O objetivo desse estudo foi avaliar a influência da técnica incremental na força coesiva de diferentes resinas compostas. Foi confeccionado para este trabalho um dispositivo bipartido de Teflon que se encaixa em um magazine metálico para manter as metades em posição durante a preparação dos corpos de prova do compósito. A partir deste dispositivo de forma cônica, e dimensões: 4mm de base, 2mm de diâmetro na interface e 4mm de altura, foram obtidos 120 espécimes, divididos em 12 grupos ( n=10), 6 grupos sem o uso de adesivo e 6 grupos com o uso de adesivo. Foram utilizadas as resinas compostas: Filtek P90-3M ESPE, St.Paul,MN,USA e Filtek Z350 XT-3M ESPE, St. Paul, MN,USA , ambas na cor A3, inseridas no dispositivo bipartido de teflon segundo a técnica incremental adotada, técnica incremental obliqua, horizontal ou incremento único. A resina foi inserida com uma espátula metálica em incrementos horizontais ou em incrementos oblíquos, conforme a inclinação dada pelo instrumental utilizado, em incrementos de 2mm de espessura, ou ainda inserida de uma só vez, em porção única de 4mm de espessura e fotoativadas por 20 segundos, segundo indicação do fabricante. Os espécimes foram submetidos aos testes de tração para avaliar a força coesiva da resina composta e a influência da técnica incremental utilizada. Os dados obtidos foram analisados quanto à sua distribuição, à Análise de Variância (ANOVA) e ao Teste de Tukey HSD (p>0,05 %). Pode - se concluir que a técnica incremental utilizando incrementos oblíquos influencia negativamente na resistência coesiva. A Resina Filtek Z350XT possui maior resistência coesiva quando comparada à resina Filtek P90. A utilização de adesivo influencia negativamente na resistência coesiva. / The aim of this study was to evaluate the influence of incremental technique on the cohesive strength of different dental resin composites. A total of 120 conical specimens of different resin composites, Filtek P90 and Filtek Z350 XT, both in color A3, were made in a bipartite teflon device with the following dimensions: 4 mm base diameter of 2mm and 8mm in height. The specimens were assigned into 12 groups (n = 10), 6 groups without the use of adhesive and 6 groups with the use of adhesive. The cavity was filled with a metal spatula in oblique or horizontal increments of 2mm thick or inserted at once in one portion 4mm thick and each increment was light-cured for 20 seconds following manufactures instructions. The specimens were subjected to microtensile tests to evaluate the cohesive strength of the resin composite and the influence of incremental technique used. Data were submitted to ANOVA and Tukey\'s HSD test (p<0,05%).Can be concluded that the incremental technique using increments oblique negatively influence the cohesive strength. The resin Filtek Z350XT has greater cohesive resistance when compared to Filtek P90. The use of adhesive negatively influence the cohesive resistance

Este trabalho apresenta formulações para a análise de associação de chapas, usando o conceito de sub-regiões. Também é apresentada a técnica da sub-estruturação para o método dos elementos de contorno. O aumento da rigidez no contínuo através de enrijecedores é considerada pela combinação do método dos elementos finitos e do método dos elementos de contorno. Neste procedimento o sistema de equações lineares torna-se semelhante ao encontrado na formulação do método dos elementos de contorno. Através desta formulação é também possível simular o escorregamento entre superfícies rígidas usando modelos plásticos e visco-plásticos simples do tipo coulomb. Isto representa a descontinuidade nos esforços e deslocamentos entre chapas. São, ainda, apresentados exemplos de aplicação para demonstrar a validade da formulação utilizada. / This work presents formulations for analysis of plate association, using the concept of sub-regions. It is also presented the substructure technique for the boundary elements method. The increasing in stiffiness in the continuous is considered by the combinations of the finite and boundary element methods. In this procedure the linear equation system becomes similar to the resulted by boundary element method. The formulation used also alows to simulate the slipping among rigid surfaces using plastic and simple viscous-plastic models of Coulomb type. This represents the descontinues in the forces and displacements among plates. It was also presented some numeric examples in order to validate the formulation used.

