bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessing the prudence of economic forecasts in the EU
Authors: Christodoulakis G. A. , Mamatzakis E. C.
Published: February 2009

We estimate the EU Commission loss preferences for major economic forecasts of 12 Member States. Based on a recently proposed method by Elliott, Komunjer and Timmermann (2005) the paper provides evidence of asymmetries in the underlying forecast loss preference of the Commission that tend to vary across Member States. In some cases, our results show that EU forecasts tend to display a rather optimistic picture for main economic variables, e.g. government balance, thus allowing a certain degree of leeway in the fiscal adjustment path towards the medium‐term objective of ‘close to balance’ or ‘in surplus’ of the recently revised Stability and Growth Pact. Over the period of our sample, 1970–2004, this apparent asymmetry in the underlying loss preferences tends to deter prudent advice over economic policy. Lastly, we provide an analysis on the trade‐off between loss and distribution asymmetries, for which simulation results show that the testing method is robust in the presence of skewness. Copyright © 2009 John Wiley & Sons, Ltd.
RedMD—Reduced molecular dynamics package
Authors: Górecki Adam , Szypowski Marcin , Długosz Maciej , Trylska Joanna
Published: February 2009

We developed a software package (RedMD) to perform molecular dynamics simulations and normal mode analysis of reduced models of proteins, nucleic acids, and their complexes. With RedMD one can perform molecular dynamics simulations in a microcanonical ensemble, with Berendsen and Langevin thermostats, and with Brownian dynamics. We provide force field and topology generators which are based on the one‐bead per residue/nucleotide elastic network model and its extensions. The user can change the force field parameters with the command line options that are passed to generators. Also, the generators can be modified, for example, to add new potential energy functions. Normal mode analysis tool is available for elastic or anisotropic network models. The program is written in C and C++ languages and the structure/topology of a molecule is based on an XML format. OpenMP technology for shared‐memory architectures was used for code parallelization. The code is distributed under GNU public licence and available at http://bionano.icm.edu.pl/software/. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009
H3K9 acetylation and radial chromatin positioning
Authors: Strašák Luděk , Bártová Eva , Harničarová Andrea , Galiová Gabriela , Krejčí Jana , Kozubek Stanislav
Published: February 2009

Histone variants and their epigenetic modifications determine genome function, particularly transcription. However, whether regulation of gene expression can be influenced by nuclear organization or vice versa is not completely clear. Here, we analyzed the effect of epigenetic changes induced by a histone deacetylase inhibitor (HDACi) on the nuclear radial rearrangement of select genomic regions and chromosomes. The HDACi, sodium butyrate (NaBt), induced differentiation of human adenocarcinoma HT29 cells as well as a genome‐wide increase in H3K9 acetylation. Three‐dimensional analysis of nuclear radial distributions revealed that this increase in H3K9 acetylation was often associated with a repositioning of select loci and chromosomes toward the nuclear center. On the other hand, many centromeres resided sites more toward the nuclear periphery, similar to sites occupied by chromosome X. In more than two‐thirds of events analyzed, central nuclear positioning correlated with a high level of H3K9 acetylation, while more peripheral positioning within interphase nuclei correlated with a lower level of acetylation. This was observed for the gene‐rich chromosomes 17 and 19, TP53, and CCND1 genes as well as for gene‐poor chromosome 18, APC gene, regions of low transcriptional activity (anti‐RIDGEs), and the relatively transcriptionally less active chromosome X. These results are consistent with a role for epigenetic histone modifications in governing the nuclear radial positioning of genomic regions during differentiation. J. Cell. Physiol. 220: 91–101, 2009. © 2009 Wiley‐Liss, Inc.
Analysis of the molecular mechanisms of targeted anti‐caries DNA plasmid enhancing antibody responses by gene arrays
Authors: Xu Qing‐An , Yu Fei , Fan Mingwen , Xing Quan , Liu Gaoxia , Liu Chang
Published: February 2009

Background

The cytotoxic T lymphocyte antigen 4 (CTLA4) represents an attractive ligand for use in the targeting of antigens to dendritic cells (DCs). Studies have shown that CTLA4 targeted DNA vaccines induced accelerated and increased antibody responses compared to nontargeted vaccines. However, little is known about the molecular events on DCs after transfection with targeted DNA vaccines.

Methods

Here we constructed a green fluorescent protein (GFP)‐labeled targeted anti‐caries plasmid pMGJGLU/GFP and a GFP‐labeled nontargeted anti‐caries plasmid pCDGLU/GFP, compared the antibody responses they induced in mice, and investigated the gene expression profiles of DCs transfected with pMGJGLU/GFP and pCDGLU/GFP by gene array analysis.

