A maioria dos líquidos encontrados na natureza são não newtonianos e o estudo do seu comportamento reológico tem uma importância significante em diferentes áreas da engenharia. Entre eles, existe uma classe de fluidos que exibem pequena deformação aparente quando sujeitos a um nível de tensões inferior a uma tensão limite de escoamento, referido como comportamento viscoplástico. Nesta classe de materiais, alguns apresentam também comportamento elástico quando submetidos a baixas taxas de cisalhamento. A presente Tese tem como objetivo o estudo numérico de escoamentos bidimensionais em regime permanente de fluidos elasto-viscoplásticos através de uma expansão-contração planar. O modelo mecânico é definido pelas equações de conservação de massa e de balanço de momentum acopladas ao modelo elasto-viscoplástico proposto nesta Tese. Esta modelagem é aproximada por um método de elementos finitos multi-campos estabilizado baseado na metodologia de Galerkin mínimos-quadrados que possui como variáveis primais os campos de tensão extra polimérica, velocidade e pressão. As condições de compatibilidade entre os sub-espaços de elementos finitos para tensão extra-velocidade e velocidade-pressão são violadas, permitindo assim a utilização de interpolações de igual ordem. O método estabilizado foi implementado no código de elementos finitos para fluidos não newtonianos em desenvolvimento no Laboratório de Mecânica dos Fluidos Aplicada e Computacional (LAMAC) da Universidade Federal do Rio Grande do Sul. Nesta Tese é adotada uma metodologia alternativa para a definição das zonas rígidas do escoamento como sendo a posição onde a taxa de cisalhamento é igual a um valor dado pela relação de parâmetros reológicos do fluido, especificamente a tensão limite de escoamento e a viscosidade newtoniana para baixas taxas de cisalhamento. Nas simulações numéricas realizadas, o tempo de relaxação adimensional, o número de salto, o coeficiente power-law, a vazão adimensional e a massa específica adimensional são variados de forma a avaliar de que modo influenciam na dinâmica de escoamentos elastoviscoplásticos. Os resultados obtidos estão qualitativamente de acordo com a literatura, atestando a estabilidade da formulação empregada. / Non-Newtonian fluids are the majority of liquids found in nature and the study of their rheological behavior has a significant importance on different areas of engineering. Among them, there is a class of materials that exhibits little apparent deformation when subjected to a stress level behind an yield stress, referenced as viscoplastic material. In this class of materials, some fluids also exhibit elastic behavior at low shear rates. The present work aimed to a numerical study of two-dimensional steady state laminar flows of elasto-viscoplastic fluids through a planar expansion-contraction cavity. The mechanical model was defined by the mass conservation and momentum balance equations coupled to the elasto-viscoplastic model porposed in this work. This modeling has been approximated by a stabilized multi-field finite element method based on the Galerkin least-squares methodology, having as primal variables the elastic extra-stress component, velocity and pressure fields. In this way, the compatibility conditions between the extra-stress-velocity and pressure-velocity (Babuška- Brezzi condition) finite element subspaces are violated, allowing to use equal-order finite element interpolations. The stabilized method has been implemented in the finite element code for non-Newtonian fluids under development at the Laboratory of Applied and Computational Fluid Mechanics (LAMAC) of the Federal University of Rio Grande do Sul. An alternative methodology is adopted to define the yield surface as the position where the strain rate is equal to a value given by the relation of the rheological parameters of the fluid, namely the yield stress and the viscosity at low shear rates. In the performed numerical simulations, the non-dimensional relaxation time, the jump number, the power-law coefficient, the non-dimensional flow rate, and the non-dimensional density are varied in order to evaluate their influence on the elasto-viscoplastic fluid dynamics. All results found are in qualitatively accordance with the affine literature, and attesting the good stability features of the formulation.

