bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative study on control concepts of a robot manipulator with multiple‐link/joint flexibilities
Authors: Staufer Peter , Gattringer Hubert , Bremer Hartmut
Published: December 2012

If one is dealing with active vibration suppression on a highly nonlinear flexible system, various techniques are needed. On the one hand a suitable dynamic model of the system is required. And on the other hand intelligent model based control concepts are necessary for active vibration damping. We deal with a basic model, where the flexibilities are approximated with linear springs and dampers, a so called lumped element model (LEM). For the control design we propose a control structure with two degrees of freedom (2DoF) for solving the tracking problem, based on the LEM. Such an approach allows designing the feedforward part independently of the feedback part. Hereby the feedforward control is based on the flatness approach, while for the feedback control several strategies are studied using acceleration‐ and gyrosensor‐measurements. The contribution is completed with a validation by measurements from a very fast trajectory on an articulated robot with two flexible links and three elastic joints. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Convergence Study of Explicit Co‐Simulation Approaches with Respect to Subsystem Solver Settings
Authors: Schmoll Robert , Schweizer Bernhard
Published: December 2012

Coupling different subsystem simulators can be accomplished by a co‐simulation [1, 2]. For this purpose, the subsystem solvers are coupled by appropriate input and output variables. In order to analyze the stability of the coupled simulation, not only the coupling technique must be taken into account, but also the subsystem integrators. On the one hand, the stability of the co‐simulation is influenced by the extrapolation of the coupling variables and by the macro‐step size. On the other hand, the numerical errors arising from the subsystem solvers may directly affect the coupled simulation. The focus of this paper lies on the question, how the subsystem solvers influence the co‐simulation. Therefore, numerical studies regarding the numerical stability and the convergence order have been carried out by using a co‐simulation test model. We restrict ourselves to explicit co‐simulation techniques, based on a zero‐stable applied‐force coupling approach. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and theoretical investigation on soft tissue remodeling enhanced by cell activity
Authors: Yi Jeong‐Hun , Stoffel Marcus , Weichert Dieter , Nebelung Sven , Rath Björn
Published: December 2012

The aim of the present work is to investigate the remodeling phenomenon of a cell‐seeded tissue. In experiments, a cell seeded condensed collagen gel is mechanically stimulated in a bioreactor for four weeks, after which the specimen is tested in compression to measure its change of stiffness. The change, regarded as remodeling, is assumed to be the result of newly synthesized collagen type II; a constitutive equation is proposed for the remodeling effect. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Biphasic Approach for the Simulation of Growth Processes in Soft Biological Tissues Incorporating Damage‐Induced Stress Softening
Authors: Schmidt Thomas , Balzani Daniel , Ricken Tim , Werner Daniel
Published: December 2012

In this contribution a coupled material framework is presented, which considers the effects of damage and growth in soft biological tissues. The tissue is described as a porous medium by taking into account a solid and a fluid phase. The fluid phase is assumed to carry nutrients supplying growth of the solid phase. The latter one is described as a fiber‐reinforced material, where a damage variable is introduced for the fiber part of the associated free energy function. The performance of the proposed model is demonstrated in a finite element analysis of a simplified human heart model. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of the biomechanical behaviour of structurally stable/unstable motion segments of the sheep spine
Authors: Strampe Malte , Stoffel Marcus , Weichert Dieter , Sellei Richard Martin , Pape Hans‐Christoph
Published: December 2012

The effects of damage of intervertebral discs on their biomechanical behaviour and the factors favouring the progression of instability are studied. Healthy and damaged movement segments are analyzed experimentally and numerically. The aim is to represent and predict the effects of tissue damage and changes in the spine by comparison with healthy segments. Since the intervertebral disc acts as a mechanical damper, relaxation tests are performed in addition to pressure experiments. The experiments are carried out in a bioreactor with tempered nutrient solution. A cultivation period in the bioreactor allows detecting cell viability, solute diffusion rates and gene expression of the discs. Numerically, the nonlinear, viscoelastic, anisotropic and diffusion‐dependent behaviour of the intervertebral disc is modelled with the FE‐program Abaqus, using a modular material law as a UMAT subroutine. With the measurement results, the relevant parameters can be determined so that the mechanical behaviour of intervertebral discs can be simulated. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A biphasic transverse isotropic FEM model for cartilage
Authors: Albrecht Daniel , Ricken Tim , Pierce David M. , Holzapfel Gerhard A.
Published: December 2012