Results

The data obtained showed that pMGJGLU/GFP induced accelerated and increased serum antibody responses in mice compared to pCDGLU/GFP. Overall, the expression levels of 28 genes were up‐regulated in pMGJGLU/GFP transfected DCs compared to pCDGLU/GFP transfected DCs by gene array analysis. Real‐time reverse transcriptase‐polymerase chain reaction analysis on pMGJGLU/GFP transfected DCs and pCDGLU/GFP transfected DCs confirmed the up‐regulation of the mRNA expression levels of seven selected genes. Notably, we identified the specific up‐regulation of mRNA expression levels of cytokines Ccl17, Ccl19, and antigen presentation receptor Cd209a of pMGJGLU/GFP transfected DCs, suggesting a more rapid migration of DCs to lymph nodes and a T helper 2 biased immune response.

Conclusions

In the present study, we confirmed our previous reports that CTLA4 targeted DNA vaccines could induce increased antibody responses compared to nontargeted vaccines. Ccl17, Ccl19 and Cd209a may play an important role in the enhanced immune responses. Copyright © 2009 John Wiley & Sons, Ltd.
Preparation of high specific activity tritium labeled 6α,9,‐difluoro‐11β,21‐dihydroxy‐16α,17‐[(1‐methylethylidene)bis(oxy)]pregna‐1,4‐diene‐3,20‐one, fluocinolone acetonide
Authors: Zhong D. , Lewin Anita H.
Published: February 2009

Fluocinolone acetonide was tritiated by selective reduction of the 1,2‐double bond of the O‐protected analog under tritium, followed by re‐establishment of the 1,2‐double bond and deprotection. Protection of both hydroxyl functionalities was required. The product was obtained with specific activity 36.8 Ci/mmol. Copyright © 2009 John Wiley & Sons, Ltd.
Turning maneuvers in sharks: Predicting body curvature from axial morphology
Authors: Porter Marianne E. , Roque Cassandra M. , Long John H.
Published: February 2009

Given the diversity of vertebral morphologies among fishes, it is tempting to propose causal links between axial morphology and body curvature. We propose that shape and size of the vertebrae, intervertebral joints, and the body will more accurately predict differences in body curvature during swimming rather than a single meristic such as total vertebral number alone. We examined the correlation between morphological features and maximum body curvature seen during routine turns in five species of shark: Triakis semifasciata, Heterodontus francisci, Chiloscyllium plagiosum, Chiloscyllium punctatum, and Hemiscyllium ocellatum. We quantified overall body curvature using three different metrics. From a separate group of size‐matched individuals, we measured 16 morphological features from precaudal vertebrae and the body. As predicted, a larger pool of morphological features yielded a more robust prediction of maximal body curvature than vertebral number alone. Stepwise linear regression showed that up to 11 features were significant predictors of the three measures of body curvature, yielding highly significant multiple regressions with r2 values of 0.523, 0.537, and 0.584. The second moment of area of the centrum was always the best predictor, followed by either centrum length or transverse height. Ranking as the fifth most important variable in three different models, the body's total length, fineness ratio, and width were the most important non‐vertebral morphologies. Without considering the effects of muscle activity, these correlations suggest a dominant role for the vertebral column in providing the passive mechanical properties of the body that control, in part, body curvature during swimming. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.
Towards the provision of site specific flood warnings using wireless sensor networks
Authors: Smith Paul J. , Hughes Danny , Beven Keith J. , Cross Philip , Tych Wlodek , Coulson Geoff , Blair Gordon
Published: February 2009

An important aspect of flood risk management is the issuing of timely flood alerts. The spatial, as well as temporal, scale of these warnings is important. In many situations efficient risk management may be aided by the provision of local flood predictions at a high spatial resolution. Examples of such situations include issuing warnings for small groups of outlying houses or key infrastructure locations such as power sub‐stations. In this paper a methodology for providing automated, detailed and location specific warnings which are computed ‘on‐site’ is presented. Copyright © 2009 Royal Meteorological Society
Development in modeling cyclic loading of sands based on kinematic hardening
Authors: Maleki Mohammad , Cambou Bernard , Dubujet Philppe
Published: February 2009

In this paper, there is presented an elastoplastic constitutive model to predict sandy soils behavior under monotonic and cyclic loadings. This model is based on an existing model (Cambou‐Jafari‐Sidoroff) that takes into account deviatoric and isotropic mechanisms of plasticity. The flow rule used in the deviatoric mechanism is non‐associated and a mixed hardening law controls the evolution of the yield surface. In this research the critical state surface and history surface, which separates the virgin and cyclic states in stress space, are defined. Kinematic hardening modulus and stress–dilatancy law for monotonic and cyclic loadings are effectively modified. With taking hardening modulus as a function of deviatoric and volumetric plastic strain and with defining the history surface and stress reversal, the model has the ability to predict the sandy soils' behavior. All of the model parameters have clear physical meanings and can be determined from usual laboratory tests. In order to validate the model, the results of homogeneous tests on Hostun and Toyoura sands are used. The results of validation show a good capability of the proposed model. Copyright © 2009 John Wiley & Sons, Ltd.
Analysis of Dynamic Stability for Milling Processes with Varying Workpiece Dynamics
Authors: Henninger Christoph , Eberhard Peter
Published: February 2009

Dynamic stability of a milling process along of a flexible cantilever beam is investigated. The moving process point and the material removal leads to a significant change of the dynamical behavior and, therefore, to a shift of the stability boundary in the space of technological parameters. Modal reduction is applied to the beam model in order to enable an efficient stability analysis. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A nonlinear model for rotor‐shaft joints of high speed rotor systems with internal damping
Authors: Fischer Jonas , Strackeljan Jens
Published: February 2009

Viscous internal damping in joints of high speed rotor systems causes instabilities above a certain frequency of revolution. In the majority of cases a nonlinearity adjusts the stability margin towards higher frequencies.

