Academic literature on the topic '2D and 3D fabric structures'

Constituant le revêtement de chaussées et caractérisés par un pourcentage volumique des vides important, les enrobés drainants apportent une réduction de bruit de 3 à 6 Db par rapport à un enrobé classique. Le travail exposé dans ce mémoire avait pour objectif l'étude de la corrélation de leurs propriétés acoustiques avec la forme de leurs vides. Le premier chapitre décrit le contexte des travaux. Le second chapitre présente la méthode de segmentation utilisée au préalable à l'analyse d'image permettant d'isoler la classe de vides, principal sujet de l'étude. Le troisième chapitre est consacré à l'estimation de la porosité et de la surface spécifique du matériau. Le quatrième chapitre porte sur la caractérisation de la forme des vides à l'aide de la squelettisation. Le cinquième chapitre montre une utilisation des méthodes de granulométrie pour caractériser la distribution des formes des vides. Le sixième chapitre est relatif à la détermination de paramètres caractérisant la propagation 3D des ondes sonores.

This thesis explores a novel methodology to fabricate three dimensional (3D) metal-dielectric structures, and two dimensional (2D) graphite layers for emerging metamaterials and graphene applications. The investigations we report here go beyond the limitations of conventional fabrication techniques that require multiple post-processing steps and/or are restricted to fabrication in two dimensions. Our method combines photoreduction mechanism with an ultrafast laser direct writing process in innovative ways. This study aims to open the doors to new ways of manufacturing nanoelectronic and nanophotonic devices. With an introductory analysis on how the various laser and chemical components affect the fabrication mechanism, this dissertation is divided into three sections.<br>Engineering and Applied Sciences

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 116-121).<br>The techniques used in the fabrication of micro-electro-mechanical systems (MEMS) were adopted from the integrated circuits (IC) industry and are mostly limited to patterning thin films on a flat substrate. As a consequence, micro-machined devices mostly comprise sets of flat two-dimensional (2D) membranes with etched patterns and undercuts that enable them to serve their intended functions. However, many mechanical, optical and biological applications, such as corner-cube retro reflectors, micro-scale magnetometers, 3D microfluidic systems and 3D photonic crystals, require three-dimensional (3D) geometries for their functionality. In addition, 3D circuits have also emerged as a way of improving connectivity and reducing power dissipation in electronic chips. However, the creation of fully 3D structures via conventional MEMS fabrication techniques typically requires processes that have low throughput, limited control over the final geometry, and higher costs. A promising alternative to 3D microfabrication that addresses these challenges while requiring minimal investment in a new infrastructure is to use the existing technologies to pattern in 2D, and then assemble the patterned segments into 3D structures. Demonstrated methods to achieve that objective have been limited in scope, requiring manual assembly or with limited applicability to specific architectures. This thesis presents a coherent modular system for folding, aligning and latching 2D-patterned precursors into prescribed 3D structures. The system presented here comprises flexure hinges to enable relative motion among the 2D precursors, a cascaded alignment system to provide progressively better alignment among precursors as they approach their final positions, and systems of reversible latches to retain the assembly in its final configuration while, optionally, permitting disassembly and reassembly of the structure. In particular, two types of systems are considered. First, the design, fabrication and testing of polymer structures with metal hinges, cascaded alignment features and integrated latching mechanisms are presented for perpendicular assembly of structures. Second, an alternative latching technique using controlled melting of photoresist polymer adhesive pads is analyzed and tested for the parallel assembly of structures. The structures discussed in this thesis consist of SU-8 polymer segments patterned on silicon wafers and linked with an underlying thin gold pattern that defines the hinges. The elasto-plastic bending of the hinges is analyzed and simulated to predict the trajectory and angular position of the membranes during folding. The design of cascaded alignment features, consisting of triangular protrusions and corresponding rhombic holes, is discussed. A kinematic model of the alignment mechanism is presented to demonstrate the effectiveness of the cascading aspect of the design to achieve a large range of angular correction and high alignment accuracy at the same time. The design of micro snap-fit latches that work in conjunction with the alignment system is also presented, and quasi-static simulations of the elastic bending of latches is used to evaluate their strength. Experimental measurements were conducted to characterize the behavior of the gold hinges during bending, demonstrating good agreement with models. The integrated folding-alignment-latching system was demonstrated by assembling corner-cube structures. The alignment process was found to be accurate to within 1 from measurements of the final assembled position of the corner cube structure. The system was also shown to support fabricating reconfigurable devices by demonstrating the ability to unlatch and re-latch segments. The latching and unlatching forces were measured to be 9.7 [mu]N and 12.3 [mu]N respectively.<br>by Nader S. Shaar.<br>Ph. D.

