131 research outputs found
Nopean jähmettymisen faasikenttämallinnusta ohutkalvoille ja materiaalia lisäävälle valmistukselle
No full textThe public defence will be organised via Zoom: https://aalto.zoom.us/s/64127861066
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https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/?lang=enSeveral advanced industrial manufacturing processes operate in rapid solidification conditions, including laser welding, thermal spray coating deposition, and additive manufacturing.
These processes lead to materials with drastically altered properties, when compared to low solidification rate manufacturing methods such as casting. This is due to the unique microstructural features emerging in rapid solidification. Rapid solidification conditions alter growth dynamics, for example through kinetically selected metastable phases, notable interface attachment kinetics, and solute trapping. Therefore there is a strong motivation to adjust these manufacturing processes to target specific microstructures, in order to reach desirable material properties. These process-structure-property links can be established by computational modeling. In the past decades, the phase field method has become the state-of-the-art model to simulate solidification on microstructural scales. Its success in the materials science community can be attributed to its connection to statistical physics and thermodynamics, simplicity, and relative ease with which new physical phenomena can be implemented.
In this thesis, a computationally efficient and quantitative phase field modeling framework is presented for the rapid solidification regime. The phase field model is made computationally efficient through adaptive mesh refinement and shared memory parallelization. A quantitative near-equilibrium alloy phase field model is extended to operate in the rapid solidification regime through matched interface asymptotics analysis, allowing for controllable solute trapping kinetics that follow the continuous growth model in the thin interface limit. The rapid solidification simulations are compared to thin film solidification experiments with time-resolved in-situ imaging. This phase field model is applied to the study of additive manufacturing, first for stainless steel to understand the process-microstructure relationships, and then as a method to investigate the effects of inoculation to alter the polycrystalline structures. The presented rapid solidification phase field modeling framework will assist systematic process-structure-properties based design of novel engineering materials.Useat teolliset metallien valmistusmenetelmät perustuvat nopeaan jähmettymiseen, kuten laserhitsaus, terminen ruiskutus ja materiaalia lisäävä valmistus eli 3D-tulostus.
Näin syntyvien materiaalien ominaisuudet eroavat huomattavasti sellaisista materiaaleista, joita valmistetaan hitaan jähmettymisen menetelmillä kuten valamisella. Ero ominaisuuksissa johtuu nopean jähmettymisen aikaansaamista erityisistä mikrorakenteista, jotka riippuvat siitä miten nopea jähmettyminen muuttaa kasvudynamiikkaa. Esimerkkejä nopeasta jähmettymisestä ovat metastabiilien faasien valikoituminen, merkittävä rajapinnankiinnittymiskinetiikka (interface attachment kinetics) ja seosaineen loukkuuntuminen (solute trapping). Näiden ilmiöiden vaikutukset jähmettymiseen pitää ymmärtää perusteellisesti, jotta nopean jähmettymisen menetelmiä voidaan säätää hallitusti, luoda materiaaliin halutut mikrorakenteelliset piirteet, ja lopulta tuottaa toivottavat materiaaliominaisuudet. Näitä riippuvuuksia valmistusmenetelmän, mikrorakenteen ja ominaisuuksien välillä voidaan määrittää laskennallisella mallinnuksella. Viime vuosikymmeninä faasikenttämenetelmästä on tullut tärkein malli jähmettymisen simulointiin mikrorakenteen tasolla. Materiaalitiedeyhteisössä faasikenttämenetelmän suosio perustuu sen yhteydellä statistiseen fysiikkaan ja termodynamiikkaan sekä sillä, että uusia fysikaalisia ilmiöitä voidaan ottaa mukaan näihin malleihin suhteellisen helposti.
