bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of the microstructure evolution caused by the strain‐induced crystallization in polymers
Authors: Aygün Serhat , Klinge Sandra 
Published: December 2018

AbstractThe strain‐induced crystallization (SIC) in polymers, such as in natural rubber, is a phenomenon manifesting itself as the natural reinforcement caused by the high deformation. Experimental data obtained from tensile tests show that the crystallization starts at a strain of 200‐400%, whereas, at maximum possible stretches of up to 700%, the volume fraction of the crystallinity reaches its highest degree. The growth and reduction of the crystalline regions cause a hysteresis in the stress‐stretch curve which indicates that the process has a dissipative character. In our work, the described material behavior is simulated by a micromechanical continuum model which involves the degree of network regularity as an internal variable. The focus is on the formulation of the dissipation potential simulating the change of the crystallinity degree during cyclic loading. The current approach furthermore simulates the dependence of the crystal orientation and form on the applied external load, which is achieved by assuming a specific coupling condition between the inelastic deformations and network regularity.
Towards structural optimization of lithium battery anodes
Authors: Werner Marek , Weinberg Kerstin 
Published: December 2018

AbstractIn lithium batteries, multicomponent compositions like LiCoO2 or LiFePO4 are used as cathode material and single substances like graphite are employed as anode material. In the latest battery developments anodes of silicon are introduced. Unfortunately, by now the high volumetric changes of silicon during intercalation — sometimes a factor of four has been reported — lead to pulverization of the anode and restrict long term use. To account for the intercalation induced volumetric swelling and phase segregation in a numerical simulation, the mechanical, thermal, chemical and electrical equations have to be coupled which leads to a complex description based on fourth order partial differential equations. Additionally, the structure of the anode needs to provide minimal compliance but maximal conductivity. In our contribution we provide a concept to combine these competing objectives with a multi‐physics model of battery charging.
Gauss‐Newton‐Secant method for solving nonlinear least squares problems
Authors: Iakymchuk Roman , Yarmola Halyna , Shakhno Stepan 
Published: December 2018

AbstractWe investigate the local convergence of the combined Gauss‐Newton‐Secant method under the classical and generalized Lipschitz conditions for solving nonlinear least squares problems with non‐differentiable operator. Instead of Jacobian, this method uses a sum of the derivative of the differentiable part and the divided difference of the non‐differentiable part of the operator. Numerical experiments are conducted on test problems.
Numerical Shape Optimization to Decrease Failure Probability of Ceramic Structures
Authors: Bolten Matthias , Gottschalk Hanno , Hahn Camilla 
Published: December 2018

AbstractCeramic is a material frequently used in industry because of its favorable properties. Common approaches in shape optimization for ceramic structures aim to minimize the tensile stress acting on the component, as it is the main driver for failure. In contrast to this, we follow a more natural approach by minimizing the component's probability of failure under a given tensile load. Since the fundamental work of Weibull [3], the probabilistic description of the strength of ceramics is standard and has been widely applied. Here, for the first time, the resulting failure probabilities are used as objective functions in PDE constrained shape optimization. To minimize the probability of failure, we choose a gradient based method combined with a first discretize then optimize approach. For discretization finite elements are used. Using the Lagrangian formalism, the shape gradient is calculated via the adjoint equation at low computational cost. The implementation is verified by comparing it with a finite difference method applied to a minimal 2d example. Furthermore, we construct shape flows towards an optimal shape in the case of a simple beam.
Gradient‐enhanced ductile damage — a finite deformation framework with application to DP800
Authors: Sprave Leon , Menzel Andreas 
Published: December 2018

AbstractGradient‐enhanced ductile damage is implemented in the finite element method by means of an additional field variable, representing non‐local damage which is linked to the local damage variable. At material point level the isotropic damage formulation uses exponential damage functions to circumvent further constraints on the value set of the local damage variable. The ductility of the model is achieved by a coupling of damage to finite strain plasticity. In a multisurface approach the onset of damage and plasticity is each governed by damage and yield criteria respectively. Linear and exponential isotropic hardening is implemented. With the help of the F‐bar method the results of the finite element simulation exhibit mesh independent behaviour. In order to model the behaviour of DP800 with the material model discussed here, elastic and plastic parameters are identified.
Investigating the Reynolds number dependency of the scalar transfer to a wall using a stochastic turbulence model
Authors: Klein Marten , Schmidt Heiko 
Published: December 2018