Le contrôle des erreurs dues à une discrétisation e. F. Et le choix d'un maillage sont deux questions très importantes pour les calculs de structures, spécialement pour celles tridimensionnelles pour lesquelles les calculs demeurent très coûteux. Ce problème est traité ici pour des structures élastiques incompressibles ou quasi incompressibles, à la fois en 2D et en 3D. La démarche utilisée est une extension d'une méthode basée sur le concept d'erreur en relation de comportement et sur des techniques explicites de construction d'un couple déplacement-contrainte vérifiant rigoureusement les contraintes cinématiques et les équations d'équilibre. Par rapport aux études précédentes, deux nouvelles difficultés ont été résolues: 1) l'application de la méthode à une première formulation mixte, celle d'Herrman formulation adaptée aux matériaux incompressibles. Il est à noter que dans le cas incompressible, la solution adoptée conduit à construire de façon locale et à partir de la solution E. F. , un champ de déplacement rigoureusement admissible; 2) l'extension des techniques de construction de champs admissibles aux éléments 3D les plus courants. Un post-processeur de calcul d'erreur a été développé au cours de cette étude et différents résultats 2D et 3D sont présentés dans ce mémoire

The aerospace structure design is one of the most challenging field in the mechanical engineering. The advanced structural configurations, introduced to satisfy the weight and strength requirements, require advanced analysis techniques able to predict complex physical phenomena. Finite Element Method, FEM, is one of the most used approach to perform analyses of complex structures. The use of FEM method allows the classical structural models to be used to investigate complex structures where a close form solution is not available. The FEM formulation can be easily implemented in automatic calculation routines therefore this approach can take advantage of the improvements of computers. In the last fifty years many commercial codes, base on FEM, has been developed and commercialized, as examples it is possible to refer to Nastran R by MSC or Abaqus R by Dassault Systémes. All the commercial codes are based on classical structural models. The beam model are based on Euler-Bernoulli or Timoshenko theories while two-dimensional models deal with Kirchhoff or Mindlin theories. The limitations introduced by the kinematic assumptions of such theories make the FEM elements based oh these models inef- fective in the analysis of advanced structures. The physical phenomena introduced by composite and smart materials, multi-field application and unconventional loads configurations can not be investigated using the classical FEM models, where the only solution improvement can be reached by refining the mesh and increasing the number of degrees of freedom. This scenario makes the development of advanced structural models very attractive in the structural engineering. With the development of new materials and structural solutions, a number of new structural models have been introduced in order to perform an accurate design of advanced structures. Classical structural model have been im- proved introducing more refined kinematics formulation. One- and two- dimensional models are widely used in aerospace structure design, the limitations introduced by the classical models have been overcame by introducing refined kinematic formulations able to deal with the complexities of the problems. On the other hand, while in the classical models each point is characterized by 3 translations and 3 rotations, the use of advanced models with complex kinematic introduces a number of complication in the analysis of complex geometries, in fact is much more difficult to combine models with different kinematics. The aim of this thesis is to develop new approaches that allow different kinematic models to be used in the same structural analysis. The advanced models used in the present thesis have been derived using the Carrera Unified Formulations, CUF. The CUF allows any structural model do be derived by means of a general formulation independent from the kinematics assumed by the theory. One-, two- and three- dimensional models are derived using the same approach. These models are therefore combined together using different techniques in order to perform structural analysis of complex structures. The results show the capabilities of the present approach to deal with the analysis of typical complex aerospace structure. The performances of variable kinematics models have been investigated and many assessment have been proposed. This walled structure, reinforced structure and composite and sandwich material have been con- sidered. The advanced models introduced in this thesis have been used to perform static, dynamic and aeroelastic analysis in order to highlight the capabilities of the approach in different field. The results show that the present models are able to provide accurate results with a strong reduction in the computational cost with respect classical approaches.

