bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Suitability of Different Online Gait Generation Methods for Pre‐Defined Footsteps
Authors: Mayr Johannes , Gattringer Hubert , Bremer Hartmut
Published: December 2011

Detailed dynamical modeling is the basis for simulation and model based control. In this contribution the Projection Equation is used for the modeling of a biped walking machine, resulting in the equations of motion which are needed for gait generation and verification of its stability. For biped robots one main issue is the generation of stable trajectories for the center of mass (CoM). Several different approaches based on the Zero Moment Point (ZMP) scheme have been presented in the past. Due to the complex dynamic structure of bipedal robots most of the considered algorithms use a linear inverted pendulum as a simplified model. This results in a decoupling of the ZMP equations in lateral and forward direction, but limits the trajectories to a constant height of the CoM. An extension of the well known LQR theory by future reference values has been proposed. This model based approach seems to perform quite well, but does not allow the consideration of constraints on the position of the ZMP. This limitation is removed by the use of Model Predictive Control (MPC) with inequality constraints. By extending this approach to a time invariant one the restriction to a constant height of the CoM is no longer necessary. Both methods as well as the time invariant approach for variable CoM heights have been evaluated in simulations and will be experimentally verified on a real robot soon. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A contribution to efficient calculation of complex drill string dynamics for deep hole drilling
Authors: Shi Minzhe , Schiefer Frank , Ostermeyer Georg‐Peter
Published: December 2011

This paper presents a hybrid model to describe drill string dynamics for deep hole drilling. Generally, a typical rotary drill string has a length of several kilometers, but the diameter is less than half a meter. Due to the large ratio of length to diameter, a drill string is a very flexible system. Consequently, an operating drill string is always affected by axial, torsional and lateral vibrations, which potentially induce serious failures. In order to avoid fatal defects, simulations to forecast vibrations are necessary. The simulation should be capable to exhibit the complex dynamical phenomena, e.g. sick‐slip, forward whirl and backward whirl, and interactions between drill string and borehole. Usually, these simulations are very time‐consuming. In this work, a hybrid model consisting of lumped masses connected with weightless beam elements representing the drill string is developed. The interaction between the drill string and the borehole is implemented by unilateral constraints to describe the nonlinear contact behavior. It was shown that accuracy and simulating time were improved by this model with respect to classical finite‐element models. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hand Vibrations of the Human Operator in the Working Space
Authors: Arghir Mariana , Rus Mariana , Macovescu Sorin Constantin
Published: December 2011

The paper contains the identification and the taking into account the vibrations produced by the machines, the lathe with different number of rotation, and them action over the human bodies inside the working space. For the identification of vibrations is applied a new method, the Moiré projection method, that did not used until this moment regarding the vibrations action over the human body. Our research was to apply the Moiré projection method to the human hand. They were compared with the measured vibrations using a classic vibrometer with three‐axial accelerometer. The results in the booth situation were in the same order of the unit scale, and the optical method named Moiré projection method can be considered a valid method for the human vibrations measurements without touch of the surface. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A continuum‐mechanical analysis of the influence of mechanical stimuli on biological tissue
Authors: Avci Arzu , Markert Bernd , Ehlers Wolfgang
Published: December 2011

Mechanical stimuli play a crucial role in the differentiation process of mesenchymal stem cells (MSC). The resulting mechanical signals are important in the regulation of various cell functions and maintenance of many tissues. The underlying molecular and biophysical mechanisms of the differentiation process are poorly understood. Present remodelling and growth models are purely phenomenological without linkage to cell mechanisms.

The presented macroscopic model of MSC mechanics is based on a multiphasic‐multicomponent formulation within the framework of Theory of Porous Media (TPM), where a single cell is considered as a mixture of interacting constituents. In particular, the constituents are the solid cytoskeleton saturated by a fluid phase (cytoplasm), which itself consists of a liquid solvent and mobile components, e. g., chemical messengers, proteins, etc. To demonstrate the capabilities of the developed model, first qualitative numerical simulations of the impact of external forces on MSC are presented. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A finite element approach for modelling hip joint contact
Authors: Fietz Kristin , Nackenhorst Udo
Published: December 2011

In this contribution a finite element model for the three dimensional investigation of hip joint contact is described. A shell‐like interface element with variable thickness is developed for modelling fluid flow in the synovial gap. For this purpose the Taylor‐Hood element is extended in order to take a spatial thickness distribution and local thickness changes into account. The interaction between the synovial fluid and the cartilage layers is solved by a staggered iteration using an artificial compressibility method. Cartilage is modelled using the theory of porous media and three dimensional geometries are reconstructed from medical imaging data. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical investigations on the fixation of cemented and uncemented endoprostheses
Authors: Hürkamp André , Lutz André , Nackenhorst Udo
Published: December 2011

