bluuebunny/crossref_metadata_2025 huggingface dataset:
Scaled norm minimization method for computing the parameters of the HSS and the two‐parameter HSS preconditioners
Authors: Yang Ai‐Li
Published: March 2018

The performance of the Hermitian and skew‐Hermitian splitting (HSS) preconditioner for the non‐Hermitian positive definite system of linear equations is largely dependent on the choice of its parameter value. In this work, an efficient scaled norm minimization (SNM) method is proposed to compute the parameter value of the HSS preconditioner. In addition, by choosing different parameters for the Hermitian and the skew‐Hermitian matrices in the HSS preconditioner, a two‐parameter HSS preconditioner is proposed. Moreover, an efficient and practical formula for computing the parameter values of this new preconditioner is also derived by using the SNM method. Numerical examples are illustrated to verify the performances of the HSS and the two‐parameter HSS preconditioners when their parameters are computed by the SNM method.
Transformational leadership and follower proactivity in a volunteer workforce
Authors: do Nascimento Thainá T. , Porto Juliana B. , Kwantes Catherine T.
Published: March 2018

This study explored how transformational leaders can enhance volunteers’ proactive behavior in an all‐volunteer nonprofit organization. Based on Parker, Bindl, and Strauss’s model of motivation, it was hypothesized that role breadth self‐efficacy, work values (self‐direction/stimulation and universalism/benevolence), and positive affect would mediate the transformational leadership—proactive behavior relationship. Data came from 141 volunteers in Brazilian chapters of an international not‐for‐profit organization. The model was tested using structural equation modeling, with mediation hypotheses tested by estimating the indirect effects using bias‐corrected intervals. Comparative fit index (.97) and standardized root mean square residual (.05) fit statistics indicate the model is plausible. These findings contribute to the understanding of the role that leaders play in increasing followers’ proactive behavior in volunteer organizations.
Nurse education and understanding related to domestic violence and abuse against women: An integrative review of the literature
Authors: Alshammari Kafi Fraih , McGarry Julie , Higginbottom Gina Marie Awoko
Published: March 2018

Aim

The aim of this study was to explore previous literature related to nurses understanding of Intimate partner violence (IPV) or domestic violence and abuse (DVA) against women and to identify the gaps in nursing education so as to use the findings as a baseline to inform potential intervention strategies, curriculum development and outline implications for future nursing practice.

Design

An Integrative review of literature.

Methods

Studies were extracted through a search of the electronic databases, such as Science direct, EBSCO host and PubMed, to identify relevant evidences published between January 2000–January 2017. “Joanna Briggs Institute (JBI) tool” was used to review primary research studies.

Results

Seventeen empirical studies were analysed. Findings supported four themes including: educational and training experiences, identification of IPV/DVA, curriculum and communication skills of nurses. Continued efforts are further needed to highlight and address IPV/DVA in nursing education and training, to scale up nursing understanding to respond and identify IPV/DVA appropriately in a clinical environment.
Microscale Modeling and Simulation of Magnetorheological Elastomers
Authors: Kalina Karl A. , Brummund Jörg , Metsch Philipp , Kästner Markus
Published: March 2018

Herein, a finite strain microscale model for magnetorheological elastomers (MREs) based on a general continuum formulation of the magneto‐mechanical boundary value problem is introduced. The modelling approach enables to consider particles with magnetically soft or magnetically hard behavior. In order to connect the microscopic fields to effective macroscopic quantities, a suitable computational homogenization scheme is used. The microstructure of the considered MRE is discretized and the problem is solved numerically in terms of a coupled nonlinear finite element approach. Using the presented framework, the influence of the particle shape on the magnetostrictive effect of MREs filled with magnetically soft particles is discussed. Furthermore, the effective macroscopic hystereses of an MRE filled with magnetically hard particles are calculated. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Challenges and applications of overset grid coupling strategies
Authors: Schubert Svenja , Rung Thomas
Published: March 2018

The paper deals with the mass conservation and geometry intersection of overset grid coupling strategies. The interpolation based grid coupling of the overset procedure violates the inherent mass conservation of finite‐volume methods. This is problematic since incompressible finite‐volume solvers directly use the mass defect when solving for the pressure. Furthermore, overset grid coupling requires a sufficient overlap for the interpolation of field values. Geometry intersection can be handled by an immersed boundary method. Applications refer to a collision simulation of two cylinders and the wall influence on the added mass of a cylinder. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural Synthesis of Parallel Robots with Unguided Linear Actuators
Authors: Schulz Stefan , Seibel Arthur , Schlattmann Josef
Published: March 2018

