bluuebunny/crossref_metadata_2025_split huggingface dataset:
The XFEM with an Implicit‐Explicit Crack Description for a Plane‐Strain Hydraulic Fracture Problem
Authors: Weber Nikolai , Fries Thomas‐Peter 
Published: November 2013

AbstractThe Extended Finite Element Method (XFEM) with an implicit‐explicit crack description is used to solve a plane‐strain hydraulic fracture problem. In its typical form, a hydraulic fracture problem combines the physical processes of fluid flow, solid deformation, and fracture propagation. The crack is described implicitly using three level‐sets to evaluate enrichment functions and to locate the enriched region. Additionally, an explicit crack description is used to update the crack during propagation. This approach is applied to a partially fluid‐filled crack in an semi‐infinite elastic solid without leak off and compared to the reference solution given in the literature. The results for the crack opening, pressure and crack length for various values of the fluid fraction are in good agreement with the analytical solutions. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dual‐mixed variational formulation and hp finite element method for axisymmetric shell problems in elastodynamics
Authors: Tóth Balázs 
Published: November 2013

AbstractA new dimensionally reduced axisymmetric shell model is presented briefly for modeling time‐dependent problems. This is based on the extended version of the three‐field dual‐mixed variational formulation of elastostatics [1, 2] to linear elastodynamics, the independent fields of which are the non‐symmetric stress tensor, the displacement‐ and the rotation vector. An important property of the related shell model is that the classical kinematical hypotheses regarding the deformation of the normal to the shell middle surface are not used, i.e., unmodified three‐dimensional constitutive equations are applied. The computational performance of the new h‐ and p‐version axisymmetric shell finite elements is tested through a representative cylindrical shell problems. The development presented in this paper has been motivated by the fact that efficient dual‐mixed hp plate and shell finite elements were managed previously to be developed for elastostatics by [1‐5]. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An improved modeling approach for circular flexure hinges with application to geometry optimization
Authors: Friedrich Robert , Lammering Rolf 
Published: November 2013

AbstractWithin this paper, a modeling approach for flexure hinges based on the Euler‐Bernoulli beam theory for beams of variable cross section is investigated in a static analysis. The proposed approach is implemented in a finite beam element routine, for which two different discretizations are discussed. The results are compared to a full scale three dimensional model. It is shown that a circular flexure hinge cannot be modeled accurately with one element. An improved model with three elements across the flexure hinge length is presented which shows excellent accordance with the reference model. A geometry optimization is realized based on the improved, low‐DOF model. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Isogeometric Collocation: Cost Comparison with Galerkin Methods and Extension to Adaptive Hierarchical NURBS Discretizations
Authors: Schillinger Dominik , Evans John A. , Reali Alessandro , Scott Michael A. , Hughes Thomas J.R. 
Published: November 2013

AbstractCollocation is based on the discretization of the strong form of the underlying partial differential equations, which requires basis functions of sufficient order and smoothness. Consequently, the use of isogeometric analysis (IGA) for collocation suggests itself, since splines can be readily adjusted to any order in polynomial degree and continuity required by the differential operators. In addition, they can be generated for domains of arbitrary geometric and topological complexity, directly linked to and fully supported by CAD technology. The major advantage of isogeometric collocation over Galerkin type IGA is the minimization of the computational effort for numerical quadrature. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Wellbore Contact of Drill Strings in a Finite Element Model
Authors: Shi Minzhe , Srisupattarawanit Tarin , Schiefer Frank , Ostermeyer Georg‐Peter 
Published: November 2013

AbstractIn drill string dynamics the Finite Element Method is usually applied to models of very long drill strings in a wellbore with arbitrary curvature. Taking account of geometrical constraint between the drill string and the wellbore, a high density of nodes is necessary. This density is much higher than the one needed to describe the natural vibrations properly, so this firstly leads to an extension of the computing time. A penalty function is frequently utilized to describe the contact problem between the drill string and the wellbore where the contact normal force acts only on the nodal points of the drill string. It was recognized that only node‐to‐surface contact models cannot fulfill this geometrical constraint, because the segment between two nodal points deeply penetrates the wellbore wall in some cases. A process with Gaussian points along the segment in time domain will be introduced, so that the drill string will be described according to this geometrical constraint with good accuracy but with a smaller density of nodes and less computing time. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of the Wear Particle Flow in Tribological Contacts
Authors: Tergeist Mathias , Müller Michael , Ostermeyer Georg‐Peter 
Published: November 2013

