O crescente aumento do uso de madeira laminada colada (MLC) em peças estruturais exige dos meios acadêmicos a pesquisa e desenvolvimento de teorias e rotinas de cálculo, que proporcionem suporte teórico para projetos estruturais que empreguem tal material. Nesta pesquisa foi desenvolvido em laboratório de modelos estruturais, um programa para o cálculo estrutural de vigas de madeira laminada colada (MLC), por meio do método dos elementos finitos para material ortotrópico e material isotrópico. Foram rompidas, em uma prensa universal, vigas de Madeira Laminada Colada (MLC), em escala natural, com e sem emendas nas lâminas, com a finalidade de comparação dos resultados assim obtidos, com os obtidos em modelos de cálculo existentes para vigas maciças de material isotrópico, como o método de cálculo da NBR 7190/97 e o método de cálculo da Teoria da Elasticidade (Timoshenko). Tais resultados também foram comparados com os resultados obtidos pelo método dos Elementos Finitos para materiais isotrópicos e ortotrópicos, acima citados. Para comparação entre as propriedades da madeira maciça e da madeira laminada colada, foram retirados corpos de prova das partes intactas das vigas sacrificadas, para realização de ensaios de cisalhamento na linha de cola e nas lâminas coladas, bem como corpos de prova para ensaios de flexão nas lâminas maciças das vigas de MLC. Para obtenção da tensão de ruptura a compressão paralela às fibras e do módulo de elasticidade, foram rompidos corpos de prova de 5cm x 5 cm x 15 cm. A comparação e análise dos resultados obtidos pelos procedimentos acima, levou à conclusão de que a madeira laminada colada (MLC), quando fabricada com cola estrutural, comporta-se como madeira maciça. Também foi possível observar que os modelos de cálculo empregando elementos finitos, ortotrópicos ou isotrópicos, reproduzem o comportamento de uma viga de madeira laminada colada. O modelo de cálculo da NBR 7190/97, pode ser empregado, mas apresenta resultados conservadores, a favor da segurança. Assim como o modelo de cálculo da Teoria da Elasticidade não deve ser empregado sem adaptação à madeira, pois apresentou resultados muito discrepantes. Os módulos de elasticidade da madeira maciça obtidos por ensaios de flexão e a partir do ensaio de compressão paralela às fibra, não representa o módulo de elasticidade representativo de uma viga de MLC. Da mesma forma a existência ou não de emendas nas lâminas, não altera os resultados. / The increasing use of glued laminated timber in structural parts requires academic research and development of theories and calculation routines that provide theoretical support for structural designs employing such material. In this research was developed in the laboratory of structural models, a program for calculating structural glued laminated timber beams by the finite element method for orthotropic material and isotropic material. Were disrupted in a press universal beam of glued laminated wood in full scale with and without splices blades, for the purpose of comparison of the results thus obtained with those obtained in calculation models exist for solid beams material isotropic, as the method of calculating the NBR 7190/97 and the calculation method of the theory of elasticity (Timoshenko). These results were also compared with results obtained by the method of finite elements for isotropic and orthotropic materials, mentioned above. To compare the properties of solid wood and glued laminated timber, specimens were removed from intact parts of the broken beams for testing shear line glue and glued the layers, as well as specimens for bending tests blades massive beam. To obtain the tensile strength parallel to the compression of the fibers and elastic modulus were broken specimens with the dimensions 5 cm x 5 cm x 15 cm. The comparison and analysis of the results obtained by the above procedure led to the conclusion that the glued laminated wood when manufactured with structural adhesive, behaves as solid wood. It was also noted that the model calculations using finite elements, both isotropic and orthotropic represent the behavior of a beam of glued laminated wood. The calculation model of the NBR 7190/97, can be employed, but has conservative results, in favor of security. As the calculation model of the theory of elasticity should not be used without adjustment to the wood, because it showed very discrepant results. The modulus of elasticity of solid wood obtained by bending tests from test and compression parallel to the fiber, it is not the representative elastic modulus of a beam of glued laminated wood. Likewise, the presence or absence of amendments in the layers, does not change the results.