In this paper, we show that a Stewart‐Gough platform with ball screw linear actuators that do not inhibit a rotation between the upper and the lower cylinder, so‐called unguided linear actuators, still has six degrees of freedom if universal joints are used as lower and upper joints. Such parallel mechanisms can be described as 6‐UHPU types. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Steps Towards More Realistic FSI Simulations of Coronary Arteries
Authors: Fausten Simon , Balzani Daniel , Heinlein Alexander , Klawonn Axel , Rheinbach Oliver , Schröder Jörg
Published: March 2018

In this contribution, results regarding fluid‐structure interaction (FSI) simulations for three‐dimensional arterial walls are presented. In detail, a benchmark problem for FSI simulations in arteries of sufficient complexity, which combines sophisticated nonlinear models for the fluid and the structure, cf. [1], as well as a short segment from a patient‐specific arterial geometry are considered. For the patient‐specific arterial geometry a specific inflow profile suited for realistic geometries and simplified boundary conditions for the outflow are taken into account. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A movement generation algorithm for FE Human Body Models
Authors: Martynenko Oleksandr , Schmitt Syn , Bayer Alexandra , Blaschke Julian , Mayer Christian
Published: March 2018

Finite element (FE) method simulations are increasingly used for the development in the area of vehicle safety nowadays. Highly detailed virtual mechanical and human body models (HBMs) available for use in connection with the increase of the processors performance and algorithms efficiency, give engineers the opportunity to simulate not only the car crash event itself but also a so‐called pre‐crash phase. This is important for the design and improvement of steering‐assist and autonomous driving systems, through the assessment of active occupant behaviour during the impact avoidance or any other complex driving manoeuvres. To enable adequate evaluation of such simulations, virtual Active Human Body Models (AHBMs) should be established, capable to not only reproduce reflex human reactions but also for simulations of human movements. This study investigates the applicability of a forward dynamics movement generation algorithm for the FE HBMs, presents first results and outlines questions, need to be solved in future to do such simulations in a robust and time effective way. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mechanobiological processes of tissue engineered cartilage replacement materials
Authors: Nachtsheim Julia , Markert Bernd , Stoffel Marcus
Published: March 2018

A new therapeutic approach in the treatment of small focal articular defects is the implantation of an acellular collagen‐based scaffold. Replacement materials need to fulfil high requirements in terms of biocompatility and mechanical properties. Ideally, they feature similar mechanical properties as native articular cartilage. The aim of this study is to experimentally and numerically analyse a clinically available implant. Therefore, we perform unconfined compression tests and use a phenomenological material model to identify material parameters of the viscoelastic material. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Heat transfer in multi‐phase porous media with application to cancer detection
Authors: Niedermeyer Angela , Heider Yousef , Stoffel Marcus , Markert Bernd
Published: March 2018

Heat transport in biological tissues and its modelling with different approaches, such as Pennes's bioheat equation and porous media theories, is investigated in this study. Breast cancer detection is envisaged as an application. The suitability of the widely‐used Pennes model for breast cancer detection by means of infrared imaging is investigated through experimental and numerical examples. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigating human thumb models via their range of motion volumes
Authors: Phutane Uday , Roller Michael , Björkenstam Staffan , Leyendecker Sigrid
Published: March 2018

The human thumb possesses joint axes with intricate descriptions, which enable the thumb to perform complex motions like opposition. To validate a thumb multibody model kinematically, we firstly study the difference in the volumes of the thumb tip workspace for the maximum range of motion (RoM) and the grasp RoM. We compare the volume difference for five models (with same joint designs but different axes locations and orientations) with data from literature. Secondly, we compute the rotation of the thumb along the longitudinal axis (internal rotation) for one joint for different postures. We compare the rotations for the five models with measured data from literature. In both checks, the results obtained from simulation are in close agreement with literature data and consequently the thumb model's kinematics is validated. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Data‐driven simulation of metastatic processes within brain tissue
Authors: Schröder Patrick , Wagner Arndt , Stöhr Daniela , Rehm Markus , Ehlers Wolfgang
Published: March 2018

The modelling of biological processes like the metastasation of lung cancer in brain tissue requires the inclusion of the major processes at the metastasis site as well as to identify model parameters from experiments. In this regard, experimental data from proliferation, malnutrition and drug experiments are embedded into a continuum‐mechanical metastases model. Successfully implemented, such models can serve as prototype tools to estimate the metastases growth and response to therapeutic applications. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A gradient‐extended damage‐plasticity model to counteract mesh dependence in finite element simulations
Authors: Brepols Tim , Wulfinghoff Stephan , Reese Stefanie
Published: March 2018

