bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact Simulations Using a Quasi‐Static Contact Submodel in Reduced Flexible Multibody Systems
Authors: Tschigg Stephan , Seifried Robert
Published: October 2016

For an efficient approximation of the local and global deformation behavior, impact simulations using reduced elastic models can be performed. Modally reduced models require a large number of eigenmodes to capture all local deformation effects. For this reason, the use of static shape functions in the contact area is recommended. However, due to high eigenfrequencies introduced by the static shape functions, the time integration is no longer efficient. Hence, this work presents an approach to reduce the influence of these high frequencies on the time integration. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Prediction Model for State Observation and Model Predictive Control of Biped Robots
Authors: Wittmann Robert , Rixen Daniel
Published: October 2016

Biped walking robots present a class of mechanical systems with many different challenges such as nonlinear multi‐body dynamics, a large number of degrees of freedom and unilateral contacts. The latter impose constraints for physically feasible motions and in stabilization methods as the robot can only interact due to pressure forces with the environment. This limitation can cause the system to fall under unknown disturbances such as pushing or uneven terrain. In order to face such problems, an accurate and fast model of the robot to observe the current state and predict the state evolution into the future has to be used. This work presents a nonlinear prediction model with two passive degrees of freedom (dof), point masses and compliant unilateral contacts. We show that the model is applicable for real‐time model predictive optimization of the robot's motion. Experiments on the biped robot LOLA [1] underline the effectiveness of the proposed model to increase the system's long term stability under large unknown disturbances. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of confocal microscopy image data of Physcomitrella chloroplasts to reveal adaptation principles leading to structural stability at the nanoscale
Authors: Asgharzadeh Pouyan , Özdemir Bugra , Müller Stefanie J. , Reski Ralf , Röhrle Oliver
Published: October 2016

Proteins of the FtsZ (filamentous temperature‐sensitive Z) family establish complex polymeric spatial patterns in plastids of the moss Physcomitrella patens. These structures represent a "plastoskeleton" that might contribute to plastid shape and stability. The aim of this work is to develop computer models of FtsZ network connectivity and dynamics. These computer models are developed from green fluorescent protein (GFP) images obtained by Prof. Reski's Plant Biotechnology group at the University of Freiburg by means of laser scanning confocal microscopy. Subsequently, structural reconstruction techniques based on cellular automata algorithm are applied on the raw image data to compensate for any information that is lost in the process of imaging. Segmentation of the processed data will result in the computer model of the targeted structures, which are used for further analysis. Model generation and experimental testing in the moss system is conducted in an iterative process with the aim of both forward and reverse biomimetics. A developed image processing algorithm with the aim of quantification of structural characteristics is utilized to extract structural features of the FtsZ network in Physcomitrella enabling us a statistical analysis on the extracted data. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A novel model to describe the intervertebral disc mechanical response
Authors: Azarnoosh Marzieh , Heider Yousef , Stoffel Marcus , Markert Bernd
Published: October 2016

The main objective of the present work is the development of a simplified, efficient and easy‐to‐implement single‐phase material model, which is able to describe the essential effects characterising the behaviour of multi‐phase saturated materials, such as of intervertebral discs (IVDs). The presented new model mainly focuses on extending a viscoelastic material model in order to not only take the mechanical behaviour of the solid part into account, but also the fluid‐flow‐dependent behaviour of the material. By applying this model, the complexity and constitutive parameters are reduced, the implementation is more convenient and the experimental investigations can be better supported in comparison to multi‐phase material models of IVDs. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale modelling of skeletal muscle tissue by incorporating microstructural effects
Authors: Bleiler Christian , Ponte Castañeda Pedro , Röhrle Oliver
Published: October 2016

The macroscopic mechanical response of skeletal muscle tissue is mainly influenced by the properties and arrangement of microstructural elements, such as, for example, sarcomeres and connective tissue. Like for many biological materials, the mechanical properties of skeletal muscle tissue can vary quite significantly between different specimens like, for example, different persons or muscle types. Current state‐of‐the‐art continuum‐mechanical muscle models often lack the ability to take into account such variations in a natural way. Further, phenomenological constitutive laws face the challenge that appropriate material parameter sets need to be found for each tissue variation.