Tässä väitöskirjassa esitellään laskennallisesti tehokas ja tarkka faasikenttämallinnusmenetelmä joka soveltuu nopeaan jähmettymiseen. Faasikenttämallista tehdään laskennallisesti tehokas mukautuvalla verkon tihennyksellä ja jaettuun muistiin perustuvalla rinnakkaistuksella. Kvantitatiivinen tasapainoa lähellä toimiva faasikenttämalli laajennetaan nopean jähmettymisen alueelle käyttäen menetelmää nimeltä Matched Interface Asymptotics Analysis. Näin seoksen ansautumisen kinetiikkaa voidaan säätää hallitusti vastaamaan niin sanottua Continuous Growth -mallia. Tässä väitöskirjassa kehitettyä nopean jähmettymisen faasikenttämallia sovelletaan materiaalia lisäävään valmistukseen. Ensin menetelmää sovelletaan ruostumattomaan teräkseen valmistusmentelmä-mikrorakenne -riippuvuuksien ymmärtämiseen. Lopuksi tutkitaan inokuloinnin vaikutusta monikiderakenteisiin. Tässä väitöskirjassa kehitetyn nopean jähmettymisen faasikenttämalli edistää uusien teknillisten materiaalien systemaattista suunnittelua
Jeca Tatu é uma vingança
No full textRESUMO
A partir do artigo de Monteiro Lobato, Mistificação ou Paranóia, Sérgio Millet tira conclusões menos favoráveis a ele, enfocando a temática da vingança. Na sua opinião o controvertido autor de Urupês, quando o escreveu, seria um recalcado; extravasaria o seu ódio de fazendeiro fracassado, criando o caboclo Jeca Tatu mirrado e doente; encontraria depois compensação no mundo encantado dos contos infantis que escreveu; tentaria uma nova experiência, escrevendo um romance sobre o problema racial americano, mas não teve êxito. O crítico prossegue sua dissecação cruel do estilo lobatiano negando-lhe inventiva na expressão vocabular. Compara-o a Mário de Andrade, que o supera. Também na técnica não trouxe novidades. Finaliza explicando os motivos de seu sucesso, apesar das deficiências expostas.
ABSTRACT
Jeca Tatu is a revenge. v. 9, n. 2, p. 231-235, jul./dez. 1981.
Starting from Lobato’s article Mystification or paranoia, Sérgio Millet takes conclusions not favorable to Lobato, emphasizing the revenge theme. In his opinion, the controverted author of Urupês would be full of complexes when he wrote the book; he would show hate as an unsuccessful farmer, creating the sick and thin “caboclo”(mestizo of Indian and white blood) Jeca Tatu; he would try a new experience writing a romance about the American racial problem, but he was not successful. The critic continues his cruel dissection of Lobato to Mário de Andrade who outdoes the first one. He also says that Lobato didn’t bring any innovation to the techniques of writing. He ends explaining the causes of Lobato´s success, notwithstanding the deficiencies shown.
RÉSUMÉ
Jeca Tatu est une vengeance. v. 9, n. 2, p. 231-235, jul./dez. 1981.
D’après l’article de Monteiro Lobato Mystification ou Paranoia, Sérgio Millet est arrivé à des conclusions moins favorables, en focalisant la thématique de la vengeance. À son avis le controversé auteur de Urupês était rempli de complexe quand il dit qu’il aurait extériorisé sa haine d’agriculteur sans succès, créant le caboclo Jeca Tatu, maigre et malade. ll trouverai après une compensation dans le monde enchanté des contes enfantins qu’il a écrit: ll tenterai une experience nouvelle en écrivant un roman sur le problème racial américain, mais sans succès. Le critique continue sa cruelle dissection du style lobatin en lui réfusant la faculté inventive dans l’expression du vocabulaire. ll le compare à Mário de Andrade qui le surpasse. Dans la téchinique aussi il n’a pas apporté des nouveaulés. ll finit en exposant les motifs de son succés, malgré les déficiences exprimées
Termisen ruiskutuksen prosessimallinnus: Kaasuvirtaus ja hiukkasten simulointi
No full textThis work studies an industrial coating method called high-velocity oxy-fuel thermal spray (HVOF), which can be used to enhance material resistance to, for example, wear and heat.
Due to the complexity of the HVOF process, and large number of adjustable process parameters, this process needs to be modeled; this can lead to a better understanding of the process, and consequently coatings of higher quality.
The goal of this thesis is to build a model for the gas flow in HVOF, and describe the resulting coating powder acceleration and in-flight melting.