The need for innovative lightweight materials are rapidly increased in the recent years, owing to their cost-effective, high-strength, environmentally-sound use of materials and process technologies, in addition to that they reduce the weight of a product. The characteristics of 3D-spacer fabrics as one of the most important lightweight materials in future are multifaceted not only owing to its extremely light materials, but also because of exceptionally high stiffness to weight ratio compared to other constructions. It is also one possible method for improving the properties of fabric-reinforced composites. It can enhance the through-the-thickness properties, such as shear strength, dimensional stability, damage, tolerance, and fracture toughness that are critical for many structural applications. Spacer fabric has been employed in high-technology applications because of its critical mechanical properties related to high tensile strength, tear strength and stiffness. Furthermore, its multidirectional structures allow with more reinforcement along the thickness direction leading to an increase in stiffness and strength properties. The fundamental aim of this thesis exists in the development of a new kind of woven spacer fabrics for the light weight composites materials, in an effort to weave spacer fabrics that can not be realized with the old technology which are mentioned above. Therefore, the work in brief focuses on two main goals: 1. Development of a new kind of spacer fabrics for composites in the lightweight constructions. 2. Development of special devices of a narrow weaving machine for standing the process of the new kind of spacer fabrics production. The slippage strength test had to be carried out for the floated warp yarns through the ground fabrics by using different elements of woven fabric structures variables represented in different fabric constructions, different weft densities and different repeats of constructions by using different materials. The importance of this test related to the backward-movement of the floated warp yarns which is the crucial stage in the weaving process of spacer fabrics during the backward-movement. The results of this test determine the required forces for the backward-movement, on the other side it is the best method to observe the behavior of structure elements during the backward movement. The results of the slippage strength had been statistically analyzed, and the weaving process for the spacer fabrics had been achieved. It was concluded that the best properties for the woven spacer fabrics and the optimum case for the weaving process on the test weaving machine had been achieved when the following items are realized: Development of the narrow weaving machine is closed in assisting operations, let-off and take-up and enhancement for take-up processes. Extra let-off and take-up devices must be constructed at the weaving machine. Extra let-off device has to be used for controlling the floated warp yarns of ground fabrics. On the other side, extra take-up and the developed take-up devices have to be used for controlling the woven spacer fabrics. The experimental results give fundamental knowledges for the next steps in research and development of woven spacer fabrics made of high-performance yarns on the wide weaving machine<br>Die Ziele der Arbeit bestanden in der Entwicklung der Geometrie der Spacer Fabrics und der notwendigen Falteneinrichtung an der Bandwebmaschine. Spacer Fabrics werden ausschließlich aus zwei Deckflächen, die durch eingewebte Stege verbunden sind, gefertigt. Zur Entwicklung der Spacer Fabrics muss eine Doppelnadel-Bandwebmaschine mit zwei Webfächern eingesetzt werden. Für die Faltenwebeinrichtung werden der entwickelte Extra-Kettablass und der Extra-Abzug benötigt. Der Antrieb und die Steuerung des Extra-Abzuges erfolgen durch einen Synchronantrieb und der Antrieb und die Steuerung des Extra-Ablasses durch Pneumatik.Eine frei programmierbare Steuerung der Faltenwebeinrichtung ermöglicht eine sichere und optimierte Synchronisation zwischen Webprozess und Faltenbildung. Im Ergebnis einer systematischen Strukturentwicklung von Spacer Fabrics und der Simulation ihrer günstigen Herstellung mittles eines speziell entwickelten Slippage Strength Tests werden die optimalen Strukturen ermittelt. Die experimentellen Untersuchungen bringen grundlegende Erkenntnisse für die folgenden Forschungsschritte zur Entwicklung von gewebten Spacer Fabrics mit Hochleistungsgarnen auf Doppelgreiferwebmaschinen

