Modeling of friction stir welding (FSW) is challenging, as there are large gradients in both strain rate and temperature that must be accounted for in the constitutive law of the material being joined. Constitutive laws are most often calibrated using flow stresses from hot compression or hot torsion testing, where strain rates are much lower than those of the FSW process. As such, the current work employed a recently developed method to measure flow stresses in AA 2219-T67 at the high strain rates typical of FSW. These data were used in the development of a finite element simulation of FSW to study the effect of the new flow stress data on temperature, torque, and load predictions, compared to standard material models calibrated with hot compression or hot torsion data. It was found that load predictions were significantly better with the new material law, reducing the error with respect to experimental measurements by approximately 79%. Because heat generation during FSW is primarily a function of friction between the rapidly spinning tool and the workpiece, the choice of friction law, and associated parameters, were also studied with respect to FE model predictions. It was found that the Norton (viscoplastic) friction law was the most appropriate for modeling FSW, because its predictions were more accurate for both the transient and steady-state phases of the FSW plunge experiment. The postulated reason for the superior performance of the Norton law was its ability to account for temperature and rate sensitivity of the workpiece material sheared by the tool, while the Tresca limited Coulomb law favored contact pressure, with essentially no temperature or rate dependence of local material properties. The combination of the new flow stress data and the optimized Norton friction law resulted in a 63% overall reduction in model error, compared to the use of a standard material law and boilerplate friction parameters. The overall error was calculated as an equally weighted comparison of temperatures, torques, and forces with experimentally measured values.

Made available in DSpace on 2014-06-11T19:29:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2003-07-30Bitstream added on 2014-06-13T20:48:14Z : No. of bitstreams: 1 santos_fl_me_ilha.pdf: 5580224 bytes, checksum: 7664797be424662e0d0d1021e9ee4dc5 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Em função da concentração de material sólido, misturas resultantes de argila e água conferem, via de regra, propriedades não-Newtonianas. Essa concentração passa a variar com a granulometria e a composição do mineral do sedimento, bem como com a qualidade da água. Algumas tentativas foram feitas na busca de melhor explicar a reologia e a dinâmica global dessas misturas nessa última década, notadamente no contexto de lavas torrenciais e misturas hiperconcentradas. Essa dissertação de mestrado tem por objetivo desenvolver uma caracterização reológica de misturas sólido-líquido (água+argila caulinítica e água+areia fina+argila caulinítica) com diferentes concentrações em volume (Cv) para as quais são determinadas, a partir de ensaios de reometria de precisão, as propriedades tais como a viscosidade aparente, tensão crítica de cisalhamento e curva de tensão de cisalhamento x taxa de deformação. Verificou-se, em condições controladas, a influência da temperatura, pH e concentração em volume (Cv) sobre a curva reológica dessas misturas, além de eventuais fenômenos de tixotropia e modo de preparo. O modelo reológico melhor ajustado para as argilas foi o de Herschel-Bulkley ( ( )n τ =τ c + k γ& ), onde: τ é a tensão de cisalhamento; τc é a tensão crítica (ou rigidez inicial); k é um termo de consistência (viscosidade aparente); n é o índice de escoamento; e dy γ& = du é a taxa de deformação. Obtém-se também, a partir de uma análise quantitativa global, leis de evolução dos diversos parâmetros reológicos em função da concentração em volume. Após a etapa de caracterização física e reológica das misturas, realizaram-se, sob condições controladas, ensaios dinâmicos através de escoamentos de lamas em canal inclinado. Nesses ensaios foram medidos os parâmetros lâmina normal, vazões... ; n is flow index; and dy γ& = du is shear rate. It is also obtained, from a global quantitative analysis, evolution laws of the several rheologics parameters in function of the solid volume concentration. After the stage of rheological and physical characterization of mixing samples, dynamics experiments were made, under controlled conditions, than the flow of mud was observed in the open channel. These analyses were made in order to examine the behavior of parameters such as: normal depth, discharge and velocities. In fact, the experience showed that is possible to deduce wall friction laws from the rheological proprieties based on high mud concentrated suspensions and the dynamic of these muds.

