bluuebunny/crossref_metadata_2025 huggingface dataset:
Uncertainty and Sensitivity Analysis of Different Models of Brake Squeal
Authors: Hanselowski Andreas , Hanss Michael
Published: December 2014

In this contribution, the brake‐squeal phenomenon is investigated using the pin‐on‐disc setup. The setup is analyzed numerically using the finite element method. The finite element model is evaluated in the time domain, and the vibration mechanism leading to squeal as well as the limit cycles of the vibration are analyzed. Against the background of the high computational costs, it is evaluated to what extent the Hoffmann‐Gaul minimal model can reproduce the results of the finite element model. Moreover, as brake squeal is very sensitive with respect to parametric uncertainties, the influence of several parametric uncertainties on the limit cycles is analyzed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Influence of High‐Frequency Excitation on Systems with Dynamic Friction
Authors: Kapelke Simon , Hetzler Hartmut , Seemann Wolfgang
Published: December 2014

By imposing high‐frequency vibrations to a system, the characteristics of dry friction for low sliding velocities can be smoothed and, consequently, undesired friction induced phenomena such as stick‐slip motion can be quenched. Many studies have been published so far, most of them focussing on the reduction of friction between metal surfaces and using classical Coulomb friction models. Within this contribution the effect of high‐frequency excitation on dry friction taking into account dynamic friction models will be discussed. To this end, the friction law suggested by Dahl is used and the resulting friction characteristics are compared to those obtained for the classical Coulomb friction model. Using Dahl's friction model, a reduction of the smoothing effect is observed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the influence of boundary conditions on the modal properties of a base frame
Authors: Renning Maik , Kracht Kerstin , von Wagner Utz , Köster Philipp , Bozkurt Taner
Published: December 2014

Supports of turbomachineries can be designed as base frames, which are constructions of steel‐plates. One of the most important design requirements of the turbomachinery system is to avoid of natural frequencies in the operating speed range. Thus, a rotor dynamics analysis (see e.g. [1]), which is usually carried out using transfer matrix methods or finite element methods has to take the dynamic stiffness of the base frame into account. However, there are several problems to identify this complex and frequency dependent parameter, for example the localization of excitation or measurement responses and the difficulty of the support of base frames, e.g jack screws.

In this article the support of a test base frames is analyzed by modal analysis experimentally. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time‐efficient analysis of nonlinear dynamic behavior
Authors: Sprock Christian , Sextro Walter
Published: December 2014

Many nonlinear mechanical oscillators show excitation‐dependent behavior. In this paper, a new measurement approach is presented to analyze such structures. The main advantage of the presented method is the high efficiency, since measurement duration and loads to the structure are significantly reduced. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Forced nonlinear oscillation of underactuated systems: the balance board example
Authors: Knoll Carsten , Röbenack Klaus
Published: December 2014

In this contribution we consider a mechanical model of the so‐called balance board or “indoboard” system, which is an unstable underactuated mechanical system. Instead of stabilizing one equilibrium point we investigate the asymptotic stabilization of a closed orbit, which results in a nonlinear oscillation. To this end the system is considered in coordinates of the real Jordan normal form, which facilitates the construction of a Control‐Lyapunov function. On this basis, a nonlinear feedback law which renders the periodic orbit asymptotically stable is easily derived via Sontags formula. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear kinematic oscillations of railway wheelsets of general surface geometry
Authors: Antali Mate , Stepan Gabor
Published: December 2014

Kinematic oscillation of railway wheelsets is investigated in the case of a straight track, focusing on the nonlinear effects of the geometry of wheel and rail profiles. Euler angles are used to describe the motion of the wheelset, the contacting bodies are modelled by two‐parametric rigid surfaces. The surface parameters of the current contact points are followed during the calculations. The curvatures and their variations are also included in the analysis. From the implicit form of the geometric constraints, the dynamics is determined by means of Taylor expansion. Equations of the local nonlinear motion are derived and the qualitative behaviour of the system is given. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Entwicklung einer Schwingungserregereinheit mit piezoelektrischen Aktoren
Authors: Krüger Thomas , Ams Alfons
Published: December 2014

In der Photovoltaik‐ und Halbleiterindustrie ist das Fertigen von Siliziumwafern ein aufwändiger Produktionsschritt. Die Wafer entstehen durch Zerschneiden eines mono‐ oder multikristallinen Siliziumblocks (Ingot). Dabei kommt das Drahttrennläppverfahren zur Anwendung. Mit dem Ziel den Drahtsägeprozess zu verbessern, wird eine Schwingungserregereinheit entwickelt. Das Gerät, betrieben mit piezoelektrischen Aktoren, ermöglicht mehrachsige Schwingungen des Siliziumblocks. Es werden für die Aktoren und die mechanische Konstruktion einzelne Modelle aufgestellt. Durch Messung des Übertragungsverhaltens gelingt anhand des gekoppelten Gesamtmodells die Identifikation von Parametern. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On stability of certain key types of rigid body motion in a nonconservative field
Authors: Shamolin Maxim V.
Published: December 2014

