INTRODUÇÃO: O osso é um tecido dinâmico e a formação e reabsorção óssea são processos contínuos que promovem alterações durante toda a vida do organismo. O objetivo deste estudo transversal é estabelecer valores normais relacionadas com a idade, peso e altura, obtidos pela tomografia computadorizada quantitativa periférica de alta resolução (HR-pQCT) quanto à densidade mineral óssea volumétrica, microarquitetura, porosidade cortical e resistência óssea estimada por análise de elemento finito no rádio distal e na tíbia de uma população miscigenada de mulheres com idade entre 20 a 85 anos. MÉTODOS: Curvas de referências da densidade volumétrica (total, trabecular e cortical), estrutura óssea, porosidade cortical e parâmetros de elementos finitos no rádio distal e na tíbia foram calculados em 450 mulheres saudáveis, incluindo mais de 50 indivíduos para cada década. Modelos de regressão linear foram desenvolvidos para prever os valores das curvas normais medidos de acordo com a idade, peso e altura. RESULTADOS: Todos os parâmetros de densidade e estrutura mostraram curvas lineares decrescentes com o envelhecimento em ambos sítios periféricos, exceto para a densidade cortical (Ct.BMD) e espessura cortical (Ct.Th) na tíbia, que apresentaram um padrão de declínio diferente na curva. O parâmetro porosidade cortical (Ct.Po) manteve um platô nas primeiras décadas de vida, seguida de um aumento da porosidade nas décadas seguintes, enquanto que o diâmetro dos poros da cortical (Ct.Po.Dm) mostrou uma curva linear crescente em ambas as regiões analisadas. Os parâmetros de resistência óssea apresentaram curvas lineares, com exceção da rigidez (S) e carga máxima estimada (F.ult) no rádio distal e estresse cortical (C.VM) na tíbia, que apresentavam diferentes curvas de declínio. Foram encontradas correlações significativas da rigidez com todos os parâmetros analisados (p < 0,001), exceto com o parâmetro diâmetro dos poros da cortical (Ct.Po.Dm) na tíbia. CONCLUSÕES: Este trabalho estabeleceu um conjunto de dados de referência para os parâmetros obtidos por HR-pQCT, com base em uma população normal miscigenada, que serão úteis para a interpretação dos dados clínicos de pacientes na prática clínica e em futuros estudos / INTRODUCTION: Bone is a dynamic tissue, and its formation and resorption are continuous processes that promote changes throughout the life of the organism. The aim of this cross-sectional study is to establish normal values related to age, weight and height using high-resolution peripheral quantitative computed tomography (HR-pQCT) regarding volumetric bone mineral density (vBMD), microarchitecture, cortical porosity and estimated bone strength at the distal radius and tibia from a miscegenated population of women aged 20 to 85 years. METHODS: References curves of vBMD (total, trabecular and cortical), bone structure, cortical porosity and finite element parameters at the distal radius and tibia were calculated in 450 healthy women, including more than 50 subjects from each decade within the age range. Linear regression models were developed to predict the values of the normal curves measured according to age, weight and height. RESULTS: All parameters of vBMD and structure showed decreasing linear curves with aging in both peripheral sites, except for compact bone density (Ct.BMD) and cortical thickness (Ct.Th) at the tibia, which had a different declining curve pattern. The cortical porosity parameter (Ct.Po) maintained a plateau in the first decades followed by an increase in porosity, whereas the cortical pore diameter (Ct.Po.Dm) showed an increasing linear curve in both regions analyzed. Parameters of bone strength presented decreasing linear curves, except for stiffness (S) and estimated failure load (F.ult) at the distal radius and cortical stress (C.VM) at the tibia, which presented with different declining curve. Significant correlations of stiffness with the remaining parameters were found (p < 0.001), except with the cortical pore diameter (Ct.Po.Dm) at the tibia. CONCLUSION: This study established a set of reference data for parameters obtained by HR-pQCT, based on a miscegenated normal population, which will be useful for interpreting clinical data from patients in clinical practice and in future studies

