
a membership value. To reproduce fuzzy numbers correctly, a large
number of system evaluations is needed. Instead of evaluating
numerically expensive full systems, we employ surrogate models with
radial basis functions. In order to find sufficiently accurate surrogate
models with as few as possible sampling points, we investigate the
influence of the sampling points on the respective fuzzy number
intervals. As an example, we investigate the tilting of an X‐ray
aperture, which shows different accuracy for different sampling
strategies. The reference results for the nonlinear multi‐body system
are calculated by a Matlab optimizer and are compared to the results of
the surrogate model},
address = {Weinheim},
author = {Oberleiter, Thomas and Willner, Kai},
booktitle = {PAMM, Volume 17},
date = {2017-03-06/2017-03-10},
doi = {10.1002/pamm.201710331},
faupublication = {yes},
pages = {725-726},
peerreviewed = {unknown},
publisher = {WILEY‐VCH Verlag GmbH & Co. KGaA},
title = {{Fuzinsumo} ‐ {Fuzzy} investigation with surrogate models},
venue = {Ilmenau/Weimar},
year = {2018}
}
@article{faucris.119639344,
abstract = {The application of fuzzy arithmetic to solve finite element problems with uncertain parameters is a powerful but problematic tool. Although the natural uncertainties associated with material variability can be taken into account successfully, the additional artificial uncertainties that arise from some computational aspects in the finite element method distort the result and must therefore be minimized. Thus, to achieve reasonable results, the different numerical techniques for the solution of finite element problems should not be applied in their common form, but should be modified with respect to a reduction of the critical fuzzy arithmetical operations that can cause artificial uncertainties.},
author = {Hanss, M. and Willner, Kai},
doi = {10.1016/S0093-6413(00)00091-4},
faupublication = {no},
journal = {Mechanics Research Communications},
note = {UnivIS-Import:2015-03-09:Pub.2000.tech.FT.FT-TM.afuzzy},
pages = {257-272},
peerreviewed = {Yes},
title = {{Fuzzy} arithmetical approach to the solution of finite element problems with uncertain parameters},
volume = {27},
year = {2000}
}
@inproceedings{faucris.118060404,
author = {Willner, Kai and Geisler, Johannes and Hanss, M.},
booktitle = {Proceedings of the 2. Workshop on Advanced Computational Engineering Mechanics},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2005.tech.FT.FT-TM.fuzzya},
pages = {167-176},
peerreviewed = {No},
title = {{Fuzzy} arithmetical modeling and simulation of structures with uncertain parameters},
venue = {Erlangen, Germany},
year = {2005}
}
@inproceedings{faucris.116297324,
abstract = {A general method for the simulation and analysis of systems with uncertain parameters is presented. In this concept, the uncertain parameters are modeled by fuzzy numbers in contrast to random numbers in stochastic approaches. After an introduction to fuzzy arithmetic, the transformation method is presented a practical implementation which allows the use of the fuzzy concept in conjunction with existing simulation environments. As a result of the simulation of the model, it is possible to quantify the overall uncertainty of the outputs, providing a worst-case scenario. Additionally, the uncertain model parameters can be rated with respect to their influence on the overall output uncertainty. As examples, some finite element applications of the fuzzy arithmetical approach are presented and discussed: the frequency response function of a vibrating plate and the vibration behavior of an engine hood in the presence of uncertain model parameters.},
author = {Hanss, M. and Willner, Kai},
booktitle = {Noise and Vibration Engineering},
date = {2004-09-20/2004-09-22},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2004.tech.FT.FT-TM.fuzzya{\_}4},
pages = {CD ROM},
peerreviewed = {Yes},
title = {{Fuzzy} arithmetical modeling and simulation of vibrating structures with uncertain parameters},
venue = {Leuven, Belgium},
year = {2004}
}
@article{faucris.221871495,
abstract = {This paper deals with the fuzzy dynamics of multibody systems with polymorphic uncertainty in the material microstructure. Macroscopic material properties are obtained using fuzzy-stochastic FEM based computational homogenization. In particular, the spectral stochastic local FEM is utilized to simulate a representative volume element of the microstructure. Forward dynamics of the macroscopic system is modeled using the Graph Follower algorithm. Thereby we propagate the uncertainty from the lowest level of material microstructure to the highest level of multibody dynamics. Differences in the propagation of epistemic and aleatoric uncertainties to the macroscale and their influence on the multibody dynamics are discussed. A particular example of a multibody system used in this paper is a multistory frame, whereby the considered heterogeneous material is a cement-based concrete.},
author = {Pivovarov, Dmytro and Hahn, Verena and Steinmann, Paul and Willner, Kai and Leyendecker, Sigrid},
doi = {10.1007/s00466-019-01737-9},
faupublication = {yes},
journal = {Computational Mechanics},
keywords = {Computational homogenization; Epistemic uncertainty; Forward dynamics simulation; Fuzzy numbers; Stochastic FEM; α-cut-optimization},
note = {CRIS-Team Scopus Importer:2019-07-09},
pages = {1601-1619},
peerreviewed = {Yes},
title = {{Fuzzy} dynamics of multibody systems with polymorphic uncertainty in the material microstructure},
volume = {64},
year = {2019}
}
@article{faucris.203494899,
abstract = {Real components always deviate from their ideal dimensions. This makes every component, even a serial production, unique. Although they look the same, differences can always be observed due to different scattering factors and variations in the manufacturing process. All these factors inevitably lead to parts that deviate from their ideal shape and, therefore, have different properties than the ideal component. Changing properties can lead to major problems or even failure during operation. It is necessary to specify the permitted deviations to ensure that every single product nevertheless meets its technical requirements. Furthermore, it is necessary to estimate the consequences of the permitted deviations, which is done via tolerance analysis. During this process, components are assembled virtually and varied with the uncertainties specified by the tolerances. A variation simulation is one opportunity to calculate these effects for geometric deviations. Since tolerance analysis enables engineers to identify weak points in an early design stage, it is important to know the contribution that every single tolerance has on a certain quality-relevant characteristic, to restrict or increase the correct tolerances. In this paper, a fuzzy-based method to calculate the sensitivity is introduced and compared with the commonly used extended Fourier amplitude sensitivity test (EFAST) method. Special focus of this work is the differentiation of the sensitivity for the total system and the sensitivities for the subsystems defined by the α-cuts of the fuzzy numbers. It discusses the impact of the number of evaluations and nonlinearity on sensitivity for EFAST and the fuzzy-based meth},
author = {Oberleiter, Thomas and Heling, Björn and Schleich, Benjamin and Willner, Kai and Wartzack, Sandro},
doi = {10.1115/1.4040919},
faupublication = {yes},
journal = {ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part B: Mechanical Engineering},
pages = {011008-1 - 011008-7},
peerreviewed = {Yes},
title = {{Fuzzy} {Sensitivity} {Analysis} in the {Context} of {Dimensional} {Management}},
url = {https://www.archiv.mfk.tf.fau.de?file=pubmfk{\_}5c1c9e401132d},
volume = {Volume 5},
year = {2018}
}
@article{faucris.227272768,
author = {Pivovarov, Dmytro and Oberleiter, Thomas and Willner, Kai and Steinmann, Paul},
doi = {10.1002/nme.5947},
faupublication = {yes},
journal = {International Journal for Numerical Methods in Engineering},
peerreviewed = {Yes},
title = {{Fuzzy}-{Stochastic} {FEM}-based homogenization framework for materials with polymorphic uncertainties in the microstructure},
year = {2018}
}
@inproceedings{faucris.118409544,
abstract = {Friction has a significant influence on the tool lifetime and the quality of products in manufacturing processes. Real surfaces are always rough, so that for moderate loads contact occurs only at surface roughness peaks. Thus the real contact area A real is smaller than the apparent contact area A 0. Adhesive forces, which are an important contribution to friction, can only be transferred within A real. Consequently A real has to be determined in order to analyse the tribological behaviour of technical surfaces. The halfspace approach is used because of its advantage in numerical effort compared to the Finite-Element-Method. Due to the fact that contact pressures can be very large the plastic deformation of roughness peaks has to be taken into account. Therefore a three-dimensional plasticity algorithm is implemented into the halfspace model.},
author = {Hauer, Franz and Willner, Kai},
booktitle = {COMPLAS XI},
date = {2011-09-07/2011-09-09},
edition = {-},
faupublication = {yes},
keywords = {Computational plasticity; Contact; Halfspace; Metal forming},
note = {UnivIS-Import:2015-04-16:Pub.2011.tech.FT.FT-TM.halfsp{\_}9},
pages = {965-975},
peerreviewed = {Yes},
title = {{Halfspace} modeling of elastic-plastic contact of rough surfaces},
venue = {Barcelona, Spain},
volume = {11},
year = {2011}
}
@inproceedings{faucris.118523944,
author = {Hauer, Franz and Willner, Kai},
booktitle = {10th World Congress on Computational Mechanics},
doi = {10.5151/meceng-wccm2012-18465},
faupublication = {yes},
isbn = {978-85-86686-70-2},
note = {UnivIS-Import:2015-04-16:Pub.2012.tech.FT.FT-TM.halfsp{\_}3},
pages = {-},
peerreviewed = {unknown},
title = {{Halfspace} {Simulation} of {Rough} {Surface} {Contact} in {Metal} {Forming}},
venue = {Sao Paulo, Brasil},
year = {2012}
}
@inproceedings{faucris.219417192,