In this activity the qualitative analysis of spatial problems of the real rigid body motions in a resistant medium is fulfilled. A nonlinear model that describes the interaction of a rigid body with a medium and takes into account (based on experimental data on the motion of circular cylinders in water) the dependence of the arm of the force on the normalized angular velocity of the body and the dependence of the moment of the force on the angle of attack is constructed. An analysis of plane and spatial models (in the presence or absence of an additional tracking force) leads to sufficient stability conditions for translational motion, as one of the key types of motions. Either stable or unstable self‐oscillation can be observed under certain conditions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Higher Order Continuum Modelling for Predicting the Mechanical Behaviour of Solid Foams
Authors: Liebenstein Stefan , Sandfeld Stefan , Zaiser Michael
Published: December 2014

A higher order continuum model is presented, which is able to capture size effects and regularize softening in rotational, shearing and especially compressive settings. It is shown that with a minimal setting of 3 additional constitutive parameters the model has all desired properties. For parameter identification an example system of a honeycomb structure is investigated. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A two‐scale simulation framework for Internal Traverse Grinding
Authors: Holtermann Raphael , Menzel Andreas , Schumann Sebastian , Biermann Dirk
Published: December 2014

We present a hybrid framework which aims at the modelling and simulation of Internal Traverse Grinding of hardened 100Cr6/AISI 52100 by using electro plated cBN grinding wheels. We focus on the thermo‐mechanical loading conditions on the workpiece that results from the interaction of workpiece and tool. The modelling framework basically consists of three components, namely representative plane strain adaptive finite element simulations on a meso‐scale, capturing the proximity of a single cBN grain when cutting through the workpiece bulk. Secondly, we incorporate a kinematic simulation on the process level to gain detailed simulation‐based information on the transient grain‐bulk‐interaction. The third component of the framework consists of a macro‐scale process model that uses the superposed results of the former two components as thermo‐mechanical boundary conditions. Using this framework, we target the prediction of metallurgical effects, such as white layers, on the workpiece on the macro scale in the near future. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary value problems in the theory of thermoporoelasticity for materials with double porosity
Authors: Svanadze Merab
Published: December 2014

In this paper the linear quasi‐static theory of thermoelasticity for solids with double porosity is considered. The system of equations of this theory is based on the equilibrium equations for solids with double porosity, conservation of fluid mass, constitutive equations, Darcy's law for materials with double porosity and Fourier's law for heat conduction. The basic internal and external boundary value problems (BVPs) of steady vibrations are formulated. The uniqueness and existence theorems for classical solutions of the above mentioned BVPs are proved by means of the potential method (boundary integral equation method) and the theory of singular integral equations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling the moisture dependent material behavior of adhesive bonds close to the glass transition temperature
Authors: Goldschmidt Florian , Diebels Stefan
Published: December 2014

In the presented work, a viscoelastic cross‐linked polyurethane is investigated. Environmental influences lead to an inhomogeneous spatial distribution of the mechanical properties in polymer adhesives. Diffusive transport mechanisms transfer water from the environment into the polymer. Further effects like temperature, also have an influence on the mechanical behavior of adhesives. The model respects these influences and takes the incompressibility of the material into account. Viscoelastic behavior can be observed, especially close to the glass transition temperature [3]. Additional to these general effects on polymers, adhesive bonds show a dependency of the mechanical behavior on the thickness of the layer. For numerical investigations, all necessary balance and constitutive equations are implemented in the open‐source C++ finite element code deal.II [1, 2]. With the help of this implementation and by comparing experimental results and results gained from simulations, material parameters of the used polymer can be identified. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Material modelling of a filled rubber material with different approaches in the representation of a statical hysteresis
Authors: Scheffer Tobias , Diebels Stefan
Published: December 2014

In this contribution, two different approaches for the description of an incompressible carbon black‐filled EPDM (ethylene propylene diene monomer) are presented. Regarding the material's behaviour, especially for cyclic loading conditions, a kind of statical hysteresis loop is present. Even for the slowest possible strain rate, a clearly visible hysteresis occurs in loading‐unloading experiments. The first shown model approach is basically a purely viscoelastic description. Because of the non‐linearities in the material behaviour, the material parameters have to be reformulated by complex functions including further parameters that are strongly coupled. This description is able to display very well the behaviour of the EPDM with respect to quasi‐statical experiments, as well as to dynamical tests for moderate strain rates. The major problem of this model liess in the parameter identification. The coupling of the material parameters leads to a difficult, long‐durating and non‐unique identification. Therefore, initial ideas for an alternative description, escpecially concerning the above‐mentioned statical part of the hysteresis, are outlined in this article. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Potential method in the steady vibrations problems of the theory of thermoviscoelasticity for Kelvin‐Voigt materials with voids
Authors: Svanadze Maia M.
Published: December 2014