Os Tabuleiros Costeiros são unidades geomorfologicamente definidas, caracterizando-se como formações sedimentares de topos aplainadas de grande extensão territorial, amplamente povoada, com intensa exploração econômica agropecuária, mas com a presença constante de restrições físicas ao uso agrícola, associadas à presença de solos com horizontes coesos em subsuperfície. A presença deste horizonte coeso reduz a profundidade efetiva dos solos, prejudicando a dinâmica da água no perfil e, principalmente, o aprofundamento do sistema radicular, reduzindo as taxas de infiltração de água, criando lençóis freáticos suspensos e que se desenvolvem particularmente sob os Latossolos Amarelos (Latossolos Amarelos) e os Argissolos Amarelos (Podzólicos Amarelos). Assim, a presença destes horizontes em áreas úmidas, pode ser associada a um maior teor de umidade nos solos, que pode ser captada pelo sensor. Devido a sua natureza pedológica e sua localização em sub superfície e sua grande extensão, estes solos demandam grandes recursos para sua efetiva localização e mapeamento. A aplicação de técnicas de processamento digital de imagens nas imagens do sensor ASTER, um sensor experimental e pouco explorado, possibilita a redução de custos, empregados nos levantamentos exploratórios para localização destes horizontes coesos. O principal objetivo deste trabalho foi submeter imagens obtidas através do sensoriamento remoto óptico orbital, do sensor ASTER, a diferentes técnicas de processamento digital de imagens, para assim identificar, reconhecer e caracterizar a presença dos horizontes coesos nos solos dos Tabuleiros Costeiros da Bahia, utilizando como critério identificador, o teor de umidade dos solos. O trabalho foi desenvolvido numa área de aproximadamente 2.475km2, onde está inserida uma área de referência de 29km2, situada no município de Esplanada, onde predominam solos da mesma Classe (Podzólicos Amarelos e Acinzentados) mas diferenciados em unidades que possuem diversos graus de coesão, com textura que varia de arenosa a argilosa. Foi utilizada uma única cena ASTER, sob a qual foi extraída oitenta amostras para determinar a relação entre o teor de umidade dos solos e as diferentes técnicas de processamento digital de imagens. Foram realizadas vinte e seis técnicas de realce (análise componentes principais, Transformação Tasseled Cap, NDVI, NDMI, SAVI e vinte e uma razões entre bandas do sensor ASTER) , além da aplicação de uma classificação supervisionada (método da máxima verossimilhança), com limiar de aceitação de 95%. Os resultados demonstraram que a sétima componente principal é o melhor produto para mapear a presença dos horizontes coesos, por melhor identificar a umidade do solo; o NDMI, o SAVI e a Umidade obtida através da Transformação Tasseled Cap têm um comportamento similar entre si, mas com resultados menos evidentes e entre as razões entre as faixas espectrais testadas, os melhores resultados foram as razões entre as faixas 1 e 8 e entre as faixas 3 e 8. / The Coastal Tableland are units geomorfologicaly defined, characterized by sedimentary formations of smoothed tops of great territorial extension, widely populated, with intense agricultural economic exploration, but with the constant presence of physical restrictions to agricultural use, that are associated to cohesion horizons in subsurface. The presence of this cohesion horizon reduces the soils depth, harming the dynamics of the water in the profile and, mainly, the radicular system of depth, reducing the water infiltration rates and creating suspended sheets particularly under Yellow Latossol and Yellow Podzolic. Thus, the presence of these horizons in humid areas can be associated with higher moisture levels in the soils that can be caught by