bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modelling the thermoplastic material behaviour of a tailored formed joining zone on a microscopic length scale with focus on the steel component
Authors: Baldrich Martina , Zeller Sebastian , Loehnert Stefan , Wriggers Peter 
Published: March 2018

AbstractSince Tailored Forming is a complex process and the joining zone of the hybrid solid component is a possible weakness, our goal is to simulate the thermomechanical material behaviour of the joining zone during the Tailored Forming process. Investigations on the steel component of the joining zone show a polycrystalline microstructure with the two constituents pearlite and ferrite. In this work, the pearlitic phase is considered to be purely thermoelastic whereas the material model for the ferritic phase represents thermoplastic material behaviour. Besides reasons for the choice of the mentioned material models, we present the thermoplastic material model developed by Zeller et al. [1]. Based on the experimental observation that the persistent deformation is a result of slip of dislocations, state variables are defined to formulate a necessary shear stress to move dislocations as well as temperature and deformation dependent evolution equations for the introduced state variables. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multi‐scale modelling of fibre reinforced composites exhibiting elastoplastic deformation
Authors: Bedzra Rex , Reese Stefanie , Simon Jaan‐Willem 
Published: March 2018

AbstractIn this paper, a scale bridging approach for modelling unidirectional tungsten fibre reinforced copper (W/Cu) composite by making use of an anisotropic elastoplastic constitutive model is described. To identify the yield surface of the composite and to further validate the constitutive model, a finite element model of a unit cell (UC) of the composite is set up. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A physically motivated model based on the strain amplification in filled elastomers
Authors: Darabi Ehsan , Itskov Mikhail , Klüppel Manfred 
Published: March 2018

AbstractA constitutive model for filled elastomers based on a combination of the Dynamic Flocculation Model (DFM) [1] framework and the continuum damage model [2] is proposed. This contribution represents an extension of the previously proposed micro‐mechanical model explaining simultaneously induced filler breakage and polymer‐filler network damage [3]. These effects are attributed to the hydrodynamic strain amplification which is the main topic of the current work. Deformation causes damage in both the network rubbery matrix and inside the filler aggregates. As a result, the probability density function of the number of segments and the filler size distribution change with the strain in all spatial directions which leads to stress softening and the Mullins effect. The model also describes the deformation induced anisotropy and permanent set. A small number of physically motivated material constants describing the average filler cluster dimensions, filler‐filler and filler‐matrix interaction properties are included in the model. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a relaxation approach to modeling the stochastic behavior of elastic materials
Authors: Junker Philipp , Nagel Jan 
Published: March 2018

AbstractThe inclusion of information on the stochastic behavior of microstructures is a key issue for modeling materials with even higher precision. To this end, stochastic series expansions offer an elegant for accounting for randomness. A prominent example is the usage of the so‐called Chaos Polynomial Expansion in the context of the Stochastic Finite Element. Although providing the desired information, the numerical effort is highly increased even for the simple linear elastic case. We aim at improving the numerical efficiency by proposing a novel approach to modeling the stochastic behavior of microstructures: we divide the material (= integration) point into a subset of domains which can be interpreted, e.g. as crystal grains. Afterwards, we employ a stochastic series expansion for the elastic constants and strains in each domain. Appropriate energy relaxation results into effective (homogenized) elastic constants and strains which are stochastic. Calculation of expectation and variance is only a technical issue yielding analytical formulas which are basically free of any additional computational effort as compared to regular deterministic linear elastic calculations. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental Investigation and Modeling of Volume Shrinkage in Curing Epoxy Resins
Authors: Leistner Chris , Wittrock Jörg , Abliz Dilmurat , Ziegmann Gerhard , Hartmann Stefan 
Published: March 2018

