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Tesi sul tema "Thixotropy"
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1
Axelson, Hans. "Muscle Thixotropy : Implications for Human Motor Control". Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5791.
Testo completo
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Anvari, Ardakani Hesam. "Rheology of pastes : effects of fibrillation, thixotropy and structure". Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46979.
Testo completoAbstract (sommario):
Three different pastes (toothpaste, PTFE paste that is mixture of polytetrafluoroethylene of submicron size particles with a liquid lubricant, and chocolate) are investigated in this thesis as model paste systems to study their processing characteristics in capillary flow using various dies. The rheological behaviour of toothpaste and melt chocolate paste is identified as that of a yield-stress, thixotropic material with a time-dependent behaviour. The rheological data obtained from a parallel-disk were used to formulate a constitutive equation with a structural parameter which obeys a kinetic equation, typically used to model thixotropy. For semi-solid paste extrusion (PTFE paste and solid chocolate), a simple phenomenological mathematical model is developed. The model takes into account the elastic-plastic (strain hardening) and viscous nature of the material in its non-melt state. In addition, it takes into account the slip boundary condition at the paste/wall interface. To study scale-up possibilities, the rheology of non-melt processible polytetrafluoroethylene (PTFE) pastes is studied using three capillary rheometers having barrels of different diameter and equipped with capillary dies of various designs. The effects of process conditions on fibrillation and mechanical properties of polytetrafluoroethylene (PTFE) paste extrudates are also studied. To describe the effects of die design on the quality of the final product, a basic phenomenological mathematical model is developed. The model consists of a simple equation that explains fibril formation, due to the compression of PTFE resins, plus a kinetic equation, which is coupled with the “radial-flow” hypothesis to predict the structure and the tensile strength of extrudates. Model predictions for structural parameter compared with the tensile strength measurements, have shown a good qualitative agreement. For all paste systems, the pressure drop is measured as a function of apparent shear rate (flow rate), reduction ratio (cross sectional area of barrel to that of die), contraction angle, length-to-diameter ratio, and diameter of the barrel (scale-up). In all cases, model shown to have coefficient of determination (R2) above 0.84. Finally, extrusion pressure predictions based on the proposed models are compared with the experimental data obtained from macroscopic pressure drop measurements and are found to be consistent.
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Assaad, Joseph. "Formwork pressure of self-consolidating concrete : influence of thixotropy = Pressions latérales développées par les bétons autoplaçants contre les coffrages : influence de la thixotropie". Thèse, Université de Sherbrooke, 2004. http://savoirs.usherbrooke.ca/handle/11143/1756.
Testo completoAbstract (sommario):
Recently, a new generation of concrete referred to as self-consolidating concrete (SCC) appeared on the market. This kind of concrete is characterized by its high fluidity and resistance to segregation. It enables the elimination of the vibration during the casting process and reduces the need for manpower on the construction site. The use of SCC has gained increased acceptance and it became essential to better understand the lateral pressure that can be developed on the vertical formwork systems. Presently, formworks are designed prudently by assuming that the plastic concrete exerts full hydrostatic pressure until the setting time. Such pressure is expressed as: P[subscript max] = p × g × H where p, g, and H correspond to the concrete unit weight, gravity, and head of concrete, respectively. Such approach can result in increased construction costs and can limit the rate of rise of the concrete in the formwork. An experimental program was undertaken in the University of Sherbrooke to evaluate the lateral pressure developed by SCC mixtures. A special emphasis was placed on the influence of concrete thixotropy on the pressure development. Various mixture parameters, including the coarse aggregate characteristics, binder type and content, as well as the water-to-binder ratio were investigated. The effect of incorporating chemical admixtures such as the set-modifying and water-reducing agents, high-range water-reducing and viscosity-modifying admixtures (HRWRA and VMA, respectively) were evaluated. The effect of consistency level, concrete temperature, and casting rate on formwork pressure were also determined. Test results showed that the variations in lateral pressure of SCC are highly affected by the development of shear strength properties, namely the internal friction and cohesion. The higher the degree of internal friction, the lower is the maximum initial pressure measured right after the end of casting. Increased degree of internal friction can be ensured by incorporating a greater volume of coarse aggregate. This can also be achieved indirectly by proportioning mixtures with lower binder contents and/or water-to-binder ratios."--Résumé abrégé par UMI.
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Thiene, Oumar. "Rhéologie des boues résiduaires : rôle de la thixotropie et de la composition sur les propriétés liquides et solides". Thesis, Université Clermont Auvergne (2017-2020), 2018. http://www.theses.fr/2018CLFAC033/document.
Testo completoAbstract (sommario):
Alors que la quantité de boues résiduaires produites à l’échelle mondiale ne cesse d’augmenter, la gestion de ces boues est désormais devenue un enjeu sociétal majeur. Dans le cadre d’une politique de développement durable, son efficacité passe nécessairement par la réduction des volumes produits (via l’optimisation des procédés de traitement) et par une meilleure valorisation. Pour cela, les procédés ainsi que les outils mis en oeuvre pour traiter puis valoriser le matériau doivent être de plus en plus performants. Les traitements étant essentiellement basés sur des écoulements, cette performance accrue nécessite la mesure et la maîtrise des caractéristiques des boues résiduaires telles que la consistance et les propriétés d’écoulement. Cependant le matériau est complexe et ses propriétés rhéologiques varient selon sa composition. Ainsi, le principal critère utilisé pour déterminer sa consistance, la teneur en matière solide, s’avère limité puisque la boue la plus consistante n’est pas nécessairement celle qui contient le plus de matière solide. Un état de l’art sur le comportement rhéologique des matériaux non-Newtoniens en général et des boues résiduaires en particulier a montré l’intérêt de s’intéresser au rôle de la matière organique et de la thixotropie dans la variabilité des propriétés rhéologiques du matériau. Dans cet objectif, une méthodologie expérimentale a d’abord été développée pour s’assurer de l’obtention de résultats fiables. Cela a permis de montrer l’influence des procédures expérimentales sur les mesures rhéologiques et de définir une procédure expérimentale robuste garantissant la répétabilité et la reproductibilité des résultats obtenus. Puis, à partir de cette procédure expérimentale, il a été montré que les effets de la thixotropie n’affectent que les propriétés solides des boues, les propriétés liquides en étant indépendantes. De plus, cette approche a permis de mettre en évidence que le comportement thixotrope est intrinsèquement lié à la matière organique contenue dans les boues : plus la matière organique est élevée, plus les boues sont thixotropes. Ensuite, à partir de la matière solide et de la proportion de matière organique contenue dans le solide, un critère plus pertinent que la teneur en matière solide a été établi pour comparer les propriétés rhéologiques entre boues d’origines différentes. Ce critère, appelé consistance équivalente, s’avère suffisant pour tenir compte de l’influence de la composition sur les propriétés rhéologiques des boues. Enfin, selon la valeur de la consistance équivalente, il a été montré que le comportement rhéologique des boues résiduaires peut être considéré comme Newtonien, non-Newtonien simple (effets thixotropes négligeables) ou non-Newtonien avec des effets thixotropesSludge management is a major issue as the production is increasing year after year while the solutions to reuse it are limited. In the context of sustainable management and circular economy, treatment processes need to be well controlled to pilot operating systems. Since treatment processes are essentially based on flowing properties, improving the efficiency requires the measurement and control of sludge rheology, among which viscous properties. However, sludge is complex material and its rheological properties highly dependent of its composition. The solid content, the most usual parameter considered to evaluate rheological properties, is quite limited as sludge consistency is not directly connected to the solid content. An in-depth state of the art review on non-Newtonian materials rheology with a focus on sewage sludge has underlined the role of organic matter and thixotropy in complex fluid rheological properties. In that purpose, an experimental methodology was defined to ensure reliable results. This allowed to highlight the impact of experimental setups on rheological measurements and to define a robust experimental methodology that ensures the repeatability and the reproducibility of the measurements. Then, thanks to this experimental methodology, it has been shown that thixotropy is a solid-like characteristic, viscous properties being independent of material history. In addition, this approach has made it possible to demonstrate that the thixotropic behavior is intrinsically connected to the organic matter content: the higher the organic matter, the more thixotropic the sludge. Moreover, from the solid matter and the ratio of organic matter in the solid, a criterion (more relevant than the solid content) has been established to compare the rheological properties between sludge of different origins. This criterion, called equivalent consistency, appears to be sufficient to take into account the impact of the composition on sludge rheological properties. Finally, it has been shown that the rheological behavior of sewage sludge can be considered as Newtonian, simple non-Newtonian (with negligible thixotropic effects) or non-Newtonian with thixotropic effects depending the value of the equivalent consistency
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MOISÉS, GUSTAVO VINICIUS LOURENÇO. "EFFECTS OF YIELD STRESS AND THIXOTROPY IN NON-NEWTONIAN ISODENSE DISPLACEMENT". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=27820@1.
Testo completoAbstract (sommario):
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
O aparecimento de tensão limite decorrente da gelificação de óleo parafínicos constitui um problema significativo em linhas submarinas nos sistemas de produção de petróleo em água profundas. Essencialmente, existem dois modos para garantir retorno da produção em oleodutos após longas paradas: aplicar um elevado diferencial de pressão suficiente para mover o gel no duto, reinício de produção, ou injetar um fluido misccível de baixa viscosidade, preferencialmente Newtoniano, na entrada do duto, processo denominado deslocamento de fluido. Nós investigamos os efeitos da tensão limite e da tixotropia no escoamento de fluidos não Newtonianos em dutos horizontais, considerando tanto o reinício de produção quanto o deslocamento de fluidos sem diferença de densidade. Tanto a tensão limite como as propriedades tixotrópicas dos óleos parafínicos foram simuladas reologicamente por fluidos base água, soluções de Carbopol e suspensões de Laponita. Os resultados experimentais e os estudos numéricos do deslocamento de fluidos com tensão limite sem diferença de densidade são apresentados. Três tipos distintos de escoamento, que pertencem a categoria deslocamento central, foram identificados nos experimentos e chamados de corrugado, ondulado e liso a depender do nível de variação da camada residual ao longo do duto. A transição entre esses regimes foi identificada como da razão entre a tensão inercial e a tensão característica do fluido viscoplástico. Além disso, a influência das concentrações de NaCl e Laponita nos parâmetros reológicos das suspensões de Laponita é detalhada e o impacto da tixotropia no reinício de produção de suspensões de Laponita foi analisada com base em dados experimentais.
The yield stress appearance when gelation occurs in wax crude oils constitutes a significant problem in subsea flowline in deepwater oil production systems. In essence, there exist two stages in a pipeline flow restart after a long shutdown: apply a large enough differential pressure in order to mobilize the gel in the pipe, i.e. a process of fluid start-up or inject miscible fluid with low viscosity, preferably Newtonian, at the pipe inlet, to flush the gelled oil out of the pipe, i.e. a process of fluid displacement. We investigate yield stress and thixotropy effects over non-Newtonian fluid flows in a horizontal pipe, considering the fluid start- up and the fluid displacement in the isodense limit. The yield stress and thixotropic properties of waxy crude oils are rheologicaly simulated by water base fluids, Carbopol solutions and Laponite suspensions. The results of experimental and numerical studies of isodense displacement of a yield stress fluid are presented. Three distinct flow types belonging to this central displacement are identified in the experiments namely corrugated, wavy and smooth depending on the level of the residual layer variation along the pipe. The transition between these flow regimes is found to be a function of the ratio between the inertial stress and the characteristic viscous stress of the viscoplastic fluid. Besides, the influence of NaCl and Laponite concentrations in the rheological parameters of Laponite suspensions is detailed and the impact of thixotropy in the start-up of Laponite suspensions are analyzed based on experimental results.
6
Seffern, Pascal. "Beitrag zur Identifizierung rheologischer Wechselwirkungen von Kaolinen in wässrigen Systemen". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2018. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-232052.
Testo completoAbstract (sommario):
The present dissertation investigates the flow behavior of concentrated Kaolin slurries and furthermore novel rheological measurement-, analysis-, and assessment procedures for characterizing static and dynamic flow behavior in industrial and research applica- tions. Ten different Kaolins with divergent property profiles were investigated in detail. At first, novel measurement and analysis procedures are presented and the raw material inherent properties are correlated with the resulting flow characteristics. The results describe the structural building and breakdown (in both static and dynamic states) of concentrated Kaolin slurry suspensions with and without deflocculant and also the determination of the point of optimal deflocculant concentration through the develop- ment of a novel analysis method and linking of the parameters to a condition matrix. The results lead to a better understanding of the flow behavior of concentrated Kaolin slurries. Due to the use of a strict measurement protocol with a focus on the elimination of external disturbances on the determination of flow behavior, the phases of dynamic structure construction and destruction (with exclusion of temporal structure effects and vice versa) can be analyzed. It was identified that the construction of particle networks requires less energy than their destruction. Furthermore it could be demonstrated that the occurrence of a transient shear stress peak in kaolin slurries is the cause for the breakdown of an existing particle network and not, as conventionally reported, due to an insufficient measurement time. Moreover, through the combination and modification of two measurement protocols described here, manufacturing companies have a potentially useful tool for composition development and quality control without the necessity of purchasing a highly precise research rheometerIn der vorliegenden Arbeit wird das Fließverhalten von konzentrierten Kaolinsuspensio- nen untersucht und neuartige rheologische Mess-, Analyse- und Bewertungsverfahren zur Charakterisierung der Belastungs- und Zeitabhängigkeit für Industrie- und Forschungsanwendungen vorgestellt. Hierzu wurden zehn Kaoline mit divergierenden Eigenschaftsprofilen untersucht. Zunächst werden neuartige Mess- und Analyseverfahren vorgestellt und die Eigenschaften der Rohstoffe mit den ermittelten Fließcharakteristika korreliert. Die Ergebnisse beschreiben den strukturellen Auf- und Abbau (zeit- und belastungsabhängig) von konzentrierten Kaolinsuspensionen mit und ohne Dispergierhilfsmitteleinsatz und darüber hinaus die Ermittlung der optimalen Dispergierhilfsmittelkonzentration durch Entwicklung einer neuartigen Analyse und Verknüpfung von Parametern an eine Bedingungsmatrix. Die Erkenntnisse tragen zum besseren Verständnis des Fließverhaltens konzentrierter Kaolinsuspensionen bei. Aufgrund der entwickelten Messvorschriften und der darin elementar verankerten Elimination von Störgrößen auf die Ermittlung des Fließverhaltens konnten die Phasen des strukturellen Auf- und Abbaus unter Belastung (unter Ausschluss von temporalen Struktureffekten und umgekehrt) analysiert werden. Es wurde festgestellt, dass die Konstruktion von Partikelnetzwerken weniger Energie benötigt, als deren Destruktion und das Auftreten des Schubspannungshügels auf den Zusammenbruch des Partikelnetzwerkes und nicht, wie allgemein beschrieben auf zu geringe Messzeiten zurück zu führen ist. Darüber hinaus wird der produzierenden Industrie, durch Abwandlung und Kombination zweier Messvorschriften ein Werkzeug zur Versatzentwicklung und Qualitätskontrolle, auch ohne die Notwendigkeit des Erwerbs von hochpräzisen Forschungsrheometern bereitgestellt
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Dimitriou, Christopher (Christopher J. ). "The rheological complexity of waxy crude oils : yielding, thixotropy and shear heterogeneities". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81696.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 305-320).