the sensor. Due to its pedologic nature, sub surface and great extension location, these soil demand great resources for its effective localization and mapping. The application of techniques of image digital processing in the images of the ASTER sensor, an experimental and few explored sensor, turns possible the reduction of costs, used in the exploratory searches for the localization of these cohesion horizons. The main objective of this work was to submit images obtained through the orbital optical remote sensed, of the ASTER sensor, the different image digital processing techniques, in order to identify, to recognize and to characterize the cohesion horizons soil of Coastal Tableland of Bahia, using as identification criteria, the soil moisture contents . The work was developed in an area of 2.475km2 approximately, where an area of reference of 29km2 is inserted, situated in Esplanada city of, where soil of the same class prevail (Yellow and Grey Podzólicos) but differentiated in predominate units that possess diverse cohesion degrees , with texture that varies of sandy the loamy. An only ASTER scene was used, under which it was extracted eighty samples to determine the relationship between the the soil moisture contents and the different images digital images processing techniques. Twenty-six techniques of distinction had been carried through (principal components analysis, Tasseled Cap Transformation, NDVI, NDMI, SAVI and twenty bands ratio on the ASTER sensor bands), beyond the application of a supervised classification (Maximum Likelihood method), with threshold of 95% acceptance. The results had demonstrated that the seventh principal component is the best product to map the cohesion horizons presence and to identify the soil moisture contents; the NDMI, the SAVI and the Wetness obtained through the Tasseled Cap Transformation have a similar behavior, but with less evidences relating the results and, the ratio bands tested, the best results had been those found between bands 1 to 8 and bands 3 to 8.

No trabalho estuda-se o crescimento de trincas em carga monotônica e cíclica nos casos de materiais quase-frágeis, introduzindo uma lei de dano cíclico. Revisam-se conceitos sobre modelos coesivos, leis de carga-descarga, leis de evolução de dano e efeito de escala. É seguido o modelo coesivo irreversível proposto por Wang e Siegmund (2006). Em particular se dá ênfase aos efeitos de escala não estatísticos. O modelo de zona coesiva irreversível apresenta uma formulação de dano e considera carregamento em fadiga. Quando o tamanho estrutural é reduzido (ou as trinca se extendem), a fratura por fadiga não mais ocorre por propagação de trinca, mas sim por uma decoesão uniforme. O objetivo desde trabalho é implementar este modelo e verificar sua potencialidade na captura de efeitos de escala, comparando com experimentos e dados disponíveis na literatura. / At present work is intended to study crack growth in cyclic and monotonic loading in the case of quasi-brittle materials, introducing a damage mechanism, is reviewed concepts of cohesive models, loading-unloading laws, damage evolution laws and effect of scale. The irreversible cohesive zone model proposed by Wang e Siegmund (2006) is followed. In particular emphasizes in the not statistical size effects. The irreversible cohesive zone model, presents a damage formulation and considers fatigue loading. It is demonstrated in this study that, when the structure size is reduced (or extend cracks), the fatigue fracture no longer occurs by crack propagation, then occurs by uniform decohesion . The objetive of this work is implementing this model and verify its capability to capture the scale effect compared with experiments and data available in literature.