address = {HEVERLEE},
author = {Willner, Kai},
booktitle = {PROCEEDINGS OF INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING (ISMA2018) / INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS (USD2018)},
date = {2018-09-17/2018-09-19},
faupublication = {yes},
month = {Jan},
note = {CRIS-Team WoS Importer:2019-06-04},
pages = {1777-1787},
peerreviewed = {unknown},
publisher = {KATHOLIEKE UNIV LEUVEN, DEPT WERKTUIGKUNDE},
title = {{Identification} of contact parameters for dry friction joints},
venue = {Leuven},
year = {2018}
}
@inproceedings{faucris.118185144,
abstract = {In this work an anisotropic material model at finite strains with nonlinear mixed (isotropic and kinematic) hardening is used for the identification of the hardening parameters of sheet steel. The algorithmic system is thereby reduced to a single equation return mapping. For the identification, a cruciform specimen is loaded biaxially in an alternating shear test to provoke the kinematic hardening behavior and prevent the sheet from buckling. The material parameters are found through an optimization strategy by comparing the deformation field from the experiment to that from a finite element (FE) simulation. The resulting cost function is minimized by means of a gradient-based metho},
author = {Söhngen, Benjamin and Willner, Kai},
booktitle = {XIV International Conference on Computational Plasticity. Fundamentals and Applications},
date = {2017-09-05/2017-09-07},
editor = {Oñate E., Owen D.R.J. , Peric D. , Chiumenti M.},
faupublication = {yes},
keywords = {Kinematic Hardening; Anisotropic Plasticity; Parameter Identification; Biaxial Loading; Sheet Metal},
pages = {373-384},
peerreviewed = {unknown},
title = {{Identification} of nonlinear kinematic hardening parameters for sheet metal from biaxial loading tests},
venue = {Barcelona},
year = {2017}
}
@inproceedings{faucris.118411304,
abstract = {In this paper the deep-drawing sheet steel DC04, representative for sheet-bulk metal forming processes, is characterized through uni- and biaxial tensile and compression tests. The orthotropic plastic material parameters for the Hill 1948 yield surface are identified in two different ways. The first one utilizes uniaxial tensile experiments with specimen in three angles to the rolling direction of the sheet (0, 45 and 90 degree) and the plastic material parameters are calculated through the Lankford coefficients. Second a Finite Element Model Updating (FEMU) procedure is introduced. By taking the measured full-field displacement data and the forces of the biaxial tensile experiments better fitting parameters are identified at reasonable experimental costs.},
author = {Schmaltz, Stefan and Willner, Kai},
booktitle = {COMPLAS XI Proceeding (CD)},
date = {2011-09-07/2011-09-09},
faupublication = {yes},
keywords = {Computational Plasticity; FEMU; Parameter Identification; Sheet steel},
note = {UnivIS-Import:2015-04-16:Pub.2011.tech.FT.FT-TM.identi},
pages = {241-250},
peerreviewed = {Yes},
title = {{Identification} of orthotropic plastic material parameters for deep-drawing steel using {DIC} and {FEMU}},
venue = {Barcelona, Spain},
year = {2011}
}
@inproceedings{faucris.121785664,
address = {Erlangen, Germany},
author = {Luchscheider, Vera and Maidorn, Mischa and Willner, Kai},
booktitle = {PAMM 2014},
date = {2014-03-10/2014-03-14},
doi = {10.1002/pamm.201410114},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2014.tech.FT.FT-TM.identi{\_}8},
pages = {253-254},
peerreviewed = {unknown},
publisher = {Wiley},
title = {{Identification} of the lamination stack's behavior simulated with a multi-scale homogenization using a progressive contact formulation},
venue = {Erlangen, Germany},
volume = {14},
year = {2014}
}
@inproceedings{faucris.108570044,
author = {Schmaltz, Stefan and Willner, Kai},
booktitle = {Proceedings of the 10th Youth Symposium on Experimental Solid Mechanics},
date = {2011-05-25/2011-05-28},
faupublication = {yes},
isbn = {978-3-941003-34-7},
note = {UnivIS-Import:2015-04-16:Pub.2011.tech.FT.FT-TM.identi{\_}2},
pages = {101-102},
peerreviewed = {No},
publisher = {IMEKO-International Measurement Federation Secretariat},
title = {{Identification} of the yield surface for sheet steel using an optical measurement system},
venue = {Germany},
year = {2011}
}
@inproceedings{faucris.223332421,
abstract = {Geometrical work piece deviations are unavoidable and directly affect the function and quality of technological products. Tolerance management is regarded as a crucial subtask of the development of technological products, because it ensures the function as well as a sufficient product quality while maintaining reasonable production costs. That means, that geometric tolerances as an essential part of the product description greatly affect the functional capability, manufacturability, mountability, verifiability and the costs of the final product. The research group FOR 2271 was founded to enable the computer-aided specification of tolerances, which meet the requirements of production, assembly, verification and function by close cooperation between the departments responsible for product design, assembly and metrology. The aim of this contribution is to determine the manufacturing process scatter as well as the measurement uncertainty and establish ways and means to include that information into efficient meta-models, ultimately enabling improved and accurate tolerance analyse},
author = {Müller, Andreas and Oberleiter, Thomas and Willner, Kai and Hausotte, Tino},
booktitle = {Proceedings of the Design Society: International Conference on Engineering Design},
date = {2019-08-05/2019-08-08},
doi = {10.1017/dsi.2019.357},
faupublication = {yes},
keywords = {Tolerance representation and management; Uncertainty; Product modelling / models;},
pages = {3501–3510},
peerreviewed = {Yes},
publisher = {Cambridge University Press},
title = {{Implementation} of {Parameterized} {Work} {Piece} {Deviations} and {Measurement} {Uncertainties} into {Performant} {Meta}-models for an {Improved} {Tolerance} {Specification}},
venue = {Delft},
volume = {1},
year = {2019}
}
@inproceedings{faucris.121763884,
address = {Donnersbach, Austria},
author = {Schmaltz, Stefan and Willner, Kai},
booktitle = {Proceedings of XXXII. Colloquium on metal forming},
edition = {-},
faupublication = {yes},
isbn = {978-3-902078-18-6},
note = {UnivIS-Import:2015-04-16:Pub.2013.tech.FT.FT-TM.implem{\_}9},
pages = {95-100},
peerreviewed = {Yes},
publisher = {Montanuniversität Leoben},
title = {{Implementierung} und {Anpassung} eines {Materialmodells} für {FE}-{Simulationen} in der {Blechmassivumformung}. {Colloquium} on metal forming},
venue = {Donnersbach, Austria},
volume = {-},
year = {2013}
}
@inproceedings{faucris.115603224,
author = {Selvadurai, A.P.S. and Gaul, L. and Willner, Kai},
booktitle = {Computational Methods in Contact Mechanics IV},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.1999.tech.FT.FT-TM.indent},
pages = {3-14},
peerreviewed = {Yes},
title = {{Indentation} of a {Functionally} {Graded} {Elastic} {Solid}: {Application} of an {Adhesively} {Bonded} {Plate} {Model}},
venue = {WIT Press},
year = {1999}
}
@article{faucris.120644744,
abstract = {In a recent paper (2004, "Elasto-Plastic Normal Contact of Three-Dimensional Fractal Surfaces Using Halfspace Theory," J. Tribol., 126, pp. 28-33) the author developed a halfspace model for the elasto-plastic normal contact of rough surfaces. This model is now used to study the inuence of intrinsic surface pa-rameters on constitutive contact laws, such as load-gap relation and load-area relation, for a specic type of surface topography known as fractal-regular surfaces. Numerical investigations show that the fractal dimension has only minor inuence on the load-gap relationship, which is mostly determined by the dimensionless ratio between the transition length and the rms values of the height data. Due to the fractal nature of the surfaces at the small wavelength limit, initial deformation will always be in the plastic range. The load-area relation becomes then completely independent of the geometric surface parameters and is determined by material properties alone, at least if the predicted plastic defor-mation occurs at a length scale larger than the atomic scale. © 2008 by ASME.},
author = {Willner, Kai},
doi = {10.1115/1.2842243},
faupublication = {yes},
journal = {Journal of Tribology},
keywords = {Elasto-plastic contact; Fractal-regular surface; Halfspace theory},
note = {UnivIS-Import:2015-03-09:Pub.2008.tech.FT.FT-TM.influe{\_}1},
pages = {1-6},
peerreviewed = {Yes},
title = {{Influence} of {Fractal} {Surface} {Parameters} on the {Elasto}-{Plastic} {Contact} {Behavior} of {Rough} {Surfaces}},
volume = {130},
year = {2008}
}
@inproceedings{faucris.214669487,
abstract = {The specific design
of components like rotor and stator as sheet-layered lamination stacks results
in a structural behavior that is heavily dependent on the sheet interactions on
the microscale. Due to the manufacturing process, these thin laminations may be
just stacked and held together e.g. by welding or clamps, such that frictional
contact of rough surfaces between single sheets is taking place and
significantly affects the overall deformation behavior. Here, the elastic anisotropic, more precisely
transversely isotropic, material parameters describing these lamination stacks
are identified with the help of the homogenization taking efficiently care of
the microstructure. For this purpose, different constitutive contact laws in
normal direction capturing the sheet interactions by a penalty formulation and
their effect on the macroscopic quantities are presented to emphasize the
importance of this model parameter. Furthermore, it is shown that the derived
stress-strain relation is identical to results of a numerical homogenization,
where a representative volume element is simulated by the Finite-Element method
incorporating Zero-Thickness elements for the contact simulation. The numerical
results are finally compared to experiments showing a good accordance.