Thus, the present work aims to identify the microstructural features and parameters governing the overall mechanical response and to incorporate them into a macroscopic material model by applying suitable homogenisation methods. The motivation hereby is that the estimation of material parameters for microstructures, such as collagen fibres, can be done in a more reliable and general way and that fluctuations between specimens are included by, for example, adapting the alignment of the collagen fibres inside the muscle. Moreover, instead of computationally expensive homogenisation methods like FE2, this work proceeds from well‐founded analytical homogenisation techniques in order to keep the model as simple as possible. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The investigation of femoroacetabular impingement using motion capture, FEM and multi‐body simulations
Authors: Cichon Robert , Raab Dominik , Hewera Simon , Lazik‐Palm Andrea , Theysohn Jens , Landgraeber Stefan , Kowalczyk Wojciech
Published: October 2016

In recent years, femoroacetabular impingement (FAI) has become increasingly common. As published in the literature, FAI is caused by an unphysiological contact between the proximal femur and the acetabular rim, which may lead to pain, limitation of movement, and damage of cartilage. In this paper, patient‐specific finite element simulations of the movement of the hip based on gait motion data and MRI segmentation were conducted to check stresses of the acetabulum and femur, and additionally whether a bony contact is present or not. The study's findings show no bony contact between femur and acetabulum, which may lead to the hypothesis that the labrum and its deformation and/or the articular capsule are involved in the mechanism of FAI. In order to verify this hypothesis more simulations including labrum and capsule must be performed. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Failure of adhesive bonds between proteoglycans causes viscoelasticity of soft tissues
Authors: Hillgärtner Markus , Linka Kevin , Itskov Mikhail
Published: October 2016

Soft tissues can be considered as a composite material where a matrix (ground substance) is reinforced by collagen fibers. These fibers consist of fibrils, which are connected by proteoglycan (PG) bridges. The time‐dependent properties of soft tissues appear to be mainly caused by proteoglycans [3]. This contribution presents a modeling approach where damage in the PG bridges arises due to the failure of the covalent bonds between two proteoglycans. The breakage of covalent bonds is reversible over time and incorporated using a healing formulation. A high PG density supports interfibrillar sliding and hence leads to a lower fibril stretch [8]. Accordingly, the damage propagation in PG bridges leads to a higher stretch in the fibrils and therefore to a stiffer material response. The strain energy of the fibrils is based on the response of single tropocollagen molecules and takes both, an entropic and an energetic regime into account [5]. Finally, the model is compared against experimental data available in the literature. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical and experimental investigation of bone fracture in the human proximal femur
Authors: Hülsmann Angelina , Stoffel Marcus , Heider Yousef , Knobe Matthias , Markert Bernd
Published: October 2016

Proximal femur fractures are very common injuries especially among older patients. Although, there are various alternatives and improvements in implant design and operating techniques, the treatment still represents a big medical challenge. Therefore, the understanding of crack initiation and propagation in the proximal femur is of great interest. The objective of this work is to present a simplified phenomenological model that is able to predict crack initiation and propagation in the proximal femur. This will be simulated by using a phase‐field modelling (PFM) approach. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational and experimental analysis of wound healing processes
Authors: Liang Jinghu , Bolea Albero Antonio , Füller Jendrik , Müller‐Goymann Christel , Böl Markus
Published: October 2016

Wound healing in epidermis is a complex physiological process in which new cells are created to repair the damaged tissue. The timing of cell division and growth mechanisms in wound healing are influenced by biological, mechanical and medical factors. In this work we aim to provide a numerical model based on the observations realised in in‐vitro experiments for the understanding of wound healing. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fatigue damage modeling of fibrous soft tissues
Authors: Linka Kevin , Itskov Mikhail
Published: October 2016

Ultimate tendon failure is often caused by fatigue loading. Recent interventions revealed a three‐phase progression of histological changes during cyclic loading of the tendon. It starts from localized kinked fiber deformations, continues with additional fiber delaminations and finally leads to fiber angulations and discontinuities [5, 6]. In the present contribution, we propose a physically motivated constitutive model able to describe fatigue evolution in tendon subject to cyclic loading. The damage of the collagen fibers is elucidated by a successive permanent opening of tropocollagen molecules [7], which represent the basic building blocks of collagen fibrils. The fibril strain increase is triggered by a time‐force depending rupture of glycosaminoglycan sidechains of adjacent collagen fibrils. The so obtained model is in line with recent experimental findings available in literature. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An examination of tissue engineered scaffolds in a bioreactor
Authors: Niedermeyer Angela , Zhou Bei , Dursun Gözde , Stoffel Marcus , Artmann Aysegül , Markert Bernd
Published: October 2016

Replacement tissues, designed to fill in articular cartilage defects, should exhibit the same properties as the native material. The aim of this study is to foster the understanding of, firstly, the mechanical behavior of the material itself and, secondly, the influence of cultivation parameters on cell seeded implants as well as on cell migration into acellular implants. In this study, acellular cartilage replacement material is theoretically, numerically and experimentally investigated regarding its viscoelastic properties, where a phenomenological model for practical applications is developed. Furthermore, remodeling and cell migration are investigated. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multi‐component modelling and simulation of metastases proliferation within brain tissue
Authors: Schröder Patrick , Wagner Arndt , Ehlers Wolfgang
Published: October 2016