In this paper the linear theory of thermoviscoelasticity for Kelvin‐Voigt materials with voids is considered. The basic internal and external boundary value problems (BVPs) of steady vibrations are formulated. The uniqueness and existence theorems for classical solutions of the above mentioned BVPs are proved by using the potential method (boundary integral equation method) and the theory of singular integral equations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A thermodynamically consistent constitutive model for fluid mud
Authors: Hülsmann Anna , Nackenhorst Udo , Wurpts Andreas
Published: December 2014

In this contribution, an approach towards a thermodynamically consistent constitutive model for fluid mud is presented. Fluid mud exhibits highly non‐Newtonian, thixotropic behaviour. It can be classified as a structured fluid. Typically, its viscosity is modeled using Bingham‐type rheological models of different complexity [1, 2]. Here, the three‐dimensional non‐Newtonian constitutive behaviour will be modeled based on a visco‐elasto‐plastic model. At the current stage, a Drucker‐Prager‐like yield function has been formulated. Viscosity is assumed to be a function of shear viscosity. First results show the general ability to represent experimental data. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimum blank design by using the FEM based on inverse motion in orthotropic elasto‐plasticity
Authors: Landkammer Philipp , Germain Sandrine , Steinmann Paul
Published: December 2014

Inverse form finding aims to determine the optimum blank design of a workpiece whereby the desired end configuration that is obtaining after a forming process, the boundary conditions and the applied loads are known. Inputting the optimal initial configuration a subsequent computation with the Finite Element Method (FEM) then has to result in exactly the nodal coordinates of the desired deformed workpiece. Germain et al. [1] recently presented a new form finding strategy for isotropic elasto‐plasticity, see also Landkammer et al. [2] for orthotropic plasticity. The corresponding algorithm uses the inverse mechanical formulation (also denoted as inverse finite element method) in addition to the common direct formulation in a recursive way. Switching between the direct and the inverse mechanical formulation, while fixing the internal plastic variables in the inverse step, uniquely detects the undeformed configuration iteratively. This contribution demonstrates within an example that the developed recursive algorithm even works with combinations of orthotropic elastic and orthotropic plastic material parameters without affecting the nearly linear convergence rate of the form finding algorithm. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the contact interfaces in sonic composites
Authors: Girip Iulian , Ioan Rodica
Published: December 2014

The paper analyses the effect of normal contact with friction on the generation of full band‐gaps in sonic composites. The behavior of contact interfaces are computed by using LISA (local interaction simulation approach). LISA is an efficient tool for numerical simulation of the acoustic wave propagation in heterogeneous material specimens, in particular those with contact interfaces between different materials, like in sonic composites. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Life Prediction of FRP Composites by a Direct Method
Authors: Hachemi Abdelkader , Vasiukov Dmytro , Panier Stéphane
Published: December 2014

A direct computational approach for lifetime prediction of fibre‐reinforced polymer (FRP) composites is presented. The approach is based on a direct method which allows predicting the fatigue life from the stabilised damage state. The classical direct method is generalised to the case of coupled plasticity with damage mechanics of the UD‐FRP composite materials [1]. The constitutive model is based on a continuous damage meso‐scale approach [2]. By analysing damage variables and thermodynamical forces associated with damage at the stabilised state, fatigue life prediction law is proposed as a power law function of stabilised thermodynamic forces. The obtained numerical results have been validated by experimental test results on standard glass‐fibre/epoxy angle‐ply and cross‐ply laminate plates. The proposed approach could serve as a useful tool for the design of FRP composites. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive textile‐reinforced composites: Modeling and application
Authors: Linse Thomas , Ulbricht Volker , Kluge Axel , Cherif Chokri
Published: December 2014

The scope of the present paper is the modeling of the mechanical behavior of textile‐reinforced composites with an integrated system of wires made of shape memory alloys. A phenomenological model for the description of the material behavior of shape memory alloys is implemented in a commercial FE code. As the textile reinforcement shows periodically repeating patterns, the inner architecture of the composite can described by a representative volume element. Effective viscoelastic material parameters of the textile‐reinforced composite are determined with the help of homogenization techniques. For the application of the developed composite structure as a simple actuator, numerical results are compared with experimental data. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bainitic variant evolution in a low‐alloyed steel including numerical aspects
Authors: Ehlenbröker Ulrich , Mahnken Rolf
Published: December 2014