This study is concerned with theoretical and numerical aspects of a thermodynamically consistent gradient‐extended damage‐plasticity model which is based on a ‘two‐surface’ approach: damage and plasticity are treated as, in principle, independent physical mechanisms by using separate yield and damage criteria as well as individual sets of loading / unloading conditions. Such a model is especially appealing from a practical point of view since it can naturally account for various situations in which the model's behavior is either (quasi‐)brittle‐like, ductile‐like or possibly anything in between. The model's algorithmic treatment at the local integration point level requires special considerations. In this regard, two inherently different strategies are implemented and tested during the study and are briefly discussed here. A numerical benchmark test reveals that the proposed gradient‐extended damage‐plasticity model is well suited for counteracting the results' mesh size dependence in finite element simulations involving damage. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigations on dynamic fracture of ultra‐high performance concrete by Brazilian tests
Authors: Khosravani Mohammad Reza , Weinberg Kerstin
Published: March 2018

In the last years significant advances in energy‐absorption capabilities of concrete and concrete‐like materials have been made and a new generation of concrete has been introduced. A greatly improved microstructure compared to traditional concrete, leads to Ultra‐high performance concrete (UHPC) which shows improved material properties and better mechanical properties. Despite of many potential applications, specific technical information about this material is still limited. This research presents a linear elastic fracture mechanic based model which is used to study fracture behavior and some mechanical fracture parameters of UHPC material. On the series of the experiments, all the specimens are tested by Split Hopkinson Pressure Bar (SHPB) experiments. The dynamic elastic modulus of UHPC material is determined by cylindrical UHPC specimens. Brazilian disc specimens are impacted by the SHPB and the dynamic tensile strength of the specimens is calculated. Data acquisition system recorded the strain history during the experiment by the help of strain gauges which are mounted on the incident and transmission bars and on the specimens. The achieved results proved that the Brazilian test is a powerful and efficient method to study dynamic fracture properties of UHPC material. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Remarks on a modified mixed least‐squares finite element formulation for small strain elasto‐plasticity
Authors: Igelbüscher Maximilian , Schwarz Alexander , Steeger Karl , Schröder Jörg
Published: March 2018

In this contribution a mixed least‐squares (LS) finite element formulation for rate‐independent elasto‐plasticity is presented within the framework of small deformations. Due to kink‐like points in the elasto‐plastic least‐squares functional, the variational approach yields to a discontinuous first variation and leads to problems by applying the standard Newton method. The proposed modification avoids this problem and guarantees the continuity of the modified weak form. We consider a least‐squares formulation, given through the balance of momentum, the constitutive equation and the consideration of an additional redundant stress symmetry condition, as a basis for the approach of a modification of the first variation. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Separate control meshes for displacements and rotations for a shear locking free isogeometric Reissner‐Mindlin plate
Authors: Kikis Georgia , Klinkel Sven
Published: March 2018

In the analysis of plate and shell bending problems using an isogeometric Reissner‐Mindlin approach, transversal shear locking effects may occur especially for thin structures. One possibility to overcome locking effects is to increase the polynomial order of the NURBS basis functions. However, there are certain examples where this method shows some deficiencies, like oscillations. For low polynomial degrees, there exist only a few effective concepts for the elimination of locking effects. One is the enhanced assumed strain (EAS) method which is used in finite element formulations and which is sensitive to distorted element geometries. Beirão da Veiga et al. [1] introduced a new approach for a Reissner‐Mindlin plate formulation where the displacements and rotations of the mesh are approximated using different control meshes. The physical space of the structure always remains the same. Hence, the method is in accordance to the isoparametric paradigm. However, the shape functions for the approximation of the displacements and the rotations may have different polynomial degrees and number of control points. In this way, the compatibility requirement for pure bending is fulfilled and shear locking is avoided. The method is tested for an isogeometric Reissner‐Mindlin plate formulation, which is based on a degenerated shell formulation [2]. Basic examples are chosen and the results are compared to the unaltered isogeometric Reissner‐Mindlin plate and the finite element Method using MITC elements. The results show that the method has similar accuracy and efficiency as the MITC element and is also applicable for skew element geometries. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A layered shell element for the computation of interlaminar shear stresses and thickness normal stresses
Authors: Knust Gregor , Gruttmann Friedrich
Published: March 2018

In this contribution a layered shell element for the computation of laminated structures is proposed. The shell kinematic is based on the Reissner‐Mindlin theory with an inextensible director field. Further a multi‐field functional is introduced including the global shell equations and additional Euler‐Lagrange equations. These Euler‐Lagrange equations enforce the correct shape of warping through the thickness and lead to continuous transverse shear stresses at layer boundaries This leads to a mixed hybrid shell element, after elimination of stresses, warping and Lagrange parameters on element level. The resulting shell element has the usual 5 or 6 degrees of freedom per node, making it possible to apply this element to complex geometrical structures. An extension of the element to compute stresses in thickness direction is shown, in order to estimate and predict interlaminar failure. The computed results show good agreement with 3D solid shell models. Numerical examples for the computation of interlaminar shear and thickness normal stresses are shown and compared to results of 3D elements. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Projection and variational approaches to spectral analysis of thick elastic beams
Authors: Kostin Georgy
Published: March 2018

