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Akıncı, Figen Pashaev Oktay K. "Geometry of moving curves and soliton equations/." [s.l.]: [s.n.], 2004. http://library.iyte.edu.tr/tezler/master/matematik/T000454.pdf.
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Aftuck, Alex Edward. "The Weil Pairing on Elliptic Curves and Its Cryptographic Applications." UNF Digital Commons, 2011. https://digitalcommons.unf.edu/etd/139.
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This thesis presents the Weil pairing on elliptic curves as a tool to implement a tripartite Diffie-Helman key exchange. Elliptic curves are introduced, as well as the addition operation that creates a group structure on its points. In leading to the definition of the Weil pairing, divisors of rational functions are studied, as well as the Weierstrass }-function, which shows the complex lattice as isomorphic to elliptic curves. Several important qualities of the Weil pairing are proved, and Miller's algorithm for quick calculation is shown. Next, the bipartite Diffie-Helman key exchange is discussed over finite fields and elliptic curves. Finally an example of a modifed Weil pairing is defined, which leads to the tripartite Diffie-Helman key exchange.
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Narmack, Kirilll. "Dynamic Speed Adaptation for Curves using Machine Learning." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-233545.
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The vehicles of tomorrow will be more sophisticated, intelligent and safe than the vehicles of today. The future is leaning towards fully autonomous vehicles. This degree project provides a data driven solution for a speed adaptation system that can be used to compute a vehicle speed for curves, suitable for the underlying driving style of the driver, road properties and weather conditions. A speed adaptation system for curves aims to compute a vehicle speed suitable for curves that can be used in Advanced Driver Assistance Systems (ADAS) or in Autonomous Driving (AD) applications. This degree project was carried out at Volvo Car Corporation. Literature in the field of speed adaptation systems and factors affecting the vehicle speed in curves was reviewed. Naturalistic driving data was both collected by driving and extracted from Volvo's data base and further processed. A novel speed adaptation system for curves was invented, implemented and evaluated. This speed adaptation system is able to compute a vehicle speed suitable for the underlying driving style of the driver, road properties and weather conditions. Two different artificial neural networks and two mathematical models were used to compute the desired vehicle speed in curves. These methods were compared and evaluated.Morgondagens fordon kommer att vara mer sofistikerade, intelligenta och säkra än dagens fordon. Framtiden lutar mot fullständigt autonoma fordon. Detta examensarbete tillhandahåller en datadriven lösning för ett hastighetsanpassningssystem som kan beräkna ett fordons hastighet i kurvor som är lämpligt för förarens körstil, vägens egenskaper och rådande väder. Ett hastighetsanpassningssystem för kurvor har som mål att beräkna en fordonshastighet för kurvor som kan användas i Advanced Driver Assistance Systems (ADAS) eller Autonomous Driving (AD) applikationer. Detta examensarbete utfördes på Volvo Car Corporation. Litteratur kring hastighetsanpassningssystem samt faktorer som påverkar ett fordons hastighet i kurvor studerades. Naturalistisk bilkörningsdata samlades genom att köra bil samt extraherades från Volvos databas och bearbetades. Ett nytt hastighetsanpassningssystem uppfanns, implementerades samt utvärderades. Hastighetsanpassningssystemet visade sig vara kapabelt till att beräkna en lämplig fordonshastighet för förarens körstil under rådande väderförhållanden och vägens egenskaper. Två olika artificiella neuronnätverk samt två matematiska modeller användes för att beräkna fordonets hastighet. Dessa metoder jämfördes och utvärderades.
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Trella, Fredrik, and Nils Paakkonen. "Development of a Cost-Effective, Reliable and Versatile Monitoring System for Solar Power Installations in Developing Countries : A Minor Field Study as a Master Thesis of the Master Programme in Engineering Physics, Electrical Engineering." Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-302815.
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This report is the result of a conducted Minor Field Study (MFS), to the greatestextent funded by the Swedish International Development Cooperation Agency(SIDA), in an attempt to design a system for evaluating smaller solar power systems indeveloping countries. The study was to the greater part conducted in Nairobi, Kenyain close collaboration with the University of Nairobi. The aim was to develop asystem that would use easily available components and keep the costs to a minimum,yet deliver adequate performance. The system would measure certain parameters of asolar power system and also relevant environmental data in order to evaluate theperformance of the system. Due to the specific competence of the collaboratinggroup at the University of Nairobi, a Kinetis Freescale K64-microcontroller with anARM-Cortex processor was selected as the core of the design. Components wereselected, schematics were drawn, a circuit board was designed and manufactured andsoftware was written. After 12 weeks a somewhat satisfying proof-of-concept wasreached at the end of the field study in Kenya. The project however proved howdifficult it is to go from first idea to a functional proof-of-concept during a limitedtimeframe, and also in an East-African country. The final proof-of-concept was testedat Mpala Research Centre in Kenya and despite containing some flaws proved that itwould indeed be possible to design a working system on the principles discussed inthis report. The system is open-source, so anyone may use and modify it.
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Khandaker, Md Shahriar K. "Investigation on the Mechanisms of Elastomechanical Behavior of Resilin." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/64362.
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Resilin is a disordered elastomeric protein and can be found in specialized regions of insect cuticles. Its protein sequence, functions and dynamic mechanical properties vary substantially across the species. Resilin can operate across the frequency range from 5 Hz for locomotion to 13 kHz for sound production. To understand the functions of different exons of resilin, we synthesize recombinant resilin-like hydrogels from different exons, and investigate the water content and dynamic mechanical properties, along with estimating surface energies relevant for adhesion. The recombinant resilin-like hydrogel has 80wt% water and does not show any sign of tack even though it satisfies the Dahlquist criterion. Finally, doubly shifted dynamic moduli master curves are developed by applying the time-temperature concentration superposition principle (TTCSP), and compared to results obtained with natural resilin from locusts, dragonflies and cockroaches. The resulting master curves show that the synthetic resilin undergoes a prominent transition, though the responsible mechanism is unclear. Possible explanations for the significant increase in modulus include the formation of intramolecular hydrogen bonds, altered structural organization, or passing through a glass transition, all of which have been reported in the literature for polymeric materials. Results show that in nature, resilin operates at a much lower frequency than this glass transition frequency at room temperature. Moreover, recombinant resilins from different clones have comparable resilience with natural resilin, though the modulus is around 1.5 decades lower. Results from the clones with and without chitin binding domains (ChBD) indicate that the transition for the clone without ChBD occurs at lower frequencies than for those with the ChBD, perhaps due to the disordered nature of the clone without ChBD.
Atomistic molecular modeling is applied on the repetitive motifs of resilin and different elastomeric proteins to better understand the relationship between elastomeric behavior and amino acid sequences. Results show that the motifs form a favorable bent conformation, likely enabled by glycine's lack of steric hindrance and held in place through intramolecular hydrogen bonds. During Steered Molecular Dynamic (SMD) pulling of these motifs, the hydrogen bonds break and they reform again when the peptides are released to move freely, returning to similar bent conformations. The transition seen in the master curves of recombinant resilins might be due to either these intramolecular hydrogen bonds or to glass transition behavior, though evidence indicates that the transition probably due to the glass transition. What we learned from the synthesized recombinant resilin and simulating the repetitive motifs of resilin may be applicable to the biology and mechanics of other elastomeric biomaterials, and may provide deeper understanding of their unique properties.Ph. D.
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Wells, Laurence Gregory. "Master John Hall's little book of cures : a critical edition." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/88160/.
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This thesis presents a critical edition of John Hall’s casebook (composed around 1634-1635) and commentaries on aspects of it. My research involved close reading of Hall’s Latin, and its translation into English. In the process it became apparent that Hall had made considerable use of unattributed borrowings from Latin medical books, making up between thirty and forty per cent of his text. These were mostly identified by detailed word searches of on-line databases. This is a use of medical texts not previously noted, and makes a clear connexion between Latin medical texts and routine medical practice. The thesis is presented in four sections, plus introduction and conclusion. The first section, the Background, gives the history of Hall’s manuscript from its composition in 1634-35 to its acquisition by the British Library. It sets out the reasons for producing a new translation, the editorial principles and practice followed, and some medical themes running through Hall’s case reports. Section two contains the critical edition itself, with parallel Latin and English texts. Footnotes to the Latin text give the sources of all of Hall’s borrowings from and references to medical and other texts. The third section (Chapter 1) analyses the process and results of identifying Hall’s working library, of forty-three authors and sixty titles, from his borrowings. It puts his library in the early modern medical context in terms of its contents and categories of composition. I show that there were changes in the books Hall acquired over time, from those suitable for a student through to his later interests in chymical practice and the diagnosis of scurvy. Despite these changes, he continued to rely on old familiar texts for most of his remedies throughout his life. The fourth section (Chapter 2) examines Hall’s manuscript in the context of casebooks generally. It differs from the majority of casebooks, the differences being explained by its composition as the draft for a book to be published. It shows that a casebook can have an internal structure related to the chronologies of its composition and the cases it draws on. This thesis demonstrates the importance of Latin sources in at least one medical casebook of the early seventeenth century. I show that borrowings such as Hall’s were not unique even if rarer in other texts. The possibility of a Latin textual source should be considered for any Latin text in a casebook of that period.