In this contribution, a constitutive model adopted from the computational plasticity‐models of Drucker‐Prager and von Mises is presented. This model captures the material behavior of osseointegration and the curing‐process of bone cement. With this basic model, both simulations of bone‐ingrowth of uncemented implants and simulations of the curing process of bone cement for cemented implants are carried out in a bone‐implant interface. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bone remodelling: A combined biomechanical and systems‐biological challenge
Authors: Krause Robert , Schittler Daniella , Reiter Michael , Waldherr Steffen , Allgöwer Frank , Karastoyanova Dimka , Leymann Frank , Markert Bernd , Ehlers Wolfgang
Published: December 2011

Bone tissues are formed by cells, bone matrix and fluids. The bone matrix is a porous structure, which is remodelled by bone‐cells. To describe this process, a coupled systems‐biological and biomechanical model is presented.

The macroscopic mechanical behaviour of bone is specified by a biphasic model embedded in the Theory of Porous Media, where the solid phase represents cells and bone matrix, and the fluid phase summarises the extracellular fluids and its components. In this context, the bone remodelling process is described on the macro‐scale by a distinct mass exchange that also results in a change of the constituents'material properties.

On the micro‐scale, the description of the bone remodelling process stems from a systems‐biological cell interaction model. Therein, the bone matrix formation and resorption are a result of the stress‐regulated activity of cells.

Here, a staggered solutions strategy is presented. Therein, snapshots of the mechanical stress distribution are calculated on the macro‐scale by use of the finite element method. The snapshots are locally evaluated on the micro‐scale by use of a cell interaction model, which calculates the long term remodelling process. The evaluation results of the micro‐scale are then used to update the reference configuration of the mechanical simulation. As an integrative modelling platform scientific workflows and web‐service technologies are employed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim
Model reduction for nonlinear biomechanical structural analysis
Authors: Radermacher Annika , Reese Stefanie
Published: December 2011

For surgery training and on‐line support during surgeries a method is required which is able to reduce simulation time possibly even to realtime. This contribution compares the effectiveness of three model reduction methods, all of which are widely used for linear problems, in the context of nonlinear structural mechanics. Three reduction methods will be extended to nonlinear elasticity including large deformations. The performance of the extended concepts is investigated for a simplified model of a human inferior turbinate in the context of the functional endoscopic sinus surgery. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Knee joint kinematics: comparison of two optimization models with respect to data noise
Authors: Reichl Irene , Auzinger Winfried , Schmiedmayer Heinz‐Bodo , Weinmüller Ewa
Published: December 2011

The interpretation of human knee joint kinematics in terms of displacements is an outcome of the underlying model of the joint and the measurement technique. Measurement errors and noise challenge the development of optimization procedures which, based on a reduction in degrees of freedom, aim for the reproducibility of joint displacements by computational techniques. So far, optimization algorithms have been applied which are based on a kinematic model of the healthy human tibio‐femoral joint (TFJ) as a compound hinge with two fixed orthogonal axes. On the other hand, empirical studies find non‐orthogonal rotational axes. Therefore, it was the aim of the present study to investigate the implications of a refined kinematic model on the accuracy of computed joint rotation angles. For the purpose of quantitative comparison, kinematic data of a TFJ with two axes intersecting at an arbitrary angle were simulated. The joint rotations were optimized for the assumption of (a) two orthogonal and intersecting axes (model A), and (b) two axes intersecting at an arbitrary angle (model B). Model B recovers the original input data closer in case of low noise level as encountered in invasive measurement techniques. Skin mounted markers tracking involves non‐normally distributed noise which is typically larger by on order of magnitude. In this case, model A exhibits a more favorable performance. These observations motivate the search for alternative kinematic descriptions of the TFJ. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Coupling of 3D‐1D Muscle Models for Lumbar Spine Mechanics
Authors: Sprenger Michael , Karajan Nils , Schmitt Syn , Röhrle Oliver
Published: December 2011

The aim of this research is to represent, within one modelling framework, selected parts of the musculoskeletal system using principles of continuum mechanics, while other parts are modelled using lumped‐parameter models and principles of Multi‐Body Dynamics. The most challenging part within such a framework will be to properly model the transition from 3D to 1D models for skeletal muscles as many of the skeletal muscles extend beyond the selected part. Hence, this paper focuses on an interface condition for the 3D‐1D transition within a skeletal muscle. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electromechanical modelling of skeletal muscle contractions
Authors: Sturmat Maike , Böl Markus
Published: December 2011