Bainite formation is of particular industrial relevance especially after hot‐forming and quenching of relatively bulky components. In these processes large portions of the component are subjected to appropriate cooling rates which yield a considerable fraction of the bainitic product phase. In our work, we develop a thermodynamically consistent multi‐scale model for phase transformations from austenite into 24 possible bainite variants. Furthermore, the model is capable to express the macroscopic effects of volume change due to phase transformation as well as to transformation‐induced plasticity (TRIP). Basic ideas for our material‐model can be found among others in [1–3]. Because of the highly complex, strongly coupled model equations, the numerical implementation is a very challenging task. Therefore, we make use of a projected Newton algorithm combined with an active‐set strategy, as an extension to the approach in [4] for austenite‐martensite transformations in shape memory alloys. Numerical examples illustrate the quadratic convergence behaviour in a Finite‐Element scheme. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Phase Field Approach for Martensitic Transformations and Crystal Plasticity
Authors: Schmitt Regina , Mayer Patrick , Kirsch Benjamin , Aurich Jan , Kuhn Charlotte , Müller Ralf , Bhattacharya Kaushik
Published: December 2014

This work is motivated by cryogenic turning which allows end shape machining and simultaneously attaining a hardened surface due to deformation induced martensitic transformations. To study the process on the microscale, a multivariant phase field model for martensitic transformations in conjunction with a crystal plastic material model is introduced. The evolution of microstructure is assumed to follow a time‐dependent Ginzburg‐Landau equation. To solve the field equations the finite element method is used. Time integration is performed with Euler backward schemes, on the global level for the evolution equation of the phase field, and on the element level for the crystal plastic material law. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase‐field simulation of piezoresponse force microscopy in consideration of different environmental conditions
Authors: Thai Huy , Keip Marc‐André , Schröder Jörg
Published: December 2014

Piezoresponse force microscopy (PFM) is a feasible tool which is widely used for investigating information of the domain structures of ferroelectrics. Nevertheless, one drawback of the technique may be that environmental conditions could effect the very small signal which is detected from the displacement of the tip. The present contribution addresses the simulation of PFM in consideration of environmental conditions. We employ a continuum‐mechanical model based on the phase‐field method which accounts for the transversely isotropic symmetry of the underlying material. The goal of this contribution is to analyze the environmental effect on the tip‐sample interaction. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of pre‐straining on the lifetime of filled elastomers
Authors: Krause Maria , Juhre Daniel
Published: December 2014

Pre‐conditioning is usually not considered in classical lifetime prediction analyses. The strong material softening observed in rubber materials, however, makes one expect a strong influence of the pre‐conditioning on the lifetime. For this contribution, experimental tests were carried out to verify and further investigate, how the pre‐loading affects the lifetime of filled natural rubber. Comparing the experimental results with according simulations using the MOdel of Rubber PHenomenology (MORPH) [1, 2] it is found that even though the simulation shows an extended lifetime with higher pre‐straining, the experimental data shows no significant influence of this pre‐conditioning. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A continuum mechanics approach for modelling arbitrary degradation and erosion processes in polymers
Authors: Seydewitz Robert , Bolea Albero Antonio , Böl Markus
Published: December 2014

Composed of rather simple components some polymers show the ability to decompose from complex structures into substances that can be easily absorbed by the surrounding environment. The responsible processes behind chain shortening and eventually the material remove are degradation and erosion. The aim of this work is to model the chemo‐mechanical condition of the polymer material based on a discretised network model. Further, the influence of erosion processes on the morphology is investigated. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular static simulations of ferroelectric material hysteresis behaviour
Authors: Endres Florian , Steinmann Paul
Published: December 2014

The present contribution deals with molecular static modelling and the simulation of ferroelectric material hysteresis behaviour. Therefore the core‐shell model is implemented in a molecular static algorithm. Moreover the algorithm is implemented as a finite element method for nonlinear trusses. Thereby the computational costs are reduced significantly compared to molecular dynamics. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Calculation of Stresses and Consistent Tangent Moduli from Automatic Differentiation of Hyerelastic Strain Energy Functions Through the Use of Hyper Dual Numbers
Authors: Tanaka Masato , Sasagawa Takashi , Omote Ryuji , Fujikawa Masaki , Balzani Daniel , Schröder Jörg
Published: December 2014