Na construção de cascos resistentes de submarinos são utilizados, frequentemente, os processos de conformação a frio e de soldagem. Estes processos produzem na estrutura deformações plásticas permanentes originando tensões residuais. A presença das tensões residuais é equivalente a introduzir uma pré-carga inicial na estrutura, o que acelera o processo de plastificação, reduzindo à capacidade de resistência da estrutura à pressão hidrostática. Para quantificar esta redução foi realizado, inicialmente, um estudo considerando a presença das tensões residuais devido à conformação a frio das chapas do casco e do flange das cavernas, para submarinos com 6, 8 e 10 m de diâmetro, em aço HY100. Para isso, um modelo não-linear foi produzido considerando não-linearidades geométricas e de material. Complementarmente, também foi estudada a influência de perfis de tensões residuais definidos a partir de resultados experimentais na redução da pressão de colapso do casco resistente do submarino espanhol S-80. Estes perfis consideram a presença simultânea de tensões residuais de conformação e de soldagem. Em todos os modelos estudados, as tensões residuais foram introduzidas no modelo numérico utilizando o comando INISTATE disponível no software comercial Ansys. Este comando é frequentemente utilizado na literatura em modelos numéricos envolvendo tensões residuais e foi validado utilizando três modelos de referência disponíveis na literatura. Ao final, pôde-se verificar que a presença das tensões residuais acelera a plastificação do casco resistente e reduz a pressão de colapso em até 5%, sendo a tensão residual de conformação a que mais contribuí nesta redução. De qualquer forma, pôde-se concluir que a influência das tensões residuais é pequena quando comparada com a pressão de colapso obtida para cada casco resistente analisado. / During the manufacturing of submarine pressure hull are often applied processes like cold forming and welding. Those processes lead to permanent plastic deformations which are associated with residual stresses. The presence of residual stresses is equivalent to the introduction of an initial pre-load in the structure, which accelerates the plastification process, decreasing hull pressure resistance. To quantify this reduction, a case study that considers residual stresses due to cold forming on hull and flange plates has been performed. The study encompasses hull diameters of 6, 8 and 10 m, made of HY100 steel. A nonlinear model has been done, considering material and geometric non-linearity. Complementarily, the influence of experimental residual stresses profiles on the reduction of collapse pressure of the Spanish S-80 submarine has been studied. These profiles consider the simultaneous presence of residual stresses due to cold forming and welding. In all studied models, the residual stresses have been introduced in the numerical models through INISTATE Ansys software command. This command has been validated using three reference models available in open source literature. In the end, it has been possible to verify that the presence of residual stresses increase the hull plastification and reduces the collapse pressure up to 5%, being the cold forming induced stress which most contributes to this reduction. Finally, it could be concluded, in the end of the study, that the influence of the residual stresses is small when compared with the collapse pressure obtained for the analyzed pressure hulls.

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / Includes bibliographical references. / M.S.

Digitized by Kansas Correctional Industries

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / Ph.D.

Na construção de cascos resistentes de submarinos são utilizados, frequentemente, os processos de conformação a frio e de soldagem. Estes processos produzem na estrutura deformações plásticas permanentes originando tensões residuais. A presença das tensões residuais é equivalente a introduzir uma pré-carga inicial na estrutura, o que acelera o processo de plastificação, reduzindo à capacidade de resistência da estrutura à pressão hidrostática. Para quantificar esta redução foi realizado, inicialmente, um estudo considerando a presença das tensões residuais devido à conformação a frio das chapas do casco e do flange das cavernas, para submarinos com 6, 8 e 10 m de diâmetro, em aço HY100. Para isso, um modelo não-linear foi produzido considerando não-linearidades geométricas e de material. Complementarmente, também foi estudada a influência de perfis de tensões residuais definidos a partir de resultados experimentais na redução da pressão de colapso do casco resistente do submarino espanhol S-80. Estes perfis consideram a presença simultânea de tensões residuais de conformação e de soldagem. Em todos os modelos estudados, as tensões residuais foram introduzidas no modelo numérico utilizando o comando INISTATE disponível no software comercial Ansys. Este comando é frequentemente utilizado na literatura em modelos numéricos envolvendo tensões residuais e foi validado utilizando três modelos de referência disponíveis na literatura. Ao final, pôde-se verificar que a presença das tensões residuais acelera a plastificação do casco resistente e reduz a pressão de colapso em até 5%, sendo a tensão residual de conformação a que mais contribuí nesta redução. De qualquer forma, pôde-se concluir que a influência das tensões residuais é pequena quando comparada com a pressão de colapso obtida para cada casco resistente analisado. / During the manufacturing of submarine pressure hull are often applied processes like cold forming and welding. Those processes lead to permanent plastic deformations which are associated with residual stresses. The presence of residual stresses is equivalent to the introduction of an initial pre-load in the structure, which accelerates the plastification process, decreasing hull pressure resistance. To quantify this reduction, a case study that considers residual stresses due to cold forming on hull and flange plates has been performed. The study encompasses hull diameters of 6, 8 and 10 m, made of HY100 steel. A nonlinear model has been done, considering material and geometric non-linearity. Complementarily, the influence of experimental residual stresses profiles on the reduction of collapse pressure of the Spanish S-80 submarine has been studied. These profiles consider the simultaneous presence of residual stresses due to cold forming and welding. In all studied models, the residual stresses have been introduced in the numerical models through INISTATE Ansys software command. This command has been validated using three reference models available in open source literature. In the end, it has been possible to verify that the presence of residual stresses increase the hull plastification and reduces the collapse pressure up to 5%, being the cold forming induced stress which most contributes to this reduction. Finally, it could be concluded, in the end of the study, that the influence of the residual stresses is small when compared with the collapse pressure obtained for the analyzed pressure hulls.

