bluuebunny/crossref_metadata_2025 huggingface dataset:
A qualitative exploration of nurses leaving nursing practice in China
Authors: Zhu Junhong , Rodgers Sheila , Melia Kath M.
Published: December 2014

Aim

This paper reports a theoretical understanding of nurses leaving nursing practice by exploring the processes of decision‐making by registered nurses in China on exiting clinical care.

Background

The loss of nurses through their voluntarily leaving nursing practice has not attracted much attention in China. There is a lack of an effective way to understand and communicate nursing workforce mobility in China and worldwide.

Design

This qualitative study draws on the constant comparative method following a grounded theory approach.

Method

In‐depth interviews with 19 nurses who had left nursing practice were theoretically sampled from one provincial capital city in China during August 2009–March 2010.

Results

The core category ‘Mismatching Expectations: Individual vs. Organizational’ emerged from leavers’ accounts of their leaving. By illuminating the interrelationship between the core category and the main category ‘Individual Perception of Power,’ four nursing behaviour patterns were identified: (1) Voluntary leaving; (2) Passive staying; (3) Adaptive staying and (4) Active staying.
Coupling‐based methods to design feedback controllers and observers for nonlinear descriptor systems
Authors: Labisch Daniel , Konigorski Ulrich
Published: December 2014

This paper presents a new approach for analysis and controller design for nonlinear descriptor systems. Thereby, we assume that the descriptor system is given in semi‐explicit form and has a continuously differentiable solution, which are very mild assumptions and are fulfilled for most practical applications. Based on the known coupling controller design we transfer the analysis and synthesis from the descriptor system to an equivalent system in state‐space form. Methods like dynamic and static input‐output decoupling, input‐output linearization, model‐based feedforward‐controller design, zero dynamics, exact descriptor linearization, linear time variant Riccati control, and causal observer design have been introduced based on the coupling procedure [9]. In the following, we summarize the new approach and an algorithm to compute the required state‐space system. Additionally, a short introduction how to use it for decoupling control, Riccati control, and causal observer design is given. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parametric Reduction of FE Models with Variable Mesh Topology
Authors: Mohring Jan
Published: December 2014

Designing whole machines or processes you may need both, an integrated dynamic simulation of all components on system level and a detailed analysis of how the macroscopic behavior of a component depends on geometry and material parameters. The former analysis is usually based on systems of differential algebraic equations representing a component by not more than a few hundred states and requires tools like Matlab‐Simulink® or Dymola®. The latter analysis solves discretized partial differential equations with several 100,000 degrees of freedom using finite element software like Ansys® or Comsol®. Model reduction bridges the gap between the two worlds providing small state space models with approximately the same input‐output behavior as the original large finite element models. Building systems from generic components, e.g. a gas transport network from pipeline models with variable length, or optimizing the design of a device with respect to mechanical or thermal properties, we need parametric reduced models. The idea is to reduce FE models offline for selected parameter sets and to generate models for new parameters by cheap interpolation rather than expensive reduction. The different approaches to parametric linear model reduction may be divided into three classes [1]. Interpolation of transfer functions is well suited for parabolic or highly damped hyperbolic problems. However, poles are duplicated rather than shifted, which is unacceptable for weakly damped hyperbolic problems like in mechanics. The second class of methods look for a basis of state space covering system behavior over the full range of parameters. They share the critical assumption that number and meaning of states do not change with the parameters. In terms of finite elements this means that the meshes for different design parameters are morphed variants of the same reference mesh.This may become a severe restriction in practice when automatic meshing is to be applied to complicated geometries. Therefore, we propose a method from the third class, which is based on interpolating reduced system matrices [2]. Only those parts of the mesh need to share a constant topology where nodal inputs are applied and outputs are collected. The inner mesh, however, may change for different parameters. The main challenges arise from the fact that state space representations of a system are unique only up to a change of basis and that interpolating matrices which refer to non‐fitting bases may cause arbitrary errors. In the article we will show how problems like leaving and entering modes or eigenvalue crossing can be overcome by using normal forms and eigenvalue tracking in parameter space. The method, which is implemented in the Fraunhofer Model Reduction Toolbox, is applied to a parametric model of a mechanical device the eigenfrequencies of which have to be kept away from some dominant excitation frequencies. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Higher order Trefftz‐like Finite Element Method on meshes with L‐shaped elements
Authors: Weißer Steffen
Published: December 2014

