Dėl sąveikos su armatūros strypais iš esmės pakinta tempiamojo betono fizikinis įtempių ir deformacijų būvis, todėl taikyti vientiso tempiamojo betono įtempių ir deformacijų diagramas negalima. Armuotojo betono atveju šios diagramos yra pakeičiamos vadinamosiomis tempiamojo sustandėjimo įtempių ir deformacijų diagramomis, tačiau iki šiol nėra priimta bendro metodo, kaip jas reikėtų apskaičiuoti. Baigiamojo magistro darbo tikslas – pasiūlyti tempiamojo betono įtempių ir deformacijų fizikinį modelį. Baigiamajame darbe atlikta kritinė literatūros šaltinių betono tempiamojo sustandėjimo tematika analizė. Atlikti tempiamųjų gelžbetoninių elementų eksperimentiniai ir skaitiniai tyrimai. Literatūros šaltiniuose aptiktų eksperimentinių tyrimų rezultatai palyginti su atliktais eksperimentiniais ir skaitiniais tyrimais. Pagal atrinktus duomenis išvestas tempiamojo betono įtempių ir deformacijų fizikinis modelis bei atlikta jo statistinė analizė. Baigiamąjį magistro darbą sudaro įvadas, trys skyriai, išvados bei literatūros sąrašas. Darbo apimtis – 64 puslapiai. Tekste pateikta 50 formulių, 41 paveikslas ir 10 lentelių. Rašant darbą remtasi 30 literatūros šaltinių. / Interaction between concrete and reinforcement changes the way tensile concrete behaves thus the stress–strain relationship for solid tensile concrete cannot be applied anymore. In the case of reinforced concrete, these graphs are changed with so–called tension stiffening diagrams but until now there has been no confirmed method that would allow us to determine it. The aim of the master thesis is to propose a physical model for stress–strain relationship of tensile concrete. In the master thesis a close analysis of a number of scientific articles about tension stiffening has been done. Experimental and numerical research for tensile reinforced concrete members has been performed. The data found in scientific articles has been compared with the data of experimental and numerical research. Based on the results of experimental research a physical model for stress–strain relationship of tensile concrete has been proposed, also a statistical accuracy analysis of the model has been performed. The master thesis consists of introduction, three chapters, conclusions and references. Total number of pages is 64. Thesis includes 50 equations, 41 figures and 10 tables. Paper refers to 30 scientific source materials.

In the present work, the effect of variation in specimen orientation and heat treatment on the Stress Corrosion Cracking (SCC) susceptibility of 7050 aluminum alloy was investigated in 3,5% NaCl solution and under freely corroding conditions. For this purpose, Constant Extension Rate Tests (CERT) was performed on precracked Compact Tension (CT) specimens and the Direct Current Potential Drop technique was applied to measure the crack lengths. In addition to crack length versus time curves, the relationship between the crack growth rate and the stress intensity factor was determined. Fractographic analysis was utilized extensively to support the findings related with basic mechanisms of cracking. The alloy was found to be in the most susceptible state in the SL orientation, in which the crack propagation direction is parallel to the rolling direction. The resistance to SCC is higher in the TS but at maximum in LT orientation where the loading direction is parallel to the rolling direction. In the peak aging treatment, T651, alloy is susceptible to SCC in SL orientation. When the over aging treatment, T7651, is applied the resistance is increased and the two step over aging treatment, T73651, has resulted in an additional improvement in this orientation. On the other hand, the alloy showed higher resistance to SCC in TS and LT orientations in T651 condition compared to the T7651 and T73651 treatments. In these orientations, the alloy is less susceptible in T73651 condition than in T7651 treatment.

Hot cracking is a serious problem that encounters during welding of aluminium-magnesium alloys. In the present study, solidification and liquation type of hot cracks in weld metal and the heat-affected zones of 5086-H32 aluminium alloy were investigated by using Modified Varestraint Test (MVT) with TIG-AC and TIG-DC welding. With determining the size, type and number of cracks, a relation was established between welding line energy and strain on the hot crack formation. This information was used to determine the hot crack safe parameter ranges. The hot cracking tendency as a function of applied parameters were discussed in the frame of temperature fields around the moving heat source. Moreover, the characteristic hot crack locations on the 5086-H32 MVT specimens were generalized. The results of the study indicated that the increase in line energy and strain increased the hot cracking tendency of the specified aluminium alloy. In the low line energy range, the main hot cracking mechanism is the solidification cracking which could be overcome by the use of a suitable filler material. At high line energy range, due to the increased amount of interdendritic liquid, the amount of solidification cracking decreases by healing mechanism. However, because of the enlarged-temperature-field around the weld zone, fraction of HAZ cracking increases. The comparison between the hot cracking tendencies in low and high line energies indicates that the low line energy ranges with low augmented strains resulted in hot crack safer parameters.

