This work is a preliminary attempt to study the effect between thermal shock and abrasive wear in WC-Co alloys. This was done by evaluating the thermal shock resistance of a WC-12wt%Co mining grade as a function of temperature, number of thermal shock cycles and making comparisons between the abrasive wear responses of samples subjected to thermal shock and samples not subjected to thermal shock. A furnace was designed for the thermal shock treatments. Abrasive wear tests were performed on a 2-body sliding wear apparatus using 80-grit SiC abrasive paper as a counter-face. Stereo and electron microscopy as well as microprobe techniques were used to analyse the effects of thermal shock. It is confirmed that thermal shock has a negative effect on the wear rate of WC-12wt%Co. The results showed an initial high mass loss rate during abrasive wear testing, which increased with increasing temperature and a decrease in wear rate with time until the wear rates converged for all samples. The surface analysis after thermal shock indicated voids on and below the surface, stained surfaces, a thin oxide layer and the possibility of WC decarburization which accelerated the wear response.

L’objectif de la thèse est la prédiction de la propagation et de l’arrêt de fissure de clivage dans un acier de cuve de type 16MND5 par un critère local en contrainte critique, calculé en pointe de fissure. Les travaux précédents ont montré que le mécanisme de rupture était du clivage,associé à des zones de cisaillement ductile entre les différents plans de fissuration. Ceci explique la dépendance de la contrainte critique de rupture à la vitesse de déformation en pointe de fissure du fait du comportement visqueux des aciers ferritiques aux vitesses de propagation considérées. Cette thèse consiste à optimiser la méthode numérique mise en oeuvre pour simuler la propagation dynamique de fissure, identifier et valider un critère local de propagation et d’arrêt sur des chargements thermomécaniques complexes, rendre compte des trajets de fissuration variés, et approfondir les connaissances sur les micro-mécanismes physiques de la rupture pour renforcer le contenu physique du critère utilisé.L’identification du critère de propagation et d’arrêt a été faite par la simulation numérique des essais de rupture fragile réalisés sur des éprouvettes CT25 à quatre températures (-150°C, -125°C, -100°C et -75°C). La méthode des éléments finis étendus (X-FEM) a été utilisée dans le code de calcul CAST3M pour ces modélisations. Les résultats des analyses en 2D et 3D ont montré que la contrainte critique de rupture augmentait avec la vitesse de déformation plastique et ils ont donc permis d’établir un critère de propagation et d’arrêt basé sur cette contrainte.Une formulation analytique du critère a été développée pour justifier le critère identifié. La contrainte critique du critère a été considérée comme la somme de la contrainte critique de clivage et de la contrainte générée par la déformation des ligaments (ponts de matières résistants sollicités en cisaillement) en arrière du front de la fissure. Afin de quantifier ce phénomène, des mesures de caractérisations des ligaments ont été effectuées sur les faciès de rupture et sur les coupes transversales des éprouvettes. Le profil de contrainte sur les lèvres de la fissure, généré par les ligaments tendant à résister à l’ouverture de la fissure, a été calculé à l’aide de modélisations éléments finis de multifissures représentatives de la géométrie réelle de la fissure observée sur une coupe transversale. Ceci a permis d’obtenir la contribution de l’effort des ligaments à la contrainte critique en pointe de fissure, et de développer ensuite une formulation analytique pour la contrainte critique. La courbe de la formulation analytique présente un très bon accord avec le critère empirique identifié.Afin de tester la pertinence de ce critère, la prédiction de la propagation et de l’arrêt de fissure a d’abord été menée sur des essais isothermes, à la fois sur des éprouvettes CT25 (la fissure étant sollicitée en mode I) et ensuite sur des anneaux fissurés sollicités en mode mixte. Les résultats numériques des prédictions ont présenté une bonne cohérence avec les expériences.Ceci montre la pertinence du critère sous chargement isotherme. Pour étudier la propagation et l’arrêt de fissure sous choc thermique, un