In 2009, the BEM‐based FEM was introduced as an numerical approach for the treatment of boundary value problems. It is a Finite Element Method (FEM) that uses Trefftz‐like basis functions which are defined to fulfil the underlying differential equation locally and which are treated by means of Boundary Element Methods (BEM). Due to the implicit definition of basis functions, this approach is applicable on general polygonal and polyhedral meshes and yields conforming approximations. The elements of the discretization do not necessarily have to be convex. After a review of the recent development of higher order basis functions the method is applied to a model problem on a sequence of meshes with L‐shaped elements. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Error analysis for co‐simulation with force‐displacement coupling
Authors: Arnold Martin , Hante Stefan , Köbis Markus A.
Published: December 2014

Co‐simulation is a simulation technique for time dependent coupled problems in engineering that restricts the data exchange between subsystems to discrete communication points in time. In the present paper we follow the block‐oriented framework in the recently established industrial interface standard FMI for Model Exchange and Co‐Simulation v2.0 and study local and global error of co‐simulation algorithms for systems with force‐displacement coupling. A rather general convergence result for the co‐simulation of coupled systems without algebraic loops shows zero‐stability of co‐simulation algorithms with force‐displacement coupling and proves that order reduction of local errors does not affect the order of global errors. The theoretical investigations are illustrated by numerical tests in the novel FMI‐compatible co‐simulation environment SNiMoWrapper. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Limitations of computing time savings in variational multirate integrations
Authors: Gail Tobias , Leyendecker Sigrid , Ober‐Blöbaum Sina
Published: December 2014

For systems that contain slow and fast dynamics, variational multirate integration schemes are used. These schemes split the system into parts which are simulated using a time grid consisting of micro and macro nodes. This leads to computing time savings, however not unlimited, for a certain number of micro steps per macro step the computing time is minimal. To find a relation between this minimum computing time and the number of variables in the system, the computing time for the Fermi‐Pasta‐Ulam problem (FPU) is measured for different numbers of masses and different numbers of micro steps. In addition, the numerical convergence of the variational multirate integration is shown for the FPU. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the history of lateral vehicle dynamics
Authors: Schiehlen Werner
Published: December 2014

The lateral motion of vehicles on tracks and roads is characterized by the rolling contact between wheels and guideway. Railway vehicles feature passive lateral guidance while road vehicles are operated by steering. Lateral dynamics is an extremely complex problem but the fundamental behaviour can already understood by strongly simplified mechanical models. In this paper the historical development of modelling approaches for lateral dynamics is reviewed what is very helpful for benchmarking and checking more complex problems, too. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A structure preserving approach to the simulation of non‐smooth dynamics
Authors: Koch Michael W. , Leyendecker Sigrid
Published: December 2014

The investigated multibody dynamics involve perfectly elastic, partially elastic and perfectly plastic contacts and a structure preserving approach is used in forward dynamics and optimal control simulations. The applied mechanical integrator is based on a constrained version of the Lagrange‐d’Alembert principle and it represents exactly the behaviour of the analytical solution concerning the consistency of momentum maps and symplecticity: it is called symplectic momentum scheme. To guarantee the geometric exactness during the establishing or releasing of contacts, the non‐smooth problem is solved including the computation of the contact configuration, time and force, instead of relying on a smooth approximation of the contact problem via a penalty potential. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New forms of the equations of the attitude kinematics
Authors: Mladenova Clementina D. , Brezov Danail S. , Mladenov Ivaïlo M.
Published: December 2014

In the present paper, a new formalism for obtaining the kinematical equations of a rigid body motion is proposed. It is based on an alternative parameterization of the Lie group SO(3). Here we provide a new description of attitude kinematics by means of decomposing an arbitrary rotation into a pair of successive rotations about a fixed axis û and a varying one v̂, which is perpendicular to û. Then û, v̂ and û × v̂ constitute a basis, in which it is most natural to obtain the kinematic equations. The latter appear to be quite simple when they are expressed in terms of the vector‐parameter provided that the rotation about the fixed axis is applied first (in the body reference frame). The procedure is illustrated in different situations, in which explicit solutions are available. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling the Physiological Behavior of Arterial Walls – Comparative Study Regarding the Viscoelastic Response
Authors: Fausten Simon , Balzani Daniel , Schröder Jörg
Published: December 2014

This contribution deals with the modeling of the physiological behavior of arterial walls, in order to enable a reliable calculation of the transmural stress distribution including also the active response of arterial tissue. Therefore, a simple viscoelastic model, which only requires few material parameters, is considered. Furthermore, a comparative study, investigating the influence of viscoelasticity on the mechanical behavior of arterial walls, is presented. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Remodeling of soft tissues due to cell activity
Authors: Yi Jeong‐Hun , Stoffel Marcus , Weichert Dieter , Rath Björn , Markert Bernd
Published: December 2014

The continuum mechanical modeling of collagenous biological tissues is of interest in the field of biomedical engineering. Particularly, the change of material properties as a result of cell activity is of great interest, as chondrocyte (cartilage cell) implantation yields significant functional improvement.