AbstractThe exothermic curing reaction of epoxy resins comes along with chemical shrinkage of the material. There do not exist established standard methods for determining the chemical shrinkage during the curing process. To this end, shrinkage measurements based on Archimedes' principle have been carried out for pure epoxy resin at different curing temperatures. In order to model the shrinkage behavior, these results can be related to the curing kinetics. For this purpose, additional DSC measurements have been carried out. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A large‐strain phase‐field model for nematic elastomers based on Landau‐de‐Gennes theory
Authors: Keip Marc‐André , Nadgir Omkar 
Published: March 2018

AbstractLiquid crystal elastomers bring together the orientational properties of liquid crystals as well as elastic properties of soft rubber.Nematicelastomers are a subclass of these materials which exhibit a phase transition from high‐symmetry isotropic state to low‐symmetry nematic state, when cooled down below a material specific temperature. We present a phase–field model based onLandau‐de‐Gennestheory for the modeling of nematic elastomers. The model is implemented within finite element framework and an initial boundary value problem of isotropic‐nematic phase transition is solved. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A stereologic approach for the spherical void size distribution in Polyurea
Authors: Reppel Thomas , Weinberg Kerstin 
Published: March 2018

AbstractPolyurea is a high performance elastomer usually used as a protective coating on steel or concrete. Various elastic properties of Polyurea have been identified in the past, cf. [2] and references therein, where in uniaxial tension tests a Young's modulus of approximately 65 MPa was measured together with an elongation up to 650%. After the long elastic range however, Polyurea fails like a porous material.This work aims at the approximation of the spherical void size distribution. To avoid the high costs for creating micro‐CT images of Polyurea specimens, stereologic methods are used to estimate the size distribution of the spherical void radii. This is done with the usage of the classical Wicksell [4] approach by calculation of the void section radii distribution from micrographs of sliced specimens. Several parametric distributions for the void section radii are considered. Results of Monte‐Carlo simulations are compared with the possible void radii distributions,which are obtained and examined in Wicksell's model. Also the deviation that occurs by chosing the same distribution for both the sphere and the section radii is investigated. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Material plasticity to track the elastic anisotropy at finite strains
Authors: Weber Martin , Glüge Rainer , Bertram Albrecht 
Published: March 2018

AbstractWe present a phenomenological finite elasto‐plasticity theory that includes the evolution of the elastic anisotropy. The theory is called Material Plasticity after [1] and [2], assuming that the axes of anisotropy deform as material line elements. It is applicable to fiber‐reinforced materials. The main feature is the different evolutions of the stiffness tetrad and of the stress‐free placement. For this purpose we extend the well known isomorphy concept (see [3]).To identify and compare the stiffness tetrads before and after large plastic deformations a representative volume element (RVE) [4] with a fiberous microstructure is used. Uni‐, bi‐ and and tridirectionally reinforced samples are considered. On the microscale a standard elastic‐plastic material model is used. After calculating the effective stiffnesses of the different material samples we investigate their evolution during different deformations. It turns out that it is possible to denote the change of the stiffness with sufficient accuracy using one additional second order tensor. After investigating the change in the stiffness tetrads we finally propose an analytical evolution equation for this tensor. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of self‐organization processes in filled rubber
Authors: Wulf Hans , Ihlemann Jörn 
Published: March 2018

AbstractA typical property of filled rubber material, known as Mullins effect, is that prestraining leads to a reduction of stresses at strain levels smaller than the maximum strain in the loading history. This softening is related to the direction of the prestrain and therefore induces a material anisotropy. The microstructural process responsible for this effect is still subject of discussion. Here, a mechanism based on the self‐organization of weak physical links is proposed. The central idea states that these links organize into a pattern of different linkage densities leading to the observed properties. The theory is tested by a simulation program. In the simulation, several typical rubber properties can be reproduced, while clearly observing self‐organization of the model elements. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Variationally‐Consistent Homogenization Approaches in Multi‐Phase Magnetic Solids
Authors: Kiefer Björn , Bartel Thorsten 
Published: March 2018

