bluuebunny/crossref_metadata_2025_split huggingface dataset:
Towards a finite element simulation of coating by means of thermal spraying
Authors: Berthelsen Rolf , Tomath Dennis , Denzer Ralf , Menzel Andreas 
Published: October 2015

AbstractMetal sheet forming processes like deep drawing are applied in order to produce carriage parts in mass production. Therefore, forming tools are required that are well protected against wear. For such forming tools, wear resistant surfaces are, e.g., produced by thermal spraying of hard material coatings. The thermal spraying process itself is a highly transient thermo‐mechanical process. In order to gain a better understanding of the heat input and transfer during thermal spraying, a simulation framework for thermal spraying processes is presented. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Primary and secondary instabilities in soft bilayered systems
Authors: Budday Silvia , Andres Sebastian , Steinmann Paul , Kuhl Ellen 
Published: October 2015

AbstractWrinkling phenomena emerging from mechanical instabilities in inhomogeneously compressed soft bilayered systems can evoke a wide variety of surface morphologies. Applications range from undesired instabilities in engineering structures such as sandwich panels, via fabricating surfaces with controlled buckling patterns of unique properties, to wrinkling phenomena in living matter such as lungs, mucosas, and brain convolutions. While moderate compression evokes periodic sinusoidal wrinkles, higher compression induces secondary instabilities ‐ the surface bifurcates into increasingly complex morphologies. Periodic wrinkling has already been extensively studied, but the rich pattern formation in the highly nonlinear post‐buckling regime remains poorly understood. Here, we establish a computational model of differential growth to explore the evolving buckling pattern of a growing layer bonded to a non‐growing substrate. Our model provides a mechanistic understanding of growth‐induced primary and secondary instabilities. We show that amongst all possible secondary bifurcations, the mode of period‐doubling is energetically favorable. We experimentally validate our numerical results by examining buckling of a compressed polymer film on a soft foundation. Our computational studies have broad applications in the microfabrication of distinct surface patterns as well as in the morphogenesis of living systems, where growth is progressive and the formation of structural instabilities is critical to biological function. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards modelling the curing process in particle‐filled electro‐active polymers
Authors: Hossain Mokarram , Steinmann Paul 
Published: October 2015

AbstractA large actuation voltage is required to produce a desired mechanical deformation in dielectric elastomers. To reduce the amount of the actuation voltage, several mechanisms can be applied and the inclusion of high dielectric permittivity fillers in the matrix material in the uncured stage is one of them. Moreover, to obtain a maximum advantage from the high dielectric permittivity fillers, an electric field is applied during the curing process which helps the particles to align in a preferred direction. The stiffness gaining during curing is modelled by an appropriate constitutive relation where the temporal evolution of the material parameters is considered. In this paper we present a phenomenologically‐inspired large strain framework for simulating the curing process of polymers that can work under the use of an electro‐mechanically coupled load. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A global damping factor for a non‐invasive form finding algorithm
Authors: Landkammer Philipp , Steinmann Paul 
Published: October 2015

AbstractInverse form finding based on the finite element method (FEM) aims in determining the optimal material (undeformed) configuration when knowing the target spatial (deformed) configuration in a discretized setting. The strategy is to iteratively update the material coordinates and recompute the spatial configuration by a FEM simulation until the computed spatial nodal positions are close enough to a priori given spatial nodal positions. A form finding algorithm is utilized, which is purely based on geometrical considerations and can be coupled with arbitrary external FEM software via subroutines in a non‐invasive fashion. At large deformations degenerated elements can occur when updating the material coordinates. Evaluating the mesh quality of the updated material configuration and adjusting a global damping factor before recomputing the next spatial configuration helps to avoid mesh distortions. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FE‐simulation of spatially graded gelation during adhesive's curing
Authors: Rudolph Martin , Landgraf Ralf , Ihlemann Jörn 
Published: October 2015

AbstractIn this contribution main aspects of material characterization and modelling of a curing adhesive are denoted. It is pointed out how to deal with the exothermic heat generation during curing, both, how to obtain it experimentally as well as how to account for it in the continuum mechanical an FE‐modelling framework. Furthermore, a strategy to simulate spatially graded gelation processes in ANSYS® is presented. An academic simulation example completes this work. By the help of this simulation tool a better understanding of a novel manufacturing process of smart semi‐finished light weight structures is ensured. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational Homogenization in Micro‐Magneto‐Elasticity
Authors: Sridhar Ashish , Keip Marc‐André , Miehe Christian 
Published: October 2015