Articular cartilage is a viscoelastic, two‐phase and fiber‐strengthen tissue; it consists of a solid and a fluid phase. We describe this tissue using the Theory of Porous Media (TPM). Some simulation results are shown. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vibrating Portable Machine‐Tools Acting on Human Operator
Authors: Gligor Anamaria , Ţepeç‐Bobescu Alina‐Sabina , Arghir Mariana
Published: December 2012

This paper will be a short presentation of the specialized literature and international standards about the importance of vibration action of portable machine tools on human body and particularly on the hand‐arm system. Exposure to harmful vibrations can lead to health problems and disorders, especially in the upper joints and dorsal region of the human body. A detailed understanding of the undesirable effects of vibration on the human body is essential to achieve administrative and technical prevention. In modern times, vibration studies become more frequent, decisive for the many machines, vehicles and construction. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mechanical modeling of medical mesh implants at the mesoscale
Authors: Röhrnbauer Barbara , Kress Gerald , Mazza Edoardo
Published: December 2012

The present study is aimed at a physically based mechanical model for prosthetic meshes at the mesoscale. The geometry and the local kinematics of a representative unit cell are mapped in an abstracted, but still physically relevant description. Such a model allows to understand the interplay between local deformation patterns and the resulting global anisotropic and nonlinear force response. It is expected to provide design criteria for mesh implant optimization, not only accounting for the global mechanical behavior but also for local mesh‐tissue interactions. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards a Method for Parameter Estimation of Articular Cartilage and a Staggered Procedure for Synovial Fluid‐Cartilage Interaction
Authors: Mabuma Joffrey , Markert Bernd , Ehlers Wolfgang
Published: December 2012

Up to now, the interaction mechanisms between cartilage and synovial fluid within diarthrodial joints are not fully understood. These joints are able to function effectively over the lifetime of an individual even under very high loads, which requires minimal wear of cartilage. In particular, the reason for the extremely low coefficients of friction has still to be explained.

The goal of this contribution is to numerically investigate the interaction between articular cartilage and synovial fluid in diarthrodial joints. In this connection, we already developed an appropriate continuum model of the articulating tissue layers as highly anisotropic and heteregeneously charged biphasic solid‐fluid aggregates based on the Theory of Porous Media (TPM). The calibration of the previously elaborated model is the next concern. To this end, a sensitivity analysis is performed to identify the relevant constitutive parameters governing the cartilage response during indentation tests. The remaining parameters are then estimated numerically using a direct search algorithm. Next, a sequential solution algorithm has to be developed in order to solve the complex contact problem at the interface between synovial fluid and articular cartilage. Thereby, the fluid and cartilage domains are iteratively calculated until equilibrium is reached. For the moment, simulations are performed on a 3‐d hip‐joint geometry reconstructed from MRI data, which proceed from a continuum‐mechanical description of the synovial fluid gap. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New three‐dimensional finite elements with embedded strong discontinuities to model solids at failure
Authors: Zhang Xiaoxuan , Linder Christian
Published: December 2012

This work focuses on the development of new finite elements which can capture strong discontinuities in three‐dimensional failure problems. The displacement jumps in the solid are approximated by a linear interpolation obtained by enforcing a new class of enhanced separation modes to exactly be satisfied by the formulation. Efforts are also put towards the development of a proper crack propagation tracking algorithm needed for the complicated crack surfaces appearing in realistic 3D failure simulations, based on a combination of the global tracking algorithm and the marching cubes algorithm. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Monitoring fatigue cracks and stress intensity factors based on local strains
Authors: Boukellif Ramdane , Ricoeur Andreas
Published: December 2012

A method for crack detection and stress intensity factor measurement in plate structures is presented by using strain gauges and applying the Body Force Method (BFM). The BFM is based on elastic solutions for concentrated loads and the principle of linear superposition allowing e.g. the calculation of the strain field in a cracked body. The inverse problem is solved applying the PSO (particle swarm optimization) and the unknown parameters are crack position, length and inclination as well as loading quantities. Experiments are carried out under cyclic loading using pre‐cracked plates made of aluminum alloy. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Damage processes coupled with phase separation in elastically stressed alloys
Authors: Heinemann Christian , Kraus Christiane
Published: December 2012

In micro‐electronic materials such as solder alloys, phase‐separation and coarsening as well as damage phenomena occur at the same time and influences each other. In this note, a unifying model which couples multi‐component Cahn‐Hilliard systems with elasticity and uni‐directional damage processes is presented. We outline the equations and their initial‐boundary conditions in a classical setting and cite some existence results for weak solutions recently proved in [8, 9]. The damage is assumed to be incomplete, i.e. the maximal damaged material parts still feature elastic properties. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relaxed Incremental Variational Formulation for Damage in Fiber‐Reinforced Materials
Authors: Balzani Daniel , Ortiz Michael
Published: December 2012