Initially, the gas flow is solved without the presence of the coating powder, assuming that the coating powder mass flux is negligible.
As the considered geometry is axisymmetric, only a small sector of the whole geometry is considered to reduce the computational cost of the simulation.
The fluid motion is governed by a compressible Navier-Stokes equation, and the turbulence is modeled using a renormalization group variant of k-epsilon model.
The oxy-fuel combustion is described using an eddy-dissipation model, and the diffusion of species and heat is modeled using Schmidt and Prandtl numbers.
The computational fluid dynamics (CFD) calculations are conducted using an open source C++ package called OpenFOAM, whose solver rhoCentralFoam is modified to support multiple species.
The coating particles are assumed to be independent of each other, and as a result they are simulated sequentially using Matlab.
Particle acceleration is dominated by drag force due to the gas, and heat transfer is governed by heat conduction and radiation.
For both the gas flow and coating particle dynamics, the results are compared to simulations and experiments found in the literature.
Gas flow is found to be in adequate agreement with experiments and earlier simulations, except for a slight overprediction of the free jet spreading.
Particle acceleration and heating is found to be in moderate agreement with experiments, with an overprediction of particle deceleration before impact.
The particle heating is systematically underpredicted, with a relatively small error.Tässä työssä tutkitaan teolliseen käyttöön soveltuvaa pinnoitusmenetelmää, suurnopeusliekkiruiskutusta (high-velocity oxy-fuel thermal spray, HVOF), jonka avulla voidaan parantaa esimerkiksi materiaalien kulumisen- ja lämmönkestävyyttä.
HVOF-menetelmä on luonteeltaan monimutkainen, ja sisältää lukuisia säädettäviä ominaisuuksia.
Laskennallisen mallin avulla voidaan ymmärtää paremmin esiintyvien ilmiöiden välisiä voimasuhteita, ja mallinnusta voidaan hyödyntää parempien pinnotteiden laatimiseen.
Tämän tutkielman tavoitteena on luoda malli HVOF-menetelmän kaasuvirtaukselle, ja tästä aiheutuvalle pinnoitusjauheen kiihtymiselle ja sulamiselle.
Ensimmäisessä vaiheessa kaasuvirtaus ratkaistaan ilman pinnoitusjauhetta, olettaen että jauheen massavuo on merkityksetön kaasuvirtaan verrattuna.
Ongelman laskennallista vaativuutta saadaan pienennettyä olettamalla kaasuvirtaus sylinterisymmetriseksi.
Kaasuvirtaus ratkaistaan käyttämällä kokoonpuristuvaa Navier-Stokesin yhtälöä, ja turbulenssia kuvataan renormalisaatio-ryhmäteoriaan perustuvalla muunnelmalla k-epsilon -mallista.
Polttoaineen palamista kuvataan eddy-dissipation -mallin avulla.
Kaasulajien ja lämmön diffuusio huomioidaan Schmidtin ja Prandtlin lukuihin pohjautuen.
Kaasuvirtaus ratkaistaan käyttäen vapaaseen lähdekoodiin perustuvaa C++ kirjastoa OpenFOAM, jonka ratkaisija rhoCentralFoam muokataan tukemaan useampaa kaasulajia.
Pinnoitushiukkasten oletetaan olevan toisistaan riippumattomia, ja yksittäisiä hiukkasia simuloidaan käyttäen Matlab-ohjelmistoa.
Hiukkasten kiihtymistä hallitsee kaasun raahausvoima, ja niiden lämpeneminen määräytyy lämmönjohtumisesta sekä säteilystä kaasun ja hiukkasten välillä.
Laskettua kaasuvirtausta ja pinnoitusjauheen lennonaikaista tilaa verrataan kirjallisuudesta löytyviin laskelmiin ja kokeisiin.
Kaasuvirtaus on hyvin yhteensopiva sekä kokeiden että aikaisempien laskennallisten tulosten kanssa, lukuun ottamatta vapaan suihkun leviämisen yliarviointia.