Une grande partie de la structure des avions modernes est fabriquée à partir des dernières générations de matériaux composites. Le principal défi des constructeurs d’avions réside dans la taille importante des pièces en composites. D’où la nécessité de développer de nouvelles technologies de fabrication telle que la dépose automatique de préimprégné. La qualité des pièces fabriquées dépend de nombreux facteurs dont notamment la maîtrise de la rhéologie de la résine du préimprégné. Cette dernière évolue fortement avec les conditions environnementales et les conditions de fabrication. Elle détermine pour partie, les instabilités de la matière particulièrement le long des trajectoires curvilignes. Ces instabilités, qui se présentent sous forme de cloques, engendrent après cuisson des pièces avec des défauts de repliement des couches dans les stratifiés. L’objectif principal de cette thèse de doctorat est l’étude du comportement mécanique d’un ruban de préimprégné prenant en compte la rhéologie de la matière ainsi que sa pégosité dans le but de mieux comprendre les conditions d’apparition des cloques en trajectoire curviligne. Une partie de mes travaux est consacrée à la caractérisation des propriétés physico-chimiques et mécaniques de la matière. Une seconde partie, complémentaire à la première, est dédiée au développement d’un modèle de comportement mécanique d’une plaque sur fondation élastique représentant le ruban de préimprégné et soumise à une rotation imposée. La méthode de Ritz a été utilisée pour l'obtention de solutions explicites des charges critiques de flambement. Il a été montré que les plus faibles rayons de courbure sans formation de cloques en trajectoire curviligne dans le plan sont obtenus avec un faible écrasement du rouleau et un niveau de collant élevé. / The evolution of composite materials in aerospace has been spectacular over the last thirty years. The main advantage provided by composites is weight gain compared to other materials. However, new aluminum lithium alloys may slow this trend because of their specific properties and exceptional manufacturing costs lower than those of composites. Much parts of the structure of the A380 are made from the latest generation of composite materials with organic matrix. The Airbus A380 is the first plane of the manufacturer composed by a center wing box made by composite reinforced with carbon fibers and organic matrix. And like the devices that preceded it, the center wing box, rudder, horizontal stabilizer and the elevators were designed with composites reinforced with carbon fibers and organic matrix. But the main challenge with the new aircraft is the size of parts ; the size of the horizontal stabilizer of the A380 for example, is similar to the wing of the A310. Hence the need to develop the intensive use of automatic prepreg lay up technology. The use of semi-finished prepregs for the manufacture of parts allows standardizing production. Indeed, these products exhibit with the desired rate of reinforcement on the final parts, all the delicate operations of pumping excess resin during the implementation of parts, as the case in the RTM process (Resin Transfer Molding) are eliminated. The quality of parts produced using automatic lay up depends on many factors including the accuracy of trajectory lay up, the control of rheology of the resin contained in the prepreg and behavior at the interface of the material and tooling. The rheology of the resin is changing considerably with environmental conditions (temperature, humidity) and processing conditions (speed of removal, compaction strength). It determines in part and in combination with the tackiness of the prepreg, the instabilities of the material particularly along curved trajectories. In curvilinear lay up, the rotation of the tow placement head imposes to this portion of slit tape, a curvature generating a circular bending phenomenon.The outer portion of the tape is then stretched while the inside is compressed. When the radius of curvature of the tow placement head is low, the result is a phenomenon of local buckling of the slit tape. The corresponding layer waviness (See figure 1) is visible after the passage of the roller so instantly or delayed, depending on the conditions of lay up (speed lay up,compaction strength, temperature, humidity) and the tackiness of the material. Thus, the formation of the layer waviness is a local phenomenon that appears in the material between the tow placement head and tools. It is this area of the material defined by the form of plate, and the extent of which depends on the compaction strength and flexibility of the roller which will be the model proposed in this communication. It is supposed that this plate is based on elastic foundation in order to reflect the tack of the material. The formation mechanism of ply waviness is very few studied and remains unclear since these defects appear at different steps in the manufacturing process. Some studies recommend, without justification, to not exceed some radius of curvature to avoid buckling [1]. Interactions between tooling and material in relation with lay up conditions were studied [2]. In this paper we study the mechanical behavior of a slit tape taking into account the rheology of the material so that his tack in order to better understand the conditions of appearance of layer waviness during circular trajectories. At first, we will present some results from the identification of physico-chemical and mechanical properties of prepreg carbon / epoxy and then we will explain the evolutions observed. A second part, complements the first,will be dedicated to the development of a model of mechanical behavior of a plate based onelastic foundation, representing the slit tape which is subjected to a rotation imposed. The mechanical model of the slit tape will be based on the theory of plate under the hypotheses of Kirchhoff-Love and Von-Karman. Determining the critical buckling load is carried by the Ritz method. The simulation results using different boundary conditions will be analyzed and compared to real cases.