Variational and projectional approaches based on the method of integro‐differential relations is applied to derive finite‐dimensional systems of ODEs approximating the natural vibrations of rectilinear elastic beams with the rectangular cross‐section. This technique involves special semi‐discrete integral projections of constitutive equations relating the stress and strain tensors as well as the velocity and momentum vectors. The spectral properties of a homogeneous isotropic beam with the square cross section are analyzed by taking into account the problem symmetry. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermomechanical measurement of a brake disc
Authors: Lamjahdy Abdelkrim , Markert Bernd
Published: March 2018

The experimental study of the thermomechanical behaviour of disc brakes is reported. The goal of this study is to better understand and explain the thermomechanical effects of disc brakes by use of an advanced measurement system. Temperature measurements with an infrared camera, pyrometer and thermocouples have been carried out on the rubbing surface of brake discs and brake pads on a flywheel test bench. The mechanical behaviour is determined with a high‐speed detecting capacitive sensor. Based on the advanced measurement system, a detailed description of the occurring phenomena is possible. From these experimental investigations, a scenario of brake cycles is conducted. Moreover, the change of the pad stiffness and pad contact length is studied in [1]. Finally, a detailed discussion of the observed experimental behaviour and the theoretical approaches [2] is proposed. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An objective and locking‐free finite‐element formulation for geometrically exact Kirchhoff rods
Authors: Schulz Matthias , Böl Markus
Published: March 2018

A new finite‐element formulation for thin, arbitrarily curved rods based on the Kirchhoff theory is presented. More specifically, the modeling approach includes the parametrization, the weak form of the problem, and the spatial discretization. Also, a numerical example is adapted to show the absence of any locking‐effects. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An experimental and numerical study of gas pressure forming under shock‐wave loading
Authors: Shirafkan Nima , Markert Bernd , Stoffel Marcus
Published: March 2018

Explosive forming is an unconventional technique, in which a fluid is used as the pressure transmission medium. To optimise the forming process, knowledge of material behaviour under very high pressures and deformation rates are required. Deformation modelling, numerical simulation, and experimental analysis of copper plates subjected to shock‐wave loading are reported in this study. The Limaitre‐Chaboche viscoplastic constitutive law [7] is used and combined with a geometrically non‐linear shell model. The aim of this research is to propose an appropriate mechanical model and to develop an experimental set‐up to predict the material forming behaviour by simulation. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐unique Equilibria of a Statically Indeterminate System with Coulomb Friction
Authors: Steiner Wolfgang
Published: March 2018

This contribution aims to show that the Coulomb friction model in a statically indeterminate system can result in ambiguous equilibrium states. We demonstrate that a simple framework may be in equilibrium and satisfy all inequalities, related to a unilateral contact, for several values of the reaction forces. A new method [3], which extends Castigliano's theorem to problems with Coulomb friction, is applied to analyze the cases of sticking, slipping or opening of the framework's supports. We think that our example is simpler and more illustrative than the rather mathematical examples in [1] or in [2] where non‐unique static solutions were found, too. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Minimal Dynamic Structure Model Considering Dry Friction Energy Dissipation in Refrigerant‐Lubricated Gas Foil Bearings
Authors: Leister Tim , Bard Sebastian , Seemann Wolfgang
Published: March 2018

In the simulation of gas foil bearing rotor systems, computational time is considered a highly critical aspect. Consequently, a great number of sophisticated foil structure models found in literature reveal to be inapplicable for a fully coupled analysis of the overall system's nonlinear dynamic response. On the other hand, most notably if considering heavily loaded bearings, phenomena such as dry friction within the foil structure cannot be neglected without introducing substantial inaccuracies. To overcome these limitations, the minimal dynamic structure model described in this contribution considers a regularized Coulomb friction law applied to a reduced spring–mass arrangement. After the successful validation against static FE results, a transient simulation is carried out, allowing for interesting insights into the mechanisms behind beneficial energy dissipation. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Oscillations of a visco‐elastic belt drive
Authors: Steindl Alois
Published: March 2018