[pt] Projetos estruturais que empregam concretos com resistências mais elevadas, ou seja, maiores que 40 MPa, nomeados Concretos de Alto Desempenho, são cada vez mais freqüentemente utilizados. Sabe-se, entretanto, que as propriedades destes concretos são diferenciadas daquelas dos concretos considerados convencionais, necessitando-se estudos que visem, principalmente, mensurar a realidade dentro dos materiais disponíveis em nosso país. Este trabalho experimental estuda as principais propriedades deste material: resistência à compressão, resistência à tração por compressão diametral, Módulo de Elasticidade e permeabilidade, através da determinação do índice de vazios. Após um estudo sobre métodos de dosagem mais utilizados e empregando-se materiais disponíveis no Rio de Janeiro, foram moldados um total de 230 corpos de prova para resistências características à compressão de 40MPa, 60 MPa, 80 MPa e 100 MPa. Foi realizado um estudo sobre compatibilidade entre superplastificante e aglomerante. Com os dados obtidos experimentalmente, foram relacionados resistências à tração por compressão diametral, módulo de elasticidade e porosidade com resistência à compressão axial. Estes resultados foram comparados com as recomendações das principais normas internacionais e com as propostas de alguns pesquisadores que foram encontradas na literatura. / [en] High Performance Concrete, i.e., those whose compressive strength is higher than 40 Mpa, have been used in a wide range of Civil Engineering applications. Notwithstanding that, it is known that their mechanical and physical properties are different from those of their conventional counterparts. In this dissertation, it is studied mixture proportion methods with good acceptance rate, preparing 230 specimens with materials available in Brazil s state of Rio de Janeiro and that have compressive strength of 40 MPa, 60MPa, 80 MPa and 100 MPa. For each prepared specimen, it is studied its mechanical properties, compressive strength, splitting tensile strength, modulus of elasticity and porosity for the determination of the emptiness ratio. It is also studied the compatibility between superplasticizer and cement materials. It is also performed a comparison between the experimental data and the expressions available in the literature, as well as the relation between the compressive strength, splitting tensile strength, modulus of elasticity and the porosity.

Este trabalho teve como objetivo principal investigar, do ponto de vista volumétrico, qual seria o número de giros necessário, no Compactador Giratório Superpave (CGS), para produzir corpos de prova com características similares aos produzidos com a energia 50 golpes no compactador Marshall, para misturas tipo Stone Matrix Asphalt (SMA) com volume de vazios igual a 4%. Como complemento, realizaram-se dosagens no CGS com 100 giros, visando avaliar o impacto do aumento da energia de compactação no teor de projeto, também para volume de vazios igual a 4%, em comparação aos CPs compactados com o número de giros equivalente à Marshall determinada anteriormente. Foram utilizadas duas faixas granulométricas de misturas SMA: a com Tamanho Máximo Nominal (TMN) 7,93 mm do DER-SP e a com TMN 12,5 mm da AASHTO. Para todas as misturas foram avaliadas as propriedades mecânicas de corpos de prova com 4% de volume de vazios. Dos resultados dos ensaios concluiu-se que o número de giros no CGS para produzir misturas com volume de vazios igual a 4% nos teores de asfalto de trabalho Marshall são similares para as duas faixas granulométricas utilizadas. Por outro lado, a dosagem com 100 giros no CGS reduziu significativamente o teor de asfalto de trabalho para as duas faixas estudadas em comparação com os teores de trabalho obtidos das dosagens Marshall e no CGS com os números de giros equivalentes. Com relação às propriedades mecânicas, as resistências à tração e os módulos de resiliência dos corpos de prova produzidos com 100 giros no CGS são, de uma maneira geral, um pouco menores que os valores obtidos nos corpos de prova compactados no compactador Marshall, independente da faixa granulométrica, porém