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L'amélioration des performances des robots est un enjeu important dans le domaine industriel. Les objectifs visés sont l'augmentation de l'espace de travail, de la capacité de charge transportable, de la vitesse de travail et de la précision du robot. Pour atteindre ces objectifs, il faut en général augmenter la rigidité, diminuer la masse et augmenter la capacité d'amortissement du robot. Les robots actuels sont généralement fabriqués en métaux : aluminium ou acier, ce qui limite leurs performances en raison des faibles capacités d'amortissement des vibrations de ces matériaux. Les matériaux composites présentent l'avantage de combiner des matériaux différents, ce qui conduit à une variété de leurs performances. Parmi les types de renforts, les fibres de carbone présentent un module d'élasticité élevé permettant la conception de pièces de grandes rigidités statiques mais elles possèdent une faible capacité d'amortissement. Les fibres végétales, par contre, possèdent une faible densité, de bonnes propriétés spécifiques et des capacités d'amortissement élevées. Cette thèse porte sur l'amélioration des performances d'un robot parallèle 3CRS en utilisant des matériaux composites pour reconcevoir des pièces initialement fabriquées en aluminium. La thèse commence d'abord par une caractérisation des comportements statiques et dynamiques du robot initial constitué de bras en aluminium. Ensuite, la forme des segments des bras robotiques est optimisée par rapport aux sollicitations mécaniques sur le robot. Un nouveau composite stratifié hybride renforcé par des fibres de carbone et des fibres de lin est alors proposé. Cette combinaison permet d'allier les avantages des deux types de fibres dans un composite pour le dimensionnement des composants sous sollicitation élevée. La structure de ce nouveau composite a été optimisée puis un segment est fabriqué pour valider la conception. Finalement, l'étude du nouveau robot avec des bras en matériaux composites a été réalisée, les résultats montrent que la rigidité du robot augmente, sa masse diminue légèrement et sa capacité d'amortissement augmente considérablement par rapport au robot initial. Donc, l'application du composite stratifié hybride peut améliorer les performances statiques et dynamiques et augmenter significativement la précision en fonctionnement du robot 3CRS.
Natural fiber-reinforced composites have the potential to replace synthetic composites, leading to less expensive, stronger and more environmentally-friendly materials. This book provides a detailed review on how a broad range of biofibers can be used as reinforcements in composites and assesses their overall performance. The book is divided into five major parts according to the origins of the different biofibers. Part I contains chapters on bast fibers, Part II; leaf fibers, Part III; seed fibers, Part IV; grass, reed and cane fibers, and finally Part V covers wood, cellulosic and other fibers including cellulosic nanofibers. Each chapter reviews a specific type of biofiber providing detailed information on the sources of each fiber, their cultivation, how to process and prepare them, and how to integrate them into composite materials. The chapters outline current and potential applications for each fiber and discuss their main strengths and weaknesses. - The book is divided into five major parts according to the origins of the different biofibers - bast, leaf, seed; grass, reed and cane fibers, and finally wood, cellulosic and other fibers including cellulosic nanofibers. - This book provides a detailed review on how a broad range of biofibers can be used as reinforcements in composites and assesses their overall performance - The chapters outline current and potential applications for each fiber and discuss their main strengths and weaknesses
Mechanical engineering, an engineering discipline borne of the needs of the in dustrial revolution, is once again asked to do its substantial share in the call for industrial renewal. The general call is urgent as we face profound issues of produc tivity and competitiveness that require engineering solutions, among others. The Mechanical Engineering Series features graduate texts and research monographs intended to address the need for information in contemporary areas of mechanical engineering. The series is conceived as a comprehensive one that covers a broad range of concentrations important to mechanical engineering graduate education and re search. We are fortunate to have a distinguished roster of consulting editors on the advisory board, each an expert in one of the areas of concentration. The names of the consulting editors are listed on the next page of this volume. The areas of concentration are applied mechanics, biomechanics, computational mechan ics, dynamic systems and control, energetics, mechanics of materials, processing, thermal science, and tribology.