Precipitate-containing crude oils are of increasing economic importance, due to diminishing oil reserves and the increased need to extract hydrate and wax-containing crude oil from ultra deep-water resources. Despite this need, the rheological behavior of these types of crude oil is often poorly understood. In this thesis, we investigate some of the underlying complexities associated with the rheology of waxy crude oils. These complex phenomena are often difficult to both quantify experimentally and capture with existing constitutive models. The contribution of this thesis is therefore to develop a detailed understanding of three of these particular phenomena, through the development and use of several new experimental and theoretical tools. A better understanding of waxy crude oil rheology is critical for developing flow assurance strategies, which can in turn ensure continuous production of precipitate-containing crude oils under adverse conditions. The three phenomena studied are, first: shear heterogeneities, i.e. the manifestation of wall slip, shear banding or other shear-localization events under imposed deformations that are assumed to be homogenous. For these purposes, flow visualization techniques capable of "Rheo-PIV" measurements are developed to detect these heterogeneities. Second: elasto-viscoplasticity, or the presence of an elastic response and a yield-like behavior in a non-Newtonian fluid. Constitutive modeling of this type of behavior is difficult to achieve using standard linear viscoelastic techniques, where the viscoelastic response is decomposed into a finite number of linear elements with a spectrum of relaxation times. For these reasons, additional concepts are adopted from plasticity models in order to describe this behavior. Finally: thixotropy, which refers to the ability of a fluid to continuously evolve, or age at rest and shear rejuvenate under a constant applied shear rate. A rigorous set of experimental tests is constructed which allow for the appropriate constitutive model parameters to be determined for a thixotropic fluid. Through quantitative study of these phenomena, we reach several conclusions about how to characterize and model the rheology of a precipitate-containing crude oil. First, measurements of shear heterogeneities are important in these fluids, so that rheological characterization may proceed with a knowledge of when these may arise and introduce artifacts into data. Second, new nonlinear rheometric techniques are necessary to develop quantitative data sets that describe the inherently nonlinear rheology of these fluids. The specific technique developed in this work is termed stress-controlled large amplitude oscillatory shear, or LAOStress. Finally, we show that the constitutive behavior of these materials is best prescribed using a framework which utilizes yielding and hardening mechanisms from plasticity theory. The resulting constitutive model for this nonlinear elasto-viscoplastic and thixotropic class of materials is expressed in a closed form that can be used in existing flow assurance simulation tools. The most relevant applications for this work are in the flow assurance challenges associated with crude oil production. Consequently, a large portion of the experimental work is carried out on a model waxy crude oil, containing a total wax content ranging from 5 to 10% by weight. However the phenomena studied here occur ubiquitously in a number of complex fluids. For this reason, the same rheological complexities are studied in the context of several other fluids, including a swollen microgel paste (Carbopol) and a shear-banding wormlike micellar solution.
by Christopher J. Dimitriou.
Ph.D.
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Whitehead, Nicholas P. (Nicholas Paul) 1975. "Factors affecting the passive mechanical properties of skeletal muscle : thixotropy and eccentric contractions". Monash University, Dept. of Physiology, 2002. http://arrow.monash.edu.au/hdl/1959.1/7883.
Testo completo
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Umerova, S. O., I. O. Dulina e A. V. Ragulya. "Rheology and Printability of Pastes Based on BaTiO3 Nanopowder Depending on Ethyl Cellulose Viscosity". Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42513.
Testo completoAbstract (sommario):
This paper is about rheology of pastes based on BaTiO3 nanopowder with ethyl cellulose 100 cP (paste P1) and 10 cP (paste P2) as organic binder. It was established, that P1 was pseudoplastic – thixotropic system and P2 was rheopexic - pseudoplastic – thixotropic one. The reduction of EC viscosity led to changing of paste structurization type from pseudoplastic (P1) to plastic one (P2). Structurization of P1 can be explained with excess of polymer in the paste composition and with dominance of the polymer – polymer bonds. Unlike P1, P2 has some elastic properties due to strong structural links because of polymer – nanoparticle bonds. Moreover, the value of initial viscosity
of P2 (2.11 Pa∙s) was much less than of P1 (37,5 Pa∙s). It was found, that the viscosity of polymer influences the paste printability. In particular, P2 was more prone to form thinner and smoother prints. Thus, composition of P2 was more promising one for obtaining prints with good quality and subsequent assembly into a multilayer object due to its elastic properties during low deformation.
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Liard, Maxime. "Suspension concentrées : systèmes non newtoniens et thixotropie sous écoulement". Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE039/document.
Testo completoAbstract (sommario):
Cette thèse de doctorat a été financée par l’entreprise SIKA spécialisée dans les matériaux de construction. Les trois chapitres de cette thèse correspondent à la tentative de résolution de trois problématiques d’origine industrielle. Dans le premier chapitre, nous avons étudié l’effet de la concentration en particules sur les propriétés d’écoulement de fluides complexes rhéofluidifiants ou rhéoépaississants et démontré l’origine microscopique de cet effet. Dans le second chapitre, nous avons étudié la floculation de particules colloïdales sous faibles perturbations et mis en évidence l’existence, au cours de la reconstruction, d’un maximum du module élastique. Enfin le troisième chapitre est l’étude d’un diagramme de phase de jet de suspensions concentrées. En régime dilué et semi-dilué, les résultats sont conformes à ceux de la bibliographie, en revanche nous avons étudié un nouveau régime à très haute fraction volumique où le jet, instable, se met à osciller. Nous avons montré que ces oscillations étaient dues au rhéoépaississement de la suspensionThis thesis has been done in collaboration with the company SIKA, one of the leader if the construction industry. This thesis report is organized in three chapters where each of them tries to answer a problem coming from industrial processes. In the first chapter, we studied the impact of particles concentration on the flowing properties of complex fluids such as shear-thinning and shear-thickening fluids. We demonstrated the importance of local contacts between particles to explain the evolution of the viscosity with the volume fraction. In the second chapter, we studied the aggregation of colloidal attractive suspensions under small perturbations and proved the existence of a maximum of elastic modulus during the rebuilding of the structure. Finally, the third chapter is a study of a phase diagram of a concentrated suspension jets. In the diluted and semi-diluted regimes, we found results in agreement with the bibliography, meanwhile at very high concentration, we studied a new regime where the jet, unstable, is oscillating. We showed those oscillations can be explained by the shear-thickening behaviour of the suspensions at those high concentrations
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Billberg, Peter. "Form pressure generated by self-compacting concrete : influence of thixotropy and structural behaviour at rest". Doctoral thesis, Stockholm : Division of Concrete Structures, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4144.
Testo completo
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Jomy, Vachaparambil Kurian. "An analytical and numerical study of droplet formation and break-off for jetting of dense suspensions". Thesis, KTH, Mekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-194501.
Testo completoAbstract (sommario):
The jet printing of solder paste from a uid dynamics perspective involves viscosity change due to varying shear rate and eventual break o of the ejected solder paste droplet from the uid in the printer head. The ability to model the jetting process in a simulation package is important as it can be used as a tool for future development of the jetting device. The jetting process is modelled as a two phase (air - solder paste) ow with interface tracking performed using phase eld method and temporal stepping based on a second-order Backward Di erence Formula with relaxed tolerences. This thesis investigates the droplet morphology, volume and speed predictions for three di erent piston actuation modes and solder paste viscosity denitions given by the Carreau- Yasuda model. A Darcy condition with the porosity parameter is calibrated equal to unity such that the droplet speed is within the realistic range of 20 m/s - 30 m/s. The simulations are compared against previous simulation results from IBOFlow, performed within a collaboration between Mycronic AB and Fraunhofer-Chalmers Centre. As the Carreau models cannot capture the dependence of the uid viscosity of ow history, an indirect structure based viscosity model is used to compare the thixotopic behaviour. The expressions for the parameters of the structure based viscosity model are derived based on an analytical model which assumes that shear rate is constant. Experimental data for constant shear rate is curve tted on a Carreau model and an initial estimate of the parameters are obtained. The parameters are then adjusted to match experimental thixotopic behaviour. This method can be used to obtain parameter values for structure based viscosity models for uids with no previous data. Once the solder paste is ejected through the nozzle and the piston retracts, the uid undergoes stretching. Studying lament stretching during jetting is dicult as it can be driven by both droplet and piston motion. The data from an extensional rheometer is analyzed to study the lament stretching phenomenon for solder pastes. An analytical model for the critical aspect ratio is derived for a Newtonian uid lament undergoing a pure extension and modelled as a cylinder whose radius is decreases with time. The exponential decrease of the lament radius predicted by the analytical model is found to reproduce the experimental observations very well. The lament radius calculated based on the lament height from the experiments and analytical model shows that the model captures the stretching process, but the formation of beads usually seen in suspensions is not accounted for.
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Wang, Taige. "Mathematical Analysis on the PEC model for Thixotropic Fluids". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/70907.
Testo completoAbstract (sommario):
A lot of fluids are more complex than water: polymers, paints, gels, ketchup etc., because of big particles and their complicated microstructures, for instance, molecule entanglement. Due to this structure complexity, some material can display that it is still in yielded state when the imposed stress is released. This is referred to as thixotropy. This dissertation establishes mathematical analysis on a thixotropic yield stress fluid using a viscoelastic model under the limit that the ratio of retardation time versus relaxation time approaches zero. The differential equation model (the PEC model) describing the evolution of the conformation tensor is analyzed. We model the flow when simple shearing is imposed by prescribing a total stress.
One part of this dissertation focuses on oscillatory shear stresses. In shear flow, different fluid states corresponding to yielded and unyielded phases occur. We use asymptotic analysis to study transition between these phases when slow oscillatory shearing is set up. Simulations will be used to illustrate and supplement the analysis.
Another part of the dissertation focuses on planar Poiseuille flow. Since the flow is spatially inhomogeneous in this situation, shear bands are observed. The flow is driven by a homogeneous pressure gradient, leading to a variation of stress in the cross-stream direction. In this setting, the flow would yield in different time scales during the evolution. Formulas linking the yield
locations, transition width, and yield time are obtained. When we introduce Korteweg stress in the transition, the yield location is shifted. An equal area
rule is identified to fit the shifted locations.Ph. D.
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Dulina, I. O., S. O. Umerova e A. V. Ragulya. "Barium Titanate Thin Films Obtained by Screen Printing Technology". Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35153.
Testo completoAbstract (sommario):
Barium titanate thin films have been obtained using screen printing of pastes based on BaTiO3 na-nopowders. Obtained pastes have been characterized by optical microscopy and optical profilometry. De-posit pattern geometry fidelity in regard to screen mask and films thickness and roughness parameter Ra during screen printing parameters changing depended on pastes rheological behavior. In addition, films roughness and thickness were strongly depended on solid and solvent content in pastes. Solvent content rising and BaTiO3 content lowering resulted in films thickness and roughness decreasing. Depending on paste solid and content barium titanate films thickness was changed from 1.56 to 3.18 m, the film rough-ness Ra from 50 to 196 nm and Rz from 160 to 393 nm.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35153
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Machado, Norma Maria Pereira. "Rheological study of nuclear glass melts containing Platinum Group Metal aggregates". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0018.
Testo completoAbstract (sommario):
En France, les produits de fission nucléaire issus du retraitement des combustibles usés sont conditionnés au sein de matrices de verres borosilicatés. Lors du processus de vitrification à haute température (1200 °C), les éléments à confiner réagissent chimiquement avec les additifs de vitrification pour former un verre homogène. Cependant, parmi ces éléments, les platinoïdes ne sont pas solubles dans le bain de verre et restent en suspension sous forme de particules de quelques microns. Ces particules présentent une forte tendance à l'agrégation et les suspensions peuvent alors présenter une viscosité apparente anormalement élevée. Ces systèmes sont caractérisés par un comportement rhéofluidifiant et thixotrope. La présente étude vise à fournir des données importantes sur le comportement rhéologique global de ces systèmes et leurs propriétés, grâce à la caractérisation d'un verre nucléaire simulé contenant 3,0 % massique (1,02 % en volume) de platinoïdes. Une modélisation mathématique du comportement thixotrope de ce verre est présentée pour la première fois en utilisant un modèle similaire à celui proposé par Houska (Houska, 1981). Ce modèle prédictif permet la description des résultats expérimentaux obtenus à partir de mesures en régimes permanent et transitoire. L'impact de la contrainte de cisaillement et du temps sur le degré d'agrégation et la cinétique de sédimentation des particules est déterminé à l'aide d'un rhéomètre à contrainte imposée opéré à haute température et d'analyses d'images obtenues par microscopie électronique à balayage (MEB). Pour la première fois, l'interaction entre le comportement rhéologique du système et le degré d'agrégation est analysé, tout comme le lien avec la sédimentation des particules. Sur la base des données expérimentales acquises, un calcul d'équilibre des forces est réalisé pour illustrer les différents scénarios d'agrégation. Ce travail fournit des nouvelles données pour la modélisation et le contrôle du processus de vitrificationIn France, borosilicate glass is used as a matrix to immobilize nuclear fission products resulting from spent fuel reprocessing. In the high-temperature vitrification process (1200 °C), most of elements to be contained react chemically with the vitrification additives to form a homogeneous glass melt. Platinum Group Metal (PGM) particles are not soluble in the melt and therefore are present as suspended particles of few microns. These particles exhibit an intense aggregation tendency and consequently the suspensions may present an anomalously high apparent viscosity. These systems are characterized by a shear-thinning and a thixotropic behaviors. The present study aims to provide important inputs for the overall rheological behavior of this system and its features through the characterization of a simulated nuclear glass melt containing 3.0 wt% (1.02 vol%) of PGM particles. A mathematical modeling of the thixotropic behavior of glass melts containing PGM particles is presented for the first time using a model similar to that proposed by Houska (Houska, 1981). This predictive model allow to describe experimental results obtained both in steady state and transient conditions. The impact of the shear stress and time on PGM aggregation degree and sedimentation kinetics is determined using an imposed-stress rheometer at high temperature and imaging analyses via Scanning Electron Microscopy (SEM). For the first time, the interplay between the rheological behavior of the system and the aggregation degree is provided, as well as the link with the particles settling. Based on the acquired experimental data, a force balance computation is executed to illustrate the different aggregation scenarios. The work provides a new input for the modeling and control of the vitrification process
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Vu, Thai Son. "Rhéologie des suspensions non newtoniennes". Phd thesis, Université Paris-Est, 2010. http://tel.archives-ouvertes.fr/tel-00598310.