In electrical machines, sheet-layered lamination stacks play an important role for the mechanical behavior of the system. Especially the interlayer between individual sheets and their interaction have a severe influence on the structure. In the context of performance and computational effort, it is desirable to avoid a full FE simulation of a lamination stack with every single sheet. Therefore, homogenization techniques are presented to identify a transversely isotropic surrogate material model, while Zero-Thickness elements are utilized during this process to cover the interplay of single sheets. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)},
author = {Baloglu, Maximilian Volkan and Willner, Kai},
doi = {10.1002/pamm.201610243},
faupublication = {yes},
journal = {Proceedings in Applied Mathematics and Mechanics},
keywords = {lamination stack; numerical homogenization; material modelling; contact mechanics},
pages = {509 - 510},
peerreviewed = {Yes},
title = {{Material} modelling of a sheet-layered lamination stack by homogenization},
url = {http://onlinelibrary.wiley.com/doi/10.1002/pamm.201610243/epdf},
volume = {16},
year = {2016}
}
@inproceedings{faucris.118524164,
address = {Taipei, Taiwan},
author = {Schmaltz, Stefan and Willner, Kai},
booktitle = {Proc. of ISEM-ACEM-SEM-7th ISEM12-Taipei Conference, (2012},
edition = {-},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2012.tech.FT.FT-TM.materi{\_}2},
pages = {-},
peerreviewed = {Yes},
publisher = {J-STAGE},
title = {{Material} {Parameter} {Identification} utilizing {Optical} {Full}-{Field} {Strain} {Measurement} and {Digital} {Image} {Correlation}},
venue = {Taipei, Taiwan},
volume = {-},
year = {2012}
}
@inproceedings{faucris.118524384,
author = {Schmaltz, Stefan and Willner, Kai},
booktitle = {Verformungskundliches Kolloquium Konferenz: XXXI},
faupublication = {yes},
isbn = {978-3-902078-17-9},
note = {UnivIS-Import:2015-04-16:Pub.2012.tech.FT.FT-TM.materi{\_}8},
pages = {13-18},
peerreviewed = {No},
title = {{Material} parameter optimization utilizing full-field strain measurement data and the {Finite} {Element} {Method}},
venue = {Donnersbach, Austria},
volume = {XXXI},
year = {2012}
}
@inproceedings{faucris.117937864,
author = {Görke, Daniel and Willner, Kai},
booktitle = {Extended Abstract in Proceedings of the 8th. World Congress on Computational Mechanics},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2008.tech.FT.FT-TM.measur},
pages = {CD-ROM},
peerreviewed = {Yes},
title = {{Measured} and {Simulated} {Contact} {Stiffness} of {Dry}, {Metallic} {Joints}},
venue = {Italy, CD-Rom},
year = {2008}
}
@article{faucris.286931101,
abstract = {Bauschinger effects typically describe a reduction of yield strength after a load path change under uniaxial loading conditions. Here, we use in-plane loading to investigate, for the first time, Bauschinger effects in the sheet metal DC06 under well-defined equi-biaxial loading conditions: We first performed equi-biaxial tensile tests with cruciform specimens up to different maximum tensile strains. Then, smaller specimens were prepared from the equi-biaxially deformed inner part of the cruciform specimens and subjected to equi-biaxial compression. The mechanical results show that the material exhibits distinct Bauschinger effects when subjected to equi-biaxial load path changes, which differ from similar observations under uniaxial loading. Specifically, biaxial Bauschinger effect factors quickly reach a level of saturation, whereas the uniaxial Bauschinger effect factors keep decreasing. These Bauschinger effects can be rationalized by considering the results of TEM and EBSD investigations at the different stages of biaxial loading, particularly by considering the evolution of dislocation densities and the formation of substructures, which are related to intergranular and intragranular stresses. Furthermore, residual stress measurements by XRD and in-situ neutron diffraction show an increase of compressive residual stresses after equi-biaxial tensile deformation and unloading. These residual stresses facilitate yielding during subsequent equi-biaxial compression and therefore also clearly contribute to the observed Bauschinger effects. },
author = {Härtel, Markus and Illgen, Christian and Panzner, Tobias and Bruder, Enrico and Schmaltz, Stefan and Van Petegem, Steven and Willner, Kai and Durst, Karsten and Van Swygenhoven, Helena and Wagner, Martin F.X.},
doi = {10.1016/j.ijplas.2022.103478},
faupublication = {yes},
journal = {International Journal of Plasticity},
note = {CRIS-Team Scopus Importer:2022-12-23},
peerreviewed = {Yes},
title = {{Mechanical}, microstructural and in-situ neutron diffraction investigations of equi-biaxial {Bauschinger} effects in an interstitial-free {DC06} steel},
volume = {159},
year = {2022}
}
@inproceedings{faucris.211308742,
address = {Stamsried},
author = {Müller, Andreas and Heling, Björn and Schleich, Benjamin and Oberleiter, Thomas and Willner, Kai and Wartzack, Sandro and Hausotte, Tino},
booktitle = {Industriekolloquium der Forschergruppe FOR 2271},
date = {2019-02-05/2019-02-05},
editor = {Wartzack},
faupublication = {yes},
isbn = {978-3-89650-477-7},
month = {Jan},
pages = {64-73},
peerreviewed = {No},
publisher = {Druck+Verlag Ernst Vögel GmbH},
title = {{Methoden} zur {Reduzierung} und {Berücksichtigung} der {Unsicherheiten} von dimensionellen {Messgrößen} in der {Toleranzanalyse}},
url = {https://www.archiv.mfk.tf.fau.de?file=pubmfk{\_}5c6a7ab3612b6},
venue = {Erlangen},
year = {2019}
}
@inproceedings{faucris.117752184,
author = {Geisler, Johannes and Willner, Kai},
booktitle = {Proceedings of 6th International Congress on Industrial Applied Mathematics and the 78th Annual Meeting of the International Association of Applied Mathematics and Mechanics},
doi = {10.1002/pamm.200700227},
edition = {1},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2007.tech.FT.FT-TM.modeli{\_}3},
pages = {4050009-4050010},
peerreviewed = {Yes},
title = {{Modeling} of jointed structures using zero thickness interface elements},
venue = {Zürich, Switzerland},
volume = {7},
year = {2007}
}
@inproceedings{faucris.115604544,
author = {Allgaier, R. and Keiper, W. and Gaul, L. and Willner, Kai},
booktitle = {Computational Methods in Contact Mechanics IV},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.1999.tech.FT.FT-TM.modelo},
pages = {35-48},
peerreviewed = {Yes},
title = {{Mode} {Lock}-{In} and {Friction} {Modeling}},
venue = {WIT Press},
year = {1999}
}
@inproceedings{faucris.201747648,
abstract = {Rotating systems are subject to gyroscopic influences which alter their dynamic behaviour. The Arbitrary Lagrangian Eulerian (ALE) formulation is a popular approach for related models, e.g. for the simulation of tire rolling contact. It allows for decoupling the rotational guiding motion from the relative deformation of the rotating structure. At the same time it complicates contact computations as the relative displacement between two material particles is not tracked naturally by the ALE observer. Model reduction techniques for (non-linear) systems face additional challenges in this context, of which a variety is discussed here for common approaches such as the Second order modal truncation, the Krylov subspace method or the Craig-Bampton method.
Friction forces between contact partners in dry friction are primarily caused by adhesion and ploughing. In adhesive contact,
tangential loads are transferred by shear forces within the real contact area. The real contact area is usually smaller than the
apparent contact area, because real surfaces are always rough and only the highest surface peaks are in contact for moderate
loads. Thus the size of the real contact area is a suitable measurement for the behaviour in dry friction. The normal contact
is simulated with a halfspace model. The contact surfaces are modelled numerically in order to enable the independent
investigation of the influence of several surface properties, namely the fractal behaviour on small scales, non-Gaussian height
distribution and anisotropy. Fractal behaviour means that asperities are covered with smaller asperities of the same shape.
Surface anisotropy means that valleys and ridges are oriented in a certain direction.