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Viehrig, H. W., and C. Zurbuchen. "Anwendung des Master Curve-Konzeptes zur Charakterisierung der Zähigkeit neutronenbestrahlter Reaktordruckbehälterstähle." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28195.
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Die Anwendbarkeit des Master Curve-(MC-)Konzepts zur Charakterisierung des Zähigkeitszustandes bestrahlter Reaktordruck¬behälter-(RDB-)Stähle wurde an drei RDB-Stählen überprüft: IAEA-Referenzstahl 3JRQ57, 1JFL11 (vergleichbar mit 22NiMoCr3-7) sowie russischer WWER-440 Grundwerkstoff KAB-B. In Zugversuchen, Charpy-V-Tests, Risswiderstandskurven nach ASTM E1820 und Master Curve Tests zur Bestimmung der Referenztemperatur T0 nach ASTM E1921 wurden der unbestrahlte Ausgangszustand, je drei Bestrahlungszustände bis hin zu Neutronenfluenzen von 100∙10^18 n/cm² (E>1MeV) sowie bei 475°C/100h thermisch ausgeheilte Zustände untersucht. Mit zusätzlichen auf dem MC-Konzept basierenden Auswerteverfahren nach SINTAP, multimodalem MC-Ansatz (MML) sowie der Unified Curve erfolgte die Bewertung des Einflusses von Materialinhomogenitäten und möglicher MC-Formänderung bei hohen Fluenzen. Wie erwartet geht Neutronenbestrahlung mit Verfestigung und Duktilitätsabnahme einher, d.h. Härte, Festigkeitskennwerte, Charpy-V-Übergangstemperaturen T28J und T41J sowie T0 steigen mit der Neutronenfluenz, während die Bruchdehnung und Hochlagenzähigkeit abnehmen. Am bestrahlungsempfindlichsten reagiert der Stahl 3JRQ57, gefolgt von KAB-B und 1JFL11. Durch die Ausheilbehandlung von 475°C/100h erholen sich die Werkstoffkennwerte der Zugversuche, Charpy-V-Tests und MC-Versuche auf den jeweiligen unbestrahlten Ausgangszustand. Die technischen Ersatzkennwerte für duktile Rissinitiierung bleiben relativ unbeeinflusst von der Neutronenbestrahlung. Die MC nach ASTM E1921 beschreibt die Bruchzähigkeits-Temperaturverläufe für alle drei RDB-Stähle in allen Bestrahlungs- und Ausheilzuständen gut. Bei den niedrig und mittel bestrahlten Zuständen liegen meist mehr als 5% der KJc(1T)-Werte unterhalb der MC-Kurve für 5% Versagenswahrscheinlichkeit. Die MC beschreibt den hoch bestrahlte Zustand (ca. 100∙10^18 n/cm², E>1MeV) aller drei RDB-Stähle sehr gut, auch für Daten außerhalb des Gültigkeitsbereiches T0±50K, und auch für den bestrahlungsempfindlichen 3JRQ57 mit inhomogenem Gefüge. Die Unified Curve überbewertet den Einfluss der Neutronenbestrahlung auf die MC-Kurvenform. Eine mögliche Formänderung der MC durch Neutronenbestrahlung konnte bei keinem der drei untersuchten RDB-Stähle nachgewiesen werden.
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Viehrig, H. W., and C. Zurbuchen. "Anwendung des Master Curve-Konzeptes zur Charakterisierung der Zähigkeit neutronenbestrahlter Reaktordruckbehälterstähle." Forschungszentrum Dresden-Rossendorf, 2007. https://hzdr.qucosa.de/id/qucosa%3A21646.
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Die Anwendbarkeit des Master Curve-(MC-)Konzepts zur Charakterisierung des Zähigkeitszustandes bestrahlter Reaktordruck¬behälter-(RDB-)Stähle wurde an drei RDB-Stählen überprüft: IAEA-Referenzstahl 3JRQ57, 1JFL11 (vergleichbar mit 22NiMoCr3-7) sowie russischer WWER-440 Grundwerkstoff KAB-B. In Zugversuchen, Charpy-V-Tests, Risswiderstandskurven nach ASTM E1820 und Master Curve Tests zur Bestimmung der Referenztemperatur T0 nach ASTM E1921 wurden der unbestrahlte Ausgangszustand, je drei Bestrahlungszustände bis hin zu Neutronenfluenzen von 100∙10^18 n/cm² (E>1MeV) sowie bei 475°C/100h thermisch ausgeheilte Zustände untersucht. Mit zusätzlichen auf dem MC-Konzept basierenden Auswerteverfahren nach SINTAP, multimodalem MC-Ansatz (MML) sowie der Unified Curve erfolgte die Bewertung des Einflusses von Materialinhomogenitäten und möglicher MC-Formänderung bei hohen Fluenzen. Wie erwartet geht Neutronenbestrahlung mit Verfestigung und Duktilitätsabnahme einher, d.h. Härte, Festigkeitskennwerte, Charpy-V-Übergangstemperaturen T28J und T41J sowie T0 steigen mit der Neutronenfluenz, während die Bruchdehnung und Hochlagenzähigkeit abnehmen. Am bestrahlungsempfindlichsten reagiert der Stahl 3JRQ57, gefolgt von KAB-B und 1JFL11. Durch die Ausheilbehandlung von 475°C/100h erholen sich die Werkstoffkennwerte der Zugversuche, Charpy-V-Tests und MC-Versuche auf den jeweiligen unbestrahlten Ausgangszustand. Die technischen Ersatzkennwerte für duktile Rissinitiierung bleiben relativ unbeeinflusst von der Neutronenbestrahlung. Die MC nach ASTM E1921 beschreibt die Bruchzähigkeits-Temperaturverläufe für alle drei RDB-Stähle in allen Bestrahlungs- und Ausheilzuständen gut. Bei den niedrig und mittel bestrahlten Zuständen liegen meist mehr als 5% der KJc(1T)-Werte unterhalb der MC-Kurve für 5% Versagenswahrscheinlichkeit. Die MC beschreibt den hoch bestrahlte Zustand (ca. 100∙10^18 n/cm², E>1MeV) aller drei RDB-Stähle sehr gut, auch für Daten außerhalb des Gültigkeitsbereiches T0±50K, und auch für den bestrahlungsempfindlichen 3JRQ57 mit inhomogenem Gefüge. Die Unified Curve überbewertet den Einfluss der Neutronenbestrahlung auf die MC-Kurvenform. Eine mögliche Formänderung der MC durch Neutronenbestrahlung konnte bei keinem der drei untersuchten RDB-Stähle nachgewiesen werden.
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McCoy, Tammy Michelle. "Extension of the master sintering curve for constant heating rate modeling." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22532.
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Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.Committee Chair: Dr. Joe K. Cochran; Committee Co-Chair: Dr. Thomas H. Sanders; Committee Member: Dr. John Elton; Committee Member: Dr. Meilin Liu; Committee Member: Dr. Robert F. Speyer.
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Jeong, Myunggoo. "Comparison of Creep Compliance Master Curve Models for Hot Mix Asphalt." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/43759.
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Creep compliance of Hot Mix Asphalt (HMA) is an important property to characterize the material's viscoelatic behavior. It is used to predict HMA thermal cracking at low temperature and permanent deformation at high temperatures. There are several experimental methods to measure the creep compliance. Two of these methods were used in this thesis; uniaxial compressive and indirect tension (IDT) creep compliance. The tests were conducted at five temperatures (-15, 5, 20, 30, and 40°C) with a static loading for 1000-sec to characterize two typical HMA mixes used in Virginia, a base and a surface mix. Creep compliance master curves (CCMC) were developed by shifting the curves to a reference temperature using time-temperature superposition. Three mathematical functions, Prony series, power and sigmoidal, were fitted to the experimental data using regression analysis. Uniaxial CCMC were also predicted based on dynamic modulus measurements using method for interconversion of vicoelastic properties recommended in the literature. Finally, the susceptibility of the mixes to thermal cracking was evaluated based on the creep compliance measurements at low temperature.
