bluuebunny/crossref_metadata_2025_split huggingface dataset:
A first order homogenization approach for structural elements: Beam kinematics
Authors: Klarmann Simon , Gruttmann Friedrich , Klinkel Sven 
Published: November 2019

AbstractThis contribution deals with a first order homogenization approach for structural elements with the focus on shear deformable beam elements. The homogenization theory itself is based on the well‐known Hill‐Mandel condition. Therefore, the numerical treatment leads to a coupled multiscale approach whose calculation can be performed with the so‐called FE2 scheme. As a result, not only cross‐sectional properties in the linear elastic case can be evaluated but also geometrical and physical nonlinearities can be considered. Since the mesoscale, which will be homogenized, is modelled by 3D brick elements, the considered global structure only needs to be periodic to allow a definition of a representative volume element (RVE). Thus, the procedure is not limited to pure cross‐sectional modelling, but is also able to consider inhomogeneities in the longitudinal direction of the system.As the beam kinematics do not describe the complete deformation gradient or strain tensor, the equilibrium condition introduces a length dependency of the homogenized shear stiffnesses and the stiffnesses which depend on them due to eccentricities. This is due to the fact that the averaged shear deformation of the RVE does not linearly depend on its length multiplied by the beam shear deformation. To overcome this problem, additional constraints are introduced which ensure this linear connection. They are chosen in a way that they do not contribute to the virtual internal work. Therefore, the Hill‐Mandel condition is not affected by them. With these assumptions, the length dependency is eliminated and the averaged shear deformation of the RVE equals the shear deformation of the beam kinematics. As a result, the method is able to reproduce well‐known cross‐sectional values known from the literature and is also capable to evaluate complex nonlinear systems. For the latter, the agreement of the results with those of continuum models is very satisfying.
An optimal design of an elastic plate in a dynamic contact with a rigid obstacle
Authors: Bock Igor , Kečkemétyová Mária 
Published: November 2019

AbstractWe deal with an optimal design problem governed by an initial‐boundary value problem for a hyperbolic variational inequality describing the perpendicular vibrations of a simply supported anisotropic elastic plate against a rigid obstacle. A variable thickness of a plate plays the role of a control variable. The set of admissible thicknesses for the design problem consists of solutions of a state problem gained as limits of the sequences of functions solving penalized problems.
Geometry Processing Problems Using the Total Variation of the Normal Vector Field
Authors: Bergmann Ronny , Herrmann Marc , Herzog Roland , Schmidt Stephan , Vidal-Núñez José 
Published: November 2019

AbstractThis paper presents a novel approach to the formulation and solution of discrete geometry processing problems including mesh denoising. The main quantity of interest is the piecewise constant unit normal vector field, which we consider on piecewise flat, triangulated surfaces. In a similar fashion as one does for images defined on ‘flat’ domains, our goal is to remove noise while preserving shape features such as sharp edges. To this end, we model a denoising problem via a quadratic vertex tracking term and a regularizer based on the total variation of the normal vector field. Since the latter has values on the unit sphere, its total variation reduces to a finite sum of the geodesic distances of neighboring normals. We solve the model numerically by applying split‐Bregmann iterations and provide results for the ‘fandisk’ benchmark.
Characterization of fiber matrix interface of continuous‐discontinuous fiber reinforced polymers on the microscale
Authors: Rohrmüller Benedikt , Schober Michael , Dittmann Kerstin , Gumbsch Peter , Hohe Jörg 
Published: November 2019