Grâce à leurs bonnes propriétés mécaniques spécifiques, les matériaux cellulaires architecturés présentent un fort intérêt pour répondre aux problématiques du secteur aéronautique. Cependant, la modélisation d'une structure macroscopique incluant un matériau cellulaire nécessite, soit de modéliser complètement l'architecture à l'échelle mésoscopique - ce qui est coûteux en temps de calcul - soit d'utiliser un Milieu Homogène Equivalent (MHE). Ainsi, cette thèse propose de caractériser un matériau cellulaire modèle constitué d'un empilement de tubes, selon un motif carré ou hexagonal, puis d'identifier un modèle phénoménologique rendant compte du comportement mécanique inélastique du matériau. Dans un premier temps, le matériau est caractérisé sous chargements multi-axiaux à l'aide de simulations éléments finis périodiques en petites déformations. Le comportement homogénéisé en petites déformations est ensuite utilisé pour l'identification d'une Loi Homogène Equivalente (LHE) compressible et anisotrope, qui permet la modélisation de structures sandwichs en remplaçant le coeur cellulaire par son MHE. Une comparaison est réalisée entre les réponses mécaniques des simulations de référence complètement maillées et celles utilisant l'approche par MHE, validant ainsi la pertinence de la méthode multi-échelle de modélisation proposée. La caractérisation en grandes déformations des deux types d'empilement est ensuite menée. D'abord, les effets de bords et les instabilités qui gouvernent le comportement macroscopique sont étudiés. Puis, après une étude du volume élémentaire représentatif des empilements, la caractérisation du comportement inélastique par la technique de l'homogénéisation périodique est réalisée. Le comportement adoucissant en compression de l'empilement hexagonal est ainsi étudié. Finalement, une extension des LHE identifiées en petites déformations est proposée pour rendre compte du comportement en compression du matériau observé en grandes déformations. / Cellular materials have excellent specific properties, which make them attractive for aeronautical applications. However, modelling macroscopic structures including a cellular material is either very costly in terms of computational time if the whole mesoscopic structure is considered or a Homogeneous Equivalent Medium (HEM) has to be used. This Ph.D. dissertation presents, the characterisation of a cellular material built from a stacking of tubes with a square or hexagonal based pattern and the identification of a phenomenological model of their inelastic mechanical behaviour. First, the material is characterised for multi-axial loadings through a periodic finite element model in small deformations for each tube stacking pattern. The macroscopic behaviour is then used to identify a compressible anisotropic Homogeneous Equivalent Law (HEL). Within the infinitesimal strain hypothesis, a comparison is carried out between reference full scale models and HEM based ones of sandwich structures with a cellular core, confirming the relevance of the proposed multi-scale method. Then, the mechanical behaviour of each tube stacking is characterised for large deformations in order to study the influence of the boundary size effects and the instabilities in the core on the macroscopic behaviour of sandwich structures. After a study on the representative volume element, the macroscopic inelastic behaviour is characterised through the periodic homogenisation technique, especially the softening observed in compression for the hexagonal pattern. Finally, an extension of the HELs identified in small deformations is proposed to model the behaviour observed in large deformations.

The increasing demand for more sustainable construction has led to the development of new structural systems that include wood as building material. Cross laminated timber (CLT) has been identified as a potential system to address this need and to provide alternative options in the range of low- to medium-rise construction. The appeal in using CLT as a shearwall is driven by the combination of the rigid panels and small dimension fasteners, which allows for significant energy dissipation in the structure. However, there is currently no reliable analytical model to accurately predict the behaviour of multi-segment CLT shearwalls. The current study aims to develop an analytical model capable of predicting the elastic and plastic phases associated with the behaviour of multi-panel CLT shearwalls. The model describes the wall behaviour as a function of the connectors’ properties in terms of stiffness, strength and ductility. This dependency means that the only input required in the model is the behavioural parameters of the connections. The proposed model contains six cases with a total of 36 different failure mechanisms. Two final wall behaviours were developed, and it was found that behaviour (i.e. single wall) could be achieved if the yielding in the hold-down occurred prior to yielding in the panel joints. Inversely, the other behaviour (i.e. coupled panels) was achieved if the yielding in the vertical joint occur prior to yielding in the hold-down. The analytical model was validated using a numerical model, and the results of the comparison showed very close match between the two models. The study proposed simplified design provisions with the aim to optimize the walls ductility (CP behaviour) or strength and stiffness (SW behaviour).