The regression analysis showed that the three mathematical models considered are appropriate to model the CCMC over a wide ranger of reduced times. The sigmoidal model provided the best fit over the entire range of reduced times investigated. This model also produced the best results when used in the interconversion procedures. However, there were noticeable differences between the CCMC predicted using interconversion and the experimental measurements, probably due to nonlinearity in the material behavior. The m-values for the base mix were higher using the creep results measured with both configurations.Master of Science
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Viehrig, H. W., and D. Kalkhof. "Application of the Master Curve approach to fracture mechanics characterisation of reactor pressure vessel steel." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-61451.
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The paper presents results of a research project founded by the Swiss Federal Nuclear Inspectorate concerning the application of the Master Curve approach in nuclear reactor pressure vessels integrity assessment. The main focus is put on the applicability of pre-cracked 0.4T-SE(B) specimens with short cracks, the verification of transferability of MC reference temperatures T0 from 0.4T thick specimens to larger specimens, ascertaining the influence of the specimen type and the test temperature on T0, investigation of the applicability of specimens with electroerosive notches for the fracture toughness testing, and the quantification of the loading rate and specimen type on T0. The test material is a forged ring of steel 22 NiMoCr 3 7 of the uncommissioned German pressurized water reactor Biblis C.
SE(B) specimens with different overall sizes (specimen thickness B=0.4T, 0.8T, 1.6T, 3T, fatigue pre-cracked to a/W=0.5 and 20% side-grooved) have comparable T0. T0 varies within the 1σ scatter band. The testing of C(T) specimens results in higher T0 compared to SE(B) specimens. It can be stated that except for the lowest test temperature allowed by ASTM E1921-09a, the T0 values evaluated with specimens tested at different test temperatures are consistent. The testing in the temperature range of T0 ± 20 K is recommended because it gave the highest accuracy. Specimens with a/W=0.3 and a/W=0.5 crack length ratios yield comparable T0. The T0 of EDM notched specimens lie 41 K up to 54 K below the T0 of fatigue pre-cracked specimens. A significant influence of the loading rate on the MC T0 was observed. The HSK AN 425 test procedure is a suitable method to evaluate dynamic MC tests. The reference temperature T0 is eligible to define a reference temperature RTTo for the ASME-KIC reference curve as recommended in the ASME Code Case N-629. An additional margin has to be defined for the specific type of transient to be considered in the RPV integrity assessment. This margin also takes into account the level of available information of the RPV to be assessed.
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Hughes, Douglas Grant Ramey G. Ed. "Bridge pile bent P-delta curves in transverse direction using FB-pier and GTSTRUDL pushover Analysis procedures." Auburn, Ala., 2005. http://repo.lib.auburn.edu/2005%20Summer/master's/HUGHES_DOUGLAS_56.pdf.
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Lejeune, Joseph. "Surface recovery and reconstruction after deformation." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE031/document.
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Les propriétés des polymères sont intéressantes pour des applications pneumatiques, de verres organiques, de joints, … Leurs propriétés mécaniques sont néanmoins mal comprises. Dans ce manuscrit, le comportement mécanique du PMMA et du CR39 est étudié en fonction du temps.Il en résulte des courbes maîtresses à partir d’expérience de relaxation de contrainte et de fluage d’indentation. D'autre part, le comportement mécanique au contact est analysé sur des expériences de fluage et recouvrance d’indentation et de rayures analysées pour la première fois dans cette thèse. Finalement, des lois de comportements sont construites, leurs précisions sont comparées grâce à des calculs par éléments finis aux expériences en contactPolymer's low weight, deformability and easy manufacturing make them attractive materials for tire, organic glasses, sealing applications … Their mechanical properties are nonetheless poorly understood. In particular, two fields are searched over this thesis: time dependency and contact behavior for two transparent polymer: PMMA and CR39. The mechanical behavior time dependency is observed by the construction of stress relaxation and contact master curves. The mechanical contact behavior is analyzed by indentation creep and recovery experiments. Moreover the immediate scratch recovery is measured in the thesis. Finally, the uniaxial data is used to build constitutive laws, which accuracy is compared by Finite Element Modeling to contact tests
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Ghasemi, Navid. "Rheology of bituminous mastics and mortars containing crumb rubber from tyres: a novel dry-hybrid technology." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
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This report studied the effect of crumb rubber in the asphalt mixture. The mixtures were also having limestone filler as a modifier. Mastic and mortar (mastic-fine aggregate system) mixture having different quantities of crumb rubber and limestone filler modifiers have been tested in order to find the best rutting resistance combination with an acceptable stiffness. The rheological tests on bituminous mastics and mortars have done in the laboratories in Nottingham Transport Engineering Centre (NTEC) and University of Bologna (DICAM).
In the second chapter, an extensive literature review about the binders, additives, asphalt mixtures, various modelling and testing methods have been reviewed. In the third chapter, the physical and rheological properties of the binders have been investigated using both traditional devices and DSRs. The forth chapter is dedicated to finding the behaviour of the modified mastics (Binder-modifier system) with different combinations. Five different combinations of crumb rubber and limestone filler mastic tested with various methods using Dynamic Shear Rheometers.
In the fifth chapter, in order to find the effect of the modifiers in the rheological properties of the complete asphalt mixture, the fine aggregates added to the same mastic combinations. In this phase, the behaviour of the system so-called mortar; binder, rubber, filler and fine aggregates) has been studied using the DSR device and the traditional tests.
The results show that using fine crumb rubber reduces the thermo sensibility of the mastic (Binder Bitumen System) and improves its elasticity. Limestone filler in the other hand increases the mixture stiffness at high Frequencies.
Another important outcome of this research was that the rheological properties of the mortars were following the same trend of the mastics, therefore study the rheological properties of the mastic gives an upright estimation of the mortar.
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Pouchlý, Václav. "Slinování pokročilých keramických materiálů s využitím vysokoteplotní dilatometrie." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2009. http://www.nusl.cz/ntk/nusl-228398.
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This diploma work is focused on exploitation of high-temperature dilatometry in sintering of advanced ceramic materials. Newly developed software is presented in this diploma work. This software is able to calculate activation energy of sintering process via concept of Master Sintering Curve. In the second part of diploma work the software was verified by evaluation of sintering of four different ceramics materials. The following activation energies of sintering were calculated: 990kJ/mol for tetragonal ZrO2 (3mol% Y2O3), 620kJ/mol for cubic ZrO2 (8mol% Y2O3) and 640kJ/mol resp. 720kJ for Al2O3 with two different particle size.
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Silva, Selma Luiza. "Cinética de sinterização do combustível nuclear 'UO IND. 2.'7%'Gd IND.2'O IND. 3' : cálculo da curva mestre de sinterização /." Sorocaba, 2010. http://hdl.handle.net/11449/99732.
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Orientador: José Roberto Ribeiro BortoletoBanca: Luciano Pagano Junior
Banca: Andrea Paesano Junior
Resumo: O processo de sinterização de pastilhas de 'UO IND. 2.'7%'Gd IND.2'O IND. 3' tem sido investigado por muito tempo devido à sua importância na indústria nuclear e ao seu comportamento complexo durante o adensamento. Vários pesquisadores tentaram explicar este comportamento utilizando uma abordagem fenomenológica. Ainda que com algum sucesso, o comportamento na sinterização é difícil de ser previsto. A densidade final e a microestrutura da pastilha sinterizada dependem das propriedades dos pós de partida, do perfil térmico, da composição da atmosfera, da presença de aditivos, entre outras variáveis. Uma abordagem diferente do problema supera esta dificuldade com a introdução do conceito da Curva Mestre de Sinterização - CMS. A CMS do combustível nuclear 'UO IND. 2.'7%'Gd IND.2'O IND. 3' foi levantada utilizando dados de dilatometria obtidos com a taxa de aquecimento constante. Este desenvolvimento foi realizado para prever e controlar a evolução da densidade durante a etapa de sinterização. As amostras foram produzidas através da mistura do pós de 'UO IND. 2' e 'Gd IN> 2'O IND. 3', compactadas e sinterizadas em um dilatômetro a 2023 k, com diferentes taxas de aquecimento na faixa de 5 a 45 'Kmin. POT. -1', sob atmosfera de 'H IND. 2'. Com base no conceito da CMS, a previsão do adensamento foi realizada e uma boa concordância entre os valores previstos e experimental foi verificada. Foi demonstrado que o conceito da CMS pode ser utilizado para planejar um perfil de temperatura adequado, visando uma densidade final desejada, mesmo para sistemas com reações mais complexas como o 'UO IND. 2.'7%'Gd IND.2'O IND. 3'. A energia de ativação aparente do processo de sinterização pode ser estimada por este método.