AbstractIn lightweight constructions fiber reinforced polymers are an important material group. They combine low density with high strength and stiffness. The characterization of fiber reinforced polymers includes the characterization of the fibers, the matrix and the intermediate interface. The fibers and the matrix can be characterized on the neat materials. Single fiber tests are typically used to characterize the interface. However, the interaction between different fibers inside a composite is not taken into account in a single fiber test. The investigated sheet molding compound (SMC) has a bundle arrangement of the fibers, where the contact of different fibers is very close and therefore also the fiber‐fiber interaction has a high influence. Here we investigate the micromechanical behavior of hourglass shaped micro specimens with several hundreds of fibers with quasi‐static tensile tests. For the interface characterization the microstructure of the specimens is rebuilt in a simulation. The glass fibers are modeled as linear elastic, the matrix as hyperelastic and the interface by means of a cohesive zone model.
Two novel Kirchhoff plate finite elements for the modified strain gradient theory
Authors: Kandaz Murat , Dal Hüsnü 
Published: November 2019

AbstractMicroplates are vastly used in MEMS and NEMS devices. Due to size effect, classical theories of continuum mechanics can not be used to model mechanical behaviour of them. Instead, higher order continuum theories should be implemented. Modified Strain Gradient Theory (MSGT) is considered to be one of the most accurate methods for this, considering both theoretical compatibility and numerical accuracy. In this study, two sets of Kirchhoff and twist‐Kirchhoff bending rectangular plate finite elements for MSGT are developed as novel aspects. This is done by first obtaining the weak forms by using variational methods and then deriving the set of algebraic equations for the finite element formulation starting with shape functions. Although non‐conforming, the finite elements are in alignment with the existing models with the given length scale parameters. The plate finite elements are then implemented to existing models. The length scale parameters for MSGT are also identified for gold using the existing experimental results in literature. This study proposes the use of higher order theories for gold microplates for thicknesses less than 40 µm.
A comparison of numerical methods for conservative and positive advection‐diffusion‐production‐destruction systems
Authors: Kopecz Stefan , Meister Andreas 
Published: November 2019

AbstractIn many simulations it is important to guarantee positivity of the numerical approximations. For standard ODE solvers positivity is usually achieved by restrictions of the time step size, in contrast, MPRK schemes are unconditionally positive, which allows for much faster computations. We compare MPRK schemes and standard ODE solvers applied to an advection‐diffusion‐produ system for which it is essential to avoid negative approximations .
A numerical approach for dynamic analysis of solids in boundary representation
Authors: Méndez Salas Arturo , Chasapi Margarita , Klinkel Sven 
Published: November 2019

AbstractThis contribution is concerned with a numerical approach for dynamic analysis of solids in boundary representation. The aim of this investigation is to provide accurate results for the dynamic analysis in cases where only the boundary of a solid is available, whether this is defined for an open or closed domain. In CAD solids are defined through their bounded surfaces. Hence, the present method is perfectly suited to analyse such kind of geometries. The proposed approach is, therefore, based on the principle to represent a computational domain by scaling its boundary with respect to a scaling center. NURBS basis functions are used to depict the geometry of a domain and to approximate the unknowns of the problem. The core of this study is formally supported, firstly by high continuity generated by the selected interpolation functions, that provide a superior approximation for the dynamic properties of a domain, and secondly, by the adopted parametrization in boundary representation. In the entire domain, which is an elastic, homogeneous and isotropic medium under plain‐strain motion, the weak form is enforced to solve the equation of motion of the problem. An implicit method is employed for time integration. The robustness and stability of this approach are studied considering higher order NURBS basis functions to calculate superior eigenvalues of an open domain. The proposed approach is compared with the standard isogeometric analysis, which differs from the parametrization in this study, in order to show the performance of this formulation.
An interface model to account for damage and plasticity at grain boundaries
Authors: Rezaei Shahed , Rezaei Mianroodi Jaber , Brepols Tim , Wulfinghoff Stephan , Reese Stefanie 
Published: November 2019

