• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 12
  • 6
  • 3
  • 1
  • Tagged with
  • 22
  • 22
  • 9
  • 8
  • 8
  • 7
  • 7
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Análise numérica bidimensional de sólidos com comportamento visco-elasto-plástico em grandes deformações e situações de contato / Two-dimensional numerical analysis of solids with visco-elasto-plastic behavior under large strains and contact situations

Carvalho, Péricles Rafael Pavão 26 March 2019 (has links)
Motivado por diversos processos de manufatura, tais como conformação de metais a frio ou mesmo manufatura aditiva, este trabalho consiste no desenvolvimento de um código computacional para a simulação numérica de problemas bidimensionais que abordam três tipos de não-linearidade: a geométrica, presente em situações de grandes deslocamentos; a física, presente no modelo constitutivo do material; e a de contato. Na primeira etapa, desenvolve-se um programa para análise dinâmica bidimensional de sólidos elásticos, utilizando a abordagem posicional do método dos elementos finitos, que engloba naturalmente a não-linearidade geométrica em sua formulação. Em seguida, implementam-se modelos constitutivos não-elásticos para problemas com grandes deformações. No modelo elastoplástico, adota-se o critério de von Mises com encruamento cinemático baseado na lei de Armstrong-Frederick. Essa formulação é então generalizada para o caso visco-plástico, onde é considerado o modelo de Perzyna em conjunto com a lei de Norton. No caso visco-elástico, utiliza-se uma formulação que parte do modelo reológico de Zener. Por fim, apresenta-se um modelo visco-elasto-plástico que consiste no acoplamento dos modelos visco-elástico e visco-plástico descritos anteriormente. Em todos os casos, utiliza-se a decomposição multiplicativa do gradiente da função mudança de configuração. Com respeito à aplicação 2D, consideram-se as hipóteses de estado plano de deformações e estado plano de tensões, onde a última é resolvida numericamente por um procedimento local de Newton-Raphson. Para o problema de contato, aplica-se a estratégia Nó-a-Segmento, sendo as condições de não-penetração impostas com a introdução de multiplicadores de Lagrange. A formulação é testada em cada uma das etapas por meio de exemplos numéricos de verificação. Além disso, para mostrar as potencialidades do código desenvolvido, são propostos diversos exemplos numéricos, sendo alguns inspirados por processos de manufatura existentes. Nesses exemplos, são estudados os efeitos de diferentes parâmetros dos materiais e diferentes taxas de deformação na resposta numérica, permitindo uma análise do comportamento dissipativo decorrente da plastificação e da viscosidade, incluindo a influência desses sobre o amortecimento dinâmico. / Motivated by several manufacturing processes, such as cold metal forming or even additive manufacturing, in this work we develop a computational code for numerical simulation of two-dimensional problems addressing three types of nonlinearities: geometric nonlinearity, present in large displacements situations; physical non-linearity, present in the material constitutive model; and contact non-linearity. In the first step, we develop a computational program for dynamic analysis of two-dimensional elastic solids using the positional finite element method, which naturally takes into account geometric non-linearity in its formulation. Following, we implement inelastic constitutive models for large strain problems. In the elasto-plastic model, we adopt von Mises yeld criteria and kinematic hardening based on the Armstrong-Frederick law. The formulation is then generalized to the visco-plastic case, where we consider Perzyna model associated with Norton\'s law. In the visco-elastic case, Zener\'s rheological model is employed. Finally, we present a visco-elasto-plastic model by coupling the visco-elastic and visco-plastic models described previously. In every case, the multiplicative decomposition of the deformation gradient is employed. Regarding the 2D application, we consider both plane strain and plane stress hypothesis, where the latter is solved numerically by a local Newton-Raphson procedure. For the contact problem, we employ the Node-to-Segment strategy, imposing non-penetration conditions with the introduction of Lagrange multipliers. The resulting computational code is tested in each step by means of numerical verification examples. In addition, to show the potentialities of the developed code, several numerical examples are proposed, some of which inspired by existing manufacturing processes. On these examples, we study the effects of different material parameters and strain rates on the numerical response, allowing an analysis of the dissipative behavior due to plasticity and viscosity, including the influence of these on the dynamic damping.
12