Originated from a lung tumour, cancer cells can spread via the blood‐vessel system, travel to the cerebrum and may pass the blood‐brain barrier. The extravasation is followed by migration, and the formation of micrometastases. Further proliferation causes interveined metastases. A pressure‐driven infusion of a therapeutic solution counteracts the disturbance by the metastases within the brain. These processes are described with a continuum‐mechanical model based on the Theory of Porous Media. Numerical applications demonstrate the feasibility of the model and include multicellular‐tumour spheroid experiments in the macroscopic simulation of metastases growth and atrophy. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On an electrical‐chemical‐mechanical approach for modelling smooth muscle excitation in bladder tissue
Authors: Seydewitz Robert , Böl Markus
Published: October 2016

The urinary bladder is characterised by its ability to withstand high deformations under harsh chemical conditions. Occurring irregularities in the bladder wall disturb the correct functioning during storage and release. In order to support the development of effective therapeutic treatments for dysfunctional urinary bladder a theoretical model was developed. Accounting for different pathways of smooth muscle activation the proposed model is based on a coupled electrical‐chemical‐mechanical approach. Finally, the model is implemented in the finite‐element framework to consider complex geometries and boundary conditions. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of active muscle contraction on whiplash injury
Authors: Sharma Nisha N. , Carmai Julaluk , Koetniyom Saiprasit , Markert Bernd
Published: October 2016

The objective of this work is to develop a finite element model of active human skeletal muscle, which can mimic its contraction behaviour. The model is then used to analyse the effects of active muscle contraction into occupant kinematics and injuries during rear‐end collision. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bi‐phasic theory vs. volumetric viscoelasticity for modelling the behaviour of thin collagenous membranes
Authors: Stracuzzi Alberto , Ehret Alexander E.
Published: October 2016

A relation is established between a recently proposed single‐phase model for human amnion [1], in which an internal state variable accounts for viscoelastic volume changes due to fluid outflow, and an explicitly bi‐phasic representation. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Three‐dimensional reconstruction of M. gastrocnemius contraction
Authors: Weichert Christine , Leichsenring Kay , Ernst Michael , Wick Carolin , Siebert Tobias , Blickhan Reinhard , Böl Markus
Published: October 2016

There exist many different approaches investigating the contraction mechanisms of skeletal muscles. Thereby, the mechanical behavior, such as force generation in association with kinematic and microstructure, play an important role in modeling of muscle behavior. Besides the mechanical behaviour, the validation of muscle models requires the geometrical environment, too. The geometry of a muscle can be divided into macrostructure, existing of aponeurosis‐tendon‐complex (ATC) and muscle tissue (MT), as well as the fascicle architecture, representing the microstructure of the MT.

In this study, the macrostructure of the isolated M. gastrocnemius was observed during isometric contraction by using three‐dimensional optical measurement systems in combination with mechanical measurement techniques. The surface deformation was reconstructed at specific force and length relationships and further the muscle tissue, aponeurosis, and tendon were distinguished, building up a macroscopic geometrical dataset. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and numerical investigation of tendons and tendon cells
Authors: Willenberg Wolfgang , Azarnoosh Marzieh , Stoffel Marcus , Markert Bernd
Published: October 2016

Tendon injuries are a common problem in medicine. While healthy tendons do not rupture, tendon injuries are mostly accompanied by pathological changes and microruptures. Unfortunately, still less is known about the underlying processes. Thus, in the present study, we introduce artificial damages into native tendon tissue and investigate its mechanical behaviour experimentally. In the second part of this study, we propose a theoretical model for predicting the mechanical behaviour of the damaged tendon and present its validity. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A regularized damage‐plasticity model: micromorphic formulation and numerical aspects
Authors: Brepols Tim , Wulfinghoff Stephan , Reese Stefanie
Published: October 2016

A gradient‐extended damage‐plasticity model is discussed which is based on a micromorphic approach according to Forest [1]. Damage and plasticity are treated as independent but strongly coupled dissipative phenomena by considering separate yield and damage loading functions to describe the onset of plastic flow and / or damage evolution. A numerical benchmark test conducted in the study reveals that the model is able to essentially cure the well‐known mesh‐dependence issue which is known from finite element simulations involving conventional (i. e. ‘local’) damage material models. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A microcrack‐based continuum damage model with application towards refractories
Authors: Gundlach Janto , Henneberg Dimitri , Ricoeur Andreas
Published: October 2016

