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1
Shin, Dongyun. "Development of High Temperature Erosion Tunnel and Tests of Advanced Thermal Barrier Coatings." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522415020378523.
2
Berny, Myriam. "High-temperature tests for ceramic matrix composites : from full-field regularised measurements to thermomechanical parameter identification." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST028.
Abstract:
Cette thèse a pour objectif de développer une méthode de mesure de champs par corrélation d’images numériques (CIN) à haute température couplée à des mesures thermiques sur une éprouvette technologique en CMC sollicitée dans des conditions thermiques représentatives d’un environnement moteur et de mettre en place une méthodologie d’identification des propriétés thermiques et thermomécaniques du matériau, en quantifiant à chaque étape de la chaîne les incertitudes associées aux quantités d’intérêt et en les réduisant. Il a pour cela été nécessaire de traiter les défis inhérents à la CIN à chaud, que ce soit au niveau de l’acquisition des images (saturation, perte du contraste) ou de la mesure (artefacts dus à l’effet mirage, aussi appelé "brume de chaleur").Ces travaux ont ainsi donné lieu au développement d’un protocole d’étalonnage d’un banc multi-instrumenté par l’utilisation soit d’une mire in-situ, soit par auto-étalonnage en utilisant l’éprouvette elle-même et son environnement. Les mesures de déplacements 3D surfaciques (approches de stéréocorrélation globales) et les mesures thermiques ont permis de mettre en évidence ce phénomène de brume de chaleur. Des stratégies de régularisation spatiotemporelles des déplacements mesurés ont été proposées et ont permis d’obtenir des résultats satisfaisants (réduction significative des incertitudes de mesure). De même, des approches par réduction de modèles (POD) ont permis de traiter les données thermiques et de quantifier les incertitudes associées aux phénomènes convectifs. Enfin, un algorithme de recalage de modèle éléments finis pondéré sur les données de températures et de déplacements a été implémenté en vue d’identifier un ensemble de propriétés thermiques et thermomécaniques, en tenant compte de la sensibilité de chaque paramètre par rapport aux incertitudes de mesuresThe aim of this thesis is firstly to develop procedures of full-field measurements with Digital Image Correlation (DIC), coupled to thermal measurements, suitable for high-temperature experiments on CMC specimens under thermal conditions representative of an engine environment. Secondly, a methodology is proposed for identifying the thermal and thermomechanical properties of the material, quantifying at each stage of the chain the uncertainties associated with the quantities of interest and strategies to reduce them. It was necessary to deal with the challenges due to high temperatures, especially for DIC, either in terms of acquisition (saturation, loss of contrast) or measurement (artefacts due to the mirage effect, also called "heat haze effect").This work has led to the development of a calibration protocol for a multi-instrumented bench using either an in-situ calibration target or by self-calibration using the specimen itself and its environment. 3D surface displacement measurements (with global stereocorrelation approaches) and thermal measurements have made it possible to highlight the heat haze effect phenomenon. Spatiotemporal regularisation strategies of the measured displacements were proposed and allowed satisfactory results to be obtained (significant reduction of measurement uncertainties). Similarly, model reduction approaches (POD) have been used to process thermal data and quantify the uncertainties associated with convective phenomena. Finally, a weighted Finite-Element Model Updating (FEMU) algorithm on both temperature and displacement data was implemented in order to identify a set of thermal and thermomechanical properties, taking into account the sensitivity of each parameter with regard to measurement uncertainties
3
Evin, Harold. "Low Cr alloys with an improved high temperature corrosion resistance." Thesis, Dijon, 2010. http://www.theses.fr/2010DIJOS082/document.
Abstract:
Les aciers ferritiques à faible teneur en chrome tel que le T/P91 sont largement utilisés dans les centrales de productions d’électricité pour leurs bonnes propriétés mécaniques et leur faible coefficient d’expansion thermique. Cependant, la demande croissante en énergie alliée à la nécessité de réduire les émissions de gaz à effet de serre, conduisent à envisager l’augmentation des conditions d’utilisation (température et pression) de ces matériaux. Des études ont montré qu’en modifiant la température de fonctionnement et la pression de vapeur d’eau de 538°C/18.5 MPa à 650°C/30 MPa, le rendement des centrales thermiques progressait d’environ 8%. Se pose alors la question de la tenue à la corrosion à haute température des aciers à 9% de chrome. Au cours de ces travaux, le comportement d’un acier ferritique/ martensitique à 9% de chrome a été étudié à 650°C sous air sec et sous vapeur d’eau de matière isotherme et en conditions de cyclage thermique. La prise de masse des échantillons renseigne sur la cinétique de la réaction d’oxydation et l’adhérence des couches d’oxydes formées. Les produits de corrosion ont été caractérisés par plusieurs techniques d’analyses dans l’optique de clairement identifiés les oxydes en présences et leurs mécanismes de formation. Des oxydes mixtes de fer et de chrome (Cr,Fe)2O3 sont dans un premier temps formés et assurent s’avèrent être temporairement protecteur. Pour des longs temps d’oxydation ou des températures supérieures à 650°C, la magnétite Fe3O4 et l’hématite Fe2O3 sont les principaux oxydes formés, montrant ainsi l’inadéquation des nuances à faible teneur en chrome pour une utilisation dans des conditions aussi drastiques. Dans l’optique d’augmenter la résistance à la corrosion à haute température de cet alliage, diverses solutions ont été envisagées tel que l’aluminisation par cémentation en caisse, les revêtements d’oxydes de terre rare par MOCVD, ou encore l’ajout d’éléments d’addition. Ces solutions ont été également testées à 650°C sous air sec et sous vapeur d’eauThe improvement of high temperature oxidation resistance of low chromium content steels, such as T/P91, is of great interest in regards with their application in thermal power generating plants. Indeed, they possess good creep properties, and low thermal expansion coefficient. Important needs in energy together with environmental issues place power generation plants under constraints which lead to develop high efficiency systems. A usual way to increase the efficiency consists in increasing temperature and pressure parameters of the power generating plant. Studies has shown that the total efficiency of a plant increases by nearly 8 % when changing the steam parameters from 538°C/18.5 MPa to 650°C/30 MPa. Then, the problem of corrosion resistance of 9% chromium steel in those conditions is asked. In this work, the behavior of a ferritic / martensitic 9% chromium steel has been studied at 650°C in dry air and in water vapor containing environment in both isothermal and thermal cyclic conditions. The weight gain of samples provides information on the kinetics of the oxidation reaction and the adhesion of formed oxide scale. Corrosion products were characterized by several analytical techniques in order to identify oxides with accuracy and to understand their formation mechanisms. Mixed iron and chromium oxides (Cr, Fe) 2O3 are initially formed and provide temporary protection to the substrate. For long time exposure or temperatures above 650°C, magnetite, Fe3O4 and hematite Fe2O3 are the main oxides formed, highlighting the fact that low chromium steel are inappropriate for applications in such drastic conditions. In order to increase the high temperature corrosion resistance of this alloy, various solutions have been proposed as aluminizing by pack cementation, reactive element oxides coatings of by MOCVD, or addition of alloying elements in the steel composition. These solutions were then tested at 650 ° C in dry air and in water vapor environments
4
Willschütz, H. G., and E. Altstadt. "Generation of a High Temperature Material Data Base and its Application to Creep Tests with French or German RPV-steel." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-29413.
Abstract:
Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. Numerous experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work /REM 1993/, /THF 1997/, /CHU 1999/. For pre- and post-test calculations of Lower Head Failure experiments like OLHF or FOREVER it is necessary to model creep and plasticity processes. Therefore a Fi-nite Element Model is developed at the FZR using a numerical approach which avoids the use of a single creep law employing constants derived from the data for a limited stress and temperature range. Instead of this a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. A main task for this approach is the generation and validation of the CDB. Additionally the implementation of all relevant temperature dependent material properties has been performed. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied. The validation of the numerical model is performed by the simulation of and com-parison with experiments. This is done in 3 levels: starting with the simulation of sin-gle uniaxial creep tests, which is considered as a 1D-problem. In the next level so called "tube-failure-experiments" are modeled: the RUPTHER-14 and the "MPA-Meppen"-experiment. These experiments are considered as 2D-problems. Finally the numerical model is applied to scaled 3D-experiments, where the lower head of a PWR is represented in its hemispherical shape, like in the FOREVER-experiments. This report deals with the 1D- and 2D-simulations. An interesting question to be solved in this frame is the comparability of the French 16MND5 and the German 20MnMoNi55 RPV-steels, which are chemically nearly identical. Since these 2 steels show a similar behavior, it should be allowed on a lim-ited scale to transfer experimental and numerical data from one to the other.
5
Willschütz, H. G., and E. Altstadt. "Generation of a High Temperature Material Data Base and its Application to Creep Tests with French or German RPV-steel." Forschungszentrum Rossendorf, 2002. https://hzdr.qucosa.de/id/qucosa%3A21768.
Abstract:
Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. Numerous experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work /REM 1993/, /THF 1997/, /CHU 1999/. For pre- and post-test calculations of Lower Head Failure experiments like OLHF or FOREVER it is necessary to model creep and plasticity processes. Therefore a Fi-nite Element Model is developed at the FZR using a numerical approach which avoids the use of a single creep law employing constants derived from the data for a limited stress and temperature range. Instead of this a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. A main task for this approach is the generation and validation of the CDB. Additionally the implementation of all relevant temperature dependent material properties has been performed. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied. The validation of the numerical model is performed by the simulation of and com-parison with experiments. This is done in 3 levels: starting with the simulation of sin-gle uniaxial creep tests, which is considered as a 1D-problem. In the next level so called "tube-failure-experiments" are modeled: the RUPTHER-14 and the "MPA-Meppen"-experiment. These experiments are considered as 2D-problems. Finally the numerical model is applied to scaled 3D-experiments, where the lower head of a PWR is represented in its hemispherical shape, like in the FOREVER-experiments. This report deals with the 1D- and 2D-simulations. An interesting question to be solved in this frame is the comparability of the French 16MND5 and the German 20MnMoNi55 RPV-steels, which are chemically nearly identical. Since these 2 steels show a similar behavior, it should be allowed on a lim-ited scale to transfer experimental and numerical data from one to the other.
6
Rahmanian, Ima. "Thermal and mechanical properties of gypsum boards and their influences on fire resistance of gypsum board based systems." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/thermal-and-mechanical-properties-of-gypsum-boards-and-their-influences-on-fire-resistance-of-gypsum-board-based-systems(d8eb4bf5-706a-4264-911f-9584ebfbbc83).html.
Abstract:
Gypsum board assemblies are now widely used in buildings, as fire resistant walls or ceilings, to provide passive fire protection. The fire resistance of such systems is fundamentally due to the desirable thermal properties of gypsum. Yet there is wide variability in reported values of thermal properties of gypsum at high temperatures and a lack of understanding of its integrity in fire. To evaluate the fire protection performance of gypsum board assemblies, it is essential to quantify its thermal properties and obtain information on its mechanical properties at high temperatures. Gypsum boards shrink and crack at high temperatures, and this leads to collapse of parts of the gypsum boards in fire. Fall-off of gypsum in fire affects the fire resistance of the assembly considerably, and cannot be overlooked when evaluating the fire resistance of gypsum board assemblies. The current research proposes a model to define the temperature-dependent thermal properties of gypsum boards at high temperatures. Thermal conductivity of gypsum is considered as the most influential parameter in conduction of heat through gypsum, and a hybrid numerical-experimental method is presented for extracting thermal conductivity of various gypsum board products at elevated temperatures. This method incorporates a validated one-dimensional Finite Difference heat conduction program and high temperature test results on small samples of gypsum boards. Moreover, high temperature mechanical tests have been performed on different gypsum board products; thermal shrinkage, strength and stress-strain relationships of gypsum products at elevated temperatures are extracted for use in numerical mechanical analysis. To simulate the structural performance of gypsum boards in fire, a two-dimensional Finite Element model has been developed in ABAQUS. This model successfully predicts the complete opening of a through-thickness crack in gypsum, and is validated against medium-scale fire tests designed and conducted as part of this research. Gypsum fall-off in fire is a complex phenomenon; however, it is believed that delaying the formation of through-thickness cracking will delay falling off of gypsum in fire, and hence improve the fire resistance of gypsum board assemblies. Finally, a study has been performed on the effects of various detailing parameters in gypsum board wall assemblies, and recommendations are offered for improving the fire resistance of such systems.
7
Guillou, Sebastien. "Etude du comportement d'un alliage chromino-formeur comme matériau d'interconnecteur pour l'Electrolyse à Haute Température." Thesis, Dijon, 2011. http://www.theses.fr/2011DIJOS082/document.
Abstract:
Dans les systèmes d’Electrolyse Haute Température (EHT), le matériau choisi comme interconnecteur doit avoir une bonne résistance à la corrosion sous air et sous mélange H2/H2O à 800 °C, et maintenir une bonne conductivité sur de longues durées. Dans ce cadre, l’objectif de ce travail était, d’une part, d’évaluer un alliage ferritique commercial (l’alliage K41X) comme matériau d’interconnecteur pour l’application EHT. Dans ce but, ont été mis en place des essais d’oxydation en four et en thermoblance pour accéder aux cinétiques d’oxydation, et des mesures de résistivité pour évaluer le paramètre ASR (Area Specific Resistance) à 800°C. D’autre part, l’étude a permis d’apporter des éléments de compréhension plus fondamentaux sur les mécanismes d’oxydation des alliages chromino-formeurs, en particulier sous mélange H2-H2O, par le biais d’essais et de caractérisations spécifiques (Photoélectrochimie, traçage isotopique, essais de longues durées). Cette double stratégie est également appliquée pour l’étude d’une solution de revêtement (obtenu à l’aide de la MOCVD) basée sur l’oxyde pérovskite LaCrO3 qui présente des propriétés de conductivité élevée particulièrement intéressante en vue de l’application EHT. Ainsi, cette étude amène également des éléments de compréhension sur le rôle du lanthane comme élément réactif dont l’effet est souvent discuté dans la littérature. Pour les deux milieux, à 800°C, la couche d’oxyde formée est une couche duplexe Cr2O3/(Mn,Cr)3O4 , recouverte dans le cas du mélange H2-H2O par une fine couche d’oxyde spinelle Mn2TiO4 . Sous air, le mécanisme de croissance déterminé ici est cationique, en accord avec la littérature. La présence d’un revêtement LaCrO3 ne modifie pas ce mécanisme mais ralentit la cinétique de croissance de la couche sur les premières centaines d’heure. De plus, le revêtement améliore l’adhérence et la conductivité de la couche d’oxyde. Sous mélange H2-H2O, le mécanisme de croissance se révèle anionique. La présence de revêtement ralentit la cinétique d’oxydation. Bien que .d’épaisseurs similaires, les couches d’oxyde présentent sous air une résistivité d’un ordre de grandeur inférieure à celle mesurée sous H2-H2O. Il est mis en évidence que la forte résistivité de l’alliage en milieu H2-H2O est liée à la présence de protons issus de la vapeur d’eau présents dans la couche d’oxyde. Le revêtement ne permet néanmoins pas d améliorer la conductivité sous H2-H2OIn High Temperature Vapor Electrolysis (HTVE) system, the materials chosen for the interconnectors should have a good corrosion behaviour in air and in H2-H2O mixtures at 800°C, and keep a high electronic conductivity over long durations as well. In this context, the first goal of this study was to evaluate a commercial ferritic alloy (the K41X alloy) as interconnect for HTVE application. Oxidation tests in furnace and in microbalance have therefore been carried out in order to determine oxidation kinetics. Meanwhile, the Area Specific Resistance (ASR) was evaluated by Contact Resistance measurements performed at 800°C. The second objective was to improve our comprehension of chromia-forming alloys oxidation mechanism, in particular in H2/H2O mixtures. For that purpose, some specific tests have been conducted: tracer experiments, coupled with the characterization of the oxide scale by PEC (PhotoElectroChemistry). This approach has also been applied to the study of a LaCrO3 perovskite oxide coating on the K41X alloy. This phase is indeed of high interest for HTVE applications due to its high conductivity properties. This latter study leads to further understanding on the role of lanthanum as reactive element, which effect is still under discussion in literature.In both media at 800°C, the scale is composed of a Cr2O3/(Mn,Cr)3O4 duplex scale, covered in the case of H2-H2O mixture by a thin scale made of Mn2TiO4 spinel. In air, the growth mechanism is found to be cationic, in agreement with literature. The LaCrO3 coating does not modify the direction of scale growth but lowers the growth kinetics during the first hundreds hours. Moreover, with the coating, the scale adherence is favored and the conductivity appears to be slightly higher. In the H2-H2O mixture, the growth mechanism is found to be anionic. The LaCrO3 coating diminishes the oxidation kinetics. Although the scale thickness is about the same in both media, the ASR parameter is one order of magnitude higher in H2/H2O than in air. Specific contact resistance tests show that the higher resistivity in the H2/H2O mixture is closely linked to the presence of protons in the scale. Moreover, tracer experiments show that these protons come from the water molecule dissociation, and not from the H2 molecule. In H2/H2O, the LaCrO3 coating does not increase the conductivity
8
Ceccon, Lorenzo. "Effetto dell'esposizione ad alta temperatura su microstruttura e proprietà meccaniche di ghise sferoidali." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
Abstract:
Lo scopo della presente ricerca è stato valutare l’effetto dell’esposizione ad alta temperatura su microstruttura e proprietà meccaniche di quattro ghise sferoidali prodotte dalle Fonderie Zanardi: ADI 1050 (ghisa duttile austemperata), IDI 800 (ghisa perlitica isotermica), GJS/800-2 (ghisa sferoidale perlitica) e GJS/400-18 (ghisa sferoidale ferritica).