AbstractThe overall macroscopic response of magneto‐mechanically coupled materials stems from complex magnetization evolution and corresponding domain wall motion occurring on a lower length scale. In order to account for such effects we propose a computational homogenization approach that incorporates a ferromagnetic phase‐field formulation into a macroscopic Boltzmann continuum. This scale‐bridging is obtained by rigorous definition of rate‐type and incremental variational principles. An extended version of the classical Hill‐Mandel macro‐homogeneity condition is obtained as a consequence. In order to satisfy the unity constraint of the magnetization on the micro‐scale, an efficient operator‐split method is proposed. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of Micro‐ and Macro‐Instability Phenomena in Computational Homogenization of Finite Electro‐Statics
Authors: Vallicotti Daniel , Miehe Christian 
Published: October 2015

AbstractDielectric materials such as electro‐active polymers (EAPs) belong to the class of functional materials which are used in advanced industrial environments as sensors or actuators and in other innovative fields of research. Driven by Coulomb‐type electrostatic forces EAPs are theoretically able to withstand deformations of several hundred percents. However, large actuation fields and different types of instabilities prohibit the ascend of these materials. One distinguishes between global structural instabilities such as buckling and wrinkling of EAP devices, and local material instabilities such as limit‐ and bifurcation‐points in the constitutive response. We outline variational‐based stability criteria in finite electro‐elastostatics and design algorithms for accompanying stability checks in typical finite element computations. These accompanying stability checks are embedded into a computational homogenization framework to predict the macroscopic overall response and onset of local material instability of particle filled composite materials. Application and validation of the suggested method is demonstrated by representative model problems. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling thermoplastic material behaviour of dual‐phase steels on a microscopic length scale
Authors: Zeller Sebastian , Löhnert Stefan , Wriggers Peter 
Published: October 2015

AbstractOn a microscopic length scale dual‐phase steels exhibit a polycrystalline microstructure consisting of ferrite and martensite. In this work a material model for the temperature dependent hardening behaviour of the ferritic phase is presented. As the dislocation structure determines the resistance to dislocation glide, dislocation densities are introduced as state variables to capture the dependence of the material behaviour on the loading history. Motivated by the elementary processes of multiplication by the Frank‐Read‐mechanism and annihilation by cross‐slip, evolution equations for the dislocation densities are introduced. Based on the interaction of dislocations on different slip systems and the Peierls‐stress, the resistance to dislocation motion with its temperature dependence is formulated to describe the hardening behaviour. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermodynamically consistent description of mass transfer in porous media by a singular surface
Authors: Häberle Kai , Ehlers Wolfgang 
Published: October 2015

AbstractPhase transition processes are important and ubiquitous physical phenomena. These processes are not limited to systems like batch reactors, but can also appear inside porous solids such as in the sequestration of CO2 or in the food industry. In these processes, mainly first‐order transitions between the liquid and the gaseous phases of a certain fluid occur and are characterised by a jump in density and the coexistence of both phases during phase change. This jump is numerically handled by introducing a singular surface, which allows for a thermodynamically consistent description of the mass transfer during phase transition. The mass transfer is driven by the change in internal energy and couples the two mass balance relations of the two fluid phases.The formulation of a model for a multiphasic porous aggregate in a non‐isothermal environment, while accounting for the thermodynamics of the fluids and the phase transition, requires a potent theory for its description. Here, the Theory of Porous Media (TPM) provides a well‐founded, continuum‐mechanical basis to model deformable, fluid‐saturated porous media. In this particular case, a three‐phasic model is proposed, consisting of the thermoelastic solid phase, which is percolated by the compressible gaseous and liquid fluid phases. The representation of the interface between the fluid phases by a singular surface results in additional terms in the balance relations. The evaluation of these terms leads to a consistent formulation of the mass transfer, which basically compares the energy added to the system with the latent heat of the phase transition. This mass‐transfer term is furthermore dependent on the interfacial area, a factor defined by porosity and saturation.Finally, the proposed model for phase transition inside a porous medium is based on the mixture momentum balance, the volume balances of the fluid phases and the energy balance. Consequently, the four primary variables are the solid deformation, the effective pore pressures of the two fluid phases and the temperature. The numerical simulation of condensation or evaporation of CO2 in a porous solid rock, which can be either caused by changes in temperature or in pressure, allows for the demonstration of possible application areas for the presented model. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydraulic fracturing based on the Theory of Porous Media
Authors: Luo Chenyi , Ehlers Wolfgang 
Published: October 2015

AbstractHydraulic fracturing is a widely‐used technology in the field of energy exploitation. The relevant study is intricate owing to the crack‐inducing instability and the coupling between different constituents in stratum. The proposed model is based on the phase‐field theory and extended to the Theory of Porous Media. The former removes crack discontinuity by substituting sharp crack with smeared one and the later provides clear and distinct description of multi‐phasic material in macroscopic scale. A new variable, the order parameter ϕ is imported to characterise material as unbroken porous media and the crack zone, the evolution of which is governed by potential energy of solid. With the change of ϕ, the stiffness of solid is decreasing while the fluid transport is transferring from Darcy‐type to Navier‐Stokes‐type. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A continuum mechanical, bi‐phasic, two‐scale model for thermal driven phase transition during solidification
Authors: Moj Lukas , Ricken Tim , Steinbach Ingo 
Published: October 2015