In this paper an analytical solution of a nonlinear four degrees of freedom rotor model with internal damping is proposed, which enables to clearly analyse the influence of shaft stiffness, connection stiffness, rotor mass and shaft mass. The steady state solution of the unbalance case and the stability boundaries are deduced analytically. The stabilizing effect of the nonlinearity is shown. The analytical solutions are in good agreement with numerical results obtained by FERAN, a rotor dynamic simulation tool. A model, representing the rotor–shaft connection with an o–ring has been analyzed by a hydro pulse rig. Beneath the linear way, two further approaches to describe the measured hysteresis, a cubic and a bilinear force law are shown in the paper. The different analytical and numerical results for the whole rotor system with these three approaches are compared. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation eines Reibvorgangs an Modellen ohne dissipative Elemente
Authors: Ostermeyer G.‐P. , Meyer‐Heye B. , Müller M.
Published: February 2009

Wie in [1] gezeigt, kann die Reibzahl μ grundsätzlich als Reibleistung bezogen auf eine charakteristische Blindleistung N·v interpretiert werden. Auf der Größenskala von Asperiten sind die durch Reibung hervorgerufenen Leistungsströme zweckmäßigerweise durch ein Modell zu beschreiben, welches keine a priori dissipativen Elemente enthält. Der in [1] vorgestellte Ansatz ist in der Lage, einen idealen Coulombschen Reiber wiederzugeben. Die lokale Reibzahl eines Asperiten ist dabei sowohl von der Geometrie in der Kontaktzone als auch von der Elastizität des Untergrundes abhängig. Dieses Modell wurde erweitert, um auch multiple Kontakte und die Kontakthistorie berücksichtigen zu können. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic properties of an individual wheelset drive of a railway vehicle
Authors: Skála Ondřej , Zeman Vladimír
Published: February 2009

Spatial vibrations of an individual wheelset drive supported by rubber silent blocks in a two–axle bogie's frame of a railway vehicle are studied. The method, used for a creation of a mathematical model, is based on a decomposition of the wheelset drive into subsystems — a drive assembled from an engine and a gear transmission, a flexible composite hollow shaft and a flexible wheelset. Subsystems are modeled in local configuration spaces and they are mutually connected by deformable couplings. An adhesive characteristic in a wheel–rail contact is described using the Kalker's theory. The nonlinear mathematical model respects spatial vibrations of the drive's components and the flexible wheelset, a deformable rail ballast and it is used for investigating transient dynamic responses on different types of excitations. Experimentally investigated spatial bogie's frame displacements or displacements derived from a total model of the bogie caused by spatial irregularities of the rail track are main sources of excitations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Avoidance of friction induced vibrations on seals
Authors: Wangenheim Matthias , Kröger Matthias
Published: February 2009

In many fields of technical and non–technical applications occur friction induced vibrations. If undesired, which applies to most of these oscillations, different methods exist for their avoidance or at least reduction. A recently investigated method, the systematic treatment of contacting surfaces by different techniques is shown in this work with the example of a pneumatic seal. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vibration using for the longitudinal elasticity modulus determination
Authors: Arghir Mariana , Solea Geamilia , Borza Dan
Published: February 2009

Longitudinal elasticity modulus, E, is a material specific feature, which,. in general, is establish on the pieces by longitudinal stress. This procedure is possible to apply to the compact material but not to the sintered power parts (or porous material test pieces). For sintered parts, the establishing of Young's modulus, in this paper, it is proposed by transmition of mechanical vibrations along to the test pieces. The test pieces of compact or porous material were strained at longitudinal vibrations. It was establish the linkage between vibration and density, respective between the density and the value of the longitudinal elasticity modulus. Using the test pieces of compact material we realized the methodology to obtain the longitudinal elasticity modulus regarding the compact material, and in this way can be establish the possibility to measure with a good result the longitudinal elasticity modulus for the pieces of sintered powders or of porous material. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation model for anisotropic fibrous materials
Authors: Ask Anna , Ristinmaa Matti
Published: February 2009

