Dans un composite stratifié, les plis orientés à 0° par rapport à la direction du chargement pilotent souvent la rupture sous chargement de traction. Les fibres procurent l’essentiel de la rigidité et la résistance de ces plis. Dans ces travaux de thèse, le comportement en fatigue des plis à 0° est analysé dans des stratifiés unidirectionnels (UD) et multidirectionnels, au moyen d’essais de fatigue multi-instrumentés. Un protocole expérimental est mis en place pour éviter les ruptures prématurées typiques des essais sur UD. L’évolution en fatigue des ruptures de fibres est identifiée par leur émission acoustique. Les mécanismes de fatigue dominés par la rupture des fibres sont analysés par un modèle aux éléments finis développé à l’échelle des constituants. / Under quasi-static and fatigue tension loads, the failure of a carbon fibre reinforced polymer laminate (CFRP) is usually driven by 0° plies. Carbon fibres give most of the stiffness and strength of these plies. In this work, the fatigue behaviour of 0° plies inside unidirectional (UD) and multidirectional laminates is analysed via multi-instrumented tension-tension fatigue tests. A numerical and experimental study is addressed to perform fatigue tests without the typical premature failures of the UD laminates. The acoustic emissions technique is used to identify the evolution law of fibre breaks. A finite element model is developed at the microscale (fibres and matrix) to analyse the fibre-driven fatigue mechanisms.

The main challenge in the design of vibration energy harvesters is the optimization of energy outcome relative to the applied excitation to reach a higher efficiency in spite of the weakness of ambient energy sources. One promising principle of vibration converters is magnetoelectricity due to the outstanding properties of magnetostrictive and piezoelectric laminate composites, which provide interesting possibilities to harvest energy from low amplitude and low frequency vibration with relatively high energy outcome. For these devices, ensuring high deformations in the magnetostricive layers, improvement of the magnto-mechanical and the electro-mechanical couplings are highly required for the optimization of the energy outcome. This thesis primarily aims to develop a model based harvester design for magnetoelectric (ME) converters. Based on a comprehensive understanding of the complex energy flow in magnetoelectric transducers, several design parameters are investigated. For instance, magnetostriction in a Terfenol-D plate is investigated by means of atomic force microscopy under similar conditions as within magnetoelectric transducers. A novel measurement approach was successfully developed to detect the evolution of magnetic domains and measure deformations in a Terfenol-D plate in response to externally non-uniform applied magnetic fields. Furthermore, a finite element model is developed to predict the induced voltage in the ME transducer as a response to the magnet’s displacement, corrected based on atomic force microscopy measurements, and used for the design of the harvester. The presented three- dimensional model takes into consideration the nonlinear behaviour of the magnetostrictive and piezoelectric materials. Additionally, three novel converters having different magnetic circuits are designed and analysed analytically based on Lindstedt-Poincaré method. The effects of the structure parameters, such as the nonlinear magnetic forces, the magnetic field distribution and the resonance frequency are discussed, and the electric output performances of the three designed converters are evaluated. In order to improve both mechanical and electrical coupling between the piezoelectric and the magnetostrictive layers, a bonding technique at room temperature is proposed which uses conductive polymer nanocomposites. Two magnetoelectric transducers are fabricated based on this technique having 1 wt.% and 2 wt.% concentration of multiwalled carbon nanotubes in epoxy resin. Another magnetoelectric transducer is fabricated by a classical technique for comparison purposes. In order to validate the design, a series of demonstrators are designed and fabricated according to the simulation and optimization results. The proposed design is composed by a cantilever beam, a magnetic circuit with several magnet arrangements and a magnetoelectric transducer, which is formed by a piezoelectric PMNT plate bonded to two magnetostrictive Terfenol-D layers. In this design, external vibrations are converted to magnetic field changes acting on the magnetostrictive layers leading to deformations, which are transmitted directly to the piezoelectric layer. The converters are tested under harmonic excitations and real vibration profiles reproduced by an artificial vibration source. Different parameters were investigated experimentally including the magnetic forces between the transducer and the magnetic circuit and the used bonding technique. Tuning the resonance frequency of the ME converter is also addressed using a simple screw/nut system, which allows to control the relative position and therefore the magnetic forces between the magnetic circuit and the transducer. The magnetoelectric transducer bonded with 2 wt.