The aim of the contribution is to present the remodeling phenomenon of a cellular material due to cell activity, which results in synthesis of collagen type‐II fibers. For the experimental study, cellular condensed gel is mechanically stimulated in a bioreactor for four weeks. The change of the stiffness of the gel is measured in a compression test. The remodeling process is theoretically derived by an appropriate evolution law in the framework of continuum mechanics. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Multi‐Component Description of Osmotic Driven Deformations in Articular Cartilage
Authors: Albrecht Daniel , Ricken Tim , Pierce David M.
Published: December 2014

This study focuses on a formulation within the theory of porous media (TPM) for continuum multicomponent modeling of osmotic driven deformation in articular cartilage. The cartilage consists of porous solid matrix (extracellular matrix(ECM)),which is reinforced by collagen fibers and saturated by a fluid phase. The solid and fluid phases are considered as immiscible constituents occupying spatially their individual volume fraction. However, both phases include electrolytes, which are responsible for the osmotic pressure. The collagen fiber induce both, a transverse‐isotropic stress and permeability behavior which is represented in the modal approach by an invariant‐based description for the stress and anisotropic permeability tensor for the fluid flow, respectively. The osmotic pressure is captured by considering the electro‐chemical potential of the electrolytes. After discussing the main details of the large‐strain coupled poro‐osmotic‐hyper‐elastic model approach, a brief numerical example is given. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and numerical investigation of a degradable collagen foil
Authors: Willenberg Wolfgang , Stoffel Marcus , Markert Bernd
Published: December 2014

A collagen foil, which plays an important role for cultivating and investigating tendon cells, is investigated experimentally and numerically: The foil, which should later serve as a scaffold for tendon cells in a custom made bioreactor, is stimulated periodically in an in situ experiment. Additionally, a material model to describe the anisotropic structure and the relaxation behaviour of the collagen foil is used to simulate the material response. By comparing the measurements and simulations, the stress and strain states in the foil can be determined. Hence, the material parameters for the presented experimental set up are identified. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experiments and numerical simulations on damage behavior of biaxially loaded specimen
Authors: Brenner Daniel , Gerke Steffen , Brünig Michael
Published: December 2014

The paper deals with the effect of stress state on damage and failure behavior of isotropic ductile metals. In the continuum damage model the damage behavior of ductile metals is adequately described by a generalized damage condition and an anisotropic damage rule. The damage criterion is based on series of uniaxial experiments with differently notched specimens and corresponding numerical simulations as well as on various numerical calculations on the micro‐scale. Different branches of the damage criterion depending on stress triaxiality and Lode parameter are considered. To be able to validate the proposed stress‐state‐dependent functions new experiments with two‐dimensionally loaded specimens have been developed. Corresponding numerical simulations show that these shear‐tension and shear‐compression tests cover a wide range of stress triaxialities and Lode parameters. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and Simulation of Damage Processes based on a Gradient‐Enhanced Free Energy Function
Authors: Schwarz Stephan , Junker Philipp , Hackl Klaus
Published: December 2014

Taking into account softening effects in connection with conventional inelastic material models can cause ill‐posed boundary value problems. These problems can be established by obtaining no unique solution for the resulting algebraic system or by having a strong mesh dependence of the numerical results. This is the consequence of losing ellipticity of the governing field equations. A possible approach to solve these problems is to introduce a non‐local field function in the model which includes an internal material length scale. For this purpose a gradient‐enhanced free energy function is used for the current continuum damage model from which two variational equations are resulting. Calculations with less effort can be achieved due to the enhancement of the free energy function in comparison to other approaches. The mentioned model is applied to a material with locally varying damage properties (yield limits). Furthermore, the model is able to describe crack propagation in cases of completely damaged material. Therewith, a matrix material including precipitates, such as carbides, is modeled. This allows to investigate ship screws, which usually exhibit the mentioned composition, with regard to the influence of cavitation. Cavitation describes the implosion of risen vapor bubbles, whereby the impact on screws causes heavy damages which can lead to a complete destruction. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micro‐mechanical analyses of the effect of stress triaxiality and the Lode parameter on ductile damage and failure
Authors: Hagenbrock Vanessa , Gerke Steffen , Brünig Michael
Published: December 2014