In the present paper, the aim was to develop a numerical method for optimisation an existing mechanical material model [1] including muscle activation concerning the excitation of skeletal muscles. The modelling idea was a weak and non‐monolithic coupling of an electric current expressed by Ohm's law with a hyperelastic muscle model with transversal isotropic characteristics, see [2]. We confirmed the ability of the proposed model by applying on real reconstructed complex muscle geometry. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Development of a biomechanical model to study the horizontal vibration transmitted from shoulder to head
Authors: Truţa Aurica , Pop Aurora‐Felicia , Bălcău Monica , Arghir Mariana
Published: December 2011

On daily activity a human operator is exposed to vibration in working environment. So, the human body will react in different way. The problem is how much from the initial signal will be sent to the other parts of the body and how much that motion will be damped along the studied parts. The vibrations in horizontal plane are some unexpected, so the human operator will not take any position to prevent them. In this condition the horizontal vibrations will have the higher effect possible. In this paper, the shoulder, neck and the head are modeled together like a mechanical system with four degree of freedom. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A new description of cracks in the XFEM
Authors: Fries Thomas‐Peter
Published: December 2011

This work outlines an approach that combines the advantages of explicit and implicit descriptions of the crack geometry in the context of the extended finite element method (XFEM). The XFEM is typically combined with an implicit description of the crack which is realized by the level‐set method. This facilitates the definition of the enrichments in the XFEM. However, the update of the crack geometry during the propagation of a crack is simpler by means of explicit crack descriptions where the crack surface is meshed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crack tip fields in rubber‐toughened polymers
Authors: Helbig Martin , Seelig Thomas
Published: December 2011

Numerical simulations of the formation and the characteristic shape of plastic zones at crack tips in rubber‐toughened polymers are performed in order to get a better understanding of the underlying micromechanisms. Complementing previous work, the present study focuses on the contribution of distributed crazing. A macroscopic constitutive model therefore has been developed that describes the overall effect of distributed crazing as an anisotropic flow process. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Phase Field Model for Three‐Dimensional Dynamic Fracture and its Efficient Numerical Implementation
Authors: Hofacker Martina , Miehe Christian
Published: December 2011

The numerical modeling of dynamic failure mechanisms in solids due to fracture based on sharp crack discontinuities suffers in situations with complex crack topologies and demands the formulation of additional branching criteria. This drawback can be overcome by a diffusive crack modeling, which is based on the introduction of a crack phase field. We focus on the extension of a recently developed phase field model for fracture from the quasi‐static setting towards the dynamic setting. It is obtained by taking into account inertial terms and associated dynamic integrators. The introduction of a history field, containing a maximum fracture‐driving energy, provides a very transparent representation of the balance equation that governs the diffusive crack topology. In particular, it allows for the construction of an extremely robust operator split technique. In a subsequent step, the proposed model is extended to three dimensional problems. The dynamic treatment opens the door to the analysis of complex fracture phenomena like multiple crack branching and crack arrest. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cohesive zone model for a transverse breathing crack in a rotor
Authors: Liong Rugerri Toni , Proppe Carsten
Published: December 2011

The breathing mechanism of a transversely cracked rotor and its influence on a rotor system that appears due to the shaft weight is studied. This breathing mechanism is based on experimental and simulation result for the crack shape reported in the literature. If the crack depth is small, the crack closure line is a straight line while for larger crack depths the crack closure becomes more curved. For both cases, a method is proposed for the evaluation of the stiffness losses in the cross section that contains the crack. This method is based on a cohesive zone model (CZM) instead of linear elastic fracture mechanics (LEFM) approach, because LEFM is valid only for the fully open crack and cannot be extended to other intermediate situations. As the crack is closed, the stress intensity factor (SIF) will not appear at the boundary between the closed cracked areas and the open cracked areas. The CZM is developed for mode‐I plane strain conditions and accounts explicitly for triaxiality of the stress state by using constitutive relations. The proposed model gives more realistic results than models based on LEFM for the stiffness losses of the crack rotor system for a wide range of the crack depth. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A strong discontinuity based adaptive refinement approach for the modeling of crack branching
Authors: Raina Arun , Linder Christian
Published: December 2011