Advances in dynamic fracture modelling have become more frequent due to increases in computer speed, meaning that its application to industrial problems has become viable. From this, the author has reviewed current literature in terms of graphite material properties, structural dynamics, fracture mechanics and modelling methodologies to be able to address operational issues related to the ageing of Advanced Gas-cooled Reactor (AGR) cores. In particular, the experimentally observed Prompt Secondary Cracking (PSC) of graphite moderator bricks which has yet to be observed within operational reactors, with the objective of supporting their plant life extension. A method known as eXtended Finite Element Method with Cohesive Zones (XCZM) was developed within Code_Aster open-source FEM software. This enabled the incorporation of velocity toughening, irradiation-induced material degradation effects and multiple 3D dynamic crack initiations, propagations and arrests into a single model, which covers the major known attributes of the PSC mechanism. Whilst developing XCZM, several publications were produced. This started with first demonstrating XCZM's ability to model the PSC mechanism in 2D and consequently that methane holes have a noticeable effect on crack propagation speeds. Following on from this, XCZM was benchmarked in 2D against literature experiments and available model data which consequently highlighted that velocity toughening was an integral feature in producing energetically correct fracture speeds. Leading on from this, XCZM was taken into 3D and demonstrated that it produced experimentally observed bifurcation angle from a literature example. This meant that when a 3D graphite brick was modelled that the crack profile was equivalent to an accepted quasi-static profile. As a consequence of this validation, the XCZM approach was able to model PSC and give insight into features that could not be investigated previously including: finer-scale heterogeneous effects on a dynamic crack profile, comparison between Primary and Secondary crack profiles and also, 3D crack interaction with a methane hole, including insight into possible crack arrest. XCZM was shown to improve upon previous 2D models of experiments that showed the plausibility of PSC; this was achieved by eliminating the need for user intervention and also incorporation of irradiation damage effects through User-defined Material properties (UMAT). Finally, while applying XCZM to a full-scale 3D graphite brick including reactor effects, it was shown that PSC is likely to occur under LEFM assumptions and that the Secondary crack initiates before the Primary crack arrests axially meaning that modal analysis would not be able to fully model PSC.

To support the trust in the design development of adhesively bonded joints, it is important to precisely predict their mechanical failure load. A numerical simulation model with a two-dimensional linear elastic cohesive zone model using a combination of a soft and a stiff adhesive is developed to optimize the strength of a lap-joint. Separation under mixed-mode conditions (normal and shear direction) is considered. By varying the length of the adhesives, the fracture load is optimized. The results obtained from the numerical experiments show an improvement in strength.

In urban areas, vibrations generated by pile driving often affect the neighboring properties vulnerable to ground shaking. These vibrations may cause damage to surrounding structures either by shaking the ground or by causing settlement of the soil beneath foundations in the proximity of pile driving. It is important to distinguish between the conditions under which the vibrations will cause damage and those under which vibrations are tolerable. The numerical studies on the analysis of pile driving have mostly focused on assessing the driving efficiency and the bearing capacity of dynamically loaded piles. A limited number of studies included the study of ground vibrations due to pile driving and its effects on adjacent structures. However, the factors affecting the ground vibrations in soils such as the nonlinear constitutive behavior of soil, soil-pile interaction and penetration depth of the pile have not been clearly identified. The objective of this research is to implement a numerical method to simulate dynamic loading of a single pile, and study the factors influencing the stress wave propagation in the soil surrounding the pile. The thesis is comprised of two main analyses: (1) the static analysis of a pile in which the phenomenon of static consolidation is studied, and (2) the dynamic analysis of a pile in which pile driving and ground vibrations are studied. In the static analysis, the load capacity of a single pile is investigated. The results from the finite element method are compared with widely recognized theoretical methods. The theoretical methods that are used to estimate the end bearing capacities are: (1) General Formula, (2) Vesic's Method, (3) Janbu's Method, (4) Meyerhof's Method, and (5) Coyle & Castello's Method. The estimation of skin friction resistance (shaft capacity) of single piles is performed using the (1) Alpha method, (2) Beta method, and (3) Lambda method. Two numerical applications are performed to predict the load capacity of single piles in normally consolidated clays. It is observed that the model with no slippage at the interface predicts almost twice as much load capacity as the model with interface. In regards with the end bearing capacities, Coyle & Castello's method is found to be most conservative followed by the finite element method, the Janbu's method, the Meyerhof's method, and finally the Vesic's method. In respect to skin friction resistance, the finite element is found to be the most conservative method, followed by the Beta, the Lambda, and the Alpha method. In the dynamic analysis, the amplitudes of ground vibrations are investigated based on the variation of: (1) the soil type, (2) the pile embedment length and (3) the released hammer energy. In the first analysis, five types of soils - loose and dense sands and, soft, medium stiff, and stiff clays - are modeled. The highest vibration amplitude is calculated for the loose sand with a peak particle velocity (PPV) of 10.0 mm/s followed by the dense sand with a PPV of around 4.0 mm/s. Among the clay types, the vibrations are higher for the stiffer clay in the near field, which is 9 m (half a pile length) or less away from the pile. In the second analysis, three different embedment lengths - full, half, and quarter pile length - are modeled. It is found that the quarter embedded piles produce greater vibration amplitudes as compared to the half and fully embedded piles. Larger amplitudes of vibrations are encountered on the ground surface for shorter pile embedment lengths. In the third analysis, three different impact forces consisting of 2,000 kN (F), 6,000 kN (3F) and 10,000 kN (5F) are applied on the pile head. It is concluded that increase in hammer energy causes increase in the peak particle velocities.

