bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lattice Boltzmann method applied to antiplane shear loading of a stationary crack
Authors: Reinirkens Thomas , Müller Ralf , Kuhn Charlotte 
Published: December 2018

AbstractIn this work, the dynamic behavior of linear elastic solids under antiplane shear deformation is studied by the Lattice Boltzmann method (LBM). The governing set of partial differential equations reduces to a scalar wave equation for the out of plane displacement in a two dimensional domain. We use the approach developed by Guangwu as starting point to solve this problem numerically. The numerical performance of the lattice Boltzmann scheme is tested for a stationary crack which can be compared to an analytical solution. Furthermore the performance of the lattice Boltzmann simulations are compared to classical Finite Element Method (FEM) computations with regard to calculation time and accuracy. Finally the stability with respect to the relaxation parameter is studied.
Variational Homogenization for Phase‐Field Modeling of Micro‐Magneto‐Mechanics at Finite Deformations
Authors: Vallicotti Daniel , Sridhar Ashish , Keip Marc‐André 
Published: December 2018

AbstractComposite materials of soft polymers with embedded ferromagnetic particles, so‐called magnetorheological elastomers (MRE), are advantageous due to the possible large deformations under moderate applied magnetic fields. In order to understand the underlying physical phenomena a multiscale view on microscopic magnetic domain evolution and its effect on the overall macroscopic response is of utmost importance. We propose a multiscale variational framework for micro‐magneto‐mechanical response at large deformations embedded into a scale‐bridging scenario by using homogenization techniques in order to define the macroscopic overall response of MREs. Starting point is a rate‐type saddle‐point variational principle at microscale yielding the Euler‐Lagrange equations including the Landau‐Lifshitz equation for the magnetization [3]. Particular challenges lie in the algorithmic treatment of the related physical unity constraint of the magnetization director and in the link of the gradient‐type continuum description of the micro‐structure to a local magneto‐mechanical macro‐continuum. A staggered solution scheme on the microscale as proposed in [2] together with a macroscopic driving routine related to [1] offers the coupled two‐scale algorithmic solution. A numerical example demonstrates the capabilities of the framework and shows the effect of particle interactions based on evolving magnetic domains on the overall macroscopic response.
Constitutive modelling of hyperelastic rubber‐like materials accounting for damage
Authors: Toups Elisabeth , Reese Stefanie , Simon Jaan‐Willem 
Published: December 2018

AbstractAdhesives are used in numerous applications such as in the automotive industry, packaging industry, civil engineering, and many others. The use of multi‐side bonded joints becomes increasingly common in glass‐façade structures instead of bolted point fixings, inter alia, for aesthetic reasons. For the simulation of glass‐façade components, it is essential to investigate constitutive models which ensure a representation of rubber‐like material behaviour. Several hyperelastic material models are available in the literature, but most of them are not suitable to represent large deformations, damage (i.e. Mullins‐Effect), and multiaxial stress states all in one. Hence, the main goal of the present work is to develop a material model which exhibits the mentioned properties.
Simulation of residual stresses and their impact on geometrical accuracy in incremental sheet metal forming
Authors: Maqbool Fawad , Bambach Markus 
Published: December 2018

AbstractThe current study presents the influence of the process parameters on residual stresses and geometrical accuracy in single point incremental forming (SPIF). In SPIF, a sheet metal is formed by the continuous localized deformation of a hemispherical tool. In this regard, pyramidal parts from an aluminum alloy are incrementally formed by varying the process parameters. Small strips are cut from the side walls of these pyramids and the resulting curvature of the strips is measured and compared. The bore‐hole‐drilling method is used to measure the residual stress state. Further, two different numerical models employing isotropic and mixed hardening rules are calibrated based on the residual stresses. The model with mixed hardening predicts better results. This validated numerical model is used to simulate the geometric deviation upon trimming. The resulting curvature of the trimmed strips from the numerical simulations is compared to the curvature of the experimental strips. A good agreement is found. Hence, the developed model can be used to accurately simulate the residual stresses and in turn the trimmed geometry after SPIF.
An Anisotropic Damage‐Mode Based Constitutive Model for Fibre‐Reinforced Polymer Composites
Authors: Chatiri Madhukar , Matzenmiller Anton 
Published: December 2018