The continuum theory of large deformation elasto-plasticity is summarized as far as it is necessary for the numerical treatment with the Finite-Element-Method. Using the calculus of modern differential geometry and functional analysis, the fundamental equations are derived and the proof of most of them is shortly outlined. It was not our aim to give a contribution to the development of the theory, rather to show the theoretical background and the assumptions to be made in state of the art elasto-plasticity.

Yes / Three-dimensional finite element models were executed and validated to investigate the performance of buried flexible high-density Polyethylene (HDPE) pipes, in unreinforced and multi-geogrid-reinforced sand beds, while varying pipe burial depth, number of geogrid-layers, and magnitude of applied cyclic loading. Geogrid-layers were simulated considering their geometrical thickness and apertures, where an elasto-plastic constitutive model represented its behaviour. Soil-geogrid load transfer mechanisms due to interlocked soil in-between the apertures of the geogrid-layer were modelled. In unreinforced and reinforced cases, pipe burial depth increase contributed to decreasing deformations of the footing and pipe, and the crown pressure until reaching an optimum value of pipe burial depth. On the contrary, the geogrid-layers strain increased with increasing pipe burial depth. A flexible slab was formed due to the inclusion of two-geogrid-layers, leading to an increase in the strain in the lower geogrid-layer, despite its lower deformation. Inclusion of more than two geogrid-layers formed a heavily reinforced system of higher stiffness, and consequently, strain distribution in the geogrid-layers varied, where the upper layer experienced the maximum strain. In heavily reinforced systems, increasing the amplitude of cyclic loading resulted in a strain redistribution process in the reinforced zone, where the second layer experienced the maximum strain.

Als elastische Koppelglieder üben Elastomere im Fahrwerk maßgeblichen Einfluss auf die Elastokinematik der Radaufhängung und damit auf die Radstellgrößen aus. Bereits einfache zylindrische Probekörper zeigten in der Vergangenheit Veränderlichkeit der Federsteifigkeiten bei mehrachsiger Belastung auf. Daraus ließ sich ableiten, dass das Bauteilverhalten von zylindrischen Elastomerkörpern, bzw. Fahrwerklagern, schwer vorhersagbar ist und dieser Effekt durch die Verwendung komplexer Geometrien zusätzlich beeinflusst wird. Eigens im Rahmen dieser Arbeit entwickelte Prüfstände ermöglichten die Untersuchung von statischen, mehrachsigen Belastungen sowie zyklischen, einachsigen Belastungen zweier Fahrwerklager einer typischen Vorderradaufhängung, dem Mc-Pherson-Federbein. Für beide Lagertypen wurden derart signifikante Federsteifigkeitsänderungen unter mehrachsiger Belastung beobachtet, dass ein Einfluss auf die Elastokinematik sicher schien. Unter einachsiger, zyklischer Belastung bestätige sich, dass einfache rheologische Ersatzmodelle, wie der Ansatz nach Kelvin-Voigt für eine Modellierung des viskoelastischen Materialverhaltens weiterhin Gültigkeit besitzen. Ein in einem Mehrkörpersimulationsprogramm erstelltes Gesamtfahrzeugmodell zeigte zunächst für die Auslegung der Prüfstände relevante Beanspruchungen in den Fahrwerklagern auf und diente weiterhin als Grundlage für die Untersuchung des Einflusses von Wechselwirkungen auf die Radstellgrößen. Dazu behandelt die Arbeit die Modellierung eines neuen Fahrwerklagermodells innerhalb dieser MKS-Umgebung. Dieses Modell bietet dem Nutzer die Möglichkeit für eine Abbildung von Wechselwirkungen an zylindrischen, zyklisch beanspruchten Bauteilen. Ein spezielles Fahrmanöver zeigte den Einfluss der Wechselwirkungen auf die Radstellgrößen auf und zeigte, dass die Berücksichtigung von Wechselwirkungen für eine Fahrwerkauslegung relevant ist. Darüber hinaus wurde mit kommerziell verfügbaren Materialmodellen für die Beschreibung es Materialverhaltens von Elastomeren innerhalb der Finite-Elemente-Methode aufgezeigt, dass bei einachsiger Belastung die Federsteifigkeiten der Fahrwerklager auf Grundlage der in der Literatur üblichen Auslegungsgleichungen näherungsweise abgebildet werden können, jedoch für mehrachsige Spannungszustände keine hinreichende Aussage über das Bauteilverhalten getroffen werden kann. Hier wurde weiterer Forschung- bzw. Erweiterungsbedarf an den FE-Programmen aufgezeigt.

