@inproceedings{BauerGwiazdaMuelleretal., author = {Bauer, Monika and Gwiazda, Maciej and M{\"u}ller, Ralf and Decker, Daniel}, title = {RTM-Materials Based on Silazane-Resin-Systems}, series = {Proceedings, 7th International Conference on High Temperature Ceramic Matrix Composites (HT-CMC 7), September 20 - 22, 2010 in Bayreuth}, booktitle = {Proceedings, 7th International Conference on High Temperature Ceramic Matrix Composites (HT-CMC 7), September 20 - 22, 2010 in Bayreuth}, publisher = {AVISO Verl.-Ges.}, address = {Berlin}, language = {en} } @misc{StohwasserGiesebrechtKraftetal., author = {Stohwasser, Ralf and Giesebrecht, Jan and Kraft, Regine and M{\"u}ller, Eva-Christiane and H{\"a}usler, Karl Georg and Kettenmann, Helmut and Hanisch, Uwe-Karsten and Kloetzel, Peter-Michael}, title = {Biochemical analysis of proteasomes from mouse microglia: induction of immunoproteasomes by interferon-gamma and lipopolysaccaride}, series = {Glia}, volume = {29}, journal = {Glia}, number = {4}, issn = {1098-1136}, doi = {10.1002/(SICI)1098-1136(20000215)29:4<355::AID-GLIA6>3.0.CO;2-4}, pages = {355 -- 365}, language = {en} } @misc{HeubergerGrillSaglametal., author = {Heuberger, Maria and Grill, Eva and Saglam, Murat and Ramaioli, Cecilia and M{\"u}ller, Martin and Strobl, Ralf and Holle, Rolf and Peters, Annette and Schneider, Erich and Lehnen, Nadine}, title = {Usability of the Video Head Impulse Test: Lessons from the Population-Based Prospective KORA Study}, series = {Frontiers in Neurology}, volume = {9}, journal = {Frontiers in Neurology}, issn = {1664-2295}, doi = {10.3389/fneur.2018.00659}, pages = {7}, language = {en} } @misc{SchmidtDornischMueller, author = {Schmidt, Simon and Dornisch, Wolfgang and M{\"u}ller, Ralf}, title = {A phase field model for martensitic transformation coupled with the heat equation}, series = {GAMM-Mitteilungen}, volume = {40}, journal = {GAMM-Mitteilungen}, number = {2}, issn = {1522-2608}, doi = {10.1002/gamm.201720005}, pages = {138 -- 153}, abstract = {In order to consider temperature dependency in a phase field model for martensitic transformations a temperature dependent phase separation potential is introduced. The kinematics and the energetic setup underlying the phase transformation are briefly explained. Parameters are identified using molecular dynamics (MD) simulations. The kinetics of the phase field model are in good agreement with those of the MD simulations. Further, the effect of temperature on the microstructure evolution is studied for varying initial austenite contents.}, language = {en} } @misc{DornischSchradeXuetal., author = {Dornisch, Wolfgang and Schrade, David and Xu, Bai-Xiang and Keip, Marc-Andr{\´e} and M{\"u}ller, Ralf}, title = {Coupled phase field simulations of ferroelectric and ferromagnetic layers in multiferroic heterostructures}, series = {Archive of Applied Mechanics}, volume = {89}, journal = {Archive of Applied Mechanics}, number = {6}, issn = {0939-1533}, doi = {10.1007/s00419-018-1480-9}, pages = {1031 -- 1056}, abstract = {The combination of materials with either pronounced ferroelectric or ferromagnetic effect characterizes multiferroic heterostructures, whereby the different materials can be arranged in layers, columns or inclusions. The magnetization can be controlled by the application of electrical fields through a purely mechanical coupling at the interfaces between the different materials. Thus, a magneto-electric coupling effect is obtained. Within a continuum mechanics formulation, a phase field is used to describe the polarization and the magnetization in the ferroelectric and ferromagnetic layers, respectively. The coupling between polarization/magnetization and strains within the layers, in combination with the mechanical coupling at the sharp layer interfaces, yields the magneto-electric coupling within the heterostructure. The continuum formulations for both layers are discretized in order to make the differential equations amenable to a numerical solution with the finite element method. A state-of-the-art approach is used for the ferroelectric layer. The material behavior of the ferromagnetic layer is described by a continuum formulation from the literature, which is discretized using a newly proposed approach for the consistent interpolation of the magnetization vector. Four numerical examples are presented which show the applicability of the newly proposed approach for the ferromagnetic layer as well as the possibility to simulate magneto-electric coupling in multiferroic heterostructures.