The paper deals with the effect of different stress states on plastic deformations, damage and fracture of ductile materials. To be able to model these effects a continuum damage model has been introduced taking into account the dependence of stress‐state on the constitutive equations. The model is based on the introduction of damaged and fictitious undamaged configurations. All parameters appearing in the constitutive equations are stress‐state‐dependent which can be characterized by the stress intensity, the stress triaxiality and the Lode parameter. Only experiments are not adequate enough to determine all constitutive parameters. Thus, additional series of three‐dimensional micro‐mechanical simulations of representative volume elements have been performed to get more insight in the complex damage mechanisms. These simulations cover a wide range of stress triaxialities and Lode parameters in tension, shear and compression domains. After all, the results from the micro‐mechanical simulations are used to suggest the damage equations and to identify corresponding parameters. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of deformation‐induced phase transformation during very high cycle fatigue (VHCF) using the boundary element method
Authors: Hilgendorff P.‐M. , Fritzen C.‐P. , Grigorescu A. , Zimmermann M. , Christ H.‐J.
Published: December 2014

A microstructural simulation model is proposed which accounts for damage accumulation in shear bands and deformation‐induced martensite formation in a metastable austenitic stainless steel (AISI304). The model is numerically solved using the two‐dimensional (2‐D) boundary element method. By using this method, sliding displacements can be directly evaluated in shear bands and austenite grains as well as generated martensite domains with their individual mechanical properties and shape deformation can be considered. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strategies for the Computation of Configurational Forces in Dissipative Media
Authors: Kuhn Charlotte , Lohkamp Richard , Müller Ralf , Schneider Frank , Aurich Jan C.
Published: December 2014

Configurational forces can be interpreted as driving forces on material inhomogeneities such as crack tips. In dissipative media the total configurational force on an inhomogeneity consists of an elastic contribution and a contribution due to the dissipative processes in the material. For the computation of discrete configurational forces acting at the nodes of a finite element mesh, the elastic and dissipative contributions must be evaluated at integration point level. While the evaluation of the elastic contribution is straightforward, the evaluation of the dissipative part is faced with certain difficulties. This is because gradients of internal variables are necessary in order to compute the dissipative part of the configurational force. For the sake of efficiency, these internal variables are usually treated as local history data at integration point level in finite element (FE) implementations. Thus, the history data needs to be projected to the nodes of the FE mesh in order to compute the gradients by means of shape function interpolations of nodal data as it is standard practice. However, this is a rather cumbersome method which does not easily integrate into standard finite element frameworks. An alternative approach which facilitates the computation of gradients of local history data is investigated in this work. This approach is based on the definition of subelements within the elements of the FE mesh and allows for a straightforward integration of the configurational force computation into standard finite element software. The suitability and the numerical accuracy of different projection approaches and the subelement technique are discussed and analyzed exemplarily within the context of a crystal plasticity model. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computation of crack propagation in 3‐dimensional anisotropic solids
Authors: Steigemann Martin , Specovius‐Neugebauer Maria
Published: December 2014

This contribution presents ideas, how crack propagation in three‐dimensional solids composed of anisotropic materials can be predicted using the Griffith energy principle. Since the work of Irwin the change of potential energy caused by a straight elongation of a crack in an isotropic two‐dimensional homogeneous structure can be expressed in quadratic terms of the stress intensities at the crack tip. This result was generalized in the last decades using methods of asymptotic analysis by many authors [1] to more complicated geometries, to anisotropic and inhomogeneous materials. With the energy release rate at hand, quasi‐static scenarios of crack propagation can be simulated for plane problems [2], but this is still a complicated task for three‐dimensional problems [3]. We show an idea how the change of energy caused by propagation of a crack surface in a fully three‐dimensional solid of nearly arbitrary shape can be computed in anisotropic materials. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Solution of the Consistently Linearized Eigenproblem by Means of a Finite Difference Expression for Approximation of a Directional Derivative in MSC.MARC
Authors: Pavlicek Stefan , Xia Jin , Mang Herbert A.
Published: December 2014

More recently, a concept of energy‐based categorization of buckling was proposed. It represents a symbiosis of mechanics of solids and spherical geometry. The fundamental mathematical background of this concept is the so‐called consistently linearized eigenproblem. The numerical solution of this eigenproblem by means of the finite element method is a key issue of the mentioned concept. This solution is obtained with the help of the commercial finite element software MSC.MARC. An iterative process, involving the programming lanuages PYTHON and FORTRAN 77 and the software MATLAB, is devised, making use of the available element library, of different types of solvers, and of further modeling tools. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shaking table tests of a plate‐column structure with semi‐active tuned mass damper
Authors: Majcher Krzysztof
Published: December 2014