Formulação do método dos elementos de contorno para materiais porosos reforçados / Boundary element method formulation for reinforced porous material

Wutzow, Wilson Wesley 16 May 2008 (has links)
Neste trabalho, propõe-se uma formulação não linear baseada no método dos elementos de contorno, para representação de domínios poro-elasto-plásticos reforçados. Esta formulação é apresentada para os casos saturado e não saturado. Para o problema poroso enrijecido um acoplamento com o método dos elementos finitos é empregado, e a técnica de mínimos quadrados permite a regularização dos deslocamentos e do vetor de forças de superfície ao longo das interfaces de acoplamento. São empregadas expressões analíticas para o tratamento das integrais de contorno e de domínio presentes na formulação do método dos elementos de contorno. A formulação de Biot é empregada para a descrição de meios porosos saturados e uma formulação energética baseada nos trabalhos de Coussy é adaptada para a extensão ao caso não saturado. Neste caso, a pressão capilar e energia das interfaces são levadas em consideração. O nível de saturação é descrito pelo modelo de Van Genuchten e o comportamento do esqueleto é descrito ou pelo modelo de Drucker-Prager ou pelo modelo de Cam-Clay modificado. O problema não linear obtido por uma descrição temporal associada a discretização espacial é resolvido pelo método de Newton-Raphson. No caso saturado, o operador tangente consistente é definido e utilizado para obtenção da solução do sistema. Exemplos numéricos são apresentados para validar a formulação proposta. / In this work a nonlinear formulation of the boundary element method (BEM) is proposed to deal with saturated and unsaturated poro-elasto-plastic 2D reinforced domains. To model reinforced porous domains a BEM/FEM (Finite Element Method) modified coupling technique is employed. The coupling is made by using the least square method to regularize the displacement and traction distributions along the interfaces. Analytical expressions have been derived for all boundary and domain integrals required for the formulation. The Biot formulation is used for the description of the saturated porous environments and an energetic consistent formulation based on work of Coussy is adopted for its extension to the framework of unsaturated porous media. In this case, the capillar pressure and the interface energy are taken into account. The Van Genuchten model is used for the determination of saturation level in non-saturated poro-elasto-plastic problems. The Drucker-Prager modified model if used for the saturated poro-elasto-plastic problems and the modified Cam-Clay model for the representation of non-saturated poro-elasto-plastic problems. For the saturated case, the consistent tangent operator is derived and employed inside a Newton procedure to solve non-linear problems. Numerical solutions are presented to validate the proposed models.
13

Approximation of nonsmooth optimization problems and elliptic variational inequalities with applications to elasto-plasticity