Hiukkasten kiihtyminen ja lämpeneminen on keskinkertaisesti yhteensopiva kirjallisuuden kanssa.
Rakennettu malli yliarvioi törmäystä edeltävää hidastumista.
Hiukkasten lämpenemistä aliarvioidaan järjestelmällisesti, kuitenkin suhteellisen pienellä virheellä
Os Brasis de Monteiro Lobato : de Jeca Tatu ao desencantamento
Get PDFOrientadora : Profª Drª Andrea Carla DoréDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Humanas, Letras e Artes, Programa de Pós-Graduação em História. Defesa: Curitiba, 04/11/2010Bibliografia: fls. 121-126Resumo: Esta dissertação tem por objetivo analisar como a questão do progresso foi assumindo diferentes formas a partir das três fases do personagem Jeca Tatu, de Monteiro Lobato, e ponderar sobre dois momentos da obra do escritor: a construção do Jeca Tatu e a crítica ao progresso, contida em seus últimos trabalhos. Para tal, discute-se a questão sanitária, racial, da identidade nacional até chegar ao descontentamento com relação ao progresso e à modernidade, baseados no contexto histórico da virada do século XIX para o XX, que gerou um amplo processo de mudanças, das quais o autor participou. Valendo-se da literatura do período como fonte histórica para compreender os processos de integração e interação vivenciados por Monteiro Lobato e o grupo social do qual fazia parte, utilizamos artigos da Revista do Brasil, no período que vai de 1916 a 1925, e várias obras do escritor.Abstract: This dissertation has for objective to analyze how the question of progress was assuming different forms from the three phases of character Jeca Tatu, of Monteiro Lobato and consider about the two moments the work of the writer: the construction of Jeca Tatu and the critical against he, contained in his later works. For this, discusses the health question, racial, the national identity until arriving at the discontent with respect to the progress and modernity, based on the historical context of the turn of century XIX for the XX, that generated an extensive process of changes, of which the author participated. Drawing on literature of the period as historical source to understand the processes of integration and interaction experienced by Monteiro Lobato and social group which was part, this dissertation uses articles published in Revista do Brazil in the period from 1916 to 1925, and others Lobato's works
Quantitative phase field modeling of solute trapping and continuous growth kinetics in quasi-rapid solidification
No full textSolute trapping is an important phenomenon in rapid solidification of alloys, for which the continuous growth model (CGM) of Aziz et al. [1] is a popular sharp interface theory. By modulating the so-called anti-trapping current and using asymptotic analysis, we show how to quantitatively map the thin interface behavior of an ideal dilute binary alloy phase field model onto the CGM kinetics. We present the parametrizations that allow our phase field model to map onto the sharp interface kinetics of the CGM, both in terms of partition coefficient k(V) and kinetic undercooling. We also show that the mapping is convergent for different interface widths, both in transient and steady state simulations. Finally we present the effect that solute trapping can have on cellular growth in directional solidification. The presented treatment for solute trapping can be easily implemented in different phase field models, and is expected to be an important feature in future studies of quantitative phase field modeling in quasi-rapid solidification regimes, such as those relevant to metal additive manufacturing.</p
Possibilidades para uma interpretação de sítios com arte pré-histórica: o caso do sítio Malacara I e Toca do Tatu
No full textThis article's main objective is to raise possible comparisons between body typefaces belonging to linguistic group Macro Jê (South Je), known from the ethnographic literature as Xoklegs and Kaingans. This body painting are described by Sergio Batista da Silva (2001), with geometric motifs recorded in prehistoric art sites located in the extreme south of Santa Catarina (Malacara I and Toca do Tatu) , to understand symbolic employees aspects in the making of prehistoric art sites through the methodology proposed by the author quoted abov
An atomistic simulation study of rapid solidification kinetics and crystal defects in dilute Al–Cu alloys