AbstractThis contribution presents a three dimensional constitutive model for anisotropic damage to describe the onset and propagation of ply failure mechanisms in unidirectional fiber reinforced laminated composites. The primary objective of the work focuses on the three dimensional relationship between damage of the material and the effective elastic properties for the purpose of stress analysis of composite structures. Damage initiation criteria are based on Puck failure criterion for first ply failure and progressive micro crack propagation is based on the idea of continuum damage evolution.
A micromechanical model of filled elastomers based on the directional hydrodynamic strain amplification factor
Authors: Darabi Ehsan , Itskov Mikhail , Klüppel Manfred 
Published: December 2018

AbstractA constitutive model for filled elastomers is proposed based on the combination of the continuum damage [1] and the dynamic flocculation [2] framework. Damage takes place in both the network rubbery matrix and inside the filler aggregates. Accordingly, the probability density functions of the number of segments and the filler size distribution in all spatial directions evolve with deformation, which causes stress softening, the Mullins effect and induced anisotropy. Multiple breakage and reaggregation of filler clusters with different sizes in various spatial directions are the main sources of the directional hydrodynamic strain amplification. The model includes a few number of physically motivated material constants characterizing the average filler cluster dimension, filler‐filler and filler‐matrix interaction properties.
Micromechanical Modeling of a Generator Stator Electrical Insulation System
Authors: Nguyen Thank Thank , Wulfinghoff Stephan , Reese Stefanie 
Published: December 2018

AbstractA gradient‐extended damage theory is shortly presented. The focus is on the internal thermodynamic forces and their extension to gradient‐extended models. This continuum mechanical framework is used for an application to an anisotropic damage model with a 2nd order damage tensor.
Combining Finite Elements and Random Fields to Quantify Uncertainty in a Multi‐phase Structural Analysis
Authors: Henning Carla , Herbrandt Swetlana , Ickstadt Katja , Ricken Tim 
Published: December 2018

AbstractFor a wide range of mechanical application fields, computational analyses are already indispensable due to their advanced impact on engineering developments. They provide a lot of information about the functioning and structural response of an arbitrary structure and the interaction with its surrounding. Nevertheless, despite preliminary investigations or the knowledge about manufacturing process of structures, assumptions of geometrical or material properties are often sources of uncertainties. These can be distinguished into aleatoric (e.g. natural scattering of properties) and epistemic (e.g. accuracy of the numerical approximation) uncertainties. Although measuring devices or process workflows are continuously improved, there always remains a residual risk. In order to provide and improve decision‐making tools for end users, the priority program SPP 1886 has been installed by the DFG with the focus on polymorphic uncertainty quantification. The present subproject, which is part of the SPP 1886 (sp12), is focused on fluid saturated soil and earth structures and their multiple uncertainty sources.The very complex micro‐structural consolidation mechanism of soil requires a suitable numerical description. For the strongly coupled fluid‐solid response behavior, the Theory of Porous Media (TPM) will be used, a macroscopic homogenization approach based on the mixture theory restricted by the concept of volume fraction. In the framework of the Finite Element Method (FEM), arbitrary Boundary Value Problems (BVP) can be investigated. Uncertainty modelling takes place on the stochastic level by introducing random fields with a defined correlation structure for the generation of model initial material parameters. By generating many random field realizations for a FEM material parameter, we receive various FEM outputs for selected scenarios of the stated BVP. These results can be used to identify typical output scenarios, which allows to identify critical material parameter combinations which may cause instabilities.
Localization studies for ground states of the Gross‐Pitaevskii equation
Authors: Altmann Robert , Peterseim Daniel , Varga Dora 
Published: December 2018