Many materials as e.g. engineering rubbers, polymers and soft biological tissues are often described by hyperelastic strain energy functions. For their finite element implementation the stresses and consistent tangent moduli are required and obtained mainly in terms of the first and second derivative of the strain energy function. Depending on its mathematical complexity in particular for anisotropic media the analytic derivatives may be expensive to be calculated or implemented. Then numerical approaches may be a useful alternative reducing the development time. Often‐used classical finite difference schemes are however quite sensitive with respect to perturbation values and they result in a poor accuracy. The complex‐step derivative approximation does never suffer from round‐off errors, cf. [1], [2], but it can only provide first derivatives. A method which also provides higher order derivatives is based on hyper dual numbers [3]. This method is independent on the choice of perturbation values and does thus neither suffer from round‐off errors nor from approximation errors. Therefore, here we make use of hyper dual numbers and propose a numerical scheme for the calculation of stresses and tangent moduli which are almost identical to the analytic ones. Its uncomplicated implementation and accuracy is illustrated by some representative numerical examples. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Law for Small Scale, Continuous Calving
Authors: Christmann Julia , Müller Ralf , Humbert Angelika
Published: December 2014

Ice shelves are formed by the viscous flow of inland ice into the ocean, they are floating and loosing mass by iceberg calving. There are two different kinds of calving: large tabular icebergs detach as singular events in time, and small scale calving occuring on a rather continuous time scale. Three visco‐elastic approaches are discussed, in order to derive a general law for calving rates applicable to small scale calving. The results are highly dependent on the termination criterium for each approach, hence the computed calving rate has to be adapted and validated with measurements to get the most qualified value. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of Autofrettage in Curvilinear Coordinates
Authors: Müller Wolfgang H. , Reich Felix A.
Published: December 2014

Pressure vessels subjected to high mechanical loadings can fail due to microscopic crack growth, i.e., stress corrosion cracking. A popular way to increase the crack resistance of a structure is by autofrettage. The standard approach to obtain a numerical solution for the involved fields is to discretize w.r.t. Cartesian coordinates as implemented in common commercial FE programs. However, this approach is computationally costly in comparison to pure elastic simulations—often rendering this method practically unfeasible. The current work shows that autofrettage can be simulated more efficiently in extensive bodies that can be described by a bijective map where certain symmetries are available in load and form. The discretization and the mathematical formalism of this approach in curvilinear coordinates are described. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling and simulation of heat exchange and transport in a geothermal plant
Authors: Koch David , Ehlers Wolfgang
Published: December 2014

The production of energy by use of the high temperature in the earth's mantle has played an increasingly important role in recent years. However, large uncertainties concerning the conditions in the subsurface make it difficult to use power plants efficiently. An appropriate modelling and simulation of the heat exchange and transport provides a promising tool for further investigations of the process and optimisation of the productivity. Starting from the isothermal state at high temperatures, a cold fluid is injected through a borehole into a porous rock by applying a pressure difference between at least two wells. Passing the fractured rock, the water is heated at the crack interfaces. In addition to the convection of the temperature due to the water flow, the conduction of heat in the rock and the water has to be considered. The modelling approach of this coupled process is based on the Theory of Porous Media (TPM). Both, the rock and the water, are assumed to be materially incompressible and the thermal expansion is solely considered for the fluid, since the expansion of the rock is negligible for the occurring temperature differences. Furthermore, it is assumed that the subsurface is saturated with water. To solve the generated 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. Since in the considered problem the convective transport is dominant, a streamline upwinding scheme is used for the numerical stabilisation to obtain non‐oscillatory solutions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Model reduction of porous‐media problems using proper orthogonal decomposition
Authors: Otto Davina , Ehlers Wolfgang
Published: December 2014

In the context of finite‐element simulations of porous media, computing time and numerical effort is an important issue because the number of degrees of freedom of such coupled problems can become very large. Following this, model reduction plays an important role. A broad variety of materials exhibit a porous microstructure. In order to evaluate the overall response of these materials, a macroscopic continuum‐mechanical modelling approach is used. Therefore, the complex inner structure of porous media is regarded in a multi‐phasic and multi‐component manner by means of the well‐founded Theory of Porous Media (TPM). The mechanical behaviour of porous media is solved using the Finite‐Element Method (FEM).

