Solid concrete Lego blocks can be used as temporary retaining wall systems or as wall separators between different materials such as sand, salt, compost, etc. The advantage of concrete blocks is that you can create temporary constructions. It is easy to move or expand the constructions when no casting is required between the blocks. The purpose of this study is to make models in the Finite Element (FE) software Abaqus/CAE that can be used for calculations of the capacity for interlocking blocks. FE method is an approximate method for solving differential equations. As the concrete blocks are stacked without casting, it is important to find out the construction’s load capacity when it is subjected to a horizontal load. Several types of structures have been modeled in the FE program Abaqus/CAE. These FE models were created with boundary conditions consisting of springs and a pinned connection that allows rotation.The evaluation has been focused on rotating the interlocking blocks. With the help of the FE models, reaction forces have been calculated. The FE results in term of reaction forces have been compared with hand calculations made ​​for the same models. Moreover, a wall and a wall with lateral supports have been simulated to determine the horizontal reaction force for the interlocking concrete blocks. / Massiva Lego betongblock kan ändvänds som tillfälliga stödmurar eller vägg avskiljare för olika material som salt, kompost, sand mm. Fördelen med betongblocken är att man kan skapa tillfälliga konstruktioner. Det är lätt att flytta eller bygga ut konstruktionen när ingen fog krävs mellan blocken. Syftet med denna studie är att skapa modeller i Finita Element (FE) programmet Abaqus/CAE som kan senare användas för beräkning av kapaciteten för sammankopplade block. FE Metoden är en approximativ metod för att lösa differential ekvationer. Eftersom betongblocken är staplade på varandra utan fog är det viktigt att ta reda på konstruktionens lastupptagnings förmåga när den är belastade med horisontalkrafter. Flera typer av konstruktioner har modellerats i FE programmet Abaqus/CAE. Dessa FE modeller har skapats med randvillkor som består av fjädrar och fasta lager som tillåter rotation. Utvärderingen har gjorts med fokus på vältningen i betongblocken. Med hjälp av dessa FE modeller har reaktionskraften tagits fram. FE resultaten i form av reaktionskrafter har sedan jämförts med handberäkningar gjorda för samma modeller. Vidare har en vägg och en vägg med sidostöd FE modellerats för att utvärdera horisontala deformationsegenskaper. / - / -

<p>Deep brain stimulation (DBS) electrodes are intended to stimulate specific areas of the brain to treat movement disorders including essential tremor, Parkinson's disease and dystonia. An important goal in the design of next generation DBS electrodes is to minimize the power needed to stimulate specific regions of the brain. A reduction in power consumption will prolong battery life and reduce the size of implanted pulse generator. Electrode geometry is one approach to increase the efficiency of neural stimulation and reduce the power required to produce the level of activation required for clinical efficacy. </p><p>We first characterized the impedance of the presently used clinical DBS electrodes <italic>in vitro</italic> and <italic>in vivo</italic>. Characterization of the electrode-tissue interface impedance is required to quantify the composition of charge transfer to the brain tissue. The composition of charge transfer was dependent on both the current density and the sinusoidal frequency. The assumption of the DBS electrode being ideally polarizable was not valid under clinical stimulating conditions. This implies that irreversible processes that can cause electrode or tissue damage might occur when high charge injection is required for DBS. </p><p>Current density distribution is an important factor in determining patterns of neural excitation, tissue damage and electrode corrosion. We developed a recursive simulation scheme to calculate the current density distribution that incorporates the nonlinear electrode-tissue interface into finite-element based models of electrodes. The current density distributions on the electrode surface were strongly dependent on the sinusoidal frequency. The primary current density distribution without including the electrode-tissue interface can be used to estimate neural excitation, tissue damage and electrode corrosion with rectangular stimulus pulses as most of the signal power is at frequencies where the secondary current density distribution matches closely the primary current density distribution.</p><p>We designed and analyzed novel electrode geometries to decrease stimulation thresholds, thus reducing power consumption of implanted stimulators. Our hypothesis was that high-perimeter electrode geometries that increase the variation of current density on the electrode surface will generate larger activating functions for surrounding neurons and thereby increase stimulation efficiency. We investigated three classes of electrodes: segmented cylindrical electrodes, serpentine-perimeter planar electrodes, and serpentine-perimeter cylindrical electrodes. An approach that combined finite element models of potentials and cable models of axonal excitation was used to quantify the stimulation efficiency of electrodes with various geometries. Increasing the electrode perimeter increased the electrode efficiency by decreasing stimulation threshold. Both segmentation and serpentine edges provided means to increase the efficiency of stimulation. Novel cylindrical electrodes that combined segmentation with serpentine edges decreased power consumption by ~20% for axons parallel to the electrode and by ~35% for axons perpendicular to the electrode. These electrode designs could potentially prolong the average battery life of deep brain stimulator by more than one year.</p> / Dissertation