AbstractGrain boundary (GB) characteristics play a major role in the understanding and prediction of polycrystalline behavior [1]. GB roles become more important when it comes to nanocrystalline metals and ceramics. To gain a deeper insight into the behavior of the grain boundary, molecular dynamics (MD) simulations are utilized. The Mode I, mode II and mixed mode loading behavior is investigated using different MD simulations. By adding the unloading path to the MD simulations it was possible to differentiate between different active mechanisms at the GB. An interface model is introduced based on our understanding from the atomistic simulation of the grain boundaries. When it comes to the grain boundary (GB) behavior, the current model is able to capture the competition between the intergranular fracture and the grain boundary sliding. The interface model is thermodynamically consistent and is able to capture the complex behavior of the GB under different loading conditions.
Optimal Bounds for the Probability of Failure of Sheet Metal Forming Processes of DP Steel
Authors: Miska Niklas , Balzani Daniel 
Published: November 2019

AbstractIn this contribution, the Optimal Uncertainty Quantification framework is extended to account for aleatory uncertainties, such that both epistemic and aleatory uncertainties can be quantified. The extended framework is demonstrated for an example of a forming process of a Dual‐Phase steel sheet, for which optimal bounds on the probability of failure are computed under polymorphic uncertainties.
Controlling Sliding Droplets with Optimal Contact Angle Distributions and a Phase Field Model
Authors: Bonart Henning , Kahle Christian , Repke Jens-Uwe 
Published: November 2019

AbstractWe consider the optimal control of a droplet on a solid by means of the static contact angle between the contact line and the solid. The droplet is described by a thermodynamically consistent phase field model from [Abels et al., Math. Mod. Meth. Appl. Sc., 22(3), 2012] together with boundary data for the moving contact line from [Qian et al., J. Fluid Mech., 564, 2006]. We state an energy stable time discrete scheme for the forward problem based on known results, and pose an optimal control problem with tracking type objective.
Solid‐fluid coupling in a fully Lagrangian framework
Authors: Bender Jens , Kuhnert Jörg 
Published: November 2019

AbstractThe simulation of multiphase flows consisting of granular and fluid phases is of great interest in a wide variety of industrial applications, such as chemical process engineering, design of conveyor systems and abrasion modeling. In this context, the granular phase is often described by the discrete element method, which calculates the trajectory of each individual solid particle in a Lagrangian manner while resolving inter‐particle and geometry collisions. While the models behind individual interactions are generally not very complex, the necessary data structures and neighbor search algorithms often have a major impact on performance. Here, we present the coupling of this approach to a Lagrangian generalized finite difference method for the fluid phase which has been successfully used in a wide variety of practical applications. Coupling these two approaches enables us to treat all phases in a common framework and to use efficient and scalable data structures and algorithms. At the same time we retain the advantages of meshfree fluid solvers in free surface problems or rapidly changing flow geometries.
Optimal inflow control in transport systems with uncertain demands ‐ A comparison of undersupply penalties
Authors: Lux Kerstin , Göttlich Simone 
Published: November 2019

AbstractWe address the challenging task of setting up an optimal production plan taking into account uncertain demand. The transport process is represented by the linear advection equation and the uncertain demand stream is captured by an Ornstein‐Uhlenbeck process (OUP). With a model predictive control approach, we determine the optimal inflow. We use two types of undersupply penalties and compare the average undersupply as well as the number of undersupply cases in a numerical simulation.
Elasto‐plastic phase‐field model for pullout tests of steel fiber embedded in high‐performance concrete: numerical calibration and experimental validation
Authors: Pise Mangesh , Brands Dominik , Gebuhr Gregor , Sarhil Mohammad , Schröder Jörg , Anders Steffen 
Published: November 2019

AbstractIn this paper, the pullout behavior of steel fiber embedded in high‐performance concrete (HPC) is investigated. First, a constitutive framework of elasto‐plastic phase‐field model of fracture is constructed and applied to simulation of pullout tests for different embedded lengths of steel fibers. Thereby, the description of the mechanical behavior the Drucker‐Prager plasticity model is used. The numerical calibration of the above mentioned model is performed by simulating pullout tests and validated by data obtained from experiments. Therefore, the mechanical behavior of high‐performance concrete is studied in experiments.
Orthotropic Hyperelastic Energy Functions for the Geometrically Nonlinear Simulation of Textile Membrane Structures
Authors: Motevalli Mehran , Balzani Daniel , Uhlemann Jörg , Stranghöner Natalie 
Published: November 2019