This paper presents selected results of experimental tests carried out on the three‐storey plate‐column structure, which is a physical model of a building. On the top floor the semi‐active tuned mass damper (STMD) is installed. That device is a kind of harmonic oscillator with a variable stiffness characteristic. The tuning of STMD is possible in the frequency range from 0 to 5 Hz, which allows to counteract the resonant vibration of plate‐column structure for the three basic frequencies. The model's vibration are kinematically excited by using the earthquake simulator. It is assumed that during an experimental tests the plate‐column structure's vibration are only excited by horizontal component of base motion (dominant influence on building's vibration). The aim of the experimental analysis presented in this paper is to verify the effectiveness of the semi‐active tuned mass damper in vibration's amplitude reduction of the main structure. The tested device is prototype of STMD, which uses a competitive constructional solution of stiffness parameter control. By reason of above, special attention is focused on the testing of vibration eliminator in two aspects: change of stiffness characteristic (the rate of change), and the accuracy of tuning to the resonant frequencies. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermomechanical contact of rubber‐like solids on rough surfaces
Authors: Beyer Robert , Nackenhorst Udo
Published: December 2014

The contact between tires and the rough road surface is characterized by large local deformations of the tread rubber at high frequency, which result from the penetration of the tread blocks by the highest asperities. These deformations have an influence on the overall performance of tires regarding rolling resistance, sustainability as well as noise radiation. As the mechanical behavior of rubber compounds is strongly rate dependent these deformations cause local energy dissipation. The induced temperature increase affects the mechanical properties of the rubber. A description of the interdependence of mechanical and thermal behavior requires the solution of a coupled problem.

In this contribution the tread rubber compound is modeled with an incompressible, thermo‐visco‐elastic constitutive law in the regime of finite deformations taking into account internal friction and the Gough‐Joule effect. The thermomechanical coupling is treated with the isothermal operator split scheme. Here, the mechanical subproblem is solved in a first phase at a constant temperature. Within this phase, the rough surface contact problem of the tread block with the road is treated. The road surface is a representation of a measured real road texture, which has been obtained by applying the fast Fourier transform. In the subsequent thermal phase the heat conduction problem is solved. Here, the mechanical dissipation within the bulk material acts as a heat source. The developed algorithm is applied for a detailed study on the thermomechanical effects occurring in the tire‐road contact interface. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface Deformation due to Shear and Ploughing in a Halfspace
Authors: Beyer Florian , Willner Kai
Published: December 2014

Sheet and bulk metal forming are widely used manufacturing methods. The interaction between worktool and workpiece in such a process causes friction which has a remarkable impact on the expended energy of the process. Therefore the influence of friction is important. Friction can be split into shearing and ploughing [1]. Ploughing is the plastic deformation of a soft surface by a hard contact partner. Shear forces are only transferred in the real contact area where material contact occurs. The investigation of the contribution of both ploughing and shearing to the total friction resistance is done with the use of an elasto‐plastic halfspace model. The multiscale character of surfaces demands a fine discretization, which results in numerical effort. While a finite element method takes into account both surface and bulk of the contact partners, the halfspace model only regards the contact surfaces and thereby consumes less computing capacity. In order to identify the friction resistance, two rough surfaces get into contact. After full application of the normal load, the surfaces are moved relatively to each other. New asperities of the contact surfaces get into contact and are plastically deformed. These deformations are used to estimate the ploughing effect in dependency on the relative displacement. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An improved mixed finite element based on a modified least‐squares formulation for hyperelasticity
Authors: Schwarz Alexander , Steeger Karl , Schröder Jörg , Starke Gerhard , Müller Benjamin
Published: December 2014

The present work deals with the solution of geometrically nonlinear elastic problems solved by the least‐squares finite element method (LSFEM). The main goal is to obtain an improved performance and an accurate approximation in particular for lower‐order elements. Basis for the mixed element is a first‐order stress‐displacement formulation resulting from a classical least‐squares method. Similar to the ideas in SCHWARZ ET AL. [1] a modified weak form is derived by the introduction of an additional term controlling the stress symmetry condition. The approximation of the unknowns follows the same procedures as for a conventional least‐squares method, see e.g. CAI & STARKE [2]. The proposed modified formulation is compared to recently developed classical LSFEMs, in order to show the improvement of performance and accuracy. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Deep drawing of a layered composite: material characterization and finite‐element simulation
Authors: Sguazzo Carmen , Harhash Mohamed , Grafenhorst Matthias , Palkowski Heinz , Hartmann Stefan
Published: December 2014

Composite materials are widely used in different industrial fields, because of their good formability and their high strength to weight ratio. In the present work a triple‐layered sandwich composite is investigated. Experimental tests at room temperature are carried out for the materials constituting the composite. A finite element model of a deep‐drawing process of the composite is performed, where a finite strain constitutive model for the metal part, with material parameters calibrated to uniaxial tensile tests, has been implemented. Experimental results are compared to the numerical simulations in view of validation purposes. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of the lamination stack's behavior simulated with a multi‐scale homogenization using a progressive contact formulation
Authors: Luchscheider Vera , Maidorn Mischa , Willner Kai
Published: December 2014