maiores que os valores obtidos para a compactação giratória nas energias equivalentes. A vida de fadiga para a faixa mais fina é significativamente maior para os corpos de prova compactados com 100 giros em comparação com a compactação Marshall e para a faixa mais grossa manteve-se na mesma ordem de grandeza da obtida para a compactação Marshall. Para as misturas ensaiadas, não foi constatado influência da compactação no dano causado pela umidade induzida / The aim of the work was to investigate, in terms of volumes properties, which would be the number of gyrations required in the Superpave Gyrations Compactor (SGC), to produce samples with characteristics similar to the energy produced with 50 blows in the Marshall Compactor, for Stone Matrix Asphalt (SMA) mixtures with voids content equal to 4%. As a complement, samples designed in the SGC with 100 gyrations, were made to evaluate the impact of increased compaction energy in the binder content, also for voids content equal to 4%, compared to the samples compacted with a number of gyrations equivalent to Marshall, as previously determined. It was used two different aggregates gradations for SMA mixtures: Nominal Maximum Size (NMS) 7,93 mm of the DER and the NMS 12,5 mm of the AASHTO. The mechanical properties of all samples were evaluated with voids content of 4%. The number of gyrations in the SGC to produce mixtures containing voids content equal to 4% for the Marshall`s binder content are similar for both aggregates gradations used. On the other hand, the SMA mixture design with 100 gyrations reduced the binder content for both gradations in comparison with the binder content obtained from Marshall Compaction and SGC with the equivalent number of gyrations. Concerning mechanical properties, the tensile strength and resilient modulus of the samples produced with 100 gyrations in the SGC are, generally, slightly lower than the values obtained with the samples compacted in the Marshall compactor, independent of the aggregate gradations, but higher than the values obtained with the samples compacted with a equivalent energy in the SGC. The fatigue life for the fine gradation (NMS=7,93mm) is significantly higher for the samples compacted in the SGC with 100 gyrations compared with the Marshall compaction, and for the coarse gradation (NMS=12,5 mm) remained in the same order of magnitude that of the Marshall compaction. It was not observed any influence of the compaction method in the induced damage caused by moisture

INTRODUÇÃO: Os ligamentos mediais responsáveis pela manutenção da estabilidade da articulação patelofemoral (PF) são o ligamento patelofemoral medial (LPFM), o ligamento patelotibial medial (LPTM) e o ligamento patelomeniscal medial (LPMM). Sobre o LPFM, existem vários estudos anatômicos, radiológicos, biomecânicos, e a evolução clínica de sua lesão e reconstrução; no entanto, pouco se sabe sobre o LPTM e o LPMM. MÉTODOS: O LPFM, o LPTM e o LPMM foram dissecados em 9 joelhos. Todos os ligamentos foram enviados para avaliação histológica, corados pelo método de hematoxilina e eosina (HE), após o teste biomecânico. Foram medidos o comprimento e a largura bem como a relação das inserções com referências anatômicas (epicôndilo medial do fêmur, tubérculo dos adutores no fêmur, linha articular, tendão patelar e menisco medial). Esferas metálicas foram introduzidas nas inserções e radiografias em ântero-posterior (AP) e perfil (P) realizadas. Foram medidas as distâncias entre as inserções e as linhas de base (na tíbia, linha do planalto, borda medial do planalto e borda medial da espinha medial; e na patela, linha da cortical posterior e bordas proximal e distal da patela). Os ensaios de tração dos ligamentos foram executados em uma máquina de ensaios mecânicos KRATOS. RESULTADOS: Todos os materiais apresentaram tecido conjuntivo denso característico de tecido ligamentar. Com o estudo anatômico verificamos que o LPFM se encontrou na camada 2, com comprimento de 60.6 mm e largura de 15,3 mm no fêmur e 20,7 mm na patela. Inseriu-se entre o tubérculo dos adutores e o epicôndilo medial no fêmur e no pólo proximal da patela. O LPTM tinha um comprimento de 36,4 mm e largura de 7,1 mm. Sua