In the current work, the physical phenomena of dynamic fracture of brittle materials involving crack growth, acceleration and consequent branching is simulated. The numerical modeling is based on the approach where the failure in the form of cracks or shear bands is modeled by a jump in the displacement field, the so called ‘strong discontinuity’. The finite element method is employed with this strong discontinuity approach where each finite element is capable of developing a strong discontinuity locally embedded into it. The focus in this work is on branching phenomena which is modeled by an adaptive refinement method by solving a new sub‐boundary value problem represented by a finite element at the growing crack tip. The sub‐boundary value problem is subjected to a certain kinematic constraint on the boundary in the form of a linear deformation constraint. An accurate resolution of the state of material at the branching crack tip is achieved which results in realistic dynamic fracture simulations. A comparison of resulting numerical simulations is provided with the experiment of dynamic fracture from the literature. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of interface cracks in layered piezoelectric composites by a SGBEM
Authors: Wünsche Michael , Zhang Chuanzeng , Sladek Jan , Sladek Vladimir
Published: December 2011

Piezoelectric materials offer many possibilities in advanced engineering structures due to their inherent coupling effects between mechanical and electrical fields and are widely applied in smart devices and structures like transducers, actuators and sensors [2]. An important application of piezoelectric materials is related to layered or laminated composites because they can be optimized to satisfy the high‐performance requirements according to different in‐service conditions. Beside cracks inside homogeneous domains, one of the most dominant failure mechanisms in layered or laminated composites is the interface failure. Interface cracks and interface debonding may be induced by the mismatch of the mechanical, electrical and thermal properties of the material constituents during the manufacturing process and the in‐service loading conditions. This paper presents a hypersingular symmetric Galerkin boundary element method (SGBEM) for crack analysis in two‐dimensional (2D), layered and linear piezoelectric solids. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reduction of vibrations using mechanical and electrical elements
Authors: Białas Katarzyna
Published: December 2011

The main aim of this work is the introduction of analysis and synthesis of mechatronical systems including mechanical and electrical elements reducing vibrations. In results of synthesis were received structures and parameters of a discrete model meeting the defined requirements concerning the dynamic features of the system, in particular, the frequency spectrum. The approach adopted makes it possible to take actions aiming at the reduction of phenomena resulting in the unwanted operation of machinery or generation of hazardous situations in the machinery environment. Thank to the approach, the above mentioned preventive activities can be conducted as early as during the designing of future functions of the system as well as during the construction of the system in question. In this work is also comparison of these two kind of elements, mechanical and electrical, of reduction of vibrations. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Monitoring fatigue cracks and SIFs in plate structures solving inverse boundary value problems
Authors: Boukellif Ramdane , Ricoeur Andreas
Published: December 2011

In this work we present methods for the detection of cracks in plate and shell structures. In contrast to most of the common monitoring methods taking advantage of the reflection of surface waves at crack faces, the presented approach is based on the strain measured at different locations on the surface of the structure. This allows both the identification of crack position parameters, such as length, location and angles with respect to a reference coordinate system and the calculation of stress intensity factors (SIF). The solution of the direct problem is performed on the basis of the BFM (body force method) and the method of assembled point dislocations. The inverse problem is solved applying the PSO (particle swarm optimization) algorithm. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extension of the scaled boundary finite element method to plate bending problems
Authors: Dieringer Rolf , Hebel Jochen , Becker Wilfried
Published: December 2011

The scaled boundary finite element method (SBFEM) is extended to the static analysis of thin plates in the framework of Kirchhoff's plate theory. The governing equations are transformed into scaled boundary coordinates. Applying a discrete form of the Kantorovich reduction method results in a set of ordinary differential equations, which can be solved in a closed‐form analytical manner. The element stiffness matrices for bounded and unbounded media can be computed, using appropriate subsets of the analytical solution. Examples show the efficiency of the method, applied to plate bending problems. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary Conditions and Multi‐Patch Connections in Isogeometric Analysis
Authors: Dornisch Wolfgang , Klinkel Sven
Published: December 2011

Isogeometric analysis is a high‐continuity alternative to the standard finite element method. However, for practical application several issues remain to be addressed. This contribution discusses the imposition of Dirichlet boundary conditions as well as the connection between multiple patches. In particular necessary manipulations of the geometrical input data are provided. Dirichlet boundary conditions can be imposed in weak or in strong form. Due to the non‐interpolatory characteristics of NURBS surfaces weak imposition of Dirichlet conditions is a viable option which avoids local transformations. The connection of multiple patches can be realized in a weak manner by adding additional terms to the variational equations, for example by the Lagrange multiplier method or the perturbed Lagrangian method. Both base on the idea of multiplying the mutual deformations with an additional unknown to force the deformations on shared edges to be equal. The numerical treatment leads to different sets of equations. In contrast to strong inter‐patch connections, where coinciding control points share the same degrees of freedom, weak imposition allows for hanging nodes and therefore local refinement. The theoretical background and issues of implementation are given. Some numerical examples compare error norms for all mentioned methods and demonstrate that in particular cases a reduction of continuity leads to more accurate results. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New solid‐shell and solid‐beam finite elements with applications to medical technology
Authors: Frischkorn Jan , Reese Stefanie
Published: December 2011