Testo completoAbstract (sommario):
Au cours de ce travail, nous nous sommes attachés à prédire les caractéristiques rhéologiques de suspensions de particules dans des situations non newtoniennes. Nous avons tout d'abord étudié expérimentalement le comportement rhéologique de suspensions bidisperses de particules non colloïdales et non browniennes immergées dans un fluide à seuil dans les situations où les interactions entre particules sont hydrodynamiques (mécaniques). Nous avons montré que l'influence de la polydispersité des particules sur le module élastique et le seuil de contrainte de la suspension pouvait être décrit en utilisant un modèle d'empilement développé pour les matériaux granulaires secs. Deux relations analytiques simples permettant d'estimer le module élastique et la contrainte seuil d'une suspension non newtonienne polydisperse en fonction des caractéristiques des constituants ont alors été proposées et validées. Nous nous sommes ensuite intéressés à la prédiction des caractéristiques globales de suspensions contenant une forte concentration de particules de taille différente dans le cadre d'une approche par changement d'échelle. Pour cela, nous avons mis en uvre une approche par motifs morphologiques permettant la prise en compte de paramètres géométriques tels que la distribution de tailles des inclusions ou les distances entre particules voisines. Les résultats de ce modèle ont été validés par comparaison avec des données expérimentales de la littérature. Nous avons ensuite montré que les modèles morphologiques permettaient également de décrire l'évolution des modules complexes d'un matériau thixotrope subissant une transition de phase liquide-solide due à la croissance et la percolation d'un réseau de particules attractives. Dans la dernière partie de cette étude, nous avons étudié expérimentalement l'influence de l'histoire de cisaillement sur la structuration et la déstructuration d'une suspension colloïdale thixotrope
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Mariam, Mohaman Daïrou Nc. "Etude du comportement rhéologique des bétons de pieux lors de la mise en place des cages d'armatures - développement d'un outil de caractérisation". Thesis, Artois, 2017. http://www.theses.fr/2017ARTO0202/document.
Testo completoAbstract (sommario):
Un des problèmes de mise en œuvre des bétons rencontrés sur des chantiers de pieux forés à la tarière creuse est la difficulté d’introduire la cage d’armatures dans le béton frais dans 15 % des cas. Cette difficulté est liée en partie au comportement rhéologique du béton et au phénomène de ressuage qui sont des problèmes de formulation du béton. En effet, des études sur des fluides à seuil (pâtes de ciment, solutions de Carbopol, émulsions) comme le béton, montrent une corrélation entre le déplacement d’objets dans ces fluides et leurs seuils de cisaillement.L’objectif de cette étude est de développer un outil de caractérisation du béton sur chantier qui permette de tester la capacité des armatures à être introduites dans le béton à partir d’une technique basée sur le principe de la pénétrométrie. Une formulation de base de béton pour pieux a été choisie sur chantier et modifiée en laboratoire de façon à obtenir des bétons aux comportements variés (seuil de cisaillement, perte d’ouvrabilité et thixotropie) représentatifs des conditions sur site. L’influence de ces différents paramètres rhéologiques sur l’enfoncement des armatures a été étudiée. Elle a permis d’identifier des valeurs seuils pour lesquels un refus d’enfoncement de la cage d’armatures (blocage) est observé : slump<18 cm; τs>780 Pa et τ0>340 Pa.Une étude complémentaire menée sur 4 chantiers de pieux forés à la tarière creuse a permis de valider et d’affiner les conclusions précédentes et de prédire les blocages éventuelsThis study is mainly concerned with a concrete placement problem encountered on continuous flight auger (CFA) pile, namely the difficulty of introducing a reinforcement cage into fresh concrete, difficulty that occurs in 15 percent of cases. These difficulties are correlated in part with the rheological behavior of the concrete as well as with the bleeding phenomenon, both of which pertain to concrete mix design problems. Indeed, studies carried out on yield stress fluids, like concrete, reveal a correlation between object displacements in these fluids and their actual yield stresses.The aim of this study is to develop a tool for the in situ characterization of concrete at rest, based on the principles of penetrometry, which can assess the capability of introducing reinforcements into concrete.A widespread pile concrete mix design was chosen on-site and modified in the laboratory to obtain concrete mixtures with various behavior (yield stress, loss of workability and thixotropy) which are representative of on-site conditions. The influence of these rheological properties on the reinforcement embedment capacity has been studied. For low viscosity values (6 to 12 Pa.s), the rejection of reinforcement becomes a real risk for some threshold values : slump<18 cm; τs>780 Pa and τ0>340 Pa. To avoid blocking τ0 should be limited during casting process.An additional study was conducted on CFA piles on-site and helps to validate previous findings. It also describes reinforcement embedment kinetic. A correlation was found between reinforcement depreciation period during its setting and concrete viscosity
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Khalil, Noura. "Formulation et caractérisation chimique et rhéologique des mortiers imprimables en 3D à base de mélanges de ciments Portland et sulfoalumineux". Thesis, Ecole nationale supérieure Mines-Télécom Lille Douai, 2018. http://www.theses.fr/2018MTLD0014/document.
Testo completoAbstract (sommario):
Ce travail s’intéresse à la formulation et à la caractérisation de mortiers cimentaires imprimables en 3D. Il a été réalisé dans le cadre du projet MATRICE cofinancé par le fonds Feder et la région Hauts de France. Un cahier des charges pour un matériau cimentaire imprimable est tout d’abord défini sur la base de trois critères : l’extrudabilité, la constructibilité et la conservation des résistances mécaniques sur matériau imprimé. Deux mortiers imprimables sont formulés en utilisant des essais simples à l’échelle du laboratoire. Le premier mortier, à prise lente, est composé d’un liant à base de ciment Portland (OPC). Le second mortier, à prise accélérée, est composé d’un liant mixte (93 % d’OPC et 7 % de ciment sulfoalumineux (CSA)). Des impressions à l’échelle réelle sont ensuite réalisées dans le cadre du projet MATRICE et permettent de valider leur imprimabilité selon l’application de chacun. Le comportement chimique de mélanges de ciment Portland et de ciment sulfoalumineux est ensuite étudié expérimentalement. Les chaleurs d’hydratation mesurées par calorimétrie isotherme augmentent avec le dosage en CSA (de 2 % jusqu’à 10 %) et sont plus élevées que celles des pâtes de ciment contenant 100 % d’OPC et 100 % de CSA. La comparaison des hydrates identifiés dans le mélange à 7 % de CSA à ceux présents dans les deux pâtes de ciment pures montre que la présence de gypse et de chaux provenant du ciment Portland entraîne une hydratation plus rapide de la ye’elimite provenant du CSA et une formation d’ettringite à très court terme. Par contre, la nature des hydrates du ciment Portland n’est pas affectée. Le comportement rhéologique, notamment, la thixotropie, de pâtes constituées de mélanges de ciment Portland et sulfoalumineux (jusqu’à 10 %) est ensuite étudié en fonction de différents paramètres de formulation pendant la première heure. L’augmentation du dosage en CSA (0 % à 10 %) entraîne une augmentation quasi linéaire du coefficient de structuration (Athix) de ces mélanges. Pour les mélanges à 7 % de CSA et 100 % d’OPC, l’influence du rapport E/C et du dosage en superplastifiant sur la thixotropie est ensuite étudiée. L’augmentation du rapport E/C entraîne une diminution quasi linéaire de Athix pour chacune des pâtes de ciment. En revanche, le superplastifiant présente une faible influence comparativement au rapport E/CThe interest of this study is the formulation and characterization of 3D printing cementitious mortars. This research work has been carried out in the frame of the MATRICE Project, co-funded by the region “Hauts de France” and the European Union with the European Regional Development Fund. Specifications for a cementitious printable material are first set based on three criteria: extrudability, buildability and conserving the compressive strength of the printed material. Two printable mortars are formulated using simple tests on a laboratory scale. The first, with slow setting, is composed of a Portland-based binder (OPC). The second, with accelerated setting, is composed of a mixed binder (93% OPC and 7% sulfoaluminous cement (CSA)). Real scale prints are then realized in the frame of the project MATRICE allowing the validation of the printability of each mortar upon its application. The chemical behavior of Portland cement and sulfoaluminate cement mixes is then studied experimentally. The heats of hydration measured by isothermal calorimetry increase with the CSA dosage (2% to 10%) and are higher than those of cement pastes containing 100% OPC and 100% CSA. The comparison of the hydrates identified in the mix mad of 7% CSA to those present in the two other cement pastes of each cement alone shows that the presence of gypsum and lime from the Portland cement lead to a faster hydration of the ye’elimite from CSA and to an early formation of ettringite. However, the nature of hydrates is not affected. The rheological behavior, in particular the thixotropy, of the cement pastes made of Portland cement and sulfoaluminate cement (up to 10%) is then studied in function of different formulation parameters during the first hour. The increase in CSA dosage (0% to 10%) leads to an almost linear increase of the structuration coefficient (Athix) of theses mixes. For mixes with 7% CSA and 100% OPC, the influence of the W/C ratio and superplasticizer on the thixotropy is then studied. The increase in W/C ratio leads to an almost linear decrease of the Athix for each of cement paste. However, the superplasticizer present a low influence compared to the W/C ratio
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Nascimento, Everton Marques 1982. "Efeito de tratamentos térmicos nas propriedades em compressão de compósitos de baixa densidade de matriz metálica". [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265896.
Testo completoAbstract (sommario):
Orientador: Maria Helena RobertDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-25T20:34:20Z (GMT). No. of bitstreams: 1 Nascimento_EvertonMarques_M.pdf: 63165933 bytes, checksum: 94cd9296c446ce1fc132e40394363fc8 (MD5) Previous issue date: 2014
Resumo: Este trabalho analisa a influência de tratamentos de solubilização e envelhecimento na estrutura e propriedades de compósitos de baixa densidade de matriz da liga AA7075 reforçada com partículas cerâmicas porosas de cinasita (SiO2/Al2O3/Fe2O3) ou vermiculita (SiO2/Al2O3/MgO), produzidos por tixoconformação. Foram empregadas as condições de tratamento: solubilização a 470ºC por 12 horas e envelhecimento a 170ºC por 24 horas. Os materiais produzidos foram caracterizados nas condições tixoconformada, solubilizada e envelhecida. Nos compósitos no estado tixoconformado foram analisadas a densidade e a usinabilidade em processo de corte por jato de água abrasivo (AWJM), para determinação do Número de Usinabildade (N) de cada tipo de compósito. Os compósitos foram também analisados quanto à sua microestrutura (por MO e MEV), a distribuição dos principais elementos de liga (Zn, Mg e Cu) na matriz metálica, a microdureza da matriz metálica, o comportamento mecânico sob compressão semi-estática e compressão dinâmica (impacto) nas três condições citadas. Resultados mostraram que os compósitos produzidos apresentam, no estado tixoconformado, densidades relativas da ordem de 0,5 e número de usinabilidade por jato abrasivo (N) cerca de 20% superior ao da liga sem reforço. Quanto ao efeito do tratamento térmico na microestrutura dos compósitos, os resultados mostraram que a solubilização nas condições testadas não promovem total solubilização das fases secundárias, devido à sua presença como contornos grosseiros na estrutura tixoconformada; e que o envelhecimento promoveu a formação de precipitados finos dispersos na matriz. Como resultado destas alterações microestruturais foram observados aumentos da ordem de 35% na microdureza da matriz metálica de ambos os compósitos. Com relação ao comportamento mecânico em compressão, os compósitos mostraram comportamento característico de materiais celulares, apresentando característico platô de deformação plástica, a baixas tensões, por adensamento de poros. Como efeito dos tratamentos térmicos foram observados aumentos da ordem de 2x na tensão máxima e de 6x na tensão de platô, e cerca de 13 a 17% de redução da deformação plástica dos compósitos analisados. De modo geral os compósitos contendo cinasita apresentaram comportamento ligeiramente menos dúctil do que os contendo vermiculita
Abstract: This work analyses the influence of heat treatments (solution/ageing) in the structure and properties of low-density composites; aluminum matrix reinforced with porous ceramic particles, cinasite (SiO2/Al2O3/Fe2O3) and vermiculite (SiO2/Al2O3/MgO), were produced by thixoforming process. The used conditions are: solution at 470°C for 12 hours and ageing at 170°C for 24 hours. The composites were characterized in different conditions: as thixoformed and after solution/ageing treatments. Density and machinability in abrasive jet cutting (AWJM) process of the thixoformed composites were analysed to determine the machinability number of each composite. The microstructure (OM and SEM), the distribution of the main alloying elements (Zn, Mg and Cu) in metal matrix, the hardness of the metal matrix, the mechanical behavior under semi-static compression and dynamic compression (impact) in the three conditions were analysed. Results showed that the composites in the as thixoformed condition present relative densities of 0.5 and their machinability number in abrasive jet (N) is 20% higher than the one of unreinforced alloy. As an effect of heat treatment on the microstructure of the composite, it was observed that the solubilization in the tested conditions does not promote complete solubilization of eutectic phases due its presence as coarse grain boundaries in thixoformed structure; formation of fine precipitates dispersed in the matrix was promoted by the aging treatment. As a result of these microstructural changes, the hardness of the metal matrix (for both composites) increased in 35%. The mechanical behaviour of the composites in compression was similar to the behaviour of cellular materials, presenting a characteristic plateau of plastic deformation at low-stress due pores densification. For the composites produced, as an effect of heat treatment, was observed that the maximum stress increases 2x, the plateau-stress increases 6x and plastic deformation decreases about 34%. Generally the composites containing cinasita showed less ductile behavior than those containing vermiculite
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
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Bhatia, Rupesh. "Effect of molecular mass, concentration and temperature on the rheological properties of non-newtonian aqueous polymeric solutions". University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1313765879.
Testo completo
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Grant, Holly Victoria. "A viscoelastic constitutive model for thixotropic yield stress fluids: asymptotic and numerical studies of extension". Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/80440.