essai a ensuite été réalisé sur un anneau fissuré. Le chargement pour l’essai est plus complexe avec un couplage des chargements mécaniques et thermiques. La prédiction par le critère a été effectuée en 2D et en 3D. Les résultats prédits sont de bonne qualité en termes de cinétique de propagation et de longueur de fissure à l’arrêt. Ceci complète la validation du critère sous chargement thermomécanique.En parallèle, des expériences ont été menées sur des éprouvettes CT25 rallongées (de même hauteur qu’une CT25 mais de largeur double), présentant une bifurcation de la trajectoire de la fissure. [...] / The purpose of this PhD study is to predict the propagation and arrest of cleavage cracks in a French PWR vessel steel (16MND5). This is accomplished through use of a local criterion based on the critical stress calculated ahead of crack tip. Previous work has shown that fracture mechanism was cleavage associated with the ductile shear zone between the different planes of cracking. Thus, the critical stress at crack tip depends on stain rate. This thesis consists ofnumerical optimization, identification and validation of a local criterion based on experimentswhich have complex thermomechanical loads. The criterion accounts for various crack paths,deepening the knowledge about micro mechanisms during crack propagation in order to justify the established criterion.Criterion identification was carried out by using numerical simulations of tension tests performed on CT (Compact Tension) specimens at four different temperatures (-150°C, -125°C,-100°C and -75°C). The eXtended Finite Element Method (X-FEM) was used in CAST3M FEsoftware to model dynamic crack propagation and arrest. The analysis results in 2D and 3Dshowed that the critical stress at crack tip increased with the inelastic strain rate. Therefore, acriterion based on the critical stress was established. An analytical model was developed to justify the identified criterion. The critical stress givenby the local criterion was considered as the sum of the critical cleavage stress and the stress generated by the deformation of ligaments behind the crack tip. In order to quantify this phenomenon, measurements of ligaments’ characteristics have been performed on facture surfaces and on cross-sections of the specimens. The stress profile of the crack lips generated by ligaments was calculated by modeling of multi-cracks on specimen’s cross-section. The contribution of stress generated by ligaments to the critical stress at crack tip was obtained with this method, and then the analytical model of the critical stress was developed. The results of this analytical model is in good agreement with the empirical criterion identified.In order to test the validity of the identified criterion, the prediction of the crack propagation and arrest by the criterion was first performed for isothermal tests. It was performed both onCT25 specimens (crack was solicited in mode I) and on ring specimens in mixed mode loadingwhich were carried out at three different temperatures. The numerical results of prediction were in good agreement with experiments. They showed the validity of the criterion for experiments under isothermal loading for two different specimen geometries. In order to test the validity of criterion for the situation of thermal shock, experiments were carried out on ring specimens. At first, one ring specimen was cooled down to -150°C, and then hot water (≈90°C) was injected through the inner side of the ring specimen. At the same time of thermal shock, this specimen was submitted to a mechanical compressive loading (-750kN). The prediction of crack propagation and arrest by the criterion for this situation was calculated in both 2D and 3D. The predicted results were in good agreement with experiments for both crack speed and crack length. This confirmed that the criterion is relevant to predict the crack propagation and arrest for thermal shock.In parallel, some experiments were performed on extended CT25 specimens (same height but double the width of the CT25 specimen). The crack path on this kind of specimen was curved.A statistical effect by a random selection in the propagation direction was introduced to takeinto account the instability during the crack propagation. The numerical results correctlyreproduce the curvature and the dispersion of the crack paths.