inserção tibial se encontrou 13,7 mm distal a articulação e 11,6 mm medial ao tendão patelar formando um ângulo de 18,5o com este. A inserção na patela foi 3,6 mm proximal a sua borda distal. O LPMM se encontrou na camada 3 e seu comprimento foi de 33,7 mm e largura de 8,3 mm. Com uma inserção meniscal no corno anterior, 26,6 mm medial ao tendão patelar e formando ângulo com tendão patelar de 42,8o. Sobre os parâmetros radiográficos, a inserção tibial do LPTM se encontrou 9,4 mm, na incidência AP, e 13,5 mm, na incidência P, distal a articulação. Quanto ao posicionamento médio lateral a inserção se encontrou a 30% do comprimento do planalto de medial para lateral e na borda medial da espinha medial. A inserção patelar era 4,8 mm proximal a sua borda distal. Na análise biomecânica verificamos que o LPTM era mais rígido que o LPFM (médias de 17,0 N/mm versus 8,0 N/mm, respectivamente) e apresentou menor deformação no limite de resistência máxima (8,6 mm Resumo Betina Bremer Hinckel versus 19,3 mm). CONCLUSÃO: Os ligamentos foram identificados em todos os joelhos. Os parâmetros anatômicos e radiográficos das inserções foram bem definidos. Os enxertos comumente utilizados para as reconstruções ligamentares do joelho são suficientes para a reconstrução do LPFM e do LPTM / INTRODUCTION: The medial ligaments responsible for maintaining the stability of the patellofemoral (PF) joint are the medial patellofemoral ligament (MPFL), the medial patellotibial ligament (MPTL) and the medial patellomeniscal ligament (MPML). There are several studies on the anatomical, imaging, and biomechanical characteristics of the MPFL, and clinical outcome of its injury and reconstruction; however, little is known about the MPTL and MPML. METHODS: The MPFL, MPTL and MPML were dissected in 9 knees. All ligaments underwent histological evaluation by hematoxylin eosin stain after the biomechanical test. The length and width and the insertions relationship with anatomical references (medial epicondyle of the femur, adductor tubercle of the femur, joint line, patellar tendon and medial meniscus) were measured. Steel balls were introduced at the insertions and radiographs in anteroposterior (AP) and profile (P) views were performed. The distance between the insertions to baselines were measured (in the tibia, the plateau line, the medial plateau border and the medial border of the medial tibial spine; and in the patella the posterior cortical line and the proximal and distal patellar borders). The tensile tests of the ligaments were performed on a mechanical testing machine KRATOS. RESULTS: All materials showed dense connective tissue characteristic of ligaments. With the anatomical study we found that the MPFL was in layer 2, it has length of 60.6 mm and width of 15,3 mm in the femur and 20,7 mm in the patella. Inserting between the adductor tubercle and the medial epicondyle on the femur and in the inferior pole of the patella. The MPTL was found in layer 2, its length was 36.4 mm and width of 7.1 mm. Its tibial insertion was found 13.7 mm distal to the joint line and 11.6 mm medial to the patellar tendon at an angle of 18,5o with it. On the patella it was 3.6 mm proximal to its distal border. The MPML was in layer 3 and its length was 33.7 mm and width of 8.3 mm. The meniscal insertion was in the anterior horn, 26.6 mm medial to the patellar tendon and a 42,8o angle with it. In regards to the radiographic parameters the tibial insertion of LPTM was 9.4 mm, in the AP, and 13.5 mm, in the P, distal to the joint line. The medial lateral position was at 30% from medial to lateral on the tibial plateau and on the medial edge of the medial spine. The patellar insertion was 4.8 mm proximal to the distal border of the patella. In the biomechanical analysis we verified that the MPTL was more rigid then the MPFL (average of 17.0 N / mm versus 8.0 N / mm, respectively) and showed less deformation in the maximum tensile strength (8,6 mm versus 19,3 mm). CONCLUSION: The ligaments were identified in all knees. The anatomical and radiographic insertion parameters were well