Testo completoAbstract (sommario):
This dissertation establishes a mathematical framework for analyzing a viscoelastic model that displays thixotropic behavior as a model parameter gets very small. The model is the partially extending strand convection model, originally derived for polymeric melts that have long strands that get in the way of fully retracting. A Newtonian solvent is added. The uniaxial and equibiaxial extensional flows are studied using combined asymptotic analysis and numerical simulations. An initial value problem with a prescribed elongational stress is solved in the limit of large relaxation time. This gives rise to multiple time scales. If the initial stress is less than a critical value, the initial elastic elongation is followed by settling to an unyielded state at the slow time scale. If the initial stress is larger than the critical value, then yielding ensues. The extensional flows produce delayed yielding and hysteresis, both associated with thixotropy in complex fluids.Ph. D.
22
Peluso, Tomais Gonçalves 1990. "Avaliação da tixoconformabilidade da liga A318". [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265807.
Testo completoAbstract (sommario):
Orientador: Eugênio José ZoquiDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-27T09:38:07Z (GMT). No. of bitstreams: 1 Peluso_TomaisGoncalves_M.pdf: 4698944 bytes, checksum: 3430f71d5bf40358338cef1d992df4fc (MD5) Previous issue date: 2015
Resumo: O objetivo desse estudo é avaliar a tixoconformabilidade da liga A318 sob três pontos de vista: o termodinâmico, o metalúrgico, e o reológico. Esse trabalho é motivado pela falta de estudos sobre a tixoconformabilidade desse material em ambientes industriais. Foram realizadas análises DSC e simulações utilizando o software Thermo-calc® para verificar a viabilidade do ponto de vista termodinâmico. Foram feitas comparações entre o material fundido com e sem agitação eletromagnética para decidir qual seria usado como material de estudo para o tratamento térmico de globularização, e em seguida análises para determinar tamanhos de glóbulo de fase primária, tamanhos de grão e fatores de forma, o que resultou no material fundido com agitação sendo escolhido. O material então passou pelo tratamento térmico de globularização, a fim de observar a evolução morfológica do material. Foram utilizadas micrografias para determinar os tamanhos de glóbulo primário e fator de forma, e micrografias coloridas para determinar os tamanhos de grão, para cada condição de ensaio proposta. O tratamento térmico globularizou com sucesso a microestrutura do material, obtendo fatores de forma de até 0,64, e tamanhos de glóbulo e grão de apenas 76 e 115 µm respectivamente. O material tratado termicamente passou então por ensaios de compressão a quente, para que fosse observado seu comportamento reológico. O maior valor de tensão obtido durante os ensaios foi de apenas 1,95 MPa, e a viscosidade aparente se manteve na ordem de grandeza de 105 Pa.s, o que de acordo com a literatura é semelhante à do vidro fundido, e apresentam ótima conformabilidade. De maneira geral, observou-se pouca variação na morfologia e na reologia do material para as condições de estudo propostas, mostrando que o material é viável para ser utilizado no estado semissólido em ambientes industriais
Abstract: The objective of this study is to evaluate the thixoformability of the A318 alloy under three points of view: the thermodynamic one, the metallurgic one, and the rheologic one. This work is motivated by the lack of that support the thixoformability of this material in industrial environment. DSC analyses, and simulations using the Thermo-calc® software were run in order to verify the viability from the thermodynamical point of view. Comparisons were made between the materials as-cast and electromagnetically stirred in order to decide which would be the feedstock material for the globularization heat treatment, analyzes to determine globule size, grain size and shape factor resulted in the stirred material being chosen. Material then went into globularization heat treatment in order to observe the evolution of the material¿s microstructure. The heat treated material then went through hot pressing tests in order to observe its rheologic behavior. Micrographs were used to determine average primary globule size and shape factor, and macrographs to determine grains size. The heat treatment successfully globularized the microstructure, giving shape factors as high as 0.64, and primary globule and grains sizes only as high as 76µm and 115µm respectively. The material then went through hot pressing tests in order to observe its rheologic behavior. The highest stress shown during the tests was only as high 1,95 MPa, and the apparent viscosity was in the order of magnitude of 105 Pa.s, which according to specialized literature is similar to that of the molten glass, which shows great conformability. In general, there was close to no variation in morphologic and rheologic behavior for the intended test conditions, showing the material¿s processing in the semisolid state in industrial environments to be viable
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
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Amaral, Alline Áurea do. "Comportamento reológico de recheios para chocolates em base gordurosa e formulados com polpas de frutas e gomas". Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/9/9133/tde-16012014-135000/.
Testo completoAbstract (sommario):
Recheios são componentes utilizados na indústria de chocolates e de confeitos. Os recheios para chocolates podem ser elaborados com gorduras vegetais, açúcar fondant, creme de leite, amido ou com preparados de frutas contendo gomas. Nesses produtos, as gomas podem ser empregadas com a função de estabilizante, espessante ou como redutores de gordura, minimizando alterações sensoriais, de textura e de separação de fases. A goma guar vem sendo utilizada em muitos produtos alimentícios. A goma chichá é extraída de uma árvore brasileira (Sterculia striata) que pertence à mesma família da goma comercial caraia (Sterculia urens). O murici (Byrsonima verbascifolia, Rich) é um fruto brasileiro de alto valor nutricional. Assim foram elaboradas formulações alterando-se a base gordurosa, com os tipos de gordura hidrogenada, low trans, de cupuaçu e manteiga de cacau em diferentes teores (10%, 7,5% e 5% p/v). A polpa de murici (13%) e as gomas chichá e guar (0,3% m/v) foram adicionadas com a finalidade de agregar valor nutricional e estabilizar os recheios. O estudo reológico das formulações foi realizado por testes oscilatórios e rotacionais realizados em conjunto com imagens de microscopia óptica, sendo importante para avaliar os aspectos estruturais e micro estruturais dos produtos decorrente dos ingredientes utilizados, verificando-se assim diferenças de comportamento e interações entre os mesmos. Avaliações físico-químicas foram efetuadas nas formulações contendo gordura low trans + suco de laranja concentrado e gordura low trans + polpa de murici. Os resultados mostraram que a adição da polpa de murici elevou os teores de proteínas e minerais das formulações. A análise reológica apontou caráter sólido ou de gel forte para todas as amostras, pois o módulo elástico foi superior ao módulo viscoso (G\' > G\"). Verificou-se que as formulações com gordura low-trans + goma guar e gordura low trans + goma chichá apresentaram comportamento semelhante; a adição dessas gomas mostrou melhora na recuperação da estrutura inicial do sistema. Em geral, os recheios produzidos apresentaram boa estabilidade e valor nutricional agregado.Fillings are components used in the chocolate and confectionery industry. The fillings for chocolates can be made with vegetable fats, fondant, cream, starch or fruit preparations containing gums. In these products, the gums can be employed as a stabilizer, thickener or a fat reducing, minimizing sensory, texture and phase separation. Guar gum has been used in many food products. Chichá gum is extracted from a Brazilian tree (Sterculia striata) that belongs to the same family of commercial karaya gum (Sterculia urens). Murici (Byrsonima verbascifolia, Rich) is a Brazilian fruit of high nutritional value. Thus formulations were prepared by changing the fat base with different fat types (hydrogenated fat, low-trans, cupuaçu and cocoa butter) and levels (10%, 7.5% and 5%). Murici pulp (13%), chichá and guar gum (0.3% w / v) were added in order to add nutritional value and stabilize. The rheological study of the formulations was performed by rotational and oscillatory tests in conjunction with optical microscopy images, being important to evaluate the structural and micro structural aspects of the products due to the added ingredients, thus verifying behavioral differences and interactions between them. Physical-chemical evaluations were leaded in the formulations containing low trans fat + concentrated orange juice and low trans fat + murici pulp. The results showed that the addition of murici pulp increased levels of proteins and minerals in formulations. The rheological analysis showed solid or strong gel character for all samples because the elastic modulus was higher than the viscous modulus (G\' > G\'\'). Formulations with low trans fat + guar gum and low trans fat + chichá gum showed similar behavior; addition of the gums showed better recovery of the initial structure of the system. In general, the produced fillings showed good stability and added nutritional value.
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Sands, William A., Melonie B. Murray, Steven R. Murray, Jeni R. McNeal, Satoshi Mizuguchi, Kimitake Sato e Michael H. Stone. "Peristaltic Pulse Dynamic Compression of the Lower Extremity Enhances Flexibility". Digital Commons @ East Tennessee State University, 2014. https://dc.etsu.edu/etsu-works/4621.
Testo completoAbstract (sommario):
This study investigated the effects of peristaltic pulse dynamic compression (PPDC) on range-of-motion (ROM) changes in forward splits. Serious stretching usually involves discomfort and large time investments. Tissue structural changes and stretch tolerance have heretofore been considered the primary mechanisms of enhanced ROM. The PPDC treatment was computer controlled. Circumferential and segmented inflation pressures were induced by feet to hip leggings. Nine subjects, experienced in stretching and a forward split position, volunteered. The subjects were familiarized with the protocol and randomly assigned to an initial condition: experimental (PPDC), or control (CONT). The study involved a crossover design. Second conditions were tested within 1–5 days. All tests were 2 trials of right and left forward splits. Split flexibility was assessed by measuring the height of the anterior superior iliac spine of the rear leg from the floor. Pelvic posture was controlled by rear leg position. The PPDC treatment was 15 minutes of seated PPDC. The control condition was the same except that leggings were not inflated. Pressures of 5 cells in the leggings were set at factory defaults, 70 mm Hg sequentially. Difference score results indicated statistically significant (p ≤ 0.05) differences by condition and the condition by leg interaction. The rapid acute changes in ROM (PPDC: right 25.3%, left 33.3%; CONT: right 12.2%, left 1.0%) support the premise that changes in ROM were dependent on mechanisms other than tissue structural changes and/or stretch tolerance. PPDC provides a means of rapidly enhancing acute ROM requiring less discomfort and time.
25
Touré, Abdoulaye. "Hydraulique en charge des fluides thixotropes". Grenoble INPG, 1995. http://www.theses.fr/1995INPG0051.
Testo completoAbstract (sommario):
Un fluide thixotrope soumis a un cisaillement constant voit sa consistance diminuer dans le temps (destructuration) et augmenter au repos (restructuration), ces deux evolutions pouvant etre simultanees. Ce travail porte sur l'exploration et l'identification des effets de la thixotropie sur les ecoulements en charge transitoires et permanents et sur leur stabilite. Pour mener a bien cette recherche, plusieurs fluides modeles transparents finement caracterises d'un point de vue rheometrique ont ete mis au point et en circulation dans une installation entierement transparente. Les mesures mecaniques globales ont montre d'une part que lors de l'ecoulement de demarrage, la presence de seuil d'ecoulement, la rheofluidification et le comportement visqueux ont peu d'effet sur le caractere et la duree du demarrage ; seule la thixotropie joue un role comparativement preponderant. Et d'autre part, en regime permanent l'augmentation de l'echelle de temps de la thixotropie par rapport au temps de residence d'une particule fluide dans la conduite, a nombre de reynolds et a nombre de seuil constants augmente considerablement les pertes de pression singuliere. L'etude locale du champ cinematique du fluide thixotrope a permis de mettre en evidence les instabilites durant la phase de demarrage ainsi que dans le regime permanent. Dans la phase de demarrage, l'instabilite de l'ecoulement prend la forme d'une digitation du fluide provenant du reservoir au travers du fluide initialement dans la conduite. Une simulation experimentale de la thixotropie au moyen d'un fluide entrant newtonien moins visqueux poussant soit un fluide rheofluidifiant plus visqueux ou un fluide a seuil sans thixotropie montre egalement l'existence d'instabilites similaires. En regime permanent, la non homogeneite spatiale de l'histoire de cisaillement est a l'origine de la variation spatiale des proprietes mecaniques du fluide thixotrope provoquant une stratification des proprietes mecaniques qui conduit a l'instabilite. Cependant la mesure globale des pertes de charge montre que le coefficient de frottement moyen en regime instable est proche de celui d'un ecoulement etabli
26
Wallevik, Jon Elvar. "Rheology of Particle Suspensions : Fresh Concrete, Mortar and Cement Paste with Various Types of Lignosulfonates". Doctoral thesis, Norwegian University of Science and Technology, Department of Structural Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-319.
Testo completoAbstract (sommario):
The major issue concerns how the different lignosulfonate types changes the rheological properties of the cement based material (concrete, mortar and cement paste) as a function of temperature and time. In such terms, it is demonstrated that the high molecular weight lignosulfonates performs far better than the low molecular weight ones. The former type also performs considerable better compared to a naphthalene based polymer.
The above investigation is done with help from the second part of this thesis, which identifies some of the parameters p1, p2,... affecting the shear viscosity η = η ( p1, p2,...) of the cement based material. This is done by investigating the thixotropic behavior of cement paste mixed with either lignosulfonates or naphthalene. The thixotropic behavior is directly related to coagulation, dispersion and re-coagulation of the cement particles. In making the analysis, a modification is applied to the Hattori-Izumi theory, which is a theory about the bookkeeping of the number of reversible coagulated connections between the cement particles. The modification consist, among other things, of include a fading memory to the analysis. That is, the cement paste is allowed to remember its recent past. By a combination of experimental results and numerical simulations, it is demonstrated that such memory term is very important.
An experimental error is present during a viscometric measurement on concrete (a coaxial cylinders viscometer is used). The error is generated by particle migration. Investigating and compensating for this error constitutes the third part of this thesis. Realizing the nature of this error, some corrections are applied. However, with these corrections, one is only extracting the viscometric values of a "fat'' concrete that surrounds the inner cylinder of the viscometer after the particle migration is basically complete, and not of the concrete in the original homogenous state.
27
Helnan-Moussa, Benjamin. "Influence de la température sur la thixotropie des bétons autoplaçants". Thesis, Artois, 2009. http://www.theses.fr/2009ARTO0203/document.