Este trabalho comparou as propriedades termomecânicas de concretos refratários comerciais para aplicação em conjunto de porta ventos de alto-forno. Dez composições diferentes de concretos refratários à base de alta alumina, alta mulita e alta andaluzita foram caracterizados. Para identificar e quantificar a composição e a microestrutura dos refratários foram utilizadas técnicas de espectroscopia de fluorescência de raios X (FRX), difratometria de raios X (DRX) qualitativa e quantitativa, microscopia eletrônica de varredura com análise de energia dispersiva de raios X (MEV-EDS), massa especifica aparente e porosidade aparente (MEA/Pa). A caracterização termomecânica foi realizada com ensaios de flexão três pontos, propagação de trinca para cálculo da energia de fratura com entalhe chevron, módulo de elasticidade dinâmico, coeficiente de Poisson e o cálculo do coeficiente de expansão térmica utilizando a regra das misturas. Para compreender o dano causado pelo choque térmico ensaios cíclicos de choque térmico foram feitos seguidos de analises de módulo de elasticidade por técnica de excitação por impulso seguido do módulo de ruptura por flexão três-pontos. Os parâmetros de resistência ao choque térmico (R e R´) e os parâmetros de resistência ao dano por choque térmico (R´´´, R´´´´ e Rst) foram calculados. Os resultados de ciclagem térmica e os parâmetros de resistência ao choque térmico mostram que para os concretos analisados, todos os materiais tem nucleação de trincas para temperaturas iguais ou superiores a 1100°C. Os parâmetros de resistência ao dano por choque térmico corroboram com os resultados das análises de MEV. O concreto D1 apresentou a melhor combinação de resistência ao dano por choque térmico e baixa condutividade térmica, propriedades requeridas para a aplicação em conjunto de porta ventos de alto-forno. Por fim é mostrado que as análises de ciclagem térmica devem ser analisadas cuidadosamente com foco na aplicação dos concretos e no desempenho da microestrutura do material, visto que as propriedades termomecânicas são caracterizadas por indiretamente por diferentes técnicas e portanto vários parâmetros precisam ser considerados. O concreto D1 apresentou boa resistência ao dano por choque térmico e baixa condutividade térmica e portanto possui o melhor desempenho para a aplicação em conjunto de porta ventos. / This work compares the thermomechanical properties of commercial castable refractories for blast furnace blowpipe application. Ten different compositions of commercial castable refractories with compositions of high alumina, high mullite, and high andalusite were characterized. In order to identify and quantify the composition and microstructure of the castables, X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning eléctron microscopy with energy dispersive spectrum (SEM-EDS), bulk density, and apparent porosity were used. The thermomechanical characterization was performed through threepoint flexural strength, work of fracture through crack propagation in notched samples, dynamic elasticity modulus, Poisson ratio, and the calculation of the thermal expansion coefficient using the mix law. Cyclic thermal shocks at 1100°C were realized in order to characterize the materials under thermal shock damage environment followed by elasticity modulus, modulus of rupture, and SEM analysis. The parameters for thermal shock resistance (R e R´) and the parameters for thermal shock damage resistance (R´´´, R´´´´ e Rst) were calculated. The thermal shock cycling tests and the thermal shock resistance correlated and showed that all castables had crack nucleation after a thermal shock of 1100°C or higher. The thermal shock damage parameters and the SEM analysis correlate. Castable D1 showed high resistance to thermal shock damage and lower thermal conductivity, which are required properties for the blast-furnace blowpipe application. Thermal shock cycling tests performed on castables should therefore be examined not only through mechanical testing, but also through microstructure analysis. Castable D1 showed high thermal shock damage resistance and lower value of thermal conductivity; therefore, it is the best castable for blast furnace blowpipe application among the samples tested.