Get PDFRapid solidification kinetics of dilute Al–Cu alloys is simulated using a quantum mechanics based bond-order potential (BOP), in free solidification conditions, to determine kinetic and thermodynamic properties of solidification, as well as point defects and chemical ordering of the solidified structures. We measure the anisotropic kinetic coefficient, anisotropic solid–liquid interface energy, as well as solute trapping kinetics in terms of partition coefficient versus velocity and solute drag coefficient. Furthermore, solid–liquid interface free energy and its anisotropy are measured in equilibrium simulations, showing reasonably good agreement with previous studies. We also verified the self-consistency of the MD simulations, by comparing the interfacial temperature vs. velocity to that predicted by the continuous growth model. These solid–liquid interface properties are important for quantitative parametrization of larger scale solidification modeling techniques such as phase field models. We also investigated the point defect content, local chemical ordering, and local crystalline structures in the rapidly solidified samples. We found clustering of solute with vacancies, whereas copper atoms repelled each other in these dilute alloy simulations. In addition to vacancies, a large number of interstitials were found. In solidification velocities approaching the complete solute trapping regime, we found that the vacancies and interstitials formed in conjunction, i.e. as Frenkel pairs. Finally, in addition to FCC, we detected BCC and HCP phases, where the latter two were accompanied by an increase in local copper content. Understanding the formation of point defects and their relationship to chemical ordering is an important step towards controlling the formation of pre-precipitates and precipitates, which are an important strengthening mechanism for aluminum–copper alloys.</p
Les relations Est-Ouest : gérer la tension
No full textEast-West Relations: Managing Tension, by Michel Tatu
Any reflection on the best way to manage the inevitable tension between East and West must take into account the fact that the 80s might well end quite differently than they began. The domestic situation in the Soviet Union will be rendered more complex by problems of succession and the balance of powers will be less favorable to the Kremlin than it is today. One must nevertheless expect an intense arms race as long as Moscow will continue to play the "law of maximal effort" in defence matters. Reaction to crises should first take place locally, even if an inevitable globalisation will follow. Trade sanctions must be concentrated on a few specific sectors (credit, high technological products) if they are to be efficient. The Third World's refusal to be used as a pawn in the chessboard of the great powers excludes the use of sanctions. Stressing the basic importance of the debate on the modernization of nuclear weapons in Europe, the author mentions the role France can play in this process.Les relations Est-Ouest : gérer la tension, par Michel Tatu
Tout effort de réflexion sur la meilleure manière de "gérer" l'inévitable tension entre l'Est et l'Ouest doit prendre en compte le point d'arrivée de la décennie 80, qui pourrait être très différent du point de départ : la situation interne en URSS sera compliquée par les problèmes de succession et le rapport des forces sera moins favorable au Kremlin qu'il ne l'est aujourd'hui. Il faut s'attendre néanmoins à une intense course aux armements aussi longtemps que Moscou continuera à faire jouer la "loi de l'effort maximal" en matière de défense. Quant à la réaction aux crises, elle doit se faire d'abord sur le terrain, ce qui n'exclue pas une inévitable "globalisation". Les sanctions commerciales doivent être concentrées sur certains secteurs spécifiques (crédits, produits à haute technologie) sous peine d'être inefficaces, tandis que le refus du Tiers-Monde de servir de pion sur l'échiquier exclut en fait le recours à la rétorsion. Soulignant l'importance de principe que revêt le débat actuel sur les armements nucléaires en Europe, l'auteur évoque enfin le rôle que la France peut jouer dans ce processus.Tatu Michel. Les relations Est-Ouest : gérer la tension. In: Politique étrangère, n°2 - 1981 - 46ᵉannée. pp. 287-298
Computational modeling of the HVOF process
No full textPrecise control of the high velocity oxygen-fuel spray (HVOF) process parameters is important to obtain high-performance coatings. The coating particle in-flight state is commonly monitored by measuring the in-flight temperature and velocity. To complement the available measurement techniques, a computational model for the gas flow and coating powder in flight, for propylene fueled HVOF process was built. The model is compared to measured nozzle exit pressure and position of the first shock diamond, together with measured particle velocities and surface temperatures. At first the gas flow is solved in absence of the coating powder, assuming a negligible powder mass flow, using the computational fluid dynamics (CFD) program “OpenFOAM”. Subsequently, the coating powder acceleration and heating is modeled in this gas flow
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