A very short and disagreeable audible and tactile response from a vehicle driveline may be excited when the throttle is abruptly applied or released, or when the clutch is rapidly engaged. The condition is most noticeable in low gear and in slow moving traffic, when other background engine and road noise levels are low. This phenomenon is known as clonk and is often associated with the first cycle of shuffle response, which is a low frequency longitudinal vehicle movement excited by throttle demand. It is often reported that clonk may coincide with each cycle of the shuffle response, and multiple clonks may then occur. The problem is aggravated by backlash and wear in the drivetrain, and it conveys a perception of low quality to the customer. Hitherto, reported investigations do not reveal or discuss the mechanism and causal factors of clonk in a quantitative manner, which would relate the engine impulsive torque to the elastic response of the driveline components, and in particular to the noise radiating surfaces. Crucially, neither have the issues of sensitivity, variability and non-linearity been addressed and published. It is also of fundamental importance that clonk is seen as a total system response to impulsive torque, in the presence of distributed lash at the vibro-elastic impact sites. In this thesis, the drivetrain is defined as the torque path from the engine flywheel to the road wheels. The drivetrain is a lightly damped and highly non-linear dynamic system. There are many impact and noise emitting locations in the driveline that contribute to clonk, when the system is subjected to shock torque loading. This thesis examines the clonk energy paths, from the initial impact to many driveline lash locations, and to the various noise radiating surfaces. Both experimental and theoretical methods are applied to this complex system. Structural and acoustic dynamics are considered, as well as the very important frequency couplings between elastic structures and acoustic volumes. Preliminary road tests had indicated that the clonk phenomenon was a, very short transient impact event between lubricated contacts and having a high frequency characteristic. This indicated that a multi-body dynamics simulation of the driveline, in conjunction with a high frequency elasto-acoustic coupling analysis, would be required. In addition, advanced methods of signal analysis would be required to handle the frequency content of the very short clonk time histories. These are the main novelties of this thesis. There were many successful outcomes from the investigation, including quantitative agreement between the numerical and experimental investigations. From the experimental work, it was established that vehicle clonk could be accurately reproduced on a driveline rig and also on a vehicle chassis dynamometer, under controlled test conditions. It then enabled Design of Experiments to be conducted and the principal causal factors to be identified. The experimental input and output data was also used to verify the mathematical simulation. The high frequency FE analysis of the structures and acoustic cavities were used to predict the dynamic modal response to a shock input. The excellent correlation between model and empirical data that was achieved, clearly established the clonk mechanism in mathematical physics terms. Localised impact of meshing gears under impulsive loads were found to be responsible for high frequency structural wave propagation, some of which coupled with the acoustics modes of cavities, when the speed of wave propagation reached supersonic levels. This finding, although previously surmised, has been shown in the thesis and constitutes a major contribution to knowledge.