AbstractIt is well known that classical homogenization schemes, such as the Taylor/Voigt and Reuss/Sachs assumptions, can also be interpreted as energetic bounds. Furthermore, energy relaxation concepts have been established that determine stable effective material responses based on appropriate (convex, quasi‐convex, rank‐one) energy hulls for non‐convex energy landscapes associated with multi‐phase materials, see [1–3] and references therein. Our goal is to propose analogous relaxation based homogenization schemes for magnetizable solids. More specifically, we propose a magnetic potential perturbation scheme which yields relaxed effective free energy densities that simultaneously satisfy magnetic induction and magnetic field strength compatibility requirements—i.e. the magnetostatic Maxwell equations—at the phase boundary. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupled SPH and Phase Field method for hydraulic fracturing
Authors: Osorno Maria , Steeb Holger 
Published: March 2018

AbstractSimulation of fracture initiation and propagation using classical mesh‐based methods involves computationally expensive operations for pre‐processing and (adaptive) remeshing of complex geometries. To overcome the difficulties we propose to use a Smoothed Particle Hydrodynamics (SPH) method to model hydraulic fracturing. SPH is a meshless Lagrangian method highly suitable for large deformations [1].The present contribution discusses a numerical approach to model fractures initiation and propagation, by coupling SPH with the Phase Field method [2]. The proposed hybrid method overcomes the instability problems that can present SPH due to kernel incompleteness. We first validate the proposed model with a stationary elastic fracture and compare the results with the classical SPH to the SPH‐Phase Field approach. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal control of a slot car racer
Authors: Penner Johann , Schlögl Tristan , Leyendecker Sigrid 
Published: March 2018

AbstractIn this contribution, we present a simulation method for the optimal control of a mechatronic system that is based on discrete variational calculus and apply it to compute the time‐minimal path of a slot car racer. Here, the DMOC (Discrete Mechanics and Optimal Control [4]) method is used to generate offline optimal trajectories for the electro‐mechanically coupled system, i.e. sequences of discrete configurations and sequences of driving voltages. The time‐minimal path is achieved by the choice of different cost functions, the sum of time steps, the negative sum of the quadratic momenta and the negative sum of the quadratic velocities. Simulation results show that the momentum formulation yields the lowest number of iterations. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A phase‐field model of hydraulic fracture in saturated binary porous media
Authors: Pise Mangesh , Bluhm Jochim , Schröder Jörg 
Published: March 2018

AbstractIn many fields of engineering, especially in geo sciences and rock mechanics, the theoretical and numerical modeling of hydraulic fracturing of porous materials plays an important role. Hydraulic fracturing is a well stimulation technology in which porous materials are fractured by a pressurized liquid. The process involves the pressure injection of the fracking fluid (primarily water, often enriched with filling materials and thickening agents) and accompanied by crack nucleation and propagation as well as mass transport. In this contribution, a macroscopic model based on the Theory of Porous Media (TPM) is presented in view of the description of the aforementioned phenomena. For simplification an incompressible binary model consisting of the phases solid and liquid is used. Attention is paid to the description of the damage of the elastic solid phase. The development of the damage parameter is controlled by an evolution equation, which corresponds to known diffusive phase field models within a continuum mechanical framework. A numerical example shows that the simplified model is indeed capable of simulating hydraulic fracturing of porous media. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical investigation of the effective Skempton coefficient in fluid‐saturated fractured rock
Authors: Pollmann Nele , Jänicke Ralf , Renner Jörg , Steeb Holger 
Published: March 2018