Abstract: The sintering process of the 'UO IND. 2.'7%'Gd IND.2'O IND. 3' system has been investigated for a long time due to its economical importance to the nuclear industry and complex behavior during densification. Most researchers tried to describe and explain it using a phenomenological approach. Even though some light has been shed on the matter, the system sintering behavior is still very difficult to predict. The final density and microstructure of the sintered body is strongly dependent on properties of raw powders, temperature profile,, atmosphere composition, presence of sintering additives, among other process variables. A different approach to the problem overcame this difficulty by introducing the concept of the Master Sintering Curve - MSC. The MSC of the 'UO IND. 2.'7%'Gd IND.2'O IND. 3' nuclear fuel was constructed using constant heating rate dilatometry data. This development was carried out to predict and control the evolution of the density during the sintering path. The samples were produced from a dry misture of "UO IND. 2' and 2' e 'Gd IN> 2'O IND. 3' powders, pressed into compacts and sintered in a dilatometer up to 2023 K with different heating rates from 5 to 45 'Kmin. POT. -1', under a 'H IND. 2' atmosphere. Based on the MSC concept, the prediction of pellet densification was performed and it was observed a good agreement between the experimental and the predicted values. It was demonstrated that the MSC approach can be used to desing a suitable sintering temperature profile in order to obtain a desidered final density, even for reacting systems such as the 'UO IND. 2.'7%'Gd IND.2'O IND. 3', where the second phase should mostley get into solution. The apparent activation energy of sintering process could also be estimated by this method.
Mestre
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Sieber, Lars. "Zur Beurteilung der Sprödbruchgefährdung gelochter Stahltragwerke aus Flussstahl." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-223593.
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Bei der Beurteilung der Sicherheit bestehender Konstruktionen aus altem Baustahl (i. A. Flussstahl) und der Entscheidung über notwendige Instandsetzungs- und Verstärkungsmaßnahmen ist der Nachweis ausreichender Werkstoffzähigkeit (der Sicherheit gegen ein sprödes Versagen) von wesentlicher Bedeutung. Die in DIN EN 1993-1-10 normativ geregelten Nachweismethoden zur Beurteilung der Sprödbruchgefährdung wurden basierend auf umfangreichen bruchmechanischen Untersuchungen entwickelt. Sie gelten für Schweißkonstruktionen und „Stähle aus neuerer Zeit“ mit in der Regel hohen Zähigkeitswerten. Die Quantifizierung der Zähigkeit in Werkstoffnormen erfolgt durch Kerbschlagbiegeversuche. Die Beziehung zwischen der Übergangstemperatur der Kerbschlagarbeit und der Referenztemperatur der Bruchzähigkeit wird durch die modifizierte Sanz-Korrelation hergestellt, die nur für diese Stähle abgeleitet wurde. Das in der Norm verankerte Verfahren ist für alte Flussstahlkonstruktionen mit Lochschwächung durch Niet- und Schraubenverbindungen nicht geeignet. Einerseits unterscheiden sich Kerbwirkung und Eigenspannungszustand von geschweißten und genieteten Konstruktionen und damit die Zähigkeitsanforderungen wesentlich voneinander. Auf der anderen Seite unterliegen die Zähigkeitseigenschaften von Flussstählen deutlich größeren Streuungen.
In der vorliegenden Arbeit werden experimentelle und rechnerische Untersuchungen zum Sprödbruchverhalten gelochter Konstruktionen aus altem Flussstahl vorgestellt. Wesentlicher Bestandteil sind dabei die umfangreichen Werkstoffanalysen zur Ermittlung der bruchmechanischen Werkstoffzähigkeit im spröd-duktilen Übergangsbereich nach dem Master-Curve-Konzept (ASTM E1921). Die Auswertungen belegen, dass in Abhängigkeit des Herstellungsverfahrens unterschiedliche Werkstoffgüten definiert werden können. Um den Einfluss des Stanzens von Löchern auf das Sprödbruchverhalten alter Flussstähle zu beurteilen, werden Gefügeuntersuchungen und Mikrohärtemessungen durchgeführt.
Ausgehend von einer umfassenden Analyse typischer Konstruktionsformen bestehender Tragwerke des Stahlhochbaus erfolgen bruchmechanische FE-Berechnungen an Anschlüssen von Winkelprofilen zur Bestimmung der Zähigkeitsanforderungen. Die dabei gewonnenen Ergebnisse des Spannungsintensitätsfaktors werden durch Modifikation bekannter Lösungen aus der Fachliteratur für die weitere Anwendung aufbereitet. Darauf aufbauend wird für die untersuchten Konstruktionsdetails im Rahmen einer bruchmechanischen Sicherheitsanalyse ein praxisgerechtes Verfahren zur Beurteilung der Sprödbruchgefährdung genieteter und geschraubter Bauteile abgeleitet. Mit Hilfe statistischer Methoden werden Streuungen der Festigkeits- und Zähigkeitskennwerte der Flussstähle erfasst und nach der Verifizierung durch Bauteilversuche in ein semi-probabilistisches Nachweiskonzept überführt.
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Schubert, Sven. "Stochastic and temperature-related aspects of the Preisach model of hysteresis." Doctoral thesis, Universitätsbibliothek Chemnitz, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-70798.
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Ziel der vorliegenden Arbeit ist es, das Preisach-Modell bezüglich stochastischer äußerer Felder und temperaturbezogener Aspekte zu untersuchen. Das phänomenologische Preisach-Modell wird oft erfolgreich angewendet, um Systeme mit Hysterese zu beschreiben. Im ersten Teil der Arbeit wird die Antwort des Preisach-Modells auf stochastische äußere Felder untersucht. Hier liegt das Augenmerk hauptsächlich auf der Autokorrelation; sie dient dazu den Einfluss des hysteretischen Gedächtnisses zu quantifizieren. Mit analytischen Methoden wird gezeigt, dass sich ein Langzeitgedächtnis, sichtbar in der Autokorrelation der Systemantwort, entwickeln kann, selbst wenn das treibende Feld unkorreliert ist. Im Anschluss werden diese Resultate, m.H. von Simulationen, auf äußere Felder ausgeweitet, die selbst Korrelationen aufweisen können. Der zweite Teil der Arbeit befasst sich mit dem Einfluss einer endlichen Temperatur auf das Preisach-Modell. Es werden unterschiedliche Methoden besprochen, wie das Nichtgleichgewichtsmodell in seiner mikromagnetischen Interpretation mit Temperatur als Gleichgewichtseigenschaft verknüpft werden kann. Eine Formulierung wird genutzt, um die Magnetisierung von Nickelnanopartikeln in einer Fullerenmatrix zu simulieren und mit Experimenten zu vergleichen. Des Weiteren wird die Relaxationsdynamik des Gedächtnisses des Preisach-Modells bei endlichen Temperaturen untersuchtThe aim of this thesis is to investigate the Preisach model in regard to stochastically driving and temperature-related aspects. The Preisach model is a phenomenological model for systems with hysteresis which is often successfully applied. Hysteresis is a widespread phenomenon which is observed in nature and the key feature of certain technological applications. Further, it contributes to phenomena of interest in social science and economics as well. Prominent examples are the magnetization of ferromagnetic materials in an external magnetic field or the adsorption-desorption hysteresis observed in porous media. Hysteresis involves the development of a hysteresis memory, and multistability in the interrelations between external driving fields and system response. In the first part, we mainly investigate the response of Preisach hysteresis models driven by stochastic input processes with regard to autocorrelation functions to quantify the influence of the system’s memory. Using rigorous methods, it is shown that the development of a hysteresis memory is reflected in the possibility of long-time tails in the autocorrelation functions, even for uncorrelated driving fields. In the case of uncorrelated driving, these long-time tails in the autocorrelations of the system’s response are determined only by the tails of the involved densities. They will be observed if there are broad Preisach densities assigning a high weight to elementary loops of large width and narrow input densities such that rare extreme events of the input time series contribute significantly to the output for a long period of time. Afterwards, these results are extended by simulations to driving fields which themselves show correlations. It is shown that the autocorrelation of the output does not decay faster than the autocorrelation of the input process. Further, there is a possibility that long-term memory in the hysteretic response is more pronounced in the case of uncorrelated driving than in the case of correlated driving. The behavior of the output probability distribution at the saturation values is quite universal. It is not affected by the presence of correlations and allows conclusions whether the input density is much more narrow than the Preisach density or not. Moreover, the existence of effective Preisach densities is shown which define equivalence classes of systems of input and Preisach densities which lead to realizations of the same output variable. The asymptotic behavior of an effective Preisach density determines the asymptotic correlation decay of the system’s response in the case of uncorrelated driving. In the second part, temperature-related effects are considered. It is reviewed how the non-equilibrium Preisach model in its micromagnetic picture can be related to temperature within the framework of extended irreversible thermodynamics. The irreversible response of a ferromagnetic material, namely, Nickel nanoparticles in a fullerene matrix, is simulated. The model includes superparamagnetism where ferromagnetism breaks down at temperatures lower than the Curie temperature and the results are compared to experimental data. Furthermore, we adapt known results for the thermal relaxation of the system’s memory in the form of a front propagation in the Preisach plane derived basically from solving a master equation and by the use of a contradictory assumption. A closer look is taken at short time scales which dissolves the contradiction and shows that the known results apply, taking into account the fact that the dividing line propagation starts with an additional delay time depending on the front coordinates in the Preisach plane. Additionally, it is outlined how thermal relaxation behavior in the Preisach model of hysteresis can be studied using a Fokker-Planck equation. The latter is solved analytically in the non-hysteretic limit using eigenfunction methods. The results indicate a change in the relaxation behavior, especially on short time scales
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Rocha, Danielle Ferrari Borges. "Obtenção de curvas mestre de compósitos poliméricos estruturais utilizando ensaios dinâmicos mecânicos sob fluência." Universidade Federal de São Carlos, 2010. https://repositorio.ufscar.br/handle/ufscar/814.