AbstractFor oscillatory high‐amplitude potentials it is known that the linear Schrödinger operator leads to exponentially localized ground states. This localization result can be quantified explicitly in terms of geometric parameters and the degree of disorder within the potential. In the present paper we study the influence of the amplitude and the importance of the periodicity in the nonlinear setting of the Gross‐Pitaevskii equation which models ultracold bosonic gases.
Global and goal‐oriented reanalysis in nonlinear structural mechanics
Authors: Materna Daniel 
Published: December 2018

AbstractReanalysis methods can be used in order to reduce the overall computational cost in numerical simulation. In this contribution an approach for global and goal‐oriented nonlinear reanalysis based on residual increment approximations (RIA) is presented. The method requires only the evaluation of residual vectors, which can be done very fast and efficient. Moreover, the results are improved by using a rational approximation method. The approach is general and can be applied to linear and nonlinear problems with different kind of design modifications. Furthermore, the proposed method is very efficient and easily to implement in existing finite element programs, because no derivatives with respect to the design variables are necessary.
Approximation of Hermitian Matrices by Positive Semidefinite Matrices using Modified Cholesky Decompositions
Authors: Reimer Joscha 
Published: December 2018

AbstractA new algorithm to approximate Hermitian matrices by positive semidefinite matrices based on modified Cholesky decompositions is presented. The approximation error and the condition number of the approximation can be controlled by parameters of the algorithm. The algorithm tries to minimize the approximation error in the Frobenius norm. It has no significant runtime and memory overhead compared to the computation of an unmodified Cholesky decomposition. Sparsity and positive diagonal entries can be preserved. A Cholesky decomposition of the approximation matrix is calculated as a byproduct.
Multi‐field formulation of large deformation ductile fracture
Authors: Dittmann Maik , Hesch Christian , Schulte Jonathan , Aldakheel Fadi 
Published: December 2018

AbstractIn the present contribution we focus on a novel computational framework for the simulation of ductile fracture in elastoplastic solids. In particular, a fully non‐linear formulation of gradient plasticity is applied together with a higher order phase‐field approach to fracture to account for large elastic and plastic deformations along with three dimensional crack propagation. The proposed formulation is based on a multiplicative decomposition of the deformation gradient into elastic and plastic contributions and a subsequent multiplicative decomposition of the elastic part into a fracture sensitive and a fracture insensitive contribution, see [1]. Postulating that fracture requires a local state of tensile/shear deformation, the latter decomposition is used to formulate the isochoric and tensile contributions to the elastic strain energy, whereas the compressive contribution remains unaffected by the crack phase‐field and vice versa. The modification of the Griffith brittle fracture theory to ductile fracture is most crucial and has to be adjusted carefully. Within our framework, this adaptation is considered as dependency of the critical fracture energy density by the equivalent plastic strain. Concerning the elastic/plastic decomposition, we assume an isochoric plastic flow which requires special attention for the update procedure of the plastic deformation. To be specific, we apply an exponential time integration scheme such that we preserve the deviatoric state of the plastic deformation and obtain a correct evaluation of the phase‐field driving force. Eventually, a number of numerical examples will demonstrate the accuracy and capability of the proposed multi‐field approach to ductile fracture.
Active control of foams by physically based destruction mechanisms
Authors: McHardy Christopher , Thünnesen Julian , Horneber Tobias , Kostova Jordanka , Hussein Mohamed A. , Delgado Antonio , Rauh Cornelia 
Published: December 2018