We investigate the loss of stability of the steady configuration of a planar visco‐elastic belt drive. The belt is considered as a linearly visco‐elastic slender beam with small bending stiffness, which is driven by a steadily rotating drum. Due to the presence of the small damping parameter and the small bending stiffness, the equations of motion are severly singularly perturbed. By variation of system parameters, like the driving speed, the damping coefficient, the tension force and the radius of the drums, we calculate the steady configuration and the stability limit of the belt. Our calculations show, that the viscous damping, the distributed load and the strong bending at the drums can decrease the critical driving speed significantly and lead to flutter oscillations. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Estimation of Heat Transfer Properties for the FE Simulation of Cryogenic Turning
Authors: Becker Steven , Hotz Hendrik , Kirsch Benjamin , Aurich Jan C. , v. Harbou Erik , Müller Ralf
Published: March 2018

In order to shorten the process chain in manufacturing and thus to optimize the manufacturing time, current researches investigate the possibility of combining two process steps, turning and hardening.

During cryogenic turning of metastable austenitic steel, deformation induced hardening in the surface layer of the workpiece can be achieved by applying high passive forces onto the workpiece [1]. This leads to an increase in the wear resistance [2] as well as the fatigue strength [3]. For the employed austenite‐martensite phase transformation it is necessary to maintain low process temperatures, typically below room temperature. Thus, cryogenic cooling has to be applied to counteract the heat, generated during machining [4].

For a better understanding of the influence of different cutting and cooling parameters on the temperature field during cryogenic turning, and thus martensite formation, knowledge of the exact temperature distribution in the workpiece and the workpiece surface temperature in the contact zone is essential. Since in situ measurements of the latter are hardly possible, an inverse determination via transient finite element simulation is performed [5].

In order to model cryogenic turning, material properties, thermal loads and heat transfer coefficients defining convective heat transfer, have to be determined first. These model parameters are investigated independently in stand‐alone experiments, applying only one thermal load at a time. The magnitudes of these values are obtained by iteratively modifying the initial values in the model until correspondence with measured temperature data from the experiment is achieved.

The present finite element approach only takes thermal loads into account and is performed in the finite element program FEAP (Finite Element Analysis Program) with an Eulerian mesh, which requires special consideration of the rigid body rotation of the workpiece. The Eulerian treatment results in an unsymmetrical system matrix, and a special stabilisation is required to avoid numerical oscillations in the time integration scheme [5]. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Robust implementation of multi‐slip crystal plasticity for micro machining simulations based on Fischer‐Burmeister complementary functions
Authors: Bischof Robert , Schneider Frank , Müller Christopher , Kuhn Charlotte , Aurich Jan C. , Müller Ralf
Published: March 2018

As opposed to macro scale machining processes, the crystalline structure of commercially pure (cp) titanium plays an important role in micro machining processes. Finite element simulations of micro machining processes involve several challenges, since the workpiece material undergoes large deformations during chip formation and eventually material separation needs to be modeled. A robust implementation of the finite deformation multi‐slip crystal plasticity model describing the material response is the basis of such simulations. One challenge is the determination of the active set of plastic slip systems. Standard explicit predictor‐corrector formulations based on the Karush‐Kuhn‐Tucker (KKT) conditions often fail. In order to circumvent the explicit determination of the set of active slip systems, the KKT conditions can be replaced by a system of Fischer‐Burmeister complementary functions. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An ignored source in the foundations of continuum physics “Die Allgemeinen Ansätze der Mechanik der Kontinua” by E. Hellinger
Authors: Eugster Simon R. , l'Isola Francesco
Published: March 2018

In 1913, Ernst Hellinger finished his remarkable article DIE ALLGEMEINEN ANSÄTZE DER MECHANIK DER KONTINUA, which appeared in German language in the “Encyklopädie der mathematischen Wissenschaften mit Einschluss ihrer Anwendungen”. Following his predecessors J.‐L. Lagrange, G. Piola and the Cosserat brothers, Hellinger presents in this paper a nonlinear field theory of continuum physics entirely based on a variational principle “the principle of virtual displacements”. Even though Hellinger focuses on the fundamentals of continuum mechanics, he presents within the very same variational framework the physics of optics, electrodynamics, thermodynamics and the theory of relativity. Accordingly, Hellinger's paper can be understood as a contribution to continuum physics in general. However, due to the establishment of English as the upcoming scientific language and due to the refusal of a variational formulation of continuum mechanics in the subsequent period, Hellinger's contribution to the foundations of continuum physics has been ignored for decades and has almost fallen into oblivion. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An Affine Micro‐Sphere Model for Strain‐Induced Crystallization in Rubbery Polymers
Authors: Nateghi Aref , Keip Marc‐André , Miehe Christian
Published: March 2018