Laminated carbon/epoxy composite structures are increasingly used in the aerospace industries. Low weight, elastic tailoring, and high durability make the composite materials well suited for replacement of conventional metallic structures. However the difficulty to capture structural failure phenomena is a significant barrier to more extensive use of laminated composites. Predictions are challenging because matrix (resin) dominated failure mechanisms such as delaminations and matrix cracking contribute to the structural failure in addition to fiber-dominated failures. A key to rigorous failure predictions for composites is availability of measurements to quantify structural model parameters including matrix-dominated stress-strain relations and failure criteria. Novel techniques for measurement of nonlinear interlaminar constitutive properties in tape composites have been recently developed at Georgia Institute of Technology. Development of methods for accurate predictions of failure in carbon/epoxy tape laminate configurations with complex lay-ups is the main focus of this work. Failures through delamination and matrix cracking are considered. The first objective of this effort is to implement nonlinear interlaminar shear stress-strain relations for IM7/8552 carbon/epoxy tape in ABAQUS finite element models and validate structural delamination failure predictions with tests. Test data for composite configurations with wavy fibers confirm that nonlinear interlaminar shear stress-strain response enables accurate failure prediction. The problem of the presence of porosity and its influence on failure was noted. The second objective is to assess the ability to simulate initiation and propagation of matrix-ply cracking. Failure models for IM7/8552 carbon/epoxy tape open-hole tensile coupons are built and validated.

The goal of this research was to investigate the tensile fatigue behavior of a carbon fiber / epoxy composite material. Specifically, the stress levels at which cracks initiated in static and fatigue loading in the 90 degree plies of a "quasi-cross ply layup" [0/905]S was investigated. For layups which contain them, cracks in composite laminates initiate and propagate from 90 degree plies (including the ubiquitous "quasi-isotropic layup" 0/±45/90). Thus, this work provides valuable insight into the fatigue behavior of the plies which originate fatigue damage. Unidirectional off-axis 90 degree and 10 degree specimens were also tested, but the bulk of testing was done on the cross-ply laminates. The project sponsors, Boeing, were in the process of extending a failure model to the case of fatigue. The body of work presented here provided empirical data for that effort. Several different inspection techniques were used to investigate for cracking in the 90 degree plies, including: x-ray images, edge replicates, dye penetrants, and optical microscopy. Plots of the stress level at which crack initiation occurred will be presented, as well as images illustrating damage development in these layups. Comparisons are made to the experimental results of other investigations of this type of layup. Explorations of the effect of R-ratio (including R = 0.1 and 0.5), loading frequency (including 3, 10, and 30 Hz), and surface roughness (hand polished specimen edges to 1500 grit smoothness) on fatigue crack initiation were also performed. For the most damaging case (10 Hz, R = 0.1, no polishing), the crack initiation strain (0.00276) was one half of the strain at which cracks initiated in static monotonic loading (0.0054), and was 16% of the cross-ply specimen's (0 degree fiber dominated) ultimate strain value of (0.018).

The dependence on oil and the fact that petroleum conventional reservoirs are becoming depleted direct attentions toward unconventional-and harder to access-reservoirs. Among those, heavy and extremely heavy oil reservoirs and tar sands form a considerable portion of all petroleum resources. Conventional thermal and thermocatalytic refining methods are not affordable choices in some cases, as they demand a considerable energy investment. On the other hand, electron irradiation, as a novel technology, provides more promising results in heavy oil upgrading. Electron irradiation, as a method of delivering energy to a target molecule, ensures that most of the energy is absorbed by the molecule electronic structure. This leads to a very efficient generation of reactive species, which are capable of initiating chemical reactions. In contrast, when using thermal energy, only a small portion of the energy goes into the electronic structure of the molecule; therefore, bond rupture will result only at high energy levels. The effect of electron irradiation on different heavy petroleum fluids is investigated in this study. Radiation-induced physical and chemical changes of the fluids have been evaluated using different analytical instruments. The results show that high energy electron particles intensify the cracking of heavy hydrocarbons into lighter species. Moreover, irradiation is seen to limit any post-treatment reactions, providing products of higher stability. Depending on the characteristics of the radiolyzed fluid, irradiation may change the distribution pattern of the products, or the radiolysis process may follow the same mechanism that thermal cracking does. In addition to that, we have studied the effectiveness of different influencing variables such as reaction temperature, absorbed dose values, and additives on radiolytic reactions. More specifically, the following subjects are addressed in this study: *Radiation?induced chain reactions of heavy petroleum fluids *Complex hydrocarbon cracking mechanism *High and low temperature radiolysis *Synergetic effects of different chemical additives in radiolysis reactions *Time stability of radiation products