In this paper, new solid‐shell and solid‐beam finite element formulations for finite deformation problems are introduced. One application of interest, concerning these types of elements, can be found in the simulation of stent implementation in the treatment of stenosis. The beam‐like structure of the stent and the shell‐like structure of the blood vessel can be modelled easily by using these types of elements. Moreover, the modelling of the interaction of the different structural types between each other and with the surounding tissue becomes more simple. A high rate of convergence, by using only one element in thickness direction that is comparable to classical structural elements, can be named as a major requirement for the element formulations. In this regard, different locking effects are cured by a special combination of the assumed natural strain method (ANS) and the enhanced assumed strain method (EAS). In addition a variable number of quadrature points can be used in thickness direction in order to capture nonlinearites. This is combined with the concept of reduced integration for the sake of computational efficiency. An adaptive hourglass stabilization that also accounts for material nonlinearities is a crucial issue in this regard. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reverse task as a designing of mechatronic vibrating branched systems
Authors: Buchacz Andrzej , Galeziowski Damian
Published: December 2011

In this paper a new approach for designing mechatronic vibrating branched structures has been presented. Mechatronic structures have been built from mechanical discrete systems connected to piezoelectric actuator and externalLxRxCx network, with different configurations. Modeling simplification has been performed by use of non dimensional transformations and retransformations. In each case reverse task has been solved by distribution into partial fraction method in respect to required dynamic properties in form of frequency spectrum: resonant and anti resonant frequencies. Furthermore, different configurations of final LxRxCx network have been presented. These considerations have been supported by calculation examples, and all results have been presented in the graphical form. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerische und Experimentelle Modalanalyse eines Statorblechpaketes
Authors: Mair Mathias , Rainer Siegfried , Weilharter Bernhard , Ellermann Katrin , Bíró Oszkár
Published: December 2011

Das Übertragungsverhalten sowie die Eigenfrequenzen und Eigenformen zweier Statorblechpakete wurden experimentell und numerisch, mittels einer Modalanalyse eines homogenen Finite‐Elemente Modells, ermittelt. Durch geeignete Abstimmung der Materialparameter des Simulationsmodells wurde die Strukturantwort an die der Messung angepasst. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mathematical modelling of heat conduction in certain functionally graded composites
Authors: Nagórko Wiesław , Woźniak Czesław
Published: December 2011

The aim of contribution is to formulate a certain extended version of the tolerance modelling technique for functionally graded composites. For the sake of simplicity, the considerations are restricted to the bidirectionally graded heat conductors. It is shown that the proposed approach enables to determine an entire class of mathematical models for which applications can be found in various specific problems. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On dynamic finite element analysis of viscoplastic thin‐walled structures with non‐local damage
Authors: Nguyen A.D. , Stoffel M. , Weichert D.
Published: December 2011

In this article we propose a non‐local damage model for dynamic finite element computation of viscoplastic thin‐shell structures. To take void nucleation and growth into account, the free energy function is enhanced phenomenologically in terms of a non‐local damage variable and its gradient on the mid‐surface of shell structures. The dynamic thin‐shell elastic theory including large rotations proposed by Simo and Tarnow (1994) is used to capture finite deformation. Local constitutive laws considering viscoplastic behaviour, isotropic hardening and isotropic ductile damage leading to softening in Velde et al. (2009) are employed. The performance of the proposed approach is demonstrated through the preliminary numerical simulations of shock‐wave loaded structures, which are validated by comparision with the experimental results. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The orders of singular stresses at plane bi‐ and trimaterial junctions ‐ Closed‐form analytical solutions
Authors: Sator Christian , Becker Wilfried
Published: December 2011

The plane problem of a bi‐ or trimaterial‐junction, consisting of dissimilar, homogeneous, isotropic and linear elastic sectors is considered. The asymptotic behaviour of the stresses of this composite situation is analyzed by the complex variable method, based on an appropriate choice of the Kolosov‐potentials which are applicable in the vicinity of the vertex. In the analyses, the identification of the singularity exponent is emphasized. With the help of a novel approach it is demonstrated how to derive some solutions for the orders of the stress singularities at bi‐ and trimaterial combinations in a closed‐form analytical manner. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the magnitude of surface stresses of buckled plates
Authors: Schagerl Martin
Published: December 2011