AbstractFoams may be undesired in technical processes and need, thus, to be actively controlled. In food science engineering it is often not possible to apply chemical measures due to the required purity of the processed products. To overcome this challenge it is necessary to apply physically based foam destruction mechanisms. The present contribution deals with the prediction of foamability and the application of acoustical foam destruction from an experimental point of view. The results show that it is possible to classify the foamability of different fluids by a correlation of dimensionless numbers containing purely physico‐chemical properties (i.e. density, surface tension, viscosity). The foam stability is a consequence of the net balance of the foam generation and the foam decay. The respective time scales may be influenced by the process conditions, the fluid properties, and the selected physically based destruction mechanism. In the case of resonance excitation of foam bubbles by acoustic waves of defined frequencies selective foam destruction can be achieved. The bubbles in the foam start to oscillate and absorb energy depending on the bubble size, fluid properties, and ultrasound frequency. The resulting bubble breakdown leads to a shortening of the time scales of the foam decay.
Parallel solution, adaptivity, computational convergence, and open‐source code of 2d and 3d pressurized phase‐field fracture problems
Authors: Heister Timo , Wick Thomas 
Published: December 2018

AbstractWe present a scalable, parallel implementation of a solver for the solution of a phase‐field model for quasi‐static brittle fracture. The code is available as open source. Numerical solutions in 2d and 3d with adaptive mesh refinement show optimal scaling of the linear solver based on algebraic multigrid, and convergence of the phase‐field model towards exact values of functionals of interests such as the crack opening displacement or the total crack volume. In contrast to uniform refinement, adaptive mesh refinement allows us to recover optimal convergence rates for the non‐smooth solutions encountered in typical test problems. We also present numerical studies of the influence of the finite domain size on functional evaluations used to approximate the infinite domain.
A discrete, two‐dimensional frictional contact model for dynamic contact between viscoelastic materials and rough counterparts
Authors: Schulte Frank , Sextro Walter 
Published: December 2018

AbstractFriction between a viscoelastic material and a rough surface occurs in many technical applications, e. g. windshield wiper, rubber gaskets or the tire‐road contact. For the investigation of friction phenomena a detailed frictional contact model is necessary. The friction of viscoelastic materials is divided into the two main effects hysteresis friction and adhesion friction. Multiple influence factors on the friction behaviour are known, e. g. material properties of the contact partners, normal force, excitation frequency through the counterpart, as well as temperature. Due to the frictional forces a system is significantly influenced in its vibrational properties. For the simulation of the complex friction processes with viscoelastic materials, a two‐dimensional friction contact model with the assumption of an isotropic roughness has been developed. The model consists of a rough rigid and a rough viscoelastic layer. The rough rigid layer represents a measured roughness profile. Due to the low stiffness of the viscoelastic material, the counter body can be assumed to be rigid. The viscoelastic layer consists of a number of point‐masses with generalised Maxwell‐models and represents the viscoelastic material. By this model the normal and tangential contact can be simulated dynamically. Effects such as changing the contact status during the friction process are taken into account. A stiffening of the viscoelastic material and thus a lower real contact surface at higher excitation frequencies or low temperatures can be shown with the model. This is especially important for the calculation of adhesion friction, as it depends directly on the actual contact area.
Stability Issues in Hardware‐in‐the‐Loop Tests of Flexible Components
Authors: Bartl Andreas , Insam Christina , Rixen Daniel J. 
Published: December 2018

AbstractThe well‐known Hardware‐in‐the‐Loop (HiL) paradigm can be applied to numerous engineering problems to test components of complex systems and their dynamical effects under realistic boundary conditions. The system is split into a virtual component and a physical testbed. Coupling both with a control system makes it possible to replicate the full system's dynamics. However, the system may exhibit stability problems, depending on dead times, actuator dynamics and dynamical properties of the test specimen. In this contribution, the properties of a simple lumped mass system and their effects on stabilty and accuracy are investigated.
Data‐driven approximation methods applied to non‐rational functions
Authors: Karachalios Dimitrios S. , Gosea Ion Victor , Antoulas Athanasios C. 
Published: December 2018