Lo studio ha previsto il degrado in temperatura dei quattro materiali, l’analisi delle proprietà meccaniche statiche dopo degrado termico mediante prove di durezza Brinell, analisi microstrutturali, XRD, prove di trazione sia a freddo che alla temperatura di degrado.
Per quanto concerne le prove di durezza, è emerso che superata la temperatura di 500 °C la durezza dei materiali ADI 1050 e IDI 800 cala significativamente, la durezza della GJS/800-2 risulta stabile fino a 550 °C, mentre per la GJS/400-18 la durezza rimane pressoché costante fino a 600 °C.
Le analisi microstrutturali hanno mostrato che nell’ADI 1050, IDI 800 e GJS/800-2 la matrice si trasforma sino a diventare quasi completamente ferritica a temperatura di degrado di 600 °C mantenuta per 120 ore. Nella ghisa sferoidale ferritica invece non vi sono mutamenti significativi nella microstruttura dopo degrado.
Le prove di trazione svolte sulla lega ADI 1050 hanno evidenziato una diminuzione di circa 50-60 % della tensione di rottura e quella di snervamento nei provini degradati e trazionati a 500°C rispetto ai provini degradati trazionati a temperatura ambiente, ed una diminuzione di circa 20 % della tensione di rottura e quella di snervamento nei provini degradati rispetto ai provini non degradati trazionati a temperatura ambiente. Le prove di trazione a temperatura ambiente su ghisa sferoidale perlitica degradata hanno mostrato un calo delle proprietà resistenziali di circa il 6% nei provini degradati a 240 ore mentre nella ghisa IDI 800 degradata si è notato un calo di circa il 10% delle proprietà resistenziali già nei provini degradati a 72 ore
9
Xian, Wei. "Development and test of a high temperature superconducting permanent magnet synchronous motor." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609701.
10
Mateus, Freire Lucie. "Évolutions microstructurales et comportement en fluage à haute température d'un acier inoxydable austénitique." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEM016/document.
Abstract:
La thèse est inscrite au sein du projet ASTRID, qui est un démonstrateur technologique pour les réacteurs de quatrième génération (Gen-IV). Le premier matériau choisi pour constituer les gaines de cœur est un acier inoxydable austénitique stabilisé au titane (type 15Cr-15Ni Ti). L’écrouissage à froid des gaines permet la précipitation de nano-carbures de titane en service sur les dislocations, retardant ainsi les phénomènes de restauration par effet d’épinglage. En conditions accidentelles (T > 650°C), et plus particulièrement dans le cas d’une perte de réfrigérant primaire, le comportement en fluage de ces gaines est très mal connu. L’objectif des travaux de thèse est donc de déterminer les mécanismes de déformation et de rupture en fluage, entre 650°C et 950°C, de cet acier à l’état non irradié.Dans un premier temps, les microstructures d’échantillons après différents recuits ont été comparées afin d’étudier l’influence de la température sur les évolutions métallurgiques. L’étude de la précipitation et des cinétiques de restauration et de recristallisation, ont permis de dresser les évolutions microstructurales sans charge appliquée.En plus d’étudier le comportement en fluage uniaxial de l’acier à haute température, les caractérisations des éprouvettes après essais ont permis de déterminer les évolutions microstructurales au cours et après essais de fluage (contributions simultanées de la température et de la contrainte). La comparaison avec les microstructures obtenues après recuits a mis en évidence une accélération de la cinétique de recristallisation sous charge, rendant l’effet de la contrainte sur ces évolutions non négligeable.Après fluage sous air aux plus basses températures (650°C et 750°C), les fractographies présentent une rupture globalement transgranulaire avec certaines zones intergranulaires. Après fluage sous vide secondaire à plus hautes températures (850°C et 950°C), un fort amincissement des éprouvettes et une striction quasiment complète dans l’épaisseur ont été observés. Ce fort amincissement se traduit par un alignement de cupules, caractéristique de ruptures 100% ductiles à très haute températureThe ASTRID project aims at designing a fast-reactor prototype for the 4th generation of nuclear power plants. The material to be used for fuel cladding is a cold-worked austenitic stainless steel stabilized with titanium (15Cr-15Ni Ti type) and optimized in minor elements. This material was developed to limit recovery and irradiation-induced swelling and to improve microstructural stability and mechanical properties in normal operating conditions. In case of incidental situations (irradiation temperature > 650°C), the cladding might rapidly reach higher temperatures up to 950°C where its stability could be affected. The present work aims at improving knowledge and understanding of the microstructural evolution and creep behaviour of this steel at these temperatures (650°C-950°C).Microstructural characterizations of thermally-aged samples have been performed in order to study the effect of temperature on metallurgical evolutions (precipitation, recovery and recrystallization). A phenomenological model including recovery and recrystallization processes was set up to reproduce hardness measurements versus ageing time and temperatures.Isothermal creep tests up to 950°C under a wide range of stress levels allowed investigation of viscoplastic flow, microstructural evolution under stress and damage/failure processes. In order to evaluate the effect of high-temperature loading, microstructural characteristics of stress-free thermally-aged samples were compared with post-mortem examinations of creep specimens.At 650°C and 750°C the value of stress exponent is higher than 7. The main deformation mechanism during creep test is power-low creep, which is consistent with the results found in the literature.Beyond 850°C, the increase in dislocation mobility promotes recovery and recrystallization processes. As a consequence, a competition between work hardening due to viscoplastic deformation and softening due to dynamic recovery takes place. At 950°C, viscoplastic flow is strongly affected by recrystallization during creep test, especially in the tertiary stage. The comparison between microstructures of crept specimens and stress-free, thermally-aged samples leads to the conclusion that the recrystallization kinetics is accelerated by application of a mechanical loading.As for the fracture behaviour, creep tests under air environment at lower temperatures (650°C-750°C), led to predominating ductile fracture but some intergranular zones were observed on fracture surfaces. Creep tests under high vacuum at higher temperatures (850°C-950°C) lead to a high fracture elongation with a reduction of area up to 100%
11
Emslie, Frank Norman. "Flownex analysis of high temperature test reactor thermo-hydraulic benchmarks / Frank Norman Emslie." Thesis, North-West University, 2005. http://hdl.handle.net/10394/469.
Abstract:
The High Temperature engineering Test Reactor (HTTR) is an experimental High
Temperature Gas-cooled Reactor (HTGR) built by the Japanese Atomic Energy Research
Institute (JAERI) to facilitate tests of HTGR technology. One of these test activities involves
the validation and verification of thermo-hydraulic codes used in the design of similar HTGR
plants. This report details the benchmarking of the Flownex simulation package as used by
PBMR (Fly.) Ltd., a South African company developing another type of HTGR known as the
Pebble Bed Modular Reactor. The benchmark is of a loss-of-off-site-power event that was
tested at the HTTR facility. The event involves a cut of the electric power supply to the
circulators, a reactor SCRAM and the activation of the Auxiliary Cooling system to remove
decay heat.
The need for verification of thermodynamic software is very important in modem nuclear
power plant designs, as so much depends on the results produced. Any errors in these results
can have serious economic and safety consequences.
This report firstly discusses the background of the study, elaborating on the need for the work
and the benefit that can be derived from it. Thereafter the process of software verification and
validation (V&V) is discussed so that the need for V&V may be clearly understood. Various
modelling and simulation methods are then compared, to provide an idea of the work already
done in this field. Following this more detail is given on the HTTR test plant and how it is
modelled in Flownex. This model is then used for both steady-state and transient simulations,
the results of which are then compared with test data.
With some exceptions, the study shows that the simulation results are very close to the
measured data. Differences are of such a magnitude that they may be attributed to
instrumentation inaccuracies.
The study contributes to the field in that the methodology of analysing thermo-hydraulic
systems is further broadened. The conclusions drawn from this study are aimed at the
simulation design engineer, to help him or her understand similar problems and to find
solutions faster.Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2005.
12
Hossain, Mohammad Ahsan. "High temperature, permanent magnet biased, homopolar magnetic bearing actuator." Thesis, Texas A&M University, 2006. http://hdl.handle.net/1969.1/4174.
Abstract:
The EEC (Electron Energy Corporation) in conjunction with the National Aeronautics and Space Administration is researching the magnetic bearings for an alternative to conventional journal or ball bearings. The purpose of this research was to design and develop a high-temperature (1000úF) hybrid Magnetic Bearing using High Temperature Permanent Magnets (HTPM), developed by the EEC for high performance jet engines at high speeds that supply loads of 500 lbf. Another objective is to design and build a test rig fixture to measure the load capacity of the designed bearing. The permanent magnet bias of the Homopolar radial magnetic bearing reduces the amount of current required for magnetic bearing operation. This reduces the power loss due to the coil current resistance and improves the system efficiency because the magnetic field of the HTPM can suspend the major portion of the static load on bearing. A high temperature radial magnetic bearing was designed via an iterative search employing 3D finite element based electromagnetic field simulations. The bearing was designed to produce 500 lbf of force at 1000úF and the design weight is 48 lbs. The bias flux of the Homopolar radial bearing is produced by EEC HTPM to reduce the related ohmic losses of an electromagnetic circuit significantly. An experimental procedure was developed to measure actual load capacity of the designed bearing at the test rig. All the results obtained from the experiment were compiled and analyzed to determine the relation between bearing force, applied current and temperature.
13
Plewacki, Nicholas. "Modeling High Temperature Deposition in Gas Turbines." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587714424017527.
14
Xu, Bing. "Design, construction and test of a 100 kVA high temperature superconducting demonstration synchronous generator." Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417398.
15
Romatoski, Rebecca R. (Rebecca Rose). "Fluoride-salt-cooled high-temperature test reactor thermal-hydraulic licensing and uncertainty propagation analysis." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112378.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 295-307).
An important Fluoride-salt-cooled High-temperature Reactor (FHR) development step is to design, build, and operate a test reactor. Through a literature review, liquid-salt coolant thermophysical properties have been recommended along with their uncertainties of 2-20%. This study tackles determining the effects of these high uncertainties by proposing a newly developed methodology to incorporate uncertainty propagation in a thermal-hydraulic safety analysis for test reactor licensing. A hot channel model, Monte Carlo statistical sampling uncertainty propagation, and limiting safety systems settings (LSSS) approach are uniquely combined to ensure sufficient margin to fuel and material thermal limits during steady-state operation and to incorporate margin for high uncertainty inputs. The method calculates LSSS parameters to define safe operation. The methodology has been applied to two test reactors currently considered, the Chinese TMSR-SF1 pebble bed design and MIT's Transportable FHR prismatic core design; two candidate coolants, flibe (LiF-BeF2) and nafzirf (NaF-ZrF4); and forced flow and natural circulation conditions to compare operating regions and LSSS power (maximum power not exceeding any thermal limits). The calculated operating region accounts for uncertainty (2 [sigma]) with LSSS power (MW) for forced flow of 25.37±0.72, 22.56±1.15, 21.28±1.48, and 11.32±1.35 for pebble flibe, pebble nafzirf, prismatic flibe, and prismatic nafzirf, respectively. The pebble bed has superior heat transfer with an operating region reduced ~10% less when switching coolants and ~50% smaller uncertainty than the prismatic. The maximum fuel temperature constrains the pebble bed while the maximum coolant temperature constrains the prismatic due to different dominant heat transfer modes. Sensitivity analysis revealed 1) thermal conductivity and thus conductive heat transfer dominates in the prismatic design while convection is superior in the pebble bed, and 2) the impact of thermophysical property uncertainties are ranked in the following order: thermal conductivity, heat capacity, density, and lastly viscosity. Broadly, the methodology developed incorporates uncertainty propagation that can be used to evaluate parametric uncertainties to satisfy guidelines for non-power reactor licensing applications, and method application shows the pebble bed is more attractive for thermal-hydraulic safety. Although the method was developed and evaluated for coolant property uncertainties for FHR, it is readily applicable for any parameters of interest.
by Rebecca Rose Romatoski.
Ph. D.
16
Bao, Yuanye. "Development and Test of High-Temperature Piezoelectric Wafer Active Sensors for Structural Health Monitoring." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc799504/.
Abstract:
High-temperature piezoelectric wafer active sensors (HT-PWAS) have been developed for structure health monitoring at hazard environments for decades. Different candidates have previously been tested under 270 °C and a new piezoelectric material langasite (LGS) was chosen here for a pilot study up to 700 °C. A preliminary study was performed to develop a high temperature sensor that utilizes langasite material. The Electromechanical impedance (E/M) method was chosen to detect the piezoelectric property. Experiments that verify the basic piezoelectric property of LGS at high temperature environments were carried out. Further validations were conducted by testing structures with attached LGS sensors at elevated temperature. Additionally, a detection system simulating the working process of LGS monitoring system was developed with PZT material at room temperature. This thesis, for the first time, (to the best of author’s knowledge) presents that langasite is ideal for making piezoelectric wafer active sensors for high temperature structure health monitoring applications.
17
Van, der Merwe Jacobus Jeremia. "Simulation of heat and momentum transfer in the high temperature test reactor / J.J. van der Merwe." Thesis, North-West University, 2003. http://hdl.handle.net/10394/45.
18
Rodriguez, Judy N. "Tritium production analysis and management strategies for a Fluoride-salt-cooled high-temperature test reactor (FHTR)." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82449.
Abstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 37-38).
The Fluoride-salt-cooled High-temperature Test Reactor (FHTR) is a test reactor concept that aims to demonstrate the neutronics, thermal-hydraulics, materials, tritium management, and to address other reactor operational and maintenance issues before a commercial Fluoride-salt-cooled High-temperature Reactor (FHR) can be deployed. The MIT Nuclear Systems Design class proposed a design for a 100 MW FHTR that uses enriched- 7Li flibe (Li2BeF4), has both thermal and fast flux testing positions for fuel and materials testing, and provides a neutron flux greater than 3E14 n/cm2 -s for accelerated irradiation testing. One of the key technical issues of the FHR and FHTR is tritium generation from the flibe coolant and its radiological control. The objectives of this study are: 1) to provide an overview of tritium production in various types of nuclear systems, 2) to estimate the tritium source term in the FHTR using the ORIGEN-S computer code, and 3) to propose a tritium management strategy for the FHTR. A review of existing nuclear systems shows that tritium is the primary radionuclide in liquid and gaseous tritium release. Light water reactors release up to several hundred curies per year for which various tritium removal and control strategies have been developed and implemented. Using the ORIGEN-S code analysis, tritium production for the MIT FHTR design at 20 MW is estimated to be about 2600 Ci per year (based on a 70% capacity factor and-10 Ci/day), with 99.99% enriched- 7Li flibe. Using this source term, a tritium removal rate of >90% is proposed as a design target for the tritium control system of the FHTR in order to maintain tritium release within the limits of existing nuclear reactors. Proposed tritium management strategies for the FHTR include increasing the 7Li enrichment, carbon-based or metallic getters, and inert gas sparging with a high-temperature recombiner system.
by Judy N. Rodriguez.