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Previous issue date: 2010-08-11The growing advanced composites appliance in aircraft s structural parts has demanded to spread the knowledge about mechanical behavior prediction in longer time periods. In this way, the main purpose of this study is to establish an accelerated test method based on mechanical-dynamical-thermal analysis (DMTA), to predict the mechanical behavior of carbon fiber/epoxy resin composites. The DMTA technique was used on two modes: multi-frequency and creep. In the first case, three point bending tests on dynamical mode did not present a good fitting to built master curves, considering the experimental parameters used. Though, creep tests showed good results. In these tests, parameters used as temperature range from 25ºC to 235ºC and isothermals at every 15ºC for 100 minutes allowed to obtain compliance modulus versus time master curves with a good fitting. From the obtained results, it is possible to conclude that the proposed method presented good adhesion to the basic concept of material viscoelasticity, therefore can be used to predict mechanical behavior of composite materials.
A crescente demanda de uso de compósitos poliméricos avançados em peças de responsabilidade estrutural na indústria aeronáutica tem exigido ampliar o conhecimento sobre a predição do comportamento mecânico desses materiais em longos períodos de tempo. Nesse sentido, este trabalho tem como objetivo estabelecer uma metodologia de ensaios acelerados, utilizando a técnica de análise térmica dinâmico-mecânica (DMTA), para prever o comportamento mecânico de compósitos de fibras de carbono em matriz de resina epóxi. O uso da técnica de DMTA foi baseado em dois tipos de ensaios: multifrequências e fluência. No primeiro caso, ensaios de flexão três pontos, em modo dinâmico, não mostraram bom ajuste na construção de curvas mestre, dentro das condições usadas neste estudo. Já ensaios realizados no modo de fluência apresentaram resultados promissores. Neste tipo de ensaio, o uso dos parâmetros, como intervalo de temperaturas de 25ºC a 235ºC e isotermas a cada 15ºC, com 100 minutos de duração, possibilitaram a construção de curvas mestre do módulo de compliância em função do tempo com um bom ajuste. A partir dos resultados obtidos pode-se concluir que o método proposto apresenta adesão aos conceitos básicos de viscoelasticidade de materiais e, portanto, pode ser utilizado para previsão do comportamento de materiais compósitos em longos períodos de tempo. A crescente demanda de uso de compósitos poliméricos avançados em peças de responsabilidade estrutural na indústria aeronáutica tem exigido ampliar o conhecimento sobre a predição do comportamento mecânico desses materiais em longos períodos de tempo. Nesse sentido, este trabalho tem como objetivo estabelecer uma metodologia de ensaios acelerados, utilizando a técnica de análise térmica dinâmico-mecânica (DMTA), para prever o comportamento mecânico de compósitos de fibras de carbono em matriz de resina epóxi. O uso da técnica de DMTA foi baseado em dois tipos de ensaios: multifrequências e fluência. No primeiro caso, ensaios de flexão três pontos, em modo dinâmico, não mostraram bom ajuste na construção de curvas mestre, dentro das condições usadas neste estudo. Já ensaios realizados no modo de fluência apresentaram resultados promissores. Neste tipo de ensaio, o uso dos parâmetros, como intervalo de temperaturas de 25ºC a 235ºC e isotermas a cada 15ºC, com 100 minutos de duração, possibilitaram a construção de curvas mestre do módulo de compliância em função do tempo com um bom ajuste. A partir dos resultados obtidos pode-se concluir que o método proposto apresenta adesão aos conceitos básicos de viscoelasticidade de materiais e, portanto, pode ser utilizado para previsão do comportamento de materiais compósitos em longos períodos de tempo.
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Raule, Giacomo. "Studio delle criticità idrauliche del Canale di Bonifica Zonara Masere." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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Nella presente tesi è stato fatto un modello idrologico della Zonara Masere tramite l'utilizzo di SWMM. Svolta la simulazione dello stato attuale sono state individuate le criticità ed in seguito sono stati ipotizzati vari scenari di soluzione delle criticità. Infine trovata la soluzione ottimale si è effettuata una prima fase di progettazione delle opere di prevenzione ed una stima economica del costo della realizzazione del progetto. La tesi è stata svolta presso il Consorzio di Bonifica della Romagna nella sede di Rimini
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Batista, Rafael Morgado. "Efeitos da atmosfera de sinterização e do tamanho de partícula na sinterização da céria-gadolínia." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-04122014-143143/.
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Os efeitos da atmosfera de sinterização e do tamanho inicial das partículas na sinterização da céria contendo 10% em mol de gadolínia (GdO1,5) foram sistematicamente estudados neste trabalho. Materiais de partida com três valores para a área de superfície específica foram utilizados, 210 m2/g, 36,2 m2/g e 7,4 m2/g. Diferentes cinéticas de sinterização foram verificadas. Quanto menor o tamanho inicial das partículas, menor é a temperatura para o início da sinterização e mais acelerada a densificação do material. Curvas mestres de sinterização foram construídas para cada um dos materiais analisados. Um programa computacional foi especialmente desenvolvido para este propósito. Diferenças significativas entre as energias de ativação para densificação foram verificadas. Para este trabalho foi determinado que, quanto menor o tamanho inicial de partícula, menores as energias de ativação. A evolução das distribuições de tamanhos de cristalitos foi investigada para os materiais de maior área superficial específica. Foi determinado que a eliminação e migração de poros (pore drag) é o mecanismo predominante para o crescimento de grãos durante o início da sinterização da céria gadolínia. Os efeitos da atmosfera de sinterização no desvio de estequiometria, na densificação, na evolução microestrutural e na condutividade elétrica da céria-gadolínia foram analisados. Atmosferas redutoras, oxidantes e inertes foram usadas para este propósito. Desvios na estequiometria da céria foram verificados no volume do material, sendo este dependente da área de superfície específica e da atmosfera utilizada. Quanto maior o potencial de redução da atmosfera utilizada, maior a concentração de Ce3+ no material. Com o aumento da concentração de Ce3+ um aumento no tamanho médio de grãos foi verificado. Uma diminuição na condutividade elétrica total, intra e intergranular foram determinadas para as amostras sinterizadas em atmosferas redutoras.The effects of the sintering atmosphere and initial particle size on the sintering of ceria containing 10 mol% gadolinia (GdO1.5) were systematically investigated. The main physical parameter was the specific surface area of the initial powders. Nanometric powders with three different specific surface areas were utilized, 210 m2/g, 36,2 m2/g e 7,4 m2/g. The influence on the densification, and micro structural evolution were evaluated. The starting sintering temperature was verified to decrease with increasing on the specific surface area of raw powders. The densification was accelerated for the materials with smaller particle size. Sintering paths for crystallite growth were obtained. Master sintering curves for gadolinium-doped ceria were constructed for all initial powders. A computational program was developed for this purpose. The results for apparent activation energy showed noticeable dependence with specific surface area. In this work, the apparent activation energy for densification increased with the initial particle size of powders. The evolution of the particle size distributions on non isothermal sintering was investigated by WPPM method. It was verified that the grain growth controlling mechanism on gadoliniadoped ceria is the pore drag for initial stage and beginning of intermediate stage. The effects of the sintering atmosphere on the stoichiometry deviation of ceria, densification, microstructure evolution, and electrical conductivity were analyzed. Inert, oxidizing, and reducing atmospheres were utilized on this work. Deviations on ceria stoichiometry were verified on the bulk materials. The deviation verified was dependent of the specific surface area and sintering atmosphere. Higher reduction potential atmospheres increase Ce3+ bulk concentration after sintering. Accelerated grain growth and lower electrical conductivities were verified when reduction reactions are significantly present on sintering.