Testo completoAbstract (sommario):
L’objectif de cette thèse est d’étudier l’influence de la température sur la thixotropie des bétons autoplaçants (BAP). L’intérêt de ce travail s’inscrit dans la perspective d’optimiser les formulations des BAP dans une large gamme de température. Un plan factoriel composite centré a été adopté dans le but de minimiser le nombre d’essais tout en étudiant les effets des facteurs (température et dosage en agent de viscosité (AV)) et leurs interactions sur les propriétés rhéologiques des BAP.La première phase de l’étude consistait à quantifier la thixotropie du béton juste après le malaxage et durant la période dormante en fonction du dosage en AV à des températures comprises entre 11.3 et 30.7°C selon le protocole proposé par Wallevik sur le rhéomètre BML4. Les résultats ont montré que l’indice de thixotropie présente un minimum respectivement pour un dosage en AV de 0.28 % (par rapport à la masse d’eau) et une température de 24°C. Cependant, ce protocole ne permet pas d’étudier la déstructuration des BAP, facteur recherché par exemple dans les coulages multicouches. Nous avons donc été amenés à retenir un protocole utilisé dans les gels et appelé protocole Dolz. L’application de ce dernier aux pâtes de ciment et aux BAP a permis de mettre en évidence une nouvelle grandeur, le potentiel de déstructuration K. Les valeurs du potentiel K montrent qu’au delà d’un certain dosage en AV et d’une certaine température, apparaissent des phénomènes d’encombrement qui réduisent le potentiel K. Ainsi, le potentiel K apporte des informations complémentaires pour l’aide à la sélection de dosages adéquats du couple superplastifiant – agent de viscosité en fonction de la température de coulageThe aim of this thesis was to study the influence of the temperature on the thixotropy of self-consolidating concrete (SCC). The research significance comes within the perspective to optimize the design of SCC in a wide range temperature. A factorial composite experimental plan was carried out in order to minimize the total number of tests while studying the effects of factors (temperature and dosage of viscosity modifying admixture (VMA)) and their interactions on the rheological properties of SCC. The first phase of the study was to quantify the thixotropy of concrete proportioned with various dosage of VMA at different temperatures ranging from 11.3 to 30.7°C just after mixing and at different time during the dormant period using the protocol proposed by Wallevik in BML4 rheometer. The results indicated that the values of thixotropy index present a minimum respectively with a VMA dosage of 0.28 % (by mass of water) and a temperature of 24°C.On the other hand, this protocol does not allow studying the destructuration of SCC, useful factor needed for example in the multi-layer casting. We therefore had to retain a protocol used in gels and called Dolz protocol. The application of this last to cement pastes and SCC has revealed a new grandeur, the potential of destructuration K. The values of K show that beyond a certain dosage in VMA and a certain temperature, the congestion phenomena appear that reduce the potential K. In this case, the potential of destructuration provides complementary information to assist in the selection of appropriate dosages of couple superlasticizer-VMA whatever the casting temperature may be
28
Cohu, Olivier. "Rhéologie des peintures et procédé de couchage au rouleau". Grenoble INPG, 1995. http://www.theses.fr/1995INPG0028.
Testo completoAbstract (sommario):
La maitrise du procede de couchage de peinture par machine a rouleaux contrarotatifs necessite la comprehension des phenomenes determinant l'epaisseur et l'aspect du film depose sur le substrat. Cela passe par le controle des proprietes rheologiques des peintures, dans les conditions de sollication correspondant au procede. Dans ce but, on developpe une methodologie adaptee au procede de laquage des aciers (coil-coating). Cela nous permet d'observer que les peintures pour coil-coating ont soit un comportement quasiment newtonien, soit sont thixotropes a seuil de contrainte. Des relations liant l'epaisseur du film liquide depose sur le substrat aux parametres du systeme, pour un fluide newtonien, sont ensuite discutees a la lumiere d'une etude experimentale, realisee sur un enducteur pilote. Elles tiennent compte notamment des deformations subies par les rouleaux revetus de materiaux elastomeres. On montre qu'elles peuvent s'appliquer aux peintures thixotropes, si l'on se refere a la viscosite de ces produits en regime permanent vers 10#4 s#-#1. Ce resultat est du a la fragilite constatee des structures responsables de la thixotropie. Il confirme ainsi la validite des mesures rheometriques prealables. Du fait de l'instabilite de l'ecoulement entre rouleaux contrarotatifs, des defauts de surface (cordage) sont inevitablement generes sur le film lors de l'enduction. L'aspect des produits peints depend donc de la capacite du fluide a niveler avant sechage les irregularites du film. La thixotropie des peintures perturbe le nivellement. Un modele semi-empirique, valide par des mesures experimentales, est presente pour evaluer la cinetique de nivellement d'un enduit thixotrope. On evoque egalement l'influence de l'evaporation du solvant et de la cuisson des peintures. Ces travaux permettent de formuler une condition suffisante, sinon necessaire, a la production de film exempts de defauts. La rheologie peut contribuer ainsi a prevoir la machinabilite d'une peinture, au regard du procede coil-coating
29
Ferreira, Lygia Maria Policarpio 1987. "Fabricação de materiais compósitos por tixoconformação de misturas de cavacos de alumínio com pós cerâmicos". [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263611.
Testo completoAbstract (sommario):
Orientador: Maria Helena RobertDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Este trabalho explora a aplicação da tecnologia de metais semi-sólidos para a fabricação de compósitos de matriz metálica (CMM), e ainda a possibilidade de reciclagem de cavacos de usinagem para a produção destes materiais, buscando o desenvolvimento de uma engenharia de baixo custo. São empregados como matriz a liga AA7075, dada a grande geração de cavacos de usinagem na indústria aeronáutica, e SiC ou NiAl2O4 particulados como reforços. O processo é baseado na tixoconformação de misturas de cavacos e partículas de reforço; é esperada a penetração destas últimas em contornos de glóbulos, contendo líquido, no interior do cavaco no estado semi-sólido. São avaliados parâmetros de processo e sua influência na qualidade do produto, em particular na distribuição de reforço na matriz e interação matriz/reforço. Compósitos tixoconformados contendo 10, 20 e 30% em peso de SiC são avaliados mecanicamente através de ensaios de microindentação instrumentada e desgaste micro-abrasivo. Os resultados mostraram, de modo geral, a viabilidade do processo proposto para a fabricação de diferentes tipos de compósitos, o qual envolve procedimento simples e de reduzido custo, além de mostrar a possibilidade de produção de materiais com boas propriedades mecânicas a partir da reciclagem de cavacos, particularmente importante em uma indústria que envolve elevada demanda de energia, como a do Al. Os resultados indicaram que a qualidade geral do produto, em termos de distribuição do reforço e interação reforço/matriz dependem da adequada seleção dos parâmetros de processo: temperatura, tempo de aquecimento, pressão de tixoconformação. Entre as várias condições estudadas, as composições nas quais foi utilizado NiAl2O4 como reforço apresentaram melhores características microestruturais, com melhor interface entre matriz e reforço e baixa porosidade. Boa dispersão das partículas de reforço e baixa porosidade também foram observados para compósitos reforçados com SiC nos quais foram adicionadas partículas finas de silício e alumina
Abstract: This work explores the application of semi-solid technology to produce metal matrix composites, and also the possibility of using machining chips as raw material. The main aim is to develop a process inserted in a low cost engineering concept. To achieve this general objective, the alloy AA7075 is used as matrix, once a significant amount of rejected chips of this high resistance, low weight alloy is generated in the aeronautical industry. As reinforcing material, SiC or NiAl2O4 particles are used. The proposed process is based on the thixoforming of pre-compacted mixtures of chips and reinforcing particles; it is expected the penetration of reinforcing particles within the semi-solid, thixotropic material. It is analyzed the influence of processing parameters in the final quality of products, particularly in the reinforcement dispersion in the matrix and matrix/reinforcement interface. Thixoformed composites containing 10, 20 and 30% weight SiC are produced and evaluated concerning mechanical properties through indentation tests and micro wear. Results showed the general viability of producing composites by the proposed technique, based on a simple and low cost procedure. It was also shown the possibility of producing materials with good mechanical properties from recycled chips, which is particularly important in the high energy demanding Aluminium industry. Results showed the importance of choosing appropriate processing parameters (temperature, heating rate / soaking time and thixoforming pressure), to achieve desired product quality. Among the various conditions studied, the compositions in which NiAl2O4 was used as reinforcement showed better microstructural characteristics with better interface between matrix and reinforcement, and lower porosity. Good dispersion of the reinforcement particles and low porosity were also observed for SiC reinforced composites in which fine particles of silicon and alumina were added
Mestrado
Materiais e Processos de Fabricação
Mestra em Engenharia Mecânica
30
Wirthová, Michaela. "Reologie v technologii anorganických materiálů". Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2013. http://www.nusl.cz/ntk/nusl-233373.
Testo completoAbstract (sommario):
Disertační práce se zabývá studiem reologického chování materiálů na bázi cementu. Úvodní část obsahuje teoretické poznatky týkající se reologie a zkoumaných materiálů (cement, samozhutnitelný beton, superplastifikátory). Poté následuje detailní popis reologických vlastností čerstvých cementových materiálů. Kromě toho je dále uvedena hydratace cementu, kalorimetrie, Vicatův test, rentgenová difrakční analýza a elektronová mikroskopie. Experimentální část práce je rozdělena do dvou částí. První část se zabývá základní charakterizací, reologickým měřením a studiem statické meze toku směsí samozhutnitelných betonů a jejich matric. Druhá část se týká cementových past, které byly podrobeny testování pomocí reometru, Vicatova přístroje, isoperibolického a modulárního kalorimetru, rentgenového difraktometru a elektronového mikroskopu.
31
Pignon, Frédéric. "Rhéologie des dispersions aqueuses thixotropes d'une argile de type hectorite". Grenoble INPG, 1997. http://www.theses.fr/1997INPG0016.
Testo completoAbstract (sommario):
Le but de cette etude est l'identification et la comprehension des mecanismes gouvernant le comportement thixotrope dans les dispersions aqueuses d'une argile de type hectorite : la laponite. Cette argile modele, constituee de particules anisotropes de taille nanometrique, a permis de combiner les mesures rheometriques avec des mesures de diffusion de rayonnements, des visualisations du champ de deformation et des mesures de birefringence. Au repos, la structure des gels est constituee d'agregats microniques denses assembles en une masse fractale d'une dimension d. Pres de la transition sol-gel, d = 1, la texture est fibreuse. Aux fractions volumiques plus elevees, d = 1,8, la structure est une connexion de zones denses et de zones moins denses en particules. Des lois d'echelles theoriques et experimentales, ont permis de correler ces dimensions fractales a l'influence de la fraction volumique sur le seuil d'ecoulement. La transition sol-gel et la stabilite de la phase gel ont ete etudiees en fonction du temps de gelification et des parametres physico-chimiques. L'existence d'instabilites d'ecoulements, telle que la localisation du cisaillement, ont ete montrees, sur ces dispersions dont la courbe d'ecoulement est a minimum de contrainte. Les differents regimes d'ecoulements ont ete identifies et ont permis d'etablir des procedures fiables pour la caracterisation du comportement thixotrope. Sous ecoulement de cisaillement, la chute de viscosite provient d'orientations et de desagregation a l'echelle de longueur de l'ordre du micron. Lors de la restructuration, les deux echelles de temps mises en evidence, correspondent respectivement a une relaxation rapide des orientations et a un processus lent d'agregation. La nature du comportement thixotrope est alors identifiee comme etant principalement un processus d'agregation reversible, pour lequel les grandes echelles de longueur, de l'ordre du micron, associees a un arrangement fractal jouent un role determinant.
32
Paiola, Johan. "Écoulement d'un fluide à seuil dans un milieu poreux". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS031/document.
Testo completoAbstract (sommario):
Solides élastiques au repos, les fluides à seuil s’écoulent comme un liquide au-delà d’une certaine contrainte. Plusieurs applications industrielles concernent l’écoulement de ces fluides dans des milieux poreux. On peut citer par exemple les émulsions dans le processus de récupération du pétrole, les opérations de cimentation dans le sol, ou le nettoyage d’un sol contaminé par une boue. Pour ces applications, il est nécessaire de connaitre la pression nécessaire pour un débit voulu à la sortie du milieu poreux. Dans de tels cas, l’écoulement est perturbé par la complexité de la géométrie. Les modèles développés pour décrire la loi de Darcy supposent une loi rhéologique appliquée localement, mais ces modèles décrivent mal ce type d’écoulement. De plus, des effets complexes peuvent s’ajouter comme le glissement à la paroi ou la thixotropie. Dans cette thèse, nous étudions l’écoulement de carbopol (ETD 2050) à travers différentes géométries. Tout d’abord au rhéomètre, nous montrons que le fluide, sous certaines conditions, correspond bien à un fluide à seuil modèle. Nous démontrons que le protocole expérimental utilisé est très important et qu’un comportement thixotropique peut apparaitre s’il n’est pas respecté. Ce comportement apparait notamment lorsque le fluide reste sous le seuil, l’impact augmentant avec le temps d’attente. Ensuite, nous comparons la loi d’écoulement obtenue au rhéomètre à l’écoulement dans un canal droit obtenu par microfabrication. Nous montrons alors l’importance du glissement proche du seuil et ses conséquences sur la loi d’écoulement. Enfin nous étudions l’écoulement du carbopol dans un milieu poreux. Le milieu poreux de 5x5cm est obtenu par microfabrication. La largeur moyenne des canaux est égale à celle du canal droit. Nous avons développé une nouvelle méthode de mesure des champs de vitesse. Nous montrons l’apparition d’une chenalisation de l’écoulement à travers quelques canaux du milieu poreux. Nous comparons ensuite la loi d’écoulement du milieu poreux à celle obtenue dans le canal droit. On remarque que la vitesse d’écoulement est plus faible dans le milieu poreux que dans le canal droitElastic solids at rest, yield stress fluids flow like a liquid beyond a certain stress. Many industrial applications required the flow of these fluids in porous media, for example: the emulsion flow in oil recovery processes, the cementing operations in the ground, or the cleaning of sludge in a contaminated soil. For many applications, it could be interesting to know the pressure required for a desired flow rate. In such cases, the flow behavior of the fluid is complicated by the complexity of the geometry. The models developed to describe Darcy's law assume a rheological law applied locally, but these models poorly describe this type of flow. Furthermore, complex effects can be added like the wall slip or the thixotropy. In this thesis, we study the flow of carbopol (ETD 2050) through different geometries. First we show that the fluid, for some conditions, corresponds to model yield stress fluids. The experimental protocol used is very important and a thixotropic behavior can appear if it is not respected. This behavior appears especially when the fluid remains below the yield stress, the impact increases with the waiting time. We then compare the flow law obtained by rheometer in a straight channel obtained by microfabrication. We show the importance of the wall slip near the yield stress and the impact on the flow law. Finally, using a new method to measure the velocity fields developed during this thesis, we study the flow of carbopol in a porous medium. This porous medium of 5x5cm is obtained by microfabrication. The mean width of the channels is equivalent to the one of the straight channel. We show the emergence of a channeling flow through some channels of the porous medium. We then compare the flow law of the porous medium to the one obtained in the straight channel. It can be observed that the flow rate is lower in the porous medium than in the straight channel
33
Cristofolini, Renato. "Estudo da potencialidade da aplicação do ferro fundido nodular ASTM A536 60-40-18 como materia prima para processos de tixoconformação". [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263560.