A new model of the erosion by water of cohesive soils is developed using physical principles. The theoretical framework which is developed recognises the changing nature of the eroding surface of a soil. Raindrop impact and overland flow are considered to act upon a soil surface so removing soil from the cohesive original (or parent) soil. Once this soil enters the overland flow, either as aggregates or primary particles, it is considered to return to the soil bed, from which it may be re-removed. The development of a deposited layer makes it necessary to distinguish between processes removing sediment from the original soil and those processes removing the deposited layer. This layer, being formed by the relatively gentle action of deposition during the current erosion event, is presumed cohesionless. The physical properties of the original soil and the deposited layer are considered to be very different. The development of two experimental apparatus, a rainfall/runoff simulator and a settling tube for the measurement of aggregate settling velocities, is first described. Experimental investigations, using these apparatus, and field observations to inform the description of the erosion and deposition processes, are then presented. The processes by which rainfall impact removes sediment from the original soil and the deposited layer are termed rainfall detachment and rainfall re-detachment respectively. Initially, descriptions of these processes in the presence of deposition, are combined in a model describing net rainfall detachment when removal of sediment from the flow bed by overland flow is not occurring. The developriient of the deposited layer is considered both quantitatively and qualitatively. The solution of the equation describing mass conservation is then given for the equilibrium situation when the mass of the deposited layer, and therefore the sediment concentration, is constant with respect to time. The processes by which overland flow removes sediment from the original soil and the deposited layer are termed entrainment and re-entrainment. The work done by the process of entrainment is considered to be done wholly against the cohesive strength of the original soil. In contrast to the process of entrainment, the work done in re-entraining sediment from the deposited layer is considered only to be done against gravity. The resulting description of these processes is then combined with the previous descriptions of rainfall detachment, rainfall re-detachment and deposition and with the equation describing the conservation of mass of sediment within any arbitary number of size (or settling velocity) classes. A plane geometry model Is developed in which the surface water flow is considered to be uniformily distributed across a plane slope on which all processes act. When the mass of the deposited layer is steady, two possible forms of equilibrium are shown to exist. When the coverage of the original soil by deposited layer is partial, the sediment concentration is limited by the removal of the cohesive original soil by entrainment and rainfall detachment, in the presence of deposition. This situation is termed 'source limiting' and is shown to provide a lower limit to sediment concentration. When the coverage of the deposited layer is complete so that entrainment and rainfall detachment of the original soil are considered not to occur, then the ability of the erosive agents to re-entrain and re-detach sediment in the presence of deposition limits sediment concentration. This situation, termed 'transport limiting', is shown to provide a practical upper limit to sediment concentration. This plane geometry flow model is followed by a revised model in which all processes are considered to occur but the flow of water on a plane surface is modified by the formation of rills. In this 'detailed geometry model' the spatial distribution of the erosive agents is shown to have a marked influence on the resulting processes and sediment concentrations. A potential description of the sediment transport across a change in land slope is also developed. Finally, a discussion of this new modelling approach is presented in which the conceptual developments of this thesis are considered and future developments are suggested. This discussion also includes a comparison of the outcomes of this new work with similar erosion models.

