bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of micro‐structure on fibre push‐out tests
Authors: Brylka Barthel , Fritzen Felix , Böhlke Thomas , Weidenmann Kay André 
Published: December 2011

AbstractIn fibre reinforced materials, the interface toughness has a significant influence on strength and damage resistance. Especially in discontinuous fibre reinforced composites, where high densities of fibre ends are apparent, it has been shown that additives which improve the interfacial toughness can increase the effective strength of the materials [1]. Due to the fact that interface properties are strongly dependent on the manufacturing process, only experimental techniques providing the possibility to take these influences into account, are promising for an integrated material characterization. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Damage and fracture behavior in dynamic tension tests: Modelling and numerical simulations
Authors: Gerke Steffen , Brünig Michael 
Published: December 2011

AbstractThe continuum damage model is based on a general thermodynamic framework for the modeling of rate and temperature dependent behavior of anisotropically damaged elastic‐plastic materials subjected to fast deformation. The introduction of damaged and fictitious undamaged configurations allows the definition of damage tensors and the corresponding free energy functions lead to material laws affected by damage and temperature. The damage condition and the corresponding damage rule strongly depend on stress triaxiality. Furthermore, the rate and temperature dependence is reflected in a multiplicative decomposition of the plastic hardening and damage softening functions. The macro crack behavior is characterized by a triaxiality dependent fracture criterion.The continuum damage model is implemented into LS‐DYNA as user defined material model. Corresponding numerical simulations of unnotched and notched tension tests with high strain rates demonstrate the plastic and damage processes during the deformation leading to final fracture numerically predicted by an element erosion technique. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On an Energetic Interpretation of a Phase Field Model for Fracture
Authors: Kuhn Charlotte , Müller Ralf 
Published: December 2011

AbstractIn the pioneering work by Griffith, it is assumed that a crack propagates, if this is energetically favorable. However, this original formulation requires a pre‐existing initial crack. In order to bypass this deficiency of classical Griffith theory, Francfort and Marigo advocate a global variational criterion, where the total energy is minimized with respect to any admissible displacement field and crack set. Bourdin's regularized approximation of this variational formulation makes use of a continuous scalar field to indicate cracks. Based on this regularization a phase field fracture model is formulated. The crack field is assumed to follow a Ginzburg‐Landau type evolution equation, and cracking is addressed as a phase transition problem. The coupled problem of mechanical balance equations and the evolution equation is solved using the finite element method combined with an implicit time integration scheme. The numerical solution naturally yields the crack evolution including crack propagation, kinking, branching and initiation without any additional criteria. In this work we study the driving mechanisms behind the crack evolution in the phase field fracture model and compare to the purely energetic considerations of the underlying variational formulation. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A tensorial framework for strain induced damage of plastically deformed metals
Authors: Zapara Maksim , Tutyshkin Nikolai , H. Müller Wolfgang , Wille Ralf 
Published: December 2011

AbstractA tensorial framework for strain induced ductile damage of plastically deformed metals is developed in terms of both plastic flow theory and continuum damage mechanics. A symmetric second order damage rate tensor is used in order to study various processes with large finite deformations in combination with damage analysis. The definition of this tensor is physically meaningful since its volumetric and deviatoric parts describe the damage increments caused by an increase in the void volume and by a change in the shape of the void, respectively. Such a view on damage kinetics leads to the introduction of two measures for damage assessment which allow predicting not only a risk of macroscopic failure but also the onset of void coalescence. Material functions appearing in the constitutive equations for damage are determined both by own experiments and by known results from literature. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stress and free vibration analysis of functionally graded beams using static Green's functions
Authors: Carl Oliver , Villamil Pedro , Zhang Chuanzeng 
Published: December 2011

AbstractIn this paper static Green's functions for functionally graded Euler‐Bernoulli and Timoshenko beams are presented. All material properties are arbitrary functions along the beam thickness direction. The closed‐form solutions of static Green's functions are derived from a fourth‐order partial differential equation presented in [2]. In combination with Betti's reciprocal theorem the Green's functions are applied to calculate internal forces and stress analysis of functionally graded beams (FGBs) under static loadings. For symmetrical material properties along the beam thickness direction and symmetric cross‐sections, the resulting stress distributions are also symmetric. For unsymmetrical material properties the neutral axis and the center of gravity axis are located at different positions. Free vibrations of functionally graded Timoshenko beams are also analyzed [3]. Analytical solutions of eigenfunctions and eigenfrequencies in closed‐forms are obtained based on reference [2]. Alternatively it is also possible to use static Green's functions and Fredholm's integral equations to obtain approximate eigenfunctions and eigenfrequencies by an iterative procedure as shown in [1]. Applying the Sensitivity Analysis with Green's Functions (SAGF) [1] to derive closed‐form analytical solutions of functionally graded beams, it is possible to modify the derived static Green's functions and include terms taking cracks into account, which are modeled by translational or rotational springs. Furthermore the SAGF approach in combination with the superposition principle can be used to take stiffness jumps into account and to extend static Green's functions of simple beams to that of discontinuous beams by adding new supports. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stabilized mixed triangular finite elements at large deformations using area bubble functions
Authors: Caylak Ismail , Mahnken Rolf , Widany Kai‐Uwe 
Published: December 2011