S.B.
19
Dilner, David. "Behavior of cutting tool coating material Ti1-xAlxN at high pressure and high temperature." Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-52773.
Abstract:
The high pressure and high temperature (HPHT) behavior of Ti1-xAlxN coatings on cutting tool inserts have been of interest for this diploma work. A literature study of HPHT techniques as well as measurement methods has been done. A diamond anvil cell (DAC) would be a good device to achieve high pressure and high temperature conditions on small samples. Another way to obtain these conditions would be a cutting test, which has been performed on a Ti1-xAlxN coated cutting tool insert with x = 0.67. Also a cubic press could be used to apply HPHT on a Ti1-xAlxN sample or a large volume press on a whole cutting tool insert. To measure hardness on thin coatings a nanoindentor could be used, which have been done on heat-treated Ti0.33Al0.67N and TiN samples. X-ray diffraction (XRD) is a suitable method to measure phase composition of a sample and was performed on the cutting tested insert as well as on an untreated reference insert. Three ways to continue this project have been outlined all starting with more comprehensive cutting tests.
20
Simms, Nigel John. "The effect of boric acid on the high temperature oxidation of a 2.25Cr-1Mo steel." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292167.
21
Arcilesi, David J. Jr. "Developmental Analysis and Design of a Scaled-down Test Facility for a VHTR Air-ingress Accident." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338387523.
22
Paolucci, Lorenzo. "High efficiency low temperature combustion in compression ignition engines for automotive and aeronautical applications." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Abstract:
Internal combustion engines are increasingly subject to ever more stringent and severe Euro-legislations about pollutants emissions in terms of nitrogen oxide, carbon monoxide, unburned hydrocarbons and soot. In last years, thanks to advanced after treatment systems and technological innovations, emission have been improved but, due to even higher costs and complexity of such systems and in a view of further emissions restrictions, advanced combustion methods leading to cleaner and improved efficiency combustion are under investigation. A possible path to follow in order to met requirements on lower emissions, is relative to so called low temperature combustion: a group of innovative combustion methods which by exploiting lean and premixed combustion decreases significantly flame temperature which is mainly responsible for nitrogen oxide production. This work of thesis focus on preliminary study, development and experimental testing of a low temperature combustion strategy, namely "gasoline direct compression ignition" also known as "GDCI".
23
Camillo, Luciano Mendes. "Estudo do ponto invariante com a temperatura (\"Zero Temperature Coefficient\") em transistores SOI Mosfet fabricados com tecnologia ultra-submicrométrica." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-05042011-155808/.
Abstract:
Neste trabalho é apresentado um estudo do ponto ZTC (Zero Temperature Coefficient) em dispositivos SOI MOSFETs, funcionando em modo parcialmente (PD-SOI) e totalmente (FD-SOI) depletados. O estudo é realizado a partir de um modelo analítico simples, proposto para determinação da tensão de polarização da porta do transistor no ponto ZTC (VZTC), através dos modelos de primeira ordem das características da corrente de dreno (IDS) em função da tensão aplicada a porta (VGF) do transistor, considerando as regiões de operação linear e de saturação. Para a validação do modelo, os resultados obtidos são confrontados com dados experimentais, e foi obtido um bom ajuste dos valores, apesar das simplificações adotadas para o modelo proposto. Foi realizada uma análise para estudar o impacto no valor de VZTC com a variação no valor de parâmetros de referência, como a concentração de portadores (Naf) e a espessura do óxido de porta (toxf). O erro máximo observado em VZTC, impondo a variação nos parâmetros Naf e toxf, para os dispositivos PD é de 3,1% e 4,6% na região linear, respectivamente; e 3,5% e 7,2% na região de saturação, respectivamente. Para os dispositivos FD o erro máximo observado, devido a variação nos parâmetros Naf e toxf, foi de 11% e 10% operando no regime linear, respectivamente e 5,3% e 8,4% no regime de saturação, respectivamente. Através do modelo proposto foi realizado o estudo da estabilidade do ponto ZTC em função da variação da degradação da mobilidade com a temperatura (fator c), comprimento de canal (L) e a tensão de dreno (VDS) para os dispositivos supracitados. A analise da influência do fator c em VZTC mostrou-se mais importante nos dispositivos parcialmente depletados (PD). A tensão VZTC, para os dispositivos nMOS, apresentou um menor valor operando na região de saturação, e torna-se mais pronunciada essa diferença para dispositivos com menor comprimento de canal, para ambos os tipos de dispositivos. Observando a variação de VZTC com VDS, nota-se uma diminuição no valor de VZTC para altos valores de VDS, para os dois tipos de dispositivos estudados, n e pMOS. Os resultados do modelo proposto foram avaliados com dados experimentais de outras tecnologias SOI MOSFET. Também foi obtido um bom ajuste com os valores para as tecnologias GC-SOI e GC-GAA SOI, operando em regime linear e saturação.This paper presents a study of ZTC point (\"Zero Temperature Coefficient) in SOI MOSFETs devices, partially (PD-SOI) and fully (FD-SOI) depleted mode. The study is performed from a simple analytical model proposed for the determination of the gate bias voltage at ZTC point (VZTC) using the first-order models of the drain current (IDS) characteristics as a function of the gate voltage (VGF), operating in the linear and saturation regimes. To validate the model proposed results were compared with experimental data, and the analytical predictions are in very close agreement with experimental results in spite of the simplification used for the VZTC model proposed. Analysis was performed to study the impact on the VZTC value with the change in the parameters used as reference, such as Naf and toxf. The maximum error observed for the PD devices is 3.1% and 4.6% in the linear region and 3.5% and 7.2% in the saturation region, respectively. For FD devices the maximum error observed was 11% and 10% operating in the linear and 5.3% and 8.4% in the saturation regime. In order to verify the stability of the ZTC point as a function of the mobility degradation (c), channel length (L) and drain voltage (VDS), the proposed model was applied to the devices mentioned above. The VZTC changes in the temperature range investigated showed a temperature mobility degradation dependence and are more pronounced in PD devices. The VZTC voltage for nMOS devices presented a lower value operating in the saturation region than in the linear region, and this difference becomes more pronounced to devices with smaller channel length for both devices, n and pMOS. Analyzing the VZTC variation with drain voltage (VDS), showed a decrease in VZTC value for higher VDS, for both studied devices. The model proposed results were evaluated using experimental data from other SOI MOSFET technologies. And also we have obtained for the GC SOI and GC-GAA-SOI technologies a very close agreement, operating in both regions, linear and saturation.
24
Mylavarapu, Sai Kiran. "Design, Fabrication, Performance Testing, and Modeling of Diffusion Bonded Compact Heat Exchangers in a High-Temperature Helium Test Facility." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1321996306.
25
Wanderley, Kristine Bruce. "Recuperação de magnésio do licor de lixiviação de minério limonítico por cristalização." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/3/3137/tde-23052018-084841/.
Abstract:
No processo de obtenção de níquel de fontes de minério limonita, a lixiviação ácida do minério resulta na dissolução de íons metálicos em uma solução aquosa. Com o uso da tecnologia apropriada, é possível recuperar esses íons metálicos em vez de descartá-los. O presente estudo tem como objetivo a recuperação de magnésio de uma solução contendo íons magnésio e sulfato utilizando-se a técnica da cristalização a alta temperatura. A aplicação da cristalização a alta temperatura para recuperar o magnésio na forma de sulfato de magnésio hidratado pode ser vantajosa uma vez que sua decomposição térmica resulta em MgO e SO2, produtos que podem ser reutilizados no processo de mineração da limonita. Isso reduz o volume de resíduo formado e custo de reagentes no processo. Foi projetado um sistema de cristalizador acoplado a filtração e foi verificado a influência da temperatura, tempo de residência e pH da solução na quantidade de magnésio cristalizado. A solução residual de cada batelada foi analisada por cromatografia de íons para quantificar o magnésio na solução. Os cristais formados foram analisados utilizando-se a técnica de difração de raios-X (DRX), por microscopia eletrônica de varredura (MEV-EDS) e agitamento de peneiras a fim de avaliar a composição química, morfologia e granulometria dos cristais. A solubilidade do sulfato de magnésio foi determinada experimentalmente com o intuito de ampliar a compreensão da solubilidade do sal e obter valores de Kps. Em 5 horas de tempo de residência o sistema foi estabilizado, indicando que não haverá mais crescimento cristalino em tempos de residência maiores que 5 horas. Em pH 5,7 a 230°C e em 5 horas de tempo de residência ocorreu a maior remoção de magnésio com cerca de 81% cristalizado. Os cristais apresentaram morfologia esférica com exceção do cristal obtido a 230 °C em pH 2, que apresentou formato retangular. A análise por DRX mostrou a presença de um produto constituído majoritariamente por sulfato de magnésio monohidratado.In the process of obtaining nickel from sources of limonite ore, the acid leaching of the ore results in the dissolution of metallic ions in solution. With the use of appropriate technology, it is possible to recover these metal ions instead of discarding them. The present study aims to recover magnesium from a solution containing magnesium and sulfate ions using high temperature crystallization. The application of high temperature crystallization to recover magnesium in the form of hydrated magnesium sulfate may be advantageous since its thermal decomposition results in MgO and SO2, products which can be reused in the limonite mining process. This reduces the volume of waste formed and the cost of reagents in the process. A crystallizer coupled to a filtration system was designed and the influence of the temperature, residence time and pH of the solution on the amount of crystallized magnesium from solution was investigated. The residual solution was analyzed by ion chromatography to quantify the magnesium in the solution. The crystals formed were analyzed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM-EDS) and sieve shakers in order to evaluate the chemical composition, morphology and grain size of the crystals. The solubility of magnesium sulphate was determined experimentally to increase the understanding of the solubility of the salt and obtain values of Kps. In 5 hours of residence time the system was stabilized, indicating that there will be no more crystalline growth at residence times greater than 5 hours. At pH 5.7 at 230 ° C and in 5 hours of residence time 81% of Mg crystallized. The crystals presented spherical morphology except for crystals obtained at 230 °C, at pH 2, which presented a rectangular shape. XRD analysis showed the presence of a product consisting mainly of magnesium sulphate monohydrate.
26
Parvatareddy, Hari. "Durability of Polyimide Adhesives and Their Bonded Joints for High Temperature Applications." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/29554.
Abstract:
The objective of this study was to evaluate and develop an understanding of durability of an adhesive bonded system, for application in a future high speed civil transport (HSCT) aircraft structure. The system under study was comprised of Ti-6Al-4V metal adherends and a thermosetting polyimide adhesive, designated as FM-5, supplied by Cytec Engineered Materials, Inc.
An approach based on fracture mechanics was employed to assess Ti-6Al-4V/FM-5 bond durability. Initially, wedge tests were utilized to find a durable surface pretreatment for the titanium adherends. Based on an extensive screening study, chromic acid anodization (CAA) was chosen as the standard pretreament for this research project. Double cantilever beam specimens (DCB) were then made and aged at 150° C, 177° C, and 204° C in three different environments; ambient atmospheric air (14.7 psia), and reduced air pressures of 2 psi air (13.8 KPa) and 0.2 psi air (1.38 KPa). Joints were aged for up to 18 months (including several intermediate aging times) in the above environments. The strain energy release rate (G) of the adhesive joints was monitored as a function of exposure time in the different environments. A 40% drop in fracture toughness was noted over the 18 month period, with the greatest degradation observed in samples aged at 204° C in ambient atmospheric air pressure. The loss in adhesive bond performance with time was attibutable to a combination of physical and chemical aging phenomena in the FM-5 resin, and possible degradation of the metal-adhesive interface(s). Several mechanical and material tests, performed on the bonded joints and neat FM-5 resin specimens, confirmed the above statement. It was also noted that physical aging could be "erased" by thermal rejuvenation, partially restoring the toughness of the FM-5 adhesive material.
The FM-5 adhesive material displayed good chemical resistance towards organic solvents and other aircraft fluids such as jet fuel and hydraulic fluid. The results from the FM-5 adhesive and its bonded joints were compared and contrasted with VT Ultem and REGULUS polyimide adhesives. The FM-5 adhesive showed the best performance among the three adhesive systems.
The effect of mode-mixity on the fracture toughness of the Ti-6Al-4V/FM-5 adhesive bonded system was also evaluated. DCB tests in conjunction with end-notched flexure (ENF) and mixed-mode flexure (MMF) tests, were used to fracture the bonded joints under pure mode I, pure mode II, and a combination of mode I and II loadings. The results showed that the mode I fracture toughness was twice as large as the mode II toughness. This was a rather surprising find, in sharp contrast to what several researchers have observed in the past. Our current understanding is that the crack path selection during the failure process plays a significant role in explaining this anomalous behavior. Finally, failure envelopes were generated for the titanium/FM-5 bonded system, both prior to and following thermal aging. These envelopes could serve as useful tools for engineers designing with Ti-6Al-4V/FM-5 bonds.Ph. D.
27
Wegman, Kevin R. "Numerical Modeling of a Printed Circuit Heat Exchanger Based on Experimental Results from the High-Temperature Helium Test Facility." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1461266010.
28
Vicente, André de Albuquerque. "Estudo da resistência à oxidação ao ar a altas temperaturas de um aço inoxidável austenítico microligado ao cério soldado pelo processo mig/mag com diferentes gases de proteção." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3137/tde-05092017-103140/.
Abstract:
A busca por alternativas para aumentar a resistência à oxidação ao ar a altas temperaturas de metais e ligas aumenta a cada dia, devido à necessidade de otimização da vida útil dos equipamentos que operam nestas condições. Novos materiais projetados para trabalhar nestas condições possibilitam reduzir custos de manutenção, aumentando a produtividade dos equipamentos, devido à redução do tempo de paradas programadas. O uso de aços inoxidáveis microligados a elementos terras raras é uma das alternativas adotadas, por exemplo, para tubulações para a indústria de petróleo e gás. Este trabalho estuda a resistência à oxidação ao ar a altas temperaturas de juntas soldadas de um aço inoxidável austenítico microligado ao cério. As juntas soldadas foram confeccionadas através do processo de soldagem MIG/MAG, depositando-se cordões de solda em chapas de aço inoxidável austenítico AISI 304L, variando-se a composição dos gases de proteção e mantendo-se os outros parâmetros de soldagem. Amostras dos diferentes metais depositados foram preparadas através de corte com disco diamantado e submetidas a ensaios de oxidação a altas temperaturas ao ar em balança termogravimétrica. Os corpos de prova oxidados foram estudados usandose microscópio óptico, microscópio eletrônico de varredura com EDS e difração de raios X. Observaram-se cinéticas de oxidação parabólicas em todas as temperaturas estudadas: 800, 900, 1000 e 1100 °C. Os Kps encontrados neste trabalho reforçam a tese de que ocorra a formação de películas protetoras de Cr2O3 e SiO2, o que reforça a hipótese que as mesmas tenham sido efetivamente formadas após os estágios iniciais de oxidação. Em todos os corpos de prova oxidados ao ar nas diferentes temperaturas, observou-se a formação de uma película não protetora de óxidos de ferro (Fe2O3, Fe3O4 e FeO) e posterior formação de uma camada protetora mais espessa de crômia (Cr2O3). Mais internamente observou-se a formação de SiO2.The search for alternatives to increase the high temperatures oxidation resistance in air of metals and alloys increases every day due to the need to optimization of the life expectancy of equipment operating in these conditions. New materials designed to work in these conditions make it possible to reduce maintenance costs, increasing productivity of equipment due to reduced shutdowns. The use of austenitic stainless steel microalloyed with rare earth elements is adopted an alternative, for example, to tubes and pipes for the oil and gas industry. This work aims to study the high temperature oxidation resistance in air of welded joints of an austenitic stainless steel microalloyed with cerium. The welded joints were welded using MIG / MAG welding process, depositing weld beads on a sheet of austenitic stainless steel AISI 304L by varying the composition of the shielding gases. Samples of the different welded joints were prepared by cutting with a diamond disk and were subjected to high temperatures oxidation testing in thermogravimetric balance. The oxidized specimens were studied using optic microscopy, scanning electron microscope with EDS and Xray diffraction. Parabolic oxidation kinetics were observed at all temperatures studied: 800, 900, 1000 and 1100 °C. The Kps found in this work reinforce the thesis that the formation of protective films of Cr2O3 and SiO2 occurs, reinforcing the hypothesis that they have been effectively formed after the initial stages of oxidation. In all specimens oxidized at different temperatures, a formation of a non-protective layer of iron oxides (Fe2O3, Fe3O4 and FeO) and subsequent formation of a thicker protective layer of chromite (Cr2O3) was observed. More internally, SiO2 formation was observed.