AbstractThis articel focuses on a bi‐scale numerical description for solidification process simulation. The macro‐scale implies two phases which are the solid and liquid metallic alloy physical states described using the theory of porous media (TPM) enhanced by strong thermal coupling and finite elastic‐plastic‐creep temperature dependent material behaviour. Furthermore, a linear viscous melt as well as a laminar melt flow are adopted. The thermal driven physics of solidification is covered by a microscopic phase‐field model. Therefore, a Ginzburg‐Landau type free energy function is employed. After discussing the main model details, a real Bridgman oven numerical pre‐model will demonstrate the principal performance. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient Simulation of the Heat Flux Input in Moving Contacts
Authors: Partzsch Marian , Beitelschmidt Michael 
Published: October 2015

AbstractIn thermal simulations moving parts can be included by discretely adjusting their position within the steps of a transient analysis, whereby frictional heating is considered as a pre‐determined, time‐depended NEUMANN‐BC within the contact zone. Now when using a coarse time discretization, the rarely conducted update of the actual loaded friction is the reason for one proportion of the occurring lack in result quality. In this paper we present an idea to counter this systematic error source by some low‐effort editing of the applied load data. The proposed method is based on the conservation of the provided frictional energy between the continuous and discrete motion and considers the actually used time discretization. Its performance is shown for a simplified case at the end of this paper. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase field simulation on mechanically induced 180 degree switching in nanomagnets
Authors: Yi Min , Xu Bai‐Xiang 
Published: October 2015

AbstractThe mechanically induced 180° switching of the magnetization in cylindrical nanomagnets is demonstrated through the switching dynamics simulation by a constraint‐free phase field model which is fully magneto‐mechanical coupled. By using the overrun behavior of the magnetization during the mechanically induced precessional switching, a deterministic 180° switching can be achieved. It is found that the residual torque resulting from the azimuthal‐angle dependence of the magneto‐elastic coupling and the overrun and precessional dynamics are responsible for the switching mechanism. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fluid‐Porous‐Media Interaction: A Decoupled Solution Algorithm via Localised Lagrange Multipliers
Authors: Zinatbakhsh Seyedmohammad , Koch David , Ehlers Wolfgang 
Published: October 2015

AbstractFluid‐porous‐media interaction (FPMI) refers to a surface interaction among several non‐overlapping subsystems, composed of either a bulk fluid or a porous medium. This could be the interaction of blood with a blood vessel wall, a body of water with an earth‐dam structure, or acoustic waves with acoustic panels used in soundproofing, etc. These are highly coupled phenomena inheriting different coupling mechanisms which take place within the interacting subdomains as well as across common boundaries. Consequently, the mathematical models of such phenomena also consist of sets of coupled differential equations, which are commonly solved numerically, following a monolithic or a decoupled approach. Here, the focus is on the latter.The design of an algorithm for the decoupled solution of the fluid‐porous‐media‐interaction problem can be advantageous in several ways. First and foremost, the process of decoupling breaks down the problem into several subproblems, which can be solved efficiently employing specialised fluid and porous‐media solvers. Furthermore, solution of several decoupled subproblems instead of one highly coupled problem may be more economical in terms of computational costs. This is especially the case if the scheme permits parallel treatment of the produced subproblems.Here, the applicability of using the method of localised Lagrange multipliers for a partitioned solution of the problem of FPMI in the 2‐dimensional space is demonstrated. In this regard, the concept of modified Eulerian description for studying the motion of fluid bodies within moving boundaries is introduced. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A two‐scale homogenisation approach for fluid saturated porous media based on TPM and FE2‐Method
Authors: Bartel Florian , Ricken Tim , Schröder Jörg , Bluhm Joachim 
Published: October 2015

AbstractThinking about the description of biomaterials, e.g. human tissue, plants or sponges, we always have to take into account a global design composed of various substructures with different characteristics on a lower level. Examples of such substructures are pores which can be saturated with fluids or gases, fibres with different orientations or cells which can be influenced by chemical reactions. For the theoretical description of the behaviour, enhanced continuum mechanical models give promising approaches. Up to now, due to the high complexity, it has not been possible to simulate a biological system with only one design model. Hence, it is necessary to think about techniques which simplify the model but still consider the essential characteristics. This contribution will present a two‐scale homogenisation approach for fluid saturated porous media with a reduced two‐phase material model, which covers the behaviour of large poro‐elastic deformation. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational characterization of magneto‐electric composites: the role of ferroelectric pre‐polarization
Authors: Labusch Matthias , Schröder Jörg , Keip Marc‐André , Lupascu Doru C. 
Published: October 2015