},
address = {Weinheim},
author = {Hauer, Franz and Willner, Kai},
booktitle = {Proceedings of the 81st Annual Meeting of the International Association of Applied Mathematics and Mechanics},
doi = {10.1002/pamm.201010198},
edition = {1},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2010.tech.FT.FT-TM.normal{\_}8},
pages = {411-412},
peerreviewed = {unknown},
publisher = {Wiley},
title = {{Normal} contact simulation of non-{Gaussian} fractal surfaces},
venue = {Karlsruhe, Germany},
volume = {10},
year = {2010}
}
@article{faucris.117359704,
abstract = {The influence of the 3D frictional crack surface interaction on the fracture mechanical parameters as well as on the crack path is numerically investigated. For the solution of the boundary value problem the 3D dual boundary element method in terms of the discontinuous formulation is utilized. This method is especially suited for contact problems because it directly deals with the discontinuities at the crack surfaces. The contact problem is solved by the application of the penalty method. Coulomb's frictional law is utilized for the consideration of the dissipative nature of friction. For discrete steps within one load cycle the stress intensity factors are determined by an extrapolation procedure from the stress field. Based on the analysis of a load cycle, the cyclic stress intensity factors are obtained. For the simulation of crack propagation an implicit time integration scheme of a crack propagation law implemented in terms of a predictor-corrector scheme is applied. The influence of the crack surface roughness on the crack path is shown by numerical examples. © 2010 Elsevier Ltd.},
author = {Weber, Wilhelm and Willner, Kai and Kuhn, Günther},
doi = {10.1016/j.engfracmech.2010.03.024},
faupublication = {yes},
journal = {Engineering Fracture Mechanics},
keywords = {3D simulation; Crack surface interaction; Fatigue crack propagation},
note = {UnivIS-Import:2015-03-09:Pub.2010.tech.FT.FT-TM.numeri},
pages = {1708-1720},
peerreviewed = {Yes},
title = {{Numerical} analysis of the influence of crack surface roughness on the crack path},
volume = {77},
year = {2010}
}
@inproceedings{faucris.119411424,
author = {Süß, Dominik and Geisler, Johannes and Willner, Kai},
booktitle = {Proceedings of the 81st Annual Meeting of the International Association of Applied Mathematics and Mechanics},
doi = {10.1002/pamm.201010124},
edition = {1},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2010.tech.FT.FT-TM.numeri{\_}9},
pages = {263-264},
title = {{Numerical} and experimental investigations of dynamic contact phenomena in jointed structures},
venue = {Karlsruhe, Germany},
volume = {10},
year = {2010}
}
@inproceedings{faucris.118082624,
author = {Willner, Kai and Görke, Daniel},
booktitle = {Experimentelle und Angewandte Mechanik Ein Querschnitt},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2006.tech.FT.FT-TM.numeri},
pages = {CD-ROM},
peerreviewed = {No},
title = {{Numerical} and experimental investigations of joint deflections under normal load},
venue = {Der Andere Verlag},
year = {2006}
}
@inproceedings{faucris.201791288,
abstract = {A test set-up for the modal analysis of gyroscopic, rotationally symmetric systems is presented. It employs laser Doppler vibrometry along with automatic impulse excitation installed on a rotary table and is applied to a glass structure rotating about its figure axis. The effects of gyroscopic influences on the modal behaviour such as the split of eigenfrequencies and the treatment of complex eigenmodes as travelling waves are deduced analytically and shown experimentally. Finally numerical computations using the Arbitrary-Lagrangian-Eulerian (ALE) finite element formulation separating the rigid body rotation from the mesh deformation are conducted. With the combination of analytical, experimental and numerical analysis a broad overview of modal characteristics of gyroscopic systems is given.
Biaxial tensile testing of sheet metals is becoming increasingly popular for sheet metal
forming. Determining equivalent stresses in biaxial tensile specimens is more
complicated than in conventional uniaxial tensile specimens. In the present study, we
compare four different approaches to calculate effective stresses during biaxial tensile
loading of a cruciform specimen: (i) partial unloading method, where stresses are
determined based on force-strain curves; (ii) identification with uniaxial tensile testing;
(iii) an analysis of equivalent biaxial tests; (iv) numerical simulations. Considering
experimental results for an AA1050 aluminum alloy and for a low-carbon steel DC06,
we show that, for the cruciform sample studied here, two methods do not yield
physically reasonable results: the uniaxial approach does not properly take into
account the effect of transverse loading, and the equivalent biaxial approach exhibits
uncertainties in strain measurement data. The most comprehensible approach is the
numerical method; because it also yields detailed information about the local stress
and strain states. The numerical results are in excellent agreement with the partial
unloading method in terms of the initial flow stress and of effective stress-strain curves
for strains up to 0.02, with both methods predicting a similar effective cross section of
18.0 mm2 for the considered specimen.
},
author = {Härtel, Markus and Pfeiffer, Stefan and Schmaltz, Stefan and Söhngen, Benjamin and Kulawinski, Dirk and Willner, Kai and Henkel, Sebastian and Biermann, Horst and Wagner, Martin F.-X.},
doi = {10.1111/str.12257},
faupublication = {yes},
journal = {Strain},
keywords = {biaxial tensile testing; cruciform specimen; effective cross section; FEM simulation; sheet metals},
peerreviewed = {Yes},
title = {{On} the identification of an effective cross section for a cruciform specimen},
volume = {54},
year = {2018}
}
@inproceedings{faucris.119943824,
abstract = {This paper examines the problem of the surface indentation of an isotropic elastic halfspace, which is reinforced by an inextensible membrane and subjected to indentation by a rigid circular punch with a smooth flat base. The inextensibility constraint is assumed to be applicable over the entire region of the membrane of infinite extent, which is located at a finite depth below the surface of the elastic halfspace. The paper presents the formal results that can be recovered as limiting cases of the analytical formulation and compares these with results obtained via a finite element modelling of the problem, which also accommodates for the elasticity of the membrane.},
author = {Selvadurai, A.P.S. and Willner, Kai and Gaul, L.},
booktitle = {Computational Methods in Contact Mechanics V},
date = {2001-06-18/2001-06-20},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.2001.tech.FT.FT-TM.onthei},
pages = {233240},
peerreviewed = {Yes},
title = {{On} the {Indentation} of a {Membrane} {Reinforced} {Elastic} {Halfspace}: {Analytical} and {Computational} {Approaches}},
venue = {WIT Press},
year = {2001}
}
@article{faucris.111734744,
abstract = {This contribution aims at introducing tribological contact properties into the stability analysis of macroscopic structural systems with focus on brake-squeal applications. First, the surfaces of several brake pads at different states of wear are analyzed experimentally. Based on these data a statistical contact model as well as a numerical simulation are presented. Using these models two constitutive contact laws are derived, which link contact pressure and stiffness. Second, a simple brake model incorporating these contact models is developed. Results of stability analyses are presented and the influence of the contact models on the steady state stability is discussed. © 2011 Elsevier Ltd.},
author = {Hetzler, H. and Willner, Kai},
doi = {10.1016/j.triboint.2011.05.019},
faupublication = {yes},
journal = {Tribology International},
keywords = {Brake squeal; Contact stiffness; Friction induced vibrations; Rough surface},
pages = {237-246},
peerreviewed = {Yes},
title = {{On} the influence of contact tribology on brake squeal},
volume = {46},
year = {2012}
}
@article{faucris.221145404,
author = {Heling, Björn and Oberleiter, Thomas and Schleich, Benjamin and Willner, Kai and Wartzack, Sandro},
doi = {10.1115/1.4043912},
faupublication = {yes},
journal = {Journal of Verification, Validation and Uncertainty Quantification},
pages = {011001:1-011001:10},
peerreviewed = {Yes},
title = {{On} the {Selection} of {Sensitivity} {Analysis} {Methods} in the {Context} of {Tolerance} {Management}},
url = {https://www.archiv.mfk.tf.fau.de?file=pubmfk{\_}5d42c82b60dc1},
volume = {4},
year = {2019}
}
@article{faucris.112515964,
abstract = {The efficient solution of the 3D crack surface contact problem utilizing the boundary element method (BEM) is presented. The dual discontinuity method (DDM), a special formulation of the BEM, is applied. This method deals directly with the relative displacements and the discontinuities of the tractions at the crack. For the normal behavior a unilateral contact is assumed and for the description of the tangential behavior Coulomb's frictional law is utilized. The hard contact formulation is regularized by the application of the penalty method. An incremental iterative procedure based on a radial return mapping algorithm is applied for the solution of this non-linear problem. Based on the stress field the fracture mechanical parameters are determined by an extrapolation method for all increments of a characteristic load cycle. By the analysis of this load cycle the cyclic fracture mechanics values are obtained. Due to the non-linear nature of crack growth the simulation is implemented in the framework of a predictor-corrector scheme. For the investigation of the influence of the crack surface roughness on the behavior of cracks two numerical examples are presented. © 2011 Trans Tech Publications.},
author = {Weber, Wilhelm and Kolk, Karsten and Willner, Kai and Kuhn, Günther},
doi = {10.4028/www.scientific.net/KEM.454.11},
faupublication = {yes},
journal = {Key Engineering Materials},
keywords = {Crack surface contact; Dual boundary element method; Dual discontinuity method; Fatigue crack propagation},
note = {UnivIS-Import:2015-03-09:Pub.2011.tech.FT.FT-TM.onthes},
pages = {11-29},
peerreviewed = {Yes},
title = {{On} the solution of the {3D} crack surface contact problem using the boundary element method},
volume = {454},
year = {2011}
}
@inproceedings{faucris.123688224,
author = {Hanss, M. and Willner, Kai},
booktitle = {Proceedings of Euromech 405 Colloquium},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.1999.tech.FT.FT-TM.onusin},
pages = {8592},
peerreviewed = {Yes},
title = {{On} {Using} {Fuzzy} {Arithmetic} to {Solve} {Problems} with {Uncertain} {Parameters}},
venue = {France},
year = {1999}
}
@inproceedings{faucris.122952324,
author = {Schmaltz, Stefan and Willner, Kai},
booktitle = {PAMM 2011},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2011.tech.FT.FT-TM.optimi{\_}2},