29
Furlan, Tarita Shiraishi. "Estudo do efeito do tratamento térmico e da adição de zircônio, vanádio, titânio e manganês nas propriedades mecânicas de uma liga AlSi12CuMgNi para aplicação em altas temperaturas." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-24122014-115046/.
Abstract:
Neste trabalho foram estudados os efeitos do tratamento térmico e da adição de zircônio, vanádio, titânio e manganês nas propriedades mecânicas em alta temperatura de uma liga AlSi12CuMgNi, comumente utilizada em pistões automotivos. Os resultados de tração a 300°C mostram que a adição de elementos de liga reduz o alongamento sem aumentar o limite de escoamento. Os ensaios de fadiga a 300°C mostram que a aplicação de um tratamento de solubilização a 525°C por 15 minutos é duas vezes melhor que a aplicação de um tratamento de solubilização a 500°C por uma hora. Estes resultados foram atribuídos ao arredondamento das partículas de silício que, por serem partículas frágeis, quando arredondadas ocupam menor área por volume, reduzindo a velocidade de propagação de trincas. Os ensaios de fadiga a 300°C mostram também que a adição de elementos de liga combinados a um tratamento de solubilização a 525°C por 15 minutos é cerca de 30% pior que o mesmo tratamento aplicado a uma liga sem a adição destes elementos de liga. Este fenômeno foi atribuído à fragilização dos intermetálicos que, por consequência, aumentam a velocidade de propagação das trincas de fadiga.The effects of heat treatment and the addition of zirconium, vanadium, titanium and manganese on the high temperature properties of an AlSi12CuMgSi alloy, usually applied to cast automotive pistons, were studied. The tensile test results at 300°C show that the addition of alloying elements decreases the elongation without significantly increasing the yield strength. The fatigue tests at 300°C show that a solution heat treatment at 525°C for 15 minutes is two times better than a solution heat treatment at 500°C for one hour. These results are due to the spheroidization of the silicone particles that are brittle and, when spheroidized, have a smaller area/volume ratio, slowing the crack propagation speed. The fatigue tests at 300°C also show that the addition of alloying elements combined with a solutionizing treatment at 525°C for 15 minutes is 30% worse than the same treatment applied to an alloy without these alloying elements. This behavior is due to the embrittlement of the intermetallic particles containing these alloying elements, increasing the fatigue crack propagation speed.
30
Araujo, Marcos Vinícius Pereira de. "Estudo do comportamento mecânico monotônico, cíclico e da evolução microestrutural em alta temperatura do aço ASTM A297 HP modificado com nióbio." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-03022016-084953/.
Abstract:
Componentes estruturais de fornos de pirólise utilizados para craqueamento de petróleo são fabricados a partir de aços inox fundidos utilizados para aplicações em alta temperatura, sendo necessária a adição de elementos químicos para a formação de fases que melhoram as propriedades mecânicas do material neste tipo de ambiente. O presente trabalho estuda os efeitos da adição de nióbio nas propriedades mecânicas e no comportamento elastoplástico/viscoelástico aos 927°C do aço inox fundido ASTM A297 grau HP na condição bruto de fusão, condição esta similar a de trabalho do forno.Para analisar as variação de propriedades mecânicas do material, foram realizados ensaios de tração em distintas temperaturas, calorimetria exploratória de varredura (DSC), ensaios de relaxação, fadiga de ciclos contínuos sob o formato de onda triangular e fadiga com formato de onda trapezoidal do tipo \"dwell\" com tempos de permanência de 120 e 300 segundos conforme especifica a norma E2714-13 e ensaios de torção a quente. O intuito da realização deste trabalho reside no fato de que equipamentos como os fornos de pirólise não mantém os parâmetros operacionais constantes, podendo variar temperatura, cargas de trabalho e também gerar cargas cíclicas com tempos de permanência em ciclos de partida, operação e parada de equipamento, sendo importante o conhecimento da resposta fenomenológica que o material oferece sob estes tipos de solicitações. Os resultados dos ensaios mecânicos e estudos da evolução microestrutural, bem como de suas posteriores análises forneceram dados, não somente sob a forma de \"data sheet\'s\" para aplicação dos valores obtidos em projetos, mas concomitantemente após a comparação de propriedade e microestrutura, aprofundar na fenomenologia do comportamento mecânico de tensão versus deformação monotônico e cíclicos, mecanismos de deformação em alta temperatura, recuperação dinâmica, do tipo de microestrutura resultante após a realização dos ensaios e também dos mecanismos de fratura associados aos tipos de solicitações mecânicas impostas ao material, obtidos por meio dos ensaios mecânicos mencionados anteriormente.Structural components pyrolysis furnaces used for oil cracking are made from cast stainless steel used for applications at high temperature, requiring the addition of chemicals to the formation of phases which improves the mechanical properties of the material in such an environment. This work studies the effects of adding niobium in the mechanical properties and elastoplastic/viscoelastic behavior to 927°C cast stainless steel ASTM A297 grade HP in as cast condition, at condition similar to the work of furnace. For study of the variation of mechanical properties, tensile tests were conducted at different temperatures, differential scanning calorimetry (DSC), relaxation tests, fatigue continuous cycles under triangular waveform and fatigue with trapezoid type waveform format \"dwell\" with residence times of 120 and 300 seconds as reflected by the E2714-13 standard and hot torsion tests. The purpose of this work lies in the fact that equipment such as pyrolysis furnaces do not maintain the constant operating parameters, varying temperature, workloads and also generate cyclic loading with residence times in starting cycles, operation and equipment stop It is important the knowledge of the phenomenological response that the material offers under these types of requests. The results of mechanical tests and micorestrutural evolution studies, as well as its further analysis provided data, not only in the form of \"data sheet\'s\" for application of the values obtained in projects, but co-after comparison of property and microstructure, deepen the phenomenology of the mechanical behavior of tension versus monotonic and cyclic deformation, deformation mechanisms at high temperature, dynamic recovery, the type of resulting microstructure after the tests and also the fracture mechanisms related to types of mechanical stresses imposed on the material, obtained by through the mechanical tests mentioned above.
31
Silva, Paulo Sergio Martins da. "Projeto, construção e testes de um sistema de medidas elétricas e estudo de compósitos de zircônia-ítria e nitreto de titânio." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-03122015-132823/.
Abstract:
Neste trabalho de mestrado são descritos o projeto, a montagem e os testes de funcionamento de uma câmara porta amostra para medidas elétricas de quatro pontas de prova dc. A estrutura da câmara porta amostra é em material cerâmico, que garante a estabilidade física e química do sistema, prolongando sua vida útil e melhorando a qualidade das análises realizadas. Este sistema permite a realização de medidas elétricas de diferentes materiais desde a temperatura ambiente até ~1500 °C em ampla faixa de pressões parciais de oxigênio. A funcionalidade da câmara porta amostras foi avaliada por meio da comparação de medidas da dependência da resistividade elétrica com a temperatura de amostras de zircônia estabilizada com ítria. Visando à aferição e a aplicação deste sistema de medidas elétricas, foram fabricados e caracterizados compósitos à base de zircônia estabilizada com ítria e nitreto de titânio, obtidos pela técnica de sinterização por plasma pulsado (\"spark plasma sintering\", SPS). As propriedades gerais destes compósitos foram investigadas por meio de análises térmicas, difratometria de raios X (DRX) e medidas elétricas de quatro pontas de prova dc, usando o sistema construído. As análises das amostras dos compósitos à base de zircônia e TiN mostraram que a técnica SPS produz amostras densas, sem reação entre as fases ou degradação do TiN por oxidação. As amostras com adição de TiN apresentaram comportamento metálico da resistividade elétrica, evidenciando a percolação do nitreto na matriz de zircônia para frações volumétricas ≤ 27 vol.%. Medidas de resistividade elétrica combinadas com análises térmicas e de DRX foram usadas para monitorar a oxidação do TiN nos compósitos em altas temperaturas. As amostras produzidas apresentam propriedades promissoras para aplicações de alta temperatura que requeiram elevada condutividade elétrica.This study describes the design, construction, and tests of a sample holder for four-probe dc electrical measurements. The structural parts of the sample holder are built using ceramic material (alumina) that ensures physical and chemical stability, prolonging its use and the quality of experiments. The sample holder allows electrical measurements from room temperature up to ~1500 °C in a wide range of oxygen partial pressures. The functionality of the constructed sample holder was assessed by comparing measurements of the temperature dependence of the electrical resistivity of yttria-stabilized zirconia samples. To further explore the capabilities of the measuring apparatus, samples of high-temperature composites based on yttria-stabilized zirconia and titanium nitride were prepared by spark plasma sintering (SPS). The general properties of these composites were investigated by thermal analysis, X-rays diffraction (XRD), and four-probe dc electrical measurements. The study of the composites showed that SPS resulted in dense samples with no detected reaction between phases and free from TiN oxidation. Samples with TiN addition displayed metallic behavior of the electrical resistivity, evidencing that the nitride attained the percolation threshold in the oxide matrix at volume fractions ≤ 27 vol.%. Electrical measurements combined with thermal analysis and XRD were used to monitor the oxidation of TiN at high temperature. The studied composites show good properties indicating that it is a promising material for high temperature applications that require high electrical conductivity.
32
Auler, Luiz Telmo da Silva. "Ressonância magnética nuclear em supercondutores de alto Tc." Universidade de São Paulo, 1994. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-08042014-142100/.
Abstract:
Nesta tese investigamos o estado normal (T > Tc) dos Yba2Cu3O6+x supercondutores de alto Tc. As técnicas da RMN e RQN foram empregadas para estudar as respostas estática e dinâmica do sistema de spins eletrônicos em função da temperatura, para diversas concentrações de oxigênio: x = 0.5 (cristal 1), 0.92 (cristal 2), 0.94 (cristal 3) e 1.0 (cristais 4 e 5). Focalizando diferentes sítios nucleares a RMN pode fornecer uma informação mais rica da susceptibilidade dinâmica, X (q.w), abrangendo diferentes regiões da Zona de Brillouin (ZB). Com os sítios do 17O(2,3) e do 89Y sensoreamos a região próxima ao centro do ZB, q == 0, enquanto que com o sitio do Cu(2) exploramos o extremo do ZB, (q == QAF). Foi realizado um estudo comparativo da RMN dos sítios do Cu(2), do O(2,3) e do Y sobre o cristal 1. Da comparação entre os deslocamentos hiperfinos magnéticos do Y e do O(2,3) extraímos as contribuições orbitais e as constantes de acoplamento hiperfino do Y. A razão entre as relaxações spin-rede do O(2,3) e do Y mostrou-se independente da temperatura, e próxima do esperado teoricamente a partir das constantes hiperfinas no cenário do hamiltoniano de Mila e Rice. Questões como a dependência da taxa de relaxação spin-rede (T1-1) com a intensidade do campo e a anisotropia da susceptibilidade estática de spin foram estudadas sobre o cristal 2. Acima de Tc, para o Cu(2), não foi encontrada nenhuma dependência de T1 com a intensidade do campo. Os resultados sobre o Y indicam uma anisotropia da susceptibilidade e do tensor de acoplamento hiperfino. Uma extensa comparação entre os resultados da RMN e da Difusão Inelástica de Nêutrons (DIN) foi realizada sobre as mesmas amostras (cristais 4 e 5), fato inédito ate então. Propõe-se um modelo gaussiano para X\"~q,o», compatível com as experiências de nêutrons, no qual o comprimento de correlação ~ foi fixado pelos resultados da DIN sobre o cristal 2. Analisando a relaxação spin-spin do Cu(2), 63(T2g)-1, em função deste modelo, extraímos a susceptibilidade estática X\'(q=QAF) em unidades absolutas e encontramos um fator de Stoner X\'(q=QAF) / X\'(q=O) ~ 10. Da análise conjunta de 63(T1T)-1 e 63 (T2g)-1 obtivemos a energia característica das flutuações AF, rAF::::3:0meV, em excelente acordo com a DIN. Estes mesmos resultados permitiram evidenciar, exclusivamente através do RMN, quando ocorre a abertura de um gap de spin. Neste trabalho mostramos que resultados da DIN são compatíveis com a RMN para o sitio do Cu(2), porem, sérias dificuldades são encontradas para explicar os resultados sobre os sítios do Y e, principalmente, do O(2,3). As alternativas para este problema são discutidas. Os resultados obtidos nesta tese levaram ao estabelecimento de um diagrama de fase, segundo a RMN, do estado normal dos Yba2Cu3O6+x supercondutores, cobrindo do regime sub-dopado ao regime sobre-dopado, passando pela composição de dopagem ótima.The normal state(T > Tc) of the high Te superconducting Yba2Cu3O6+x was studied. The NMR and NQR techniques were employed in order to investigate the static and dynamic responses of the electronic spin system as function of temperature, for the following oxygen contents: x = 0.5 (crystal 1), 0.92 (crystal 2), 0.94 (crystal 3) e 1.0 (crystals 4 and 5). Focusing various nuclear sites the NMR could give a more rich information of the dynamical susceptibility, X(q,ffi), probing different regions of the Brillouin Zone (ZB). With 17O(2,3) and 89Y sites the BZ center, q:: 0, was studied, while with the Cu(2) site it was the BZ extreme, (q:: QAF) that was investigated. In crystal 1 we have compared the NMR of the Cu(2), O(2,3) and Y sites. From the comparison between the Y and O(2,3) magnetic hyperfine shift we have extracted the orbital contributions and the Y hyperfine coupling tensor. The ratio between the O(2,3) and Y nuclear spin lattice relaxation rate was found to be temperature independent, and its value was in fair agreement with what it was expected theoretically from the coupling constants within the picture of the Mila-Rice Hamiltonian. Problems such as the field intensity dependence of the spin-lattice -relaxation rate (T1-1) and the anisotropy of the static susceptibility where investigated in crystal 2. Above Tc, for the Cu(2) site, we have not found any field dependence of T1. Our results on the Y site indicate an anisotropy of both the static susceptibility and the Y coupling tensor. An extensive comparison between the NMR and the Inelastic Neutron Diffusion (IND) results was done in the very same samples, crystals 2 and 4. In accordance to neutron data a Gaussian model for X\"AF( q,ro) is proposed, in which the coherence length ~ was fixed by the IND results in crystal 2. Analyzing the Cu(2) nuclear spin-spin relaxation rate, 63(T2g)-1, as function of this model, we have extracted the staggered susceptibility X\'(q=QAF) in absolute units, finding a Stoner factor X \'( q=QAF) / X\'( q=O) ~ 10. From the analysis of 63(T1T)-1 together with 63(T2g)-1 we have obtained the AF characteristic energy, rAF ::::l 30meV, in excellent agreement with IND. These results provided us a powerful method to evidence the opening of a spin pseudo gap, exclusively from the NMR results. A consistent picture arise from the comparison between IND and the Cu(2) NMR. In contrast, it is hard to explain the Y and, specially, the O(2,3) results within this same picture. The theoretical alternatives to this puzzle are discussed. The whole set of results we have obtained led us to propose a NMR based phenomenological phase diagram for the normal state of the superconducting Yba2Cu3O6+x, covering from the under doped regime to the over doped regime, passing through the optimal doping.