Les paramètres de loi de comportement s'identifient habituellement à partir d'éprouvettes standardisées présentant des champs de déformations homogènes. L'essor actuel des méthodes inverses incite à l'utilisation d'essais plus hétérogènes. L'objectif de cette thèse est de développer une procédure d'identification inverse en utilisant une méthode de recalage de modèles éléments finis basée sur des expériences à hétérogénéités croissantes des champs de déformation. À cette fin, des essais plans avec différentes géométries d'éprouvettes, en titane commercialement pur, ont été effectués et un essai original hors plan fortement hétérogène a été mis au point. Dans ce dernier cas, un essai unique réalisé à l'aide d'une machine de traction uni-axiale permet d'obtenir des sollicitations d'expansion, mais aussi de traction et de cisaillement selon deux directions orthogonales. Des mesures de champs cinématiques planes et non planes (stéréo-corrélation d'images) sont utilisées afin d'évaluer les déformations jusqu'à striction. À partir de ces mesures en grandes déformations, on propose de mener une comparaison entre les informations issues de l'expérience et un modèle dupliquant les conditions expérimentales (conditions aux limites issues de la corrélation d'images). Cette comparaison conduit, via un processus d'optimisation, à l'actualisation itérative du jeu de paramètres de la loi de comportement utilisée dans le modèle éléments finis. Le nombre de paramètres ainsi identifiés varie selon le modèle de comportement : élastique anisotrope puis élasto-plastique anisotrope. Différentes validations ont mis en évidence l'intérêt de considérer des champs de déformation fortement hétérogènes. Dans ce cadre, des prédictions numériques d'opérations d'emboutissage, réalisées à l'aide des différents jeux de paramètres identifiés sont comparées à l'expérience. On montre que la prise en compte d'un modèle élastique anisotrope plutôt qu'isotrope fournit un état de contrainte plus réaliste en début de plasticité, améliorant considérablement l'identification du modèle plastique. Enfin, une approche couplée entre mesures de champs cinématiques et thermiques (thermographie infrarouge) a été développée. Les paramètres d'un modèle mécanique sont identifiés puis utilisés pour l'évaluation d'un modèle thermique calculant les sources de chaleur. Par cette méthode, plusieurs modèles d'évolution de la fraction d'énergie dissipée sous forme de chaleur ont été identifiés (coefficient de Taylor et Quinney).

Les Robots Parallèles à Câbles (RPCs) sont des robots parallèles dont les jambes se composent de câbles. Les applications industrielles potentielles des RPCs sont nombreuses telles que le grenaillage et la peinture de structures massives et de grandes dimensions.La première partie de ce manuscrit est dédié à la modélisation des RPCs. Deux modèles élasto-statiques ont été introduits dans ce manuscrit, pour décrire le petit déplacement de la plate-forme mobile en raison de la nature non-rigide des câbles. Le modèle élasto-statique basé sur des câbles pesants a été exprimé en faisant la différence entre la matrice de raideur active et la matrice de raideur passive du RPC.La deuxième partie de ce manuscrit traite de l’analyse d’espaces de travail de RPCs vis-à-vis de leurs performances statiques et dynamiques. Deux nouveaux espaces de travail ont été définis : (i) l'Espace des Vitesses Générables (EVG);(ii) l’Espace de Travail Dynamique Amélioré (ETDA). La troisième partie de ce manuscrit décrit une stratégie de conception générique de RPCs et des Robots Parallèles à Câbles Reconfigurables (RPCRs). Les reconfigurations sont limitées uniquement aux points de sortie des câbles. Dans ce manuscrit, les points de sortie des câbles peuvent être placés dans une large mais limité ensemble de positions. La stratégie proposée envisage la possibilité de déplacer les points de sortie des câbles du RPCR sur une grille prédéfinie d'emplacements.La quatrième partie de ce manuscrit présente un algorithme pour calculer une stratégie de reconfiguration optimale pour les RPCRs. Cette stratégie peut être utilisée lorsque l'environnement de travail de RPCRs est extrêmement encombré et qu’il n'est pas possible de prévoir le nombre de configurations nécessaires pour compléter la tâche.L'efficacité de l'algorithme a été analysée en étudiant les reconfigurations d’un robot parallèle à câbles planaire et d’un robot parallèle à câbles spatial en lien avec des applications industrielles. / Cable-Driven Parallel Robots (CDPRs) are parallel robots whose legs consist of cables. CDPRs may be used successfully in several industrial applications such as sandblasting and painting of large and heavy