AbstractIn this paper stabilized mixed triangular finite elements are presented in order to avoid volume locking and to damp stress oscillations. Geometrically non‐linear elastic problems are addressed. The mixed method of incompatible modes and the mixed method of enhanced strains are considered as special cases. As a key idea, volume and area bubble functions are used for the method of incompatible modes and the enhanced strain method [1], thus giving both the interpretation of a mixed finite element method with stabilization terms. Concerning non‐linear problems these are non‐linearly dependent on the current deformation state, however, linearly dependent stabilization terms are used [1]. The approach becomes most attractive for the numerical implementation, since the use of quantities related to the previous Newton iteration step is completely avoided. The variational formulation for the standard two‐field method, the method of incompatible modes and the enhanced strain method in finite deformation problems is derived for a hyper elastic Neo‐Hookean material. In the representative example Cook's membrane problem illustrates the good performance of the presented approaches compared to existing finite element formulations. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient Series Solutions for Shear Forces of Vibrating Thin Rectangular Plates on Elastic Foundation with Thermal Loads
Authors: Holl Helmut J. , Liu Wenqi 
Published: December 2011

AbstractSimply supported rectangular Kirchhoff‐plates with two‐parametric Pasternak‐type foundation are studied under the action of a transient temperature moment, which is span‐wise constant. In extension to a previous study it can be shown, that an excellent convergence of the series solutions of the static problem can be achieved by means of Kummer's transformation and Cesaro's generalized C1‐Summation. The convergence improvement of the other types of the solutions can be performed analogously. The dynamic solution for the deflection and shear forces is computed using the derived efficient solution for the quasi‐static case with fast convergent Fourier series. Modal expansion is applied for the computation of the vibrations about this quasi‐static part. The results of he analytical solution for defined parameters of the foundation are shown for some characteristic points of the plate and compared to the FE computation results . (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Hilbert‐Huang transform based identification method for general linear time‐varying systems and weakly nonlinear systems
Authors: Hu Han , Proppe Carsten 
Published: December 2011

AbstractThis paper proposes an identification method for general linear time‐varying (LTV) MDOF systems and weakly nonlinear systems based on the Hilbert‐Huang Transform (HHT)[1]. The proposed method uses Empirical mode decomposition (EMD) to decompose the response signals of systems into intrinsic mode functions (IMFs) and residues, and then analyzes the IMFs and the residues by Hilbert transform (HT) to obtain the analytical IMFs and analytical residues. After that, the above signals are synthesized to form new response signals and new analytical response signals. Finally, the new synthesized signals are used to identify the stiffness and damping coefficients of the systems. Three types of variation: smooth, abrupt and periodical variations are considered in the numerical simulations of LTV chainlike[2] and nonchainlike systems as well as weakly nonlinear systems such as Duffing oscillators and Van der Pol oscillators with white noise added in the system responses to demonstrate the effectiveness, accuracy and robustness of the proposed method. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of Damping Mechanisms in Free and Forced Vibrations of Some Structural Members
Authors: Pham Thanh Chung , Wauer Jörg , Seemann Wolfgang 
Published: December 2011

AbstractFor continuous vibrating systems, such as bars and beams, end‐mounted in the environment, knowledge about the mass, damping and stiffness properties of the resonating environment is important for analyzing free and forced vibrations of such structural members which are also damped themselves. To finally get an identification of the clamping parameters, examinations of both vibrating structural members for various restraint conditions and dynamic interaction with viscoelastic halfspaces, etc., are required. As a first step, longitudinal bar vibrations are studied in detail. The method of separation of variables combined with the reformatted orthogonality relation, and numerical integration is applied for calculating the free and forced oscillations. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shear strength of webs with holes
Authors: Schröder Kai‐Uwe 
Published: December 2011

AbstractIn lightweight design the webs of beams which are loaded by bending are often provided with holes. Aim of this article is to present a method to calculate the shear strength of webs with certain holes. The semi‐analytical method is derived with respect to the results of geometrically and physically non‐linear numerical simulations in which the shear strength of the web is calculated. The method consists of a plastic failure approach for rather thick webs and a framework analogy to model the failure of a solid web after onset of buckling. To take the influence of the holes into account the shear strength of the solid web is reduced as a function of geometry parameters. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Buckling of a non‐Euclidean annular plate
Authors: Schwarzbart Michael , Steindl Alois 
Published: December 2011