Rösel, Simon 09 May 2017 (has links)
Optimierungsprobleme und Variationsungleichungen über Banach-Räumen stellen Themen von substantiellem Interesse dar, da beide Problemklassen einen abstrakten Rahmen für zahlreiche Anwendungen aus verschiedenen Fachgebieten stellen. Nach einer Einführung in Teil I werden im zweiten Teil allgemeine Approximationsmethoden, einschließlich verschiedener Diskretisierungs- und Regularisierungsansätze, zur Lösung von nichtglatten Variationsungleichungen und Optimierungsproblemen unter konvexen Restriktionen vorgestellt. In diesem allgemeinen Rahmen stellen sich gewisse Dichtheitseigenschaften der konvexen zulässigen Menge als wichtige Voraussetzungen für die Konsistenz einer abstrakten Klasse von Störungen heraus. Im Folgenden behandeln wir vor allem Restriktionsmengen in Sobolev-Räumen, die durch eine punktweise Beschränkung an den Funktionswert definiert werden. Für diesen Restriktionstyp werden verschiedene Dichtheitsresultate bewiesen. In Teil III widmen wir uns einem quasi-statischen Kontaktproblem der Elastoplastizität mit Härtung. Das entsprechende zeit-diskretisierte Problem kann als nichtglattes, restringiertes Minimierungsproblem betrachtet werden. Zur Lösung wird eine Pfadverfolgungsmethode auf Basis des verallgemeinerten Newton-Verfahrens entwickelt, dessen Teilprobleme lokal superlinear und gitterunabhängig lösbar sind. Teil III schließt mit verschiedenen numerischen Beispielen. Der letzte Teil der Arbeit ist der quasi-statischen, perfekten Plastizität gewidmet. Auf Basis des primalen Problems der perfekten Plastizität leiten wir eine reduzierte Formulierung her, die es erlaubt, das primale Problem als Fenchel-dualisierte Form des klassischen zeit-diskretisierten Spannungsproblems zu verstehen. Auf diese Weise werden auch neue Optimalitätsbedingungen hergeleitet. Zur Lösung des Problems stellen wir eine modifizierte Form der viskoplastischen Regularisierung vor und beweisen die Konvergenz dieses neuen Regularisierungsverfahrens. / Optimization problems and variational inequalities over Banach spaces are subjects of paramount interest since these mathematical problem classes serve as abstract frameworks for numerous applications. Solutions to these problems usually cannot be determined directly. Following an introduction, part II presents several approximation methods for convex-constrained nonsmooth variational inequality and optimization problems, including discretization and regularization approaches. We prove the consistency of a general class of perturbations under certain density requirements with respect to the convex constraint set. We proceed with the study of pointwise constraint sets in Sobolev spaces, and several density results are proven. The quasi-static contact problem of associative elasto-plasticity with hardening at small strains is considered in part III. The corresponding time-incremental problem can be equivalently formulated as a nonsmooth, constrained minimization problem, or, as a mixed variational inequality problem over the convex constraint. We propose an infinite-dimensional path-following semismooth Newton method for the solution of the time-discrete plastic contact problem, where each path-problem can be solved locally at a superlinear rate of convergence with contraction rates independent of the discretization. Several numerical examples support the theoretical results. The last part is devoted to the quasi-static problem of perfect (Prandtl-Reuss) plasticity. Building upon recent developments in the study of the (incremental) primal problem, we establish a reduced formulation which is shown to be a Fenchel predual problem of the corresponding stress problem. This allows to derive new primal-dual optimality conditions. In order to solve the time-discrete problem, a modified visco-plastic regularization is proposed, and we prove the convergence of this new approximation scheme.
14

Comportement couplé des géo-matériaux : deux approches de modélisation numérique / Objective thermo-hydro-mechanical modelling of the damaged zone around a radioactive waste storage site.

Marinelli, Ferdinando 21 January 2013 (has links)
Nous présentons deux approches différentes pour décrire le couplage hydromécanique des géomatériaux. Dans une approche de type phénoménologique nous traitons le milieu poreux comme un milieu continu équivalent dont les interactions entre la phase fluide et le squelette solide constituent le couplage du mélange à l'échelle macroscopique. En caractérisant le comportement de chaque phase nous arrivons à décrire le comportement couplé du milieu couplé saturé.Nous utilisons cette approche pour modéliser des essais expérimentaux faits sur un cylindre creux pour une roche argileuse (argile de Boom). Les résultats expérimentaux montrent de façon claire que le comportement de cette roche est fortement anisotrope. Nous avons choisi de modéliser ces essais en utilisant une lois de comportement élasto-plastique pour laquelle la partie élastique est transversalement isotrope.Le problème aux conditions aux limites étudié met en évidence des déformations localisées autour du forage intérieur. Afin de décrire de façon objective le développement de ces bandes de cisaillement nous avons considéré un milieu continu local de type second gradient qui permet d'introduire une longueur interne. De ce fait nous avons pu étudier le problème d'unicité en montrant qu'un changement de la discrétisation temporelle du problème aux limites peut conduire à des solutions différentes.Dans la deuxième approche étudiée nous caractérisons la microstructure du matériau avec des grains et un réseau de canaux pour la phase fluide. À l'aide d'un processus numérique d'homogénéisation nous arrivons à calculer numériquement la contrainte du mélange et le flux massique. Cette méthode d'homogénéisation numérique a été implémentée dans un code aux éléments finis afin d'obtenir des résultats macro. Une validation de l'implentation est proposée pour des calculs en mecanique pure et en hydromécanique. / We present two different approaches to describe the hydromechanical behaviour of geomaterials. In the first approach the porous media is studied through an equivalent continuum media where the interaction between the fluide and solid phases caracterize the coupling behaviour at the macroscale.We take into account this approach to model experimental tests performed over a hollow cylinder sample of clay rock (Boom Clay), considered for nuclear waste storage. The experimental results clearly show that the mechanical behaviour of the material is strongly anisotropic. For this reason we chose an elasto-plastic model based on Drucker-Prager criterion where the elastic part is characterized by cross anisotropy.The numerical results of boundary value problem clearly show localised strains around the inner hollow section. In order to regularize the numerical problem we consider a second gradient local continuum media with an enriched kinematic where an internal lenght can be introduced making the results mesh independent. The uniqueness study is carried out showing that changing the temporal discretization of the problem leads to different solutions.In the second approach we study the hydromechanical behaviour of a porous media that it is characterised by the microstructure of the material. The microstructure taken into account is composed by elastic grains, cohesives interfaces and a network of fluid channels. Using a periodic media a numerical homogenization (square finite element method) is considered to compute mass flux, stress and density of the mixture. In this way a pure numerical constitutive law is built from the microstructure of the media. This method has been implemented into a finite element code (Lagamine, Université de Liège) to obtain results at the macroscale. A validation of this implementation is performed for a pure mechanical boundary value problem and for a hydromechanical one.
15