AbstractWe numerically investigate the Reynolds number dependency of the transport of a passive scalar in incompressible, fully‐developed turbulent channel flows. The stochastic one‐dimensional turbulence (ODT) model is used to make such numerical simulation feasible up to the friction Reynolds number Reτ = uτ δ/ν ≈ 5200 (channel half‐height δ, friction velocity uτ, kinematic viscosity ν) in the Schmidt number range 1 ≤ Sc = ν/Γ = 400 (mass diffusion coefficient Γ). The ODT simulations exhibit a turbulent boundary layer for which we show that the simulated mass transfer coefficient K+ follows the functional dependency suggested by Schwertfirm and Manhart, Int. J. Heat Fluid Flow 28, 1204–1214 (2007). The agreement is good for Sc ≤ 25 but a different scaling is obtained for Sc ≥ 49 investigated.
Couette flow with geometrically induced unsteady effects
Authors: Scholle Markus , Marner Florian 
Published: December 2018

AbstractFilm flow over surfaces containing topography is a key feature of a number of coating technologies. To date, detailed theoretical investigations of the same, underpinned by the long‐wave approximation, have been used to study the nature of the associated free‐surface disturbance formed; the internal flow structure being more‐or‐less of secondary importance. In the work reported here, a recently developed approach is used to explore the internal flow, embodying unsteady effects, for a related model problem in which the free‐surface is replaced by a moving upper boundary with its own topographical profile.
Feature‐based Classification of Protein Networks using Confocal Microscopy Imaging and Machine Learning
Authors: Asgharzadeh Pouyan , Özdemir Bugra , Reski Ralf , Birkhold Annette I. , Röhrle Oliver 
Published: December 2018

AbstractFluorescence imaging has become a powerful tool to investigate complex subcellular structures such as cytoskeletal filaments. Advanced microscopes generate 3D imaging data at high resolution, yet tools for quantification of the complex geometrical patterns are largely missing. Here we present a computational framework to classify protein network structures. We developed a machine‐learning method that combines state‐of‐the‐art morphological quantification with protein network classification through morphologically distinct structural features enabling live imaging–based screening. We demonstrate applicability in a confocal laser scanning microscopy (CLSM) study differentiating protein networks of the FtsZ (filamentous temperature sensitive Z) family inside plant organelles (Physcomitrella patens).
On the analysis of microstructural residual stresses in hot bulk forming parts under specific cooling
Authors: Brands Dominik , Chugreev Alexander , Kock Christoph , Niekamp Rainer , Scheunemann Lisa , Uebing Sonja , Behrens Bernd‐Arno , Schröder Jörg 
Published: December 2018

AbstractA precise representation of the residual stresses, their development in numerical simulations as well as their interpretation in experimental results requires a profound knowledge of the thermal, mechanical as well as metallurgical properties of the considered material. This publication presents initial approaches for the calculation of residual stresses. For this purpose, the thermo‐mechanical behaviour of two steel alloys 42CrMo4 and 100Cr6 with regard to the martensitic phase transformation is investigated. Using a quenching and forming dilatometer by TA Instruments Inc., the martensite start temperatures are investigated depending on different deformation states of the materials. In addition, an artifitial microstructure is investigated regarding the inducing of residual stresses, representing the volumetric change after temperature related microscopic phase transformations.
Mathematical models of bio‐inspired rotatable sensors with elasticities for object scanning
Authors: Merker Lukas , Will Christoph , Steigenberger Joachim , Behn Carsten 
Published: December 2018

AbstractRats and mice use some special tactile hairs in their snout region for a non‐visual exploration of their environment. These hairs, known as mystacial macro‐vibrissae, are each embedded in their own elastic support, called follicle‐sinus complex. This consists of several mechanoreceptors converting tactile information into neural impulses for the central nervous system (CNS). Using their vibrissae, rats and mice are capable of detecting distances to objects, object contours and surface textures. Due to this outstanding ability vibrissae frequently serve as a paradigm for technical tactile sensors. In this paper, we present a model for object shape scanning and contour reconstruction. Here, we especially focus on the important property “elasticity” of the follicle‐sinus complex, which has rarely been taken into account for object scanning in literature. We set up models for three different elastic supports. Based on solutions of the arising boundary‐ and initial‐value problems, we simulate the scanning process, investigate the related support reactions during a single rotational quasi‐static sweep of a straight vibrissa along a strictly convex object contour and reconstruct its shape. In doing this, we investigate the influence of the different elasticities of the model on the scanning and reconstruction procedure.
Hydro mechanical coupling using a hybrid dimensional approach and interface element formulations
Authors: Schmidt Patrick , Steeb Holger 
Published: December 2018

AbstractCharacteristics of underground fluid storage and properties related to heat transport and underground matter are of high interest in the community of porous and fractures media. Especially once hydro‐mechanical phenomena in fluid filled fractures are of interest, such as inverse waterlevel fluctuations during well stimulations (Noordbergum effect), the numerical coupling of the fluid and the porous domain is challenging. Existing strategies such as direct numerical simulations or coarse‐grained approaches (Biot's theory) either fail due to technical issues (number of Degrees of Freedom (DoF)) or are not capable of intuitively taking permeability changes based on the deformation state into account. This work proposes a fully coupled scheme using hybrid‐dimensional element formulations and zero‐thickness interface elements that naturally describes flow in deformable fractures surrounded by porous media.
Fast generation of initial estimates for indirect optimal control
Authors: Callies Rainer 
Published: December 2018