pages = {-},
peerreviewed = {Yes},
title = {{Optimization} of elastic material parameters of sheet metal with {FEMU} and {DIC}},
venue = {Graz, Austria},
year = {2011}
}
@inproceedings{faucris.119431444,
author = {Süß, Dominik and Willner, Kai},
booktitle = {Proceedings of Applied Mathematics and Mechanics (PAMM)},
edition = {1},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2011.tech.FT.FT-TM.parame{\_}4},
pages = {293-294},
title = {{Parameter} identification for nonlinear dynamical systems using multiharmonic balance techniques},
venue = {Graz, Austria},
volume = {7},
year = {2011}
}
@article{faucris.229702604,
abstract = {Abstract In this contribution we examine the influence of strain rate on the isotropic hardening of two sheet metals. The nominal strain rates vary between 0.0005 s−1 and 20 s−1 and the full field deformation is captured with the help of digital image correlation (DIC) technique. For modelling the strain rate dependent behaviour, we introduce a rate dependent part in the definition of the hardening stress, distinguishing between approaches that incorporate the rate dependency in an additive or multiplicative manner. The hardening laws are thereby embedded in a large strain plasticity framework based on the logarithmic strain space. The material parameters are identified both in a “direct” fashion, where the gap between constitutive equation and measured stress-strain curve is minimized and inverse, by using the finite element method (FEM) to generate force-displacement curves and the virtual fields method, which compares internal and external virtual work.},
author = {Söhngen, Benjamin and Willner, Kai},
doi = {10.1002/pamm.201900339},
faupublication = {yes},
journal = {Proceedings in Applied Mathematics and Mechanics},
peerreviewed = {Yes},
title = {{Parameter} identification of strain rate dependent hardening for sheet metals},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/pamm.201900339},
volume = {19},
year = {2019}
}
@inproceedings{faucris.119481824,
abstract = {Non-linear normal modes (NNMs) can be considered as a kind of parallel theory to the description of linear systems with linear normal modes (LNMs) but for non-linear ones. In this paper a NNM is not defined as harmonic or synchronous oscillation but as periodic one. Therefore one has to search for periodic solutions of the governing equations of the system to get an NNM. This periodicity condition leads to a mathematical formulation as a two-point-boundary-value problem. Small systems with a low number of degrees of freedom and non-linear couplings (cubic springs) are investigated. The approach is also adopted to a finite-element model with a cubic non-linearity. With increasing the energy in the system the progressive non-linearity leads to a hardening effect. One typical dynamical property of non-linear systems is the frequency-energy dependency of their oscillations. A good graphic illustration is to plot such dependency in a so called frequency-energy plot (FEP) because here this dependency of energy and eigenfrequency is given explicitly. Thereby the points on a branch in the FEP represent a family of NNM oscillations with qualitatively equal motion properties, quasi a family of periodic orbits. A NNM branch can be calculated by a numerical continuation method with starting at low energy level in a quasi linear regime and increasing the energy and reducing the period of the oscillation iteratively. In non-linear systems internal resonances and other phenomena can occur. Several tongues can bifurcate from a NNM branch. Therefore normal continuation methods fail at such bifurcation points. To overcome this problem a predictor-corrector-method is used. As correction a probability one homotopy algorithm is implemented, in particular the normal flow algorithm. The predicted solution point gets iterated by a Newton-Raphson approach. The gradual iteration steps to the solution of the periodicity condition are along a path which is normal to the so-called Davidenko flow. The Davidenko flow can be seen as family of solution curves around the periodic solution caused by small perturbations to the non-linear system equations and varying these perturbations. These correction steps are continued until convergence is achieved. Different corrector approaches are compared to the normal flow algorithm and the results are discussed.},
author = {Jerschl, Martin and Süß, Dominik and Willner, Kai and Jerschl, Martin},
booktitle = {Proceedings of the International Conference on Noise and Vibration Engineering ISMA},
date = {2014-09-15/2014-09-17},
faupublication = {yes},
isbn = {9789073802919},
note = {UnivIS-Import:2015-10-26:Pub.2014.tech.FT.FT-TM.pathco},
pages = {3059-3064},
publisher = {KU Leuven},
title = {{Path} continuation for the concept of non-linear normal modes using a normal flow algorithm},
venue = {Leuven, Belgium},
volume = {-},
year = {2014}
}
@article{faucris.110432344,
abstract = {Different models of rails for the high frequency range are compared. In addition to known models, a new model based entirely upon the finite element method is presented. The models are used to calculate the dispersion relations for wave propagation in free rails up to 15 kHz. The results for different models are compared. The deviations are explained and the validity ranges for the different models are given.},
author = {Knothe, Kl. and Strzyzakowski, Z. and Willner, Kai},
doi = {10.1006/jsvi.1994.1009},
faupublication = {no},
journal = {Journal of Sound and Vibration},
note = {UnivIS-Import:2015-03-05:Pub.1994.tech.FT.FT-TM.railvi},
pages = {111-123},
peerreviewed = {Yes},
title = {{Rail} {Vibrations} in the {High} {Frequency} {Range}},
volume = {169},
year = {1994}
}
@inproceedings{faucris.201116816,
abstract = {One approach for the simulation of rotating systems is the Arbitrary-Lagrangian-Eulerian (ALE) finite element formulation, which is well-established in the field of rolling contact mechanics for tires. With this formulation the rotational motion is handled from an Eulerian viewpoint and thus can be separated from the occurring Lagrangian deformation of the finite element mesh. In this context of (non-linear) systems undergoing gyroscopic and/or contact forces, e.g. for tires or disc brakes, model reduction techniques such as the Second order modal truncation, the Krylov subspace technique and the Craig-Bampton method are employed and analysed in their applicability.
},
author = {Weidauer, Tim and Willner, Kai},
booktitle = {Nonlinear Dynamics, Volume 1; Proceedings of the 36th IMAC, A Conference and Exposition on Structural Dynamics 2018},
date = {2018-02-12/2018-02-15},
doi = {10.1007/978-3-319-74280-9{\_}31},
editor = {Gaetan Kerschen},
faupublication = {yes},
keywords = {Gyroscopic system; ALE; non-linear dynamics; model order reduction; contact},
pages = {287-302},
peerreviewed = {unknown},
publisher = {Springer International Publishing},
title = {{Reduced} {Order} {Modelling} for {Non}-{Linear} {Rotating} {Systems} in {ALE} {Formulation} with {Contact}},
venue = {Orlando, FL, USA},
year = {2018}
}
@article{faucris.265229148,
abstract = {The paper presents an investigation of the accuracy of surrogate models for systems with uncertainties, where the
uncertain parameters are represented by fuzzy numbers. Since the underlying fuzzy arithmetic using alpha-level optimisation requires a large number of system evaluations, the use of numerically expensive systems becomes prohibitive with
a higher number of fuzzy parameters. However, this problem can be overcome by employing less expensive surrogate
models, where the accuracy of the surrogate depends strongly on the choice of the sampling points. In order to fnd a
sufciently accurate surrogate model with as few as possible sampling points, the infuence of various sampling strategies on the accuracy of the fuzzy evaluation is investigated. As well suited for fuzzy systems, the newly developed Fuzzy
Oriented Sampling Shift method is presented and compared with established sampling strategies. For the surrogate
models radial basis functions and a Kriging model are employed. As test cases, the Branin and the Camelback function
with fuzzy parameters are used, which demonstrate the varying accuracy for diferent sampling strategies. A more application oriented example of a fnite element simulation of a deep drawing process is given in the e},
author = {Oberleiter, Thomas and Willner, Kai},
doi = {10.1007/s42452-021-04801-3},
faupublication = {yes},
journal = {SN Applied Sciences},
keywords = {Surrogate modelling · Fuzzy numbers · Kriging · DACE · Radial basis function · Uncertainty},
peerreviewed = {Yes},
title = {{Sampling} strategy for fuzzy numbers in the context of surrogate models},
volume = {3},
year = {2021}
}
@inproceedings{faucris.279718287,
abstract = {An investigation of the influence of constitutive friction laws on the damping behavior of dry friction joints is presented. The modeling starts at the micro- scale of the surface roughness leading to constitutive laws with regard to both the normal and tangential contact. These laws are used in a 3D finite element simulation of a simplified model joint. Numerical simulations show the influence of various levels of sophistication of the used contact laws. Here, the influence of high level contact laws proves to be limited in a spatially resolved joint model.},
author = {Willner, Kai},
booktitle = {Conference Proceedings of the Society for Experimental Mechanics Series},
date = {2016-01-25/2016-01-28},
doi = {10.1007/978-3-319-29763-7{\_}34},
editor = {Daniel Rixen, Matt Allen, Randall L. Mayes},
faupublication = {yes},
isbn = {9783319297620},
keywords = {Dissipation; Friction; Joint; Rough surface; Simulation},
note = {CRIS-Team Scopus Importer:2022-08-05},
pages = {349-356},
peerreviewed = {unknown},
publisher = {Springer New York LLC},
title = {{Scale}-dependent modeling of joint behavior},
venue = {Orlando, FL, USA},
volume = {4},
year = {2016}
}
@incollection{faucris.107426264,
abstract = {Reibeigenschaften von Oberflächen für Umformwerkzeuge gezielt einzustellen (Tailored Friction) nimmt bei der Entwicklung moderner Umformprozesse in technischer und ökonomischer Hinsicht eine zentrale Rolle ein. Dies betrifft insbesondere die Blechmassivumformung, die im Rahmen des SFB Transregio 73 erforscht wird. Ein neues Verfahren, das im SFB entwickelt wird, ist die Strukturierung durch regenerative Werkzeugschwingungen beim Fräsen. Ziel dabei ist es, einen separaten Prozessschritt, in dem nur strukturiert wird, einzusparen. Beim Fräsen mit Werkzeugschwingungen ist aufgrund der hohen Komplexität eine simulationsgestützte Auslegung unentbehrlich. Realitätsnahe Ergebnisse können dabei nur durch eine hinreichend gute Parametrisierung der Simulation erzielt werden, was im Besonderen für die Zerspankraftparameter gilt. In diesem Artikel wird die Sensitivität von tribologisch relevanten Kenngrößen auf die Zerspankraftparameter mit dem Ziel diskutiert, eine Aussage über die notwendige Güte zu treffen, mit der diese ermittelt werden müssen, um die Reibeigenschaften gefräster Oberflächen zuverlässig vorhersagen zu können. Um aus den simulierten gefrästen Oberflächen tribologische Kennwerte zu ermitteln, die für die Blechmassivumformung mit ihren hohen Flächenpressungen realitätsnah sind, findet ein Halbraummodell Anwendung.},