Le matériau principal de cette étude est l’acier inoxydable austénitique 316L(N) (X2CrNiMo17-12-2 à teneur en azote contrôlée) envisagé dans la conception de la cuve et des structures du circuit primaire des futurs réacteurs de quatrième génération refroidis au sodium. Pour assembler des composants de forte épaisseur, il faut réaliser des soudages multipasses avec métal d'apport. Lors du soudage, il a parfois été constaté des défauts de fissuration à chaud de solidification au refroidissement dans la zone pâteuse, près du bain de fusion. Ces fissures sont des décohésions du matériau apparaissant à haut température le long des joints de grains lorsque la déformation dépasse un seuil critique. Il est donc nécessaire de prévenir ce risque en utilisant un critère de fissuration à chaud. L'approche utilisée dans cette étude est double : développer un essai de fissuration à chaud à chargement extérieur, puis simuler numériquement ces expériences pour déterminer un seuil critique en déformation en utilisant un critère proposé par Kerrouault. Une version améliorée d’un essai de fissuration à chaud (Controlled Restraint Weldability (CRW) test) a été proposé dans cette étude afin d'analyser la susceptibilité à la fissuration de solidification du matériau 316L(N) et d’un métal d'apport de nuance Thermanit 19-15H. L'objectif de ce test est, en fonction de l'intensité du chargement extérieur, d'amorcer une fissure dans un régime thermique établi, puis d’arrêter la propagation de cette fissure si les conditions thermomécaniques locales sont remplies. Le modèle de comportement du matériau choisi est une loi élasto-visco-plastique à écrouissage mixte. Des essais thermomécaniques sur un simulateur Gleeble ont été réalisés à haute température afin d'identifier et d’améliorer la loi de comportement du matériau 316L(N). Le grossissement des grains dans la zone affectée thermiquement a été modélisé et intégré dans ce modèle. Les intervalles de fusion et de solidification du matériau 316L(N) ont été déterminés par des essais ATD (Analyse Thermique Différentielle). Des analyses des microstructures de solidification ont été également menées afin de mieux comprendre le phénomène de fissuration à chaud. Certains essais CRW ont ensuite été modélisés et simulés par éléments finis en utilisant les logiciels Cast3M et Abaqus afin valider le critère de fissuration à chaud et de déterminer un seuil critique de fissuration pour l'acier 316L(N). / The austenitic stainless steel AISI 316L(N) (X2CrNiMo17-12-2) with controlled nitrogen content is widely used for manufacture of vessel and primary circuit structures of the 4th Generation sodium- cooled fast reactors. Multi-pass welds with an appropriate filler metal is used to assemble thick components. Solidification cracks may occur in the mushy zone near the melting weld poor during solidification when a liquid film is distributed along grains boundaries and interdendritic regions and the shrinkage strains across the boundaries cannot be accommodated. It is therefore necessary to prevent this defect using a hot cracking criterion. The approach used in this study is to initiate experimentally a hot crack by a weldability test, and then to simulate these tests to identify a critical strain using a hot crack criterion for the prediction of solidification cracking. Therefore, a hot cracking test (Controlled Restraint Weldability (CRW) test) is proposed in the present study to analyze the susceptibility to hot cracking for base metal 316L(N) and its filler metal 19-15H Thermanit grade. This test is designed to initiate a hot crack in thermal steady state, and then to stop the crack once the local thermomechanical conditions are met. The initiation and stop of the crack depend on external mechanical preload. The material constitutive equations chosen for the material is a visco-plastic model with isotropic and kinematic hardening. The Gleeble thermomechanical tests have been performed at high temperature in order to identify material parameters. The increase of the grain size in the thermally affected zone was modeled and integrated into constitutive equations. The temperature range of melting and solidification of 316L(N) were determine by using the Differential Thermal Analysis (DTA). The analysis of the solidification microstructures were also carried out in order to better understand the phenomenon of hot cracking. Some CRW tests were then simulated by finite element method using the Cast3M and Abaqus software in order to valid the hot cracking criterion and to determine a thermomechanical criterion of hot cracking for 316L(N).