% concentration of multiwalled carbon nanotubes shows better output performances than the two other ME transducers under similar excitations. A maximum power output of 2.42 mW is reached under 1 mm applied vibration at 40 Hz. This performance presents an improvement of minimum 20 % of the reached energy outcome by other magnetoelectric vibration converters using single ME transducer at comparable applied excitations. / Die größte Herausforderung bei der Konstruktion von Vibrations-Energiewandlern ist die Optimierung der gewonnenen Energie im Verhältnis zur angewandten Anregung, um trotz schwacher Umgebungsenergiequellen einen hohen Wirkungsgrad zu erreichen. Ein vielversprechendes Prinzip von Vibrationswandlern ist die Magnetoelektrizität aufgrund der hervorragenden Eigenschaften von magnetostriktiven und piezoelektrischen Verbundwerkstoffen, die interessante Möglichkeiten bieten, Energie aus niederfrequenten Schwingungen mit kleinen Amplituden zu gewinnen. Bei diesen Wandlern ist die Sicherstellung hoher Verformungen in den magnetostriktiven Schichten, die Verbesserung der magnetisch-mechanischen und der elektromechanischen Kopplungen für die Optimierung des Energieertrages sehr wichtig. Diese Arbeit zielt in erster Linie auf die Entwicklung eines modellbasierten Entwurfs für magnetoelektrische (ME) Wandler ab. Basierend auf einem umfassenden Verständnis des komplexen Energieflusses in magnetoelektrischen Wandlern werden mehrere Entwurfsparameter untersucht. So wird beispielsweise die Magnetostriktion in einer Terfenol-D-Platte mittels Rasterkraftmikroskopie unter ähnlichen Bedingungen untersucht wie in magnetoelektrischen Wandlern. Dabei wurde eine neuartige Messmethode erfolgreich entwickelt, um die Entwicklung von magnetischen Domänen zu erfassen und die Deformation in einer Terfenol-D-Platte als Reaktion auf extern ungleichmäßig angelegte Magnetfelder zu messen. Darüber hinaus wird ein Finite-Elemente-Modell entwickelt, um die induzierte Spannung im ME-Wandler als Reaktion auf die Verschiebung des Magneten vorherzusagen, welches auf der Grundlage von Atomkraftmikroskopie Messungen korrigiert und für den Entwurf des Energiewandlers verwendet wird. Das vorgestellte dreidimensionale Modell berücksichtigt das nichtlineare Verhalten der magnetostriktiven und piezoelektrischen Materialien. Zusätzlich werden drei neuartige Wandler mit unterschiedlichen Magnetkreisen nach dem Lindstedt-Poincaré Verfahren konzipiert und analytisch analysiert. Die Auswirkungen der Strukturparameter, wie die nichtlinearen Magnetkräfte, die Magnetfeldverteilung und die Resonanzfrequenz, werden diskutiert und die elektrischen Ausgangsleistungen der drei ausgelegten Wandler ausgewertet. Um die mechanische und elektrische Kopplung zwischen der piezoelektrischen und der magnetostriktiven Schicht zu verbessern, wird eine bei Raumtemperatur prozessierbare Verbindungstechnik vorgeschlagen, bei der leitfähige Nanokomposite verwendet werden. Zwei magnetoelektrische Wandler werden basierend auf dieser Technik mit einer Konzentration von 1 wt.% und 2 wt.% an mehrwandigen Kohlenstoff-Nanoröhren in Epoxidharz hergestellt. Ein weiterer magnetoelektrischer Wandler wurde zu Vergleichszwecken mit einer klassischen Technik hergestellt. Für die Validierung des Entwurfes wird eine Reihe von Demonstratoren entsprechend den Simulations- und Optimierungsergebnissen konstruiert und gefertigt. Der vorgeschlagene Entwurf besteht aus einem Trägerbalken, einem Magnetkreis mit mehreren Magnetanordnungen und einem magnetoelektrischen Wandler, der aus einer piezoelektrischen PMNT-Platte besteht, die mit zwei magnetostriktiven Terfenol-D-Schichten verbunden ist. Bei dieser Konstruktion werden externe Schwingungen in Magnetfeldänderungen umgewandelt, die auf die magnetostriktiven Schichten wirken und zu Verformungen führen, die direkt auf die piezoelektrische Schicht übertragen werden. Die Wandler werden unter harmonischen Anregungen und mit realen Schwingungsprofilen getestet, die von einer künstlichen Schwingungsquelle reproduziert werden. Verschiedene Parameter wurden experimentell untersucht, darunter die magnetischen Kräfte zwischen dem Wandler und dem Magnetkreis sowie die verwendete Verbindungstechnik. Die Abstimmung der Resonanzfrequenz des ME-Wandlers erfolgt ebenfalls über ein einfaches Schrauben-Mutter-System, das es ermöglicht, die relative Position und damit die magnetischen Kräfte zwischen Magnetkreis und Wandler zu steuern. Der magnetoelektrische Wandler, der mit einer Konzentration von 2 wt.