The basic idea of model reduction is to transform a high dimensional system, in terms of the system's degrees of freedom, to a low dimensional subspace to minimise the computational effort while maintaining the accuracy of the solution. The method of proper orthogonal decomposition (POD) can be seen as a method to approximate a given data set with a low dimensional subspace. Furthermore, the POD method is independent of the type of the model and can be used for nonlinear systems as well as for systems of second order. In several applications, such as consolidation problems of partially saturated soils, commonly occurring motion sequences can be found, which can be used as typical “snapshots” of the system. Therefore, the application of the POD method to the simulation of porous media is discussed in the present contribution. Investigated computations of a biphasic standard problem show that the POD method reduces the numerical effort to solve the linearised system of equations in each iteration step. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Powder compaction. Experiments, modeling and simulation
Authors: Rothe Steffen , Hartmann Stefan
Published: December 2014

Field‐assisted sintering technology (FAST) is a combined thermal and mechanical loading process to compact and sinter a powder material within one process step. In this short essay a constitutive model of thermo‐viscoplasticity is proposed representing most of the phenomena observed in the experiments. The constitutive model is calibrated to the experimental data and some predicted experiments are compared with constitutive model showing appropriate results. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the necessity of alternative approaches towards finite elastoplasticity
Authors: Schröder Bettina , Kuhl Detlef
Published: December 2014

In order to simulate elastoplasticity within metal forming processes different approaches towards numerical implementation have been realized. Nevertheless, most of them or consider only the quasistatic case or use distinct time discretization schemes for the balance and the evolution equations. In the following, the effects of latter will be outlined on the basis of a numerical example exploiting a conventional ansatz towards finite elastoplasticity. This access should serve as a motivation for identifying why it is still important to investigate the implementation of elastoplastic phenomena beyond the well established methods. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of Self‐Healing phenomena in a Polymer matrix within the Framework of the Theory of Porous Media
Authors: Specht Steffen , Bluhm Joachim , Schröder Jörg
Published: December 2014

In this work, a multiphase material model will be presented in order to simulate self‐healing effects in a polymer. The material model is developed using the Theory of Porous Media (TPM). In order to describe the damage behavior of the polymer, the well known (1 − D)‐approach is included, and for the description of the healing, a phase change between the liquid like healing agents and the solid healed material is considered. This phase change depends on the amount of catalysts inside the polymer matrix. The applicability of the developed model, in order to describe the time dependency of the healing mechanism, will be shown by a virtual experiment of a self‐healing tapered double cantilever beam (TDCB). (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Damage model for ferroelectric materials and its applications to multilayer actuators
Authors: Gellmann Roman , Ricoeur Andreas
Published: December 2014

In this paper a damage model for ferroelectric materials is presented. It is implemented in terms of a user element in the commercial FEM‐code Abaqus. The model is based on micromechanical considerations of domain switching and its interaction with microcrack growth and coalescence. Finite element analysis of a multilayer actuator is performed, showing principal stresses leading to crack initiation and damage of the actuator. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A condensed microelectromechanical constitutive and damage model for tetragonal ferroelectrics
Authors: Lange Stephan , Ricoeur Andreas
Published: December 2014

A condensed model for ferroelectric solids with tetragonal unit cells is presented. The approach is microelectromechanically and physically motivated, considering discrete switching processes on the level of unit cells and quasi‐continuous evolution of inelastic fields on the domain wall level. To calculate multiple grain interactions an interaction tensor is introduced. Hysteresis loops are simulated for pure electric and electromechanical loading, demonstrating e.g. the influence of a compressive preload on the poling process and interaction between statistically arranged crystallits. The residual stresses and the corresponding principle stresses are used to simulate fatigue damage in ferroelectric materials. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational Based Stability Analysis in Coupled Electro‐Mechanics at Finite Strains
Authors: Vallicotti Daniel , Zäh Dominic , Miehe Christian
Published: December 2014

Smart or functional materials are in focus in broad fields of recent research. In particular, electroactive polymers (EAPs) with their large actuator strains are used for innovative design in robotics. These materials become practical as soon as the material is robust, reliable and long lived. However, EAPs suffer from different types of instabilities, such as unstable thinning of actuators, local buckling induced by coexistent states and electrical breakdown. One distinguishes between structural instability, i.e. instabilities in the global structural response like buckling or wrinkling and local or material instability, e.g. the formation of microstructures and phase decompositions. These effects are well known and analyzed for purely mechanical phenomena, but not fully developed in the context of electro‐mechanically coupled problems. To this end, we develop new variational‐based stability criteria in finite electro‐elastostatics, by postulating an electro‐mechanical quasi‐convexity condition for weakly convex energy and weakly convex‐concave energy‐enthalpy formulations. Starting from distinct variational principles, we develop criteria for local and global stability and construct stability checks, which accompany equilibrium paths for the detection of critical points in finite element models. Numerical examples validate the developed concepts for boundary value problems. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A thermodynamically consistent and numerically stable formulation for the description of diffusion in polymeric gels
Authors: Krischok Andreas , Tkachuk Mykola , Linder Christian
Published: December 2014