Esta pesquisa foi baseada em um projeto de Stone Matrix Asphalt - SMA na faixa 0/8S com asfalto CAP 20, feito para a execução de revestimento delgado em trecho experimental na Rodovia Presidente Dutra, ligando São Paulo ao Rio de Janeiro. A ocorrência de alguns defeitos neste trecho experimental motivou o estudo de misturas SMA 0/8S alternativas empregando dois asfaltos convencionais: CAP 20 e CAP 50/60, e dois modificados por polímeros: um com 3,0% de SBS e outro com 6,5% de SBS. Foram realizados ensaios laboratoriais para a verificação da dosagem das misturas asfálticas e determinação de propriedades mecânicas em laboratório por meio de ensaios de deformação permanente em trilha de roda, de resistência à tração por compressão diametral e de módulo de resiliência. Observou-se que o uso de asfalto modificado por polímero e do asfalto convencional CAP 50/60 acarreta uma redução significativa de afundamentos em trilha de roda. O módulo de resiliência a 25°C também apresenta redução de valor nas amostras com asfalto modificado por polímero e com CAP 50/60, em comparação com o convencional CAP 20. A resistência à tração sofre pouca variação quando se comparam os asfaltos empregados, considerando-se ensaios realizados na mesma temperatura. Foram feitos ensaios em campo para a avaliação funcional e de aderência no trecho experimental da Rodovia Presidente Dutra, tendo sido realizados monitoramentos logo após a execução do trecho e decorridos 2 anos e 7 meses de operação. Os resultados demonstraram que o revestimento do trecho experimental apresenta atualmente poucos defeitos de superfície, com fechamento da macrotextura nas trilhas de roda e pequena diminuição do conforto ao rolamento. / This research was based on a Stone Matrix Asphalt SMA in the band 0/8S design made with asphalt binder AC 20, used as a thin wearing course of a test section on the Presidente Dutra Highway, that connects São Paulo to Rio de Janeiro. The occurrence of some distresses in the test section motivated the study of alternative SMA 0/8S mixtures using two conventional asphalt binders: AC 20 and AC 50/60, and two modified by polymer: one with 3.0% of SBS and other with 6.5% of SBS. Laboratory tests were conducted to verify the mix design and to determine their mechanical behavior such as the resistance against rutting, the indirect tensile strength and the resilient modulus. It was observed that the use of SBS polymer modified binders and asphalt binder AC 50/60 causes a significant reduction of rutting. The resilient modulus at 25°C also presents a reduction in the samples with SBS polymer modified binders and AC 50/60 in comparison with AC 20. The indirect tensile strength suffers little variation across the different types of asphalt binders, tested at the same temperature. Field tests related to functional evaluation and skid-resistance of the test section were carried out. The test section was monitored immediately following the construction and after 2 years and 7 months of continuous use. The results showed that the wearing coarse presented a few distresses in the surface, in particular a reduction of the macrotexture at the wheel tracks and a slight worsening of the riding quality.

Nowadays, thin-walled load bearing structures can be realised using textile reinforced concrete (BRAMESHUBER and RILEM TC 201-TRC [1]). The required tensile strength is achieved by embedding several layers of textile. By means of the laminating technique the number of textile layers that can be included into the concrete could be increased. To further increase the first crack stress and the ductility as well as to optimize the crack development, fine grained concrete mixes with short fibres can be used. By a schematic stress-strain curve the demands on short fibres are defined. Within the scope of this study, short fibres made of glass, carbon, aramid and polyvinyl alcohol are investigated in terms of their ability to fit these requirements. On the basis of these results, the development of hybrid fibre mixes to achieve the best mechanical properties is described. Additionally, a conventional FRC with one fibre type is introduced. Finally, the fresh and hardened concrete properties as well as the influence of short fibres on the load bearing behaviour of textile reinforced concrete are discussed.