Rupture of atherosclerotic plaque is one of the primary causes of death due to cardiovascular disease. The factors directing plaque progression to instability are poorly understood. It is well-known that arteries respond to changes in mechanical stress by remodeling, and that remodeling is mediated by the inflammatory response. Studies have shown that both mechanical stress and markers of inflammation are increased in the fibrous cap and shoulder regions of plaque, where rupture most often occurs. In this study we hypothesized that there are spatial relationships between the local mechanical environment and expression of markers of inflammation in atherosclerosis, and that these relationships are plaque-progression dependent. To test these hypotheses, we analyzed cross-sections at intervals along the length of human coronary atherosclerotic arteries. For each cross-section, a heterogeneous finite element model was developed to determine the spatial distribution of stress. In addition, novel techniques for quantifying inflammatory markers at high spatial resolution were used to determine the distributions of inflammatory markers. The distributions of stress and five markers of inflammation activated NF-kB, macrophages, MMP-1, nitrotyrosine, and microvessels - were then compared to determine whether spatial relationships exists. We demonstrated that the probability of activated NF-kB expression increases monotonically with increasing stress in all stages of plaque progression. This indicates that the relationship between mechanical stress and NF-kB activation is a player throughout the disease process. We found that the relationship between mechanical stress and macrophages is highly dependent on the state of plaque progression. In intermediate stages of progression macrophages increase with moderate stress but drop off again at very high stresses, while in the advanced stage macrophages continue to increase monotonically with stress. We found that MMP1 increases with stress in stages of progression where active remodeling is occurring, but decreases with stress in mature stable plaque. We found no relationship between mechanical stress and nitrotyrosine expression or microvessels. Taken together, these results support the role of mechanical stress in instigating and maintaining the inflammatory response, and help explain how mechanical input is able to direct the complex biological changes involved in remodeling.

This paper presents a method of parameter identification for a finite-element model of the human middle ear. The parameter values are estimated using a characterization of the difference in natural frequencies and mode shapes of the tympanic membrane between the model and the specimens. Experimental results were obtained from temporal bone specimens under sound excitation (300–3,000 Hz). The first 3 modes of the tympanic membrane could be observed with a laser scanning vibrometer and were used to estimate the stiffness parameters for the orthotropic finite-element model of the eardrum. A further point of discussion is the parameter sensitivity and its implication for the identification process. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Dans ce mémoire, une méthode subspace fitting (SF) destinée à l’identification des paramètres mécaniques et l’évaluation de l’état de santé de structures vibrantes, est présentée. La méthode SF s’attache à extraire, à partir des méthodes d’identification par sous-espaces (4SID), une matrice d’observabilité du système et de la corréler, au sens de la norme, à une matrice d’observabilité théorique. L’originalité de ce travail est de construire la matrice d’observabilité théorique sur la base d’un modèle éléments finis (EF) de la structure considérée. En ajustant les paramètres inconnus du modèle EF, les propriétés mécaniques de la structure vibrante sont identifiées. Les coûts de calcul d’une telle procédure sont réduits en considérant une méthode de réduction de modèle basée sur la position des excitations et des capteurs. La méthode est évaluée pour l’identification des fréquences propres d’une structure vibrante. Des applications numériques et expérimentales s’attachent à montrer la pertinence d’une telle approche. En particulier, il est mis en évidence que la méthode SF permet d’identifier précisément les fréquences propres d’une structure, pour des niveaux de bruit importants. / In this thesis, a subspace fitting (SF) method is presented for the identification of mechanical parameters and assessment of the health condition of vibrating structures. The SF method attempts to extract, from subspace identification methods (4SID), a system observability matrix of the system and correlate them with a theoretical observability matrix. The originality of this work is to obtain the theoretical observability matrix from a finite element model (EF) of the structure. By adjusting unknown parameters of the FE model, the mechanical properties of the vibrating structure are identified. Computational costs of such a procedure are reduced by considering a model reduction method based on the excitations and sensors location. The method is evaluated for the identification of natural frequencies of a vibrating structure. Numerical and experimental applications are assessed to show the relevance of such an approach. In particular, it is highlighted that the SF method can accurately identify the natural frequencies of a structure to high noise levels.