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Silva, Wanderson Santana da. "Avaliação do comportamento mecânico e tribológico de ligas Ni-Cr-Al-C." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-20042007-173509/.
Abstract:
Este trabalho traz contribuições à linha de pesquisa \'Nova Família de Ligas Baseada no Sistema Ni-Al-Cr-C Resistentes ao Desgaste em Elevadas Temperaturas\', estudando o comportamento mecânico, tribológico e a estabilidade superficial destas ligas. Esta família de ligas fundidas, denominada NICRALC - busca conjugar algumas características das superligas à base de níquel e dos ferros fundidos brancos, aliando ao comportamento mecânico anômalo do Ni3Al - aumento da resistência mecânica com a temperatura, até valores da ordem de 800°C - a uma dispersão de carbonetos de cromo de alta dureza. Desta forma, busca-se desenvolver uma alternativa às ligas ferrosas nas temperaturas acima das quais estas ligas perdem significativamente sua resistência mecânica (notadamente 600 °C), assim como uma alternativa mais econômica às ligas a base de cobalto resistentes ao desgaste, em virtude das altas cotações e instabilidades no preço deste elemento. Neste trabalho foram avaliadas as propriedades mecânicas em elevadas temperaturas (compressão e dureza), tenacidade à fratura na temperatura ambiente, comportamento tribológico (cavitação, abrasão, deslizamento e erosão) e a resistência à oxidação ao ar e à carburação em atmosfera redutora, em temperaturas elevadas, de ligas Ni-Al-Cr-C (NICRALC) fundidas. Ligas NICRALC fundidas com diferentes teores de carbono e submetidas a diferentes tratamentos tiveram seu comportamento mecânico e tribológico comparado ao comportamento do STELLITE 6 fundido, a uma liga NICRALC produzida por deposição por \'SPRAY\', a um ferro fundido branco alto cromo fundido convencionalmente e a um ferro fundido branco alto cromo depositado por \'SPRAY\'. Os ensaios de compressão confirmaram o comportamento anômalo da matriz ordenada Ni3Al. As ligas NICRALC apresentaram aumento ou manutenção da resistência ao escoamento com o aumento da temperatura de ensaio. A mesma tendência foi encontrada nos ensaios de dureza a quente. As demais ligas apresentaram tendência de queda da resistência ao escoamento e da dureza com o aumento da temperatura de ensaio. Esta tendência é mais acentuada na liga STELLITE, desta forma, as ligas NICRALC apresentaram em altas temperaturas maior resistência ao escoamento e maior dureza que o STELLITE. Os diferentes ensaios de desgaste mostraram, em geral, uma maior resistência do STELLITE em comparação com as ligas NICRALC na temperatura ambiente. Nestas condições verifica-se que a menor resistência mecânica da matriz ordenada nas ligas NICRALC é determinante para definir uma menor resistência ao desgaste na temperatura ambiente. Nos ensaios de erosão-oxidativa realizados a 600 e 800°C as ligas NICRALC mostraram perdas de massa menores que as experimentadas pelo STELLITE e pelos ferros fundidos. As ligas NICRALC com microestrutura de carbonetos mais homogênea, próxima do eutético, mostraram melhor comportamento sob desgaste abrasivo e erosivo se comparadas às ligas NICRALC 05 e 13. Os ensaios de resistência à oxidação mostraram que as ligas NICRALC são mais resistentes à oxidação que o STELLITE. Além disso, observou-se grande propensão ao destacamento dos filmes de óxidos formados nos STELLITES em temperaturas acima de 800°C. Os ensaios de resistência à carburação mostraram que no caso das ligas NICRALC ocorreu a precipitação de um depósito de grafita e, subjacente a esta, a formação de uma zona de fragmentação microestrutural, na qual se observa empobrecimento ora do Al ora do Cr, que aparentemente impede o avanço do processo. No caso do STELLITE verificou-se a ocorrência do aumento da fração volumétrica de carbonetos, típico dos casos clássicos de carburação. Os procedimentos de simulação termodinâmica utilizados indicam a necessidade de se implementar a descrição da solubilidade do carbono na fase ordenada de forma a permitir o pleno uso do software THERMOCALC no projeto e aprimoramento de ligas NICRALC.This work contributes to the research line \'New Family of High Temperature Wear Resistant Alloys based on the Ni-Al-Cr-C System\', studying the mechanical and tribological behaviour and the surface stability of these alloys. This family of foundry alloys, called NICRALC, tries to unite some of the characteristics of the Ni based superalloys and the high-chromium-white-cast-irons, associating the anomalous behaviour of the ordered intermetallic phase Ni3Al - which increases its strength with the increase of temperature - with a dispersion of hard chromium carbides. The aim is to develop an alternative to iron-based wear resistant alloys at temperatures where they loose significantly their strength, as well as substituting cobalt based high temperature wear resistant alloys, which suffer from the instability and high cost of the Co metal. The high temperature mechanical properties (hardness and compression), room temperature fracture toughness, tribological behaviour (cavitation, abrasion, sliding and erosion) and resistance to high temperature oxidation and carburization of cast Ni-Al-Cr-C (NICRALC) alloys are studied. Cast NICRALC alloys with different C contents and different heat treatments were compared with a cast STELLITE 6, a conventionally cast high chromium white cast iron, a spray formed high chromium white cast iron and a spray formed NICRALC. Mechanical tests in compression confirmed that NICRALC alloys share the anomalous behaviour of the ordered intermetallic phase Ni3Al, increasing or maintaining their yield strength with increased testing temperature. The same occurred with hot hardness tests. STELLITE and all other alloys showed loss of strength with increased testing temperatures. Thus NICRALC alloys showed higher strength and hardness than STELLITE at high temperatures. All wear tests showed a higher wear resistance of STELLITE in comparison with NICRALC at room temperature. This result can be explained by the higher matrix hardness of STELLITE at room temperature. Oxidative-erosion tests run at 600 and 800° C showed that NICRALC suffered smaller mass loss than STELLITE and the white cast irons. NICRALC alloys with more homogeneous carbide distributions (eutectic alloys) obtained the best results under severe oxidation-erosion conditions. NICRALC alloys were more oxidation resistant than STELLITE alloy, which tended to break and detach the oxide layer formed above 800°C under air. During carburization essays in a reducing atmosphere the NICRALC alloys tended to form a coke-like graphite layer, over a layer with a fragmented microstructure depleted alternatively in chromium and aluminum, which effectively stopped the advance of the process. The STELLITE alloy suffered an increase in carbide volume fraction, a classic carburizing behaviour. The thermodynamic simulation results show that it is still needed to introduce the solubility of carbon on the ordered Ni3Al phase in the model in order to be able to fully calculate the NICRALC phase diagrams.
34
Dilner, David. "Behavior of cutting tool coating material Ti1-xAlxN at high pressure and high temperature." Thesis, Linköping University, Department of Physics, Chemistry and Biology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-52773.
Abstract:
The high pressure and high temperature (HPHT) behavior of Ti1-xAlxN coatings on cutting tool inserts have been of interest for this diploma work. A literature study of HPHT techniques as well as measurement methods has been done. A diamond anvil cell (DAC) would be a good device to achieve high pressure and high temperature conditions on small samples. Another way to obtain these conditions would be a cutting test, which has been performed on a Ti1-xAlxN coated cutting tool insert with x = 0.67. Also a cubic press could be used to apply HPHT on a Ti1-xAlxN sample or a large volume press on a whole cutting tool insert. To measure hardness on thin coatings a nanoindentor could be used, which have been done on heat-treated Ti0.33Al0.67N and TiN samples. X-ray diffraction (XRD) is a suitable method to measure phase composition of a sample and was performed on the cutting tested insert as well as on an untreated reference insert. Three ways to continue this project have been outlined all starting with more comprehensive cutting tests.
35
Rodrigues, Julia da Rosa Howat. "Projeto e construção de um simulador solar concentrador." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3150/tde-25082016-093701/.
Abstract:
Segundo o Atlas Brasileiro de Energia Solar, apesar das diferentes características climáticas observadas no Brasil, pode-se constatar que a média anual de irradiação solar global apresenta boa uniformidade e elevados índices por todo o país. Os valores desta grandeza em quase toda a extensão do território brasileiro (4200-6700 Wh/m2/dia) são superiores aos da maioria dos países da União Europeia, como Alemanha (900-1250 Wh/m2/dia), França (900-1650 Wh/m2/dia) e Espanha (1200-1850 Wh/m2/dia), onde projetos para aproveitamento de energia solar, alguns contando com fortes incentivos governamentais, são amplamente disseminados. Grande parte dos avanços científicos obtidos nos estudos sobre aproveitamento da energia solar se deve à utilização de simuladores solares compactos nos experimentos de longa duração. Ao substituir o Sol por fontes artificiais, como lâmpadas capazes de emitir radiação próxima à solar, os simuladores eliminam a dependência de fatores naturais como condições climáticas, horário do dia, intermitência e movimento de direção da radiação solar. O projeto proposto para esta dissertação de Mestrado teve como objetivo o domínio do processo de concepção e fabricação de um simulador solar concentrador formado por lâmpadas e um refletor ótico. Uma vez dominada a técnica, um modelo piloto de simulador solar foi construído e alguns testes executados para avaliar a qualidade do projeto, a resistência dos componentes e o fator de concentração do aparato.According to the Brazilian Atlas of Solar Energy, despite the different climatic characteristics observed in Brazil, the annual average of global solar irradiation has good uniformity and high levels throughout the country. The values of global solar irradiation in almost the entire length of Brazil (4200-6700 Wh/m2/day) are higher than those observed in most European Union countries, like Germany (900-1250 Wh/m2/day), France (900-1650 Wh/m2/day) and Spain (1200-1850 Wh/m2/day), where projects for solar energy applications, some of them relying on strong government incentives, are widely disseminated. Several scientific and technological advances made in the study of solar energy applications are due to the use of compact solar simulators in long-term experiments. Replacing the Sun by artificial sources, such as arc lamps with radiation emission similar to the Sun spectrum, indoor simulators avoid the dependence on natural conditions such as the weather, the daytime, the sunlight intermittence and the directional change of the solar radiation. The project proposed for this dissertation aimed to master the design and manufacturing processes of a high-flux solar simulator consisting of arc lamps and an optical reflector. Once technique was understood, a solar simulation pilot model was built and some tests were performed to assess the project quality, the resistance of components and the apparatus concentration factor.
36
Sertorio, Daiane Franciele Francisco. "Avaliação de aspectos fisiológicos e bioquímicos da interferência da radiação e aquecimento sob perspectiva futura, em quatro espécies arbóreas tropicais." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/59/59139/tde-07052013-230340/.
Abstract:
Nos últimos 100 anos, a temperatura média global aumentou aproximadamente 0,6ºC e deverá continuar a subir a uma taxa rápida podendo atingir 2ºC. No entanto, não se sabe como as plantas responderão a essa mudança climática, pois existem poucas informações sobre as respostas fisiológicas das plantas a incrementos de temperatura. Este trabalho tem por objetivo avaliar os efeitos de duas condições luminosas e duas condições de temperatura (com interação entre eles), em perspectiva futura, sobre o comportamento morfológico, fisiológico e bioquímico de quatro espécies da Floresta Mesófila Semidecídua: Aspidosperma cylindrocarpon e Aspidosperma polyneuron (Apocynaceae); Cariniana estrellensis e Cariniana legalis (Lecythidaceae). As plantas foram submetidas aos seguintes tratamentos: 100% de radiação e temperatura ambiente (100%RTA), 100% de radiação e temperatura elevada em +2ºC (100%RTE), 20% de radiação (por sombreamento) e temperatura ambiente (20%RTA), e 20% de radiação e temperatura elevada em +2ºC (20%RTE). Aspidosperma polyneuron apresentou-se como a espécie mais sensível a radiação intensa, seguida de C. legalis ambas já ameaçadas de extinção. Os parâmetros morfológicos confirmam a teoria de que plantas cronicamente fotoinibidas continuam crescendo, porém, em menores taxas. Os dados bioquímicos reforçam os fisiológicos mostrando fragilidade das espécies secundárias à radiação intensa e os efeitos principalmente negativos do aquecimento aplicado.In the last 100 years the average global temperature increased by 0.6ºC and it might increase in a fast rate reaching up to 2ºC. However, little is known about how plants might respond to the climate change because there is not enough information about the physiological alterations plants might suffer due to increased temperature. We evaluated morphological, physiological and biochemical alterations under the effects of two light/temperature conditions and its interactions in four different plant species of the Semideciduous Mesophitic Forest: Aspidosperma cylindrocarpon and Aspidosperma polyneuron (Apocynaceae); Cariniana estrellensis and Cariniana legalis (Lecythidaceae). All plants suffered the following treatments: 100% radiation and environment temperature (100%RTA), 100% radiation and environment temperature +2ºC (100%RTE), 20% radiation (shade) and environment temperature (20%RTA), and 20% radiation (shade) and environment temperature +2ºC (20%RTE). Aspidosperma polyneuron was shown to be the most sensible specie to high radiation, followed by C. legalis, both threatened with extinction. Morphological parameters confirmed the theory that chronically photo-inhibited plants keep growing, but at lower rates. Biochemical findings also confirmed our physiological data showing increased fragility of the secondary species to high radiation and heating.
37
Richard, Joshua (Joshua Glenn). "Design optimization and analysis of a fluoride salt cooled high temperature test reactor for accelerated fuels and materials testing and nonproliferation and safeguards evaluations." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103657.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 212-221).
Fluoride Salt Cooled High Temperature Reactors (FHRs) are a new reactor concept that have recently garnered interest because of their potential to serve missions and generate revenue from sources beyond those of traditional base-load light water reactor (LWR) designs. This potential is facilitated by high-temperature, atmospheric-pressure operation enabled by the incorporation of liquid fluoride salt coolants together with solid microparticle TRISO fuel. Since no FHR has been built, an important technology development step is the design, construction, and operation of a FHR test reactor (FHTR). The FHTR's strategic goals cannot be satisfied using small-scale experiments or test loops: (1) develop the safety and licensing basis for a commercial plant; (2) demonstrate technological viability and provide operational and maintenance experience; and (3) test alternative fuels, fluoride salt coolants, and structures in an actual reactor configuration. The goals of the FHTR support the development of the commercial FHR, but are different. The programmatic goals for the FHTR drive the specification of the technical design goals: (1) capability to switch between any one of various potential liquid fluoride salt coolants; (2) provide an irradiation facility for accelerated fuels and materials testing. The first stage of the present work included an exploration and characterization of the available design space for an FHTR. Many different core, reflector, and assembly designs were evaluated to determine configurations that possessed acceptable performance while satisfying all design constraints. This work resulted in a novel prismatic block assembly design termed Fuel Inside Radial Moderator (FIRM), which leverages spatial selfshielding of the fuel microparticles to increase core reactivity by ~10,000 pcm relative to a traditional prismatic block design, enabling operation with any of the proposed liquid fluoride salt coolants. This stage of work served to focus the search space for the application of formal optimization algorithms to further improve the feasible design. The second stage of the present work involved the development of a methodology to perform full-core optimization of the feasible FHTR design and its implementation into usable software. The OpenFRO (Open source Framework for Reactor Optimization) code implements the Efficient Global Optimization (EGO) surrogate-based optimization framework, which has been successfully applied to aerospace and automotive engineering optimization problems in the past. OpenFRO extends the EGO framework to full-core reactor optimization in the presence of uncertainty, enabling an effective, automated, and efficient approach for earlystage reactor design. OpenFRO's EGO implementation imposes minimal computational overhead while reducing the number of required high-fidelity simulations for optimization by 96%. The final stage of the present work involved the identification and analysis of the optimal design of the FHTR. The optimal design was selected based on its capability to provide the best performance across potential salt coolants and power levels. The optimal design achieved irradiation position fluxes 90%-130% greater than the feasible design initially identified, while satisfying all safety and performance constraints.
by Joshua Richard.