AbstractCharacterization of hydro‐mechanical processes in reservoir rocks is an essential issue for many geo investigations such as characterization of subsurface fluid flow or geothermal exploitation. For geothermal applications, the role of fractures as storage and transport components of a hydraulic system are highly important. In the present contribution we focus on investigating the effective Skempton coefficient

of a damaged porous rock analyzing a modified Cryer problem, which provides a simple model of a porous rock containing a storage and transport pat. The effective Skempton coefficient is defined as the ratio of the increase in mean pore pressure induced by change in confining pressure for undrained boundary conditions. Using approaches from computational homogenization, we evaluate the confining pressure as the negative volume average of the total mean stress. Similarly, we compute the effective fluid pressure in terms of the volume‐averaged fluid pressure in the rocks. We compare the numerical results to those from typical experiments and highlight the problems with the latter. The proposed concept for determination of an effective Skempton coefficient based on numerically evaluated volume averages helps to generate a better understanding of the process‐inherent constituents. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling the solidification process in mortar due to internal mass exchange
Authors: Sauerwein Malte , Steeb Holger 
Published: March 2018

AbstractAim of the investigation is to model phase transition processes induced by mass transfer in multi‐phase and multi‐species mixtures. More specific, the innovative concept of using Superabsorbent Polymers (SAPs) as additives in grouting mortars represents a promising practical application, e. g. in mechanized tunneling. In this contribution, we focus on both the driving force for mass transfer as well as the kinetics for water migration, whereas an extension to the classical Theory of Porous Media (TPM) provides a reasonable modeling framework. As a result, the gelation process of the mixture can be described with respect to time. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A temperature‐based GENERIC approach for the thermodynamically consistent integration of thermoelastic solids
Authors: Schiebl Mark , Betsch Peter , Hesch Christian 
Published: March 2018

AbstractThis work deals with the thermodynamically consistent (TC) time integration of thermoelastic systems with polyconvex density functions using the notion of the tensor‐cross‐product. While energy‐momentum preserving integrators are well‐known for conservative (isothermal) mechanical systems, Romero introduced in [7, 8] the new class of TC integrators. While [8] dealt with the sample application of thermo‐elastodynamics, the scope of application was extended in [2] to coupled thermo‐viscoelastodynamics in temperature form. A first step towards the systematic design of a TC integrator is to cast the evolution equations into the GENERIC (General Equation for Non‐Equilibrium Reversible‐Irreversible Coupling) framework [6] which reveals additional underlying physical structures of the system. Relying on a polyconvex density function and using the notion of the tensor‐cross‐product [1] we arrive at a polyconvex version of the GENERIC framework. Further applying the notion of a discrete gradient leads to a TC integrator.Using the entropy as the thermodynamical state variable as in [5, 8] the GENERIC framework possesses an easy structure. However, this choice of thermodynamical state variable only allows to prescribe entropy Dirichlet boundary conditions directly. This drawback can be compensated by using Lagrange‐multipliers to be able to handle temperature Dirichlet boundary conditions leading to an extended system of algebraic equations to be solved, see [5]. Alternatively, the present work uses the temperature as the thermodynamical state variable, see also [2, 3] and the use of an energy‐based Newton‐Raphson termination criterion. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient numerical modelling of hydro‐mechanical effects in fractures using a hybrid dimensional approach and non‐conformal mesh coupling
Authors: Schmidt Patrick , Steeb Holger 
Published: March 2018

AbstractThe investigation of subsurface fluid flow in porous and fractured media is of interest in particular to determine the properties of matter and heat transport below the earth surface and the characteristics of the underground storage of fluids. Classical approaches such as extended diffusion equations are lacking the possibilities to capture key phenomena such as inverse water‐level fluctuations (Noordbergum effect) obtained during pumping tests performed on aquifers [1, 2, 4]. In order to efficiently model hydro‐mechanical effects, this contribution presents an implementation of the newly introduced hybrid‐dimensional approach [3] in the DUNE‐PDELab environment. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Untersuchung des Schließvorgangs von Notfallschützen und ihres Einflusses auf die Strömung von Laufwasserkraftanlagen
Authors: Seidel Christian 
Published: March 2018