Paper and paper–based materials such as cardboard are used in a wide variety of applications and in the development of new applications such as boxes an accurate simulation model is of major importance. Industrially made paper material typically has an orthotropic fibrous structure, due to the manufacturing process, where the fibers tend to align in the direction of motion in the machine. In this work a plasticity–based material model allowing for finite strains is developed. The model is suitable for materials with an anisotropic fibrous structure such as paper. The general framework is based on separate mappings describing the deformations of the continuum and the substructure and a multiplicative split of these mappings into elastic and plastic parts. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of two different models to account for induced flow anisotropy during complex loading processes
Authors: Barthel Clemens , Svendsen Bob , Levkovitch Vladislav , Wang Jian
Published: February 2009

Some metals exhibit an increase of the yield stress after orthogonal strain path changes, i.e. so–called cross hardening. Two approaches are discussed in this work which are capable of taking that effect into account in an appropriate manner. The first approach is closely related to that of Teodosiu and Hu. The second model considers besides the movement of the center of the yield surface and its proportional expansion also the change of its shape and is able to describe the induced anisotropic behavior with regard to complicated loading histories. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A micro‐macro approach to the failure of rubber‐like materials
Authors: Dal Hüsnü , Kaliske Michael
Published: February 2009

Rubbery polymers are modelled with hyperelastic constitutive laws by which the material can be stretched indefinitely or up to a certain locking stretch value. However, no material can sustain indefinite stretch and store infinite energy. Failure occurs after a threshold value for stress and/or energy is attained. Within this context, an approach for failure analysis of rubber–like materials based on the constitutive description of material is presented. The model is based on a hyperelastic material law representing the energy stored in rubber network due to the chain conformations connected in series to an interatomic bond potential representing the energy stored in the polymer chain due to the interatomic displacement. For the representation of the micro–macro transition in terms of non–affine kinematics, micro–sphere model is utilized. Morse potential is used for the description of the interatomic bond, which describes the energetic contribution to rubber–like materials and governs the failure of the polymer chain. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the constitutive inequalities and acceleration waves in micropolar media
Authors: Altenbach Holm , Eremeyev Victor A.
Published: February 2009

Acceleration waves in nonlinear thermoelastic micropolar media are considered. We establish the kinematic and dynamic compatibility relations for a singular surface of order 2 in the media. An analogy to the Fresnel–Hadamard–Duhem theorem and an expression for the acoustic tensor are derived. The condition for acceleration wave's propagation is formulated as an algebraic spectral problem. It is shown that the condition coincides with the strong ellipticity of equilibrium equations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exploitation of Configurational Forces in Extended Nonlocal Continua with Microstructure
Authors: Frankenreiter Ilona , Zimmermann Dominik , Miehe Christian
Published: February 2009

We investigate aspects of the application of configurational forces in extended nonlocal continua with microstructure. Focussing on multifield approaches to gradient–type inelastic solids, the coupled problem is governed by the macroscopic deformation field, while nonlocal inelastic effects on the microstructure are described by a family of order parameter fields. The dual macro– and micro–field equations are derived within an incremental variational framework. Using an incremental principle, due to the variation with respect to the material position, an additional balance in the material space appears with the dual macro–micro–balances in the physical space. In view of the numerical implementation of this coupled problem by a finite element method, the incremental variational framework is recast into a discrete format in terms of discrete macro– and micro–physical nodal forces and configurational nodal forces. Applying a staggered solution scheme, the configurational branch is used as a postprocessing procedure with all the ingredients known from the solution of the coupled macro–micro–problem. The procedure is implemented for a nonlocal, viscous damage model. The consequences with regard to the configurational nodal forces are assessed by means of a numerical example. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and theoretical investigation on the microstructure of aluminum alloys during extrusion
Authors: Kayser Tobias , Parvizian Farhad , Svendsen Bob
Published: February 2009

The purpose of this work is the investigation of the material behavior of aluminum alloys during extrusion and cooling. In particular, the alloys of the 6000 series (Al–Mg–Si) and 7000 series (Al–Zn–Mg) are relevant here. Under the corresponding conditions, their behavior is controlled mainly by dynamic recovery during the extrusion and static recrystallization during cooling. For the development of a suitable material model EBSD measurements are done on different parts of an extruded Al6060 specimen. For this sample a microstructure picture is generated and a statistical analysis is performed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Aspects of a direct homogenization procedure for electro‐mechanically coupled problems
Authors: Keip Marc‐André , Schröder Jörg
Published: February 2009

The aim of this work is to discuss a micro–macro homogenization procedure for electro–mechanically coupled problems. In this context a two–scale homogenization ansatz for ferroelectric ceramics based on an FE2‐approach is presented. The microscopic discretization of the heterogeneous structure of the polycrystalline material allows for the incorporation of microscopic effects, which are necessary to determine the corresponding overall macroscopic material response. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Eulerian Rate Model for Pseudoelastic NiTi Shape Memory Alloys
Authors: Luig Patrick , Bruhns Otto
Published: February 2009