% mehrwandiger Kohlenstoff-Nanoröhrchen verbunden ist, zeigt bessere Ausgangsleistungen als die beiden anderen ME-Wandler bei ähnlichen Anregungen. Eine maximale Ausgangsleistung von 2,42 mW wird bei 1 mm angelegter Vibration bei 40 Hz erreicht. Diese Leistung stellt eine Verbesserung von mindestens 20 % im Vergleich zu anderen magnetoelektrischen Schwingungsumrichtern dar, welche mit einem einzigen ME-Wandler bei vergleichbaren Anregungen getestet werden.

The topic of this thesis is the numerical simulation of transversely isotropic 3D structures and laminates by means of the adaptive finite element method. To achieve this goal, the theoretical background of elastic deformation problems, transverse isotropy, plate theory, and the classical laminate theory is recapitulated. The classical laminate theory implies a combination of the membrane problem and the plate problem with additional coupling terms. The focus of this work is the adjustment of two integral parts of the adaptive FE algorithm according to the classical laminate theory. One of these parts is the solution of the FE system; a good preconditioner is needed in order to use the conjugate gradient method efficiently. It is shown via a spectral equivalence bound that the combination of existing preconditioners for the membrane and plate problems poses a capable preconditioner for the combined laminate problem. The other part is the error estimation process; the error estimator determines where the current mesh has to be refined for the next step. Existing results on residual error estimators for the elasticity problem, the biharmonic problem, and the plate problem are combined and extended to obtain a posteriori local residual error indicators for the classical laminate theory problem. The effectiveness of both results is demonstrated by numerical examples.:1 Introduction 1.1 Motivation 1.2 Organisation of this work 1.3 Notation and basic definitions 2 Basic theory of 3D simulation 2.1 Differential geometry 2.1.1 Initial and deformed domain 2.1.2 Strain tensor 2.2 Energy functional 2.2.1 Linearly elastic material law 2.2.2 Equilibrium of forces 2.2.3 Large deformations 2.2.4 Small deformations 2.3 Voigt notation and elasticity matrix 3 Transversely isotropic material law 3.1 Elasticity tensor 3.2 Conversion of the material constants 3.3 Elasticity matrix 3.4 Eigenvalues 3.5 State of plane strain 3.6 State of plane stress 4 Plate theory and classical laminate theory 4.1 The Kirchhoff–Love hypothesis 4.2 Constitutive law and bilinear form of the laminated plate 4.3 Definition of resultants 4.4 Boundary conditions 4.5 From the equilibrium conditions to the weak formulation 4.5.1 Membrane equilibrium 4.5.2 Plate equilibrium 4.5.3 Combined weak formulation 4.5.4 The CLT problem in Voigt notation 5 Discretisation 5.1 Short introduction to FEM 5.2 Adaptive FEM 5.3 Finite elements for 3D elasticity problems 5.4 Finite elements for plates 5.4 Finite elements for plates 5.4.1 BFS rectangles 5.4.2 rHCT triangles 5.5 CLT elements 5.5.1 Rectangles 5.5.2 Triangles 6 Solver and preconditioner 6.1 The preconditioned conjugate gradient method 6.2 Hierarchical basis and BPX preconditioners 6.3 Preconditioning of CLT problems 6.3.1 General laminates 6.3.2 Some special cases and examples 7 A posteriori residual error estimation 7.1 Residual error estimator for 3D elements 7.2 Residual error estimator for plate and CLT elements 7.2.1 Auxiliary definitions and assumptions on the mesh 7.2.2 Interpolation operators 7.2.3 Important inequalities 7.2.4 Cut-off functions 7.2.5 Definition of the error 7.2.6 Reliability inequality 7.2.7 Efficiency inequality 8 Some details of the implementation 8.1 The adaptive FE package SPC-PM 8.2 Remarks on some added features 8.2.1 Capability of the current code 8.2.2 Cuntze’s failure mode concept 8.3 Coordinate transformation of higher-order derivatives 8.3.1 Mapping of coordinates 8.3.2 Transformation of derivatives of up to the third-order 8.3.3 Recursive construction of transformation matrices 8.3.4 Simplification for axis-parallel rectangles 9 Numerical examples 9.1 A three-dimensional example from eniPROD 9.2 Example problems for laminates 9.2.1 Rectangular plate under in-plane load 9.2.2 Rectangular plate under vertical load 9.2.3 L-shaped plate with inhomogeneous natural boundary conditions 10 Conclusion and outlook Bibliography Acknowledgements List of main symbols Theses