Nous avons étudié théoriquement et expérimentalement la formation de réseaux en relief sur des surfaces active ou passive, avec deux types de polymères photosensibles : résine photosensible négative et copolymère azobenzene. Le mécanisme de formation des structures est attribué à l'effet de transport de masse, qui déplace la matière dans des directions opposées dans ces deux matériaux. La technique de fabrication est basée sur l'utilisation de la lithographie par interférence, ce qui a permis de créer des structures grandes et uniformes. Dans le premier cas, des structures passives de surface en relief en 1D et 2D ont été créés sur la résine photosensible négative SU8 grâce à l'effet de rétrécissement durant le processus de réticulation. Dans le second cas, des structures périodiques actives en 1D, 2D et 3D ont été obtenues grâce à la migration des matériaux copolymères DR1/PMMA des régions de forte intensité d’irradiation à celles de faible intensité. L'amplitude de modulation de la structure est optimisée par le contrôle de l'épaisseur du film, de la périodicité de la structure, de la dose d'exposition, et des polarisations des faisceaux laser. Les applications de ces structures pour des lasers DFB à multiples longueurs d'onde, les cristaux photoniques non-Linéaires, et le couplage dans les guides d'ondes ont été discutés<br>We have theoretically and experimentally investigated the formation of both active and passive surface relief gratings on two kinds of photosensitive polymers: negative photoresist and azobenzene copolymer. The common mechanism of the structures formation was attributed to mass transport effect, which however pushes the materials in opposite directions in these two materials. The fabrication technique is based on the use of interference lithography, which allowed to create large and uniform structures. In the first case, 1D and 2D passive periodic surface relief structures were created on the negative photoresist SU8 thanks to the shrinkage effect during the crosslinking process. In the second case, 1D, 2D and 3D active periodic structures have been obtained thanks to the movement of DR1/PMMA copolymer materials from regions of high intensity to those of low intensity irradiation. The modulation amplitude of structures is optimized by controlling the film thickness, the structure periodicity, the exposure dosage, and the polarizations of interference laser beams. Applications of these structures for multiple wavelength DFB laser, nonlinear photonic crystals, and waveguide coupling have been discussed

Cette these aborde le probleme de la structuration des donnees relatives aux images 2d et 3d, et leur transformation sous forme d'un schema relationnel. Apres un apercu sur les problemes poses par les systemes graphiques en matiere de structures de donnees, deux modeles de description d'images sont presentes: le modele syntaxique et le modele bases de donnees. Pour representer les images 2d, la structure de donnees graphique quadkey est proposee. Outre un gain tres considerable en espace memoire et en temps de calcul, le quadkey presente l'avantage majeur de transformer les donnees images sous forme de relations adaptees au modele de bases de donnees relationnel. Le quadkey est ensuite etendu en octkey pour representer les images 3d. En utilisant l'octkey, deux methodes de reconstitution d'objets 3d a partir des projections 2d sont decrites. La premiere methode, reconstitue l'objet 3d par intersection des trois faces de vision d'objet: x-y, y-z, et z-x. La seconde, le reconstitue par fusion de ses coupes en serie. Enfin, un systeme de gestion de bases de donnees images (s. G. B. D. I. ) est presente. Base sur le modele relationnel, cet s. G. B. D. I. Utilise les structures de donnees graphiques quadkey et octkey. Il est dote d'un langage de requete non procedural et d'une bibliotheque graphique