A phenomenological material model for the pseudoelastic material behavior of polycrystalline NiTi is presented. It is consistently derived within the Eulerian framework using the Kirchhoff stress (weighted Cauchy stress) and the stretching tensor. Deformation–like variables such as elastic or inelastic strains are omitted. The model is based on a non–convex Helmholtz free energy function for the phases austenite and martensite, which is formulated in terms of the Kirchhoff stress, temperature, mass fraction of martensite, and a tensorial internal variable accounting for the average orientation of the martensite variants. Evolution equations for the mass fraction of martensite as well as for the average orientation of the martensite variants are derived, taking into account the restrictions imposed by thermodynamics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A higher gradient theory for solid mixtures
Authors: Müller W.H. , Brandmair A.
Published: February 2009

During use the microstructure of solders will change over time. To enable us to determine the lifetime and reliability of these materials, a theory to predict such changes is needed. In this paper two kinds of changes are considered: The forming of intermetallic compounds due to chemical reactions of two components and spinodal decomposition of a binary alloy followed by coarsening. A theoretical approach is presented and evaluated numerically. For this purpose, an extended diffusion equation is needed and derived within the framework of undisputed concepts of the entropy principle. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Amplitude‐ and temperature effects of filler‐reinforced rubber: Experiments and Modelling
Authors: Rendek Martin , Lion Alexander
Published: February 2009

Rubber–like materials exhibit special mechanical properties in a wide range of technical applications. To achieve a desired behaviour of the end product, the materials are reinforced with active fillers like carbon black. In the focus of this paper are selected cyclic–monofrequent experiments with constant strain amplitudes. Special attention will be focused to the excitation with small dynamic amplitudes. The amplitude dependence of the storage and loss moduli is known as the Payne–effect. We study the amplitude– and temperature dependence of storage and loss modulus as well as dissipation effects. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theory and Numerics of Rate‐Dependent Incremental Variational Formulations in Ferroelectricity
Authors: Rosato Daniele , Miehe Christian
Published: February 2009

This paper is concerned with macroscopic continuous and discrete variational formulations for domain switching effects at small strains, which occur in ferroelectric ceramics. The developed new three–dimensional model is thermodynamically–consistent and determined by two scalar–valued functions: the energy storage function (Helmholtz free energy) and the dissipation function, which is in particular rate–dependent. The constitutive model successfully reproduces the ferroelastic and the ferroelectric hysteresis as well as the butterfly hysteresis for ferroelectric ceramics. The rate–dependent character of the dissipation function allows us also to reproduce the experimentally observed rate dependency of the above mentioned hysteresis phenomena. An important aspect is the numerical implementation of the coupled problem. The discretization of the two–field problem appears, as a consequence of the proposed incremental variational principle, in a symmetric format. The performance of the proposed methods is demonstrated by means of a benchmark problem. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modellierung der Umwandlungsplastizität und Viskoplastizität niedrig legierter Stähle
Authors: Schneidt Andreas , Mahnken Rolf
Published: February 2009

Bei dem Hybridumformprozess zur Einstellung gradierter Strukturen werden Kalt– und Warmumformung kombiniert. Dabei ist die gleichzeitige Umformung erwärmter und nicht erwärmter Bereiche eine verfahrensspezifische Besonderheit des Prozesses. Durch die Einstellung eines vordefinierten Temperaturprofils werden Werkstücke mit gradierten und somit flexiblen Werkstoffeigenschaften erreicht. Aufgrund der simultan auftretenden kalten und erwärmten Bereiche während des Hybridumformprozesses herrschen in dem Bauteil verschiedene Gefügezustände vor. Es treten sowohl weiche perlitische und ferritische als auch harte martensitische und bainitische Gefüge auf. Der Schwerpunkt unserer Arbeit wird auf die Austenit—Martensit Umwandlung gelegt. Für die numerische Simulation wird ein makroskopisches viskoplastisches Materialmodell mit Berücksichtigung der Umwandlungsplastizität (TRIP) präsentiert. Auf der Basis experimenteller Daten wird das Materialmodell kalibriert. Aufgrund fehlender Experimente wird ein numerisches Homogenisierungsverfahren eingesetzt, um das Fließverhalten des Mischgefüges zu berücksichtigen. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Plane constrained shear of single crystal strip with one and two active slip systems
Authors: Le Khanh Chau , Sembiring Pramio
Published: February 2009

The plane constrained shear problems of a single crystal strip with one and two active slip systems are considered within the continuum dislocation theory. Analytical solutions are found for single slip and symmetric double slip systems which exhibit the energetic and dissipative thresholds for dislocation nucleation, the Bauschinger translational work hardening and the size effect. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary value problems in the theory of binary mixtures of thermoelastic solids
Authors: Svanadze Merab
Published: February 2009

In this paper the diffusion model of the linear theory of thermoelasticity of binary mixtures is considered. The basic properties of wave numbers of the longitudinal and transverse plane waves are established. The interior boundary value problem (BVP) of steady vibration of binary mixtures of thermoelastic solids is formulated. The existence theorems of eigenfrequencies of the BVP of steady vibrations are proved. The connection between plane waves and existence of eigenfrequencies is established. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of shear localization in elastic material by means of energy relaxation
Authors: Trinh Bach Tuyet , Hackl Klaus
Published: February 2009