Ph. D.
38
Nince, Andréia Azeredo. "Lascamento do concreto exposto a altas temperaturas." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/3/3146/tde-27072007-143816/.
Abstract:
Esta pesquisa foi motivada pela existência de controvérsia na literatura sobre concreto exposto a altas temperaturas, das dúvidas ainda por solucionar acerca da matéria e da lacuna na norma brasileira para a matéria. Este tema reapareceu após os vários acidentes em túneis ao redor do mundo ocorridos nos últimos dez anos, nos quais se verificou a ocorrência de lascamento explosivo de forma intensa, afetando a estabilidade estrutural. O objetivo principal da tese é correlacionar os parâmetros tecnológicos de dosagem (relação água/cimento, teor de argamassa e consumo total de água) às condições de risco de lascamento, associados à umidade ambiente, que indiretamente, influencia no grau de saturação do concreto. O segundo objetivo é otimizar o uso de fibras de polipropileno para minimizar o efeito do lascamento. Adotou-se empregar a curva-padrão H durante 55 minutos em corpos-de-prova cúbicos aquecidos apenas em uma das fases com sua dilatação térmica lateral restringida. O nível de lascamento foi avaliado usando o volume lascado, obtido pela espessura medida diretamente nos corpos-de-prova, multiplicada pela área lascada, calculada pelo AUTOCAD 2000. Os resultados mostraram que o parâmetro tecnológico mais relevante na ocorrência de lascamento foi a relação água/cimento e a umidade ambiente apresentou capacidade de alterar as condições de risco de lascamento. No estudo com as fibras percebeu-se diferentes teores de fibras e diferentes características das fibras para cada grupo de a/c. Conclui-se que a relação água/cimento mais baixa associada a umidade a ambiente mais elevada é a condição mais propícia a ocorrência de lascamento. Conclui-se também que o teor de fibras de 600g/m³ é o teor mínimo para se reduzir o lascamento no grupo a/c=0,50 e 1750g/m³ no grupo a/c=0,25. A fibra L=12mm F=36µm PF=140°C mostrou-se a mais eficaz no grupo a/c=0,50 apenas o comprimento L=6 mm mostrou-se eficiente na redução do lascamento.The present research was motivated by the going controversy in the literature about concrete exposed to high temperatures, the yet unanswered doubts existent on this subject and in the absence of regulation on the matter in Brazil. The theme gained significance after the occurrence of several accidents in tunnels all over the world in the last ten years, in which were observed a very intense form of explosive spalling that affected structural stability of the sites. The main purpose of this work is set up a correlation between technological parameters of dosage in concrete (water cement rate -w/c, mortar content - a, and total water consumption - H) and risk conditions of spalling, which are related to environment humidity that indirectly effects concrete saturation level. The second goal is to optimize the use of polypropylene fiber in order to minimize spalling. The standard H curve was applied during 55 minutes in cubic samples with only a single surface exposed to heat and with restrained lateral thermo dilatation. The response variable was the observed volume of spalling (with multiplied by area of spalling in the sample). The results showed the rate water/cement as the most relevant technology parameter related to spalling risk conditions. Whereas the use of fiber is concerned, efficiency required different fiber content and characteristic for each water/cement rate combined with higher environment humidity provides proper conditions for the occurrence of spalling were 600g/m³ and 1750g/m³ for water/cement ratios of 0,5 and 0,25 respectively. It was also found that the fiber with L=12mm, F=36µm PF=140°C was the most effective in reducing spalling for a water/cement ratio of 0,50 whilst for a effective in reducing spalling for a water/cement ratio of 0,50 whilst for a water/cement ratio of 0,50 whilst for a water/cement ratio 0,25 only the length (L=6 mm) appeared as a significant factor.
39
Van, der Merwe Jacobus Johannes. "Modelling silver transport in spherical HTR fuel." Thesis, Pretoria : [s. n.], 2009. http://upetd.up.ac.za/thesis/available/etd-10172009-102536/.
40
Dornelas, Dante Antonucci. "Caracterização mecânica em temperaturas elevadas da Superliga MAR-M247." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-01102013-105701/.
Abstract:
A necessidade de trabalhos em altas temperaturas exige o desenvolvimento de materiais com elevada resistência química e mecânica em temperaturas que podem chegar próximas ao seu ponto de fusão. Em especial, os materiais empregados devem apresentar bom comportamento em fluência, de modo a suportar a combinação de altas tensões e altas temperaturas com o mínimo de deformação. O presente trabalho visa caracterizar a superliga MAR-M247, fornecida pela empresa Açotécnica, em condições de fluência para a produção de rotores empregados em turbocompressores automotivos. Os trabalhos são divididos em duas etapas. Na primeira estuda-se a melhor combinação de tratamentos térmicos de solubilização e envelhecimento, chegando à condição de solubilização por 5 horas a 1250?C e envelhecimento por 20 horas a 980?C. Um trabalho de outro aluno (SILVA, 2011) realiza o mesmo estudo para uma variação da superliga MAR-M247 em que o tântalo é totalmente substituído por nióbio. Neste caso, a melhor condição de tratamento é solubilização a 1260?C por 8 h seguida de envelhecimento duplo por 5 h a 880?C e 20 h a 780?C. Na segunda etapa, os materiais dos dois trabalhos, nas melhores condições de tratamento para cada um, são testados em condições de fluência a 850?C a 370, 390, 410 e 430 MPa. A superliga convencional apresenta os maiores valores de vida em fluência enquanto a modificada apresenta os maiores valores de ductilidade. A análise de fratura dos materiais ensaiados a 390 e 430 MPa mostra a presença massiva de carbonetos em toda a extensão da microestrutura, apresentando, em muitos casos, uma morfologia de \"escrita chinesa\". Apesar disso, todas as amostras apresentam grande quantidade de vazios, indicando que sua nucleação e crescimento são os responsáveis pela fratura do material.The needing for high temperature work claim for new materials capable of maintain high strength and good corrosion resistance at temperatures that could reach values near their melting point. Such materials must be creep resistant to withstand high levels of tension and temperature. The aim of this work is the characterization of MAR-M247 under creep conditions for the production of automotive turbocharger rotors made by Açotécnica. The work is split in two steps. In the first one, the material is studied to find the best conditions for solution and ageing heat treatments. The result is a solution treatment at 1250?C for 5 h followed by aging at 980?C for 20 h. A work made by another student (SILVA, 2011) makes the same with a modification of MAR-M247 in which tantalum is completely substituted for niobium. The best condition for this case is a solution treatment at 1260?C for 8 h and a double aging treatment at 880?C for 5 h and 780?C for 20 h. At the second part of the work, both the materials are tested under creep conditions at 850?C with 370, 390, 410 and 430 MPa. The conventional superalloy shows the highest values for creep strength and the modified superalloy shows the highest ductility. Fracture surfaces for 390 and 430 MPa showed brittle carbides with \"chinese script\" morphology. Conversely, holes are present on all four materials what shall mean that its nucleation and growth was the most probably fracture path.
41
Oliveira, Ana Cláudia Costa de. "Propriedades mecânicas de fadiga de baixo ciclo à temperatura de 300ºC do aço inoxidável austenítico do sistema Fe-Cr-Mn-N." Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-11072017-163136/.
Abstract:
Os colares das sondas de prospecção petrolíferas são fabricadas de aço inoxidável austenítico devido as suas características eletromagnéticas e de corrosão. Normalmente, a temperatura de serviço é de aproximadamente 300ºC, meio aquoso e a sonda é submetida a carregamentos cíclicos. Várias foram as tentativas de desenvolvimento de um aço que atendesse as necessidades de serviço destes colares. Neste trabalho foram determinadas as propriedades mecânicas de tração e de fadiga de baixo ciclo de um aço inoxidável austenítico do sistema Fe-Mn-Cr-N, quando ensaiado mecanicamente nas temperaturas ambiente e à 300ºC. Foi observado que os valores dos limites de escoamento e de resistência e o alongamento diminuem significativamente quando a temperatura é elevada para 300ºC. Como conseqüência destas alterações, ocorreu uma diminuição da vida em fadiga. A comparação entre as curvas tensão-deformação monotônica e cíclica mostrou que este material, ensaiado à 300ºC e nas amplitudes de deformações estudadas, apresenta amolecimento cíclico. A expressão encontrada para a relação deformação-vida é dada por Δεt/2=0,0054 (2Nf)-0,064 + 0,438 (2Nf)-0,595 com ponto de transição em 2Nt = 9,5 x 103. Quanto aos métodos estimativos das propriedades mecânicas de fadiga, obtidos a partir das propriedades mecânicas de tração, foi verificado que o Método da Inclinação Universal Modificado se aproxima mais da curva experimental obtida neste trabalho. A análise fratográfica mostrou a presença de estrias no estágio II de propagação de trinca.In this work the monotonic and low cycle fatigue mechanical properties of an Cr-Mn-N austenitic stainless steel, used to produce drill collars used for deep drilling in offshore industry, were evaluated. The low cycle fatigue testing was carried out according to the ASTM E606 standard, under strain control and R = - 1, at temperature of 300°C, which is the temperature that the drill collar reaches in service. It was observed that the yield and the ultimate tensile strength and the elongation decreased sharply with increasing temperature. As a consequence, in both high and low cycle regions, the fatigue life decreased with increasing temperature. The comparison between the stress - strain monotonic and cyclic curves, showed that this material exhibited cyclic softening for the applied strain amplitudes. The correlation between strain and number of cycles to failure was can be given by Δεt/2 = 0,0054 (2Nf)-0,064 + 0,438 (2Nf)-0,595 with transition in 2Nt = 9,5x103 reverses. The experimental results were compared with some models used to predict the fatigue life based on the tensile monotonic properties. The Modified Universal Shopes a better fitting with the experimental data. The fractographic analysis showed the presence of stage II striations.
42
Ruy, Marcos Cesar. "Efeito do jateamento a quente na vida em fadiga de um aço mola SAE 5160." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-20092016-111735/.
Abstract:
O processo de jateamento com granalhas é um tratamento superficial, muito utilizado em peças, com o intuito de melhorar as propriedades de resistência à fadiga. A deformação controlada do impacto das esferas introduz tensões residuais compressivas na camada superficial do material. Geralmente, este processo é executado na temperatura ambiente. Existem poucos estudos exploratórios de se executar este tratamento superficial em temperaturas acima da ambiente, para a promoção de um aumento na vida em fadiga causada por uma maior deformação plástica. Este trabalho teve como principal objetivo o estudo do efeito do jateamento com granalhas, executados em temperaturas fora da ambiente, no comportamento em fadiga de lâminas fabricadas de aço mola SAE 5160, utilizado pela indústria automobilística. Foram realizados ensaios de fadiga por flexão em três pontos em corpos de prova no formato do componente original. Estas amostras foram jateadas nas temperaturas de 25, 100, 150, 200, 250 e 300ºC. Os resultados deste trabalho permitiram a obtenção de algumas conclusões importantes quanto ao processo de jateamento que deverão influir diretamente no processo de fabricação destas lâminas e possivelmente de outros componentes mecânicos. Com o aumento da temperatura, ocorreu primeiramente um acréscimo no nível das tensões residuais na faixa de temperatura de 25 a 100ºC, passando a decrescer continuadamente até a temperatura de 300ºC e um aumento crescente da rugosidade superficial. O jateamento a 200ºC promoveu um melhor desempenho, pois executado nesta temperatura, proporcionou a melhor associação de tensão residual introduzida e encruamento, resultando em, um acréscimo de aproximadamente 10 vezes na vida em fadiga.Shot peening is a surface treatment commonly used in parts with the aim of improving fatigue properties. The controlled plastic deformation caused by the impact of the shots introduces compressive residual stresses on the surface layer of the material. Normally, this process is performed at room temperature, however a few studies propose to perform this surface treatment above room temperature in order to increase the fatigue strength due to the associated higher plastic deformation. The aim of this work was to study the effects of shot peening process above room temperature on the fatigue properties of a SAE 5160 leaf spring steel used by the automotive industry. Three point bending fatigue tests were performed in test pieces with the same geometry of the original component. Test pieces were peened at 25, 100, 150, 200, 250 and 300ºC. Increasing temperature, it was observed an increase in surface roughness (i.e. plastic deformation). However, residual stress values increase up to 100ºC and decrease continuously above this temperature. Fatigue strength was the highest for parts peened at 200ºC possibly due to an optimized association of residual stress and hardening effects caused by the plastic deformation. These results may directly affect the fabrication process of spring leaves and other mechanical parts.
43
Grajales, Dairo Hernan Mesa. "Análise dos mecanismos de dano de aços inoxidáveis austeníticos com elevado teor de nitrogênio durante desgaste erosivo por cavitação." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-21102016-104831/.