Testo completoAbstract (sommario):
Orientador: Maria Helena RobertTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Este trabalho analisa a tixohabilidade, a viabilidade de produção de pastas tixotrópicas e as transformações de fase que ocorrem na tixofundição do ferro fundido nodular ASTM A536 60-40-18. A análise da tixohabilidade é feita através de análises térmicas utilizando técnicas de Análise Térmica Diferencial (ATD) e Calorimetria Exploratória Diferencial (CED) em diferentes condições operacionais (tipo de ciclo e taxas de aquecimento/resfriamento), e através de simulação termodinâmica utilizando software THERMOCALC®. São discutidas a influência das condições dos ensaios nas temperaturas de transformações e intervalos de solidificação, e os resultados comparados com os obtidos por simulação. São discutidas as transformações de fases que ocorrem e as respectivas temperaturas, sendo proposto diagrama de fases para a liga específica em estudo. São determinadas a sensibilidade da variação da fração líquida com a temperatura (dFL/dT) e sugeridas janelas de tixoconformação, para todas as condições analisadas. Os resultados obtidos indicam uma faixa de operação para a tixoconformação da ordem de 20oC, onde uma transformação eutética se faz presente e a variação da fração líquida com a temperatura pode ser controlada adequadamente. A janela de tixoconformação depende da taxa de transferência de calor empregada: quanto maior a taxa, maior o intervalo de transformação eutética e maior a janela de tixoconformação. Quanto à análise da viabilidade de produção de pastas tixotrópicas, foram produzidas pastas por fusão parcial controlada a distintas temperaturas dentro da faixa de operação para tixoconformação determinada previamente. As microestruturas resultantes foram analisadas por microscopia ótica (MO) e eletrônica de varredura (MEV), difratometria de raios-x e microanálise utilizando energia dispersiva (EDS). Os resultados mostram a viabilidade de produção de pastas com características tixotrópicas, nas condições analisadas, apesar da estreita faixa de temperaturas da janela de tixoconformação do material estudado. Mostram ainda que a temperatura de tratamento influencia a quantidade e dimensões dos nódulos de grafita presentes na matriz da pasta, sendo que temperaturas de tixofundição superiores à faixa de transformação eutética podem levar à rápida dissolução desses nódulos e como consequência, o aumento da dureza da liga e redução de sua ductilidade. O produto tixofundido apresenta, à temperatura ambiente, estrutura constituída essencialmente de martensita, resultado do resfriamento rápido da austenita, grafita nodular de pequenas dimensões e de fases complexas em contornos de grãos martensíticos.
Abstract: This work analyses the thixoability, the viability of actual production of thixotropic semi-solid of ferritic nodular cast iron ASTM A536 60-40-18, as well as the phase transformations taking place in the process. Thixoability evaluation is made through thermal analysis by Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC) tests in different conditions (cycle type and heating/cooling rate), and also through thermodynamic simulations using THERMOCALC® software. Related to these analysis it is evaluated the influence of tests conditions on transformations temperatures and ranges; results are compared to those obtained by simulation. Phase transformations are discussed and a specific phase diagram for the alloy investigated is proposed. Liquid fraction sensitivities with temperature (dFL/dT) are determined, and thixoforming windows are suggested. Results indicate that a thixoforming window in the order of 20°C are available; in this range a eutectic transformation takes place and the liquid fraction can be controlled. Beyond the eutectic temperature liquid fraction increases significantly with temperature variation and processing control can not be assured. Thixoforming windows depend on heat transfer rates: higher the rate, higher the eutectic range and the thixoforming window. To analyse the viability of actually producing thixotropic slurries by partial melting, samples were heated to temperatures within the thixoforming windows previously suggested. Resulting microstructures were analysed by optical and electronic microscopy, X-R diffraction and EDS microanalysis. Results show the feasibility of producing thixotropic semi-solid of the studied nodular iron, in spite of its narrow thixoforming field; treatment temperature influences the size and amount of graphite nodules in the matrix. Higher temperatures can lead to fast dissolution of graphite, jeopardizing the ductility of the material. Thixocast product presents, at room temperature, small nodules of graphite in a martensitic matrix and a complex phase in grain boundaries.
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica
34
Babadopulos, Lucas. "Phenomena occurring during cyclic loading and fatigue tests on bituminous materials : Identification and quantification". Thesis, Lyon, 2017. http://www.theses.fr/2017LYSET006/document.
Testo completoAbstract (sommario):
La fatigue est un des principaux mécanismes de dégradation des chaussées. En laboratoire, la fatigue est simulée en utilisant des essais de chargement cyclique, généralement sans période de repos. L’évolution du module complexe (une propriété du matériau utilisée dans la caractérisation de la rigidité des matériaux viscoélastiques) est suivie de manière à caractériser l’endommagement. Son changement est généralement interprété comme étant dû au dommage, alors que d’autres phénomènes (se distinguant du dommage par leur réversibilité) apparaissent. Des effets transitoires, propres aux matériaux viscoélastiques, apparaissent lors des tout premiers cycles (2 ou 3) et produisent une erreur dans la détermination du module complexe. La non-linéarité (dépendance du module complexe avec le niveau de déformation) est caractérisée par une diminution réversible instantanée du module et une augmentation de l’angle de phase qui est observée avec l’augmentation de l’amplitude de déformation. De plus, pendant le chargement, de l’énergie mécanique est dissipée en raison du caractère visqueux du comportement du matériau. Cette énergie se transforme principalement en chaleur ce qui induit une augmentation de température. Cela produit une diminution de module liée à cet auto-échauffement. Quand le matériau revient à la température initiale, le module initial est alors retrouvé. La partie restante du changement de module peut être expliquée, d’une part par un autre phénomène réversible, appelé dans la littérature « thixotropie », et d’autre part par le dommage « réel », qui est irréversible. Cette thèse explore ces phénomènes dans les bitumes, mastics (bitume mélangé avec des particules fines, dont le diamètre est inférieur à 80μm) et enrobés bitumineux. Un chapitre (sur la nonlinearité) présente des essais de « balayage d’amplitude de déformation » avec augmentation ou/et diminution des amplitudes sont présentés. Un autre se concentre sur l’auto-échauffement. Il comprend une proposition de procédures de modélisation dont les résultats sont comparés avec des résultats des cycles initiaux d’essais de fatigue. Finalement, un chapitre est dédié à l’analyse du module complexe mesuré pendant le chargement et les phases de repos. Des essais de chargement et repos ont été réalisés sur bitume (où le phénomène de thixotropie est supposé avoir lieu) et mastic, de manière à déterminer l’effet de chacun des phénomènes identifiés sur l’évolution du module complexe des matériaux testés. Les résultats de l’étude sur la nonlinearité suggèrent que son effet vient principalement du comportement non linéaire du bitume, qui est déformé de manière très non-homogène dans les enrobés bitumineux. Il est démontré qu’un modèle de calcul thermomécanique simplifié de l’échauffement local, ne considérant aucune diffusion de chaleur, peut expliquer le changement initial de module complexe observé au cours des essais cycliques sur enrobés. Néanmoins, la modélisation de la diffusion de chaleur a démontré que cette diffusion est excessivement rapide. Cela indique que la distribution de l’augmentation de température nécessaire pour expliquer complètement le module complexe observé ne peut pas être atteinte. Un autre phénomène réversible, qui a des effets sur le module complexe similaires à ceux d’un changement de température, doit donc avoir lieu. Ce phénomène est considéré être de la thixotropie. Finalement, à partir des essais de chargement et repos, il est démontré qu’une partie majeure du changement de module complexe au cours des essais cycliques vient des processus réversibles. Le dommage se cumule de manière approximativement linéaire par rapport au nombre de cycles. Le phénomène de thixotropie semble partager la même direction sur l’espace complexe que la nonlinéarité. Cela indique que les deux phénomènes sont possiblement liés par la même origine microstructurelle. Des travaux supplémentaires sur le phénomène de thixotropie sont nécessairesFatigue is a main pavement distress. In laboratory, fatigue is simulated using cyclic loading tests, usually without rest periods. Complex modulus (a material stiffness property used in viscoelastic materials characterisation) evolution is monitored, in order to characterise damage evolution. Its change is generally interpreted as damage, whereas other phenomena (distinguishable from damage by their reversibility) occur. Transient effects, proper to viscoelastic materials, occur during the very initial cycles (2 or 3) and induce an error in the measurement of complex modulus. Nonlinearity (strain-dependence of the material’s mechanical behaviour) is characterised by an instantaneous reversible modulus decrease and phase angle increase observed when strain amplitude increases. Moreover, during loading, mechanical energy is dissipated due to the viscous aspect of material behaviour. This energy turns mainly into heat and produces a temperature increase. This produces a modulus decrease due to self-heating. When the material is allowed to cool back to its initial temperature, initial modulus is recovered. The remaining stiffness change can be explained partly by another reversible phenomenon, called in the literature “thixotropy”, and, then, by the “real” damage, which is irreversible. This thesis investigates these phenomena in bitumen, mastic (bitumen mixed with fine particles, whose diameter is smaller than 80μm) and bituminous mixtures. One chapter (on nonlinearity) presents increasing and/or decreasing strain amplitude sweep tests. Another one focuses on selfheating. It includes a proposition of modelling procedures whose results are compared with the initial cycles from fatigue tests. Finally, a chapter is dedicated to the analysis of the measured complex modulus during both loading and rest periods. Loading and rest periods tests were performed on bitumen (where the phenomenon of thixotropy is supposed to happen) and mastic in order to determine the effect of each of the identified phenomena on the complex modulus evolution of the tested materials. Results from the nonlinearity investigation suggest that its effect comes primarily from the nonlinear behaviour of the bitumen, which is very non-homogeneously strained in the bituminous mixtures. It was demonstrated that a simplified thermomechanical model for the calculation of local selfheating (non-uniform temperature increase distribution), considering no heat diffusion, could explain the initial complex modulus change observed during cyclic tests on bituminous mixtures. However, heat diffusion modelling demonstrated that this diffusion is excessively fast. This indicates that the temperature increase distribution necessary to completely explain the observed complex modulus decrease cannot be reached. Another reversible phenomenon, which has effects on complex modulus similar to the ones of a temperature change, needs to occur. That phenomenon is hypothesised as thixotropy. Finally, from the loading and rest periods tests, it was demonstrated that a major part of the complex modulus change during cyclic loading comes from the reversible processes. Damage was xivfound to cumulate in an approximately linear rate with respect to the number of cycles. The thixotropy phenomenon seems to share the same direction in complex space as the one of nonlinearity. This indicates that both phenomena are possibly linked by the same microstructural origin. Further research on the thixotropy phenomenon is needed
35
Tabatabaei, Sorour. "Numerical prediction for thixotropic and non-thixotropic material systems in complex flow". Thesis, Swansea University, 2014. https://cronfa.swan.ac.uk/Record/cronfa43154.
Testo completo
36
Jarny, Sébastien. "Thixotropie des pâtes cimentaires". Phd thesis, Ecole des Ponts ParisTech, 2004. http://tel.archives-ouvertes.fr/tel-00011192.
Testo completoAbstract (sommario):
Les nouveaux matériaux cimentaires fluides présentent des propriétés de thixotropie, phénomène réversible de gélification (au repos) - liquéfaction (en écoulement), qu'il est nécessaire de comprendre et de caractériser. Des essais croisés de rhéométrie globale (rhéomètre classique) et locale (vélocimétrie IRM) permettent d'obtenir le comportement complet en régime permanent et transitoire d'une pâte de ciment blanc. En particulier nous mettons en évidence une bifurcation de viscosité, traduisant un changement brutal de comportement en dessous d'une contrainte et d'un gradient de cisaillement critique. Un modèle simple, basé sur ces observations, permet de retrouver les propriétés observées. Son application à des essais d'écoulements sur plan incliné montre que cette configuration peut s'avérer un moyen simple de caractérisation pratique de la thixotropie.
37
Mollet, Frédéric. "Contribution à l'étude de l'écoulement d'un fluide thixotrope". Nancy 1, 1996. http://www.theses.fr/1996NAN10211.
Testo completoAbstract (sommario):
L’écoulement des fluides thixotropes en conduite est très mal connu. Pourtant le nombre de ces fluides est très important ; en particulier dans l'industrie agro-alimentaire. Le but de cette étude de thèse était donc de mettre en place une installation expérimentale permettant l'étude de l'écoulement d'un fluide modèle thixotrope, de caractériser rhéologiquement notre fluide modelé et de donner des éléments de mécanique de ces fluides. Le fluide modèle que nous utilisons est à base d'argile et d'un polymère de cellulose. En ce qui concerne l'installation expérimentale, celle-ci permet de créer un écoulement de fluide à débit contrôlé ; le fluide laisse au repos est en mis en écoulement par déplacement d'un piston, comme pour une seringue. Rhéologiquement, nous avons modélisé notre fluide modèle à partir d'une relation contrainte-structure et d'une cinétique d'évolution de la structure. Grâce à ce modèle, nous avons simulé très correctement les cycles d'hystérésis obtenus à vitesse de cisaillement imposée. L’étude de l'évolution des chutes de pression et des profils de vitesse, obtenus par vélocimétrie ultrasonore à effet doppler pulsé, dans le temps mais aussi dans l'espace nous a permis de donner des éléments de mécanique des fluides thixotropes et de mettre en évidence, par exemple, une très nette restructuration du fluide sous écoulement
38
Valová, Kristýna. "Reologické vlastnosti modifikovaných polymer-kompozitních kostních past". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2018. http://www.nusl.cz/ntk/nusl-438888.
Testo completoAbstract (sommario):
Předložená diplomová práce je zaměřená na studium viscoelastického chování kostních past na bázi fosforečnanu vápenatého a vodného roztoku termosenzitivního triblokového kopolymeru, zlepšujícího tokové vlastnosti pasty. V teoretické části je zpracována stručná charakteristika cementů na bázi fosforečnanu vápenatého. Rovněž se zabývá charakteristikou reologických vlastností injektabilních kostních past. Součástí je také stručný přehled aditiv ovlivňujících právě reologické a mechanické vlastnosti past. Experimentální část je zaměřena na charakterizaci triblokového kopolymeru pomocí nukleární magnetické rezonanční spektroskopie a reologie. Dále byly připravovány modifikované fosfátové cementy, u kterých byly posléze studovány viskoelastické vlastnosti. Kostní pasta byla modifikována přídavkem adhezivních sloučenin (dopamin a jodičnan sodný) a antibakteriálním činidlem (selenové nanočástice). Analýza viskoelastických vlastností byla provedena reologickou analýzou, během níž byl primárně sledován proces vytvrzování a tixotropní chování jak nemodifikovaných, tak modifikovaných fosfátových past. Proces vytvrzování probíhal při teplotě 23 °C a 37 °C, imitující fyziologické prostředí. Morfologie fosfátové keramiky byla charakterizována pomocí rastrovací elektronové mikroskopie a velikost částic byla zjištěna pomocí laserového analyzátoru částic. Bylo prokázáno, že výše zmíněná aditiva mají pozitivní vliv na kinetiku procesu vytvrzování kostních past. Selenové nanočástice navíc vylepšily tixotropní chování polymer-fosfátových past. Z tohoto důvodu jsou tyto nové injektabilní kompozitní pasty vhodné pro miniinvazivní chirurgii. Díky aditivům, vykazujících adhezivní vlastnosti, mají potenciál uplatnit se při léčbě zlomenin. Stejně tak se nabízí možnost využít pasty při léčbě osteomyelitidy, a to díky možnému uvolňování antibakteriálních nanočástic.