Formulação do método dos elementos de contorno para materiais porosos reforçados / Boundary element method formulation for reinforced porous material

Wilson Wesley Wutzow 16 May 2008 (has links)
Neste trabalho, propõe-se uma formulação não linear baseada no método dos elementos de contorno, para representação de domínios poro-elasto-plásticos reforçados. Esta formulação é apresentada para os casos saturado e não saturado. Para o problema poroso enrijecido um acoplamento com o método dos elementos finitos é empregado, e a técnica de mínimos quadrados permite a regularização dos deslocamentos e do vetor de forças de superfície ao longo das interfaces de acoplamento. São empregadas expressões analíticas para o tratamento das integrais de contorno e de domínio presentes na formulação do método dos elementos de contorno. A formulação de Biot é empregada para a descrição de meios porosos saturados e uma formulação energética baseada nos trabalhos de Coussy é adaptada para a extensão ao caso não saturado. Neste caso, a pressão capilar e energia das interfaces são levadas em consideração. O nível de saturação é descrito pelo modelo de Van Genuchten e o comportamento do esqueleto é descrito ou pelo modelo de Drucker-Prager ou pelo modelo de Cam-Clay modificado. O problema não linear obtido por uma descrição temporal associada a discretização espacial é resolvido pelo método de Newton-Raphson. No caso saturado, o operador tangente consistente é definido e utilizado para obtenção da solução do sistema. Exemplos numéricos são apresentados para validar a formulação proposta. / In this work a nonlinear formulation of the boundary element method (BEM) is proposed to deal with saturated and unsaturated poro-elasto-plastic 2D reinforced domains. To model reinforced porous domains a BEM/FEM (Finite Element Method) modified coupling technique is employed. The coupling is made by using the least square method to regularize the displacement and traction distributions along the interfaces. Analytical expressions have been derived for all boundary and domain integrals required for the formulation. The Biot formulation is used for the description of the saturated porous environments and an energetic consistent formulation based on work of Coussy is adopted for its extension to the framework of unsaturated porous media. In this case, the capillar pressure and the interface energy are taken into account. The Van Genuchten model is used for the determination of saturation level in non-saturated poro-elasto-plastic problems. The Drucker-Prager modified model if used for the saturated poro-elasto-plastic problems and the modified Cam-Clay model for the representation of non-saturated poro-elasto-plastic problems. For the saturated case, the consistent tangent operator is derived and employed inside a Newton procedure to solve non-linear problems. Numerical solutions are presented to validate the proposed models.
16

Simulation multi-échelle des procédés de fabrication basée sur la plasticité cristalline / Multi-scale simulation of manufacturing processes based on the crystal plasticity