Cette thèse porte sur les problèmes d'optimisation robustes et fiables avec l'incertitude d'entrée.Tout d'abord, les différentes catégories de méthodes d'optimisation stochastique pour traiter l'incertitude sont présentées. Ces méthodes visent à trouver une solution plus robuste et fiable en minimisant la variance de l'objectif et/ou en réduisant la probabilité de violer les contraintes en différentes manières. Chaque catégorie a diverses approches et après la comparaison, les plus efficaces sont sélectionnées.Cependant, comme ces méthodes augmentent le nombre d'évaluations par rapport à l'optimisation déterministe et nécessitent l'information de gradient qui peut être bruyante fournie par des modèles lourds comme les modèles d'éléments finis, elles ne conviennent pas aux modèles qui prennent du temps. Des stratégies de méta-modèles basées sur le krigeage sont proposées dans ce manuscrit car elles pourraient utiliser la détermination d'une petite taille d’échantillons pour approcher des fonctions complexes et donner des dérivés précis. La fonction objectif initiale et les contraintes sont progressivement remplacées par des méta-modèles de krigeage utilisant le critère d’enrichissement pour ajouter des échantillons dans le processus d'optimisation. Différentes stratégies compris le choix du critère et le positionnement de l'enrichissement de l'échantillon pour chaque catégorie sont comparées et mettent en évidence les plus efficaces.Ensuite, les approches d'optimisation développées dans ce travail de recherche sont appliquées aux modèles analytiques et aux éléments finis d'un transformateur pour résoudre des problèmes d'optimisation électromagnétique. / This PhD thesis deals with the robust and reliability-based optimization problems under input uncertainty.First, the different categories of stochastic optimization methods to treat the uncertainty are presented. These methods aim to find a more robust and/or reliable solution by minimize the variance of objective and reducing the probability to violate the constraints in different ways. Each categories has various approaches and after comparison, the most effective ones are selected.However, as these methods increase the number of evaluation than deterministic optimization and need the gradient information which may be noisy provided by time-consuming models like finite element models, they are not suitable for the heavy models. So kriging-based meta-model strategies are proposed in this manuscript as it could use the determination of small size sample to approach complex functions and give accurate derivatives. The original objective function and constraints are progressively replaced by kriging meta-models using infill sampling criterion to add samples in the process of optimization. Different strategies including the choice of the criterion and the positioning of sample enrichment for each categories are compared and highlight the most effective ones.Then the optimization approaches developed within this research work are applied to the analytic and finite element models of a transformer for solving an electromagnetic optimization problems.