The present work discusses numerical results of damage evolution due to thermoshock processes at refractory ceramics. Damage patterns have been generated using a two‐scale approach for brittle materials, implemented into a finite element framework. For this purpose, a cell model has been employed, incorporating cracks on a microscopic level. The impact of these discontinuities on macroscopic material properties and damage evolution is determined with the help of analytical homogenization techniques. Finally, the potential of the numerical tool is demonstrated by means of refractory bricks, being imposed by thermomechanical loading. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A numerical approach to simulate printed electronics on fiber reinforced composites
Authors: Heinrich Felix , Lammering Rolf
Published: October 2016

Printed conductive paths can transmit electrical information and form an alternative to conventional wiring. In lightweight applications, where the reduction of weight is crucial, printed conductive paths and electronics could help to diminish the total mass of the structure. A possible application in aeronautics is Structural Health Monitoring (SHM) ‐ a collective term describing the structural integration of electronics that serve as a central nervous system to detect damages. As the electronics cannot only be printed on surfaces but also in between the layers of CFRP materials, it is currently under investigation whether the electronics favor delamination. To describe the electronics‐CFRP interface failure numerically, a suitable approach for a finite element analysis shall be found. Based on a homogenized and simplified description of the interface, different numerical approaches are presented and advantages and disadvantages are considered. The most promising approach is discussed in greater detail and first numerical simulations are shown. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of singularity exponents in 3D elasticity problems using enriched base functions in the Scaled Boundary Finite Element Method
Authors: Hell Sascha , Becker Wilfried
Published: October 2016

The SBFEM is employed for the extraction of 3D stress singularity exponents and their associated deformation modes. It makes use of a separation of variables approach, which is substituted into the virtual work equation so that only parts of the boundary need to be discretized while the 3D boundary value problem is considered analytically in a scaling variable. The enrichment of the standard separation of variables representation for the displacements with a decomposition of the analytical crack displacement field yields a substantial improvement of the method's accuracy and convergence properties. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A combined molecular dynamics‐phase‐field modelling approach to fracture
Authors: Patil Sandeep P. , Heider Yousef , Hernandez Padilla Carlos Alberto , Cruz‐Chú Eduardo , Markert Bernd
Published: October 2016

In order to better understand and ease the determination of material and model parameters required for the macroscopic modelling of brittle fracture, a bottom‐up comparative study between molecular dynamics (MD) simulations and the continuum phase‐field modelling (PFM) is carried out. In particular, based on the MD simulations of fracture of a highly brittle material, a number of PFM parameters such as the width of the transition zone between the damaged and the undamaged material, the crack resistance and the elasticity modulus are estimated. This study opens the door for an efficient way for multi‐scale modelling of fracture. To illustrate this approach, a comparative two‐dimensional numerical initial‐boundary‐value problem (IBVP) for the highly brittle aragonite (CaCO3) is presented. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Comparison of Algorithmic Approaches to Damage‐Plasticity Modeling in the Context of Gradient‐Enhancement
Authors: Kiefer Björn , Waffenschmidt Tobias , Sprave Leon , Menzel Andreas
Published: October 2016

A gradient‐enhanced damage‐plasticity formulation is proposed, which prevents the loss of well‐posedness of the governing field equations in the post‐critical damage regime. The non‐locality of the formulation then manifests itself in terms of a free energy contribution that penalizes the occurrence of damage gradients. A second penalty term is introduced to force the global damage field to coincide with the internal damage state variable at the Gauss point level. An enforcement of Karush‐Kuhn‐Tucker (KKT) conditions on the global level can thus be avoided and classical local damage models may directly be incorporated and equipped with gradient enhancement. An important emphasis of this research is to investigate the efficiency and robustness of different algorithmic schemes to locally enforce the KKT conditions in the multi‐surface damage‐plasticity setting. Response simulations for a representative inhomogeneous boundary value problem are studied to assess the effectiveness of the gradient enhancement regarding stability and mesh objectivity. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of a Phase Field Model for Elasto‐plastic Fracture
Authors: Noll Timo , Kuhn Charlotte , Müller Ralf
Published: October 2016

Phase field modelling of brittle fracture is very well understood today. However, the attempts of investigation of elasto‐plastic fracture by the phase field approach are limited. This contribution deals with the investigation of a phase field model for elasto‐plastic fracture. Based on a free energy density comprising elastic, fracture and plastic contributions, the model describes an extension of the linear elastic model towards von Mises plasticity. In this work it is analyzed numerically to which extend analytical findings concerning the interpretation of the model parameters in 1D are transferable to 2D scenarios. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parametric shape optimization of biaxial tensile specimen
Authors: Bauer Julian , Priesnitz Konstantin , Schemmann Malte , Brylka Barthel , Böhlke Thomas
Published: October 2016