Soho, Komi Dodzi Badji 21 March 2016 (has links)
Dans cette thèse, deux méthodes de couplage sont proposées pour la simulation multi-échelle des procédés de mise en forme. Dans la première partie, une procédure simplifiée (couplage indirect) est adoptée pour coupler les codes éléments finis (Abaqus et LAM3) au modèle polycristallin avec un schéma de transition autocohérente basée sur le comportement élastoplastique du monocristal écrit dans le formalisme des grandes déformations. Cette procédure simplifiée consiste à lier le modèle polycristallin avec l'analyse EF par l'extraction de l'histoire de l'incrément de déformation et de contrainte macroscopique, obtenue à partir d'une simulation EF préliminaire avec une loi phénoménologique, et à l'utiliser comme trajet de chargement dans le modèle polycristallin. Cette méthode est appliquée pour la simulation multi-échelle du procédé de skin-pass. Le suivi du trajet de chargement extrait dans la demi-épaisseur de la tôle a permis de prédire l'évolution des grandeurs physiques associées au modèle de plasticité en particulier la texture cristallographique, la texture morphologique et l'écrouissage. Dans la seconde partie de cette thèse, un modèle polycristallin élastoplastique du type autocohérent en petites déformations est couplé au code EF Abaqus via la routine utilisateur UMAT. Ce couplage (dit couplage direct) consiste à utiliser la théorie de la plasticité cristalline comme loi de comportement à chaque point d'intégration du maillage EF. Le polycristal est représenté par un ensemble de N monocristaux. Chaque fois que le code EF a besoin d'information sur le comportement mécanique aux points d'intégration de chaque EF, le modèle polycristallin est appelé. Pour valider ce couplage développé, nous avons effectué des cas tests de simulation de trajets rhéologiques. Les résultats issus de ce couplage ont été validés avec des modèles de référence. À la différence des modèles phénoménologiques, ce couplage permet non seulement d'avoir des informations sur le comportement macroscopique de la structure mais aussi d'obtenir des informations sur l'état de la microstructure du matériau. / In this thesis, two coupling methods are proposed for the multiscale simulation of forming processes. In the first part, a simplified procedure (indirect coupling) is adopted to couple the finite element codes (Abaqus and LAM3) with a polycrystalline selfconsistent model based on the large strain elastoplastic behavior of single crystals. This simplified procedure consists in linking the polycrystalline model with the FE analysis by extracting the history of the increment of macroscopic strain and stress, obtained from a preliminary FE simulation with a phenomenological law, and then using it as loading path prescribed to the polycrystalline model. This method is applied to multiscale simulation of skin-pass processes. By following on the loading path extracted at the halfthickness of the sheet, we can predict the evolution of some physical parameters associated with the plasticity model, in particular the crystallographic texture, the morphological texture and hardening. In the second part on this thesis, a small strain version of the elastoplastic polycristalline self-consistent model is coupled to the Abaqus FE code via the user material subroutine UMAT. This coupling (called direct coupling) consists in using crystal plasticity theory as constitutive law at each integration point of the FE mesh. The polycristal is represented by a set of N single crystals. Each time the FE code needs information on the mechanical behavior at the integration points considered, the full polycrystalline constitutive model is called. In order to validate this coupling, simulations of simple mechanical tests have been conducted. The results of this coupling have been validated through comparison with reference models. Unlike phenomenological models, this coupling provides not only information on the overall macroscopic response of the structure, but also important information related to its microstructure
17

Microscopic origin of the rheological and surface properties of embryonic cell aggregates / Origine microscopique des propriétés rhéologiques et de surface des agrégats de cellules embryonnaires