An incremental variational formulation for damage at finite strains is proposed based on the classical continuum damage mechanics. Since loss of convexity is obtained at some critical deformations a relaxed incremental stress potential is constructed which convexifies the original non‐convex problem. The resulting model can be interpreted as the homogenization of a micro‐heterogeneous material bifurcated into a strongly and weakly damaged phase at the microscale. A one‐dimensional relaxed formulation is derived and based thereon, a model for fiber‐reinforced materials is given. Finally, some numerical examples illustrate the performance of the model. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crack growth in elastic materials with internal boundaries and interfaces
Authors: Judt Paul , Ricoeur Andreas
Published: December 2012

This work presents numerical methods used for predicting crack paths in technical structures based on the theory of linear elastic fracture mechanics. The FE‐method is used in combination with an efficient remeshing algorithm and a post processor to calculate crack tip loading. The interaction of cracks and internal boundaries and interfaces is investigated. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase Field Modeling of Fracture in Plates and Shells
Authors: Ulmer Heike , Hofacker Martina , Miehe Christian
Published: December 2012

The numerical modeling of failure mechanisms in plates and shells due to fracture based on sharp crack discontinuities is extremely demanding and suffers in situations with complex crack topologies. This drawback can be overcome by a diffusive crack modeling, which is based on the introduction of a crack phase field. In this paper, we extend ideas recently outlined in [1, 2] towards the phase field modeling of fracture in dimension‐reduced continua with application to Kirchhoff plates and shells. The introduction of history fields, containing the maximum reference energy obtained in history, provides a very transparent representation of the coupled balance equations and allows the construction of an extremely robust operator split technique. The performance of the proposed models is demonstrated by means of representative numerical examples. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Phase Field Model for Ductile to Brittle Failure Mode Transition
Authors: Hofacker Martina , Miehe Christian
Published: December 2012

The computational modeling of failure mechanisms in solids due to fracture based on sharp crack discontinuities suffers in dynamic problems with complex crack topologies. This can be overcome by a diffusive crack modeling based on the introduction of a crack phase field. We outline a conceptual framework for phase field models of crack propagation in brittle elastic and ductile elastic‐plastic solids under dynamic loading and investigate the ductile to brittle failure mode transition observed in the experiment performed by Kalthoff and Winkeler [3]. We develop incremental variational principles and consider their numerical implementations by multi‐field finite element methods. To this end, we define energy storage and dissipation functions for the plastic flow including the fracture phase field. The introduction of local history fields that drive the evolution of the crack phase field inspires the construction of robust operator split schemes. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A comparative study of deformations of elastic‐viscoplastic plates using different structural hypotheses
Authors: Stoffel Marcus , Vu Thang Duy , Schmidt Rüdiger , Weichert Dieter
Published: December 2012

In the present study, circular metal plates are subjected to impulsive loadings leading to geometrically and physically non‐linear deformations. In the theoretical model, different structural hypotheses are implemented into a finite element code and the hypotheses leading to the most precise numerical predictions are studied. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructural Model of a Closed‐Cell Foam on the Basis of Image Analysis
Authors: Fahlbusch Nina‐Carolin , Becker Wilfried
Published: December 2012

The focus of this work is the identification of a unit cell that is able to represent the microstructure of a closed‐cell solid foam to predict the effective behaviour of the foam numerically. For the investigation, a finite element model consisting of a repeating unit cell with periodical boundary conditions is implemented. A tetrakaidecahedral foam microstructure is considered as simplified cell geometry, and a strain‐energy based homogenisation concept is utilized. On the basis of image analysis imperfections are applied to the cell. The obtained model is used as a representative volume element (RVE) for further investigations of the postbuckling behaviour of the foams. Different analyses are performed and the results are compared to literature and experimental data. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simplified assessment of high‐speed train induced bridge vibrations considering shear effects
Authors: Salcher Patrick , Adam Christoph
Published: December 2012

A novel response spectrum methodology for rapid assessment of the dynamic peak acceleration response of simple railway bridges subjected to high‐speed trains is presented. This methodology is based on non‐dimensional characteristic bridge and train parameters, and on the shear beam theory. The effect of shear deformations should be considered, if the considered bridge is a truss structure. Depending on the train load model, response spectra are derived for each modal coordinate separately as a function of a non‐dimensional speed parameter and the bridge length to wagon length ratio. An estimate of the peak response is found by statistical combination of the individual modal responses applying different rules. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Failure analysis of highly predeformed beams used as flexure hinges
Authors: Kern Dominik , Rösner Malte , Seemann Wolfgang
Published: December 2012