address = {Bamberg},
author = {Breitsprecher, Thilo and Hense, Rouven and Beyer, Florian and Biermann, Dirk and Wartzack, Sandro and Willner, Kai},
booktitle = {Tagungsband zum 2. Erlanger Workshop Blechmassivumformung 2013},
editor = {Merklein, M.; Behrens, B. A., Tekkaya, A. E.},
faupublication = {yes},
isbn = {978-3-87525-353-5},
keywords = {Tailored Friction, Sensitivitätsanalyse, Knowledge Discovery in Databases},
pages = {121-136},
peerreviewed = {unknown},
publisher = {Meisenbach},
title = {{Sensitivitätsanalyse} der tribologischen {Eigenschaften} gefräster {Oberflächenstrukturen} bei der {Blechmassivumformung}},
year = {2013}
}
@inproceedings{faucris.123827044,
address = {Montpellier, France},
author = {Schmaltz, Stefan and Willner, Kai},
booktitle = {PhotoMechanics},
faupublication = {yes},
note = {UnivIS-Import:2015-04-16:Pub.2013.tech.FT.FT-TM.sheets{\_}4},
pages = {-},
peerreviewed = {Yes},
publisher = {-},
title = {{Sheet} steel material parameter identification utilizing a biaxial tensile test and optical full-field measurements},
venue = {Montpellier, France},
volume = {-},
year = {2013}
}
@inproceedings{faucris.109593924,
abstract = {In the context of lightweight design, the so-called tailored blanks are more frequently used to improve sheet-bulk metal forming process results. In order to meet the requirements of tailored blank designs for subsequent sheet-bulk metal forming process steps, design engineers can influence many process or geometry parameters. A crucial task for design engineers is to find the optimal process and geometry parameter setting that is an optimal design with respect to multiple design requirements. A simulation-based approach to face this challenge is presented in this pape},
address = {Glasgow},
author = {Küstner, Christof and Beyer, Florian and Kumor, Dustin and Loderer, Andreas and Wartzack, Sandro and Willner, Kai and Blum, Heribert and Rademacher, Andreas and Hausotte, Tino},
booktitle = {DS 84: Proceedings of the DESIGN 2016 14th International Design Conference},
date = {2016-05-16/2016-05-19},
editor = {Marjanovic, D.; Storga, M.; Pavkovic, N.; Bojcetic, N.; Skec, S.},
faupublication = {yes},
keywords = {pareto-optimized design, simulation study, friction law},
pages = {291-300},
peerreviewed = {Yes},
publisher = {Design Society},
title = {{Simulation}-based development of {Pareto}-optimized tailored blanks for the use within sheet-bulk metal forming},
url = {https://www.mfk.uni-erlangen.de?file=pubmfk{\_}5742b0e022d9f},
venue = {Dubrovnik},
year = {2016}
}
@inproceedings{faucris.122297604,
abstract = {In this article, we consider the simulation of sheet-bulk metal forming processes, which makes high demands on the underlying models and on the simulation software.We present our approach to incorporate new modelling approaches from various fields in a commercial simulation software, in our case Simufact.forming. Here, we discuss material, damage, and friction models as well as model adaptive techniques.},
author = {Beese, Stefan and Beyer, Florian and Blum, Heribert and Isik, Kerim and Kumor, Dustin and Löhnert, Stefan and Rademacher, Andreas and Tekkaya, A. Erman and Willner, Kai and Wriggers, Peter and Zeller, Sebastian},
booktitle = {19th ESAFORM Conference},
date = {2016-04-27/2016-04-29},
faupublication = {yes},
peerreviewed = {Yes},
title = {{Simulation} of {Sheet}-{Bulk} {Metal} {Forming} {Processes} with {Simufact}.forming using {User}-{Subroutines}},
venue = {Nantes},
year = {2016}
}
@inproceedings{faucris.121541464,
author = {Leitz, Thomas and Willner, Kai},
booktitle = {Proc. Appl. Math. Mech. (PAMM)},
date = {2012-03-26/2012-03-30},
faupublication = {yes},
peerreviewed = {unknown},
title = {{Simulation} of the elastohydrodynamic contact with a piezo-viscous fluid},
venue = {Darmstadt},
year = {2012}
}
@inproceedings{faucris.117998144,
author = {Gaul, L. and Fischer, M. and Nackenhorst, U. and Willner, Kai},
booktitle = {Proceedings of the FENET/NAFEMS Seminar: FEM in Structral Dynamics},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.2001.tech.FT.FT-TM.soluti},
pages = {-},
peerreviewed = {No},
title = {{Solution} of {Multi}-{Field} {Problems} using {Finite} and {Boundary} {Element} {Methods}},
venue = {Germany},
year = {2001}
}
@article{faucris.265784858,
abstract = {Computational homogenization is a powerful tool allowing to obtain homogenized properties of materials on the macroscale from simulations of the underlying microstructure. The response of the microstructure is, however, strongly affected by variations in the microstructure geometry. In particular, we consider heterogeneous materials with randomly distributed non-overlapping inclusions, which radii are also random. In this work we extend the earlier proposed non-deterministic computational homogenization framework to plastic materials, thereby increasing the model versatility and overall realism. We apply novel soft periodic boundary conditions and estimate their effect in case of non-periodic material microstructures. We study macroscopic plasticity signatures like the macroscopic von-Mises stress and make useful conclusions for further constitutive modeling. Simulations demonstrate the effect of the novel boundary conditions, which significantly differ from the standard periodic boundary conditions, and the large influence of parameter variations and hence the importance of the stochastic modeling.},
author = {Pivovarov, Dmytro and Mergheim, Julia and Willner, Kai and Steinmann, Paul},
doi = {10.1007/s00466-021-02099-x},
faupublication = {yes},
journal = {Computational Mechanics},
note = {CRIS-Team WoS Importer:2021-11-05},
peerreviewed = {Yes},
title = {{Stochastic} local {FEM} for computational homogenization of heterogeneous materials exhibiting large plastic deformations},
year = {2021}
}
@inproceedings{faucris.108297024,
abstract = {In the 1960s Rosenberg extended the definition of linear normal modes (LNM) for conservative systems to nonlinear systems: On a Nonlinear Normal Mode (NNM) every degree-of-freedom (DOF) vibrates in unison. Later Shaw and Pierre provided a definition for nonconservative systems and defined NNMs as invariant manifolds in phase space. If the system vibrates on such a manifold all other modes shall remain quiescent for all time. Nowadays there are many publications using the concept of NNMs to investigate systems with polynomial nonlinearities. But until now the upper mentioned definition is mostly used to investigate viscously damped systems. In this paper an oscillator containing a geometrically nonlinear (cubic) spring and a dry friction damper is considered. The system is driven into resonance and decay processes are evaluated. Wavelet analysis is used to identify which frequencies and harmonics remain during the decay process.},
author = {Jerschl, Martin and Süß, Dominik and Willner, Kai and Jerschl, Martin},
booktitle = {34th IMAC, A Conference and Exposition on Structural Dynamics, 2016},
doi = {10.1007/978-3-319-29763-7{\_}33},
faupublication = {yes},
isbn = {9783319297620},
keywords = {Friction; Nonlinear coupling; Nonlinear dynamics; Nonlinear normal modes (NNMs); Optimal system design},
pages = {341-348},
peerreviewed = {Yes},
publisher = {Springer New York LLC},
title = {{Studies} of a geometrical nonlinear friction damped system using {NNMs}},
volume = {4},
year = {2016}
}
@article{faucris.122165384,
abstract = {Sheet and bulk metal forming are widely used manufacturing methods. The interaction between worktool and workpiece in such a process causes friction which has a remarkable impact on the expended energy of the process. Therefore the influence of friction is important. Friction can be split into shearing and ploughing [1]. Ploughing is the plastic deformation of a soft surface by a hard contact partner. Shear forces are only transferred in the real contact area where material contact occurs. The investigation of the contribution of both ploughing and shearing to the total friction resistance is done with the use of an elasto-plastic halfspace model. The multiscale character of surfaces demands a fine discretization, which results in numerical effort. While a finite element method takes into account both surface and bulk of the contact partners, the halfspace model only regards the contact surfaces and thereby consumes less computing capacity. In order to identify the friction resistance, two rough surfaces get into contact. After full application of the normal load, the surfaces are moved relatively to each other. New asperities of the contact surfaces get into contact and are plastically deformed. These deformations are used to estimate the ploughing effect in dependency on the relative displacement. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)},
author = {Beyer, Florian and Willner, Kai},
doi = {10.1002/pamm.201410107},
faupublication = {yes},
journal = {Proceedings in Applied Mathematics and Mechanics},
pages = {239-240},
peerreviewed = {Yes},
title = {{Surface} {Deformation} due to {Shear} and {Ploughing} in a {Halfspace}},
url = {http://onlinelibrary.wiley.com/doi/10.1002/pamm.201410107/pdf},
volume = {14},
year = {2014}
}
@inproceedings{faucris.115772624,
abstract = {Contact laws for rough surfaces are used to obtain, e.g., contact stiffness or contact conductivity. Usually contact laws are derived on the basis of asperity deformation models in conjunction with a stochastic roughness model. As the stochastic parameters depend strongly on the measurement procedure, the obtained contact laws have to be used carefully. Fractal surface parameters can be obtained, which are independent of sampling interval or length, but the resulting contact laws are still dependent on these values.},
author = {Willner, Kai},
booktitle = {Computational Methods in Contact Mechanics V},
date = {2001-06-18/2001-06-20},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.2001.tech.FT.FT-TM.surfac},
pages = {3-10},
peerreviewed = {Yes},
title = {{Surface} {Models} for {Contact} {Laws}},
year = {2001}
}
@article{faucris.121093104,
abstract = {This paper presents an analytical solution to the problem of the interaction between a thin plate that is adhesively bonded to the surface of an isotropic elastic halfspace and a concentrated Mindlin-type force that acts parallel to the bonded surface. The model is an idealization of a surface-stiffened region that has potential applications ranging from mechanics of thin films, thermal barrier coatings, layering created by attrition and wear of surfaces and functionally graded materials. The solution also illustrates the influence of the flexural plate model in mitigating the development of unbounded displacements during the application of localized loading directly at the bonded plate. © 2006 Elsevier Ltd. All rights reserved.},