Common cruciform specimen for biaxial tensile testing of sheet moulding compound, take damage and finally fail in uniaxially loaded areas. When using these specimen, an observation of damage initialization and failure in biaxially loaded areas is, therefore, not possible. In this paper, a parametric shape optimization is described to find a more suitable specimen shape. The parametrization of the specimen is presented. Objective functions are introduced to measure the appropriateness of specimen. A weighted summation transfers the constraint multiobjective optimization problem into a constraint scalar‐valued problem. Findings of experiments suggest that a specimen shape with straight, non‐tapering arms and slits along the arms is reasonable. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydraulic fracturing with a simplified fluid model and XFEM
Authors: Schätzer Markus , Fries Thomas‐Peter
Published: October 2016

In hydraulic fracturing, the pressure exerted by the fracking fluid onto the surrounding solid, is typically obtained from solving the Reynolds equation. This is not always robust and leads to a complex behaviour at the crack front (toughness or viscous regimes). In the presented work, the Reynolds equation is replaced by a simplified fluid model, where pre‐defined pressure distributions are assumed which lead to a simpler and robust coupled problem. The surface integration of the fluid pressure onto the surrounding solid is outlined without any limitations on the distributions. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of short crack propagation under hydrogen influence using a hybrid boundary element technique for anisotropic elastic solids
Authors: Schippl Volker , Fritzen Claus‐Peter , Brück Sven , Christ Hans‐Jürgen , Schwarz Martina , Weihe Stefan
Published: October 2016

A two‐dimensional model for stage I short crack propagation on multiple slip planes under the influence of hydrogen is presented. It considers elastic‐plastic material behaviour by allowing sliding on the active slip planes in the corresponding slip directions. A crack propagation law based on the crack tip sliding displacement is used to simulate crack growth. The activation of slip bands and the sliding on these active slip bands will be influenced by the local hydrogen concentration. The model is solved numerically using the boundary element method. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On configurational forces in a dynamic phase field model for fracturing
Authors: Schlüter Alexander , Kuhn Charlotte , Müller Ralf
Published: October 2016

Dynamic fracturing is an active field of research in which some phenomena like crack branching are only partly understood. The origin for most theoretical studies of fracturing ‐ analytical as well as numerical investigations ‐ are classical concepts of fracture mechanics such as Griffith's energy‐based description. The same is true for phase field fracture models that represent cracks by means of an additional scalar field. The evolution of this field can be found from minimization of a regularized energy functional which corresponds to a generalized Griffith criterion. This work discusses configurational forces as a means to highlight the relation between fracture evolution in a phase field model and the classical fracture mechanical concepts. In contrast to other numerical tools that rely on configurational forces to model the crack propagation, the configurational forces serve a different purpose in a phase field model for fracture. Here, they are a result of a post‐processing step that enhances the understanding of the simulated fracture problem. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A relaxation‐based approach to damage modeling
Authors: Schwarz Stephan , Junker Philipp , Hackl Klaus
Published: October 2016

Common material models that take into account softening effects due to damage have the problem of ill‐posed boundary value problems if no regularization is applied. This condition leads to a non‐unique solution for the resulting algebraic system and a strong mesh dependence of the numerical results. A possible solution approach to prevent this problem is to apply regularization techniques that take into account the non‐local behavior of the damage [1]. For this purpose a field function is often used to couple the local damage parameter to a non‐local level, in which differences between the local and non‐local parameter as well as the gradient of the non‐local parameter can be penalized. In contrast, we present a novel approach [2] to regularization that no longer needs a non‐local level but directly provides mesh‐independent results. Due to the new variational approach we are also able to improve the calculation times and convergence behavior. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Phase‐Field Model of Ductile Fracture at Finite Strains
Authors: Teichtmeister Stephan , Aldakheel Fadi , Miehe Christian
Published: October 2016

This work outlines a variational‐based framework for the phase field modeling of ductile fracture in elastic‐plastic solids at large strains. The phase field approach regularizes sharp crack discontinuities within a pure continuum setting by a specific gradient damage model with geometric features rooted in fracture mechanics. Based on the recent works [1, 2], the phase field model of ductile fracture is linked to a formulation of gradient plasticity at finite strains in order to ensure the crack to evolve inside the plastic zones. The thermodynamic formulation is based on the definition of a constitutive work density function including the stored elastic energy and the dissipated work due to plasticity and fracture. The proposed canonical theory is shown to be governed by a rate‐type minimization principle, which determines the coupled multi‐field evolution problem. Another aspect is the regularization towards a micromorphic gradient plasticity‐damage setting which enhances the robustness of the finite element formulation. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The stress state of the finite cylinder with the circular cracks
Authors: Vaysfeld Natalya , Protserov Yuriy
Published: October 2016