The trend to extend the working ranges of flexure hinges implies large deformations during operation. To conduct a failure analysis the total deformation is decomposed into desired deformation and deviations. In particular, a flexure hinge of leaf‐spring type is examined. It is modeled by the theory of elastica. The resulting boundary value problem is solved numerically for the static case by Ritz's method. It is discretized into trial functions and their free coefficients are determined from the minimum of potential energy by optimization methods. The crucial point is that the elastic energy stored in the beam is formulated intrinsically, while the potential of external conservative loads is formulated in a space‐fixed coordinate system. The well‐known special case of buckling of a straight cantilever beam is used for verification. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elastic limit analysis of a thick‐walled cylindrical panel subject to radial heating
Authors: Arslan Eray , Mack Werner
Published: December 2012

Subject of the investigation is a cylindrically curved thick‐walled shell guided at the ends which is heated at its outer surface. In particular, the thermal conditions at the elastic limit according to Tresca's yield criterion as well as the couples occuring in the elastic and elastic‐plastic state are studied. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solid‐Shell Finite Elements for Tesselated Geometries
Authors: Wimmer Johannes , Reese Stefanie
Published: December 2012

Sandwich structures made of sheets of composite materials are in widespread use, particularly in the transportation industry. Finite Element simulation of the thin, tesselated structures with complex, three‐dimensional material behaviour is a challenging task for the underlying element technology. In particular, frequently used linear isoparametric approaches exhibit unphysical stiffening phenomena. Recent developments in solid‐shell finite element technology aim to overcome these undesirable effects. Here, they are applied to an example of a corrugated sandwich core under transversal compression. A study of convergence is conducted with respect to commercially available shell and solid finite elements, and their ability to reproduce the bending dominated deformation state. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Homogenization of thin structured sheet metals by using FEM
Authors: de Silva Tina , Kühhorn Arnold , Golze Mark
Published: December 2012

Thin structured sheet metals promise high potential concerning lightweight design in industrial applications regarding the classical mechanical engineering and vehicle construction as well as the aeronautics.

Compared to flat, unstructured sheet metals the component stiffness and buckling behavior can significantly be improved by structuring especially in out of plane direction.

To be able to calculate the elastic behavior of large structures from structured sheet metals a mechanical surrogate model is developed which describes effectively average material parameters based on processes of homogenization.

For the surrogate properties symmetry and antisymmetry boundaries and periodic boundaries respectively are contemplated on elementary cells whose structural mechanical behavior is decisive.

By using an energetic approach [3] the stiffnesses of large plate and shell structures can be determined by a cooperatively small amount of finite elements. By means of these material properties elastic behavior can easily be calculated. With it an efficient numerical design is guaranteed.

This explained analysis can be applied to other periodically built up plate structures. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elastic‐plastic states of two‐layer curved bar under pure bending
Authors: Sülü Ismail Y. , Arslan Eray
Published: December 2012

Analytical solution of an elastic‐partially plastic two‐layer curved bar subjected to couples at both ends is obtained. The solution is based on Tresca's yield criterion and its associated flow rule. Numerical results for real engineering materials in partially plastic stress state are presented in graphical form. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sensitivity analysis of weakened beams on elastic foundation with Green's functions
Authors: Schwartpaul Kai , Zhang Chuanzeng , Carl Oliver
Published: December 2012

The approach of Sensitivity Analysis with Green's Functions (SAGF) [1,2] was developed to predict changes in deformations, stresses or eigenfrequencies of structures resulting from stiffness modifications or cracking by considering only the weakened or damaged parts of the structures. This approach results in a local analysis instead of a global analysis by recalculating the whole structure. Consequently, it is computationally less time‐consuming than the conventional methods based on a global analysis. The key idea of the SAGF approach is based on the comparison between the elastic strain energies of the original and the weakened structures and the substitution of the virtual displacements by the corresponding Green's functions [1, 2].

Furthermore, an approximate approach for the sensitivity analysis was suggested which is described in [1, 3] in details. This approach enables us to predict the changes in the structural responses due to the stiffness weakening in the beam or in the elastic Winkler foundation by considering only the internal forces or the deflections of the original unweakened system. In addition, an iterative method was developed to enhance the accuracy of the SAGF approach.

In this paper, the local SAGF method for sensitivity analysis of elastic beams on Winker foundation with stiffness weakening is presented. The accuracy and the efficiency of the proposed method are verified by using a numerical example. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Oscillations of a channel with a flexible wall conveying viscous flow
Authors: Bach Karolina , Hetzler Hartmut , Seemann Wolfgang
Published: December 2012

The interaction between a flexible structure and flowing fluid can cause flow‐induced vibrations and the steady state may loose stability by divergence or flutter, thus leading to undesirable dynamic behaviour.