AbstractIn this contribution new orthotropic hyperelastic energy functions are proposed for the geometrically nonlinear simulation of woven textile membranes. The new models are investigated and compared with a competitive formulation with respect to mathematical characteristics, accuracy in representation of experimental data and their robustness in numerical simulations. Part of the models is polyconvex and thus, a physically meaningful and mathematically sound formulation is obtained. The models are adjusted to stress‐strain paths of a glass‐PTFE fabric under cyclic uniaxial and biaxial tension tests. Moreover, a new large scale experimental setup is presented which enables the study of the material behavior in real structural problems.
Free Material Optimization of Multilayer Composite Materials
Authors: Loske Simon , Barthold Franz-Joseph 
Published: November 2019

AbstractThe use of composite materials in various types of devices has increased steadily in the past decades. Hence, it is worth investigating into the structural behaviour of these materials. The optimization of stacking sequences in multilayer composite materials opens a large field of improvements in industrial applications of composite materials. The center of investigation is set on fiber reinforced laminate plies, which are examined in the case of linear anisotropic theory of elasticity. One very auspicious way for optimization of these laminates is the implementation of Free Material Optimization (FMO). In these optimization procedures arbitrary values of parameters of the elasticity matrix are obtained under constraints which only claim the elasticity matrix to be symmetric and positive semidefinite. Also the trace of the elasticity matrix is restricted to avoid the total stiffness of the material to get unnaturally large. The sensitivity information are received by the variational approach for sensitivity analysis [1] which represents the most efficient known way of computing sensitivity information.
Application of higher‐order strain gradient theories in the phase‐field modelling of fracture mechanics
Authors: Juhre Daniel , Makvandi Resam 
Published: November 2019

AbstractThe simulation of crack propagation has always been a challenging task from a computational point of view. In the past, many mathematical and mechanical assumptions had to be taken into account to successfully simulate this process. The problem of tracking the sharp crack surface was among the first issues which was alleviated by the introduction of phase‐field models. The appearance of stress singularities near the crack tip in the classical continuum mechanics theory is considered to be another source of problem which makes the selection of proper mesh sizes for numerical models very cumbersome, and leads to unphysical results. In the presence of a singularity, the crack propagation starts earlier in problems with a finer discretization which is only natural considering that the strain energy density is higher and increases faster for smaller mesh sizes. Likewise, a loading which normally could not cause a crack to nucleate or propagate inside a structure, will do so in the numerical simulation due to over‐estimated stresses. Therefore, it stands to reason that removing this singular field from the results is a very crucial step in achieving physically meaningful results. The goal of the current contribution is twofold: first, existing models are shown to exhibit a singular stress behavior, and second, a possible remedy is proposed based on the application of higher‐order strain gradients.
Nonlinear bilateral caloric–electromechanical couplings in polycrystalline ferroelectrics
Authors: Warkentin Andreas , Lange Stephan , Wingen Marius , Ricoeur Andreas 
Published: November 2019

AbstractThis research is about irreversible domain wall motion leading to a temperature change of the material. The materials are mostly subjected to high frequencies and large electrical loads, which is why insufficient heat dissipation can lead to undesirable temperature developments, so–called self heating. Predictions concerning polycrystalline material behavior are made by the condensed method.
Development of a Macro‐Model for Magnetorheological Elastomers based on Microscopic Simulations
Authors: Kalina Karl A. , Metsch Philipp , Brummund Jörg , Kästner Markus 
Published: November 2019