Advanced composites are playing a rapidly increasing role in all fields of material and structural related engineering practices. Damage tolerance analysis must be a critical integral part of composite structural design. The predictive capabilities of existing models have met with limited success because they typically can not account for multiple damage evolution and their coupling. As a result, current composite design is heavily dependent upon lengthy and costly test programs and empirical design methods. There is an urgent need for efficient numerical tools that are capable of analyzing the progressive failure caused by nonlinearly coupled, multiple damage evolution in composite materials. Such numerical tools are a necessity in achieving virtual testing of composites and other heterogeneous materials. In this thesis, an advanced finite element method named augmented finite element method (A-FEM) has been developed. This method is capable of incorporating nonlinear cohesive damage descriptions for major damage modes observed in composite materials. It also allows for arbitrary nucleation and propagation of such cohesive damages upon satisfactory of prescribed initiation and propagation criterion. Major advantages of the A-FEM include: 1) arbitrary cohesive cracking without the need of remeshing; 2) full compatibility with existing FEM packages; and 3) easy inclusion of intra-element material heterogeneity. The numerical capabilities of the A-FEM have been demonstrated through direct comparisons between prediction results and experimental observations of typical composite tests including 3-point bending of unidirectional laminates, open-hole tension of quasi-isotropic laminates, and double-notched tension of orthogonal laminates. In all these tests, A-FEM can predict not only the qualitative damage patterns but also quantitatively the nonlinear stress-strain curves and other history-dependent results. The excellent numerical capability of A-FEM in accurately accounting for multiple cracking in composites enables the use of A-FEM as a multi-scale numerical platform for virtual testing of composites. This has been demonstrated by a series of representative volume element (RVE) analyses which explicitly considered microscopic matrix cracking and fiber matrix interface debonding. In these cases the A-FEM successfully predicted the cohesive failure descriptions which can be used for macroscopic composite failure analyses. At the sublaminate scale, the problem of a transverse tunneling crack and its induced local delamination has been studied in detail. Two major coupling modes, which depends on the mode-I to mode-II fracture toughness ratio and cohesive strength values, has been revealed and their implications in composite engineering has been fully discussed. Finally, future improvements to the A-FEM so that it can be more powerful in serving as a numerical platform for virtual testing of composites are discussed.

Finding subgroups within social networks is important for understanding and possibly influencing the formation and evolution of online communities. This thesis addresses the problem of finding cohesive subgroups within social networks inferred from online interactions. The dissertation begins with a review of relevant literature and identifies existing methods for finding cohesive subgroups. This is followed by the introduction of the SCAN method for identifying subgroups in online interaction. The SCAN (Social Cohesion Analysis of Networks) methodology involves three steps: selecting the possible members (Select), collecting those members into possible subgroups (Collect) and choosing the cohesive subgroups over time (Choose). Social network analysis, clustering and partitioning, and similarity measurement are then used to implement each of the steps. Two further case studies are presented, one involving the TorCamp Google group and the other involving YouTube vaccination videos, to demonstrate how the methodology works in practice. Behavioural measures of Sense of Community and the Social Network Questionnaire are correlated with the SCAN method to demonstrate that the SCAN approach can find meaningful subgroups. Additional empirical findings are reported. Betweenness centrality appears to be a useful filter for screening potential subgroup members, and members of cohesive subgroups have stronger community membership and influence than others. Subgroups identified using weighted average hierarchical clustering are consistent with the subgroups identified using the more computationally expensive k-plex analysis. The value of similarity measurement in assessing subgroup cohesion over time is demonstrated, and possible problems with the use of Q modularity to identify cohesive subgroups are noted. Applications of this research to marketing, expertise location, and information search are also discussed.