The influence of the lamination stack on the mechanical behavior of an electrical motor is significant, especially for lightweight designs. Information about the stack's behavior is relevant for a proper calculation of the whole motor. This behavior is dependent on the contact between the single sheets resulting from the roughness and the behavior of the roughness peaks. The normal behavior is an elasto‐plastic and progressive one, which results mainly of the number of roughness peaks in contact. Whereas the tangential micro‐slip behavior is dependent on the single contacts and the friction coefficient. Both behaviors can be described by models and thus it is possible to calculate the behavior of a whole stack using an homogenization based on representative volume elements. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Energy harvesting by coupled oscillators forced by excitations with harmonic and random components
Authors: Litak Grzegorz
Published: December 2014

We examine an energy harvesting system of two magnetopiezoelastic oscillators coupled by electric circuit and driven by a combination of harmonic and stochastic ambient disturbances. The effects of synchronization and escape from a single potential well are discussed. In the system with relative mistuning in the stiffness of the harvesting oscillators, we show the dependence of the voltage output for different noise levels and excitation frequency. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Untersuchung von Einflussparametern auf das Phänomen der Regen‐Wind induzierten Schwingungen
Authors: Seidel Christian , Dinkler Dieter
Published: December 2014

Regen‐Wind induzierte Schwingungen sind ein hydroaeroelastisches Schwingungsphänomen, welches bei gleichzeitigem Auftreten von Regen und Wind an geneigten Kabeln, Hängern oder Seilen entstehen kann. Das Phänomen tritt bei turbulenzarmem Wind mit Geschwindigkeiten von 5 bis 30 m/s und Reynoldszahlen im unterkritischen und kritischen Bereich (5 · 104 bis 3 · 105) auf. In der Literatur werden Schwingungen sowohl in Längs‐ als auch in Querrichtung des Windes mit Amplituden bis zu 1,73 m und mit Frequenzen bis zu 9 Hz beschrieben. Der Wind kommt beim Auftreten der Schwingungen meist aus ausgezeichneten Anströmrichtungen zur Zylinderlängsachse. Die untersuchten Zylinderstrukturen sind i.a. geneigt und besitzen Durchmesser von 4 bis 25 cm. Neben einer geringen Dämpfung weisen alle Zylinderstrukturen eine glatte Oberfläche (i.a. HDPE‐Überzüge) auf. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generalized distortional hardening in a thermomechanically coupled framework
Authors: Bartels Alexander , Mosler Jörn
Published: December 2014

In many metals like aluminum the evolution of the microstructure leads to an evolution of the macroscopic yield surface. Clearly, isotropic and kinematic hardening models cannot capture this effect realistically. For that purpose, a new generalized distortional hardening model is proposed. This novel approach belongs to the class of so‐called generalized standard materials and is thermodynamically consistent. Although the approach is relatively simple, it shows several advantages like yield surface convexity and yield limit saturation. This novel model is embedded into a thermomechanically coupled finite strain framework. Several numerical simulations show the predictive capabilities. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Compendium on the Principle of the Minimum of the Dissipation Potential for Non‐Isothermal Processes
Authors: Junker Philipp , Makowski Jerzy , Hackl Klaus
Published: December 2014

In this paper we present a compendium of the original paper “The Principle of the Minimum of the Dissipation Potential for Non‐Isothermal Processes”, published in Continuum Mechanics and Thermodynamics [1]. There, a contribution to the methodology of material modeling was introduced by presenting a potential‐based approach for non‐isothermal processes. It was based on the principle of the minimum of the dissipation potential which was used previously only for isothermal material models. In contrast to the principle of maximum dissipation, the presented procedure resulted in mathematically simplified equations. Due to its potential character, the inclusion of constraints was very simple. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Configurational Forces in Cutting Processes of Microstructured Titanium
Authors: Lohkamp Richard , Kuhn Charlotte , Müller Ralf , Aurich Jan C. , Schneider Frank
Published: December 2014

The micro cutting process of microstructured material is influenced by the heterogeneity of the microstructure. In case of cp‐titanium an hcp crystal structure is present. Therefore the material response is described with elastic anisotropy and crystal plasticity with the prismatic and basal slip systems of cp‐titanium. Also self and latent hardening are considered. The rate dependency is taken into account by a visco‐plastic evolution law. In order to investigate a micro cutting process the concept of configurational forces for standard dissipative media is used. Within the finite element method an example illustrates the effects of the heterogeneity and the grain boundary on the configurational force. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On physics‐based crystal plasticity models: Application to virtual material testing of sheet metals
Authors: Pagenkopf Jan , Baiker Maria , Helm Dirk
Published: December 2014