AbstractIn this study, four data‐driven interpolation‐based methods are compared. The aim is to construct reduced‐order models for which the corresponding rational transfer function matches the original non‐rational one at selected interpolation points. The primary method of this study is the Loewner framework [2] which addresses this problem in a natural and direct way. The other methods that were studied, vector fitting (VF) [5], and adaptive Antoulas‐Anderson (AAA) [4], are instead based on an iterative and adaptive selection procedure. In order to present the adaptive selection as a feature in the Loewner framework and to reduce the time complexity at the same time, we introduced a Loewner CUR method based on the cross approximation algorithm [6,7]. The performance of the above methods is tested by a classical example in approximation theory: the inverse of the Bessel function of the first kind.
Optimal Power Flow Subject to Non‐Gaussian Stochastic Uncertainties: An L2‐based Approach
Authors: Mühlpfordt Tillmann , Faulwasser Timm , Hagenmeyer Veit 
Published: December 2018

AbstractThe optimal power flow (OPF) problem—i.e., the task to minimize power system operation costs while maintaining technical and network limitations—is key for the operational planning of power systems. The influx of inherently volatile renewable energy sources calls for methods that allow to consider stochasticity directly in the OPF problem. Modeling uncertainties as second‐order continuous random variables, the OPF problem subject to stochastic uncertainties can be posed as an infinite‐dimensional L2‐problem. A tractable and exact reformulation thereof can be obtained using polynomial chaos expansion, under mild assumptions. Polynomial chaos as such is a Hilbert space series expansion for random variables that is frequently employed for uncertainty propagation and uncertainty quantification. Polynomial chaos offers several advantages for OPF subject to stochastic uncertainties. For example, multivariate non‐Gaussian uncertainties can be considered straightforwardly. Also, the solutions from polynomial chaos are effectively feedback laws in terms of the realizations of the uncertainty that are determined in a single numerical run.
Finite element formulation of elastoplastic structures by using the symplectic Brezis‐Ekeland‐Nayroles principle
Authors: Shirafkan Nima , Nguyen An Danh , Stoffel Marcus , Markert Bernd 
Published: December 2018

AbstractIn this contribution, we present a finite element formulation to study elastoplastic structures by using the symplectic Brezis‐Ekeland‐Nayroles (BEN) principle. The approach that provides a minimum principle for the whole trajectories is suitable for dissipative systems dealing with non‐smooth dissipation cases, such as collision, surface friction, viscosity, plasticity, fracture and damage. To derive the variational formulation, the Legendre‐Fenchel transform is performed to establish the null minimisation problem of the power balance. The formalism is specialised to the small strain plasticity and is illustrated by solving a plane strain problem subjected to tensile force. The continuum is discretised with mixed finite element method and implemented into Finite Element Analysis Program (FEAP).
Modeling of Ductile Fracture by a Phase Field Approach
Authors: Müller Ralf , Noll Timo , Kuhn Charlotte 
Published: December 2018

AbstractA phase field model for ductile fracture with linear isotropic hardening is proposed. The chosen coupling between the fracture field and the elastic‐plastic material law is chosen such that a monolithic iteration scheme to solve the discretized partial differential equations for the evolution of the fracture field and for the mechanical field is feasible. 3D examples of ductile fracture are considered.
Simulation of a hollow profile extrusion process for a semicrystalline polymer
Authors: Descher Stefan , Wünsch Olaf 
Published: December 2018

AbstractIn this contribution the flow inside a simplified device for profile extrusion is investigated. Focus of this work is the cooling rate dependent crystallization model describing the latent heat release and state of solidification. The flow behavior is described using the exponential form of the Phan‐Thien Tanner model. Calculations are performed using OpenFOAM.
Numerical = periodic homogenization
Authors: Peterseim Daniel , Varga Dora 
Published: December 2018

AbstractIn our work, we try to bridge the existing theory of classical homogenization and the practical methods in numerical homogenization. We suggest an effective coefficient, which stems from the LOD method and which is based on a triangulation of the underlying domain. It turns out that in the case the diffusion coefficient has periodic structure and for a suitable choice of the mesh, the suggested coefficient coincides with the homogenized coefficient from classical homogenization.