As a model for fluid‐structure‐interaction a planar channel guiding a flowing fluid is studied. It can be shown that for thin channels the coupling effects are strong [1] and therefore the focus of this contribution is to investigate the behaviour of a channel, where the structural displacements are non‐negligible compared to the gap width. Due to this comparatively large amplitudes a linear description of the interface between fluid and structure will not be sufficient anymore and the relation between the Eulerian description of the fluid and the Lagrangian description of the structure must be taken into account: eventually, this yields nonlinear boundary conditions. Furthermore in narrow gaps the viscosity of the fluid cannot be ignored [2]. Hence the effect of viscosity will also be considered within this contribution. In order to allow for analytical results and keep the focus on the effects due to the moving interface, the fluid flow is modelled using lubrication theory. The linear stability of the steady state ist investigated as well as the influence of the inherent nonlinearities of the coupled problem. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Network evolution model: thermodynamics consistency, parameter identification and finite element implementation
Authors: Khiêm Vu Ngoc , Dargazany Roozbeh , Navrath Uwe , Itskov Mikhail
Published: December 2012

In this contribution, the previously proposed network evolution model [1] for carbon black filled elastomers is further studied. First, we show that the model does not contradict the second law of thermodynamics and is thus thermodynamically consistent. On the basis of new experimental data the influence of filler concentration on the material parameters is further examined. Accordingly, this influence concerns only three material parameters and is approximated by phenomenological relations. These relations enable one to simulate rubbers based on the same compound with various filler concentrations. Finally, the model is implemented into the FE‐Software ABAQUS and illustrated by a number of numerical examples. The examples demonstrate good agreement with experimental results with respect to the Mullins‐Effect, permanent set and induced anisotropy. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shakedown analysis of periodic composites with kinematic hardening material model
Authors: Chen Min , Hachemi Abdelkader , Weichert Dieter
Published: December 2012

Lower‐bound limit and shakedown analysis of periodic composites with the consideration of kinematic hardening are carried out on the representative volume element level. In combination with homogenization theory, the homogenized macroscopic admissible loading domains are determined. Furthermore, the strengths of periodic composites by using elastic perfectly plastic, unlimited and linear limited kinematic hardening material models are calculated and compared. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of phase‐transformations based on numerical minimization of intersecting Gibbs energy potentials
Authors: Ostwald Richard , Bartel Thorsten , Menzel Andreas
Published: December 2012

We present a novel approach for the simulation of solid to solid phase‐transformations in polycrystalline materials. To facilitate the utilization of a non‐affine micro‐sphere formulation with volumetric‐deviatoric split, we introduce Helmholtz free energy functions depending on volumetric and deviatoric strain measures for the underlying scalar‐valued phase‐transformation model. As an extension of affine micro‐sphere models [5], the non‐affine micro‐sphere formulation with volumetric‐deviatoric split allows to capture different Young's moduli and Poisson's ratios on the macro‐scale [1]. As a consequence, the temperature‐dependent free energy assigned to each individual phase takes the form of an elliptic paraboloid in volumetric‐deviatoric strain space, where the energy landscape of the overall material is obtained from the contributions of the individual constituents. For the evolution of volume fractions, we use an approach based on statistical physics–taking into account actual Gibbs energy barriers and transformation probabilities [2]. The computation of individual energy barriers between the phases considered is enabled by numerical minimization of parametric intersection curves of elliptic Gibbs energy paraboloids. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Steady vibrations problem in the theory of viscoelasticity for Kelvin‐Voigt materials with voids
Authors: Svanadze Maia M.
Published: December 2012

In this paper the linear theory of viscoelasticity for Kelvin‐Voigt materials with voids is considered. The uniqueness and existence theorems for internal boundary value problem (BVP) of steady vibrations are proved by means of the potential method (boundary integral method) and the theory of singular integral equations. The application of this method to the 3D BVP of the considered theory reduces this problem to 2D singular integral equation. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carbon Fibre Prepregs: Simulation of a Thermo‐Mechanical‐Chemical Coupled Problem
Authors: Hankeln Frederik , Mahnken Rolf
Published: December 2012