Stirbat, Tomita Vasilica 28 September 2012 (has links)
Ces travaux de thèse portent sur l'étude expérimentale des propriétés physiques et de la biomécanique des agrégats cellulaires embryonnaires. Le but de cette thèse était d'une part de mieux comprendre l'origine biologique de la viscosité et de la tension de surface tissulaire, d'autre part d'étudier quantitativement en détail l'élasticité cellulaire par des nouvelles mesures de rhéologie en cisaillement. Un premier chapitre concerne les mesures de tension de surface tissulaire par la méthode de compression et de viscosité tissulaire par analyse de la cinétique de fusion de deux agrégats en faisant varier comme paramètre principal la contractilité cellulaire que certains suspectent comme étant la principale origine biologique de ces paramètres. Nous utilisons le formalisme du DITH (Haris, 1976: Differential Interfacial Tension Hypothesis) pour interpréter les données. Le deuxième chapitre concerne les mesures rhéologiques en cisaillement à l'aide d'un rhéomètre commercial plan-plan sur plusieurs centaines ou milliers d'agrégats cisaillés ensembles. Nous montrons que les cellules deviennent moins rigides pour une déformation minimale d'environ 4%, mais sur l'échelle de l'heure les cellules sont capables de se rigidifier à nouveau. Ces expériences sont analysées à l'aide d'un modèle de ressorts qui cassent sous contrainte puis se ressoudent à contrainte nulle / This thesis focuses on the experimental study of physical properties and biomechanics of embryonic cell aggregates. The aim of this thesis was on one hand to better understand the biological origin of tissue viscosity and tissue surface tension, and on the other hand to study quantitatively in detail cell elasticity by means of new rheological measurements in shear. A first chapter deals with measurements of tissue surface tension by tissue compression method and tissue viscosity by analysis of the fusion kinetics of two aggregates. We vary key parameters such as cell contractility that some people suspect to be the main biological origin of these parameters. We use the formalism of DITH (Haris, 1976: Differential Interfacial Tension Hypothesis) to interpret the data. The second chapter deals with rheological measurements in shear using a commercial plate-plate rheometer over several hundred of aggregates. We showed that cells become softer after a minimal deformation of 4% is reached, and can harden again on the timescale of hour. These experiences are analyzed using a model of springs that break under stress and then reattach at zero strain
18

Analysis of Bolted Connections in Creo Simulate - Theory, Software Functionality and Application Examples / Analyse von Schraubenverbindungen mit Creo Simulate - Theorie, Softwarefunktionalität und Anwendungsbeispiele

Jakel, Roland 25 June 2013 (has links) (PDF)
Die Präsentation stellt kurz die Grundlagen der Berechnung von Schraubenverbindungen in Anlehnung an die VDI-Richtlinie 2230 Teil 1 dar. Auch die vier FEM-Modellklassen, die die VDI 2230 Teil 2 (Entwurf) zur Berechnung von Mehrschraubenverbindungen vorschlägt, werden behandelt, und die in Creo Simulate vorhandenen Softwarefeatures zu deren Umsetzung vorgestellt. Es folgt eine Darstellung, was bei der Linearisierung von Schraubenverbindungen zur vereinfachten Berechnung zu beachten ist, und wieso bei der Berechnung im FEM-System dann nicht notwendigerweise eine Vorspannung benötigt wird. Ausführlich wird das neue Schraubenfeature in Creo Simulate betrachtet, das eine weitgehend automatisierte Modellierung und Berechnung von Standardverschraubungen erlaubt. Weitere Features, wie die neuen Vorspannelemente, werden erläutert, sowie auch die Grenzen der Software aufgezeigt. Abschließend werden zwei anspruchsvolle Anwendungsbeispiele vorgestellt: Eine zentrisch belastete Verschraubung mit Berücksichtigung von Elasto-Plastizität und einer komplexen Lasthistorie (Anziehen durch Anzugsmoment, Setzeffekte, Entfall des Torsionsmomentes durch das Anziehen, Betriebskraft) sowie eine exzentrisch belastete Verschraubung, die wegen eines relativ dünnen Flansches starke Biegezusatzbeanspruchungen erfährt. / The presentation shows the foundations of bolt analysis according to VDI-guideline 2230 part 1. In addition, the four FEM model classes proposed in VDI 2230 part 2 (draft) are described, as well as the features available in Creo Simulate to realize these model classes. Next, the presentation shows the requirements for linearizing bolted connections, and why in a FEM analysis with a linearized connection no preload is necessary. The new fastener feature introduced in Creo Simulate is explained in detail. This feature allows the automated modeling and analysis of bolted connections having standard geometry. Further software features, like pretension elements, as well as the current software limitations are shown. Finally, two advanced application examples are shown: A centrically loaded bolted connection taking into account elasto-plasticity and a complex load history (tightening torque, embedding, removal of tightening stress, operational load), and an eccentrically loaded flange connection, which is subjected to high additional bending loads because the flange is relatively thin.
19