Natural rubber crystallizes under stretch and its amorphous structure becomes semi‐crystalline. Tensile strength, fatigue life and crack growth resistance of rubber increases with crystallization. Crystallization leads to a hysteresis in the stress‐stretch diagram of rubber, see [1]. Recently, computational modeling of strain‐induced crystallization has drawn the attention of researchers, see [2, 3] and [4]. In this work, we propose a micromechanically motivated material model for strain‐induced crystallization in rubbers. To this end, we construct a microscopic model for a single crystallizing polymer chain based on non‐Gaussian chain statistics. A thermodynamically consistent evolution framework for crystallization in the chain level is proposed. The chain model is then integrated into the affine micro‐sphere model. Finally, numerical results obtained by the model are compared to experimental data. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of inelastic material parameters using component‐oriented specimen with design of experiments
Authors: Nostitz Niklas , Hendrik Kröger Nils , Ihlemann Jörn
Published: March 2018

For the simulation of the mechanical behaviour of components, an appropriate material model and a good experimental data base to identify the material parameters are needed. Due to the fact that the typically used standard test specimen do not include any inhomogeneous effects, an alternative component‐oriented specimen is introduced. To improve the identification, a design of experiments strategy is employed. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Biomaterial spider silk: Potential candidate for airbag fabric material
Authors: Prajapati Kaushik Govindbhai , Patil Sandeep P. , Carmai Julaluk , Koetniyom Saiprasit , Markert Bernd
Published: March 2018

In the present work, the mechanical properties of spider silk are assigned to the airbag fabric material. Finite element simulations were performed on the airbag model in order to study its benefits over the traditional fabric material. We designed the airbag model with spider silk material and performed impact analysis. Finally, the obtained results are compared with the standard airbag test. Our analysis pave the way towards the new promising material for airbags. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of PLLA near glass transition temperatures
Authors: Raza Syed Hasan , Klusemann Benjamin
Published: March 2018

The treatment for Coronary Heart Diseases – caused by the deposition of plaque on arterial walls – which has been the deployment of a metal stent in the blocked artery, poses serious complications in the form of accumulation of blood clots due to the permanent and rigid nature of metals. Meanwhile, Bioresorbable Vascular Scaffolds (BVSs) – made up of poly l‐lactide (PLLA) – are transient implants offering support to the artery for 6–9 months and leaving no trace behind once dissolved after 2 years. PLLA, however, has lower strength compared to metals and thus requires a higher thickness to make it useful for transplants. Thermal annealing, which can alter the microstructure of PLLA to make it thinner and stronger, is a good solution for this problem. In order to implement thermal annealing, experimentation and simulations are required to study the behaviour of the microstructure during the process. In general, its behaviour below glass transition temperature and at short time‐scale is glassy, while above glass transition temperature and at long time scale is rubbery. With constitutive models available for other polymers, such as polyethylene terephthalate (PET), it is intended to develop a constitutive model for PLLA accordingly. In this regard, the Buckley model is implemented. The model allows studying the behaviour in PLLA at the temperatures of interest during thermal annealing. Numerical results will be presented and compared for neat PLLA samples for different strain rates and temperatures. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite Element Approximation of Fluid‐Structure Interaction with Coupled Wave Propagation
Authors: Ebna Hai Bhuiyan Shameem Mahmood , Bause Markus
Published: March 2018

In this contribution, a concept of coupling the fluid‐structure interaction (FSI) with an ultrasonic wave propagation is proposed. It is referred to as the extended Fluid‐Structure Interaction (eXFSI) problem. The eXFSI is a one‐directional coupling of typical FSI problem with an ultrasonic wave propagation in fluid‐solid and their interaction (WpFSI). Notably, the WpFSI is a strongly coupled problem of acoustic and elastic wave equations and automatically adopts the boundary conditions from the FSI problem at each time step. To the best of our knowledge, such a model is novel in the literature. The principal aim we pursue is to explore and develop concept of the efficient numerical solution of the eXFSI problem. The solution of the eXFSI and WpFSI models constitute an important part of on‐live and off‐live structural health monitoring (SHM) systems design for composite material and lightweight structures. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermo‐mechanical modeling of turbine blades taking into account structural defects
Authors: Kunin Artsem Boris , Loehnert Stefan , Wriggers Peter
Published: March 2018

In turbine blades of aero‐engines typical defects are cracks due to high mechanical and thermal loads. The extended finite element method (XFEM) is used for simulations of fracture mechanics problems with cracks. Discontinuities in the displacement and temperature field are allowed and the crack opening displacement and crack tip stress field are reproduced accurately. Since crack closure and non‐physical penetration of the crack surfaces may occur under certain load conditions, it becomes necessary to enforce the non‐penetration condition for crack surfaces. This contact formulation is assumed to be frictionless. The node‐to‐segment approach proposed in [3] is extended to ten‐node tetrahedral elements with quadratic shape functions. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Description of the Damage and Healing Behavior of an Extrinsic and Autonomous Self‐Healing Anisotropic Material
Authors: Specht Steffen , Bluhm Joachim , Schröder Jörg
Published: March 2018