Abstract:
Neste trabalho são estudados os mecanismos de desgaste, atuantes na escala do tamanho de grão (meso-escala), durante ensaios de cavitação vibratória, para diferentes amostras de aços inoxidáveis austeníticos ligados com nitrogênio. Amostras com teores superficiais de nitrogênio de aproximadamente 0, 9 % massa, 1, 4%massa e 20%massa, obtidas a partir do a¸co inoxidável dúplex UNS S31803, foram estudadas. As amostras do a¸co inoxidável duplex UNS S31803, com aproximadamente 0, 9 % N massa, foram obtidas por nitretação gasosa em alta temperatura (temperatura de nitretação entre 1050 e 1200 C) e consistiram em três grupos diferentes: amostras com nitrogênio em solução sólida e solubilizadas, amostras com precipitação de nitretos e amostras com nitrogênio em solução sólida e encruadas. Já as amostras com teor de nitrogênio próximo de 20 % N massa foram processadas por meio de nitretação a plasma na temperatura de 400 C, obtendo-se uma camada superficial de austenita expandida. As amostras de ensaio foram submetidas à caracterização de textura por difração de elétrons retroespalhados, EBSD, e posteriormente à cavitação vibratória em ´agua destilada. Os ensaios de cavitação foram periodicamente interrompidos com o intuito de estudar a deteriora¸cao das amostras por exame das mesmas no microscópio eletrônico de varredura, MEV, e por medidas de perda de massa. Quando comparadas com os aços inoxidáveis austeníticos convencionais (UNS S30403 solubilizado e UNS S31803 como recebido), sem adição de nitrogênio e livre de encruamento, as amostras estudadas apresentaram resistência ao desgaste por cavitação superior, quantificada tanto pelo tempo de incubação do dano com perda de massa quanto pela taxa máxima de perda de massa nos estágios avançados do dano. A taxa máxima de perda de massa para cada tipo de amostra estudada, com relação `a taxa máxima do material de comparação, o aço inoxidável convencional sem adição de nitrogênio e livre de encruamento (UNS S30403) solubilizado, foi de: amostras com precipitação de nitretos (318HTGN+Nit), 6,9 vezes menor; amostras com nitrogênio em solução sólida e solubilizadas (318HTGH+Sol) e laminadas e solubilizadas (318HTGN+Lam+Sol), 26,8 e 25 vezes menor, respectivamente; amostras com nitrogênio em solução sólida e encruadas (318HTGN+Enc) 145 vezes menor; e amostras com camada superficial de austenita expandida (obtidas por nitretação a plasma), (318HTGN+Plas e 304LSol+Plas) 290 e 1,77 e vezes menor respectivamente. O efeito benéfico da adição de nitrogênio na resistência à erosão por cavitação dos aços inoxidáveis austeníticos estudados foi atribuído a: (i) aumento na resistência à deformação plástica; (ii) distribuição mais homogênea da deformação plástica induzida pelas ondas de choque e micro-jatos característicos do processo de cavitação; e (iii) aumento da importância relativa dos mecanismos de perda de massa com elevado consumo de energia de impacto. Nos primeiros estágios do dano erosivo por cavitação se observou clara evidência de deformação plástica, acompanhada de formação de microreelevo superficial e de protrusão de bandas de escorregamento. A perda de massa em nível microscópico (observações no MEV) começa como destacamento de material em microtrincas e micropites. Observou-se que tanto a nucleação do dano como o seu crescimento se apresenta de forma heterogênea na escala do tamanho de grão. Os sítios microestruturais nos quais se iniciou o dano com perda de massa foram preferencialmente protuberâncias nas protrusões de bandas de escorregamento, protuberâncias nos contornos de grão e as interfaces matriznitreto. O incremento do teor de nitrogênio (em solução sólida) na amostra aumentou a importância relativa dos contornos de grão como locais de nucleação do dano, em relação ao dano iniciado no interior dos grãos. Observou-se que o interior dos grãos com planos 100 ou 111 orientados de forma aproximadamente paralela à superfície das amostras são regiões muito suscetíveis à incubação do dano e ao crescimento do mesmo. Já os grãos com planos 101 orientados aproximadamente paralela à superfície das amostras, apresentam regiões com resistência ao dano bem maior. Esses resultados são discutidos, considerando as diferenças de tensão (resultantes da ação de ondas de choque causadas pela implosão de bolhas de cavitação) crítica projetada para cisalhamento de grãos com diferentes orientações. O dano ocorre preferencialmente em contornos de grãos com acentuados gradientes de tensão resolvida para a deformação plástica, onde se desenvolve elevada concentração de tensões. Em particular, os contornos de macla CSL 3 são acentuadamente mais suscetíveis à incubação do dano que os outros tipos de contornos CSL e que os contornos não CSL.High nitrogen austenitic stainless steels containing 0.9 wt-% N and 20 wt- % N were tested in a ultrasonically induced vibratory cavitation testing device. Incubation times for damage initiation and mass losses were periodically measured during the cavitation-erosion tests. Scanning Electron Microscopy observation of the damaged surfaces allowed identifying the wear mechanisms operating during each step of the cavitation-erosion test. 0.9 wt-% N specimens were obtained through High Temperature Gas Nitriding UNS S31803 duplex stainless steel, at temperatures between 1050 and 1200 oC. Three groups of specimens were obtained: solubilized with all nitrogen in solid solution, solubilized and work hardened specimens and nitride containing specimens. The 20 wt- % N specimens were obtained through Low Temperature Plasma Nitriding the already High Temperature Gas Nitrided specimens and getting an expanded austenite layer at the surface. The specimens were firstly characterized by Electron Backscattered Diffraction - EBSD techniques and then submitted to the cavitation-erosion tests in distilled water. When compared to conventional UNS S30403 lean nitrogen solubilized austenitic stainless steel specimens, greater incubation times and smaller maximum wear rates were observed. The maximum wear rates (compared to those of the solubilized UNS S30403 steel) were: for the nitride containing specimen 6.9 times smaller; for textured and non-textured all nitrogen in solid solution specimens 26.8 and 25 times smaller, respectively; for the solubilized and work hardened specimen 145 times smaller; for the expanded austenite layer, with circa 20 wt- % N, specimens 300 times smaller. The beneficial effect of nitrogen on the cavitation-erosion resistance of the studied specimens was attributed to: (i) an increase in resistance to plastic deformation; (ii) a more homogeneous distribution of the plastic deformation; and (iii) an increase of the relative participation of energy consuming mass loss mechanisms. Plastic deformation accompanied by formation of micro relief at the surface and slip bands protrusions were clearly identified, during the first stages of cavitation erosion. The first evidences of mass loss (detected by SEM observations) were seen as particles detaching from micro cracks and micro pits formed at the grain surface. Nucleation and growth of cavitation damage was heterogeneously distributed at the grain scale. Slip bands protrusions, grain boundary protrusions and nitride matrix interfaces sites were more prone to nucleating the damage. Increasing nitrogen contents in solid solution increased the relative contribution of grain boundary nucleated damage, compared to the total amount of nucleation sites. Grains with 100 and 111 crystallographic planes approximately parallel to the surface were more prone to nucleation and growth of cavitation damage. Grains with 101 planes // surface were much more resistant to cavitation-erosion damage. These results are discussed considering differences of critical resolved shear stresses for grains with different orientations. Cavitation erosion damage occurs preferentially at grain boundaries across which steep stress gradients arise. Particularly, CSL -3 twin boundaries are much more susceptible to cavitation erosion damage incubation than other types of CSL boundaries and non CSL boundaries.
44
Castro, Danilo Borges Villarino de. "Estudo do comportamento em fadiga do aço ASTM A297 Gr HP modificado com nióbio em altas temperaturas." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-20122012-092456/.
Abstract:
Este trabalho teve por objetivo estudar o comportamento mecânico em elevadas temperaturas do aço ASTM A-297 Gr HP modificado ao nióbio. Este tipo de aço é utilizado em suportes de tubos que permanecem longos períodos de tempo expostos em temperaturas de operação próximas a 900ºC. Nesta pesquisa, foram estudadas a microestrutura, a resistência mecânica, a tenacidade ao impacto e a resistência à fadiga, considerando o efeito da temperatura de ensaio. Para a avaliação do efeito da temperatura e tempo de permanência na microestrutura e, consequentemente, nas propriedades mecânicas, foram realizados ensaios de dureza, tração e impacto para cada uma das condições apresentadas. Todas as condições do material envelhecido apresentaram a presença de precipitados nos contornos interdendríticos e precipitados secundários no seio da matriz austenítica, fazendo com que o material elevasse seus parâmetros de resistência mecânica, quando comparado com a condição de como-recebido (CR). Após esta etapa, foi estudado o comportamento mecânico em temperaturas elevadas, apenas para as condições CR e T1000 (envelhecido a 927°C durante 1000 horas). Ensaios mecânicos de tração, impacto e fadiga (E-N e da/dN-\'delta\'K) foram realizados nas seguintes temperaturas: 25ºC, 871ºC, 899ºC, 927ºC, 954ºC e 982ºC. Para a avaliação dos ensaios de impacto, utilizaram-se corpos de prova Charpy do tipo convencional (presença do entalhe) e pré-trincados (entalhe mais pré-trinca). Em todas as temperaturas de ensaio de tração, observou-se que a condição T1000 resultou em aumento do valor dos parâmetros de resistência mecânica e diminuição da sua ductilidade, em relação à condição CR. Em ensaios nas temperaturas elevadas, observou-se que a precipitação de carbetos secundários na matriz austenítica da condição T1000 é capaz de evitar uma queda acentuada dos parâmetros de resistência mecânica, quando comparada com a condição CR. As duas condições (CR e T1000) mostraram-se sensíveis à presença de um concentrador de tensão (entalhe mais pré-trinca), quando submetidas a ensaios de impacto. Os resultados de tração e impacto corroboram as evidências fractográficas encontradas para cada condição, indicando que há uma maior parcela de fratura dúctil nas amostras ensaidas em temperaturas elevadas do que na temperatura ambiente. Em relação ao comportamento em fadiga do material, observou-se que a vida em fadiga do material ensaiado em 25ºC foi muito maior do que a 927ºC, principalmente na região de fadiga de alto ciclo. Este fato pode ser atribuído a dois fatores dependentes do tempo: nucleação prematura decorrente de uma significativa redução do limite de escoamento e devido ao efeito da oxidação superficial das bandas de deslizamento permanentes. Os ensaios de propagação de trinca por fadiga mostraram que a taxa da/dN foi maior na temperatura de 927ºC do que em 25ºC, devido ao fato da maior ductilidade que o material apresenta em elevadas temperaturas, associado aos efeitos de oxidação e de fluência. Alguns resultados de fadiga de baixo ciclo foram confrontados com modelos teóricos de plasticidade. As curvas teóricas foram capazes de simular relativamente bem os resultados experimentais.This work aims to study the mechanical behavior at high temperatures of ASTM A-297 Gr HP steel changed with niobium. This type of steel is used for pipe supports that remain exposed long periods of time at operating temperatures near 900°C. In this study, was studied the microstructural composition, the mechanical strength, impact toughness and fatigue resistance, considering the effect of temperature test. To evaluate the effect of temperature and residence time in the microstructure and hence the mechanical properties were performed hardness, tensile and impact test for each of the conditions presented. All conditions of the aged material showed the presence of precipitates in the interdendritic boundaries and secondary precipitates within the austenitic matrix, causing the material to elevate its mechanical strength, compared to CR condition. After this step was studied the mechanical properties at elevated temperatures only for the conditions CR and T1000 (aged at 927°C for 1000 hours). Tensile, impact and fatigue tests (E-N and da/dN-\'delta\'K), were performed at the following temperatures: 25°C, 871ºC, 899ºC, 927ºC, 954ºC and 982°C. To evaluate the impact tests, were used Charpy specimens of the conventional type (presence of the notch) and pre-cracked (pre crack more notch). In all test temperatures of traction, it was observed that the T1000 condition resulted in an increase of the value of mechanical strength and reduction of its ductility, compared to CR conditions. In tests at elevated temperatures, it was observed that the precipitation of carbides in the austenitic matrix of the secondary condition T1000 is able to avoid a sharp decline in mechanical strength compared with the proviso CR. The two conditions (CR and T1000) were sensitive to the presence of a stress raiser (notch further pre-crack) when subjected to impact tests. The results of tensile and impact fractographies corroborate the evidence found for each condition, indicating a greater share of ductile fracture in testing samples at elevated temperatures than at room temperature. Regarding the fatigue behavior of the material, it was found that the fatigue life of the material tested at 25°C was much greater than 927°C, especially in the region of high cycle fatigue. This fact can be attributed to two factors dependent on the time: premature nucleation due to a significant reduction in yield strength and due to the effect of surface oxidation of permanent slip bands. The tests of crack propagation by fatigue showed that the rate da/dN was greater at a temperature of 927°C than at 25°C, because of higher ductility that the material exhibits at high temperatures associated with the effects of oxidation and creep.
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Albertin, Kátia Franklin. "Estudo de camadas dielétricas para aplicação em capacitores MOS." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-08012008-144158/.
Abstract:
Foram estudados filmes de oxinitreto de silício obtidos por PECVD à 320°C, a partir da mistura gasosa de N2O+SiH4+He, com diferentes valores de pressão e potência de deposição com o objetivo de produzir boa qualidade de interface deste material com o Si e de obter uma baixa densidade de carga efetiva visando a aplicação desses filmes em dispositivos semicondutores MOS. Os resultados mostraram que com uma pressão de deposição de 0,160 mbar e potências menores que 125 W/cm2 é possível obter um valor de densidade de estados de interface (Dit) de 4x1010 eV-1.cm-2, campo elétrico de ruptura (Ebd) de 13 MV/cm, valores comparáveis ao SiO2 térmico e uma densidade de carga efetiva (Nss) de 4x1011 cm-2. Segundo resultados experimentais esse valor de Nss é o mínimo possível que se pode atingir com a limpeza química utilizada em nosso laboratório. Pode-se dizer que estes são resultados bastante interessantes considerando que se trata de um material obtido por PECVD à baixa temperatura, porém viável para aplicação em dispositivos MOS. Iniciando os estudos com dielétricos de maiores valores de constante dielétrica optamos por estudar filmes de TiOx (k=40-100), obtidos por sputtering reativo, a partir da mistura gasosa de Ar+O2 e utilizando alvo de Ti. Foram fabricados capacitores MOS com estes filmes e obteve-se valores de constante dielétrica que variaram de 40-160. Porém esses materiais ainda apresentavam valores apreciáveis de corrente de fuga que foram minimizadas em ordens de grandeza quando utilizados dielétricos de dupla camada com SiO2 ou SiOxNy (otimizado neste trabalho) na interface, além de se observar uma melhora significativa da qualidade de interface. Utilizando dupla camada dielétrica com filmes de SiOxNy e SiO2, ainda espessos (³ 1nm) para camada intermediária, obteve-se uma constante dielétrica efetiva em torno de 20. Vale ressaltar que os dois filmes SiOxNy e TiOx, conseqüentemente a dupla camada, foram fabricados a baixas temperaturas.Silicon oxynitride films obtained by the PECVD technique from N2O+SiH4+He gaseous mixtures, at 320°C, with different deposition pressure and RF power were studied intending to improve the interface quality with Si, decreasing the effective charge density and the interface state density in order to utilize them in MOS semiconductor devices. The results showed that with a deposition pressure of 0.160 mbar and a RF power density lower than 125 W/cm2 it is possible to obtain interface state density (Dit) values of 4x1010 eV-1.cm-2, Electrical Breakdown (Ebd) of 13 MV/cm, comparable with the obtained for thermally grown SiO2 , and an effective charge density (Nss) of 4x1011 cm-2. According with experimental results this Nss value is the minimum attainable with our chemical cleaning process. In this way it can be said that these results are very promising, considering that these materials were obtained by PECVD at low temperatures, but still viable for MOS devices application. In order to initiate studies with high dielectrics constant material, TiOx films (k= 40-180), obtained by reactive sputtering through the Ar+O2 gaseous mixture utilizing a Ti target, were chosen. MOS capacitors with these films were fabricated and dielectric constant values varying from 40 to 160 were obtained. However, until now, these materials have presented appreciable leakage current values, which were, minimize by orders of magnitude with the addition of a thin SiO2 or SiOxNy (optimized in this work) layer at the interface were utilized. This thin layer also resulted in a significant improvement of the interface quality. Utilizing double dielectric layer with SiOxNy or SiO2, still thick (³ 1nm) as intermediate layer a dielectric constant value of 20 was obtained. Its important to mention that the SiOxNy and TiOx films, and consequently the double layer, were deposited at low temperatures.
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Majda, Tomáš. "Lomové testy vybraných těles se speciálním plnivem: experimenty a numerická simulace." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2019. http://www.nusl.cz/ntk/nusl-392121.
Abstract:
The diploma thesis deals with selected fracture tests and evaluation of fracture parameters of cement-based composite. One part of the thesis deals with cement-based composite with glass spherical aggregate of a single fraction of 2 mm. After production, the beams with dimensions of 20×40×200mm exposed to temperatures in the range from 100 to 1000 °C for one hour. Using the non-destructive ultrasonic pulse method, the degree of damage caused by termal load was determined. Selected specimen with central edge notch were then tested in three-point bending and fragments after these tests were tested in compression. In the second part, attention was paid to the evaluation of fracture tests conducted on specimen from drill-cores taken from selected objects located at the former Transgas Gas Control Center in Prague. The specimen were provided with a chevron notch before being tested in three-point bending. The measured data was modified by the GTDiPS program and in the case of the glass composite the StiCrack program was used to evaluate fracture parameters.
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Ramos, Masana Ana. "Estudio de la reactividad a alta temperatura de aleaciones ligeras sobre recubrimientos cerámicos." Doctoral thesis, Universitat Ramon Llull, 2020. http://hdl.handle.net/10803/669953.
Abstract:
La interacció entre metalls fosos i les superfícies de materials ceràmics o metàl·lics és protagonista en diversos processos de fabricació, com ara la injecció d'aliatges lleugers, la foneria de ferro o la síntesi de materials compostos metall-ceràmics (MMC, Metall Matrix Composites). Aquesta interacció es tradueix en un fenomen de mullat en major o menor mesura de la superfície, fet que es pot modular mitjançant l'aplicació de tractaments superficials. El procés d'injecció d'aliatges d'alumini és probablement un dels processos amb metalls fosos amb més impacte industrial.