The present work describes investigations on the anisotropic strength behavior of rocks in the splitting tensile test (Brazilian test). Three transversely isotropic rocks (gneiss, slate and sandstone) were studied in the Lab. A total of more than 550 indirect tensile strength tests were conducted, with emphasis was placed on the investigation of the influence of the spatial position of anisotropic weakness plane to the direction of the load on the fracture strength and fracture or fracture mode. In parallel, analytical solutions were evaluated for stress distribution and developed 3D numerical models to study the stress distribution and the fracture mode at the transversely isotropic disc. There were new findings on the fracture mode of crack propagation, the influence of the disc thickness, the influence of the applying loading angle and angle of the loading-foliation for transversely isotropic material. / Inhalt der Arbeit sind Untersuchungen zum anisotropen Festigkeitsverhalten von Gesteinen beim Spaltzugversuch (Brazilian Test). Laborativ wurden drei transversalisotrope Gesteine (Granit, Schiefer und Sandstein) untersucht. Insgesamt wurden mehr als 550 Spaltzugversuche durchgeführt, wobei der Schwerpunkt auf die Untersuchung des Einflusses der räumlichen Lage der Anisotropieebene zur Richtung des Lasteintrages auf die Bruchfestigkeit und das Bruchbild bzw. den Bruchmodus gelegt wurde. Parallel dazu wurden analytische Lösungen zur Spannungsverteilung ausgewertet sowie numerische 3D-Modelle entwickelt, um die Spannungsverteilung sowie den Bruchmodus bei einer transversalisotropen Scheibe zu untersuchen. Es wurden neue Erkenntnisse zum Bruchmodus, der Rissausbreitung, des Einflusses der Scheibendicke, dem Einfluss des Lasteinleitungswinkel sowie des Winkels Lasteintrag - Anisotropieebene für transversalisotropes Material gewonnen.

For paper producers, an understanding of the development of strength properties in the paper is of uttermost importance. Strong papers are important operators both in the traditional paper industry as well as in new fields of application, such as fibre-based packaging, furniture and light-weight building material. In the work reported in this thesis, three approaches to increasing paper strength were addressed: mixing different pulps, multilayering and reinforcement with man-made fibres. In specific: The effects of mixing Swedish softwood kraft pulp with southern pine or with abaca (Musa Textilis) were investigated. Handsheets of a softwood kraft pulp with the addition of abaca fibres were made in a conventional sheet former. It was seen that the addition of abaca fibres increased the tearing resistance, fracture toughness, folding endurance and air permeance. Tensile strength, tensile stiffness and tensile energy absorption, however, decreased somewhat. Still it was possible to add up to about 60% abaca without any great loss in tensile strength. As an example, with the addition of 30% abaca, the tear index was increased by 36%, while the tensile index was decreased by 8%. To study the effect of stratification, a handsheet former for the production of stratified sheets, the LB Multilayer Handsheet Former was evaluated. The advantage of this sheet former is that it forms a stratified sheet at low consistency giving a good ply bond. It was shown to produce sheets with good formation and the uniformity, evaluated as the variation of paper properties, is retained at a fairly constant level when the number of layers in the stratified sheets is increased. The uniformity of the sheets produced in the LB Multilayer Handsheet Former is generally at the same level as of those produced in conventional sheet formers. The effects of placing southern pine and abaca in separate layers, rather than mixing them homogeneously with softwood pulp were studied. Homogeneous and stratified sheets composed of softwood and southern pine or softwood and abaca were produced in the LB Multilayer Handsheet Former. It was found that by stratifying a sheet, so that a pulp with a high tear index and a pulp with a high tensile index are placed in separate layers, it was possible to increase the tear index by approximately 25%, while the tensile index was decreased by 10-20%. Further, by mixing a pulp with less conformable fibres and no fines with a pulp with more flexible fibres and fines, a synergy in tensile strength (greater strength than that predicted by linear mass fraction additivity) was obtained. The effects of stratifying sheets composed of softwood and abaca were compared to the effects of refining the softwood pulp. Homogeneous and stratified sheets composed of softwood with three different dewatering resistances and abaca were also produced in the LB Multilayer Handsheet Former. It was found that by stratifying the sheets the tear index was retained while the tensile index was increased by the refining. The effects of reinforcing softwood pulp of different dewatering resistances with man-made fibres with low bonding ability were also investigated. Man-made fibres (i.e. regenerated cellulose, polyester and glass fibres) were added in the amounts 1, 3, or 5 wt% to softwood pulp of three different dewatering resistances. It was found that with refining of a softwood pulp and subsequent addition of long fibres with low bonding ability the tensile-tear relationship can be shifted towards higher strength values. The bonding ability of the man-made fibres was evaluated by pull-out tests and the results indicated that, in relation to the fibre strength, regenerated cellulose (lyocell) was most firmly attached to the softwood network while the glass fibres were most loosely attached.