It is possible to pursue a multi‐scale modeling approach for sheet forming simulations by applying the concept of virtual material testing to determine the yield surface from the microstructure of a given material. Full‐field simulations with phenomenological crystal plasticity models are widely used for this kind of investigations. However, recent developments focus on incorporating physical quantities like dislocation density into these models. In this work, a dislocation density based crystal plasticity model is used to investigate the plastic anisotropy of the deep drawing steel DC04. In particular, we focus on the prediction of R‐values, which can be used to calibrate macroscopic plasticity models. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Distribution of dislocation density and residual stresses in plastically deformed specimens: numerical studies
Authors: Shutov A. V. , Silbermann C. , Ihlemann J.
Published: December 2014

A two‐scale approach to the simulation of mechanical properties of metallic materials is considered. On the macroscopic level, the material behavior is described by a phenomenological model of finite strain viscoplasticity with nonlinear kinematic hardening. In particular, the process‐induced plastic anisotropy is captured by backstresses. On the microstructural level, the so called “load path sensitive two‐population dislocation cell model” is implemented. It describes an evolving dislocation cell structure with dislocation populations for dislocation cell walls and the cell interior. Owing to the coupling with the phenomenological plasticity model, it can describe the evolution of the dislocation densities depending on the load path. The applicability of the multiscale approach to the FEM simulation of severe plastic deformation processes such as Equal Channel Angular Pressing is demonstrated. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extension of a uniaxial model with Payne effect by the description of the Mullins effect and generalization to three dimensions
Authors: Freund Michael , Rabkin Michael , Ihlemann Jörn
Published: December 2014

In order to simulate the Payne effect of filler reinforced elastomers under cyclic loading a one‐dimensional material model for uniaxial tension and compression has been developed. It is able to cover the decrease of the dynamic stiffness with increasing loading amplitude (Payne effect) as well as the dependency of the stiffness on the static preload. The model has been extended by the description of the Mullins effect using modified strains for the computation of the uniaxial stresses. The subsequent generalization to a fully three‐dimensional constitutive model for the finite element method is achieved by using the concept of representative directions in form of a numerical integration of uniaxial stresses over a unit sphere. Finally, the generalized model is validated by means of experimental data of different rubber materials and testing procedures. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the parameter identification of visco‐hyperelastic material models for adhesive tapes
Authors: Kröger Nils Hendrik , Juhre Daniel
Published: December 2014

In this work we investigate the performance of a visco‐hyperelastic material model to predict the time‐dependent deformation behaviour of highly elastic adhesives. The model is based on the hyperelastic Arruda‐Boyce model with a Prony series approach. The parameter identification is conducted for fixed relaxations times which are predicted via evaluating an integral ansatz for the shear modulus. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On operator split technique for the time integration within finite strain viscoplasticity in explicit FEM
Authors: Silbermann Christian B. , Shutov Alexey V. , Ihlemann Jörn
Published: December 2014

In this contribution, the operator split technique is applied to the time integration within viscoplasticity for explicit FEM. As an example, the finite strain viscoplastic material model of Shutov and Kreißig is analyzed. In the new solution scheme, some evolution equations are solved using an explicit update formula for implicit time stepping. The solution procedure is split into three steps: an elastic predictor and two viscoplastic corrector steps. Aspects of accuracy and stability of the algorithm are discussed. As shown, the proposed method is superior compared to a fully explicit integration of evolution equations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A finite elasto‐plasticity model for thick adhesive layers based on generalized stress‐strain measure
Authors: Kieser Florian , Klinkel Sven
Published: December 2014

The collective term adhesives includes a wide field of materials with a diversity of different material properties. Regarding high‐strength adhesives, the assumption of small strains often holds according to their brittle behavior. The experience with plasticity models based on the additive decomposition into elastic and inelastic strains indicates an appropriate approach to characterize such materials. In some cases, due to a more ductile material response, the assumption of infinitesimal strains is not valid anymore. In particular this is the case for high‐strength adhesives with additives like rubber. But ductile behavior is also observed for specific stress states in one adhesive, e.g. when the behavior for tensile is quite brittle while large shear‐strains could appear. The objective of this work is to overcome the theoretical restriction of small strains and to archive the practical experiences. For the failure criterion two stress invariants are used, which involves the hydrostatic pressure as well as the deviator stress state. The flowrule is introduced for the evolution of the inelastic variables. Herein the flow rule has to be of non‐associated type to ensure the thermodynamical consistency of the model. The plasticity model also includes hardening as well as softening. The presented finite strain model makes use of the fact that the eigenvalues for Green‐Lagrange strains and generalized strains are the same. Thus the limit of applicability is extended to finite strains. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On effects of discretization and the selection of constitutive equations on stability of continua
Authors: Béda Peter
Published: December 2014