Good optical design is not in itself adequate for optimum performance of optical systems. The mechanical design of the optics and associated support structures is every bit as important as the optics themselves. Optomechanical engineering plays an increasingly important role in the success of new laser systems, space telescopes and instruments, biomedical and optical communication equipment, imaging entertainment systems, and more. This is the first handbook on the subject of optomechanical engineering, a subject that has become very important in the area of optics during the last decade. Covering all major aspects of optomechanical engineering - from conceptual design to fabrication and integration of complex optical systems - this handbook is comprehensive. The practical information within is ideal for optical and optomechanical engineers and scientists involved in the design, development and integration of modern optical systems for commercial, space, and military applications. Charts, tables, figures, and photos augment this already impressive handbook. The text consists of ten chapters, each authored by a world-renowned expert. This unique collaboration makes the Handbook a comprehensive source of cutting edge information and research in the important field of optomechanical engineering. Some of the current research trends that are covered include:
This Guide is primarily intended for applicants and holders of international registrations of marks, as well as officials of the competent administrations of the Member States of the Madrid Union. It leads them through the various steps of the international registration procedure and explains the essential provisions of the Madrid Agreement, the Madrid Protocol and the Common Regulations.
Repackaged with a new afterword, this "valuable and entertaining" (New York Times Book Review) book explores how scientists are adapting nature's best ideas to solve tough 21st century problems. Biomimicry is rapidly transforming life on earth. Biomimics study nature's most successful ideas over the past 3.5 million years, and adapt them for human use. The results are revolutionizing how materials are invented and how we compute, heal ourselves, repair the environment, and feed the world. Janine Benyus takes readers into the lab and in the field with maverick thinkers as they: discover miracle drugs by watching what chimps eat when they're sick; learn how to create by watching spiders weave fibers; harness energy by examining how a leaf converts sunlight into fuel in trillionths of a second; and many more examples. Composed of stories of vision and invention, personalities and pipe dreams, Biomimicry is must reading for anyone interested in the shape of our future.
The book intends to give a state-of-the-art overview of flexoelectricity, a linear physical coupling between mechanical (orientational) deformations and electric polarization, which is specific to systems with orientational order, such as liquid crystals. Chapters written by experts in the field shed light on theoretical as well as experimental aspects of research carried out since the discovery of flexoelectricity. Besides a common macroscopic (continuum) description the microscopic theory of flexoelectricity is also addressed. Electro-optic effects due to or modified by flexoelectricity as well as various (direct and indirect) measurement methods are discussed. Special emphasis is given to the role of flexoelectricity in pattern-forming instabilities. While the main focus of the book lies in flexoelectricity in nematic liquid crystals, peculiarities of other mesophases (bent-core systems, cholesterics, and smectics) are also reviewed. Flexoelectricity has relevance to biological (living) systems and can also offer possibilities for technical applications. The basics of these two interdisciplinary fields are also summarized.
An era has ended. The political expression that most galvanized evangelicals during the past quarter-century, the Religious Right, is fading. What's ahead is unclear. Millions of faith-based voters still exist, and they continue to care deeply about hot-button issues like abortion and gay marriage, but the shape of their future political engagement remains to be formed. Into this uncertainty, former White House insiders Michael Gerson and Peter Wehner seek to call evangelicals toward a new kind of political engagement -- a kind that is better both for the church and the country, a kind that cannot be co-opted by either political party, a kind that avoids the historic mistakes of both the Religious Left and the Religious Right. Incisive, bold, and marked equally by pragmatism and idealism, Gerson and Wehner's new book has the potential to chart a new political future not just for values voters, but for the nation as a whole.
Mathematical methods play a significant role in the rapidly growing field of nonlinear optical materials. This volume discusses a number of successful or promising contributions. The overall theme of this volume is twofold: (1) the challenges faced in computing and optimizing nonlinear optical material properties; and (2) the exploitation of these properties in important areas of application. These include the design of optical amplifiers and lasers, as well as novel optical switches. Research topics in this volume include how to exploit the magnetooptic effect, how to work with the nonlinear optical response of materials, how to predict laser-induced breakdown in efficient optical devices, and how to handle electron cloud distortion in femtosecond processes.