Neste trabalho enfoca-se o efeito da variação térmica na degradação da aderência de revestimentos de argamassa. Dentre os diversos fatores que condicionam a aderência dos revestimentos de argamassa, destaca-se aqui o cenário crítico definido pela presença de macrodefeitos na interface revestimento-base e também pela intensidade com que ocorre a variação de temperatura, encontrando-se uma situação extrema quando da ocorrência do choque térmico. Assim, o objetivo desta pesquisa é avaliar, de maneira experimental, o efeito de sucessivos ciclos de choque térmico na resistência de aderência de revestimentos de argamassa, em duas situações limites de taxa de macro-defeitos no contato entre o revestimento e a base e para duas distintas argamassas. Para dar suporte ao trabalho experimental foi elaborado um modelo computacional paramétrico, utilizando modelagem com elementos finitos. Com ele foi possível obter a distribuição de temperaturas, bem como as deformações e tensões geradas no revestimento, variando-se a intensidade do contato revestimento-base e alterandose as características da argamassa de revestimento. A partir de então, definiram-se as variáveis de maior influência e a geometria dos corpos prova, bem como as condições de contorno a serem utilizadas no programa experimental. O programa experimental foi desenvolvido em duas etapas: uma etapa piloto e outra definitiva. Para sua realização foram desenvolvidos e construídos os equipamentos para execução e controle dos ensaios cíclicos de choque térmico. Finalmente, foram realizados ensaios de resistência de aderência do revestimento e avaliados os efeitos de cada uma das variáveis estudadas, empregando-se suporte estatístico. Pelos resultados pode-se comprovar que os macro-defeitos na interface revestimento-base provocam diminuição na resistência de aderência a qual é agravada quando da ocorrência de cíclicos choques térmicos, ocorrendo a situação mais crítica para os revestimentos com maior módulo de elasticidade. / The present study focus on thermal variation effects on mortar rendering bonding degradation. Among the variety of factors that condition the bonding of mortar renderings, a critic scenario can be defined by the existence of interface macro-flaws between mortar rendering and substrate, and by the thermal variation intensity in the extreme situation of thermal shock. This research aims to experimentally evaluate the effects of continuous thermal shock cycles on the bonding strength of mortar renderings in two macro-flaw rate extreme situations in the contact surface between mortar rendering and substrate for two types of mortar. A parametric model based on finite element analysis has been developed to support the experimental work, which allowed ascertaining temperature profile as well as stress and strain distribution in the mortar rendering by changing the macro-flaws rate and mortar rendering properties. As a result, one could define the variables with higher influence and test panel geometry, as well as the boundary conditions to be used in the experimental program. The experimental program has been performed first in pilot scale and then in a definite stage, which required designing and building of equipment for the execution and control of cyclic thermal shock laboratory tests. Furthermore, bond strength tests have been performed on the mortar rendering samples, and effects of variables have been analyzed by using statistical help. Results have shown that the existence of interfacial macro-flaws decreases bond strength values between mortar rendering and substrate, and this scenario worsens under thermal shock. Mortar renderings with higher Youngs modulus (E) are more affected.

O desempenho é foco de diversos estudos atuais, a comunidade técnica está buscando melhorar os sistemas construtivos. Apesar de ser discutido há décadas, este tema foi recentemente revigorado pela elaboração e publicação da norma de desempenho NBR 15575 (ABNT, 2013a). Este documento apresenta requisitos mínimos a serem atingidos pelas edificações, bem como metodologia para a avaliação destes parâmetros. Dentre os ensaios apresentados, consta em seu anexo E um método para avaliação de vedações verticais frente a choques térmicos. Inúmeras pesquisas adotam os choques térmicos como agente de degradação, contudo não existe um consenso quanto às condições de contorno ou mesmo as dimensões dos corpos de prova. A norma brasileira recomenda que as essas possuam 120 cm de largura e altura equivalente a 1 pé direito, entretanto em determinadas situações tais dimensões inviabilizam o programa experimental, dado a falta de equipamentos deste porte. Assim, encontram-se na literatura técnica pesquisas realizadas sobre protótipos reduzidos de sistemas de vedação. Este trabalho buscou identificar a influência das dimensões e condições de contorno dos corpos de prova nos resultados obtidos em ensaios