In automotive industry research is done to replace high strength steel by combinations of steel and carbon‐fibre prepregs (pre‐impregnated fibres). It is planned to form both steel and uncured prepregs in one step followed by the curing process under pressure in the forming die. The ability to simulate the mechanical behaviour during forming and curing would allow more economical processes. The simulation of prepregs must regard highly anisotropic, viscoelastic and thermal‐ chemical properties. For this the model is split into an anisotropic elastic part, which represents the fibre fraction and an isotropic, viscoelastic part, representing the matrix. This part also contains curing, causing a dependency on time and temperature. During deep‐drawing large deformations are occurring, so a large strain model regarding anisotropy, viscoelasticity and curing has been developed. Also experiments were made to validate this model. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of nanoindentation experiments by means of rheological models
Authors: Müller Wolfgang H. , Worrack Holger
Published: December 2012

The nanoindentation technique is established in the field of material characterization at small dimensions. It is daily practice to analyze nanoindentation data with an almost “classical” formula based on the publications by Oliver and Pharr and Fischer‐Cripps. The procedure works well for elastic‐time independent plastic material behavior, for example copper and the calibration material fused silica, even at higher test temperatures. However, low melting solder materials are susceptible to creep behavior. For this reason, additional analysis procedures are required to determine the material parameters more precisely. In this paper the authors want to give an introduction to an “enhanced” analysis of nanoindentation data based on rheological models, which are often used to describe the time‐dependence of material response. Two examples of such models are the MAXWELL‐ and the KELVIN‐body. The authors present a rheological model, published by Mencik in 2011 [1], in context with the corresponding equation which is used to extract the material properties from the recorded data. Results of the analysis at the calibration material fused silica are presented and discussed together with the material parameters published in the literature. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computation of material forces for the thermo‐mechanical response of dynamically loaded elastomers
Authors: Behnke Ronny , Kaliske Michael
Published: December 2012

Elastomers are widely used in today's life. The material is characterized by large deformability upon failure, elastic and time dependent as well as non‐time dependent effects which can be also a function of temperature. In addition, cyclically loaded components show heat build‐up which is due to dissipation. As a result, the temperature evolution of an elastomeric component can strongly influence the material properties and durability characteristics. Representing best the real thermo‐mechanical behaviour of an elastomeric component in its design process is one motivation for the use of sophisticated, coupled material approaches within numerical simulations. In order to assess the durability characteristics, for example regarding crack propagation, material forces (configurational forces) are one possible approach to be applied. In the present contribution, the implementation of material forces for a thermo‐mechanically coupled material model including a continuum mechanical damage (CMD) approach is demonstrated in the context of the Finite Element Method (FEM). Special emphasis is given to material forces resulting from internal variables (viscosity and damage variables), temperature field evolution and dynamic loading. Using the example of an elastomeric component, for which the material model parameters have been previously identified by a uniaxial extension test, material forces are evaluated quantitatively. The influence of each contribution (internal variables, temperature field and dynamics) is illustrated and compared to the overall material force response. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale modelling and simulation of micro machining of titanium
Authors: Lohkamp Richard , Müller Ralf , Schneider Frank , Aurich Jan
Published: December 2012

The microscale morphology of micro machined component surfaces is directly connected to the heterogeneous microstructure. The deformation depends on the crystal structure, in case of the considered cp‐titanium, the hcp crystal structure. In a first approach the crystal plastic deformation is modeled with isotropic hardening. A visco‐plastic evolution law accounts for the rate dependency. The concept of configurational forces is used with the framework of crystal plasticity to model the cutting process of cp‐titanium. The setting is implemented into the finite element method. The examples show the effect of the material heterogeneity on the deforamtion behavior and on the related configurational forces. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Material parameter identification using model reduction to uniaxial tensile test
Authors: Krämer Stephan , Rothe Steffen , Hartmann Stefan
Published: December 2012

Material parameter identification is the necessary link between constitutive modeling and application of material models in complex simulations of real world problems. We present an approach to make use of already developed stress algorithms for three‐dimensional finite‐element computations in terms of a reduction to uniaxial tensile tests for material parameter identification. Strain‐driven stress algorithms lead to the approach of solving differential‐algebraic equations. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A stochastic model for the direct and inverse problem of adhesive materials
Authors: Nörenberg Nicole , Mahnken Rolf
Published: December 2012

This work deals with the generation of artificial data based on experimental data for adhesive materials and the application of this data to the inverse and the direct problem. In reality there are only a very limited number of experimental data available. Therefore, the prediction of material behaviour is difficult and a statistical analysis with a stochastic proved thesis is nearly impossible. In order to increase the number of tests a method of stochastic simulation based on time series analysis is applied.