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Shamu, John. "On the measurement and application of cement grout rheological properties". Licentiate thesis, KTH, Jord- och bergmekanik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-251745.
Testo completoAbstract (sommario):
The rheological properties of cement-based grouts play a key role in determining the final spread in grouted rock formations. Rheologically, cement grouts are known to be complex thixotropic fluids, but their steady flow behavior is often described by fitting the simple Bingham constitutive law to flow curve data. The resultant Bingham parameters are then used in grouting design of e.g. tunnels, to estimate the penetration length. Since cement grouts are thixotropic suspensions, the interpretation of their flow curves as obtained from flow sweeps in concentric cylinder rotational rheometers is often complicated by: the presence of wall slip, sedimentation and unstable flow at low shear rates. A systematic approach to study these effects within the constraints of the concentric cylinder geometry (Couette) and for different cement grout concentrations was carried out as part of the Licentiate research work. Of particular interest was the influence of geometry and flow sweep measurement interval on flow curves, including the characteristic unstable flow branch that appears at applied shear rates that are below the critical shear rate. The unstable flow branch observed below the critical shear rate has been described as a characteristic feature in the flow curves of thixotropic suspensions, e.g. cement grouts, laponite. From a practical standpoint, this information can then be readily used to improve rheological measurements of cement grouts. The existence of the critical shear rate below which no stable flow occurs, plus the complex wall slip phenomenon are then discussed by considering how they affect actual spread in rough and smooth rock fractures. Another major part of the research presented in this thesis relates to the measurement of model yield stress fluid (YSF), i.e. Carbopol, velocity profiles within the radial flow geometry. Radial flow between parallel plates, is an idealized fundamental flow configuration that is often used as a basis for grout spread estimation in planar rock fractures. Compared to other flow configurations with YSFs, e.g. channels, only a limited amount of work has presented analytical solutions, numerical models and especially experimental work for radial flow. Thus, as a first step towards more systematic studies of the plug flow region of YSFs in radial flow the current work presents the design, manufacture and for the first time velocity profile measurements that were conducted by using the pulsed Ultrasound Velocity Profiling (UVP) technique. The current observations for tests carried out with different disk spacings and flow rates show a distinct plug region, coupled with wall slip effects for the Carbopol model YSF fluid that was used. The theoretically predicted velocity profiles and the measured ones agree reasonably well, and the main discrepancies are discussed. Future studies, would then be targeted at improving the current experimental setup, for detailed measurements of the plug flow region along the radial length, which remains a challenging issue for studies on YSFs and engineering applications such as rock grouting design.Cementbaserade injekteringsmedels reologiska egenskaper har en stor påverkan på strömning och inträngningslängd i sprickigt berg. Medlens reologi är komplex, inklusive tixotropi, men strömningen beskrivs ändå oftast med den enkla linjära Bingham modellen i injekteringssammanhang. De två parametrarna från denna modell, flytgräns och viskositet, används sedan inom injekteringsdesign, för t.ex. tunnlar och dammar, för att bedöma inträngningen. Eftersom cementbaserade medel är tixoptropa suspensioner försvåras utvärderingen vid mätning med konventionella rotationsviskometrar på grund av glidning vid fasta begränsningsytor, sedimentation/separation av partiklarna och instabila flöden vid låga deformationshastigheter. En systematisk mätprocedur för att studera ovanstående problem med rotationsviskometer och koncentriska cylindrar samt olika vanliga vattencementtal, har utförts inom ramen för detta licentiatarbete. Av särskilt intresse har varit att studera effekten av olika geometrier och tidsintervallet mellan mätningarna, inklusive den instabila delen av flödeskurvan då deformationshastigheten är lägre än ett kritiskt värde. Denna del av kurvan har i litteraturen beskrivits som karakteristisk för tixotropa suspensioner, som t.ex. cementbaserade injekteringsmedel. Praktiskt kan ovanstående kunskap användas för att förbättra mätningen av de reologiska egenskaperna. Existensen av en kritisk deformationshastighet under vilken det inte finns något stabilt flöde, i kombination med glidning vid fasta begränsningsytor, diskuteras särskilt med hänsyn till dess påverkan på faktisk inträngning i släta och råa bergsprickor. Ett annat fokus i licentiatarbetet har varit att studera icke-Newtonska modellvätskors (Carbopol) radiella strömning mellan parallella plattor. Denna typ av strömningsgeometri används ofta som en idealiserad konfiguration för strömning i bergsprickor. I jämförelse med andra enklare geometrier, finns endast en begränsad forskning utförd för denna geometri både då det gäller analytiska och numeriska beräkningar men framförallt då det gäller experiment. Som ett första steg inför en mer systematisk undersökning av icke-Newtonsk radiella strömning presenteras i detta arbete framtagandet av en fysisk laboratoriemodell där hastighetsprofilerna mellan plattorna för första gången visualiserats med hjälp av ultraljud. De utförda mätningarna med tre olika öppningar mellan plattorna sam tre olika värden på det konstanta flödet, visar på en distinkt plugg som är ett resultat av vätskans flytgräns samt glidning i gränsskiktet mellan vätskan och plattornas fasta begränsningsytor. En jämförelse mellan uppmätta hastighetsprofiler och analytiskt beräknade diskuteras där resultaten överensstämmer relativt väl, med beaktande av de långtgående förenklade antaganden som krävs för beräkningarna. Fortsatta studier kommer att fokuseras på att förbättra laboratoriemodellen för en mer detaljerad studie av icke-Newtonska vätskors strömning och hur pluggen utvecklas under den radiella inträngningen, vilket fortsättningsvis är av betydelse för design av injektering i bergsprickor.
QC 20190521
40
Kadlec, Martin. "Reologie jakožto účinný nástroj ke komplexní charakterizaci hydrogelových systémů". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2020. http://www.nusl.cz/ntk/nusl-414166.
Testo completoAbstract (sommario):
This diploma thesis investigates the suitability of relaxation tests as a part of complex characterization of hydrogel materials using classical rheology methods. With respect to the current research, creep and three interval thixotropy tests were taken into account. For them, general optimization was done aiming to find an ideal parameter settings. The optimization was performed using physically crosslinked agarose (AG) hydrogel and the tuned tests were also applied to two more samples: hyaluronan (HyA) and polyvinyl alcohol (PVAl) gel. These materials were selected due to their mutually different crosslinking principle. The experiments showed, the AG gel proved to have the best ability to recover after deformation of all studied samples. On the other hand, the HyA gel relaxed the worst. Although the final results of both tests were comparable, the regeneration process itself was different. Hence, the complex relaxation characteristics cannot be described using one of the performed tests alone and both the creep and three interval thixotropy tests have great importance in the scope of complex relaxation behaviour. The obtained results may lead to more precise description of deformation and relaxation, which are frequent phenomena occurring during treatment and application of hydrogel materials.
41
Unseld, Peter. "Ein Beitrag zur Herstellung metallischer Verbundwerkstoffe durch teilflüssige/thixotrope Formgebung". Frankfurt, M. MAT-INFO, Werkstoff-Informationsges, 2009. http://d-nb.info/994916434/04.
Testo completo
42
Moreira, Epiphane. "Etude du comportement thixotrope de suspensions de bentonite en conduite". Strasbourg 1, 2008. http://www.theses.fr/2008STR13189.
Testo completoAbstract (sommario):
La manière habituelle de prévoir le comportement en conduite de fluides Non Newtoniens consiste à effectuer une étude rhéologique, à en déduire un modèle de comportement introduit dans les équations de l’écoulement. Cette approche peut s’avérer insuffisante dans le cas de fluides présentant à la fois un seuil d’écoulement et un comportement thixotrope complexe tels que les suspensions de Bentonite ou de Laponite. Dans cette thèse nous avons réalisé des écoulements de suspensions de Bentonite et de Laponite sous différentes conditions : rampes de débits, écoulements à charge constante ainsi que des écoulements oscillatoires. Nous mesurons simultanément les profils de vitesse et les pertes de charge. Ces écoulements sont caractérisés par une zone bouchon au cœur de l’écoulement et une zone cisaillée localisée à la paroi. La connaissance de la localisation du rayon de transition ou rayon critique entre ces zones est d’un intérêt ou d’un point de vue non seulement fondamental mais aussi pratique. D’un point de vue pratique il s’agit d’un paramètre indispensable au calcul des contraintes pariétales et donc des pertes de charge. D’un point de vue théorique il révèle les conditions de transition entre état fluide et état gel. Dans le cas de fluides à seuil le rayon critique est supposé être localisé à l’endroit ou la contrainte est égale à la contrainte seuil. Nous montrons qu’une mince couche fluidifiée existe à la paroi quelque soit la contrainte appliquée. L’épaisseur de cette couche fluidifiée s’accroit lentement et continument avec le temps lors de la mise en écoulement tant que la contrainte à l’interface reste supérieure à un certain seuil. Cette contrainte limite à l’interface ne peut être assimilée à une contrainte seuil au sens classique du terme puisque des contraintes supérieures en dehors de la zone d’interface ne conduisent pas à une déstructuration de la suspension. Nous en déduisons que le mécanisme principal de déplacement du rayon critique dans nos conditions expérimentales est de type érosif. Un modèle de la cinétique d’érosion couplé à un modèle d’évolution des paramètres rhéologiques de la zone fluidifiée est proposé. Ce modèle permet de reproduire de façon satisfaisante les principaux résultats expérimentauxThe usual approach to predict pipe flow characteristics of non Newtonian fluids consists in performing rheological studies leading to a rheological model of the fluid introduced in pipe flow momentum equation. This approach can be a difficult task in case of fluid having yield stress and complex thixotropic behaviour such as bentonite or laponite suspensions. In the present thesis we present pipe flow experiments of bentonite and laponite suspensions in various flow conditions: constant and increasing flow rates, constant pressure head and oscillations flow. We simultaneously measure the instantaneous velocity profiles and pressure drop. Such flows are characterized by a plug zone at the pipe centre and a sheared zone at the pipe wall. Knowing the location of the transition radius or critical radius is of fundamental interest from practical as well as theoretical point of view. From practical point of view it is one of the parameter that permit to determine wall shear stress hence pressure drop. From theoretical point of view it reveals the conditions of transition from solid to fluid state. For fluid having a yield stress the critical radius is supposed to be located at a position where local stress is equal to yield stress. We show that a thin fluid layer exists at the wall whatever the applied stress. The thickness of this fluid layer increases slowly and continuously with flow time till the stress at the solid fluid interface is larger than a limit value. This limit interfacial stress can not be assimilated to a yield stress since suspension volumes in the bulk fluid having experienced much larger stress continue to behave as a solid. We conclude that the location of the critical radius is not governed by an instantaneous mechanical rupture of the particle structure but rather by an erosion mechanism of the solid zone. The erosion kinetic as well as the rheological behaviour of the fluid film are modelled. The model appears capable to predict all the observed flow phenomena
43
Idris, Azmi. "Non-contact ultrasonic study on thixotropic alloys". Thesis, University of Warwick, 1995. http://wrap.warwick.ac.uk/34704/.
Testo completoAbstract (sommario):
Thixotropic metals have better fluid flow behaviour in the semi-solid state when compared to conventional metals and have been increasingly used commercially for the production of high quality engineering components using the technique of thixoforming. However in industrial production, there is no proper quality control system available at present to monitor the softness or to estimate the percentage of solid/liquid fractions of the metal before it is forged into the required shapes. Due to the existence of a temperature gradient within the sample when heated in the RX furnace a bulk measurement is needed. This thesis examines the capability of non-contact ultrasound to make acoustic wave measurements in to the semi-solid state. In particular we have identified pulsed laser generation and EMAT reception as being the most appropriate approach. The Nd: YAG laser has proved capable of generating broadband ultrasound and a water-cooled spiral coil permanent magnet EMAT an efficient detector of both shear and longitudinal waves. The system enables both the longitudinal and shear waves to be detected simultaneously. Investigations have been conducted on various thixotropic metals ranging from lower melting temperature Al-Si alloys (≃570°C) to the higher melting point M2 tool steel (≃1200°C). A Cu-Sn alloy that has a melting temperature of around 830°C was also used for the investigation. Due to the high price and difficulty in obtaining the thixotropic materials preliminary measurements were carried out on non-thixotropic Al-Si alloys and a commercial mild steel. A water-cooled shear EMAT, furnace systems and an ultrasonic cell have been designed and constructed for the thesis. The experiment was carried out in a through transmission arrangement with the laser and the EMAT on epicentre. The experimental work is presented in chapters 4 to 6. Chapter 4 covers the investigation on the Al-Si alloys, chapter 5 covers investigations on the higher melting point materials, and chapter 6 presents investigations into the efficiency of the chosen laser-EMAT system and analyses systematic errors. The laser-EMAT system has proved capable of making measurements not only in the partially molten state but also in the fully molten state with sample temperatures up to 1140°C. The sudden drop in the longitudinal wave to shear wave transit time ratio indicates that the onset of melting could be detected. Since the ratio depends only on the temperature and the percentage of solid and liquid present in the sample and is independent of the sample dimensions it could be a suitable parameter for monitoring the percentage of liquid/solid fractions necessary for thixoforging. However work has yet to be carried out in the industrial environment to prove the capability of the system in monitoring the softness of the metal during thixoforming.
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McArdle, Catriona R. "Mathematical modelling of thixotropic and antithixotropic fluids". Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=22404.
Testo completoAbstract (sommario):
In this thesis we consider two fundamental flow problems, the Stokes problem and flow in a slowly-varying channel, for complex fluids. Specifically, we investigate these problems for thixotropic and antithixotropic fluids described by Mewis and Wagner's [Advances in Colloid and Interface Science, 147-148, 214-227 (2009)] general structure parameter model together with a version of the constitutive law proposed by Moore [Transactions and Journal of the British Ceramic Society, 58, 470-494 (1959)]. In certain limits, this model reduces to the generalised Newtonian power-law model, which we also consider. In chapters 2 and 3 we consider the Stokes problem for power-law, and thixotropic and antithixotropic fluids, respectively. Our main motivation for studying the Stokes problem is to investigate the interplay between the timescales of the fluid response and the forcing. Therefore, the emphasis of our investigations is on the periodic oscillatory behaviour of the systems, rather than on the transient initial phase during which the system adjusts to the attracting periodic solution. In chapter 4 we consider the two-dimensional flow of a thixotropic or antithixotropic fluid along a slowly-varying channel. Although previous studies have considered similar geometries, ours appears to be the first systematic development of a thin-film theory for a thixotropic or antithixotropic fluid. Like the conventional lubrication approach for a Newtonian fluid, our approach is based on an asymptotic expansion in powers of the aspect ratio d in the limit δ - 0. Under appropriate assumptions concerning the Reynolds number and the dimensionless structure response rates, we obtain the governing equations for the velocity, pressure and structure parameter up to O(δ). In contrast to the Newtonian case, the lubrication equations include terms at O(δ), and it is at this order that thixotropic and antithixotropic effects occur.