In this contribution, the damage and healing behavior of a fiber reinforced polymeric composite will be investigated. Therefore, the considered Helmholtz free energy function for the polymeric matrix material consists of two parts, an isotropic part for the description of the isotropic polymer and an anisotropic part for the reinforcement. As theoretical framework, the Theory of Porous Media is used, where internal interactions (phase transitions, temperature exchange, ...) can be described by so‐called production terms. At the end a numerical example of an anisotropic self‐healing polymer is presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromorphic homogenisation and its application to a model of ductile damage
Authors: Hütter Geralf
Published: March 2018

Heuristic gradient extensions of classical damage models are established to overcome their spurious mesh dependency. In contrast, an extension of Gurson's model of ductile damage towards the microdilatational theory is presented through a straight‐forward homogenization. FEM simulations prove the regularization capabilities of the model. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Contact Mechanics in Computational Homogenization
Authors: Leichner Alexander , Andrä Heiko , Simeon Bernd
Published: March 2018

Concerning homogenization, we consider in this contribution periodic boundary‐interface value problems (BIVP) within representative volume elements (RVE), which contain porous materials consisting of possibly many separate objects. For instance, these RVEs are available from micro scans in voxel resolution. However, the occurrence of contact between deformable, solid objects requires advanced techniques of methods solving common elasticity problems. With regard to that, we will demonstrate the treatment of contact between each of those by means of an implicit boundary description, used for both surface reconstruction and contact detection. Furthermore, a new technique for solving contact problems is introduced which can be easily integrated as material law routine into so called fast solvers [1], performing on Cartesian grids and exploiting the fast Fourier transform (FFT). In the end, we will present numerical results for a standard problem from contact mechanics, obtained by this new approach. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interaction boundary layer theory applied to a benchmark flow problem
Authors: Braun Stefan
Published: March 2018

Consider planar, incompressible laminar high Reynolds number (Re) flow between two parallel plates: fluid is removed through the permeable upper wall in order to generate adverse pressure gradient conditions in mean flow direction. As a consequence of relatively weak suction, the boundary layer at the impermeable lower wall is forced to separate locally. The corresponding reverse flow region (separation bubble) is known to react very sensitively to perturbations of any kind and typically undergoes rapid transition to the turbulent flow state. The present paper briefly summarizes the current status of the corresponding asymptotic flow description in the limit as Re → ∞. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of crystallization processes in viscoelastic polymer melt flows
Authors: Descher Stefan , Wünsch Olaf
Published: March 2018

A simplified model for plate extrusion is presented. Calculations for the exponential form of the Phan‐Thien Tannner fluid combined with a nonisothermal crystallization model are performed. A Study for the Deborah‐ and Péclet‐number is carried out to investigate if stress is transported in regions of crystallization. It is shown that for the presented model, this is only the case for regions close to walls. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Attractors for the motion of finite‐size particles in a two‐sided lid‐driven cavity
Authors: Wu Haotian , Romanò Francesco , Kuhlmann Hendrik C.
Published: March 2018

Particle trajectories in an incompressible cavity flow are investigated experimentally. The flow is driven by two facing walls moving with same speed in opposite directions. When the flow is steady and three‐dimensional, finite‐size and neutrally‐buoyant particles are rapidly attracted to periodic orbits. Three‐dimensional particle tracking is used to reconstruct single particle trajectories. Experimental results are presented and compared with numerical simulations. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Steady transonic dense gas flow past two‐dimensional compression/expansion ramps
Authors: Kluwick Alfred , Cox Ted
Published: March 2018

The dynamic behaviour of compressible fluids depends crucially on the curvature of isentropes in the pressure/specific volume diagram. Most conveniently this curvature is expressed in form of a non‐dimensional quantity Γ now commonly referred to as the fundamental derivative of gasdynamics, Thompson [5]. Bethe‐Zel'dovich‐Thompson (BZT) fluids have the distinguishing property that they exhibit embedded regions in the general neighbourhood of the thermodynamic critical point where Γ is negative in contrast to classical gases of low molecular complexity including perfect gases where Γ is strictly positive.