The axysimmetrical torsion problem for a finite cylinder with an arbitrary quantity of the cylindrical layers is solved. The cylinder is weaked by the parallel circular cracks in the first internal layer. The stated boundary valued problem problem is reduced to the system of the integro‐duferential equations solving with the help of the orthogonal polinomials method. The stress intensity factors (SIF) are obtained. The dependences of SIF values from the cracks' sizes, their location, and ratio of the layers' shear moduluses are concretized for the case of the two layers. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Nonlinear Deterministic Mode Decomposition Strategy for High‐Dimensional Monte Carlo Simulations
Authors: Bamer Franz , Markert Bernd
Published: October 2016

We present a new reduced Monte Carlo simulation strategy for nonlinear high‐order systems based on an extension of the proper orthogonal decomposition for transient excited structures. This novel approach enables the evaluation of the response statistics in a fractional amount of time compared to the full Monte Carlo simulation procedure. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The discontinuous Galerkin method with reduced integration scheme for the boundary terms in almost incompressible linear elasticity
Authors: Bayat Hamid Reza , Wulfinghoff Stephan , Reese Stefanie , Cavaliere Fabiola
Published: October 2016

In this paper, the discontinuous Galerkin (dG) method is introduced and applied for a problem of nearly incompressible material behavior, where the standard finite element method, namely the conventional continuous Galerkin (cG) method faces the well‐known problem of volumetric locking. The highlight of the work lies in the reduced integration scheme for the boundary terms of the dG method. Two different reduced and mixed integration schemes are presented and applied to reduce the calculation time. The dG method converges much faster than standard cG method with respect to the number of the elements, provided that the penalty value is sufficiently large. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Layer‐wise theory and finite elements for laminated poroelastic shells
Authors: Gfrerer Michael , Schanz Martin
Published: October 2016

In order to consider growing expectations on vibro‐acoustic performance of products within the design process, reliable simulation tools are necessary. In this paper, we present a approach for the simulation of laminated shells composed of elastic and poroelastic layers. We assume that the shell is given by a parametrization, which allows us to work witn the exact geometry. The three‐dimensional problem is reduced to a two‐dimensional one, by choosing a set of through‐the‐thickness functions for each quantity and through‐the‐thickness integration. The implemented high order finite element approach for the reduced problem on the reference surface relays on hierarchical shape functions. In a numerical example, we show the influence of poroelastic materials attached to a aluminium shell. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the performance of the Prange‐Hellinger‐Reissner finite element formulation for elasto‐plasticity at small strains
Authors: Igelbüscher Maximilian , Schröder Jörg , Schwarz Alexander
Published: October 2016

This contribution deals with a stress‐displacement mixed finite element formulation for elasto‐plasticity within the framework of small deformations based on the Prange‐Hellinger‐Reissner (PHR) functional. The interpolations for the displacements are given by standard Lagrangian shape functions and a 5‐parameter discontinuous interpolation is introduced for the stresses which was published by [1]. Based on the principle of maximum plastic dissipation the flow rule and hardening law will be derived by regarding a von Mises yield criterion, see [2]. In contrast to [3], we apply a point‐wise enforcement of the flow rule, hardening law and loading/unloading conditions. This work is related to the physically nonlinear mixed finite element based on the Prange‐Hellinger‐Reissner formulations for elasto‐plasticity, [4]. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structure‐preserving space‐time discretization of nonlinear structural dynamics based on a mixed variational formulation
Authors: Janz Alexander , Betsch Peter , Hesch Christian
Published: October 2016

The present work deals with the design of structure‐preserving numerical methods in the field of nonlinear elastodynamics and structural dynamics. Structure‐preserving schemes such as energy‐momentum consistent (EMC) methods are known to exhibit superior numerical stability and robustness. Most of the previously developed schemes are relying on a displacement‐based variational formulation of the underlying mechanical model. In contrast to that we present a mixed variational framework for the systematic design of EMC schemes. The newly proposed mixed approach accomodates high‐performance mixed finite elements such as the shell element due to Wagner & Gruttmann [1] and the brick element due to Kasper & Taylor [2]. Accordingly, the proposed approach makes possible the structure‐preserving extension to the dynamic regime of those high‐performance elements. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A variational approach to modelling and optimization of viscoelastic structure motions
Authors: Kostin Georgy
Published: October 2016

Locomotion of a flexible rack feeder consisting of two viscoelastic beams clumped on a mobile carriage are studied. The optimal control problem is to move the rack feeder from its initial state to terminal one in a fixed time and to minimize the mean mechanical energy of the system. The solution of the problem is based on the method of integro‐differential relations. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of Friction‐Induced Vibrations during Tightening of Bolted Joints
Authors: Baramsky Nicolaj , Seibel Arthur , Schlattmann Josef
Published: October 2016