AbstractFor the numerical solution of optimal control problems for large systems of ordinary differential equations (ODE) the indirect approach can be applied: Using optimal control theory based on the Maximum Principle the problem is transformed into a boundary value problem which is then solved numerically. In addition to the equations of motion, a set of differential equations for the adjoint variables is derived from the Hamiltonian. A main challenge for indirect methods was up to now the generation of initial estimates for the adjoint variables. A new approach is presented based on the estimated or experimentally observed controls of a suboptimal solution. They are formally integrated backwards; together with the algebraic constraints on optimal solutions (optimality condition and constant Hamiltonian) an inverse problem is formulated and solved to obtain reliable estimates for the adjoint variables on a predefined grid. By homotopy techniques the so obtained optimal solution of a modified problem is transferred into the solution of the original problem. As an example the optimal flight trajectory of an aerobatic aircraft in an Red Bull Air Race is calculated.
Layout of a Driver‐in‐the‐Loop Simulator for Validation of Human Body Models
Authors: Kempter Fabian , Fehr Jörg 
Published: December 2018

AbstractIn the field of crash simulation, advanced human body models (HBMs) with muscle representation become more and more important because of their ability to emulate the behavior of real human occupants more accurately than dummy models. To get experimental validation data for these models concerning muscle activation and time‐variant stiffness properties, a low‐cost Driver‐in‐the‐Loop (DiL) simulator based on a Porsche exhibition driving simulator is implemented. Driver kinematics and muscle activation are tracked by computer stereo vision and surface electromyography (SEMG). For improved driver immersion, kinematic feedback is provided by a six DoF motion platform, a force‐feedback wheel and a bassshaker at the back of the driving seat. The DiL‐simulation is based on a Simulink model, generated by the software package PreScan, with included mathematical models of vehicles, sensors, drivers, etc. The vehicle states, available in the generated Simulink model, are used to activate the motion platform via UDP protocol. Because of the physical limitations of the platform movement, the so‐called Motion Cueing Algorithms (MCA) are necessary to emulate real driving sensation by providing motion cues which minimize the required translational platform movements.
On extremum seeking controllers based on the Lie bracket approximation in domains with obstacles
Authors: Grushkovskaya Victoria , Zuyev Alexander , Ebenbauer Christian 
Published: December 2018

AbstractIn this paper, we consider the problem of extremum seeking in the presence of obstacles. The analytical expression of the cost function as well as locations and shapes of the obstacles are assumed to be partially or completely unknown. We describe a broad family of control algorithms for a unicycle type system, which provides a solution of the above problem based on Lie bracket approximation ideas. The obtained controllers generalize some known results and allow to construct new control strategies. Furthermore, it is shown that gradient‐free control algorithms can be used for excluding the attraction of trajectories to undesirable equilibriuma in obstacle avoidance problems.
On construction of general solutions of equations of elastostatic problems for the elastic bodies with voids
Authors: Gulua Bakur , Janjgava Roman 
Published: December 2018

AbstractThe linear theory of thermo‐elastic materials with voids was for the first time considered in the work Iesan. A two‐dimensional system of equations of plane deformation is written in the complex form and its general solution is represented by means of two analytic functions of a complex variable and one solution of Helmholtz equation. The constructed general solution enables one to solve analytically a sufficiently wide class of plane boundary value problems of the elastic equilibrium with voids.
A semi‐analytical approach for prediction of volume flow rate in nip‐fed reverse roll coating process
Authors: Jang Zia , Litfin Oliver , Delgado Antonio 
Published: December 2018

AbstractReverse roll coating, one of the most widely adopted coating techniques, is considered as a self‐metered process. Its volume flow rate in the coating bead is analytically unpredictable due to the presence of the dynamic contact point. In an attempt to approximate the volume flow rate in the coating bead, the position of the dynamic contact point was numerically approximated by computational fluid dynamics (CFD) and then introduced to Navier‐Stokes equations. As a result, this semi‐analytical approach represented a non‐linear correlation of the volume flow rate with speed ratio and capillary number.
A Computational Two‐Scale Model for the Simulation of Dual‐Phase Steels under Cyclic Loading
Authors: Gandhi Ashutosh , Balzani Daniel , Brands Dominik , Scheunemann Lisa , Schröder Jörg 
Published: December 2018