A new approach to the problem of shear localization is proposed. It is based on the energy minimization principle associated with micro–structure developments and the micro–shearing of a rank–one laminate which is aligned to shear band. The thickness of the shear band represented by the volume fraction is assumed to tend to zero. The non–convex energy due to the formation of the shear band is solved by energy relaxation in order to ensure that the problem is well–posed. An application of the proposed formulation to isotropic linear elastic material is presented. The capability of the proposed energy relaxation is demonstrated through numerical simulation of a plane strain tension. The numerical results demonstrate that there is no mesh–dependence. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromechanical Generalization of the Mises‐Hill Anisotropy Yield Criterion
Authors: Tsotsova R. , Böhlke T.
Published: February 2009

This paper proposes a new micromechanically motivated yield criterion expressed in terms of the leading tensorial texture coefficient of the crystallite orientation distribution function. The central finding is that although only a 4th–order anisotropy tensor occurs in the expression for the yield locus, the ansatz provides significantly better results in comparison to the quadratic Hill condition. The improvement is due to cubic and quartic tensorial contributions in terms of the stress direction. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational Formulations and FE Active‐Set Strategies for Rate‐Independent Nonlocal Material Response
Authors: Welschinger Fabian , Miehe Christian
Published: February 2009

We propose a variational framework for the description of rate–independent nonlocal materials with microstructure and outline details of its numerical implementation. On the theoretical side, we focus on a multifield approach to microstructural dissipative mechanisms. To this end, the current state of the evolving microstructure is described by global fields of microscopic order parameters and their gradients, which together with the macroscopic deformation field define the multifield character of the problem under consideration. Focussing on rate–independent standard dissipative materials, the constitutive response is governed by an energy storage and a non–smooth dissipation function. For this scenario, we outline an incremental variational framework whose Euler equations define the macroscopic equilibrium along with the non–smooth global evolution of the order parameters. The formulation features fully–coupled macroscopic and microscopic field equations and associated boundary conditions. The key difficulty on the numerical side is the implementation of the global non–smooth evolution of the order parameters. Here, we outline a new active set strategy for the global finite element discretization of the multifield problem, where inequality constraints on the microscopic fields are taken into account by active nodal sets. An important consequence of the proposed variational approach is the symmetry of the coupled algebraic system. The proposed setting is specified for model problems of isotropic damage mechanics and crystal plasticity. The applicability of the proposed approach to nonlocal solids is highlighted by means of representative numerical examples. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ermittlung (der Temperaturabhängigkeit) materialspezifischer Kennwerte von Miniaturproben aus Lotgut mittels Nanoindentation
Authors: Müller Wolfgang H. , Worrack Holger , Sterthaus Jens , Wilden Johannes
Published: February 2009

Für die zuverlässige Herstellung und den Gebrauch immer kleiner werdender Geräte und Strukturen ist die Kenntnis der zugehörigen Werkstoffeigenschaften unerlässlich. Deren Ermittlung muss an Miniaturproben durchgeführt werden, da die gebräuchlichen, auf Standardproben beruhenden Verfahren keine verlässlichen Aussagen über das Materialverhalten im µm–Bereich geben. Aus diesem Grund wird hier die Ermittlung lokaler Parameter von Werkstoffen in Bauteilen in Anlehnung an die Untersuchung bleifreier Lotwerkstoffe mit Hilfe der sog. Nanoindentation beschrieben. Das Verfahren dient in erster Linie der Bestimmung von Standardwerkstoffkennwerten wie dem Elastizitätsmodul, der Fließgrenze und der Härte. Des Weiteren ist die Nanoindentation in der Lage, über den Ansatz der i nversen Methode ein vollständiges Spannungs–Dehnungs–Diagramm zu ermitteln, welches in dieser Arbeit mit dem Ergebnis eines herkömmlichen Zugversuchs verglichen wird. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A comparison of the flow around a flexible and a non‐flexible airfoil for flapping wing propulsion
Authors: Bansmer S. , Unger R. , Kähler C. , Haupt M. , Radespiel R. , Horst P.
Published: February 2009

The flow around flapping airfoils is evaluated using the Stereoscopic Particle Image Velocimetry (PIV) technique. Resulting from the measurements is the distribution of the turbulent shear stress. This serves as an indicator for the position of transition from laminar to turbulent flow. The distributions were compared for both a flapping non–flexible airfoil and a flexible airfoil. It was determined that there are differences between the flow around the flexible and the non–flexible airfoils. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nuclear solitary waves
Authors: Chen X.‐N. , Maschek W.
Published: February 2009