structures.The first part of this manuscript is dedicated to the modelling of CDPRs. Two elasto-static models have been introduced in this manuscript, in order to describe the small displacement of the moving platform due to the non-rigid nature of the cables. These models can be used for the modal analysis of the CDPRs, as well. The elasto-static model based on linear cables has been computed including the effect of the pulleys orienting the cables into the CDPR workspace.The second part of this manuscript deals with the investigation of the workspace of CDPRs, in terms of their moving platform static and dynamic equilibria, and in terms of their moving platform kinematic constraints. Two novel workspaces have been defined: (i) the Twist Feasible Workspace (TFW); (ii) the Improved Dynamic Feasible Workspace (IDFW). The third part of this manuscript describes a generic design strategy for CDPRs and a novel design strategy for Reconfigurable Cable-Driven Parallel Robots (RCDPRs). In this manuscript, reconfigurations are limited to the thedisplacement of the cable exit points, assuming the cables exit points can be installed on a large but finite set of locations.The fourth part of this manuscript introduces an algorithm to compute an optimal reconfiguration strategy for RCDPRs. This strategy can be used when the working environment of the RCDPR is extremely cluttered and when it is not possible to predict how many configurations are necessary to complete the task. The effectiveness of the algorithm hasbeen analysed by means of a planar and a spatial casestudies reproducing some industrial tasks.

Les fils composites nanostructurés et architecturés cuivre-niobium sont de candidats excellents pour la génération de champs magnétiques intenses (>90T); en effet, ces fils allient une limite élastique élevée et une excellente conductivité électrique. Les fils Cu-Nb multi-échelles sont fabriqués par étirage et empaquetage cumulatif (une technique de déformation plastique sévère), conduisant à une microstructure multi-échelle, architecturée et nanostructurée présentant une texture cristallographique de fibres forte et des formes de grains allongées le long de l'axe du fil. Cette thèse présente une étude compréhensive du comportement électrique et élasto-plastique de ce matériau composite, elle est divisée en trois parties: modélisation multi-échelle électrique, élastique et élasto-plastique. Afin d'étudier le lien entre le comportement effective et la microstructure du fil, plusieurs méthodes d'homogénéisation sont appliquées, qui peuvent être séparées en deux types principaux: la méthode en champs moyens et en champs complets. Comme les spécimens présentent plusieurs échelles caractéristiques, plusieurs étapes de transition d'échelle sont effectuées itérativement de l'échelle de grain à la macro-échelle. L'accord général parmi les réponses de modèle permet de suggérer la meilleure stratégie pour estimer de manière fiable le comportement électrique et élasto-plastique des fils Cu-Nb et économiser le temps de calcul. Enfin, les modèles électriques prouvent bien prédire les données expérimentales anisotopique. De plus, les modèles mécaniques sont aussi validés par les données expérimentales ex-situ et in-situ de diffraction des rayons X/neutrons avec un bon accord. / Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (>90T) as they combine both high strength and high electrical conductivity. Multi-scaled Cu-Nb wires are fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured and nanostructured microstructure exhibiting a strong fiber crystallographic texture and elongated grain shapes along the wire axis. This thesis presents a comprehensive study of the effective electrical and elasto-plastic behavior of this composite material. It is divided into three parts: electrical, elastic and elasto-plastic multiscale modeling. In order to investigate the link between the effective material behavior and the wire microstructure, several homogenization methods are applied which can be separated into two main types: mean-field and full-field theories. As the specimens exhibit many characteristic scales, several scale transition steps are carried out iteratively from the grain scale to the macro-scale. The general agreement among the model responses allows suggesting the best strategy to estimate reliably the effective electrical and elasto-plastic behavior of Cu-Nb wires and save computational time. The electrical models are demonstrated to predict accurately the anisotropic experimental data. Moreover, the mechanical models are also validated by the available ex-situ and in-situ X-ray/neutron diffraction experimental data with a good agreement.