Knowledge of structural stability theory is of paramount importance to the practicing structural engineer. In many instances, buckling is the primary consideration in the design of various structural configurations. The first chapter introduces a simplified treatment of the elastic stability of a battened column using classical methods without getting involved with lengthy and complicated mathematical operations. In chapter two, a treatment of the elastic stability of a frame is presented, including effects of elastic restraints. In this study, a theoretical treatment is given which although approximate, is believed to constitute a satisfactory solution of the structure.

Abstract not available

This thesis investigates the effects of elastic restraint at the supports on the behaviour of shallow concrete arches, and the time-dependent effects of shrinkage and creep of concrete on the nonlinear behaviour of shallow arches. The nonlinear behaviour of shallow circular arches with elastic rotational restraints at each support and subjected to a uniformly distributed radial load is firstly investigated. A virtual work formulation is used to establish both the nonlinear equilibrium equations and the buckling equilibrium equation for shallow arches. The analytical results show that the effects of the stiffness of the rotational restraints on the prebuckling and buckling response are significant. An analytical model is developed for the in-plane elastic stability analysis of shallow parabolic arches with horizontal spring supports subjected to a uniformly distributed vertical load. A parametric study is undertaken using the proposed analytical model. It is found that the effects of the stiffness of the horizontal springs on the prebuckling response, buckling load and buckling behaviour of arches are significant. An analytical model is developed to simulate the time-dependent behaviour of shallow concrete parabolic arches with horizontal spring supports subjected to a sustained loading, and in particular to investigate creep buckling. The time-dependent buckling load and the critical time (or age) of the arches are calculated by using an iterative process based on the proposed model. A systematic parametric study is undertaken, and the results show that the various parameters have a profound effect on the time-dependent buckling load and the prebuckling life of arches. Both short-term and long-term experimental investigations of shallow parabolic tied concrete arches are described and used to validate the analytical models. For the short-term tests, three concrete arches were subjected to a uniformly distributed vertical load and were loaded to failure. For the long-term tests, seven concrete arches were subjected to sustained service loads. The instantaneous and time-dependent deflections were recorded throughout the period of loading, together with the distribution of the horizontal thrust at the supports. Comparisons between the experimental results and the analytical predictions using the analytical models are made to verify the accuracy of the theoretical models.