}, language = {en} } @misc{NadgirDornischMuelleretal., author = {Nadgir, Omkar and Dornisch, Wolfgang and M{\"u}ller, Ralf and Keip, Marc-Andr{\´e}}, title = {A phase-field model for transversely isotropic ferroelectrics}, series = {Archive of Applied Mechanics}, volume = {89}, journal = {Archive of Applied Mechanics}, number = {6}, issn = {0939-1533}, doi = {10.1007/s00419-019-01543-y}, pages = {1057 -- 1068}, abstract = {We propose an electro-mechanically coupled phase-field model for ferroelectric materials that show cubic-tetragonal phase transition. The cubic phase is idealized by an isotropic formulation, and the tetragonal phase is idealized by a transversely isotropic formulation. We consider a classical phase-field model with Ginzburg-Landau-type evolution of the order parameter. The order parameter drives the transition of all involved moduli tensors such as elastic, dielectric and piezoelectric moduli, which in turn maintain their typical features and stability as a result of a selected phase-transition function. The model is described in coordinate-invariant form and implemented into a finite element framework with implicit time integration of the evolution equation. Representative numerical examples in two and three dimensions demonstrate the main features of the constitutive model and the numerical stability of the formulation.}, language = {en} } @misc{DornischStoecklerMueller, author = {Dornisch, Wolfgang and St{\"o}ckler, Joachim and M{\"u}ller, Ralf}, title = {Dual and approximate dual basis functions for B-splines and NURBS - Comparison and application for an efficient coupling of patches with the isogeometric mortar method}, series = {Computer Methods in Applied Mechanics and Engineering}, volume = {316}, journal = {Computer Methods in Applied Mechanics and Engineering}, issn = {0045-7825}, doi = {10.1016/j.cma.2016.07.038}, pages = {449 -- 496}, abstract = {This contribution defines and compares different methods for the computation of dual basis functions for B-splines and Non-Uniform Rational B-splines (NURBS). They are intended to be used as test functions for the isogeometric mortar method, but other fields of application are possible, too. Three different concepts are presented and compared. The first concept is the explicit formula for the computation of dual basis functions for NURBS proposed in the work of Carl de Boor. These dual basis functions entail minimal support, i.e., the support of the dual basis functions is equal to the support of the corresponding B-spline basis functions. In the second concept dual basis functions are derived from the inversion of the Gram matrix. These dual basis functions have global support along the interface. The third concept is the use of approximate dual basis functions, which were initially proposed for the use in harmonic analysis. The support of these functions is local but larger than the support of the associated B-spline basis functions. We propose an extension of the approximate dual basis functions for NURBS basis functions. After providing the general formulas, we elaborate explicit expressions for several degrees of spline basis functions. All three approaches are applied in the frame of the mortar method for the coupling of non-conforming NURBS patches. A method which allows complex discretizations with multiple intersecting interfaces is presented. Numerical examples show that the explicitly defined dual basis functions with minimal support severely deteriorate the global stress convergence behavior of the mechanical analysis. This fact is in accordance with mathematical findings in literature, which state that the optimal reproduction degree of arbitrary functions is not possible without extending the support of the dual basis functions. The dual basis functions computed from the inverse of the Gram matrix yield accurate numerical results but the global support yields significantly higher computational costs in comparison to computations of conforming meshes. Only the approximate dual basis functions yield accurate and efficient computations, where neither accuracy nor efficiency is significantly deteriorated in comparison to computations of conforming meshes. All basic cases of T-intersections and star-intersections are studied. Furthermore, an example which combines all basic cases in a complex discretization is given. The applicability of the presented method for the nonlinear case and for shell formulations is shown with the help of one numerical example.