Variační metody v termomechanice kontinua pevné fáze / Variational Methods in Thermomechanics of Solids

Pelech, Petr January 2020 (has links)
The thesis is devoted to study of continuum mechanics and thermodynamics and the related mathematical analysis. It consists of four self-contained chapters dealing with different aspects. The first chapter focuses on peridynamics, a non-local theory of continuum mechanics, and its relation to conventional local theory of Cauchy-Green elasticity. Similar compar- isons has been used for proving consistency and for determining some of the material coefficients in peridynamics, provided the material parameters in the local theory are known. In this chapter the formula for the non-local force-flux is computed in terms of the peridynamic interaction, relating the fundamental concepts of these two theories and establishing hence a new connection, not present in the previous works. The second and third chapters are both devoted to Rate-Independent Systems (RIS) and their applications to continuum mechanics. RIS represents a suitable approximation when the internal, viscous, and thermal effects can be neglected. RIS has been proven to be useful in modeling hysteresis, phase transitions in solids, elastoplasticity, damage, or fracture in both small and large strain regimes. In the second chapter the existence of solutions to an evolutionary rate-independ- ent model of Shape Memory Alloys (SMAs) is proven. The model...
20

Analysis of Bolted Connections in Creo Simulate - Theory, Software Functionality and Application Examples

Jakel, Roland 25 June 2013 (has links)
Die Präsentation stellt kurz die Grundlagen der Berechnung von Schraubenverbindungen in Anlehnung an die VDI-Richtlinie 2230 Teil 1 dar. Auch die vier FEM-Modellklassen, die die VDI 2230 Teil 2 (Entwurf) zur Berechnung von Mehrschraubenverbindungen vorschlägt, werden behandelt, und die in Creo Simulate vorhandenen Softwarefeatures zu deren Umsetzung vorgestellt. Es folgt eine Darstellung, was bei der Linearisierung von Schraubenverbindungen zur vereinfachten Berechnung zu beachten ist, und wieso bei der Berechnung im FEM-System dann nicht notwendigerweise eine Vorspannung benötigt wird. Ausführlich wird das neue Schraubenfeature in Creo Simulate betrachtet, das eine weitgehend automatisierte Modellierung und Berechnung von Standardverschraubungen erlaubt. Weitere Features, wie die neuen Vorspannelemente, werden erläutert, sowie auch die Grenzen der Software aufgezeigt. Abschließend werden zwei anspruchsvolle Anwendungsbeispiele vorgestellt: Eine zentrisch belastete Verschraubung mit Berücksichtigung von Elasto-Plastizität und einer komplexen Lasthistorie (Anziehen durch Anzugsmoment, Setzeffekte, Entfall des Torsionsmomentes durch das Anziehen, Betriebskraft) sowie eine exzentrisch belastete Verschraubung, die wegen eines relativ dünnen Flansches starke Biegezusatzbeanspruchungen erfährt. / The presentation shows the foundations of bolt analysis according to VDI-guideline 2230 part 1. In addition, the four FEM model classes proposed in VDI 2230 part 2 (draft) are described, as well as the features available in Creo Simulate to realize these model classes. Next, the presentation shows the requirements for linearizing bolted connections, and why in a FEM analysis with a linearized connection no preload is necessary. The new fastener feature introduced in Creo Simulate is explained in detail. This feature allows the automated modeling and analysis of bolted connections having standard geometry. Further software features, like pretension elements, as well as the current software limitations are shown. Finally, two advanced application examples are shown: A centrically loaded bolted connection taking into account elasto-plasticity and a complex load history (tightening torque, embedding, removal of tightening stress, operational load), and an eccentrically loaded flange connection, which is subjected to high additional bending loads because the flange is relatively thin.

Page generated in 0.4337 seconds