AbstractThe dynamics of tribological systems with pronounced memory effects are characterized by the complex coupling of mechanical, thermal, and chemical processes. At the Institute of Dynamics and Vibrations in Braunschweig, Cellular Automata have been developed that facilitate the evaluation of dynamics in technically relevant systems within a reasonable time. The flow of wear material is decisive for the formation, localization, and reconstitution of load‐bearing structures or films. In this paper, two opposed frictional contacts are chosen exemplarily for the investigation of the wear particle flow: a vehicle brake system and the sanding of wood. For this purpose, a modeling technique is proposed that is based on established force laws for micro particles and differentiates mechanisms of transport for different phases of the particle movement. The resulting transport of a single particle interacting with the topology of the frictional gap is analyzed for varying particle properties and process parameters. In a second step the insights are transferred to a set of rules for a Cellular Automaton which allows for quick evaluation and the incorporation of coupled effects. The validity and quality of the model transfer are discussed. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Algorithmic Consistency in Computational Inelasticity – a Conceptual Completion
Authors: Eidel Bernhard , Stumpf Felipe , Schröder J. 
Published: November 2013

AbstractThis paper communicates a new algorithmic concept, how higher‐order Runge‐Kutta (RK) methods for time integration of viscoelastic constitutive laws can be introduced into nonlinear finite element methods in order (i) to obtain the full nominal order p in time integration, (ii) to ensure that global equilibrium is only required at the end of time intervals Δt but not in the interior at RK‐stages, and (iii) to obtain –based on (i) and (ii)– a considerable speed‐up compared with Backward‐Euler. The condition to realize (i)–(iii) is, that the approximation of total strain in time must be of the same order as the time‐integration method, which is a completion of the concept of algorithmic consistency in computational inelasticity. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase‐field simulation of the electro‐mechanical response of ferroelectrics during Piezoresponse Force Microscopy
Authors: Thai Huy , Keip Marc‐André , Schröder Jörg 
Published: November 2013

AbstractThe contribution adresses the simulation of ferroelectric matrials in the framework of the Piezoresponse Force Microscopy (PFM). Based on the PFM, ferroelectric domain structures can be analyzed in great detail by measuring the electrically induced mechanical deformations of the surface of a ferroelectric. We employ a flexible continuum‐mechanical model based on the phase‐field method in order to analyze the behavior of ferroelectric microstructures numerically. Since ferroelectric materials are often highly anisotropic, the phase‐field formulation will account for transversely isotropic symmetry. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Molecular Statics Simulation of Ferroelectric Barium Titanate
Authors: Endres Florian , Steinmann Paul 
Published: November 2013

AbstractThe present contribution deals with the atomistic modelling of ferroelectric barium titanate. In this context a core‐shell model is implemented in a Molecular Static algorithm. Furthermore, Coulomb forces are simulated by the Wolf summation method in order to allow for a small cut off radius. We discuss the core‐shell model, molecular statics as a finite elements approach and present some numerical results. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational modeling of shape memory fibers in conforming and non‐conforming compound structures
Authors: Kohlhaas Benedikt , Klinkel Sven 
Published: November 2013

AbstractIn this work a material model for shape memory alloy (SMA) fibers is presented. A constitutive model is provided which aims for computational use. The presented model incorporates all relevant material nonlinear phenomena. It takes pseudoplasticity into account as well as pseudoelasticity and further the shape memory effect (SME). The constrained SME (CSME) and the two‐way SME are covered by the presented material model. The constitutive model is implemented in a one‐dimensional truss formulation and in a 3D‐rebar element. Both formulations are used to model fiber composite structures. Those are described by the use of a non‐conforming and a conforming mesh on the mesoscale. The numerical examples show the capability of the formulation. Different meshing strategies for the fiber–matrix compound are discussed. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the absence of a preferred configuration in constitutive relations of finite strain elasto‐plasticity
Authors: Shutov A. V. , Ihlemann J. 
Published: November 2013

AbstractThere exists a large variety of different techniques used to generalize the Prandtl‐Reuss relations of small strain elasto‐plasticity to finite strains. Obviously, any systematic study of such generalization techniques should be based on some sound principles. In this work, one aspect is taken into account, concerning arbitrary isochoric change of the local reference configuration. We analyze some models of finite strain elasto‐plasticity in order to find out if the specific choice of the reference configuration can affect the predicted stress response. For material models which remain invariant under the reference change, no preferred reference configuration exists. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Liquefaction in fluid‐saturated soils
Authors: Schenke Maik , Markert Bernd , Ehlers Wolfgang 
Published: November 2013