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-08-17T19:08:47Z No. of bitstreams: 1 DANIELLE DE LIMA VIEIRA – DISSERTAÇÃO (PPGEM) 2017.pdf: 2977283 bytes, checksum: 76868ac7a0711cd9560eee5a78b8bf43 (MD5) / Made available in DSpace on 2018-08-17T19:08:47Z (GMT). No. of bitstreams: 1 DANIELLE DE LIMA VIEIRA – DISSERTAÇÃO (PPGEM) 2017.pdf: 2977283 bytes, checksum: 76868ac7a0711cd9560eee5a78b8bf43 (MD5) Previous issue date: 2017-09 / Na indústria petroquímica e de processamento de petróleo o riser é o principal equipamento da unidade de craqueamento catalítico fluido (FCC), utilizado para o refino de frações pesadas do petróleo. Para o projeto e otimização do riser é essencial compreender a termofluidodinâmica da mistura gás -sólido no seu interior. Neste aspecto a fluidodinâmica computacional (CFD) tem demonstrado ser uma boa alternativa para o estudo de sistemas complexos. Portanto, este trabalho tem como objetivo estudar a termofluidodinâmica de um riser de FCC com alto fluxo, via CFD usando o software comercial Ansys Fluent versão 15. O modelo matemático é baseado na abordagem Euleriana – Euleriana, considerando a Teoria Cinética do Escoamento Granular (KTGF) e o modelo de turbulência de duas equações k - ϵ Disperso. Resultados numéricos dos campos de velocidade, fração volumétrica e pressão das fases gasosa e particulada, a temperatura constante, são apresentados, analisados e comparados com dados de uma planta experimental com 76 mm ID e altura de 10 m, apresentando boa concordância, exceto nas regiões com alta densidade de partículas. Assim, o modelo proposto mostrou-se mais adequado a representação do fluxo em regiões e condições operacionais que resultam em menores concentrações de partículas (menor fluxo de sólidos e/ou maior vazão do gás). / In the petrochemical and oil processing industry riser is the main equipment of the fluid catalytic cracking (FCC) unit, used for the refining of heavy petroleum fractions. For design and optimization of riser, it is essential to understand the thermo fluid dynamics of the gas-solid mixture inside. In this respect, computational fluid dynamics (CFD) has been shown to be a good alternative for the study of complex systems. Therefore, this work aims to study the thermo fluid dynamics of a FCC riser with high flux, via CFD using commercial software Ansys Fluent version 15. The mathematical model is based on the Eulerian - Eulerian approach, considering a Kinetic Theory of Granular Flow (KTGF) and the k - ϵ two equations turbulence model. Numerical results of fields of velocity, volumetric fraction and pressure of the gas and particulate phases, at constant temperature, are presented, analyzed and compared with data of an experimental plant with 76 mm ID and 10 m height, presenting good agreement, except in regions with high particle density. Thus, the proposed model showed better representation of the flow in regions and operating conditions that result in lower particle concentrations (lower solids flow and / or higher gas flow).

Currently there is a clear trend of increased production of heavier oils, as oil reserves with better quality are being depleted. This implies the development of new refining technologies for the processing of these oils in order to maximize the acquisition of liquid fuels that are the main demand of the markets. The main process of refining is the fluidized catalytic cracking (FCC process) that requires an acid catalyst able to crack the hydrocarbon molecules present in the feed. The problem is that the current catalysts, formulated with Y zeolite, which has small pores, do not allow access of large molecules. This project will be studied the synthesis of mesostructure materials from a gel formed by seeds of Y and ZSM-5 zeolites. Therefore, in this project, we studied the synthesis of materials mesoestruturados from a gel formed by seeds of zeolite Y and ZSM-5 which has been submitted or not to adjust the pH to the range of 8-10 by addition of acid. From the physico-chemical characterizations was observed that all samples formed a phase mesoporous MCM-41 type. It was found that the materials synthesized from seeds of zeolite ZSM-5 had evidence of the presence of seeds of the solid mesoporous zeolites, regardless of whether or not samples subjected to pH adjustment. While the materials synthesized from seeds of zeolite Y with only those adjust the gel pH to the range 8 to 10 before the hydrothermal crystallization seeds showed evidence of the X-ray diffractograms and infrared spectra, indicating that the use of gel with lower basicity to forming the mesophase preserves the seeds which were formed in the aging process / Fundação de Amparo a Pesquisa do Estado de Alagoas / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Atualmente há uma tendência clara do aumento da produção de óleos mais pesados, à medida que as reservas com petróleo de melhor qualidade forem sendo exauridas. Isto implica no desenvolvimento de novas tecnologias de refino para o processamento destes óleos, de modo a maximizar a obtenção de combustíveis líquidos que são a principal demanda dos mercados. O principal processo de refino de correntes pesadas é o craqueamento catalítico em leito fluidizado (Processo FCC) que exige um catalisador ácido capaz de “quebrar” as moléculas de hidrocarbonetos presentes na carga. O problema é que os catalisadores atuais, a base de zeólita Y, possui poros pequenos que não permitem o acesso de grandes moléculas. Neste projeto, foi estudada a síntese de materiais mesoestruturados a partir de um gel formado por sementes de zeólitas Y e ZSM-5 que foi submetidos ou não ao ajuste de pH para a faixa de 8-10 pela adição de ácido. A partir das caracterizações físico-químicas foi observado que todas as amostras formaram uma fase mesoporosa do tipo MCM-41. Constatou-se que os materiais sintetizados a partir de sementes de zeólita ZSM-5 apresentaram evidências da presença de sementes de zeólitas no sólido mesoporoso, independentemente das amostras serem ou não submetidas ao ajuste de pH. Enquanto que os materiais sintetizados a partir de sementes de zeólita Y apenas aqueles com ajuste do pH do gel para faixa de 8 a 10 antes da cristalização hidrotérmica mostraram evidência das sementes nos difratogramas de raios X e nos espectros de infravermelho, indicando que a utilização de um gel com menor basicidade na etapa de formação da mesofase, preserva as sementes que foram formadas no processo de envelhecimento (pré-tratamento).