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The aim of this work is to explore the joining of inspiration, such as different garments and materials, in relation to commonly used methods in the fashion industry when it comes to joining of different trends and references such as clashing and collaging. The work proposes a new method and framework for join- ing inspiration which generates different results depending on what kind of inspiration that is put in to it. A garment can roughly be broken down to a silhouette and shape, materials and details. The material put in to the method and framework is based on information from trend seminars for SS16, because that is how many of today’s trend-oriented fashion brands get there inspiration. Trendy garment silhouettes are mixed through processes of computational morphing in Adobe Flash by a generation of spin in the mixing process were shape hints are used in a new manner. The new generated silhouettes are further developed and materialized through procedures of interpretation and figuration. Different trendy materials are melded in a direct and concrete way through mixed media techniques such as laminating, fusing and vacuum-techniques. The final steps of the method is a garment shape and material synthesis with starting point in the generated shape with the final material. The projects intention is to let the physical experimentation, interpretation and figuration play a central role in the research process for new types of methods, garments, materials and expressive pos- sibilities.

Ce travail de thèse qui a pour objet la génération et l'étude des couches absorbantes dans les problèmes impliquant la dynamique des sols, est divisé en trois parties essentielles. La première consiste à proposer une méthode de dimensionnement des couches absorbantes par l'amortissement de Rayleigh afin de simuler des problèmes de propagation d'ondes dans les milieux infinis. Cette méthode repose sur une analyse mathématique du problème de propagation d'ondes dans un milieu caractérisé par la matrice de Rayleigh, qui nous permet, d'une part, d'établir des conditions de minimisation des réflexions parasites aux interfaces, et d'autre part, de proposer une simple relation de dimensionnement du domaine absorbant basée sur la notion de décrément logarithmique. On se propose dans la deuxième partie d'appliquer une stratégie de couplage des schémas temporels pour des problèmes de propagation d'ondes dans les milieux infinis 1D et 2D. L'approche proposée est d'intégrer le domaine d'étude par un schéma explicite et le domaine absorbant par un schéma implicite, et d'évaluer le potentiel de cette méthode en faisant varier les rapports de pas de temps entre les sous domaines. Une attention particulière est accordée au cas 1D pour lequel l'effet de la finesse du maillage définie par le nombre d'éléments finis par longueur d'onde est également analysé. Par ailleurs, l'évolution du temps de calcul en fonction du rapport entre les pas de temps est étudiée afin d'estimer les gains réalisés par rapport à un calcul de référence où le problème global est intégré uniquement avec un schéma explicite. La dernière partie est dédiée à l'étude des couches amortissantes de type PML ("Perfectly Matched Layer") dans le cadre des couplages hybrides multi-pas de temps. Cette partie est introduite par une étude de stabilité des schémas temporels dans le cas d'une PML en 1D. La couche absorbante PML est intégrée selon un schéma implicite en adoptant des pas de temps plus importants que le domaine d'intérêt intégré selon un schéma explicite. Bien que cette méthodologie de couplage s'avère très efficace pour la reproduction des milieux infinis, les études paramétriques montrent une sensibilité à la taille du pas de temps plus forte que celle exhibée par les couches amortissantes de Rayleigh. / This thesis which deals with the study of absorbing layers for soil dynamics problems, is divided into three essential parts. The first part aims to propose a design method of absorbing layers by the Rayleigh damping to simulate wave propagation problems in infinite media. This method is based on a mathematical analysis of the wave propagation problem in a media characterized by a Rayleigh damping matrix, which allows us, firstly, to establish conditions for minimizing spurious waves at the interfaces, and another hand, to provide a simple design relationship for the absorbing domain based on the notion of the logarithmic decrement. The second part aims to apply the multi-time step strategy for wave propagation problems in 