En el present treball s'han estudiat experimentalment el procés de mullat per Al9Si3Cu i alumini pur fosos sobre mostres d'acer recobertes utilitzant el mètode de la gota jacent en buit en un equip d'angle de contacte dissenyat i construït expressament per a aquest projecte. D'una banda s'han assajat recobriments de capa prima dipositats per la tècnica MS-PVD (Magnetron Sputtering Physical Vapor Deposition) o HiPIMS-PVD (High Power Impulse Magnetron Sputtering) de TaN, TiB2, TiN, (Ti,Al)N, MoN i DLC (CrN) . D'altra banda, s'han utilitzat recobriments gruixuts dipositats per HVOF (High Velocity Oxyfuel) de Cr3C2-NiCr i WC-CoCr.
L'evolució de l'angle i el radi de contacte s'han estudiat mitjançant el registre de seqüències d'imatges i s'han determinat les corbes de mullabilitat mitjançant el posterior tractament i anàlisi d'imatges.
El mecanisme de mullat s'ha determinat a partir de les corbes de mullabilitat i de la caracterització metal·logràfica de la superfície i de les seccions transversals que mostren l'evolució de la interfase líquid-sòlid i la formació de compostos intermetàl·lics.
Es discuteixen l'efecte de l'aliatge, de la composició i morfologia del recobriment en la mullabilitat de el sistema i es comparen els resultats obtinguts amb la mullabilitat en sistemes no recoberts.
Els resultats mostren que els recobriments retarden la reacció entre el substrat metàl·lic i l'alumini fos.La interacción entre metales fundidos y las superficies de materiales cerámicos o metálicos es protagonista en diversos procesos de fabricación, tales como la inyección de aleaciones ligeras, la fundición de hierro o la síntesis de materiales compuestos metal-cerámicos (MMC, Metal Matrix Composites). Esta interacción se traduce en un fenómeno de mojado en mayor o menor medida de la superficie, hecho que puede modularse mediante la aplicación de tratamientos superficiales. El proceso de inyección de aleaciones de aluminio es probablemente uno de los procesos con metales fundidos con más impacto industrial. En el presente trabajo se han estudiado experimentalmente el proceso de mojado por Al9Si3Cu y aluminio puro fundidos de muestras de acero recubiertas utilizando el método de la gota yaciente en vacío en un equipo de ángulo de contacto diseñado y construido ex profeso para este proyecto. Por un lado se han ensayado recubrimientos de capa delgada depositados por la técnica MS-PVD (Magnetron Sputtering Physical Vapor Deposition) o HIPIMS-PVD (High Power Impulse Magnetron Sputtering) de TaN, TiB2, TiN, TiAlN, MoN y DLC(CrN). Por otro lado, se han utilizado recubrimientos gruesos depositados por HVOF (High Velocity Oxyfuel) de Cr3C2-NiCr y WC-CoCr. La evolución del ángulo y el radio de contacto se han estudiado mediante el registro de secuencias de imágenes y se han determinado las curvas de mojabilidad mediante el posterior tratamiento y análisis de imágenes. El mecanismo de mojado se ha determinado a partir de las curvas de mojabilidad y de la caracterización metalográfica de la superficie y de las secciones transversales que muestran la evolución de la interfase líquido-sólido y la formación de compuestos intermetálicos. Se discuten el efecto de la aleación, de la composición y morfología del recubrimiento y en la mojabilidad del sistema y se comparan los resultados obtenidos con la mojabilidad en sistemas no recubiertos. Los resultados muestran que los recubrimientos retardan la reacción entre el sustrato metálico y el aluminio fundido.
The interaction between molten metals and the surfaces of ceramic or metallic materials is the key in various manufacturing processes, such as the injection of light alloys, iron foundry or the synthesis of metal-ceramic composite materials (MMC, Metal Matrix Composites). This interaction translates into a phenomenon of wettability to a greater or lesser extent of the surface, which can be modulated by the application of surface treatments. The process of injection of aluminum alloys is probably one of the processes with molten metals with more industrial impact. In the present work, the wetting process for Al9Si3Cu and pure aluminum were analyzed experimentally with coated steel samples using the sessile drop method in vacuum in a contact angle device designed and constructed specifically for this project. On one hand, thin coating deposits deposited by the MS-PVD (Magnetron Sputtering Physical Vapor Deposition) or HiPIMS-PVD (High Power Impulse Magnetron Sputtering) of TaN, TiB2, TiN, (Ti,Al)N , MoN and DLC (CrN). On the other hand, thick coatings deposited by HVOF (High Velocity Oxyfuel) of Cr3C2-NiCr and WC-CoCr have been used. The evolution of the angle and the contact radius have been studied by recording sequences of images and the wettability curves have been determined through the subsequent treatment and image analysis. The wetting mechanism has been determined from the wettability curves and the metallographic characterization of the surface and the cross sections that show the evolution of the liquid-solid interface and the formation of intermetallic compounds. The effect of the alloy, the composition and morphology of the coating in the wetting behavior are discussed, and the results are compared to those obtained with uncoated system. The results show that coatings delay the reaction between the metal substrate and the molten aluminum.
48
Brandão, Lincoln Cardoso. "Estudo experimental da condução de calor no fresamento de materiais endurecidos utilizando altas velocidades de corte." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/18/18135/tde-14092006-165321/.
Abstract:
Modernas empresas buscam a melhoria dos seus sistemas de produção a fim de aumentar a produtividade e a qualidade de produtos. A tecnologia de usinagem com alta velocidade de corte (HSC High Speed Cutting) permite aumentar as taxas de remoção de material, as tolerâncias dimensionais das partes, assim como a melhoria do acabamento superficial. Esta tecnologia tem sido muito utilizada na área de moldes e matrizes, pois minimiza o problema de tempos de usinagem longos na produção e facilita a obtenção de elevada qualidade, normalmente requerida em produtos injetados/estampados. Atualmente diversos estudos em HSC buscam a compreensão de todos os fatores envolvidos nesta nova tecnologia, a qual ainda apresenta diversas lacunas para o seu domínio completo. Este trabalho apresenta um estudo teórico-experimental da condução de calor nos materiais utilizados na fabricação de moldes e matrizes, submetidos à usinagem com altas velocidades de corte. Os materiais utilizados foram os aços AISI D2 e AISI H13, muito utilizados nas indústrias de moldes e matrizes. Os ensaios foram realizados com fresas de ponta esférica (Ball-Nose) com e sem angulação de hélice e com ângulo de saída neutro, com revestimento de ('TI'AL')N e com uma ferramenta com uma placa de PcBN soldada. A geometria dos corpos-de-prova foi projetada para aproximar-se dos casos reais encontrados na indústria, casos em que superfícies complexas e paredes finas são comumente usinadas em matrizes e moldes. Dois sistemas de resfriamento foram utilizados o ar comprimido e o ar gelado utilizando o princípio de vórtice. Os resultados demonstraram uma pequena variação da temperatura em função dos materiais empregados e das ferramentas utilizadas em todos os testes. Os dois sistemas de resfriamento alternativos à usinagem sem sistema de resfriamento, o ar comprimido e o ar frio, também se mostraram influentes na variação da temperatura, apresentando-se como sistemas capazes de remover o calor no processo durante a usinagem. Os desvios de forma encontrados nos corpos-de-prova devem ser considerados na usinagem de perfis muito precisos. Foram encontrados valores da ordem de 0,05 mm, oriundos da combinação de distorções térmicas e tensões residuais, os quais podem ser signifcativos, por exemplo, na área de matrizariaModern industries improve their production systems aiming at increasing productivity and product quality. The high speed cutting (HSC) technology allows increasing material removal rates, workpiece dimensional tolerance and surface finishing as well. Such technology has been extensively used in mold and dies areas, since it minimizes long lead time problems and facilitates high quality machining, normally required in injected/formed products. Nowadays, several studies in HSC search for understanding all aspects involved in that new technology, which still presents many blanks for its complete knowledge. The present work shows a theoretical and experimental study on heat conduction flux in materials applied to mold and die manufacturing, submitted to HSC. It was used AISI D2 and AISI H13, which are very common in mold and die industry. Two types of cylindrical ball nose end milling tool were used in the experiments: coated with ('TI'AL')N and tipped with PcBN. The workpiece geometry was conceived to simulate real cases found in industry, in which complex surfaces and slim walls are commonly machined in molds and dies. Two cooling systems were used in the tests, compressed air and frozen air using vortex principle. Results indicated a small temperature variation as a function of machined materials and tools throughout the tests. Both alternative cooling systems, besides dry machining, compressed air and cool air, also demonstrated to affect temperature variation. They presented themselves as capable of remove heat from the process during the cutting operation. The form deviation found in the workpiece after machining must be considered when machining very precise profiles. Variation values of around 0.05 mm were found, coming from a combination of thermal distortion and residual stress, which could be significant, for example, in die manufacturing area
49
Kimura, Érica Fernanda Aiko. "Comportamento estrutural de perfis formados a frio com seção transversal composta de U enrijecido em temperaturas elevadas." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-24092014-150704/.
Abstract:
No contexto da construção civil brasileira, é reconhecido o fato de que os perfis de aço formados a frio têm grande demanda em diversos tipos de sistemas estruturais. Uma das aplicações refere-se às barras com seções transversais compostas em duplo U enrijecido, comumente presente no sistema de vigas e pilares de edificações. Quando submetido à ação térmica decorrente de um incêndio, o comportamento dos perfis formados a frio se torna de avaliação relativamente complexa, pois há ocorrência de dois fenômenos que levam à perda da sua capacidade portante: a ocorrência dos modos de instabilidade e a redução da resistência do material. Dessa forma, neste trabalho foi desenvolvido um estudo sobre perfis de aço formados a frio submetidos a temperaturas elevadas. As seções transversais adotadas foram do tipo I enrijecido e tubular retangular do tipo caixão, compostas por dois perfis U enrijecido unidos por solda intermitente. A ação mecânica aplicada consistiu em uma compressão centrada, bem como uma ação térmica, cuja taxa de aquecimento segue a curva de incêndio padrão definida pela International Organization for Standardization. A investigação aqui apresentada foi desenvolvida em campo experimental e numérico. Foram realizados ao todo 17 ensaios de compressão, cinco à temperatura ambiente e 12 com aplicação da ação térmica. A ação mecânica dos ensaios termoestruturais, ao ser aplicada, foi mantida constante em patamares de 40% e 70% da capacidade resistente à temperatura ambiente. Em seguida foram desenvolvidos modelos numéricos calibrados com parâmetros obtidos experimentalmente, com vistas a futuras análises paramétricas a partir desta pesquisa. Por fim, tais resultados foram comparados com valores obtidos por procedimentos de cálculo das principais normas em vigor. Com base nesta investigação e no conjunto de resultados apresentados, é possível avaliar a viabilidade da aplicação de tais procedimentos normativos diretamente aos perfis de aço formados a frio, bem como propor adequações onde houver necessidade. Deve-se ressaltar que o trabalho aqui apresentado é o primeiro a realizar ensaios termoestruturais em perfis formados a frio com abordagem na realidade brasileira da construção civil e reconhece a necessidade de abranger novos estudos.Due to its known versatility, cold formed steel has been widely used in civil construction as load bearing members in several types of structural systems. Built-up lipped I and box cross section are often used as beams and columns of commercial and even industrial buildings. When such structural cold formed steel members are submitted to a thermal load arising from a fire condition, their structural behavior becomes complex, inasmuch as two phenomena that lead to loss of strength is likely to occur: the reduction of materials properties of the cold formed steel and the buckling modes thin walled steel are susceptible. Hence, in this doctoral thesis, a study on the behaviour of built-up cold formed steel subjected to compression load and submitted to high temperature is presented. In the first stage of this research, 21 specimens were subjected to axial compression load; in which 11 specimens were lipped I and 10 were box built-up cross section. Five tests of the total amount were carried out at ambient temperature and 16 in hugh temperature. Such tests in high temperature were carried out in thermal transient condition whose magnitude of the applied compression load was equivalent to 40% and 70% of the one obtained at ambient temperature. Thus, the ultimate time and temperature of the specimens were determined. In the second phase of this research, numerical analysis was developed and the numerical models were validated by the comparison with experimental results. Since this numerical strategy has considered geometric and material non linearity varying according to increasing thermal load, it has shown to be suitable for future parametric analysis. Regarding to standard codes, based on this reseach, the suitability of design method for fire condition recommended by Brazilian, European and North American standards applied to cold formed steel were evaluated. The ultimate load capacity obtained from Brazilian and European fire design codes resulted conservative in comparison with experimental results. The Direct Strength Method available in North American, Brazilian and Australian standards, considering appropriated reduction of materials properties according to its temperature conducted to satisfatory results for built-up lipped I and box cold formed steel columns. In addition, this thesis emphasizes the need for an extensive research on cold formed steel structures under fire condition in accordance with Brazilian civil construction.
50
Narciso, Maurício Roberto Tosti. "Inativação de Mycobacterium bovis (espoligotipos SB0120 e SB1033) em leite integral submetido à pasteurização lenta e rápida em banho Maria." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/10/10134/tde-09102012-102158/.
Abstract:
O Mycobacterium bovis causa a tuberculose zoonótica, doença que afeta os animais e o homem podendo causar a morte, sendo o leite uma importante via de transmissão da doença para o homem. A pasteurização do leite é a principal medida para quebrar essa cadeia de transmissão, cujos parâmetros de tempo e temperatura foram definidos através de experimentos que datam desde o fim do século XIX, com base na resistência térmica do M. bovis e da Coxiella burnetti, então considerados os mais resistentes patógenos não formadores de esporos que contaminam o leite. No Brasil são aprovados os binômios 62ºC a 65ºC por 30 minutos e 72ºC a 75ºC por 15 a 20 segundos. Entretanto, com o passar dos anos e surgimento de novas tecnologias (PCR, Spoligotyping e outras técnicas biomoleculares) foi possível observar diferenças genéticas intra-espécie. Assim, este projeto tem por objetivo avaliar e comparar o comportamento de dois espoligotipos de M. bovis (SB0120 e SB1033) frente aos dois protocolos de pasteurização utilizados no país. Para tanto, leite integral UHT foi contaminado com esses espoligotipos e submetido aos dois processos térmicos, em Banho-Maria. O leite foi semeado em meio sólido Stonebrink-Leslie e a contagem de colônias foi feita após 45 dias de incubação a 37ºC. Não houve neste experimento diferença entre as resistências térmicas dos dois espoligotipos, no entanto detectou-se uma maior importância da fase de aquecimento na redução do agente do que da fase de manutenção da temperatura, para os dois espoligotipos, nos dois processos.Mycobacterium bovis causes zoonotic tuberculosis disease that affects animals and humans and can cause death, the milk is an important route of disease transmission to humans. The pasteurization of milk is the main measure to break the transmission chain, whose time and temperature parameters were defined by experiments dating from the late nineteenth century, based on thermal resistance of M. bovis and Coxiella burnetti, considered then the most resistant non-spore-forming pathogens that contaminate the milk. In Brazil, there are two approved binomials 62ºC to 65ºC for 30 minutes and 72ºC to 75ºC for 15 to 20 seconds. However, over the years and the emergence of new technologies (PCR, spoligotyping and other biomolecular techniques) was observed genetic differences intra-species. Thus, this project aims to evaluate and compare the behavior of two spoligotypes of M. bovis (SB0120 and SB1033) compared to the two pasteurization protocols used in the country. To this end, UHT milk was contaminated with these spoligotypes and subjected to two thermal processes in a water bath. The milk was streaked on solid medium Stonebrink-Leslie and colony counting was done after 45 days of incubation at 37ºC. This experiment showed that there was no difference between the thermal resistances of the two spoligotypes, however it was detected a greater importance of the heating phase in reducing the agent that the maintenance phase of temperature for the two spoligotypes, in both cases.