AbstractLiquefaction phenomena can be observed if fluid‐saturated soils are subjected to transient loading conditions, as they arise, for instance, during earthquakes. The term “liquefaction” comprises more specific liquefaction phenomena, such as flow liquefaction, which is an instability phenomenon in loose soils, and cyclic mobility, which is associated with medium‐dense to dense soils, where, in contrast to flow liquefaction, the overall stability of the granular assembly is maintained. However, soil liquefaction is always associated with a pore‐pressure build‐up, which consequently reduces the intergranular frictional forces, and thus, the load bearing capacity of the fluid‐saturated soil. In order to model these particular liquefaction phenomena, we proceed from a continuum‐mechanical framework based on the Theory of Porous Media (TPM), where the solid skeleton is described as an elasto‐(visco)plastic material with isotropic hardening and a stress‐dependent failure surface. The numerical solution of the resulting coupled system of partial differential equations is carried out by the finite‐element method (FEM). (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Multi‐Mechanism Model for Cutting Simulations Combining Visco‐plastic Asymmetry and Phase Transformation
Authors: Cheng Chun , Mahnken Rolf , Uhlmann Eckart , Ivanov Ivan Mitkov 
Published: November 2013

AbstractWe develop a multi‐mechanism model for strainrate‐ and temperature‐dependent asymmetric plastic material behavior accompanied by phase transformations, which are important phenomena in steel production processes. To this end the well‐known Johnson‐Cook model is extended by the concept of weighting functions, and it is combined with a model of tranformation‐induced plasticity (TRIP) based on Leblond's approach. The bulk model is formulated within a thermodynamic framework at large strains, and it will be specialized and applied to cutting processes in steel production. In the examples parameters are identified for the material DIN 100Cr6, and we illustrate the characteristic effects of our multimechanism model, such as strain softening due to temperature, rate dependence and temperature dependence as well as the SD‐effect. A finite‐element simulation illustrates the different mechanisms for a cutting process. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Implicit stress integration method of Shape Memory material model
Authors: Dunić Vladimir , Slavković Radovan , Busarac Nenad , Slavković Vukašin , Živković Miroslav 
Published: November 2013

AbstractThe phenomenological SMA material model proposed by Lagoudas [1] is modified and implemented in finite element software PAK [2]. Critical thermodynamic force is derived to match implicit integration method. All variables are derived to depend on effective values of stress, strain and martensitic volume fraction. One scalar equation need to be solved in the integration point using trial stress direction for each time step. The integration in the trial deviatoric stress direction provides possibility to solve large strain problems using the algorithms developed for small strains. Two one‐dimensional and one non‐proportional large strain example verified accuracy of proposed modifications. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the wear of brake pads
Authors: Ren Haichuan , Ostermeyer Georg‐Peter 
Published: November 2013

AbstractWithin measurements of brake pads on the IDS high load Tribometer, the wear of pads was investigated by a new non‐contact wear measurement under low normal pressures and low temperatures. The first results show that the wear of the pad in the sliding friction is nearly proportional to the friction work, and inversely proportional to the shear strength. The results are also interpreted by the adhesion theory of friction and Archard's equation. On the basis of further interpretations of shear strength and extension of adhesion theory of friction, the wear is derived as a piecewise linear function, which can evaluate explicitly the effect factors of wear and relative correlations at different pressures and different temperatures. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mixed Variational Principles and Robust Finite Element Design of Gradient Plasticity at Finite Strains
Authors: Aldakheel Fadi , Mauthe Steffen , Miehe Christian 
Published: November 2013

AbstractThe modeling of size effects in elastic‐plastic solids, such as the width of shear bands or the grain size dependence in polycrystals, must be based on non‐standard theories which incorporate length‐scales. This is achieved by models of strain gradient plasticity, incorporating spatial gradients of selected micro‐structural fields which describe the evolving dissipative mechanisms. The key aspect of this work is to provide a rigorous incremental variational formulation and mixed finite element design of additive finite gradient plasticity in the logarithmic strain space. We start from a mixed saddle point principle for metric‐type plasticity, which is specified for the important model problem of isochoric plasticity with gradient‐extended hardening/softening response. To this end, we propose a novel finite element design of the coupled problem incorporating a local‐global solution strategy of short‐ and long‐range fields. This includes several new aspects, such as extended Q1P0‐type and MINI‐type finite elements for gradient plasticity [4]. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a Deformation‐Driven Continuum‐Related Parrinello‐Rahman Molecular Dynamics
Authors: Ulz Manfred H. 
Published: November 2013

AbstractInvestigations into the atomistic‐to‐continuum coupling are recently pursued in literature. A hierarchical modelling in terms of a macroscale treated by continuum mechanics and the microscale governed by statistical mechanics may be a very fruitful combination. If the microscale is simulated with the help of molecular dynamics, the isostress‐isoenthalpic ensemble as proposed by Parrinello and Rahman presents a beneficial choice. This statistical ensemble is remarkable as the equations of motion are derived from a Lagrangian. Recently, this Lagrangian was situated into a continuum mechanics setting. This paper investigates the behavior of this continuum‐related Lagrangian in a kinetics‐driven setting (by imposing an external stress) and a kinematics‐driven setting (by imposing the shape of the molecular dynamics cell) in terms of a numerical example. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inverse analysis of a non‐linear viscous fluid based on dissipated energy measured with a simple‐shear rheometer
Authors: Abali B. Emek , Müller Wolfgang H. , Georgievskii D. V. 
Published: November 2013