AbstractThe effect of free edges of a monoatomic graphene sheet leads to excess edge energy due to the reconstruction of dangling bonds. Molecular static calculations show, that individual carbon atoms near the edge are displaced out of plane for relaxed nanoribbons [1]. In this work we are considering the effect of excess edge energy for almost circular graphene patches. To tackle this problem in the framework of continuum mechanics we are modelling the edge effect with a non‐Euclidean plate model. A linear stability analysis of the flat configuration leads to the stability boundary in the parameter plane. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural health monitoring of hybrid composite structure with piezoelectric patches
Authors: Zemčík Robert , Kroupa Tomás̆ , Bartos̆ek Jan 
Published: December 2011

AbstractStructural health monitoring is performed on a hybrid structure specially designed for simple assembly and disassembly or replacement of components. The net‐like structure is composed of composite beams connected with aluminum pads and it is fixed to a frame in selected locations. Modal analysis is performed both experimentally and numerically. The experiment is carried out using impact hammer, accelerometer and spectrum analyzer and the frequency and damping characteristics are thus obtained. The numerical model using finite element method is validated by comparison of the calculated and measured eigenfrequencies and eigenshapes. Furthermore, piezoelectric patches are applied on selected beam. The modal analysis is carried out again using the piezoelectric patches and with some of the composite beams replaced by damaged beam. The variation in modal characteristics between original and damaged configurations is analyzed both experimentally and numerically. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Chaotic nonlinear dynamics of cantilever beams under the action of signs‐variables loads
Authors: Krysko A. V. , Koch M. I. , Yakovleva T. V. , Nackenhorst U. , Krysko V. A. 
Published: December 2011

AbstractIn this study we investigate the nonlinear chaotic dynamics of structures, consisting of three contacting isotropic Euler‐Bernoulli beams under alternating transverse load. The beams are connected to each other via weak contact conditions. Geometric as well as physical nonlinearity and contact interaction between the beams are taken into account. A new method was proposed for the analysis of chaotic phase synchronization for the multilayered construction consisting of three titanium beams by using Morlet wavelets. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rotation of an axisymmetric particle in a plane flow
Authors: Renner Barbara , Altenbach Holm , Naumenko Konstantin 
Published: December 2011

AbstractThe rotation of an inertialess ellipsoidal particle in a shear flow of a Newtonian fluid has been firstly analyzed by Jeffery [1]. He found that the particle rotates such that the end of its symmetry axis describes a closed periodic orbit. Based on the balance equation of the angular momentum we derived the equation of rotational motion of a cylindrical particle, that is suspended in a plane shear flow field of a viscous fluid, and solved numerically. The rotary inertia is taken into account. The solution is compared with the rotation of a slender particle. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A comparison between elastohydrodynamic and dry hertzian line contacts with regard to their nonlinear vibration behaviour
Authors: Wiegert Benedikt , Hetzler Hartmut , Seemann Wolfgang 
Published: December 2011

AbstractThe nonlinear dynamic behaviour of a simple system employing two different types of contact is compared: elastohydrodynamic line contact and Hertzian line contact with appropriate damping. The elastohydrodynamic problem is solved with finite elements. For the Hertzian line contact problem an analytical solution is known.It is found that for highly loaded cases Hertzian and elastohydrodynamic contacts lead to very similar frequency response curves. This means that instead of solving the computational expensive elastohydrodynamic problem the Hertzian contact can be used. However, considering weakly loaded contacts the two types of contact show very different behaviour. In particular the natural frequencies are different and the elastohydrodynamic contact exhibits rich nonlinear dynamic behaviour including jump phenomena as well as sub‐ and superharmonic bifurcations. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hysteresis Behaviour of 51CrV4 and Viscoplastic Modeling Aspects
Authors: Al‐Baldawi Ammar , Schreiber Lothar , Wünsch Olaf 
Published: December 2011

AbstractIn this work we investigate the material behaviour of steel 51CrV4 in classical uniaxial strain controlled tension tests of different strain rates interposed by relaxation steps, in which the equilibrium stress observed is significantly smaller than the stresses seen in slowest strain rate test. Also, some cyclic experiments with different strain rates and amplitudes were done to analyze the hysteresis behaviour of the material. Against this background of experimental data the modeling possibilties of two models are explored: the Lion model and the Chaboche model with kinematic hardening ansatz. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A novel constitutive law for Silicon under contact loading
Authors: Budnitzki Michael , Kuna Meinhard 
Published: December 2011