Considering a simply supported plate under uni‐axial compression it is well‐known that after buckling the stress concentrates at the unloaded boundaries as the out‐of‐plane displacement at the buckle causes an in‐plane relaxation, i.e. a decrease of the mid‐plane stress. This stress distortion is described by the so‐called effective width. The knowledge of the effective width allows the calculation of the stress at the unloaded boundaries, which is usually considered as the highest stress in the plate. However, the out‐of‐plane displacement also bends the plate, which produces additional stresses. This article analysis the fundamental question, if the total stress at the surface of the buckle is higher than the stress at the unloaded boundaries. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A consistent second‐order plate theory for monotropic material
Authors: Schneider Patrick , Kienzler Reinhold
Published: December 2011

Mathematical homogenization (or averaging) of composite materials, such as fibre laminates, often leads to non‐isotropic homogenized (averaged) materials. Especially the upcoming importance of these materials increases the need for accurate mechanical models of non‐isotropic shell‐like structures. We present a second‐order (or: Reissner‐type) theory for the elastic deformation of a plate with constant thickness for a homogeneous monotropic material. It is equivalent to Kirchhoff's plate theory as a first‐order theory for the special case of isotropy and, furthermore, shear‐deformable and equivalent to R. Kienzler's theory as a second‐order theory for isotropy, which implies further equivalences to established shear‐deformable theories, especially the Reissner‐Mindlin theory and Zhilin's plate theory. Details of the derivation of the theory will be published in a forthcoming paper [3]. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of structural hypotheses on the elastic‐viscoplastic response of shock wave‐loaded plates
Authors: Stoffel Marcus , Vu Thang Duy , Nguyen An Danh , Schmidt Rüdiger , Weichert Dieter
Published: December 2011

If circular metal plates are subjected repeatedly to impulsive loadings, damage and failure of the structures can occur. In order to predict the damage evolution in finite element simulations, a structural theory combined with viscoplastic constitutive equations acounting for damage is used. However, different structural hypotheses, used in the theoretical model, can lead to variations in the numerical result. Therefore, first‐ and third‐order shear deformations theories are applied in a finite element code. Moreover, local and non‐local damage approaches are used. The aim is to determine the numerical model, which leads to the most accurate results compared to experiments. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear transient FE analysis of piezolaminated smart structures
Authors: Vu Thang Duy , Schmidt Ruediger
Published: December 2011

The presented paper focuses on the modeling and finite element simulation of thin composite structures with integrated piezoelectric layers. Geometrically nonlinear piezolaminated finite elements are based on the Reissner‐Mindlin or third‐order transverse shear deformation hypotheses and the assumptions of small strains but moderate rotations. The numerical results are compared to results in literature. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The piezoelectric phenomena analysis of the material internal damping
Authors: Wrobel Andrzej
Published: December 2011

In the manufacturing of technical systems piezoelectric materials are used. These materials have one or more variables. Under the influence of applied voltage they change shape or generate on the linings the potencial under the influence of deformation. In the foregoing analysis, for both simple and complex systems, the ideal model was used, not taking into account the damping value. Assuming, that the bodies deformation under the influence of vibration is a partially irreversible process, which is due to damping of the internal part of the dissipated energy, the piezoelectric system was analyzed. The level of damping value is mainly affected by the structure of the material. This article presents an analysis of piezoelectric phenomena, taking into account internal damping. A description of the rheological properties of materials using a Kelvin ‐ Voigt model was used. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the parametric excitation of rotors with rolling element bearings
Authors: Fritz Felix , Seemann Wolfgang , Krousgrill Charles M.
Published: December 2011

In this approach a 1‐DOF‐model for a rotor in rolling element bearings is derived. The nonlinear equation of motion with a cubic restitution force and harmonic time dependent variation is solved by Multiple Time Scales Approach. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of the vibrations due to thermal deflection of the drum in the coiling process
Authors: Holl Helmut J. , Hammelmüller Franz
Published: December 2011

The modelling of the coiling process involves a mechanical model of the dynamic system that consists of the rotating coiling drum and the axially and transversally moving strip. Due to the coiling a change of mass in the system takes place. For such a variable mass system a control volume concept has to be introduced in order to get the equations of motion of the dynamic system with variable parameters. A Runge Kutta time integration algorithm is applied to compute the solution. It is assumed that the outer radius of the coiling drum increases linear with the rotation angle. The bending deflection of the shaft results from an inhomogeneous temperature distribution within the coiled material on the coiling drum. Two different boundary conditions of the moving strip have been considered and it is demonstrated that the thermal deflection of the drum has a high influence upon the fluctuation of the strip force. For a given geometry and strip speed we obtain a critical thermal deflection where the minimum strip tension force is zero. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Jumping and hopping motion on sports surfaces – Energetic aspects vs. risk of injury
Authors: Körner Claudia , Seemann Wolfgang
Published: December 2011