The behaviour of steady transonic flows of such fluids is essentially governed by two non‐dimensional parameters: (Γ) and its derivative with respect to the density at constant entropy (Λ), Cramer and Fry [2], Kluwick [4]. The resulting response to external forcing is surprisingly rich in nonclassical phenomena such as rarefaction shocks, sonic shocks, split shocks, etc. and is studied in detail for the canonical problem of two‐dimensional flow past compression/expansion ramps. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An infinite mapping layer for deep water waves
Authors: Toth Florian , Schoder Stefan , Kaltenbacher Manfred
Published: March 2018

In order to accurately and efficiently model the propagation of surface gravity waves in infinitely deep domains, we introduce an infinite mapping layer which transforms the unbounded physical domain into a bounded computational domain by means of a mapping function. The method was implemented in the framework of the finite element method, where it can be straightforwardly combined with a perfectly matched layer to model unbounded domains in horizontal direction. Finally, the application of the method is demonstrated by a simple 3D example. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modal analysis of wingtip vortices by means of Proper Orthogonal Decomposition
Authors: Dufhaus Sebastian , Brautmeier Sarina , Uhl Anna , Hörnschemeyer Ralf , Stumpf Eike
Published: March 2018

This paper discusses the influence of different wingtip geometries on the first eigenmodes of wingtip vortices. With the use of Proper Orthogonal Decomposition (POD) of a turbulent velocity field, a modal decomposition of coherent structures, high energetic eigenmodes are determined. Based on the results found by Fabre et al. [1], these eigenmodes may be a key factor for the stability analysis. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of chemotactical biofilm growth in evolving microstructures
Authors: Schulz Raphael
Published: March 2018

The work is concerned with the growth of biofilms made by chemotactical bacteria within a two‐dimensional saturated porous media. The increase of a biomass on the surface of the solid matrix changes the porosity and impede the flow through the pores. By formal periodic homogenization an averaged model describing the process via Darcy's law and upscaled transport equations with effective coefficients given by the evolving microstructure at the pore‐scale was derived in [3]. Based on the assumption of uniform evolve of the underlying pore geometry and slight self‐diffusivity of the bacteria, solvability in a weak sense global in time or at least up to a possible clogging phenomenon can be shown. Furthermore, by assuming sufficient regularity on the data we prove boundedness of the solution. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal Control in Autonomous Driving
Authors: Cobus Andreas , Rick Matthias , Sommer Laura , Backfisch Niels , Probst Alexander , Echim Mitja , Büskens Christof
Published: March 2018

Autonomous driving is no longer a subject of science fiction. Instead it has become a field of highly topical developments and has already reached numerous milestones. The Audi Autonomous Driving Cup provides a stage for students to participate in this development process. This competition, carried out in Germany, Austria and Switzerland, provides miniature vehicles of normed hardware to the participants which have the task of implementing algorithms for autonomous handling of problems such as lane tracking, obstacle detection, adaptive cruise control, overtaking, turning as well as entering and exiting parking spaces. To present the concept of optimal control based on a single track model in combination with image processing methods we focus in this paper on the parking manoeuvre only. Thereby we show that optimization and control techniques can play a key role in the design of autonomous vehicles. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Direct Computation of the Byrnes‐Isidori Normal Form
Authors: Röbenack Klaus
Published: March 2018

If an input‐affine single‐input single‐output control system has a well‐defined relative degree, there exists a (local) change of coordinates transforming the system into the Byrnes‐Isidori normal form. By this transformation, the system is decomposed into two subsystems. The first subsystem can be linearized by feedback, and the second subsystem does not directly depend on the input. To achieve this structure, the last components of the transformation have to fulfill a partial differential equation. Practically, the appropriate choice of these coordinates is usually left to the (experienced) user. In this note, the author suggests a direct calculation based on the computation of flows of certain vector fields. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Project scheduling under uncertainty and resource constraints
Authors: Hartmann Veronika , Lahmer Tom , Smarsly Kay
Published: March 2018

This paper proposes a method to improve the reliability of construction schedules by optimizing schedule robustness of construction projects. The schedule robustness is measured by a criterion evaluating the impact of deviations from the initial schedule on the makespan, which arise during the realization phase of a construction project. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic Equilibrium of a Coupled ODE‐PDE Problem for Surface Nanobubbles
Authors: Kimmerle Sven‐Joachim , Sverdrup Knut , Berg Peter
Published: March 2018

We consider a mathematical model for surface nanobubbles arising from hydrogen electrolysis in polymer electrolyte membrane (PEM) electrolyzers. Experimental advances in recent years indicated longer lifetimes of surface nanobubbles than may be explained by classical theories. Contrary to [5], we state a full model of an evolving single surface nanobubble yielding a coupled system consisting of a partial differential equation (PDE) for the hydrogen concentration in water and an ordinary differential equation (ODE) for the radius evolution. In the special case of dynamic equilibrium conditions, we prove the well‐posedness of this steady state problem by a fixed‐point strategy, assuming an acute‐angled contact angle, and that the corresponding algorithm allows for its numerical simulation. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)