AbstractHerein, the parametrization of a macro‐model for magneto‐rheological elastomers based on microscopic simulations is presented. Within a computational homogenization, the effective response of the composite system is calculated and the data are used for parameter identification. The merit of this strategy is the adjustment of the model independent of any macroscopic sample geometry. With the developed model, the magnetostrictive behavior of a macroscopic sample is simulated.
Adaptive space‐time finite element solvers for parabolic initial‐boundary value problems with non‐smooth solutions
Authors: Langer Ulrich , Schafelner Andreas 
Published: November 2019

AbstractWe consider conforming finite element schemes on completely unstructured simplicial space‐time meshes for the numerical solution of non‐autonomous parabolic problems with coefficients that may discontinuously depend on the space and time variables. We present a priori estimates for low‐regularity solutions. We compare two adaptive procedures that are based on residual and functional a posteriori error indicators.
Parameter Identification of Brake Pad Shims for Complex Eigenvalue Analysis
Authors: Schmid Dominik , Sessner Vincent , Gräbner Nils , von Wagner Utz , Weidenmann Kay André 
Published: November 2019

AbstractComposite structures called shims are bonded to brake pad backplates to increase the damping in brake systems. The aim of this measure is to avoid squeal which is a high‐frequency audible brake vibration disturbing customers and the environment. This NVH problem originates from self‐excited vibrations resulting from the friction contact between pad and disk. Multi‐layer shim compounds consisting of steel and elastomer layers use the shear deformation of the viscoelastic core obtaining a high energy dissipation potential.In this contribution parameter identification for Finite Element brake simulations, so called complex eigenvalue analyses is focused. Therefore dynamic mechanical analyses on constrained layer damping structures are carried out receiving loss factors for a broad temperature and therefore frequency band. The results are compared with experimental modal analyses and possible differences between the two procedures are pointed out. The main goal is to identify input parameters for a subsequent implementation of damping characteristics for complex eigenvalue analysis.
Cycle‐based Adaption of a Model‐Predictive Control Strategy for Injection Molding Machines
Authors: Froehlich Christoph , Kemmetmüller Wolfgang , Kugi Andreas 
Published: November 2019

AbstractInjection molding is one of the most important manufacturing processes in the polymer industry. It is a cyclic process, where the phases of the process are repeated for each produced part. An accurate control of the process variables (e.g. the injection pressure and speed) to their desired values is essential to obtain a constant high product quality. In a recent publication [5], it was shown that the control accuracy can be significantly improved compared to the state of the art by means of a nonlinear model‐predictive control (MPC) strategy. Thereby, an essential point to achieve a high control accuracy is the estimation of the (bascially unknown) volume flow into the mold. In the present work, the benefits of utilizing the measurement information of the previous and the current cycles are examined. An estimator concept is presented which combines the advantages of the high accuracy of an offline estimation with the capability to account for variations of the injection process by an online estimation. The improved control accuracy of the proposed method is shown by simulation studies.
Identification of Radiation Damping Using a Coupled FE/BE Formulation and a Nonlinear Eigenvalue Solver
Authors: Baydoun Suhaib Koji , Marburg Steffen 
Published: November 2019

AbstractWhile acoustic radiation damping is a rather small and insignificant aspect of many engineering applications, it is the primary energy‐dissipating mechanism for lightweight structures with large radiating surfaces. Attempts to reduce the vibrational response of those lightweight structures by additional mechanical damping can only be successful if the extent of mechanical damping is comparable or larger than the extent of radiation damping. In this regard, engineers are in need of reliable and flexible methods for the quantification of radiation damping, as well as for the modeling of its effect in an early stage of the design process. In this paper, the modal radiation loss factors are obtained from an eigenvalue analysis of the coupled structural acoustic system. The equations of linear elasticity and acoustics are addressed by finite and boundary element methods respectively. The nonlinear eigenvalue problem is solved by contour integration. The thereby obtained modes represent the structural modes subject to acoustic loading. The modal radiation damping values can be obtained from the complex eigenvalues. The approach is verified based on the example of a honeycomb sandwich panel in air.