This work proposes a stable equal‐order element formulation for polymeric gels at finite deformations. From the numerical point of view the description of flow in incompressible elastic media such as gels leads to singularities in the coupled system of equations of the corresponding finite element discretization unless certain requirements are met to satisfy the Ladyženskaja‐Babuška‐Brezzi (LBB) condition. The proposed computationally efficient mixed enhanced assumed strain method allows to satisfy the LBB condition and to account for locking phenomena without the requirement of higher order interpolations for the displacement field. The proposed model can be employed in various fields where the modeling of flow in incompressible media undergoing finite deformations is of interest such as Computational Soil Mechanics or Computational Biomechanics. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of Debonding on Thermal Conduction and Humidity Diffusion at Mesoscale of Concrete
Authors: Wu Tao , Wriggers Peter
Published: December 2014

In order to numerically describe the phenomena that the debonding at interfacial transition zone (ITZ) between hardened cement paset (HCP) and aggregates could affect thermal conduction and humidity diffusion in the concrete, cohesive zone model (CZM) characterized by traction‐separation law combined with micromechanically motivated thermal flux‐separation relation and diffusion flux‐separation relation is established at ITZ. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cardiovascular fluid‐structure interaction: A partitioned approach utilizing the p‐FEM
Authors: Radtke Lars , Larena‐Avellaneda Axel , Kölbel Tilo , Debus Eike Sebastian , Düster Alexander
Published: December 2014

In this paper, we propose a technique for simulating the fluid‐structure interaction in blood vessels. A partitioned approach is used, which allows for an independent discretization of the fluid domain and the structural domain. We choose the finite volume method to solve the Navier‐Stokes equations and the p‐version of the finite element method (p‐FEM) to solve the equations of geometrically nonlinear structural dynamics. The solution strategy can be seen as a first approach towards a comprehensive study of the hemodynamics in vascular substitutes with the goal of improving their long term functionality. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of a long slender structure in turbulent flow
Authors: Tschisgale Silvio , Fröhlich Jochen
Published: December 2014

The dynamic behaviour of a long slender structure in turbulent flow can vary considerably, depending on the particular excitation. Regimes from simple static deformation, over periodic to irregular and chaotic behaviour are observed. An example is the self‐excited periodic motion of a long slender structure in cross flow. In such cases, the fluid flow and the structure movement are strongly coupled. The paper presents a robust partitioned coupling approach based on the Immersed Boundary Method which integrates the geometrically exact Cosserat rod model. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Analysis of Heat Transfer for Cooling of Photovoltaic Cells
Authors: Lotfi Abdelhakim
Published: December 2014

Photovoltaic cells are devices which convert solar radiation directly into electricity. However, solar radiation increases the photovoltaic cells temperature [1] [2]. The temperature has an influence on the degradation of the cell efficiency and the lifetime of a PV cell. This work reports on a cooling water technique for cells, whereby the cooling system was placed at the front surface of the cells to dissipate away excess heat and to block unwanted radiation. Using water as a cooling medium for the cells, the overheating of closed panel is greatly reduced without prejudicing luminosity and water acts as a filter to remove a portion of solar spectrum in the infrared band but allows transmission of the visible spectrum most useful for the PV operation. The aims of this study are to develop a 3D thermal model to simulate the cooling and heat transfer in Photovoltaic panel and recommend a cooling technique for the PV panel. In order to have a good estimation for the temperature distribution, the three‐dimensional flow and heat transfer across the cooling block is investigated numerically by solving the continuity, momentum and energy equations using FLUENT. The second objective of this work is to study the influence of the geometrical dimensions of the panel, water mass flow rate and water inlet temperature on the flow distribution and the solar panel temperature. The results obtained by the model are compared with experimental results from testing the prototype of the cooling device. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Assessment of Stabilization Techniques for Coupled Poro‐plastic Analysis using Low‐Order Finite Elements
Authors: Khisamitov Ildar , Alsahly Abdullah , Meschke Günther
Published: December 2014

For the numerical modeling of geomaterials in general, and soft, water saturated soils in particular, the nonlinear constitutive behavior of the skeleton and its strong coupling with the pore fluid must be considered. In the limit of zero compressibility of water and soil grains and very low permeability (which correspond to the classical “undrained” assumption in soil mechanics), the functions used to interpolate displacements and pressures must fulfill either the Ladyženskaja‐Babuška‐Brezzi inf‐sup condition [1] or the much simpler patch test proposed by Zienkiewicz and Taylor. These requirements exclude the use of elements with equal order of linear interpolation for pressures and displacements, for which spurious oscillations may appear. Low‐order elements with linear approximation of displacements and pressure variables may be used if stabilization techniques are employed. The work is concerned with the numerical assessment and investigation of several stabilization techniques and their application to strain localization problems in coupled poro‐plastic analyses of soft, saturated soils [2,3]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of numerical homogenization techniques in BT‐CFO multiferroic particle composites
Authors: Wang Zhibin , Avakian Artjom , Ricoeur Andreas
Published: December 2014