The aim in high‐performance sports activities is reaching the optimum between high efficiency and low risk of injuries during workout. The goal of this contribution is to increase the understanding of these two facts while interaction between athletes and sports surfaces. A typical movement in sports activities is human hopping. Several studies on this topic have already been done, but to the best of our knowledge any of them uses a continuous model of the sports surface. Therefore, an Euler‐Bernoulli beam with visco‐elastic foundation is analysed. The human modelling is represented by a one‐dof‐oscillator. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the complexity of hydromount‐models in full vehicle simulation
Authors: Vilsecker Johannes , Mack Werner , Falkner Anton , Hanfstingl Robert
Published: December 2011

The influence of the complexity of hydromount‐models on the results in full vehicle simulation is studied. In particular, a Kelvin‐Voigt model, a linear lever model and a non‐linear model are assessed with respect to their predictive capabilities as compared to the necessary parameterization and computation efforts. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of dynamic brake pad properties on automotive disk brake squeal
Authors: Hornig Sylwia , Gräbner Nils , von Wagner Utz
Published: December 2011

Comparing different methods of characterizing dynamic properties of brake pad materials clearly shows, that those properties strongly depend on the boundary conditions as well as on amplitude and frequency in the excitation. Actually simulations of brake squeal suffer on the missing of correct material parameters identified under conditions relevant for squeal. The present paper gives inside into a method for the measurement and identification of linear and nonlinear brake pad material parameters identified under correct boundary conditions. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Longer time steps in explicit dynamics subject to small nonlinearities
Authors: Wolff Sebastian
Published: December 2011

An approach that increases the critical time step in explicit time integration is presented. By derivation as a variational integrator, symplecticity and momentum preservation are ensured. The linear response is assumed to be dominant and is integrated implicitly, while the nonlinear forces are explicitly integrated. MOLLY filters the high‐frequent portions of the nonlinear forces and increases the critical time step. An SDOF example and a structural example using modal reduction verify the improved stability. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A thermodynamically consistent model of shape‐memory alloys
Authors: Benešová Barbora
Published: December 2011

This contribution presents a non‐isothermal mesoscopic model of single‐crystalline shape‐memory alloys within the framework of continuum mechanics. We briefly recall static mesoscopic modeling concepts as presented in e.g. [4, 5] and propose a thermomechanically consistent model featuring the heat equation and thermo‐mechanical coupling. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micro‐mechanical study of interactions between polymers and filler aggregates
Authors: Dargazany Roozbeh , Itskov Mikhail
Published: December 2011

Filled rubber‐like materials exhibit a complex, history‐dependent hysteretic behavior which is mostly due to damage of micro‐structures inside the rubber matrix. In this paper, we study the contribution of filler aggregates inside the elastomer to this damage behavior. To this end, a recently proposed multi‐scale model of single aggregates [1] is applied. The network decomposition concept adopted there is further extended here to an additional network [1] which takes into account elasticity of filler aggregates and polymer chains in their vicinity. This network is described by means of a 3D statistical volume element (SVE) obtained by homogenization over the aggregate size distribution within the rubber matrix. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface energies in microstructure of martensite
Authors: Goodarzi Mehdi , Hackl Klaus
Published: December 2011

A continuum model for laminate geometry in microstructure of martensite, employing energy minimization, is presented. Ansatzes for twin interface energies as well as grain boundary energy are proposed. The model is applied to predict scale properties and geometrical characteristics of refinement and accommodation of microstructure. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Creep‐fatigue analysis of the steel AISI type 316 component failure
Authors: Gorash Yevgen , Altenbach Holm
Published: December 2011

The purpose of this work is to extend a typical creep‐damage model in order to describe material behavior under variable thermal and mechanical loading in wide stress range. The model basis is creep constitutive law in form of hyperbolic sine stress response function proposed by Nadai. The constitutive law is extended to assume the damage process under creep and fatigue by the introduction of scalar damage parameters and appropriate evolution equations according to Kachanov‐Rabotnov concept. The material constants for model are identified by fitting the experimental creep and low‐cycle fatigue data for the steel AISI type 316 at the range of temperatures 500°C – 750°C. The development of such model is motivated by the well described failure case study of high‐temperature components at unit 1 of Eddystone power plant, which have operated during 130520 hours under creep‐fatigue interaction conditions. The main steam piping (MSP) from this power plant is selected for thermo‐mechanical creep‐fatigue analysis applying the proposed material model. The estimated values of damage parameters comply with the real location of the component failure and a scatter of experimental data on creep‐fatigue interaction diagram. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Softening in Nanocrystalline Metals: Modeling of Grain Growth Induced Creep and Relaxation
Authors: Gürses Ercan , El Sayed Tamer
Published: December 2011