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Silva, Selma Luiza [UNESP]. "Cinética de sinterização do combustível nuclear 'UO IND. 2.'7%'Gd IND.2''O IND. 3': cálculo da curva mestre de sinterização." Universidade Estadual Paulista (UNESP), 2010. http://hdl.handle.net/11449/99732.
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silva_sl_me_bauru.pdf: 3711265 bytes, checksum: eb24a775c76173627880925720fa6766 (MD5)O processo de sinterização de pastilhas de 'UO IND. 2.'7%'Gd IND.2''O IND. 3' tem sido investigado por muito tempo devido à sua importância na indústria nuclear e ao seu comportamento complexo durante o adensamento. Vários pesquisadores tentaram explicar este comportamento utilizando uma abordagem fenomenológica. Ainda que com algum sucesso, o comportamento na sinterização é difícil de ser previsto. A densidade final e a microestrutura da pastilha sinterizada dependem das propriedades dos pós de partida, do perfil térmico, da composição da atmosfera, da presença de aditivos, entre outras variáveis. Uma abordagem diferente do problema supera esta dificuldade com a introdução do conceito da Curva Mestre de Sinterização - CMS. A CMS do combustível nuclear 'UO IND. 2.'7%'Gd IND.2''O IND. 3' foi levantada utilizando dados de dilatometria obtidos com a taxa de aquecimento constante. Este desenvolvimento foi realizado para prever e controlar a evolução da densidade durante a etapa de sinterização. As amostras foram produzidas através da mistura do pós de 'UO IND. 2' e 'Gd IN> 2''O IND. 3', compactadas e sinterizadas em um dilatômetro a 2023 k, com diferentes taxas de aquecimento na faixa de 5 a 45 'Kmin. POT. -1', sob atmosfera de 'H IND. 2'. Com base no conceito da CMS, a previsão do adensamento foi realizada e uma boa concordância entre os valores previstos e experimental foi verificada. Foi demonstrado que o conceito da CMS pode ser utilizado para planejar um perfil de temperatura adequado, visando uma densidade final desejada, mesmo para sistemas com reações mais complexas como o 'UO IND. 2.'7%'Gd IND.2''O IND. 3'. A energia de ativação aparente do processo de sinterização pode ser estimada por este método.
The sintering process of the 'UO IND. 2.'7%'Gd IND.2''O IND. 3' system has been investigated for a long time due to its economical importance to the nuclear industry and complex behavior during densification. Most researchers tried to describe and explain it using a phenomenological approach. Even though some light has been shed on the matter, the system sintering behavior is still very difficult to predict. The final density and microstructure of the sintered body is strongly dependent on properties of raw powders, temperature profile,, atmosphere composition, presence of sintering additives, among other process variables. A different approach to the problem overcame this difficulty by introducing the concept of the Master Sintering Curve - MSC. The MSC of the 'UO IND. 2.'7%'Gd IND.2''O IND. 3' nuclear fuel was constructed using constant heating rate dilatometry data. This development was carried out to predict and control the evolution of the density during the sintering path. The samples were produced from a dry misture of UO IND. 2' and 2' e 'Gd IN> 2''O IND. 3' powders, pressed into compacts and sintered in a dilatometer up to 2023 K with different heating rates from 5 to 45 'Kmin. POT. -1', under a 'H IND. 2' atmosphere. Based on the MSC concept, the prediction of pellet densification was performed and it was observed a good agreement between the experimental and the predicted values. It was demonstrated that the MSC approach can be used to desing a suitable sintering temperature profile in order to obtain a desidered final density, even for reacting systems such as the 'UO IND. 2.'7%'Gd IND.2''O IND. 3', where the second phase should mostley get into solution. The apparent activation energy of sintering process could also be estimated by this method.
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Pouchlý, Václav. "Slinování pokročilých keramických materiálů." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-234142.
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Sintering is a one of the key step in a processing of bulk ceramic materials. New sintering methods were invented in the last years. These new sintering methods, according to their authors, can be used for obtaining finer final microstructure of ceramics only by modifying the heating schedule. This work is focused on an influence of the Two Step Sintering method on the final microstructure for oxide ceramics. Obtained experimental results have shown that the effectivity of the Two Step Sintering method is rising with crystallographic symmetry of used material. Thesis is also focused on a high-temperature dilatometry and concept of the Master Sintering Curve. This concept was used for calculation of the activation energy of sintering and finding different sintering mechanisms acting in the intermediate and final stage of sintering. Activation energy of sintering was compared with activation energy of grain growth with target to find the kinetic window. Kinetic window can allow a sintering without a grain growth. Master Sintering Curve method was also used in a pressure assisted unconventional sintering technique Spark Plasma Sintering. Master Sintering Curve applied to a Spark Plasma Sintering technique reveals and quantified different sintering mechanisms acting in Spark Plasma Sintering. These findings led to preparation of transparent tetragonal ZrO2.
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Uccellatori, Martina. "Modelli particellari per lo studio delle miscele bituminose." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5423/.
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Marashdeh, Wajeeh. "Relaxation Behavior and Electrical Properties of Polyimide/Graphene Nanocomposite." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595850361812632.
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Al, Khaddour Samer. "Fracture Behaviour of Steels and Their Welds for Power Industry." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-263409.
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Práce byla zaměřena na ověření platnosti koncepce master křivky pro hodnocení heterogenních svarových spojů, resp. teplotně stárnutých svarů. Současně bylo cílem disertace vyvinout kvantitativní model pro predikci referenční teploty lokalizující tranzitní oblast na teplotní ose za použití dat získaných z tahové zkoušky, a to za použití metody umělých neuronových sítí. Studie je současně zaměřena na heterogenní svarový spoj připravený tavným svařováním. Je zacílena na hodnocení lomového chování v tranzitní oblasti nejméně odolné části svaru, tj. tepelně ovlivněné zóny ferritické oceli v blízkosti zóny natavení s vysokolegovaným materiálem. Pro predikci referenční teploty master křivky je použita zmíněná metoda neuronových sítí, a to za použití dat z tahových zkoušek a měření tvrdosti. Predikovaná referenční teplota byla ověřována na základě výsledku experimentálních měření. Vytvoření modelu za použití neuronových sítí vyžaduje dostatečné množství dat a není vždy snadno tuto podmínku splnit. V případě sledovaného problému to znamenalo použití dat z dostatečně věrohodných zdrojů (skupiny Křehký lom ÚFM AVČR) a se známou metalurgickou historií. Smysl práce je tak možno spatřovat ve vývoji modelu neuronové sítě, která bude dostatečně přesně predikovat referenční teplotu. Celkově byla pro tyto účely použita data z 29 nízkolegovaných ocelí. Pro účely vývoje byly použity kromě hladkých zkušebních tyčí, rovněž tahové zkoušky s obvodovým vrubem testované při kritické teplotě křehkosti (mez makroplastických deformací) a při teplotě pokojové. Při tvorbě modelu byla postupně v různých kombinacích využita všechna data z uvedených zkoušek. Studie ukázala, že referenční teplota charakterizující tranzitní chování lomové houževnatosti oceli s převažující feritickou strukturou je jedinečným parametrem predikovatelným na základě vybraných charakteristik tahových zkoušek.
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Calamelli, Filippo. "Studio reologico di mastici per miscele di conglomerato bituminoso drenante contenente polverino di gomma da pfu." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
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Le prestazioni meccaniche di una miscela di conglomerato bituminoso dipendono principalmente dai materiali che la compongono e dalla loro interazione. La risposta tenso-deformativa delle sovrastrutture stradali è strettamente legata al comportamento reologico del legante bituminoso e dalla sua interazione con lo scheletro litico. In particolare nelle pavimentazioni drenanti, a causa dell’elevato contenuto di vuoti, il legame che si crea tra il legante (mastice bituminoso) e l’aggregato è molto forte, per questo motivo è importante migliorarne le prestazioni. Additivando il mastice con polverino di gomma da PFU (pneumatici fuori uso), non solo si migliorano prestazioni, resistenza alle deformazioni permanenti ed elastoplasticità del materiale, ma si sfruttano anche materiali di recupero, portando vantaggi anche dal punto di vista ambientale.