AbstractSilicon (Si) remains the most important semiconductor material to date. The understanding of its deformation behavior under contact (indenter‐) loading is crucial to improving technologically relevant abrasive machining techniques (lapping, sawing, grinding). While it has been long established that Si undergoes a series of stress driven phase transitions upon compression and subsequent pressure release, to the authors' knowledge, no material model is available that adequately captures this behavior. In particular, reverse transformation in unloading has received too little attention. A novel phenomenological, thermomechanical model based on experimental observations and MD predictions is presented in this work. It captures both the cd‐Si → β‐Si transition upon compression and the β‐Si → a‐Si transition upon rapid decompression, which are most relevant for indenter loading. To control inelasticity in unloading, the dissipation function was augmented by a kinematic constraint on the tensorial internal variable. In stress space, the transformation surfaces are hyperboloids of revolution aligned along the hydrostatic axis. The non‐linear model was numerically implemented in a finite element code using an iterative implicit algorithm and successfully applied to simple loading cases. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of the Green Tensor to the Modeling of Solution‐Precipitation Creep
Authors: Günther Christina , Ilic Sandra , Hackl Klaus 
Published: December 2011

AbstractOur aim is to present a mechanical model for solution‐precipitation creep, a diffusive deformation process occurring in polycrystalline and granular materials. Within the scope of the model, a Lagrangian consisting of the elastic power and dissipation is proposed. The former is kept in a standard form typical for linear material behavior while the latter is assumed as a surface integral depending on the velocity of the material transport and the velocity of the motion of the boundary. The minimization with respect to the total deformations leads to the equilibrium equation which is solved analytically, by using Green's function. The evolution equations are obtained as the result of the minimization with respect to the internal variables and are solved via finite element method. The contribution closes with a numerical example showing the deformation of a polycrystal consisting of hexagonal crystals. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards the simulation of grinding processes – a thermoplastic single grain approach
Authors: Holtermann Raphael , Menzel Andreas , Hortig Christian , Svendsen Bob 
Published: December 2011

AbstractThe current work aims at the modelling and simulation of metal grinding processes with focus on the thermal behaviour resulting from the interaction of tool and workpiece. Starting from a two‐dimensional model of a single grain, representative numerical experiments are carried out based on the variation of grain geometry and its spatial position relative to the workpiece to predict the resulting load‐displacement‐behaviour.Here, a thermoelastic viscoplastic constitutive model is used to capture thermal softening of the material taken into account. Referring to previous research, an adaptive remeshing scheme, based on a combination of error estimation and refinement indication is used to overcome mesh dependence, allowing to resolve the complex deformation patterns and to predict a realistic thermomechanical state of the resulting workpiece surface. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Zur Modellierung von Aushärtevorgängen in Polymeren unter Verwendung von Stoffgesetzen der Viskoelastizität und Viskoplastizität
Authors: Landgraf Ralf , Ihlemann Jörn 
Published: December 2011

AbstractPolymere finden ein breites Anwendungsgebiet sowohl im Ingenieurbereich als auch in weiteren Disziplinen, wie zum Beispiel der Medizintechnik. Neben einer Vielzahl von Anwendungen für kunststofftechnische Bauteile spielen Polymere ebenso als Füge‐, Füll‐ oder Dichtwerkstoffe eine große Rolle. Als Beispiele seien Klebeverbindungen oder der Einsatz von akrylischen Knochenzementen (PMMA) in der Medizin genannt. Ein phänomenologischer Ansatz zur Modellierung der Aushärtung solcher Werkstoffe geht zurück auf Lion und Höfer (2007). Auf Grundlage des bestehenden Ansatzes werden unterschiedliche mechanische Teilstoffgesetze zur Abbildung der mechanischen Eigenschaften untersucht und in das bestehende Konzept eingearbeitet. Hierbei kommen Stoffgesetze der Viskoelastizität und Viskoplastizität bei großen Deformationen zum Einsatz. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromechanical creep model for pure copper
Authors: Ozhoga‐Maslovskaja Oksana , Altenbach Holm , Naumenko Konstantin , Prygorniev Oleksandr , Vodka Oleksii 
Published: December 2011

AbstractA Unit Cell made of copper is simulated and investigated under creep conditions within the framework of micromechanics. Geometrical 3D model of the copper microstructure is represented as a Unit Cell with grains of random crystallographical orientation and geometry. Such simulation enables algorithm of Voronoi tessellation. The stress‐strain behavior of grains in the general case is anisotropic due to the ordered crystalline structure. The anisotropic model for a material with a cubic symmetry is implemented in Abaqus and used to assign behavior of grain interior in elastic and creep regions. Material parameters for elastic model are taken from elastic tests of single crystal copper [1]. Power law material parameters for creep model are taken from creep test performed for single crystal copper [2]. The model parameter ξ is validated numerically. Creep results are presented for the case of proportional loading during the primary and secondary creep. Statistical analysis of creep curves received for 55 different realizations of Unit Cell geometry is carried out. As a result confident interval and mathematical expectation of creep data are calculated. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)