During the automated tightening process of bolted joints, the preload force can only be determined with greater effort. This is usually realized by using indirect methods, one of which is the torque‐controlled procedure. The dependency between the tightening torque and the preload force is deeply connected to the frictional conditions under the screw head and in the screw thread. Several methods exist to support the tightening process. Nonetheless, errors occur, which are, besides other reasons, due to friction‐induced vibrations. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extending the classification of devices in single‐degree‐of‐freedom vibrating systems
Authors: Franze Andreas
Published: October 2016

This contribution investigates existing descriptions of electro‐mechanical analogies and attempts of an extension by memristive elements. Therefore, the electro‐dynamical role of memristors is analyzed and translated into the context of system dynamics. This analysis leads to a generalized classification of devices for dynamical systems with a single degree of freedom (SDOF). (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the influence of the lamella's elasticity on self‐excited vibrations in gearboxes
Authors: Jehle Georg , Fidlin Alexander
Published: October 2016

Eek noise in a gearbox of a vehicle drivetrain is a phenomenon, which can arise while shifting between gears and which is not accepted by customers. Beneath audible squeaking, it can cause damage of mechanical components. There is a wide range of possible reasons for the occurrence of this effect, which strongly depends on properties of the considered gearbox (physical parameters, geometry, operation, …). From the mathematical point of view, the occurrence can be predicted using linear stability analysis of the stationary behaviour of a physically motivated gearbox model.

The components of a gearbox are clutch discs being in contact, gears and elastically supported shafts. In this contribution, a rigid multibody model of the device [4] is extended by the elastic modelling of the motor's side disc (rotating Kirchhoff plate). The aim of the overall system is to analyze the shifting process.

The analysis reveals that beneath instability mechanisms which are known from systems with rigid bodies, new instabilities occur incorporating of out‐of‐plane vibrations of the plate. In a reasonable parameter region, the first two unsymmetrical modes of the lamella have the main contribution to the instability. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An extended LuGre friction model incorporating frictional aging
Authors: Krasmik Viktor , Schlattmann Josef
Published: October 2016

In this contribution, the LuGre model is extended and the effect of frictional aging is incorporated using the state variable approach. The adapted friction model is used in combination with a single‐degree‐of‐freedom oscillator to investigate the basic effects on the stick‐slip amplitude and period. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of micro‐cutting considering finite deformation crystal plasticity
Authors: Bischof Robert , Schneider Frank , Kuhn Charlotte , Aurich Jan C. , Müller Ralf
Published: October 2016

Micro‐machining processes on metalic microstructures are influenced by the crystal structure, i. e. the grain orientation. Furthermore, the chip formation underlies large deformations. To perform finite element simulations of micro‐cutting processes, a large deformation material model is necessary in order to model the hyperelastic and finite plastic material behaviour. In the case of cp‐titanium material with hcp‐crystal structure the anisotropic behaviour must be considered by an appropriate set of slip planes and slip directions. In the present work the impact of the grain orientation on the plastic deformation is demonstrated by means of finite element simulations of a finite deformation single slip crystal plasticity model. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and numerical investigation of PUR foam under dynamic loading
Authors: Bogunia Lukas , Weinberg Kerstin
Published: October 2016

Various factors may subject buildings to shock which continues in their structure and is perceived by the people living in them as noticeable vibrations or noise. In this context, polyurethane (PUR) foams, which have been developed to isolate vibrations, have shown to be very effective in practical use. However, whereas static properties of open‐cell structures have already been determined numerically in good agreement to experimental results, cf. [1], there are hardly any investigations on the dynamical properties characterizing acoustic damping.

In order to validate experimental measurements of eigenfrequencies for different PUR foam specimen we present here a strategy to reproduce the foam behavior numerically. In doing so, PUR foams are modeled using a three dimensional Voronoi‐tessellation technique. The resulting Voronoi cells correspond to open pores and are scaled in such a way that the volume ratio between the pores and material matches the given PUR foam. For finite element analysis the connections between the cells are modeled as beam elements, the beam shape follows Bezièr curves. The generated model is analyzed with a finite element software and the dynamical parameters are determined. The numerical results are compared to our experimental data. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular statics simulations of ferroelectric nanofilms
Authors: Endres Florian , Steinmann Paul
Published: October 2016

Smart materials are of great interest not only for scientific, but also for technological reasons due to ongoing miniaturization and rapid developments in manufacturing technologies of nanocomponents [1]. Therefore, simulations on the nanometer length scale are becoming more important in order to fundamentally understand and predict the complex material behavior of ferroelectric nanocomponents, such as ferroelectric nanofilms or nanowires. We apply a previously developed extended molecular statics algorithm [2] to simulate ferroelectric barium titanate nanofilms. The algorithm is able to also consider mechanical stress explicitly whereas most molecular simulations of ferroelectrics are restricted to NVT‐ensembles. We simulate a stress relaxed ultra thin barium titanate film and apply compressive strain in order to investigate size effects of ferroelectric nanofilms. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On intrinsic time measure concept with application to the modeling of smart materials
Authors: Ioan Rodica , Ioan Stefan
Published: October 2016