In quest’ottica la ricerca effettuata nella tesi si pone come obiettivo l’analisi reologica e lo studio di mastici additivati con polverino di gomma ricavato da PFU, per la realizzazione di conglomerati bituminosi drenanti. In particolare, partendo da un bitume di base, sono stati preparati due mastici: il primo ottenuto miscelando bitume modificato e filler calcareo, il secondo aggiungendo al precedente anche il polverino di gomma. Tale studio è stato eseguito mediante l’utilizzo del DSR (Dynamic Shear Rheometer – UNI EN 14770), con il quale sono state affrontate tre prove:
Amplitude Sweep test, per la valutazione del valore di deformazione di taglio γ entro il quale il materiale si mantiene all’interno del campo di viscoelasticità lineare (Linear visco-elasticity, LVE);
Frequency Sweep test, per l’estrapolazione delle master curves;
Multiple stress Creep Recovery, per valutare la resistenza del materiale alle deformazioni permanenti. Dall’analisi dei dati è stato possibile definire il comportamento reologico di entrambi i mastici e, in seconda analisi, confrontarne le caratteristiche e le prestazioni.
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Martelli, Luca. "Studio delle proprietà reologiche di leganti bituminosi modificati ad "alta lavorabilità" mediante Dynamic Shear Rheometer." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amslaurea.unibo.it/2009/.
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Guimarães, Valdir Alves. "Determinação da temperatura de referência T0 da curva mestre na região de transição dúctil-frágil de aços ARBL /." Guaratinguetá : [s.n.], 2006. http://hdl.handle.net/11449/116078.
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Resumo: Materiais estruturais utilizados no projeto de equipamentos e instalações industriais podem apresentar mudança de seu comportamento à fratura quando se varia a temperatura. Este tipo de comportamento caracteriza-se pela existência de uma curva de transição, onde 3 regiões ficam bem definidas: os patamares inferior e superior e a região de transição. Na região de transição, os resultados experimentais apresentam alto espalhamento e são bastante dependentes da geometria ensaiada. Para solucionar este problema, foi desenvolvido um modelo analítico experimental, que resultou na edição da norma ASTM E1921-97. O trabalho inclui um estudo da influência de diversas rotas de tratamentos térmicos aplicadas em um aço 4130 utilizado pela indústria aeronáutica, um aço de qualidade API utilizado pela indústria petrolífera e um aço da classe A516 atualmente utilizado pela indústria nacional de vasos de pressão, na microestrutura, propriedades mecânicas de tração e tenacidade à fratura. Os resultados mostraram que o aço 4130 A450, apresentou a melhor correlação entre resistência e tenacidade entre as microestruturas pesquisadas. Este comportamento deve estar associado a rota de tratamento térmico aplicada a esta condição. O tratamento de austêmpera possibilita a formação de bainita que, tradicionalmente é conhecida por apresentar elevados valores de tenacidade. O método proposto pela ASTM pode ser considerado viável para as diversas microestruturas pesquisadas ampliando a aplicação da metodologia que recomenda o ensaio apenas para aços ferríticos. No entanto, a metodologia da Curva Mestra em materiais tratados termicamente deve ser conduzida de forma a se estabelecer parâmetros que considerem as modificações microestruturais sofridas pelo material.Abstract: Structural materials used in industrial equipments design can change fracture behavior when the temperature is varied. This type of behavior is characterized by the existence of a transition curve, where 3 areas are well defined: inferior and superior landings and the ductile brittle transition. In ductile brittle transition, experimental results present high scatter and depend highly of specimen geometry. In order to solve this problem, an analytical experimental model was developed, resulting in ASTM E1921-97 standard edition. This work includes the influence of several heat treatments analysis applied in a 4130 steel used by the aeronautical industry, a API X70 steel used by the line pipe industry and a ASTM A516 steel used by pressure vases national industry, where it was analyzed the influence in the microstructure, mechanical properties and fracture toughness. The results showed that the 4130 A450 steel presented the best correlation between resistance and toughness among the researched microstructures. This behavior should be associated with the heat treatment route applied. The isothermal quenching treatment makes possible bainite formation which, traditionally it is known by its high toughness values. The methodology proposed by ASTM is considered viable for the several researched microstructures enlarging the application of the methodology that just recommends the rehearsal for ferritics steels. However, Master Curve methodology in heat treated materials must have some parameters settling down considering the microstructure modifications suffered by the material.
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Julian, Michael Robert. "Material characterization of viscoelastic polymeric molding compounds." Connect to resource, 1994. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1137616726.
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Thesis (M.S.)--Ohio State University, 1994.Advisors: Vernal H. Kenner and Carl H. Popelar, Dept. of Engineering Mechanics. Includes bibliographical references (leaf 106). Available online via OhioLINK's ETD Center
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Runge, Annette. "Die Genauigkeit der menschlichen Hand im Vergleich mit einem Mikromanipulator- präklinische Evaluation für die Ohrchirurgie." Doctoral thesis, Universitätsbibliothek Leipzig, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-90122.
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Manual accuracy in microsurgery is reduced by tremor and limited access. A surgical approach through the middle ear also puts delicate structures at risk, while the surgeon is often working at an unergonomic position. At this point a micromanipulator could have a positive influence. A system was developed to measure “working accuracy”, time and precision during manipulation in the middle ear. 10 ENT- surgeons simulated a perforation of the stapedial footplate on a modified 3D print of a human skull in a mock OR. Each trial was repeated more than 200 times aiming manually and using a micro-manipulator. Data of over 4000 measurements was tested and graphically processed. Work strain was evaluated with a questionnaire. Accuracy for manual and micromanipulator perforation revealed a small difference. Learning curves showed a stronger decrease both in deviation and time when the micromanipulator was used. Also a lower work strain was apparent. The micromanipulator has the potential as an aiding device in ear surgeryDie manuelle Genauigkeit in der Mikrochirurgie wird duch Tremor und limitierten Zugang eingeschränkt. Ein chirurgischer Eingriff am Mittelohr birgt außerdem ein Verletzungspotential für empfindliche anatomische Strukturen. Überdies ist die Sitzposition des Operateurs oft unergonomisch. Ein neuartiger Mikromanipulator kann auf diese Faktoren einen positiven Einfluss haben. Eine spezielle Software wurde entwickelt und Genauigkeit, Zeit und Präzision bei einem Eingriff am Mittelohr zu bestimmen. 10 Kopf- Hals- Chirurgen simulierten die Perforation der Steigbügelfußplatte an einem 3D Modell eines menschlichen Schädels in einem Demonstrations- OP. Jeder Versuch wurde mehr als 200 mal zunächst manuell und später mit Hilfe des Mikromanipulators wiederholt. Die Daten von mehr als 4000 Messversuchen wurden getestet und grafisch dargestellt. Die Arbeitsbelastung wure mittels eines Fragebogens evaluiert. Manuelle und mikromanipulatorgestütze Genauigkeit zeigten einen signifikanten, jedoch ,absolut betrachtet,sehr geringen Unterschied der Genauigkeit. Die Lernkurven zeigten einen steileren Verlauf sowohl im Hinblick auf Genauigkeit als auch Versuchszeit, wenn der Mikromanipulator zur Anwendung kam. Weiterhin war eine geringere Arbeitsbelastung zu erkennen. Der Mikromanipulator birgt Potential als kompaktes Hilfsmittel für die Ohrchirurgie
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Baloochestani, Farshad. "Estimation of Hydraulic Properties of the Shallow Aquifer System for Selected Basins in the Blue Ridge and the Piedmont Physiographic Provinces of the Southeastern U.S. Using Streamflow Recession and Baseflow Data." Digital Archive @ GSU, 2008. http://digitalarchive.gsu.edu/geosciences_diss/2.
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The objectives of this research are to measure the aquifer properties (S, T, and K) of selected watersheds delineated to the U.S. Geological Survey gauging stations using streamflow recession and baseflow data and to describe the relations among the properties of shallow aquifers and the physical properties of the basins, such as slope, regolith type and thickness, and land use type. Geographic Information System (GIS) techniques are utilized to investigate critical physiographic controls on transmissivity and storage coefficients on a regional basis. Moreover, the effect of evapotranspiration on recession index is illustrated. Finally, a detailed quantitative comparison of results for the Piedmont and the Blue Ridge Physiographic Provinces in southeast of the U.S. is provided. Recession index, annual groundwater recharge, and annual baseflow data were obtained from 44 USGS-gauging stations with drainage areas larger than 2 (mi2) and less than 400 (mi2). These gauging stations are located in Georgia and North Carolina. Analyses of data focused on GIS techniques to estimate watershed parameters such as total stream length, drainage density, groundwater slope, and aquifer half-width. The hydraulic diffusivity, transmissivity, and storage coefficient of watersheds were computed using hydrograph techniques and the Olmsted and Hely, and Rorabaugh mathematical models. Median recession index values for the Blue Ridge and Piedmont Provinces are 87.8 and 74.5 (d/log cycle), respectively. Median areal diffusivity values for the Blue Ridge and Piedmont are 35,000 and 44,200 (ft2/d), respectively. Median basin-specific estimates of transmissivity for basins in the Blue Ridge and Piedmont are 150 and 410 (ft2/d), respectively. The large values of transmissivity obtained for the Piedmont regolith may be attributed to the thick regolith, low values of basin relief, and voids that develop as a result of fracturing, foliation, weathering, and fractured quartz veins in the saprolite. Median basin-specific estimates of storage coefficient for basins in the Blue Ridge and Piedmont are 0.005 and 0.009, respectively. In general, the results from this study reveal great differences in basin-specific hydraulic parameters of the regolith material within the Piedmont compared to that of the Blue Ridge Physiographic Province.