AbstractDual‐Phase (DP) steels exhibit excellent macroscopic properties such as high strength, ductility and energy absorption. However, the increase of strength also results in a large springback behavior which should be considered for an optimal production process design. Thus, accurate modeling of springback during forming applications is important. The macroscopic behavior of DP steels is closely tied to the phenomena taking place on the microstructural level. The presence of kinematic hardening and graded properties in ferrite together with complex interactions of the different phases at the microscale have a large influence on the macroscopic springback response. Therefore, a micro‐macro scale bridging approach is proposed wherein statistically similar representative volume elements (SSRVEs) are considered to capture the DP‐steel microstructure, c.f. [1], [2], [5]. This ensures effective modeling of the microstructure while significantly reducing the complexity of the microstructural morphology and thus reducing the computing time. A mixed hardening model, see [8], along with the initial volumetric strain approach, see [3], enables incorporating the kinematic hardening as well as graded properties in the microstructure. Multiscale calculations of cyclic tests show the performance of the model by measuring the Bauschinger factor and the attained stress levels during deformation.
Simulation of cardiac electromechanics of a rat left ventricle
Authors: Duong Minh Tuan , Holz David , Alkassar Muhannad , Dittrich Sven , Leyendecker Sigrid 
Published: December 2018

AbstractThis work presents the modelling and simulation of the cardiac electromechanics of a rat left ventricle (LV) under normal and pathological conditions. The 3D LV model is constructed from MRI images of a rat heart. The electrical wave propagates through the whole heart to trigger the mechanical contraction. Our coupled electromechanical problem is formulated based on the mono‐domain and the active stress approach. An implicit finite element‐based method is employed to monolithically solve the problem for the LV. The numerical results show significant differences in the electromechanical behaviour of the healthy and infarcted model.
On efficient computation of 3‐d simulation within TPM2‐Framework
Authors: Bartel Florian , Ricken Tim , Schröder Jörg , Bluhm Joachim 
Published: December 2018

AbstractWith this contribution we would like to communicate the state of the art of TPM2 application to realistic engineering problems. First of all, a conceptional overview of TPM2 is shortly given, secondly we illustrate the benefit of Computer Tomography (CT) technology to capture geometry and create finite element meshes. Further, the application of the domain decomposition (DD) method for parallel execution will be shown on an example of a fluid saturated porous unit cube and finally we give advise for additional acceleration of computational runtime via model order reduction (MOR) for the TPM2‐Framework.
Multi‐field modeling of thermomechanical coupled fracture problems
Authors: Schulte Jonathan , Krüger Melanie , Dittmann Maik , Hesch Christian 
Published: December 2018

AbstractIn this contribution we focus on a novel variationally consistent formulation for thermomechanical coupled fracture problems. To be specific, we aim on a phase‐field approach to fracture such that the resulting system consists of three fields, the deformation map, the thermal field as well as the crack phase‐field. In the sense of Griffith energy criterion for brittle fracture, a crack initiates or continues upon the attainment of a critical crack energy density. This critical energy exhibits strong temperature dependence, which is approximated by a linear interpolation within our framework. The material behaviour is governed by a modified Helmholtz free energy function in terms of the elastic part of the deformation gradient and the temperature. Postulating that fracture requires a local state of tension, we apply an anisotropic decomposition of the principle stretches of the deformation gradient and reduce the tensile contributions by a suitable degradation function, see [1] for more details. Accordingly, we are able to derive local constitutive relations for the first Piola‐Kirchhoff stress tensor, the entropy density and the phase‐field driving force in variationally consistent manner, see [2]. A further constitutive relation is the Duhamel's law of heat conduction. In case of fracture, the conduction degenerates locally such that we achieve a pure convection problem and the heat transfer depends on the crack opening width. Here, we formulate the conductivity tensor in terms of the phase‐field parameter. Eventually, various numerical examples will show the accuracy and capability of the proposed multi‐field approach to fracture.
Numerical modeling of solid particles motion in suspensions using Smoothed Particle Hydrodynamics
Authors: Kijanski Nadine , Steeb Holger 
Published: December 2018

AbstractSuspensions and their applications can be found in many fields of mechanical, civil and environmental engineering. To consider the flow behavior as well as fluid‐solid interactions in dilute suspensions, we present 3D Direct Numerical Simulations (DNS) of a single‐phase fluid with discrete solid particles. We therefore developed a numerical implementation based on the general‐purpose particle simulation toolkit HOOMD‐blue [1, 3] extended for the usage of Smoothed Particle Hydrodynamics (SPH) [2, 5]. Since both the fluid and the solid part can be discretized by particles, SPH as a Lagrangian particle method presents a good choice to model this particular non‐linear problem. To describe solid contact and interaction forces, we consider two solid contact models. The first model is a simplified Hertz‐Mindlin contact model [4] as used in classical DEM simulations. The second model is a lubrication force model as presented by [6]. To review the results of the approach, we discuss an example with two non‐spherical solid grains in a single‐phase fluid under shear flow.