In this paper, the cyclic behavior of a Nitinol cubic block is described by using the Bouc‐Wen model [2] coupled to the intrinsic time measure, other than the clock time which governs the behavior of the materials [4]. The modified Bouc‐Wen model consists from the classical Bouc‐Wen model coupled to the intrinsic time measure, other than the clock time which governs the behaviour of the materials. As a consequence, the thermodynamic admissibility of the Bouc–Wen model is provided by the endochronic theory of plasticity. The role of the intrinsic time measure is described by capturing the stiffness and strength degradation and the opposite phenomena. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling additive manufactured materials using a crystal plasticity model
Authors: Kergaßner Andreas , Mergheim Julia , Steinmann Paul
Published: October 2016

In this contribution the macroscopic behaviour of additively manufactured Inconel 718 will be identified using a crystal plasticity model on the meso‐level. The experimentally observed grain structures will be used to generate a representative volume element. Based on this RVE macroscopic mechanical parameters will be identified and compared with experimental results. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large strain transversely isotropic viscoplasticity by directly connected rheological elements
Authors: Kießling Robert , Ihlemann Jörn
Published: October 2016

Precise material models at large strains for the components of an intrinsic hybrid composite, such as a fibre‐matrix composite, are required to perform finite element simulations. This contribution considers the development of a transversely isotropic viscoplastic material model to predict the mechanical behaviour of a polymer matrix with unidirectional fibre‐reinforcement. To this end, a rheological model of the matrix material is deduced from the phenomenological description of an unreinforced polymer. The application of a concept, which enables material modelling at large strains by directly connected rheological elements, yields the according viscoplastic material model. Based on the results of finite element simulations of a representative volume element consisting of a polymer matrix and a fibre constituent, the matrix's material model is modified by an anisotropic extension, which results in a homogenised viscoplastic material model for an unidirectional fibre‐matrix composite. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extension of DFM and MORPH in representative directions to viscous effects via Prony series approach
Authors: Kröger Nils Hendrik , Raghunath Rathan , Juhre Daniel
Published: October 2016

In this paper we present an extension of the material models DFM and MORPH formulated in representative directions via an approach for viscohyperelasticity based on a Prony series resp. integral approach. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental Validation of RVE Based Failure Simulations of Macro‐Porous Materials
Authors: Krummrich Phil Daro , Schneider Patrick , Hochrainer Thomas
Published: October 2016

Connections between inhomogeneities and the failure behavior of brittle material may be investigated by finite element simulations of representative volume elements. Representative volume elements are typically subjected to periodic boundary conditions. Moreover, representative volume elements are often chosen as planar, i. e., two dimensional in order to reach reasonable statistics with regard to random distributions of inhomogeneities. The significance of such strongly simplified simulations needs to be validated, especially if the matrix failure is potentially dominated by defects, as is the case, e. g., in macro‐porous ceramics. We propose a quasi‐periodic concept to design specimens with cylindrical pores, which reproduce the stress state in a two dimensional representative volume element. This is achieved by a partial periodic replication of the region of interest. We suggest that material models used in simulations can be assessed by comparison between simulated and experimentally observed failure. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A finite element analysis of effects of ultrasonic welding parameters on the temperature distribution in wire bonding
Authors: Mostafavi Shimaalsadat , Markert Bernd
Published: October 2016

Wire bonding is an essential process in the automotive industry. Multi‐strand flexible aluminium cables are used for connection of different electronic components and electrical centres in cars. As an alternative for crimping technology in wire bonding, ultrasonic welding (USW) is applied, which is a rapid manufacturing process used to create solid joints between mating materials at low energy consumption compared to the known welding processes, such as oxy‐fuel welding and arc welding. An ultrasonic welding machine consists of different parts, such as pneumatic cylinder, piezoelectric converter, booster, welding sonotrode and anvil. Despite of the simplicity of the USW process, choosing the right machine and process parameters, like pressure of the pneumatic cylinder, welding time as well as vibration amplitude of the piezo‐converter, is a tricky and complicated task for obtaining an adequate bond. Experimental investigations done in this area are extremely time‐consuming and require a lot of effort. Therefore, some new approaches must be developed to understand the process in more detail. The present study focuses on the influence of the ultrasonic welding parameters, such as sonotrode pressure and vibration amplitude, on the temperature distribution at interfaces of two mating pieces in wire bonding [1,2]. Investigations are done by means of FEM simulations as well as by experiments. The results are then extended to thermo‐mechanical analysis of multi‐strand models. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)