}, language = {en} } @misc{SobotaDornischMuelleretal., author = {Sobota, Paul M. and Dornisch, Wolfgang and M{\"u}ller, Ralf and Klinkel, Sven}, title = {Implicit dynamic analysis using an iso- geometric Reissner-Mindlin shell formulation}, series = {International Journal for Numerical Methods in Engineering}, volume = {110}, journal = {International Journal for Numerical Methods in Engineering}, number = {9}, issn = {1097-0207}, doi = {10.1002/nme.5429}, pages = {803 -- 825}, abstract = {In isogeometric analysis, identical basis functions are used for geometrical representation and analysis. In this work, non-uniform rational basis splines basis functions are applied in an isoparametric approach. An isogeometric Reissner-Mindlin shell formulation for implicit dynamic calculations using the Galerkin method is presented. A consistent as well as a lumped matrix formulation is implemented. The suitability of the developed shell formulation for natural frequency analysis is demonstrated by a numerical example. In a second set of examples, transient problems of plane and curved geometries undergoing large deformations in combination with nonlinear material behavior are investigated. Via a zero-thickness stress algorithm for arbitrary material models, a J2-plasticity constitutive law is implemented. In the numerical examples, the effectiveness, robustness, and superior accuracy of a continuous interpolation method of the shell director vector is compared with experimental results and alternative numerical approaches.}, language = {en} } @misc{DornischMuellerKlinkel, author = {Dornisch, Wolfgang and M{\"u}ller, Ralf and Klinkel, Sven}, title = {An efficient and robust rotational formulation for isogeometric Reissner-Mindlin shell elements}, series = {Computer Methods in Applied Mechanics and Engineering}, volume = {303}, journal = {Computer Methods in Applied Mechanics and Engineering}, issn = {0045-7825}, doi = {10.1016/j.cma.2016.01.018}, pages = {1 -- 34}, abstract = {This work is concerned with the development of an efficient and robust isogeometric Reissner-Mindlin shell formulation for the mechanical simulation of thin-walled structures. Such structures are usually defined by non-uniform rational B-splines (NURBS) surfaces in industrial design software. The usage of isogeometric shell elements can avoid costly conversions from NURBS surfaces to other surface or volume geometry descriptions. The shell formulation presented in this contribution uses a continuous orthogonal rotation described by Rodrigues' tensor in every integration point to compute the current director vector. The rotational state is updated in a multiplicative manner. Large deformations and finite rotations can be described accurately. The proposed formulation is robust in terms of stable convergence behavior in the nonlinear equilibrium iteration for large load steps and geometries with large and arbitrary curvature, and in terms of insensitivity to shell intersections with kinks under small angles. Three different integration schemes and their influence on accuracy and computational costs are assessed. The efficiency and robustness of the proposed isogeometric shell formulation is shown with the help of several examples. Accuracy and efficiency is compared to an isogeometric shell formulation with the more common discrete rotational concept and to Lagrange-based finite element shell formulations. The competitiveness of the proposed isogeometric shell formulation in terms of computational costs to attain a pre-defined error level is shown.}, language = {en} } @misc{DornischMueller, author = {Dornisch, Wolfgang and M{\"u}ller, Ralf}, title = {Modeling of electric field-induced magnetization switching in multi- ferroic heterostructures}, series = {Proceedings in Applied Mathematics and Mechanics}, volume = {19}, journal = {Proceedings in Applied Mathematics and Mechanics}, number = {1}, issn = {1617-7061}, doi = {10.1002/pamm.201900103}, pages = {2}, abstract = {Multiferroic heterostructures consist of materials with either pronounced ferroelectric or ferromagnetic effect. The combination of both types of material, be it in layers, columns or inclusions, potentially yields a significant magneto-electric coupling effect even at room temperature. The magnetization in the ferromagnetic material can be controlled by the application of electric fields to the ferroelectric material. In this contribution a linear elastic continuum formulation is coupled with a phase field formulation for the polarization and magnetization in the ferroelectric and the ferromagnetic layer, respectively. The strain transfer at the interface of the layers yields a magneto-electric coupling effect within the heterostructures. The finite element method is used to discretize the arising differential equations. A numerical example provides a proof of concept for the simulation of the magneto-electric coupling effect in multiferroic heterostructures.}, language = {en} }