L’amélioration du caractère prédictif des simulations numériques requiert une meilleure maîtrise des modèles constitutifs. Des procédures d’identification exploitant des mesures de champs ont été développées afin de valider les modèles et d’identifier un jeu de paramètres constitutifs à partir d’un nombre réduit d’essais hétérogènes. Bien évidemment, les résultats de telles procédures dépendent grandement des incertitudes des mesures. Dans cette thèse, une stratégie d’identification de paramètres constitutifs à partir de mesures de champs par corrélation d’images numériques éléments finis (CIN-EF) multi-échelles est proposée et développée. Une variante régularisée du recalage par éléments finis (FEMU-R) est adaptée à cette approche multi-échelles. Elle exploite des champs de déplacements mesurés par CIN-EF d'une part à l’échelle de la structure (fournissant les conditions aux limites pour la simulation EF) et d’autre part à une échelle plus locale (fournissant des champs de déplacements mieux résolus pour la comparaison essais/calculs). Un algorithme de recalage d’images est développé pour faire le lien entre les échelles. D’abord validée à l’aide d’images de synthèse, la procédure est ensuite appliquée à un essai de traction sur plaque trouée réalisé sur un composite stratifié verre/époxy. On montre qu’une telle stratégie permet de diminuer nettement non seulement les incertitudes de mesure mais également les incertitudes d’identification. Finalement, la question d’un mouchetis adapté à cette approche multi-échelles est évoquée et des éléments de solutions sont proposés et testés. / Improving the prediction of numerical simulations requires a better control of constitutive models. Identification methods exploiting full-field measurements have been developed in order to validate models and to identify a set of constitutive parameters from a reduced number of heterogeneous tests. The results of those methods largely depends on measurement uncertainties. In this PhD thesis, a strategy is proposed and developed for the identification of constitutive parameters from full-field measurements obtained by multiscale finite element digital image correlation (FE-DIC). A Regularised Finite Element Model Updating method (FEMU-R) is adapted to this multiscale approach. It exploits displacement fields measured by FE-DIC at a structural scale (in order to obtain the boundary conditions for FE simulation)and at a local scale (giving a better resolution on the displacement field for the comparison between experiment and simulation). An image registration algorithm is developed to bridge these scales. First validated on synthetic images, the multiscale approach is then applied to an open-hole tensile test of a glass/epoxy composite laminate. It is shown that such a strategy allows to reduce not only the measurement uncertainties but also the identification uncertainties. Finally the question of a speckle pattern suitable for this approach is discussed and some first technical solutions are proposed and tested.

L' arthroplastie de la hanche par prothèse non cimentée est une solution couramment employée pour les patients rencontrant des problèmes du système locomoteur. Une telle solution présente toutefois un inconvénient majeur, souligné par tous les utilisateurs : le manque de stabilité primaire de la prothèse. Or, cette faiblesse peut provoquer des complications graves, voire l'échec de l'opération chirurgicale. Par conséquent, parvenir à une bonne fixation primaire est un point crucial de ce type d'opération chirurgicale pour assurer cliniquement une satisfaction à court et long terme.Dans le but de mieux appréhender cette problématique centrale, une piste préopératoire a été adoptée. Un modèle éléments finis permettant de décrire le comportement mécanique du système couplé « os-prothèse non cimentée : DePuy Corail® » a été développé et validé par des expérimentations in vitro. Puis, pour tenir compte de la forte variabilité des paramètres du modèle, inhérente à la nature même du problème, une modélisation stochastique de ces derniers a été introduite et une stratégie mécano-probabiliste proposée, destinée d'une part à quantifier en termes probabilistes l'effet sur la réponse des incertitudes affectant les paramètres du modèle, et d'autre part à évaluer la stabilité primaire du système os-prothèse en contexte fiabiliste. La mise en oeuvre pratique de cette approche a été réalisée à l'aide d'outils numériques basés sur la méthode de Monte-Carlo standard et une procédure de collocation stochastique.L'originalité du travail présenté réside avant tout dans la proposition d'une méthodologie probabiliste capable de prendre en compte les incertitudes dans la problématique de la stabilité primaire des prothèses de hanche non cimentées. Elle tient également dans la potentialité de cette méthodologie à être facilement transplantable en contexte industriel. / The hip arthroplasty with cementless hip prosthesis is a solution usually used for the patients suffering the problems of the musculoskeletal system. However, such a solution has a major disadvantage, pointed by all users : the lack of primary stability of the prosthesis. This weakness can cause serious complications or failure of the surgery. Therefore, to achieve a good primary fixation is a crucial point of this type of surgery to ensure a short and a long term clinical satisfaction. In order to better understand this central issue, a preoperative track is adopted. A finite element model to describe the mechanical behavior of the coupled system " femur-cementless prosthesis : DePuy Corail® "has been created and validated by the experiments in vitro. Then, in order to take into account the high variability of model parameters, inherent to the nature of the problem, the stochastic modeling of random input parameters has been introduced and a mechanical-probabilistic strategy has been proposed, on the one hand to quantify, in probabilistic terms, the effect, on the response, of the uncertainties affecting the input parameters of the model, and on the other hand to evaluate the primary stability of the bone-prosthesis system in reliability context. The practical implementation of this approach is realized by using the numerical tools based on the standard Monte Carlo method and the stochastic collocation procedure. The originality of the work presented is primarily in the proposition of a probabilistic methodology capable of taking into account the uncertainties in the problem of primary stability of cementless hip prostheses. It also lies in the potentiality of this methodology to be transplantable easily in industrial context.