Digital image correlation techniques (DICT), a non-contact deformation measuring technique based on gray value digital images, have become increasingly used over the last years. By using the DIC technique during a tensile test, the deformation behavior of different engineering material under an applied load can be determined and analyzed. Digital images, acquired from a tensile test, can be correlated by using DICT software and from that the local or global mechanical properties can be calculated. The local or global mechanical properties determination of a flat test specimens are based on the displacements or changes in a previous stochastic sprayed or natural pattern. The used material for this purpose is cast silicon (Si) based aluminium (Al) component, designated as AlSi7Mg0.3 (Anticorodal-78 dv). The hypoeutectic Al- Si alloy is widely applicable for engine constructions, vehicle and aerospace constructions, shipbuilding, electrical engineering and constructions for food industry. There are many microstructural parameters in a binary system Al- Si alloys, which the mechanical properties can be depended on, for instance phase distribution, Secondary Dendrite Arm Spacing (SDAS), morphology of Si particles (Roundness) and microscopic defects or pores. All these parameters can contribute to enhance the proper mechanical performance (e.g. Strength and ductility) in the Al-Si cast components.

Made available in DSpace on 2014-12-17T14:07:19Z (GMT). No. of bitstreams: 1 PedroLSF_DISSERT.pdf: 5571248 bytes, checksum: d237019829d37099df0ac47168668556 (MD5) Previous issue date: 2014-07-21 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Composite laminates with plies in different directions finely dispersed are classified as homogenized. The expected benefits of homogenization include increased mechanical strength, toughness and resistance to delamination. The objective of this study was to evaluate the effect of stacking sequence on the tensile strength of laminates. Composite plates were fabricated using unidirectional layers of carbon/epoxy prepreg with configurations [903/303/-303]S and [90/30/-30]3S. Specimens were subjected to tensile and open hole tension (OHT) tests. According to the experimental results, the mean values of strength for the homogenized laminates [90/30/-30]3S were 140% and 120% greater for tensile and OHT tests, respectively, as compared to laminates with configuration [903/303/-303]S. The increase in tensile strength for more homogenized laminates was associated with the increment in interlaminar interfaces, which requires more energy to produce delamination, and the more complicated crack propagation through plies with different orientations. OHT strength was not affected by the presence of the hole due to the predominance of the interlaminar shear stress in relation to the stress concentration produced by the hole / Laminados formados por l?minas com diferentes orienta??es, finamente dispersas, s?o classificados como homogeneizados. Os benef?cios esperados da homogeneiza??o incluem aumento de resist?ncia mec?nica, da tenacidade e da resist?ncia ? delamina??o. O objetivo deste trabalho foi avaliar o efeito da sequ?ncia de empilhamento na resist?ncia ? tra??o de laminados quase-isotr?picos. Placas de comp?sitos foram fabricadas com l?minas unidirecionais de ep?xi/carbono com configura??es [903/303/-303]S e [90/30/-30]3S. Corpos de prova foram submetidos a ensaios de tra??o e de open hole tension (OHT). De acordo com os resultados experimentais, os valores m?dios de resist?ncia para os laminados mais homogeneizados [90/30/-30]3S foram incrementados em 140% e 120% nos ensaios de resist?ncia ? tra??o e OHT, respectivamente, em rela??o aos laminados com configura??o [903/303/-303]S. O aumento de resist?ncia ? tra??o para laminados mais homogeneizados foi relacionado com o maior n?mero de interfaces interlaminares, que aumenta a quantidade de energia necess?ria para produzir delamina??o, e a maior dificuldade de propaga??o de trincas atrav?s de l?minas com orienta??es diferentes. A resist?ncia medida nos ensaios de OHT n?o foi afetada pela presen?a do furo devido ? predomin?ncia da influ?ncia da tens?o de cisalhamento interlaminar em rela??o ao efeito de concentra??o de tens?o provocado pelo furo