This work is restricted to linear material behavior, i.e. the structure is considered to be in a perfectly poled state. Different numerical homogenization methods are investigated and used to calculate effective properties of a 0‐2 composite modelled in reprensentative volume elements. Bariumtitanate (BT) and cobaltferrite (CFO) are employed in the Finite Element model, where the roles of matrix and inclusion are mutable in principle. Mixed magnetoelectromechanical boundary conditions based on different homogenization theories are applied to the model. The calculated macroscopic behaviors described by the different approaches are compared and presented in the paper. The special focus is on the prediction of coefficients of magnetoelectric coupling with respect to an optimization of the structural arrangement of the composite. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of a viscous soft dielectric elastomer generator operating in an electrical circuit
Authors: Bortot Eliana , Denzer Ralf , Menzel Andreas , Gei Massimiliano
Published: December 2014

Dielectric Elastomer Generators (DEGs) are able to convert mechanical work into electric energy. A soft dielectric elastomer generator can be modelled as a strain‐dependent variable capacitor undergoing large viscoelastic deformation. In this work we analyze an electrical circuit for energy harvesting in which the DEG is stretched periodically by a source of mechanical work. Since these devices undergo a high number of electro‐mechanical loading cycles at large deformation, it turns out that viscous effects must be carefully taken into account as they strongly affect the generator performance. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of the Crosstalk Phenomenon within Electro‐Magnetic Systems from a Differential‐Algebraic Equations Point of View
Authors: Niroomand Rad Helia , Steinbrecher Andreas
Published: December 2014

In this paper, we consider modeling of the crosstalk phenomenon in electro‐magnetic systems and, in particular, in electrical circuit where electrical devices such as inductors, capacitors, and resistors are located closely together. In principle, we model the crosstalk phenomenon by bilateral coupling of two fundamental components: Electro‐magnetic induction and dynamical behavior of the electrical circuit. First, in order to describe the electro‐magnetic induction the Maxwell equations are presented. Then, to prescribe dynamical behavior of the circuit we introduce the modified nodal analysis system which is derived by the circuit equations. Finally suitable coupling relations will be outlined. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Acceleration methods for the convergence of vector sequences applied to multi‐physics problems
Authors: Erbts Patrick , Düster Alexander
Published: December 2014

Partitioned solution approaches are well‐known strategies to solve coupled problems and have demonstrated their applicability in a wide range of multi‐physical simulations. Applying a partitioned approach opens up numerous possibilities, such as connecting different solvers or combining non‐matching meshes and time‐step sizes. On the other hand such a procedure has the drawback of only conditional stability, leading to poor convergence rates or ‐ as a worst case scenario ‐ to divergent behavior. In this contribution, we will give an interpretation of the iterative coupling process as a sequence of vectors converging to an unknown limit, which indeed represents a solution to the coupled problem. In order to improve computational efficiency, there are several practicable methods to accelerate the convergence of vector sequences. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupled differential algebraic equations in the simulation of flexible multibody systems with hydrodynamic force elements
Authors: Fiedler Robert , Arnold Martin
Published: December 2014

The mathematical modelling of elastohydrodynamic bearings in combustion engines leads to a coupled system of (partial) differential algebraic equations, which is represented by a flexible multibody system model of the engine including crankshaft and bearing and by the Reynolds equation that describes the non‐linear effects in the fluid film. The hydrodynamic forces depend strongly on the position and the elastic deformation of crankshaft and bearing shell. We discuss the influence of the spatial discretization on accuracy and numerical effort. Since a fine spatial discretization substantially slows down the numerical solution, we propose a semi‐analytical method based on singular perturbation theory to speed‐up time integration. Numerical tests for a simplified benchmark problem illustrate the advantages of this approach. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐local modeling of size effects in amorphous metals
Authors: Klusemann Benjamin , Xiao Tao , Bargmann Swantje
Published: December 2014

The present contribution is concerned with the modeling of lengthscale‐dependent behavior of submicron sized amorphous metal. As these samples reach the size of a few hundred nanometers, the main deformation mechanism changes from catastrophic to a stable shear localization. For the underlying model description, we resort to a thermodynamically consistent approach. Klusemann & Bargmann [1] presented results for a small strain formulation which was extended recently to finite strains by Bargmann et al. [2]. The non‐local material model is formulated with a dual mixed finite element approach. It is shown that the proposed finite deformation model is well suited to predict the stable shear localization process in submicron‐sized metallic glasses and its size effect. The model confirms the experimental observation that with decreasing sample size the shear localization process becomes stable and delayed. The finite deformation model is able to predict the failure process in submicron‐sized metallic glasses as well as the delay of it with decreasing sample size. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)