author = {Willner, Kai and Selvadurai, A.P.S.},
doi = {10.1016/j.ijmecsci.2006.05.008},
faupublication = {yes},
journal = {International Journal of Mechanical Sciences},
keywords = {Adhesively bonded plate; Cerruti's problem; Functionally graded solid; Internal loading of halfspace; Mechanics of thin films; Thermal barrier coatings},
note = {UnivIS-Import:2015-03-09:Pub.2006.tech.FT.FT-TM.surfac{\_}1},
pages = {1072-1079.},
peerreviewed = {Yes},
title = {{Surface}-{Stiffened} {Halfspace} {Under} the {Action} of a {Horizontally} {Directed} {Mindlin} {Force}},
volume = {48},
year = {2006}
}
@inproceedings{faucris.222393112,
abstract = {Virtual approaches to manufacturing processes are a common tool in developing components today. Simulations are always containing uncertainties like simplifying assumptions in computer aided modelling, material deviations, fluctuating external loads or other known and unknown influences. To integrate such uncertainties in an early design stage, the input parameters should be defined as intervals, because insufficient data may be available at this stage to provide probability distributions. To consider such epistemic uncertainties, a large number of intervals can be merged into a fuzzy number. For each interval a membership value is assigned which depends on the interval limits and an expert estimation. However, this interval modelling leads to a very high number of expensive evaluations, which is not feasible for a high number of uncertain input parameters. To reduce the calculation time, surrogate models are used. Here, the full model is evaluated only at some grid points and the system response is approximated by mathematical approaches. Design and Analysis of Computer Experiments (DACE) offers a suitable surrogate model based on the Kriging method. The system model substituted in this way can be evaluated in an efficient way, but in addition to the uncertain simulation results, the approximation error dependent on the surrogate model has to be considered. Investigations of first prototypes lead to new knowledge that can be used to improve the surrogate model. Measurements, however, also include errors that are composed of systematic and random errors. The systematic measurement errors are specific errors for each measuring system and task, which are usually corrected during the measurement. However, an estimation of the random measurement error, which represents the precision of the measurement can be taken into account. Two methods are presented. Either an additional constant term is implemented in the standard Kriging or a superposition of two standard Kriging models, which are based on the simulation data and the measurement data, is used. As an application example a cold forging process of a steel gearwheel is employe},
author = {Oberleiter, Thomas and Müller, Andreas and Hausotte, Tino and Willner, Kai},
booktitle = {Uncecomp 2019 Proceedings},
date = {2019-06-24/2019-06-26},
doi = {10.7712/120219.6347.18786},
editor = {M. Papadrakakis, V. Papadopoulos, G. Stefanou},
faupublication = {yes},
keywords = {Kriging; Measuring Data; Measuring Uncertainty; Surrogate Modeling},
peerreviewed = {Yes},
title = {{SURROGATE} {MODELING} {CONSIDERING} {MEASURING} {DATA} {AND} {THEIR} {MEASUREMENT} {UNCERTAINTY}},
url = {https://2019.uncecomp.org/proceedings/},
venue = {Crete},
year = {2019}
}
@book{faucris.279718535,
author = {Süß, Dominik and Janeba, Anton and Willner, Kai},
doi = {10.1007/978-3-319-56818-8{\_}6},
faupublication = {yes},
isbn = {9783319568188},
note = {CRIS-Team Scopus Importer:2022-08-05},
peerreviewed = {unknown},
publisher = {Springer International Publishing},
title = {{The} {Gaul} resonator: {Experiments} for the isolated investigation of a bolted lap joint},
year = {2017}
}
@article{faucris.319729355,
abstract = {Violins incorporate numerous interfaces and anisotropic behaviour due to natural materials. Hence, the modelling of these instruments is extremely complex. The present work investigates the structural dynamics of a specific violin corpus (violin resonant body) with the aim of using numerical modelling to accurately understand the modal behaviour of the violin using a novel stepwise approach. In the first step, an inverse material parameter identification via experimental and numerical modal analysis of the raw woods is performed to obtain the material parameters of the individual woods. In the second step, an experimental modal analysis of the violin substructures is performed using 2D scanning laser Doppler vibrometry and building finite element models based on accurate 3D scans of the parts manufactured by a luthier. The experimentally obtained modal parameters of the individual parts are compared with the numerical results. In the third step, the whole violin corpus, i.e. the resonant body of the instrument, is assessed. The good agreement between the numerical and the experimental results demonstrates that the application of standard techniques of modal analysis on a very complex mechanical system, the violin body, is possible. Our methodology offers a novel approach to analysing individual components of bowed string instruments, facilitating a comprehensive vibrational analysis with implications for broader musical research, including luthier optimisation tools, digital reconstruction of historical violins, and advancements in instrument design for improved playability and tonal quality.},
author = {Akar, Özge and Willner, Kai},
doi = {10.1080/09298215.2024.2321869},
faupublication = {yes},
journal = {Journal of New Music Research},
keywords = {Digital twin; Finite elements; Laser-Doppler vibrometry; Modal analysis; Violin},
note = {CRIS-Team Scopus Importer:2024-03-15},
peerreviewed = {Yes},
title = {{The} modal behaviour of a violin corpus},
year = {2024}
}
@article{faucris.279715777,
abstract = {The computationally most expensive part of stochastic FEM based homogenization is the inversion of the stochastic stiffness matrix. Previously we studied different combinations of global and local basis functions in the stochastic domain while keeping the common FEM discretization in the physical domain. Simulation results showed that a local basis (SL-FEM) results in a sparse but bigger stiffness matrix compared to a global basis (SG-FEM). In this work we introduce a SFEM modification involving global basis functions in both the physical and the stochastic domain. We introduce two different strategies for the implementation of the global basis. The first is the application of a trigonometric basis within a global Galerkin framework. The second is the use of vibration modes of some simple deterministic auxiliary model as global basis functions. The second approach in particularly results in a basis reduction technique. However this approach differs markedly from stochastic spectral decomposition which uses the matrix of the original stochastic problem. We address two very important questions, namely the treatment of the Gibbs phenomenon in the case of physical-stochastic trigonometric basis functions and the evaluation of the eigenvectors for the stochastic problem which are suitable for further basis reduction. Convergence studies and detailed comparison with Monte-Carlo results are presented for both methods.},
author = {Pivovarov, Dmytro and Steinmann, Paul and Willner, Kai},
doi = {10.1016/j.cma.2018.01.002},
faupublication = {yes},
journal = {Computer Methods in Applied Mechanics and Engineering},
keywords = {Computational homogenization; eXtended FEM; Global basis; Random geometry; Reduced order modeling; Stochastic FEM},
note = {CRIS-Team Scopus Importer:2022-08-05},
pages = {488-519},
peerreviewed = {Yes},
title = {{Two} reduction methods for stochastic {FEM} based homogenization using global basis functions},
volume = {332},
year = {2018}
}
@article{faucris.111413764,
abstract = {Fuzzy arithmetic provides a powerful tool to introduce uncertainty into mathematical models. With Zadeh's extension principle, one can obtain a fuzzy-valued extension of any real-valued objective function. An efficient and accurate approach to compute expensive multivariate functions of fuzzy numbers is given by fuzzy arithmetic based on sparse grids. In this paper, we illustrate the general applicability of this new method by computing two dynamic systems subjected to uncertain parameters as well as uncertain initial conditions. The first model consists of a system of delay differential equations simulating the periodic outbreak of a disease. In the second model, we consider a multibody mechanism described by an algebraic differential equation system. © World Scientific Publishing Company.},
author = {Willner, Kai and Wohlmuth, B. I. and Klimke, A.},
doi = {10.1142/S0218488504003181},
faupublication = {no},
journal = {International Journal of Uncertainty Fuzziness and Knowledge-Based Systems},
keywords = {Computing fuzzy functions; Differential equations; Extension principle; Fuzzy numbers; Multibody mechanism; Uncertainty modeling},
note = {UnivIS-Import:2015-03-09:Pub.2004.tech.FT.FT-TM.uncert{\_}9},
pages = {745-759},
peerreviewed = {Yes},
title = {{Uncertainty} modeling using fuzzy arithmetic based on sparse grids: {Applications} to dynamic systems},
volume = {12},
year = {2004}
}
@misc{faucris.229321899,
abstract = {Due to the high Péclet-number occurring in Earth mantle dynamics, the energy equation can be approximated by a pure advection equation for the temperature. However, conventional approaches like the Finite Element Method introduce undesired diffusion. Therefore, the task of our BGCE Honours Project is to develop and evaluate unconventional discretisations of the temperature equation that tackle the problem of artificial diffusion. We come up with two different methods: One is based on the Bresenham algorithm stemming from computer graphics. It uses offset values to determine the advection direction of the temperature. The other method features a Lagrangian description of the problem. We achieve this by deploying particles that incorporate temperature values and are advected only by the underlying velocity field. Simulations in one- and two-dimensional domains reveal inherent shortcomings of the Bresenham Method which cannot be overcome by several attempts. On the other hand, the Lagrangian Method yields promising results that can be further improved by additional treatments. We extend the Lagrangian Method to work on triangle and tetrahedron grids to offer an interface to the implementation of the Earth mantle dynamics solver of the Terra-Neo project. Additional advantages of the proposed method are the parallelisation capability, a straight-forward extension for advecting other physical quantities and the possible inclusion of physical diffusion in an operator-splitting approach.