This paper gives an overview of our recent work on the fission solitary wave reactor concept. In order to gain an insight into this problem a simple but appropriate model, namely a one–group diffusion equation coupled with simplified burn–up equations of e.g. the common U238–Pu239 conversion chain is studied. It is shown that this coupled system is analytically solvable in its one–dimensional case and a permanent plane solitary wave exists in a fertile medium, e.g. natural uranium. This wave mechanism could realize a nuclear reactor, which possess a constant reactivity and, more importantly, improves significantly the utilization of nuclear fuel. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Finite Element Algorithm for Electromechanical Contact Problems
Authors: Weißenfels C. , Wriggers P.
Published: February 2009

In the last hundred years a lot of work is done in describing and measuring the influence of the pressure on the resistance and wear in electrical contacts. But up to now there exists a lack of knowledge in predicting and optimizing the behavior of electrical contacts with numerical simulation tools considering the pressure dependency. The present work provides a new constitutive model for the contact interface in the case of current flow and a new friction law including electrical wear phenomena. Additionally numerical investigations are made to compare the numerical results with experimental data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Point defect interaction in tranversally isotropic ferroelectrics
Authors: Goy Oliver , Mueller Ralf
Published: February 2009

Functional materials, especially ferroelectrics are used in many devices like actuators, sensors and electronic devices. Due to high amounts of mechanical and electrical load cycles, fatigue phenomena may occur. This so called electric fatigue causes a decrease of the electromechanical coupling capability. It is assumed, that the ability to switch polarisation states, which is the reason for the ferroelectric effect, is decreased in the presence of point defects. These defects are ionic and electronic charge carriers, which can interact with each other, with microstructural elements in the bulk and with interfaces. Accumulation of defects can primarily lead to degradation, because of the loss of polarisation switchability.

The interaction of defects in the bulk is simulated to get a better understanding of the defect accumulation processes. A model based on configurational forces can be used to obtain thermodynamic consistent kinetic laws. The material used is transversally isotropic and modelled with linear electromechanical coupling. The focus is on the influence of this material anisotropy on the defect interaction. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stable long‐term simulation of dynamically loaded elastomers
Authors: Groß Michael , Betsch Peter
Published: February 2009

A well–known problem in long–term simulations of flexible solid bodies is the restriction to small time steps of standard time integrators in order to obtain a stable simulation. One approach is to achieve exact energy conservation while simulating a nonlinear elastic body (see Reference [1] and the references therein). Additionally, total linear and total angular momentum is conserved for a free motion. This approach leads to a qualitatively improved solution, because the approximated time evolution exactly fulfills the same physical laws as the exact time evolution. Incorporating energy dissipation, the energy conserving time integration is extended to an energy consistent time integration. It turned out that such an energy consistent time integration is also of great advantage when computing finite motions of flexible solid bodies with material dissipation (see References [2,3]). This paper points out that an energy consistent time discretisation is also advantageous for dynamic finite deformation thermoviscoelasticity under dynamic loads. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupled Problems of Dynamics in Materially Incompressible Saturated Porous Media
Authors: Heider Yousef , Markert Bernd , Ehlers Wolfgang
Published: February 2009

The mechanical behavior of saturated porous materials is largely governed by the interaction between the solid skeleton and the pore fluid. This interaction is particularly strong in dynamic problems and leads to numerical challenges especially in the case of incompressible constituents. In fact, the permeability plays a significant role in this coupling and influences the choice of a proper time integration scheme. Proceeding from the macroscopic Theory of Porous Media (TPM) within the isothermal and geometrical linear regime, the governing balance equations of the dynamic binary solid–fluid model are the solid and fluid momentum balances, and the overall volume balance of the biphasic mixture. This set of coupled partial differential equations (PDEs) is solved within the framework of the mixed Finite Element Method (FEM) applying two different time solution methods, viz., a monolithic implicit and a splitted implicit–explicit scheme. The time stepping algorithms are implemented into the FE program PANDAS and a Scilab FE routine and compared on a one–dimensional wave propagation example. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A phenomenological constitutive model for magnetostrictive materials and ferroelectric ceramics
Authors: Klinkel Sven , Linnemann Konrad
Published: February 2009

The contribution is concerned with a thermodynamic consistent constitutive model for magnetostrictive materials and ferroelectric ceramics. It captures the nonlinear phenomenological behavior which is described by hysteresis effects. Magnetostrictive alloys and ferroelectric ceramics belong to the multifunctional materials. In recent years these materials have become widely–used in actor and sensor applications. They characterize an inherent coupling between deformation and magnetic or electric field. Due to the similarities of the coupled differential equations a uniform approach is applied for both phenomena. The presented three–dimensional material model is thermodynamically motivated. It is based on the definition of a specific free energy function and a switching criterion. Furthermore an additive split of strain and the magnetic or electric field in a reversible and an irreversible part is suggested. The irreversible quantities serve as internal variables, which is analog to plasticity theory. A one–to–one–relation between the two internal variables provides conservation of volume for the irreversible strains. The presented material model can approximate the ferromagnetic or ferroelectric hysteresis curve and the related butterfly hysteresis. Furthermore an extended approach for ferrimagnetic behavior, which occurs in magnetostrictive materials, is presented. Some numerical simulations demonstrate the capability of the presented model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermomechanical modeling and simulation of aluminum alloys during extrusion process
Authors: Parvizian Farhad , Kayser Tobias , Hortig Christian , Svendsen Bob
Published: February 2009