AbstractOscillatory rheometer measurements are used to determine the material parameters of a NEWTONian fluid model, which can be expressed by a linear constitutive relation. However, rheological materials, such as polymer melts, mixture of oils, or food paste, can only be modeled as non‐NEWTONian fluids by using non‐linear constitutive relations. Since the rheometer measures the energy loss in the induction motor due to shear loading of the viscous material, this can be used as the objective function for a regression analysis. The dissipated energy will be obtained as outlined in [1]. The goal of this work is to explain how to determine the parameters of a non‐linear material model by using the energy loss that is measured in a rheometer. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some Remarks on the Numerical Solution of a Strain Gradient Plasticity Theory
Authors: Bayerschen Eric , Wulfinghoff Stephan , Böhlke Thomas 
Published: November 2013

AbstractA one‐dimensional strain gradient plasticity model is reviewed in the context of Finite Element Method (FEM) solvability. It is found that under certain conditions specified the resulting system of two coupled partial differential equations in space and time leads to a symmetric global stiffness matrix. This is achieved upon standard weak form approach and yields a favorable system for an efficient numerical solution. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromechanical modeling of Common yew and Norway spruce
Authors: Bader Thomas K. , de Borst Karin , Eberhardsteiner Josef 
Published: November 2013

AbstractIn this contribution, a micromechanical modeling approach in the framework of poromechanics is adopted to study structure‐stiffness relations of two quite different species, namely spruce and yew, in detail. In particular, microstructural specialties of yew and spruce are assessed. A dominant influence of the cellulose content and its orientation on the stiffness of the cell wall is revealed, while on the macroscopic scale, density is found to be the governing microstructural characteristic for elastic properties. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A constitutive model for granular materials with microstructures using the concept of energy relaxation
Authors: Khan Muhammad Sabeel , Hackl Klaus 
Published: November 2013

AbstractIn this paper, we present a constitutive model for granular materials exhibiting microstructures using the concept of energy relaxation. Within the framework of Cosserat continuum theory the free energy of the material is enriched with an interaction energy potential taking into account the counter rotations of the particles. The enhanced energy potential fails to be quasiconvex. Energy relaxation theory is employed to compute the relaxed energy which yields all possible displacement and micro‐rotations field fluctuations as minimizers. Based on a two‐field variational principle the constitutive response of the material is derived. The developed constitutive model is then implemented in a finite element analysis program using the finite element method. Numerical simulations are presented to observe the localized deformation phenomenon in a granular medium. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bacterial methane oxidation in landfill cover layers ‐ a coupled FE multiphase description
Authors: Sindern Andrea , Ricken Tim , Bluhm Joachim , Widmann Renatus , Denecke Martin 
Published: November 2013

AbstractLandfill gas is composed of methane (CH4) and (CO2) at a ratio of about (60% – 40%), whereby the impact of methane on the greenhouse effect is about 25 times higher than that of carbon dioxide. Bacterial methane oxidation, taking place in the landfill cover layer, helps to reduce the climate active emissions from landfill sites. This contribution presents a theoretical and numerical approach to model the coupled processes of bacterial methane oxidation. An isothermal biphasic model based on the Theory of Porous Media (TPM) and Mixture Theory is introduced as well as the coupled finite element (FE) calculation concept. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On heat exchange and heat transport in a geothermal plant
Authors: Koch David , Ehlers Wolfgang 
Published: November 2013

AbstractIn the long term, the only way to address the challenging task of power supply, is to make renewable energy sources economically attractive and to use them efficiently. In particular, geothermal energy is promising to take over the base load of the power supply. Nevertheless, a lot of investigations needs to be made to use the almost inexhaustible source of thermal energy in the interior of the earth effectively.Starting from the initially isothermal state, a cold fluid is injected through a borehole into a rock. By the rising pressure gradient, the fluid flows through the porous rock and escapes through another borehole. While the fluid passes the micro cracks in the hot rock, the water is heated by the rock due to the heat exchange between the constituents. This process is simulated based on the Theory of Porous Media (TPM). The presented modelling approach of the heat transport and the flow processes in a fully saturated subsurface includes two non‐isothermal constituents: an elastically deformable, materially incompressible solid skeleton where thermal expansion is neglected, and a viscous, materially incompressible fluid constituent.To solve the initial‐boundary‐value problem, the governing primary variables of the coupled model are spatially approximated by mixed finite elements, and the time‐discretisation is carried out by an implicit Euler time‐integration scheme. The aim of the presented numerical simulations is to study the heat transport and to evaluate the efficiency by varying flow rates. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)