de choques térmicos Para tal, foram ensaiadas amostras em 3 tamanhos diferentes, as dimensões propostas pela NBR 15575 e duas variações reduzidas. Os corpos de prova reduzidos foram ensaiados livres e com restrições as dilatações. Todas as combinações foram sujeitas a 10 e 30 choques térmicos e as avaliações foram realizadas antes e após os ciclos. As variáveis de resposta adotadas foram a resistência à aderência, fissuração e permeabilidade, também foram mensuradas as variações lineares em momentos pré-determinados. Os choques térmicos não provocaram a perda da aderência, uma vez que as amostras apresentaram aderências estatisticamente iguais antes e após os ciclos, com exceção da amostra grande exposta a 30 choques, que teve sua aderência majorada. Apenas nas amostras grandes ocorreu alteração do índice de fissuras decorrente da exposição aos choques. Majoritariamente, a permeabilidade das amostras não foi alterada com a exposição aos choques, com exceção das amostras reduzidas livres expostas a 30 choques que apresentaram uma redução da absorção, indicando o fechamento dos poros. / Performance is the focus of many current researches, the technical community is searching to improve building systems. Despite being discussed for decades, this subject has recently been reinvigorated by the elaboration and publication of performance standard NBR 15575 (ABNT, 2013a). This document presents minimum requirements to be achieved by the buildings, as well a methodology for the evaluation of these parameters. Among the tests presented, attachment E shows a method for evaluating vertical seals against thermal shocks. Numerous researches adopt thermal shocks as a degradation agent, however, there is no consensus regarding the boundary conditions or even about the dimensions of the specimens. The Brazilian standard recommends that these specimens have at least 120 cm wide and height equivalent to room's height, however in certain situations such dimensions make the experimental program unfeasible, given the lack of equipment of this size. Thus, we find in the technical literature researches on reduced prototypes of walls. This study aimed to identify the influence of the dimensions and boundary conditions of the specimens on the results of thermal shock tests. For this, samples were tested in 3 different sizes, the dimensions proposed by NBR 15575 and two reduced variations The reduced specimens were tested without and with dilation restrictions. All combinations were subjected to 10 and 30 thermal shocks and the evaluations were performed before and after the cycles. The tests adopted to evaluate were resistance to adhesion, cracking and permeability, and linear variations were also measured at predetermined moments. The thermal shocks did not cause the loss of adhesion, since the samples had statistically equal adhesions before and after the cycles, except for the large sample exposed to 30 shocks, which had its adherence increased. Only in large samples occurred change of cracks index from exposure to shocks. The permeability of the samples was not altered with the exposure to shocks, except for the unrestricted reduced samples exposed to 30 shocks that showed a reduction of the absorption, indicating the closure of the pores.

A produção de fundidos com baixo nível de defeitos e com propriedades mecânicas adequadas é facilmente alcançada com a previsão do comportamento do metal durante a solidificação. A transferência de calor entre o metal-líquido e o molde, nos primeiros instantes de contato, compromete definitivamente as propriedades mecânicas e a qualidade do produto final. O comportamento da transferência de calor entre o metal e o molde foi explorado através da análise térmica experimental e confrontado com o Modelo de Schwarz Modificado (MSM). Para comprovar experimentalmente os fenômenos previstos no MSM tais como: superesfriamento aparente, posição das interfaces líquido-superaquecido/líquido- superesfriado e da sólido/líquido durante a solidificação foram realizados experimentos com alumínio puro, gálio puro e estanho. Para a análise térmica foram utilizados dois sistemas de solidificação vertical descendente (Griffiths et al., 1993; Jinho et al., 1996; Jamgotchian et al., 1987). O sistema A e o sistema B, sendo que o sistema B também permitia a solidificação vertical ascendente. Em ambos os casos, o fluxo de calor foi direcionado através de uma barra de alumínio (na temperatura ambiente) que foi inserida verticalmente no banho (técnica do “dedo frio”). A barra extrai calor do líquido em função da diferença de temperatura entre a massa líquida e a massa sólida e simula o choque térmico do metal líquido com as paredes de um molde. Os resultados experimentais e os obtidos pela simulação foram confrontados. Apresenta-se a relação experimental entre o superesfriamento e a taxa de solidificação. Discute-se o redimensionamento da