Le stockage de grains est une problématique qui date du développement de l’agriculture afin de répondre au besoin de conservation des céréales. Afin de faciliter la vidange de silos, l’entreprise Vibrafloor propose une solution de vidange automatisée basée sur l’agitation du contenu par vibration d’un plancher flexible. L’objectif de cette thèse est de développer un modèle numérique robuste qui puisse prédire le comportement du système vibrant sous charge, au cours d’un cycle de vidange. Ces travaux peuvent être décomposés en trois parties principales : - Le développement d’un modèle numérique fiable d’un module vibrant ; - Le développement d’un modèle numérique du milieu granulaire ; - La mise en interaction de ces deux modèles. Enfin, l’exploitation de ces modèles numériques a permis de proposer des règles d’utilisation du système à l’industriel et de proposer les prémisses d’un outil d’étude du procédé de vidange dans sa globalité. / The grain storage is an issue that dates agricultural development to address the need for cereal preservation. In order to facilitate the emptying silos process, Vibrafloor provides an automated emptying solution based on the agitation of the contents by vibration of a flexible floor. The objective of this thesis is to develop a reliable numerical model that can predict the behavior of the vibrating system under load during a drain cycle. These works can be divided into three main parts: - The development of a reliable digital model of a vibrating module - The development of a numerical model of the granular media - The interaction of these two models. Finally, the exploitation of these numerical models helped provide system usage rules for industrial and the beginnings of a study tool for the entire automatic drain process.

abstract: Polymer matrix composites (PMCs) are attractive structural materials due to their high stiffness to low weight ratio. However, unidirectional PMCs have low shear strength and failure can occur along kink bands that develop on compression due to plastic microbuckling that carry strains large enough to induce nonlinear matrix deformation. Reviewing the literature, a large fraction of the existing work is for uniaxial compression, and the effects of stress gradients, such as those present during bending, have not been as well explored, and these effects are bound to make difference in terms of kink band nucleation and growth. Furthermore, reports on experimental measurements of strain fields leading to and developing inside these bands in the presence of stress gradients are also scarce and need to be addressed to gain a full understanding of their behavior when UDCs are used under bending and other spatially complex stress states. In a light to bridge the aforementioned gaps, the primary focus of this work is to understand mechanisms for kink band evolution under an influence of stress-gradients induced during bending. Digital image correlation (DIC) is used to measure strains inside and around the kink bands during 3-point bending of samples with 0°/90° stacking made of Ultra-High Molecular Weight Polyethylene Fibers. Measurements indicate bands nucleate at the compression side and propagate into the sample carrying a mixture of large shear and normal strains (~33%), while also decreasing its bending stiffness. Failure was produced by a combination of plastic microbuckling and axial splitting. The microstructure of the kink bands was studied and used in a microstructurally explicit finite element model (FEM) to analyze stresses and strains at ply level in the samples during kink band evolution, using cohesive zone elements to represent the interfaces between plies. Cohesive element properties were deduced by a combination of delamination, fracture and three-point bending tests used to calibrate the FEMs. Modeling results show that the band morphology is sensitive to the shear and opening properties of the interfaces between the plies. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2016