1D and 2D infinite media. The proposed approach is to integrate the physical domain by an explicit scheme and the absorbing domain by an implicit scheme and to evaluate the potential of this method by varying the time step ratio between subdomains. Special attention is given to the 1D case for which the effect of the mesh fineness, defined by the number of finite elements per wavelength, is also analyzed. Furthermore, the evolution of computing time depending on the time ratio is studied in order to estimate the gains made with respect to a reference computation achieved by a full explicit integration. The last part is dedicated to the study of the Perfectly Matched Layer (PML) as part of hybrid couplings multi-time step. This section is introduced by a stability study of temporal scheme for 1D cases. The absorbing layer PML is integrated by an implicit scheme with a time step larger than that of the domain of interest. Although this coupling methodology is very effective for the reproduction of infinite media, parametric studies show a sensitivity to the time ratio greater than that exhibited by the Rayleigh damping layers.

Natural fiber-reinforced composites are now finding extensive uses in various fields from household articles to automobiles. These composites can score high compared to common synthetic fiber-based composites, notably glass fiber-reinforced composites, in areas such as occupational safety and health, and impact on environment. The current research work is motivated by the need for exploring jute fibers as replacement for glass fibers for various engineering design applications including more demanding impact protection applications as in automotive body structures. In the current work, detailed mechanical characterization of jute-polyester (JP) composite laminates till failure has been carried out for tensile, compressive and flexural loads by varying volume fraction of jute fibers. The effect of fiber volume fraction on mechanical properties is shown. Because of the potency of closed thin-walled components as structural energy-absorbers, a comprehensive experimental study has been performed, for the first time, comparing the behaviors of various geometric sections of JP and glass-polyester (GP) composite tubes under axial quasi-static and low velocity impact loading. Additionally, for jute-reinforced plastic panels to be feasible solutions for applications such as automotive interior trim panels, laminates made of such materials should have adequate perforation resistance. Thus, a detailed comparative study has been carried out for assessing the performance of JP laminates vis-a-vis GP plates under low velocity impact perforation conditions. As high-end product design is heavily driven by CAE (Computer-Aided Engineering), the current research work has also focused on the challenging task of developing reliable modeling procedures for explicit finite element analysis using LS-DYNA for predicting load-displacement responses and failures of JP composites under quasi-static and impact loading conditions. In order to extend the applications of JP composites to structurally demanding applications, hybrid laminates made of jute-steel composites and jute with nanoclay-reinforced polyester have been investigated and the considerable enhancement of mechanical properties due to hybridization is shown. Furthermore, a comprehensive study has been conducted on the behavior of JP laminates for varying degrees of moisture content until saturation, and the efficacy of hybrid laminates in this context has been shown.

Topic of this Master's Thesis is a design and a statical evalution of a load bearing structure of an observation tower in Beskydy mountains. Ground plan of this structure is in a shape of a nonagon with a non-roofed interior space. Height of the observation tower is 38,5 m, the shape of a ground plan doesn't change with a radius of a circumscribed circle of 12 m. The structure is designed from glued laminated timber, solid wood and steel. Columns bear horizontal beams and their stiffness is ensured by horizontal and inclined reinforcing beams. Main load bearing columns, upper and lower beams are designed from glued laminated timber GL24h. Upper beams and beams of a gallery are designed from glued laminated timber GL36h. Horizontal stiffener is designed from solid wood C24. Central column, inclined beams, stairway, water slide cantilevers, rod and central rod are designed from steel of a strength class S235. Cantilever for gallery is designed from steel of a strength class S355. Connections are designed from steel elements. Statical evaluation, technical report and construction drawing are included