Ti (temperatura de interface) na solução de Schwarz e a comprovação experimental da solução do MSM. / The production of casting with low level of defects and adjusted mechanical properties can be obtained with the previous knowledge of the metal solidification behavior. The transference of heat between the metal-liquid and the mold, in the first instants of the contact, compromises definitively the mechanical properties and the final product quality. The behavior of the transference of heat between the metal and the mold was carried out through the experimental thermal analysis and the results were compared with the Modified Schwarz Model (MSM). To experimentally prove, the cooled phenomena in the MSM such as: apparent supercooling, liquid superheated/liquid supercooled interfaces position and of the liquid/solid during the solidification experiments had been carried out with pure aluminum, pure gallium and tins. Two systems A and B, one of descending vertical solidification and another one of descending and ascending solidification, had been used for the thermal analysis. In both systems, the heat flow was directed through a bar of aluminum (in the ambient temperature) that was inserted vertically in the bath (“cold finger” technique). The bar extracts heat of the liquid, had the difference of temperature between the liquid mass and the solid mass, and simulates the thermal shock of the metal with the mold walls. The experimental results were compared with simulated data. In this work are presented experimental relation between the supercooling and the rate of solidification. The new dimension of the Ti (temperature of interface) in the Schwarz equation and the experimental evidence of MSM solution, are considered.

Joining of electronic components onto the circuit boards is done by soldering operation, during production of all electronic devices. In many countries, including Turkey, traditionally used tin-lead (Sn-Pb) solder alloys have been restricted to be used in consumer electronics appliances because of the toxic effects of lead (Pb) within these alloys. Tin-silver-copper (Sn-Ag-Cu) based alloys have been developed as the most promising candidate that can replace the Sn-Pb alloys. However, various problems have emerged with the increasing trend in use of Sn-Ag-Cu solder alloys in electronics industry, namely large intermetallic compound formation, low wettability and thermal shock resistance. Many researches have been done in the past decade to overcome these problems. The solutions are based on changing the undercooling of the solder alloy / which was determined to be done by either changing the composition of the solder alloy by micro-alloying or changing the cooling rate during soldering operation. In this thesis study Sn-3.5Ag-0.9Cu (wt. %) lead-free solder having the eutectic composition, was micro-alloyed with additions of aluminum (Al), iron (Fe) and titanium (Ti). Experimental results were compared with commercially available near-eutectic Sn-40Pb (wt. %) solder, a commercially available Sn-3.0Ag-0.5Cu (wt. %) solder and also eutectic Sn-3.5Ag.0.9Cu (wt. %) and near-eutectic Sn-3.7Ag-0.9Cu (wt. %) solders that were produced for this thesis study. In the first stage of the study, the effects of 0.05 wt. % of Al, Fe and Ti micro-alloying were investigated. When preliminary results of mechanical and thermal test were compared, Fe was found to make positive effect on shear strength and undercooling. Further research was carried out to establish a relationship between the Fe compositions and solder properties. Therefore, 0.01, 0.03, 0.07 and 0.1 wt. % Fe additions were also studied and results were reported. 0.01 wt. % and 0.07 wt. % Fe added solders were found to have a smaller undercooling, resulting with dispersed intermetallic compound (IMC) and thus has highest shear strength. Different cooling rates / 0.017, 0.17 and 1.7 &deg / C/sec were applied to solder-copper joints and microstructures were investigated. Large IMC-free microstructure was achieved by 0.01 wt. % Fe micro-alloyed solder, which was cooled with 1.7 &deg / C/sec rate. Wetting of copper substrate was found to be improved by additions of Al, Fe and Ti compared to alloy with eutectic composition of Sn-Ag-Cu alloy. Selected SAC+X alloys have been subjected to thermal shock experiments for crack formation analysis on the copper substrate-solder joints. The results showed that SAC+0.05Al solder has the higher thermal shock resistance, which no cracks were observed after 1500 cycles of thermal shock. In order to understand the insights of SAC performance, some of the lead-free solders were applied onto printed circuit boards for thermal shock resistance test. These results have indicate that the cracking may occur after thermal shock cycles due to process conditions of soldering operation (i.e. cooing rate), independent of the solder alloy composition.