AbstractVerschlussorgane wie Notfallschütze sind bei Wasserkraftanlagen sicherheitsrelevante Bauteile, die bei unvorhergesehenen Ereignissen wie Lastabwurf des Kraftwerks, Blitzschlag, Wellen‐ oder Getriebebruch sowie anderer Arten von Havarien die Trennung des Volumenstroms zum Kraftwerk bewirken. Auf Grund der hohen Empfindlichkeit der elektrischen Komponenten eines Kraftwerkes wie z.B. Generatoren oder Umrichter gegen Überdrehzahlen und der daraus resultierenden Wärmeentwicklung in den elektrischen Bauteilen ist es erforderlich, die Notfallschütze in sehr kurzer Zeit zu schließen. Der Vorgang des schnellen Schützverschlusses löst dabei instationäre Strömungsprozesse wie Schwall‐ und Sunkerscheinungen aus, deren Intensität mit der Abnahme der Verschlusszeit stark zunimmt. Gleichzeitig besitzen die instationären Strömungsprozesse einen entscheidenden Einfluss auf die Unterströmung des schließenden Notfallschützes, auf den dabei noch abfließenden Volumenstrom und auf die Strömungsgeschwindigkeiten. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electric leakage current density in phase field simulations for nanogenerator concepts
Authors: Wöhler Franziska J. , Münch Ingo , Wagner Werner 
Published: March 2018

AbstractFor the purpose of energy harvesting on the nanoscale with ferroelectric barium titanate (BaTiO3), our nanogenerator concept transforms parasitic mechanical oscillations into usable electric energy. Experimental difficulties occur in sample preparation, e.g., surface roughness, bonding contact, and leakage currents. Latter can be considered in our finite element phase field model, such that the nanogenerator concept can be optimized. Leakage current density is implemented from different phenomenological approaches. First, Ohm's law represents a linear relation between leakage and electric field. Second, the Space‐Charge‐Limited Current (SCLC) relation assumes a quadratic dependency on the electric field. So far, SCLC is suitable for one‐dimensional problems, however, in two or three dimensions it is not found in literature. Therefore, we discuss a reformulation to bring into account that the electrical field E is a vector out of ℝ3 in our model. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
From particle mechanics to microcontinuum theories
Authors: Bidier Sami , Ehlers Wolfgang 
Published: March 2018

AbstractMicrocontinuum theories enable the consideration of particle‐based microstructures within a continuum mechanical framework. Several classes of microcontinua, such as the micromorphic, the micropolar, the microstrain or the microstrech formulation, have been successfully applied to engineering applications, although a clear physical determination and interpretation of the kinematical extensions and the resulting higher‐order stresses within the formulation is frequently missing. In this regard, the present contribution focuses on establishing the physical link between discrete contact forces, stresses and deformation of particle‐based microstructures and the characteristic stress states of microcontinuum theories. Representative Elementary Volumes (REVs) are therefore constructed on the mesoscale as ensembles of deformable particles from the mircoscale. Establishing the REV balance relations justifies the common generalisation of the angular momentum balance commonly applied in microcontinuum theories. It furthermore leads to the identification of the continuum stresses based on micro‐quantities and enables the application of homogenisation techniques by exploitation of the equilibrium conditions of a REV. In order to investigate the hereby established link from the micro‐ to the macroscale, granular materials are simulated using the Discrete‐Element Method (DEM). In particular, localisation phenomena in granulates, e. g. in biaxial compression tests or during ground‐failure processes are studied. This implies the formulation of the contact between particles in an appropriate constitutive manner in accordance to the envisaged granular material behaviour, e. g. whether loose material, such as sand, or bonded multi‐component material, such as polyurethan‐sand compounds for metal casting applications are of interest. With the full solution of a particle‐based initial‐boundary‐value problem, the homogenisation formalism is applied and enables the study of the extended continuum field quantities, essentially demonstrating the applicability of microcontinuum theories in the field of granular material. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)