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Zarrouk, Ziad Ben Mohamed. "Etude de la transition solide-liquide au sein d'un fluide thixotrope". Poitiers, 2010. http://theses.edel.univ-poitiers.fr/theses/2010/Zarrouk-Ben-Mohamed-Ziad/2010-Zarrouk-Ben-Mohamed-Ziad-These.pdf.
Testo completoAbstract (sommario):
Ce travail propose un modèle mathématique permettant de décrire le comportement thixotrope des suspensions de laponite. Ce modèle de comportement est élaboré afin de contrôler les propriétés physicochimiques de la suspension. Dans un premier temps, nous avons utilisé un modèle simple cinétique découlant directement du modèle d'Herschel-Bulkley. Par la suite nous avons mis en avant le modèle à double cinétique développé au cours de ce travail. Par la suite grâce aux techniques de mesures rhéologiques classiques, les protocoles de détermination des paramètres de ces deux modèles ont été mis en place. Une étude à l'échelle locale du comportement du fluide permettait de mieux comprendre comment s'organise la structure de la suspension en écoulement. Dans cette perspective nous avons, grâce à la technique de vélocimétrie par images de particules (PIV), réalisé des mesures de champs de vitesses locales. Ceci nous a permis d'observer le comportement de la suspension dans ses différents états, en écoulement et au repos. De plus, cette étude nous a permis de mettre en évidence dans le cas de la géométrie employée "disques coaxiaux", la formation d'un cône statique dont la taille dépend de la vitesse imposée au disque tournant. L'étude de la validité et de la bonne adéquation du modèle développé passe par une étude comparative mettant en jeux d'une part le modèle déjà existant d'Herschel-Bulkley et notre modèle. Une étude numérique faisant appel au code de calcul commercial Star-CD a été effectuée. Les deux modèles utilisés ont été introduits dans le code et des simulations ont été effectuées. La comparaison entre les résultats des mesures de PIV et les simulations ont mis en évidence que le modèle mis en place est plus représentatif de la physique de l'écoulement de la suspension de laponite que le modèle d'Herschel-BulkleyWe have studied the behaviour of thixotropic fluids : especially the suspension of laponite. The study of the local level of this suspension, with the help of PIV technique, which allows to better understanding how the organisation of suspension structure when the fluid starts to flow. The study of the validation and the good response of the developed model are achieved by a comparative study between the existing model of Herschel-Bulkley and the measuring of velocity fields. In the case of studied geometry “coaxial disks”, the PIV experimental measuring allows us to identify the existence of two distinct layers when the fluid flows. Indeed, we have observed that the first layer is near to the rotating disc where the fluid is motionless and takes the form of a cone which corresponds to a region near the bottom of the cylinder. The use of commercial CFD code Star-CD has enabled us to highlight the limitations of the model of Herschel-Bulkley in relation to the experimental results. These results were used as reference for comparison with the model of dual kinetic behaviour developed in this work. It was shown that the behaviour of the latter model presents a better matching with the actual behaviour of the flowing suspension although some problems still remain
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NARVAEZ, EDGAR HERNAN CANDO. "FLOW OF THIXOTROPIC FLUID THROUGH AXISYMMETRIC EXPANSIONS-CONTRACTIONS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2012. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=21782@1.
Testo completoAbstract (sommario):
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
Neste trabalho estuda-se experimentalmente o comportamento dos fluidos tixotrópicos. Conseguiu-se imagens de fluidos tixotrópicos escoando através de uma expansão seguida de uma contração, ambas abruptas e axissimétricas. A existência de uma superfície de cedêndia produto da fronteira entre o fluido que escoa e o que não escoa, que estende-se da entrada da expansão até a saída da contração, é o principal fenômeno a ser estudado. O número de Re, o tempo para vazão mássica constante e as dimensões da geometria são as variáveis do experimento. Para o desenvolvimento do experimento utilizou-se uma dispersão de laponita RD, que é um fluido transparente com boas características tixotrópicas. Este fluido foi caracterizado reologicamente através da obtenção da flow curve e de testes oscilatórios Strain sweep e frequency sweep. A caracterização reológica apresentou alguns problemas com respeito ao envelhecimento, tipo de geometria e reômetro utilizado, além da falta de repetitividade para baixas taxas de deformação devido ao não pré-cisalhamento da amostra. Todos os problemas foram analisados para dar solução. Os resultados mostraram que a laponita RD é um fluido tixotrópico com característica elástica na região viscoelástica linear. O escoamento do fluido através de uma expansão seguida de uma contração axissimétrica apresentou três tipos de forma que dependem da relação L-D, D-d e o número de Reynolds: escoamento de regime tubular, escoamento de regime tubular expandido e escoamento de regime descontinuo.
The behavior of thixotropics fluids through axisymmetrics expansionscontractions is studied in this research. The main objective is to visualize the shear banding in the flow of a thixotropic fluid, which is the interface between a flowing fluid and a non-flowing fluid. This research uses an experimental procedure to visualize the shear banding within the fluid. The variables used in the experimental procedure were: steady flow rate time, flow rate and geometric characteristics. A dispersion of laponite RD was utilized as the experimental fluid due to its thixotropic and transparent properties. The flow curve , strain sweep and frequency sweep of the fluid were used to obtain the rheology characterization. The rheology characterization showed lack of repeatability due to several factors, such as: aging, type of rheometers, geometry used in the rheometers and lack pre shearing of the sample. All of these issues have been analyzed to give solutions. Finally, the results showed that laponita RD is a thixotropic fluid and elastic in the viscoelastic region. Also that the flow of the fluid through the axisymmetrics expansion-contraction device has three types of behaviors: constant flow area, variable flow area with an expansion in the middle zone and variable flow area with layers of different velocities.
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O'Neill, Deirdre A. (Deirdre Anne). "Undrained strength anisotropy of an overconsolidated thixotropic clay". Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14634.
Testo completo
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Rahman, Mashuqur. "Rheology of cement grout : Ultrasound based in-line measurement technique and grouting design parameters". Doctoral thesis, KTH, Jord- och bergmekanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176885.
Testo completoAbstract (sommario):
Grouting is performed in order to decrease the permeability and increase the stiffness of the material, especially soil and rock. For tunnelling and underground constructions, permeation grouting is done where cement based materials are pumped inside drilled boreholes under a constant pressure, higher than the ground water pressure. The aim of permeation grouting is to reduce the water flow into tunnels and caverns and to limit the lowering of the surrounding groundwater table. Cement based materials are commonly used as grout due to their availability and lower costs. To obtain a proper water sealing and reduce the lowering of the ground water table, a desired spread of grout must be achieved and the rheology of the cement grout is the governing factor for estimating the required spread. Rheological properties of cement grout such as viscosity and yield stress are commonly measured off-line using laboratory instruments, and some simple tools are available to make field measurements. Although the rheological properties of the grout that is used play a fundamental role in design and execution, no method has yet been developed to measure these properties in-line in field work. In addition to the real time measurement, there is no standard method for determining the yield stress for grouting applications. Despite the common usage of Bingham model fitting to determine the yield stress, the range of shear rate is often not specified or is neglected. In this work, an in-line rheometry method combining the Ultrasound Velocity Profiling (UVP) technique with Pressure Difference (PD) measurements, known as “UVP+PD”, was successfully tested for continuous in-line measurements of concentrated micro cement based grouts. A major obstacle of using the ultrasound based methodology was the transducers, which would be capable of emitting sufficient acoustic energy and can be used in field conditions. The transducer technology was developed in a parallel project and the Flow-Viz industrial rheometer was found to be capable of detail measurement of the velocity profiles of cement grout. The shape of the velocity profiles was visualized, and the change in the shape of the profiles with concentration and time was observed. The viscosity and yield stress of the grout were determined using rheological models, e.g. Bingham and Herschel-Bulkley. In addition, rheological properties were determined using the non-model approach (gradient method) and the tube viscometry concept and were compared with results obtained using the rheological models. The UVP+PD method was found to be capable of determining the rheological behavior of cement grout regardless of the rheological model. The yield stress of cement grout was investigated using off-line rheometry techniques and UVP+PD in-line measurements. Tests were performed applying different shear histories and it was found that two ranges of yield stress indeed exist. Therefore, the design value of yield stress should be chosen with respect to the prevailing shear rate at the grout front for the required spread of grout. In addition, an appropriate shear rate range should be used when a Bingham fitting is done to determine the yield stress. In order to estimate the shear rate, plug thickness and velocity for one dimensional and two dimensional geometry, a non- dimensional nomogram was developed. The advantage of using the nomogram is that it does not depend on the applied pressure and the rheological properties of the grout and can therefore, be used as a simple design tool. Analytical approaches were used for the estimation and good agreements were found with numerical calculations and experimental results. In conclusion, in this work, it was found that it is possible to continuously measure the velocity profiles and determine the change of the rheological properties of cement grout using the ultrasound based UVP+PD method under field conditions. The yield stress was also investigated and it was found that two range of yield stress exist depending on the prevailing shear rate of the grout, which should be used for designing the grouting time at different conditions. In order to decide the design value of yield stress for grouting applications, a non-dimensional nomogram was developed that can be used to estimate the plug thickness, shear rate and velocity of the grout.Funding for the project was provided by the Swedish Rock Engineering Research Foundation (BeFo), The Swedish Research Council (FORMAS) and The Development Fund of the Swedish Construction Industry (SBUF), who are gratefully acknowledged. QC 20151112
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CANDELA, WILLIAM FERNANDO LOPEZ. "FLOW OF GAS BUBBLES IN VISCOPLASTIC AND THIXOTROPIC FLUIDS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36094@1.
Testo completoAbstract (sommario):
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE EXCELENCIA ACADEMICA
O escoamento de gás em fluidos complexos é um fenômeno presente em industrias como alimentos e bebidas, farmacêutica, química e petróleo e gás. Nesta pesquisa foi abordado o fenômeno de invasão de gás em pastas de cimento durante o processo de cimentação de poços de petróleo. Este problema é governado por diferentes parâmetros como tamanho, geometria e velocidade das bolhas, reologia do fluido, histórico de cisalhamento do material, pressão e vazão de injeção. Neste trabalho estuda-se experimentalmente a dinâmica de uma bolha de ar não esférica em regime de Stokes ou laminar, escoando em materiais que simulam pastas de cimento com diferentes níveis de viscosidade. As pastas de cimento e suas propriedades viscoplásticas e tixotrópicas são reproduzidas usando suspensões de Carbopol e Laponita, respectivamente. Apresenta-se também um modelo matemático simplificado para a dinâmica do fenômeno de migração de gás, com aplicação na indústria do petróleo. No estudo com Carbopo, investiga-se o efeito da tensão limite de escoamento e a relação entre forças viscosas e inerciais, e sua influência na dinâmica e na geometria da bolha de gás. A análise com Laponita visa simular o processo de invasão e migração de gás durante o processo de cura do cimento. O efeito da tixotropia no formato e na dinâmica de migração das bolhas é analisado. Estes resultados simulam também a complexa dinâmica da migração de gás em fluidos com reologia dependente do tempo, como as pastas de cimento ao longo de seu processo de cura. Observou-se a formação de bolhas de gás com geometria plana, que permitem o escoamento com baixa resistência e formam caminhos preferenciais, que podem se tornar canais de escoamento de gás a alta vazão.
The gas flow in complex fluids is a phenomenon present in industries such as foods and beverage, pharmaceuticals, chemistry and oil and gas. In this research the phenomenon of gas invasion in cement pastes during the cementation process of wells of petroleum was analyzed. This problem is governed by different parameters such as bubble size, geometry and velocity, fluid rheology, material shear history, injection pressure and flow rate. In this work, we perform an experimental study of the dynamics of a non-spherical air bubble under a Stokes or laminar regime, flowing in materials that simulate cement pastes with different levels of viscosity. Cement pastes and their viscoplastic and thixotropic properties are reproduced using suspensions of Carbopol and Laponite, respectively. A simplified mathematical model for the dynamics of the phenomenon of gas migration, with application in the petroleum industry, is also presented. In the Carbopol study, the effect of the yield stress and the relationship between viscous and inertial forces and their influence on the dynamics and geometry of the gas bubble is investigated. The analysis with Laponite aims to simulate the process of invasion and gas migration during the cement cure process. The effect of thixotropy on the shape and dynamics of bubble migration is analyzed. These results also simulate the complex dynamics of gas migration in fluids with time dependent rheology, such as cement pastes during their curing process. The formation of gas bubbles with flat geometry has been observed, allowing the gas to flow with lower resistance and to form preferred paths that can become channels with high gas flow rates.
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Barguès, Stéphane. "Gels corrosifs thixotropes pour la décontamination en milieu nucléaire". Montpellier 2, 1998. http://www.theses.fr/1998MON20268.
Testo completoAbstract (sommario):
Initie par une problematique industrielle, ce travail a consiste a mettre au point des gels corrosifs pour la decontamination de surfaces metalliques. La formulation de ces gels, a base d'un oxydant puissant (le cerium (iv)), d'un acide fort (l'acide nitrique), d'une charge minerale (la silice) et d'un coviscosant organique (un tensioactif non ionique), a ete developpee en respectant les contraintes specifiques du nucleaire. Notre objectif a ete de preparer des gels thixotropes devenant liquides sous agitation pour permettre une pulverisation facile, et reprenant rapidement leur etat initial au repos, pour assurer une parfaite adherence sur les parois a traiter. Cette etude du comportement rheologique des gels a ete completee par une evaluation de leurs proprietes corrosives : mesures d'erosions generalisees, controles de l'etat de surface avant et apres attaque par microscopie electronique a balayage l'aspect chimie en solution a egalement ete aborde, en particulier en ce qui concerne le devenir chimique du coviscosant organique et de l'oxydant. La diffraction des rayons x sur poudre nous a permis de decrire le sel de cerium (nh#4)#3ce#2(no#3)#9. La derniere phase de ce travail a consiste a presenter les resultats de plus de deux ans d'utilisation industrielle de ces gels oxydants tant en france qu'a l'etranger.