AbstractThe interaction between electric and magnetic fields enables smart devices which can find applications in sensor technology and data storage. Materials showing magneto‐electric (ME) coupling combine different ferroic characteristics. In the present contribution we focus on composites, which combine ferroelectric and ferromagnetic phases due to strain couplings, such that they generate a strain‐induced ME coupling. We derive a two‐scale homogenization approach for the determination of effective properties in consideration of microscopic morphologies. Furthermore, we demonstrate the strong influence of ferroelectric polarization states on the ME‐coefficient by modeling the switching of remanent polarizations on the microscale. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Block Conjugate Gradient Iteration for Fourier‐Galerkin Homogenization of Periodic Media
Authors: Mishra Nachiketa , Vondřejc Jaroslav , Zeman Jan 
Published: October 2015

AbstractThe Fourier‐Galerkin method is considered here for the solution of the unit cell problem that describes the homogenized properties of periodic materials in the scalar elliptic setting. The method is based on a Galerkin approximation with trigonometric polynomials and leads to linear systems suitable for iterative solvers. In [1], Zeman et al show the effectiveness of Conjugate gradients (CG) which is compared here with its block version (BCG). We show that the latter version outperforms the CG especially for anisotropic materials with non‐symmetric distribution of material properties. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupling atomistic and continuum models with nodes having translational and rotational degrees of freedom
Authors: Niederhöfer Florian , Wackerfuß Jens 
Published: October 2015

AbstractThis paper deals with the coupling of atomistic simulations and nodes having translational and rotational degrees of freedom (dof). Especially the (non‐)occurrence of boundary effects is a main issue of the following remarks. The presented approach is formulated within the finite element method and can be the groundwork for multiscale simulations, when coupled with continuum models. In particular, atomistic models can be coupled with continuum ones having translational and rotational dofs like beams and shells. After the introduction of the main ideas of the approach, it is applied to an atomistic chain. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability analysis of the flow past miniature vortex generators in a Blasius boundary layer
Authors: Siconolfi Lorenzo , Camarri Simone , Fransson Jens H. M. 
Published: October 2015

AbstractIt is shown in the literature that Tollmien−Schlichting waves can be damped and transition delayed by a proper modulation of the streamwise velocity in a boundary layer (BL), which can be obtained using miniature vortex generators (MVGs). Experiments show that the amplitude of TS waves is not always monotonically damped past the MVGs. In this study, direct numerical simulations and local stability analysis have been performed in order to provide an interpretation of the experiments and to characterize further the stabilization mechanism induced by this type of control. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of wake effects of windfarms using an Actuator Disk implementation
Authors: Hornung Cordula , Viellieber Mathias , Class Andreas 
Published: October 2015

AbstractWind turbines extract energy from the approaching flow field resulting in reduced wind speeds, increased turbulence and a wake downstream of the wind turbine. Wakes extending up to 20 km downstream of a windfarm are reported [1]. In [2] a multi‐scale numerical method is proposed that addresses length scales of the boundary layer, windfarm and meso‐scale. As a step towards full realization of the multi scale approach the implementation of an Actuator Disk (AD) model into OpenFOAM including a proper atmospheric boundary layer (ABL) is presented. For a meso‐scale area of open sea, the standard ABL conditions of OpenFOAM can not be used. The pre implemented ABL boundary condition for OpenFOAM is restricted to roughness lengths greater than 0.001 m. The boundary condition are modified in order to achieve adequate homogeneous flow properties throughout the considered domain enabling almost constant velocity profiles. A new AD class is implemented in OpenFOAM to establish an arbitrary number and location of windturbines. The class uses the standard k‐ϵ turbulence model. The wake effect of windfarms composed of windturbines with different heights and different lateral spacing is investigated. Specifically the windfarm Trianel Borkum in the North Sea of Germany is simulated. Within this work wakes extending up to 20 km in length could be observed, suggesting to study the ABL‐windfarm interaction in more detail. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Local and instantaneous turbulence modification induced by small spherical bubbles
Authors: Santarelli Claudio , Roussel Jean , Fröhlich Jochen 
Published: October 2015

AbstractThe paper provides insight into the local and instantaneous turbulence modification induced by small spherical bubbles in an upward directed turbulent channel flow. This is accomplished by analyzing each term of the transport equation of the local and instantaneous kinetic energy for bubbly flows and dedicated flow visualizations are provided to address the mechanisms involved in the turbulence modification. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)