A análise de painéis de concreto armado submetidos a corte puro é um tópico que tem recebido atenção de pesquisadores ao longo dos anos. Isto se deve, principalmente, à dificuldade encontrada na aplicação do carregamento e das condições de vinculação sobre a estrutura. Esta dificuldade é constatada tanto experimentalmente como na análise numérica. O objetivo deste trabalho é apresentar um modelo numérico para simular o comportamento de painéis de concreto simples e de concreto armado submetidos ao corte. Na análise computacional via Elementos Finitos, será utilizado um modelo de fissura incorporada que considera a contribuição da armadura no equilíbrio interno de forças do elemento. Estes modelos se baseiam no conceito de descontinuidades incorporadas dentro de elementos finitos padrão. O modelo incorporado implementado é uma continuação dos trabalhos desenvolvidos por d’Avila (2003) e Brisotto (2006), baseados no modelo de Dvorkin, Cuitiño e Gioia (1990). O modelo de transferência de tensão por aderência de Russo, Zingone e Romano (1990) foi usado por d’Avila para incluir a contribuição da armadura no equilíbrio interno de forças do elemento. Para representar as barras de aço da armadura, é utilizado o modelo incorporado desenvolvido por Elwi e Hrudey (1989) que permite a disposição arbitrária das barras no interior dos elementos de concreto. Os resultados dos ensaios numéricos de painéis de concreto armado submetidos ao corte puro com diferentes taxas de armadura são comparados com os resultados experimentais apresentados por Vecchio (1981). São incluídos dois diferentes modelos de efeito de pino (resistência ao corte das barras da armadura), analisando-se a influência dos mesmos no comportamento dos painéis ensaiados. O efeito do engrenamento dos agregados na fissura também foi estudado. Vários painéis com diferentes formas de ruptura experimental foram simulados, obtendo-se respostas muito boas para a maioria deles. Comparações da resposta tensão tangencial x distorção com e sem efeito de pino foram feitas, verificando-se a grande importância deste efeito na resposta global. / The analysis of reinforced concrete panels submitted to in-plane shear has received the attention of researchers along the years. It is mainly due to the difficulty to simulate the application of the external loads and the structural boundary conditions. The purpose of this work is to present a numerical model to represent reinforced concrete panels submitted to inplane shear. In the computational analysis via Finite Elements, an embedded crack model that considers the inclusion of the reinforcement contribution in the internal force equilibrium of the element is presented. This type of model is based in discontinuities embedded into standard finite elements. The implemented formulation uses the model presented by Dvorkin, Cuitiño and Gioia (1990), which does not have the reinforcement contribution in the element internal equilibrium. The adherence stress transfer model of Russo, Zingone and Romano (1990) is used to include this reinforcement contribution. An embedded model was employed to represent the reinforcement bars, allowing that they can be placed in an independent position and shape in the FEM elements. The numerical results are compared with Vecchio’s work. Also are included two different dowel action models (transversal shear resistance of the bars) and is studied their influence in the panels’ behavior. Panels with different experimental rupture modes were simulated with good responses in the most cases. Comparisons of shear stress x shear strain curve with and without dowel action are performed, showing the importance of this effect on the global response.