},
author = {Baloglu, Maximilian Volkan and Nadjafabadi Farahani, Mohammad Hassan and Rettinger, Christoph and Vogel, Constantin},
faupublication = {yes},
peerreviewed = {automatic},
title = {{Unconventional} {Discretisations} of the {Temperature} {Equation} in {Earth} {Mantle} {Dynamics}},
url = {https://www10.cs.fau.de/publications/reports/2014{\_}BalogluFarahaniRettingerVogel-BGCE.pdf},
year = {2014}
}
@article{faucris.111567544,
author = {Allgaier, R. and Gaul, L. and Willner, Kai and Keiper, W.},
faupublication = {no},
journal = {Konstruktion},
note = {UnivIS-Import:2015-03-09:Pub.2005.tech.FT.FT-TM.unters},
pages = {1-3},
peerreviewed = {Yes},
title = {{Untersuchungen} zum {Bremsenquitschen} am {Balken}-{Scheibe} {Modell}},
url = {http://www.konstruktion-online.de/kon/article.php?data[article{\_}id]=14217},
volume = {6},
year = {2005}
}
@inproceedings{faucris.123354924,
author = {Gaul, L. and Willner, Kai and Hurlebaus, S.},
booktitle = {Proceedings of the 4th International ESPI User Meeting},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.1997.tech.FT.FT-TM.usingt},
pages = {1-6},
peerreviewed = {Yes},
title = {{Using} the {ESPI}-{Technique} to {Determine} {Material} {Properties} of {Plates}},
venue = {Dr. Ettemeyer GmbH},
year = {1997}
}
@article{faucris.119780364,
abstract = {Although different discrete formulations for contact problems have been widely studied during the last decade, the numerical simulation of complex industrial applications is still challenging. While suitable Lagrange multiplier based formulations are well-known for their consistency and stability in the case of classical model problems of Coulomb type, rough surface contact laws and additional multi-point constraints are much less understood. In this paper, we focus on a quadratic finite element approach for quasi-static calculations and extend ideas from our previous work on constitutive contact laws combined with suitable solutions for multi-point constraints like cyclic symmetry on the contact boundary. The popular dual mortar method is used to enforce the contact constraints in a variationally consistent way without increasing the algebraic system size. To avoid possible consistency errors of the dual mortar approach in case of large curvatures or gradients in the contact zone, an alternative quadratic Petrov-Galerkin mortar formulation is presented. Numerical examples demonstrate the robustness of the derived numerical algorithm. Special focus is set to industrial motivated applications involving large deformations and plastic effects as well as rough surfaces on the micro-scale.},
author = {Sitzmann, Saskia and Willner, Kai and Wohlmuth, B. I.},
doi = {10.1016/j.finel.2015.09.009},
faupublication = {yes},
journal = {Finite Elements in Analysis and Design},
keywords = {Contact with regularization; Dual mortar methods; Industrial applications; Perturbed Lagrangian formulation; Petrov-Galerkin; Quadratic elements},
pages = {37-53},
peerreviewed = {Yes},
title = {{Variationally} consistent quadratic finite element contact formulations for finite deformation contact problems on rough surfaces},
volume = {109},
year = {2016}
}
@incollection{faucris.311719279,
abstract = {Within the Priority Programme Calm, Smooth and Smart, a new approach for deliberately introduced damping through variation of stiffness was presented. The proposed approach is a novel way of combining the concepts of damping and absorption inherently in a structure. By dynamically adapting the stiffness of a slender, beam-like structure through the use of shape adaption in the cross-section, energy is transferred from critical low-frequency modes into a specifically designed, higher frequency absorber mode, which can then be damped in an optimal way. Experimental studies were first conducted to examine the suitability of shape adaption for the proposed approach. Various investigations were carried out regarding application of the presented concept with different time laws for free and forced oscillations. In addition, thorough analytical and numerical studies were conducted to understand the internal energy transfers and provide the basis for decoupling of active and semi-active effects related to the reduction of vibrations. Another focus was on the synthesis of a structural layout that enables a defined stiffness change to be induced and an absorber mode (defined in shape and eigenfrequency) to be integrated into the structure.},
author = {Nowak, Alexander and Willner, Kai and Hasse, Alexander},
doi = {10.1007/978-3-031-36143-2{\_}14},
faupublication = {yes},
note = {CRIS-Team Scopus Importer:2023-10-06},
pages = {265-284},
peerreviewed = {unknown},
publisher = {Springer Science and Business Media Deutschland GmbH},
series = {Lecture Notes in Applied and Computational Mechanics},
title = {{Vibration} {Reduction} by {Energy} {Transfer} {Using} {Shape} {Adaption}},
volume = {102},
year = {2024}
}
@inproceedings{faucris.117944244,
address = {Weinheim},
author = {Willner, Kai and Strzyzakowski, Z.},
booktitle = {Zeitschrift für angewandte Mathematik und Mechanik},
doi = {10.1002/zamm.19920720404},
faupublication = {no},
note = {UnivIS-Import:2015-04-16:Pub.1992.tech.FT.FT-TM.vibrat},
pages = {T132-134},
peerreviewed = {Yes},
publisher = {WILEY-VCH Verlag},
title = {{Vibrations} in the {High} {Frequency} {Range}},
volume = {72},
year = {1992}
}
@incollection{faucris.118648244,
abstract = {In diesem Artikel wird ein Simulationsbenchmark vorgestellt, der einen repräsentativen Prozess der Blechmassivumformung beschreibt und sich eignet, Phänomene der Materialmodellierung, der Formoptimierung, der Modelladaptivität und des Einflusses von Reibmodellen aufzuzeigen. Als Demonstrator-Prozess dient die Herstellung eines Mitnehmerrings. Hierzu werden in eine Ronde acht Stempel eingedrückt. Für die Simulation eines solchen Umformprozesses ist es hinsichtlich der Materialmodellierung von Bedeutung, dass anisotrope Materialeigenschaften berücksichtigt werden. Auch der Einfluss des Reibmodells ist entscheidend. Die stark variierenden auftretenden Spannungen während des Umformprozesses führen dazu, dass die Reibschubspannungen in einigen Kontaktbereichen durch herkömmliche Modelle, wie Reibzahl- oder Reibfaktormodell, nicht korrekt wiedergegeben werden. Daher wird ein komplexeres konstitutives Reibgesetz vorgeschlagen, welches die Defizite des Reibzahl- und des Reibfaktormodells kompensiert. Die modelladaptive Rechnung zeigt, dass bei adaptiver Verwendung der verschiedenen Reibmodelle es nicht unbedingt erforderlich ist, auf das konstitutive Reibgesetz zurückzugreifen. Bereits das weniger komplexe Reibfaktormodell reicht aus, um ein bestimmtes Fehlermaß zu erreichen. Dadurch kann hinsichtlich des numerischen Aufwands in den Algorithmen Rechenzeit eingespart werden. Ferner ist es mittels der Formoptimierung möglich, eine undeformierte Rondengeometrie so zu berechnen, dass durch den nachfolgenden Referenz-Umformprozess eine gewünschte deformierte Bauteilform entsteht.},
address = {Bamberg},
author = {Schmaltz, Stefan and Landkammer, Philipp and Beyer, Florian and Kumor, Dustin and Rademacher, Andreas and Blum, Heribert and Steinmann, Paul and Willner, Kai},
booktitle = {Tagungsband zum 2. Erlanger Workshop Blechmassivumformung 2013},
editor = {Merklein, M., Behrens, B.-A., Tekkaya, A. E.},
faupublication = {yes},
isbn = {978-3-87525-353-5},
keywords = {Blechmassivumformung, Materialmodellierung, Reibeinfluss, Formoptimierung, Modelladaptivität},
note = {UnivIS-Import:2015-04-16:Pub.2013.tech.FT.FT-TM.vorste},
pages = {53-68},
peerreviewed = {unknown},
publisher = {Meisenbach},
title = {{Vorstellung} eines {Simulationsbenchmarks} für die {Blechmassivumformung}},
year = {2013}
}