The purpose of this work is to simulate the microstructure development of aluminum alloys during hot metal forming processes such as extrusion with the help of the Finite Element Method (FEM). To model the thermomechanical coupled behavior of the material during the extrusion process an appropriate material model is required. In the current work a Johnson–Cook like thermoelastic viscoplastic material model is used. To overcome the numerical difficulties during simulation of extrusion such as contact problem and element distortion an adaptive meshing system is developed and applied. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asynchronous method for the coupled simulation of mechatronic systems
Authors: Petridis Kosmas , Klein Andreas , Beitelschmidt Michael
Published: February 2009

A new method for coupled simulation of mechatronic systems based on a comparison of the actual time step of the simulation tools and the utilization of inter– and extrapolation methods will be presented in this contribution. Since the method does not use constant synchronization time points, the problem of setting the appropriate macro step size is avoided. The example of a drill driver model is used to compare the results of the proposed method with those obtained by a conventional approach. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Implementation of a Free‐locking Composite Piezoelectric Shell Element
Authors: Lammering Rolf , Yang Fan
Published: February 2009

In this contribution, a free–locking shell element with piezoelectric ceramic layers is presented. The material law and the constitutive equations of the coupled electro–mechanical problem are derived in convective coordinates, so that the presented element accounts for geometrical nonlinearities [2]. To avoid zero–energy mode and locking effects of the thin shell structure, assumed natural strain (ANS) method [1] is implemented. Finally, some numerical examples demonstrate the ability of this element to solve linear and nonlinear problems. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Homogenization of Linear Elastic Properties of Silicon Nitride
Authors: Böhlke Thomas , Jöchen Katja , Langhoff Tom‐Alexander
Published: February 2009

The effective linear elastic properties of silicon nitride (Si3N4) are estimated based on first–, third–, and fifth–order bounds of the strain energy density. This specific type of material is a mixture of two linear elastic materials with different material symmetries. The β‐Si3N4 grains have a hexagonal symmetry with significant amount of anisotropy, whereas the glassy phase is approximately isotropic. The results are as follows: i) The fifth–order upper and lower bounds are almost identical. Therefore, these bounds are sufficient for estimating the effective elastic properties. ii) For fixed elastic constants of the hexagonal β‐Si3N4 grains, the effective properties of Si3N4 are determined as a function of properties of the glassy phase and its volume fraction. The corresponding diagrams allow for the inverse identification of the elastic properties of the glassy phase. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite element (FE) simulation of textile‐reinforced composites using a COSSERAT Element
Authors: Branke D. , Brummund J. , Haasemann G. , Ulbricht V.
Published: February 2009

The efficient simulation of textile reinforced composites requires reliable material parameters describing the macroscopic material behavior. Due to the micro–structure, decoupled tensile and bending stiffnesses are observed in experimental investigations. This motivates the use of higher order continuum theories. For numerical simulation of this material behavior, the formulation and application of a volume element based on the Cosserat continuum theory is presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigations on an elastic micropolar continuum model for large deformations
Authors: Jänicke R. , Sehlhorst H.‐G. , Steeb H. , Diebels S. , Düster A. , Rank E.
Published: February 2009

The mechanical behaviour of cellular materials is dominated by the influence of the microtopology. If the characteristic microstructural length scale becomes comparable to the macroscopical length scale, classical homogenisation strategies fail and have to be replaced by extended approaches. In the present contribution, we present a micropolar continuum model for large deformations introducing the microrotation as an additional degree of freedom. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On estimates for the effective shear modulus of cubic crystal aggregates
Authors: Jöchen Katja , Böhlke Thomas , Fritzen Felix
Published: February 2009

To avoid time–consuming computations, several analytical approaches can be used to estimate the elastic properties of polycrystalline aggregates. In this paper we compute some well–known bounds and estimates for the effective shear modulus of aggregates of cubic crystals and compare them with results from finite element simulations using a representative volume element (RVE). It is shown that among the evaluated approaches, the singular approximation results in the best agreement with the RVE simulations for the examined materials. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Multiscale Approach for the Modelling of Failure
Authors: Mergheim Julia
Published: February 2009

In the present contribution a multi–scale – or rather two–scale – framework for the modelling of propagating discontinuities is introduced. The method is based on the Variational Multiscale Method. The displacement field is additively decomposed into a coarse– and a fine–scale part. This kinematic assumption implies a separation of the weak form in two equations, corresponding to the coarse–scale and the fine–scale problem. Both scales are discretized by means of finite elements. On the fine–scale, due to a much finer discretization, a heteregeneous mesostructure and propagating mesocracks can be considered. The propagation of the mesocracks is simulated independently of the underlying finite element mesh by discontinuous elements. The performance of the multi–scale approach is shown by a numerical example. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)