With artificial data an arbitrary number of data is available and the process of the parameter identification can be statistically analysed. Additionally, one example is shown, which adapts the analysed material parameter to the direct problem. The stochastic finite element method is used to take into account the distribution and deviation of the fracture strain. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of induced anisotropy at large deformations for polymers
Authors: Caylak Ismail , Mahnken Rolf
Published: December 2012

In this work we develop a model to describe the induced plasticity of polymers at large deformations. Polymers such as stretch films exhibit a pronounced strength in the loading direction. The undeformed state of the films is isotropic, whereas after the uni‐axial loading the material becomes anisotropic. In order to consider this induced anisotropy during the stretch process, a spectral decomposition of the inelastic right CAUCHY‐GREEN tensor is done. Therefore, the yield function can be formulated as a function of the anisotropic tensor, where again the anisotropic tensor is a function of the maximum eigenvalue. A backward EULER scheme is used for updating the evolution equations, and the algorithmic tangent operator is derived. The numerical implementation of the resulting set of constitutive equations is used in a finite element program and for parameter identification. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Deformation induced martensite transformation in a cold‐worked forming process of austenitic stainless steel
Authors: Dally Tim , Weinberg Kerstin
Published: December 2012

Within the last years the goal of industrial manufacturing processes – such as tube forming – has shifted towards an optimization of technological as well as mechanical properties of the manufactured structures. For example, during the forming procedure of sheets made of austenitic stainless steel X5CrNi18‐10, the content of strain‐induced martensite needs to be controlled. In order to achieve optimal structural properties of the manufactured tube with respect to very high‐cycle fatigue (VHCF), a martensite ratio of approximately 25% needs to be obtained [1].

On the basis of experimental investigations this contribution deals with the numerical simulation of the tube‐forming process with special consideration of the martensite ratio c as a function of temperature and deformation field. For this purpose we extend an existing martensite model on polyaxial states of stress and compare experimental results and numerical simulations for the modified model. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A solid‐shell finite element for fibre reinforced composites
Authors: Simon Jaan‐Willem , Stier Bertram , Reese Stefanie
Published: December 2012

Fibre reinforced composites consisting of several layers, each of which is composed of a woven fabric embedded in a matrix material, are investigated in this paper. Such materials are characterized by a complex anisotropic behavior, which necessitates a fully three‐dimensional formulation of the constitutive equations. On the other hand, they are frequently used in thin shell‐like applications. In order to account for the three‐dimensional material law while still providing the suitable shape for thin structures, a solid‐shell finite element for fibre composite materials is presented herein. Locking phenomena are treated by both the enhanced assumed strain (EAS) concept and the assumed natural strain concept (ANS). Using reduced integration together with hourglass stabilization leads to high computational efficiency. The anisotropic constitutive behavior of the composites is reflected by a micromechanically motivated continuum model, which –together with the solid‐shell formulation– allows for an accurate representation of the through‐the‐thickness stress distribution even for thin structures. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On response functions in linear thermoelastic models of shape memory polymers
Authors: Aydin Aycan O. , Kazakeviciute‐Makovska Rasa , Steeb Holger
Published: December 2012

This paper is concerned with the broad class of Liner Thermoelastic (LTE) models for Shape Memory Polymers (SMPs) which unifies numerous constitutive theories proposed in the literature for this kind of smart material. It is shown that the response functions for the general model of this class may be determined directly from experimental data measured in standard thermomechanical cyclic tests. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A new continuum approach to the coupling of shear yielding and crazing with fracture in glassy polymers
Authors: Schänzel Lisa , Dal Hüsnü , Miehe Christian
Published: December 2012

Over the past decades, several constitutive models accounting for finite viscoplasticity and failure in glassy polymers were developed. However, depending on thermal and loading rate conditions, the response might change from ductile to brittle. This brittle response is characterized by inelastically deformed zones, so‐called crazes, having the thickness of micrometers and spanning at some fractions of a millimeter, containing a dense array of fibrils interspersed with elongated voids, detailed discussion e.g. [1]. The shear yielding and crazing are not completely independent excluding each other. Present models introduce crazing either discrete by cohesive surfaces, e.g. [2], or continuous, see [3]. In this work, we outline an extension of a ductile plasticity model towards (i) the description of volumetric directional plasticity effect due to crazing and (ii) the modeling of the local failure due to fracture. The ultimate amount of volumetric plastic craze strain is bounded by a limiting value, where failure occurs. In a second step, the modeling of subsequent failure mechanisms is realized by introducing a fracture phase field, characterizing via an auxiliary variable the crack. Here, we adopt structures of a continuum phase field model of fracture in brittle solids [4], and modify it for a fracture driving term related to the volumetric plastic deformation of the crazes. We demonstrate the performance of proposed formulation by means of a representative boundary value problem. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and Simulation of Microwave Heating for Spalling of Radioactive Contaminated Concrete
Authors: Melcher Andreas , Lepers Benjamin , Umminger Martin , Kayser Thorsten , Link Guido , Haist Michael , Jelonnek John , Müller Harald
Published: December 2012