In der Reaktorsicherheitsforschung sind auftriebsgetriebene Strömungen von Relevanz für Störfall-szenarien mit Verdünnung der Borkonzentration und für thermische Schockbelastungen des Reak-tordruckbehälters. In der numerischen Simulation der Strömungen werden neben der Berücksichtigung der Auftriebskräfte Quell- und Korrekturterme in die Bilanzgleichungen für die turbulente Energie und die turbulente Dissipation eingeführt. Es wurden erweiterte Modelle entwickelt, in die zusätzliche Gleichungen für die Turbulenzgrößen turbulenter Massenstrom und Dichtevarianz eingehen. Die Modelle wurden in den CFD-Code ANSYS-CFX implementiert. Die Validierung der Modelle erfolgte an einem speziellen Versuchsaufbau (VeMix-Versuchsanlage), mit Einspeisung von Fluid höherer Dichte in eine Vorlage. Als Kriterien für die Validierung wurde der Umschlag zwischen impulsdominiertem Strömungsregime mit vertikalem Jet oder ein vertikales Absinken bei Dominanz von Dichteeffekten herangezogen sowie lokale Konzentrationsmessungen mit Hilfe eines speziell entwickelten Leitfähigkeits-Gittersensors. Eine Verbesserung der Simulation dichtedominierter Vermischungsprozesse mit den erweiterten Turbulenzmodellen konnte allerdings nicht nachgewiesen werden, da die Unterschiede zwischen den Rechnungen mit verschiedenen Turbulenzmodellen zu gering sind. Andererseits konnte jedoch die Simulation der Stratifikation von Fluiden unterschiedlicher Dichte im kalten Strang einer Reaktoranlage deutlich verbessert werden. Anhand der Nachrechnung von Ver-suchen am geometrisch ähnlichen Reaktor-Strömungsmodell ROCOM wurde gezeigt, dass diese Stratifikation von bedeutendem Einfluss auf die Vermischung und somit letztendlich auch auf die Temperatur- bzw. Borkonzentrationsverteilung innerhalb des Reaktordruckbehälters ist. Sie lässt sich nur korrekt simulieren, wenn ausreichend große Abschnitte des kalten Stranges mit modelliert werden. Somit konnte doch eine bessere Vorhersagegenauigkeit der Simulation der Vermischung erreicht werden. In reactor safety research, buoyancy driven flows are of relevance for boron dilution accidents or pressurised thermal shock scenarios. Concerning the numerical simulation of these flows, besides of the consideration of buoyancy forces, source and correction terms are introduced into the balance equations for the turbulent energy and its dissipation rate. Within the project, extended turbulence models have been developed by introducing additional balance equations for the turbulent quantities turbulent mass flow and density variance. The models have been implemented into the computati-onal fluid dynamics code ANSYS-CFX. The validation of the models was performed against tests at a special experimental set-up, the VeMix facility, were fluid of higher density was injected into a vertical test section filled with lighter fluid. As validation criteria the switching-over between a momentum controlled mixing pattern with a horizontal jet and buoyancy driven mixing with vertical sinking down of the heavier fluid was used. Additionally, measurement data gained from an especially developed conductivity wire mesh sensor were used. However, an improvement of the modelling of buoyancy driven mixing by use of the extended models could not be shown, because the differences between calculations with the different models were not relevant. On the other hand, the modelling of the stratification of fluids with different density in the cold leg of a reactor primary circuit could be significantly improved. It has been shown on calculations of experi-ments at the ROCOM mixing test facility, a scaled model of a real reactor plant, that this stratification is relevant as a boundary condition for the mixing process inside the reactor pressure vessel. It can be correctly simulated only if sufficient large parts of the cold legs are included in the modelling. On this way, an improvement of the accuracy of the prediction of mixing processes was achieved.