Orientador : Geraldo de Freitas Maciel. / Banca: Podalyro Amaral de Souza / Banca: Adriano Souza / Resumo: Em função da concentração de material sólido, misturas resultantes de argila e água conferem, via de regra, propriedades não-Newtonianas. Essa concentração passa a variar com a granulometria e a composição do mineral do sedimento, bem como com a qualidade da água. Algumas tentativas foram feitas na busca de melhor explicar a reologia e a dinâmica global dessas misturas nessa última década, notadamente no contexto de lavas torrenciais e misturas hiperconcentradas. Essa dissertação de mestrado tem por objetivo desenvolver uma caracterização reológica de misturas sólido-líquido (água+argila caulinítica e água+areia fina+argila caulinítica) com diferentes concentrações em volume (Cv) para as quais são determinadas, a partir de ensaios de reometria de precisão, as propriedades tais como a viscosidade aparente, tensão crítica de cisalhamento e curva de tensão de cisalhamento x taxa de deformação. Verificou-se, em condições controladas, a influência da temperatura, pH e concentração em volume (Cv) sobre a curva reológica dessas misturas, além de eventuais fenômenos de tixotropia e modo de preparo. O modelo reológico melhor ajustado para as argilas foi o de Herschel-Bulkley ( ( )n τ =τ c + k γ& ), onde: τ é a tensão de cisalhamento; τc é a tensão crítica (ou rigidez inicial); k é um termo de consistência (viscosidade aparente); n é o índice de escoamento; e dy γ& = du é a taxa de deformação. Obtém-se também, a partir de uma análise quantitativa global, leis de evolução dos diversos parâmetros reológicos em função da concentração em volume. Após a etapa de caracterização física e reológica das misturas, realizaram-se, sob condições controladas, ensaios dinâmicos através de escoamentos de lamas em canal inclinado. Nesses ensaios foram medidos os parâmetros lâmina normal, vazões... (Resumo completo, clicar acesso eletrônico abaixo). / According to solid concentration material, clay-water mixture can exhibit non- Newtonian properties. Mixture concentrations vary with the grain size distribution and the composition of the mineral sediment, as well as, with the water quality. In the last decade some attempts were realized to explain the rheology and the global dynamics of those mixtures, mainly in the context of mudflows and high mud concentrated suspensions. The purpose of this work is develop a rheological characterization of solid-liquid mixture (water + clay kaolinitic and water + fine sand + clay kaolinitic) with different solid volume concentrations (Cv) for which are determined, using a R/S Rheometer (Brookfield), rheological properties such as the apparent viscosity, yield stress and shear stress x shear rate curve. It was verified, under controlled conditions, the influence of the temperature, pH and solid volume concentration (Cv) on the rheological curve those mixtures, besides eventual tixotropy phenomenon and way of prepare. The rheological model adjusted for the clays was Herschel-Bulkley ( ( )n τ =τ c + k γ& ), where: τ is shear stress; τc is yield stress; k is a consistency term (apparent viscosity); n is flow index; and dy γ& = du is shear rate. It is also obtained, from a global quantitative analysis, evolution laws of the several rheologics parameters in function of the solid volume concentration. After the stage of rheological and physical characterization of mixing samples, dynamics experiments were made, under controlled conditions, than the flow of mud was observed in the open channel. These analyses were made in order to examine the behavior of parameters such as: normal depth, discharge and velocities. In fact, the experience showed that is possible to deduce wall friction laws from the rheological proprieties based on high mud concentrated suspensions and the dynamic of these muds. / Mestre

Cette thèse s’inscrit dans le cadre du projet ANR (Agence National de la Recherche) "Flowres" ayant pour objectif d’améliorer la prédiction des crues extrêmes. Il a récemment été démontré que le dérèglement climatique tend à augmenter la fréquence et l’intensité de ces événements extrêmes, provoquant ainsi de nombreux dégâts, notamment dans les zones urbaines. L’objectif de ce travail de thèse a été d’étudier les configurations extrêmes, où une "canopée urbaine" est faiblement immergée. Cette étude repose sur une série de mesures expérimentales réalisées en canal hydraulique à surface libre, dans lequel différentes profondeurs de canopée et niveau d’immersion ont été considérées. Les canopées étudiées sont composées d’alignements d’éléments prismatiques. La première partie de ce travail à consister à élaborer le dispositif expérimental permettant d’acceder à la structure complète D de ces écoulements. Pour