Microwave heating is becoming of growing importance in material sciences in the last two decades. Due to the volumetric heating effect, microwave heating offers an energy efficient way of processing materials in several ways. The modeling and simulation of material processing with microwaves with respect to the material structure is a challenging task. The corresponding mathematical modeling results in a coupled, multiscale problem in space and time consisting of Maxwell equations, the heat equation and a temperature‐dependent description of the dielectric properties of them material under investigation. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the flow characteristics of a geothermal plant in a heterogeneous subsurface
Authors: Koch David , Ehlers Wolfgang
Published: December 2012

Due to the scarcity of fossil fuel with a simultaneous rising in global energy demand, it is important to gain access to other energy sources. Geothermal energy holds great potential, and has therefore been studied increasingly in recent years. Within the construction of a geothermal plant, a fluid is introduced via a borehole into the initially gas‐filled porous rock. Due the rising pressure gradient, the fluid distributes, displaces the gas and escapes through a second borehole. The modelling approach of these processes in a heterogeneous subsurface proceeds from the Theory of Porous Media (TPM) including an elastically deformable solid, an incompressible fluid, and a gaseous phase [1]. To solve the initial‐boundary‐value problem, the governing primary variables of the strongly coupled three‐phase model are spatially approximated by mixed finite elements, whereas the time‐discretisation is carried out by an implicit Euler time‐integration scheme. The goal of the presented numerical simulations is to study the specific flow characteristics in a heterogenous subsurface. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Approximate Galerkin method applied to an analysis of vibration of continuous mechanical systems
Authors: Płaczek Marek
Published: December 2012

Paper presents fundamental assumptions of the approximate Galerkin method application in order to vibration analysis of continuous mechanical systems with different form of vibration and different boundary conditions. Flexural vibration of beams, longitudinal vibration of rods and torsional vibration of shafts with all possible ways of fixing were considered. Analyzed mechanical systems were treated as subsystems of mechatronic systems with piezoelectric transducers. This work was done as an introduction to the analysis of mechatronic systems with piezoelectric transducers used as actuators or passive vibration dampers [1–3]. It is impossible to use an exact Fourier method in this case. This is the reason why the approximate Galerkin method was chosen and analysis of its exactness was done as a first step of this work. Dynamic flexibilities of considered mechanical systems were calculated twice, using exact and approximate methods. Obtained results were juxtaposed and it was proved that in some cases the approximate method should be corrected while in the other it is precise enough. A correction method was proposed and it was assumed that the approximate method can be used in mechatronic systems analysis. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis and modeling of the hydro‐mechanics of deformable fractures
Authors: Vinci Carlo , Renner Jörg , Steeb Holger
Published: December 2012

In the present contribution, we investigate and model the flow of a viscous fluid into a single deformable fracture and the associated elastic deformation of the surrounding porous rock. Due to the coupled nature of the problem, conceptually and technically different strategies can be applied to model and solve the resulting hydro‐mechanical system. Therefore, two different modeling approaches are analyzed. On the one hand, we derive the governing equations from the conservation of mass avoiding any of the frequently used approximations or simplifications. On the other hand, we describe the physics based on Biot's quasi‐static poroelastic equations. We compare and critically discuss the results obtained with the presented different solution approaches. The results show that both models are able to capture the same physical effects, also those caused by the fracture deformation. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiphase FEM Modeling of Infiltration Processes in Cohesionless Soils
Authors: Schaufler A. , Becker C. , Steeb H.
Published: December 2012

The aim of this work is to develop a continuum multiphase model to describe infiltration processes for cohesionless soils. For this purpose, a Representative Volume Element (RVE) is considered and described by the continuum mixture theory extended by the concept of volume fractions (Theory of Porous Media – TPM). The thermodynamically consistent TPM is a macroscopical multiphase modeling approach, extended from classical single‐phase continuum mechanics. Futhermore a 1‐dim example for an infiltration problem is presented. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A three‐phase model for polymer curing including diffusive motion and agglomeration of inclusions.
Authors: Lenhof Bernd , Diebels Stefan
Published: December 2012

In this work, a phenomenological three‐phase model is formulated to simulate agglomeration and breakup of particles contained in a polymer. It shall serve as a starting point for modelling the same phenomena in curing polymers. While isothermal processes are assumed, the model is stated in the framework of continuum mechanics of mixtures. The phenomenological model consists of a polymer phase, and two particle phases. Agglomeration and breakup is modeled as a concentration exchange between the two particle phases. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)