In classical continuum mechanics the set of basic equations consists of the equation of motion, the kinematic equation and the constitutive equations. The study concentrates on constitutive modeling and the effects of discretization on stability problems. The method of investigation is analytic, the spectra of linear mapping operators of continuous and discrete dynamical systems are studied. As results cases are found, when a hidden incursive nature of a material model leads to unstable behavior of the continuum. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An anisotropic large strain plasticity model for multifilament yarns
Authors: Donner Hendrik , Ihlemann Jörn
Published: December 2014

Important industrial rubber components like tyres, driving belts and air springs are usually reinforced by twisted polymer cords. A cord itself is a twisted structure of several multifilament yarns. Each yarn is a twisted strand consisting of a large number of polymer filaments. In this work, an anisotropic large strain plasticity model is presented which captures the yarn's filament structure and frictional behaviour. The material model is implemented in Abaqus adopting its user subroutine UMAT and validated by a simulation of a cord's twisting process and the comparison with microscope images. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A macroscopic consitutive model on induced anisotropy for polymers with weighting functions
Authors: Dammann Christian , Mahnken Rolf
Published: December 2014

The alignment of polymer chains is a well known microstructural evolution effect due to straining of polymers. This has a drastic influence on the macroscopic properties of the initially isotropic material, such as a pronounced strength in the loading direction of stretched films. Experiments on strain induced anisotropy at room temperature are analyzed by optical measurements. For modeling the effect of strain induced anisotropy a macroscopic constitutive model is presented. As a key idea, weighting functions are introduced to represent a strain‐softening/hardening‐effect to account for induced anisotropy. These functions represent the ratio between the total strain rate and a structural tensor. In this way, material parameters are used as a sum of weighted direction related quantities. In the finite element examples we simulate the cold‐forming of amorphous thermoplastic films below the glass transition temperature subjected to different re‐loading directions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multi‐scale modeling of double network hydrogels
Authors: Külcü İsmail Doğan , Dargazany Roozbeh , Itskov Mikhail
Published: December 2014

A double network hydrogel (DN gel) is a class of elastomeric gels formed by polyelectrolyte and neutral polymer networks. The DN gel is the toughest material among the conventional hydrogels. It shows inelastic features such as necking instability [1] and the stress softening [2], similar to that one known in elastomers. In this contribution, we purpose a micro‐mechanically motivated model to characterize relation between internal damage and inelastic deformations in the DN gel. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of Single Crystal Magnetostriction Based on Numerical Energy Relaxation Techniques
Authors: Buckmann Karsten , Kiefer Björn , Bartel Thorsten , Menzel Andreas
Published: December 2014

In this work, an incremental energy minimization technique is proposed to simulate the magnetomechanically‐coupled, nonlinear, anisotropic and hysteretic response of single crystalline magnetic shape memory alloys (MSMA). The model captures the three key physical mechanisms that cause this characteristic behavior, namely the field‐ or stress‐induced martensite variant reorientation (twin boundary motion), magnetic domain wall motion, and local magnetization rotation, through an (incremental) energy minimizing evolution of internal state variables. Representative numerical response predictions are presented, compared to experimental observations, and discussed with respect to the associated microstructure evolution. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and Simulation of Rate‐Dependent Magneto‐Active Polymers
Authors: Haldar Krishnendu , Kiefer Bjoern , Menzel Andreas
Published: December 2014

In the present work, the magneto‐viscoelastic behavior of MAPs is studied by a thermodynamically consistent constitutive model. A finite deformation based framework of nonlinear magneto‐viscoelastic coupling is introduced with a multiplicative decomposition of the deformation gradient. The viscosity is captured by evolution equations of the internal variables introduced. We propose energy functions for pure magnetic and magneto‐mechanical coupling such that saturation behavior of the magnetostriction and magnetization is captured. After having established the general framework, the model is studied for homogeneous deformations for the purpose of a least‐square‐based parameter identification from experimental data. The model predictions of non‐linear magneto‐mechanical responses with strong rate and field dependency are presented. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Laminate‐based modelling of microstructure and switching in ferroelectrics
Authors: Dusthakar Dinesh K , Menzel Andreas , Svendsen Bob
Published: December 2014

The purpose of the work is the thermodynamics‐based modelling of the polarisation and the deformation microstructure in the ferroelectric single crystal with the help of a laminate‐based approach. The incremental variational‐based rate‐dependent macroscopic model for dissipative ferroelectric material [1] and the laminate‐based microscopic model [2] established in the literature are taken as basis and shall be further extended to a single crystal laminate structure dependent on the loading frequency based on the coupled electromechanical framework taking the effect of polarisation into account. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)