A variational multiscale model is presented for grain growth in face‐centered cubic nanocrystalline (nc) metals. In particular, grain‐growth‐induced stress softening and the resulting relaxation and creep phenomena are addressed. The behavior of the polycrystal is described by a conventional Taylor‐type averaging scheme in which the grains are treated as two‐phase composites consisting of a grain interior phase and a grain boundary affected zone. Furthermore, a grain growth law that captures the experimentally observed characteristics of the grain coarsening phenomena is proposed. The model is shown to provide a good description of the experimentally observed grain‐growth‐induced relaxation in nc‐copper. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Regularized Sharp Interface Model for Martensitic Phase Transformations at Large Strains
Authors: Hildebrand Felix , Miehe Christian
Published: December 2011

The macroscopic mechanical behavior of many functional materials crucially depends on the formation and evolution of their microstructure. When considering martensitic shape memory alloys, this microstructure typically consists of laminates with coherent twin boundaries. We suggest a variational‐based phase field model for the dissipative evolution of microstructure with coherence‐dependent interface energy and construct a suitable gradient‐extended incremental variational framework for the proposed dissipative material. We use our model to predict laminate microstructure in martensitic CuAlNi. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The effect of deposition in a model for quantum dot self‐arrangement
Authors: Maciek D. Korzec
Published: December 2011

In a recently derived thin‐film model that describes the self‐assembly of quantum dots, an atom deposition flux is added and its influence on the evolution of the nano‐crystals is analyzed. A qualitative agreement to experiments is achieved: A realistic Stranski‐Krastanov growth mode can be simulated, where the dot density grows with increased rates as it can be observed in experiments. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational Homogenisation of Polycrystalline Elastoplastic Microstructures at Finite Deformation
Authors: Lehmann Eva , Loehnert Stefan , Wriggers Peter
Published: December 2011

During sheet bulk metal forming processes both, flat geometries and three‐dimensional structures change their shape significantly while undergoing large plastic deformations. As for forming processes, FE‐simulations are often done before in situ experiments, a very accurate material model is required, performing well for a huge variety of different geometrical characteristics.

Because of the crystalline nature of metals, anisotropies have to be taken into account. Macroscopically observable plastic deformation is traced back to dislocations within considered slip systems in the crystals causing plastic anisotropy on the microscopic and the macroscopic level. A finite crystal plasticity model is used to model the behaviour of polycrystalline materials in representative volume elements (RVEs) of the microstructure. A multiplicative decomposition of the deformation gradient into elastic and plastic parts is performed, as well as a volumetric‐deviatoric split of the elastic contribution. In order to circumvent singularities stemming from the linear dependency of the slip system vectors, a viscoplastic power‐law is introduced providing the evolution of the plastic slips and slip resistances.

The model is validated with experimental microstructural data under deformation. Through homogenisation and optimisation techniques, effective stress‐strain curves are determined and can be compared to results from real forming processes leading to a suitable effective material model. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Damping Behaviour of Vibrating Shape Memory Alloy Rods Investigated by a Novel Constitutive Model
Authors: Leindl Mario , Fischlschweiger Michael , Oberaigner Eduard Roman
Published: December 2011

Hysteretic behaviour of shape memory alloys (SMAs) is highly important for design and applicability of these materials in active structural elements like rods. Especially the damping performance of SMAs depend strongly on their hysteretic characteristics. Experimental investigations show the influences of stress on the hysteretic cycle. The current study shows some computational results of a constitutive model which is capable to investigate the effect of an external applied stress field on the hysteretic cycle according to a recently developed method on the basis of statistical mechanics method. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A one‐dimensional approach to the chemical and thermo‐mechanical coupled modeling of curing adhesives including plasticity
Authors: Liebl Christoph , Lion Alexander
Published: December 2011

The modeling and simulation of curing adhesives is of great importance for industrial applications, mainly for the automotive industry. The one‐dimensional model proposed here combines known viscoelastic models for curing material with effects of plasticity. To describe these plasticity effects, a yield stress with isotropic hardening is formulated as an equation of temperature and degree of cure. The proposed model therefore includes viscoelastic properties, thermo‐chemical shrinkage and the aforementioned plasticity characteristics, all as functions of temperature and degree of cure. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)