cela, un dispositif de PIV 2D-2C a été mis en place, couplé à l’utilisation de moyens techniques sophistiqués, comme des prismes transparents en verre BK7 ainsi qu’une optique télécentrique. Ce dispositif a permis d’obtenir des statistiques hautement résolues tant temporellement que spatialement, et ont aussi permis d’étudier la sensibilité de ces statistiques à l’échantillonnage spatial. Une fois le système de mesure mis en place, l’effet de l’immersion et de la profondeur de canopée sur la structure verticale 1D de ces écoulements a ensuite été étudiée. Les résultats montrent que la structure d’un écoulement dans une canopée profonde (k/` = 6) fortement immergée peut être décrite par différentes couches (sillage, couche de mélange, couche logarithmique). Cependant, la diminution de l’immersion et/ou de la profondeur de canopée tend à forcer les interactions entre les couches, et en supprimer certaines dans certains cas. De plus, on remarque que pour de très faibles immersions, le tenseur total devient négatif. Afin de comprendre et caractériser ce phénomène inattendu, une analyse par quadrant du tenseur de Reynolds a été effectuée. Dans le cas d’écoulements fortement immergés, les éjections (Q 2 ) et les balayages (Q4 ) contribuent majoritairement à l’écoulement. Cependant, la diminution de l’immersion est accompagnée d’une augmentation importante d’événements Q 3 dans la canopée, conduisant à un tenseur de Reynolds négatif pour des cas extrêmes. Pour finir, la compréhension de ces écoulements turbulents par l’intégration des profils verticaux 1D a permis de déterminer les lois de frottement globales associées. Il a été montré qu’il est nécessaire de définir correctement les grandeurs utilisées pour le coefficient de frottement f 0 , comme une vitesse débitante prenant en compte la porosité de la canopée ou encore une vitesse de frottement u 0 basé sur le fond du canal et non sur le sommet des prismes. On observe une corrélation entre l’immersion de la canopée et le coefficient de frottement f 0 . De plus, deux comportements distincts semblent émerger pour les faibles (h/k < 4) ou fortes (h/k > 4) immersions. / This PhD work is part of the ANR project "Flowres" where aims is to improve the prediction of nextreme flood events. It has been shown that the climate change will increase the frequency and intensity of these extreme events, leading to major damages, especially in urban areas. The objective of this PhD was to investigate extrem configurations where urban canopy is weakly submerged. This work is based on experimental analysis carried out in a hydraulic open-channel flume in which various canopy depth and submergence levels were investigated. The canopies were built by alignment of prismatic roughness elements. The first part of this PhD work aimed at developping the experimental set-up allowing to obtain the complete structure of the flow. To this end, a PIV 2D-2C apparatus was used, paired with the use of advanced technical tools, such as prisms of BK7 glass and a telecentric optics. This set-up has enabled to obtain highly converged statistics (spatially and temporally), allow an investigation of sensitivity of these statistics to the spatial sampling. Once the experimental set-up designed, the effect of the flow immersion and of canopy depth on the 1D vertical structure was then investigated. Our results have shown that the flow structure of a depth canopy with an high submergence can be described by different (layers wake layer, mixing layer, logarithmic zone). A decrease of the submergence and/or the canopy depth increase interactions between the different layers, and sometimes, cancel it. Additionally, for some low submergence flow regimes, the total stress becomes negative. In order to understand and better characterize this unexpected result, we performed a quadrant analysis of the Reynolds stress. In the case of highly submerged flow, ejections (Q 2 ) and sweeps (Q 4 ) mostly contribute to the flow. By contrast, the decrease of the submergence is coupled with an significant increase of the Q3 event within the canopy. It can lead to a negative Reynolds stress in some flow regimes. Finally, the understanding of turbulent flows through integration of the 1D vertical profiles allowed calculation of thes associated global friction law. It has been shown that it is necessary to properlydefine the quantities used for the friction coefficient f 0 , such as a flow rate taking into account the porosity of the canopy, and a speed of friction u 0 based on the bottom of the channel (and not on the top of the prisms). There is a correlation between canopy submergence and the coefficient of friction f 0 . Moreover, two different behaviour appear for low submergence (h/k < 4) or high submergence (h/k > 4).