This paper describes the analytical work done by modelling and evaluating a thermal shock in a WWER-440 reactor pressure vessel due to an emergency case. An axial oriented semielliptical underclad/surface crack is assumed to be located in the core weld line. Threedimensional finite element models are used to compute the global transient temperature and stress-strain fields. By using a three-dimensional submodel, which includes the crack, the local crack stress-strain field is obtained. With a subsequent postprocessing using the j-integral technique the stress intensity factors KI along the crack front are obtained. The results for the underclad and surface crack are provided and compared, together with a critical discussion of the VERLIFE code.

A produção de fundidos com baixo nível de defeitos e com propriedades mecânicas adequadas é facilmente alcançada com a previsão do comportamento do metal durante a solidificação. A transferência de calor entre o metal-líquido e o molde, nos primeiros instantes de contato, compromete definitivamente as propriedades mecânicas e a qualidade do produto final. O comportamento da transferência de calor entre o metal e o molde foi explorado através da análise térmica experimental e confrontado com o Modelo de Schwarz Modificado (MSM). Para comprovar experimentalmente os fenômenos previstos no MSM tais como: superesfriamento aparente, posição das interfaces líquido-superaquecido/líquido- superesfriado e da sólido/líquido durante a solidificação foram realizados experimentos com alumínio puro, gálio puro e estanho. Para a análise térmica foram utilizados dois sistemas de solidificação vertical descendente (Griffiths et al., 1993; Jinho et al., 1996; Jamgotchian et al., 1987). O sistema A e o sistema B, sendo que o sistema B também permitia a solidificação vertical ascendente. Em ambos os casos, o fluxo de calor foi direcionado através de uma barra de alumínio (na temperatura ambiente) que foi inserida verticalmente no banho (técnica do “dedo frio”). A barra extrai calor do líquido em função da diferença de temperatura entre a massa líquida e a massa sólida e simula o choque térmico do metal líquido com as paredes de um molde. Os resultados experimentais e os obtidos pela simulação foram confrontados. Apresenta-se a relação experimental entre o superesfriamento e a taxa de solidificação. Discute-se o redimensionamento da Ti (temperatura de interface) na solução de Schwarz e a comprovação experimental da solução do MSM. / The production of casting with low level of defects and adjusted mechanical properties can be obtained with the previous knowledge of the metal solidification behavior. The transference of heat between the metal-liquid and the mold, in the first instants of the contact, compromises definitively the mechanical properties and the final product quality. The behavior of the transference of heat between the metal and the mold was carried out through the experimental thermal analysis and the results were compared with the Modified Schwarz Model (MSM). To experimentally prove, the cooled phenomena in the MSM such as: apparent supercooling, liquid superheated/liquid supercooled interfaces position and of the liquid/solid during the solidification experiments had been carried out with pure aluminum, pure gallium and tins. Two systems A and B, one of descending vertical solidification and another one of descending and ascending solidification, had been used for the thermal analysis. In both systems, the heat flow was directed through a bar of aluminum (in the ambient temperature) that was inserted vertically in the bath (“cold finger” technique). The bar extracts heat of the liquid, had the difference of temperature between the liquid mass and the solid mass, and simulates the thermal shock of the metal with the mold walls. The experimental results were compared with simulated data. In this work are presented experimental relation between the supercooling and the rate of solidification. The new dimension of the Ti (temperature of interface) in the Schwarz equation and the experimental evidence of MSM solution, are considered.