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Mendes, Paulo Gedeão. "ESTUDO DA CINÉTICA DE SINTERIZAÇÃO EM SISTEMAS NANOPARTICULADOS DE SnO2." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2009. http://tede2.uepg.br/jspui/handle/prefix/1443.
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Previous issue date: 2009-08-21Several synthesis methods exist for ceramic materials. According to the method of synthesis used to prepare oxide materials different morphologic and microstructural properties can be obtained. This work consisted of studying the Co-doped tin dioxide powders synthetized by microwave-assisted hydrothermal synthesis (MAHS) and the results were compared to powders synthesized by Pechini method. Powders synthesized by MAHS presented size of particles in the order of 5 nm while the size of particles obtained by Pechini was about five times greater. Besides the characterization of those materials in the powder form, the material was compacted and sintered. Sintering at different constant hating rates of constant heating allowed the calculation of the apparent global energy of sintering using the master sintering curve model. The material synthesized by MAHS presented a smaller apparent global energy of sintering than that obtained by Pechini route, and in the same proportion of their size differences. The results of this work lead to the conclusion that the sintering process and the saturation of dopants are strongly influenced by the particle size of starting powders.
Vários são os métodos de síntese dos materiais cerâmicos. Conforme o método de síntese utilizado para preparar materiais óxidos, diferentes serão suas propriedades morfológicas e microestruturais. Este trabalho consistiu em estudar o dióxido de estanho dopado com óxido de cobalto a partir da síntese de hidrotermalização assistida por micro-ondas (HTMW) e os resultados foram comparados aos da síntese via método Pechini. Pós sintetizados via HTMW apresentaram tamanho de partículas da ordem de 5 nm enquanto via Pechini em torno de cinco vezes maior. Além da caracterização desses materiais na forma de pó, o material foi compactado e sinterizado em dilatômetro. A sinterização a partir de diferentes taxas de aquecimento constante tornou possível o cálculo da energia global aparente de sinterização a partir do modelo da curva mestre de sinterização. O material sintetizado via HTMW apresentou energia global aparente de sinterização menor que o sintetizado via Pechini, na mesma proporção de suas diferenças de tamanho. Assim com este trabalho conclui-se que o processo de sinterização e a saturação de dopantes são fortemente influenciados pelo tamanho de partícula do pó de partida.
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Václavík, Martin. "Predikce teplotní závislosti lomové houževnatosti." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231943.
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The thesis is focused on the prediction of the fracture toughness temperature dependence through a universal curve of fracture toughness (also known as the master curve). To determine the parameters of the universal curve of fracture toughness, values acquired from the measurement results of fracture toughness and tensile tests of structural steel P91 are used. The theoretical part is based on a summary of the relevant information from the field of fracture mechanics and brittle-ductile fracture behavior of steels that are important for the understanding of fracture-strain response of materials depending on load conditions. The experimental part of the thesis contains the results from practical measurements and analyses, which were used for determining the parameters of a universal curve of fracture toughness as well as for the evaluation of fracture behavior and description of the impact of structural parameters on this behavior in case of steel P91.
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Shrestha, Alina. "Fatigue Testing and Data Analysis of Welded Steel Cruciform Joints." ScholarWorks@UNO, 2013. http://scholarworks.uno.edu/td/1670.
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In this study, ABS Publication 115, “Guidance on Fatigue Assessment of Offshore Structures” is briefly reviewed. Emphasis is on the S-N curves based fatigue assessment approach of non-tubular joints, and both size and environment effects are also considered. Further, fatigue tests are performed to study the fatigue strength of load-carrying and non-load-carrying steel cruciform joints that represent typical joint types in marine structures. The experimental results are then compared against ABS fatigue assessment methods, based on nominal stress approach, which demonstrates a need for better fatigue evaluation parameter. A good fatigue parameter by definition should be consistent and should correlate the S-N data well. The equivalent structural stress parameter is introduced to investigate the fatigue behavior of welded joints using the traction based structural stress approach on finite element models of specimens, and representing the data as a single Master S-N curve.
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Ferreño, Blanco Diego. "Integridad estructural de vasijas nucleares en base a la curva patrón obtenida mediante probetas reconstruidas." Doctoral thesis, Universidad de Cantabria, 2008. http://hdl.handle.net/10803/10603.
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En esta tesis se ha caracterizado el acero, virgen e irradiado, de la vasija de una central nuclear española actualmente en servicio, en la región de temperaturas conocida como Zona de Transición Dúctil-Frágil. Para ello, se han ensayado probetas propias de la Mecánica de Fractura, reconstruidas a partir de mitades de probetas de impacto previamente ensayadas. Para describir la tenacidad a fractura en la Zona de Transición se ha empleado el modelo de la Curva Patrón.Finalmente, se ha analizado el impacto del procedimiento de caracterización y del modelo de la Curva Patrón sobre la Integridad Estructural de la vasija, comparando sus predicciones con las que se obtienen de aplicar los procedimientos convencionales que contempla la normativa vigente, representada por el Código ASME. En esta comparación se ha hecho uso del procedimiento FITNET de Integridad Estructural.In this thesis, the steel, virgin and irradiated, from the vessel of a Spanish Nuclear Plant currently operating, has been characterized in the range of temperatures known as Ductile to Brittle Transition Region. For this purpose, Fracture Mechanics specimens, reconstituted from halves of impact specimens previously broken, have been tested. To describe fracture toughness in the Transition Region, the Master Curve method has been used.Eventually, the influence of the characterization procedure together with the Master Curve method on the Structural Integrity of the vessel has been analyzed, comparing their predictions with those coming from applying conventional procedures proposed by the current regulations, represented by the ASME Code. In this comparison, the FITNET Structural Integrity procedure has been used.
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Shaheen, Ehab T. "Long Term Performance of Corrugated HDPE Pipes Produced with Post-Consumer Recycled Materials Under Constant Deflection." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1541422245636659.
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Barbier, Thibaut. "Modélisation de la consommation électrique à partir de grandes masses de données pour la simulation des alternatives énergétiques du futur." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEM032/document.
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L’évolution de la consommation électrique est un point clé pour les choix à venir, tant pour les moyens de production d’électricité, que pour le dimensionnement du réseau à toutes ses échelles. Aujourd’hui, ce sont majoritairement des modèles statistiques basés sur les consommations passées et des tendances démographiques ou économétriques qui permettent de prédire cette consommation. Dans le contexte de la transition énergétique, des changements importants sont en cours et à venir, et la consommation future ne sera certainement pas une continuation des tendances passées. Modéliser ces changements nécessite une modélisation fine de type bottom-up de chaque contributeur de la consommation électrique. Ce type de modèle présente des challenges de modélisation, car il nécessite un grand nombre de paramètres d’entrée qui peuvent difficilement être renseignés de façon réaliste à grande échelle. En même temps, les données et informations de tout type n’ont jamais été autant disponibles. Cela représente à la fois un atout pour la modélisation, mais aussi une difficulté importante notamment à cause de l’hétérogénéité des données. Dans ce contexte, cette thèse présente une démarche de construction d’un simulateur de consommation électrique bottom-up capable de simuler différentes alternatives énergétiques à l’échelle de la France. Un travail de recensement, de classification et d’association des bases de données pour expliquer la consommation électrique a d’abord été mené. Ensuite, le modèle de consommation électrique a été présenté ; il a été validé et calibré sur une grande quantité de mesures de consommation électrique des départs HTA fournie par Enedis. Ce modèle a enfin pu être utilisé pour simuler différentes alternatives énergétiques afin d’aider au dimensionnement du réseau de distributionFuture trend of electricity demand is a key point for sizing both the electricity network and the power plants. In order to forecast future electricity demand, current models mostly use statistical approaches based on past demand measurements and on demographic and economic trends. Because of current context of energy transition which comes along with important changes, future electricity demand is not expected to be similar to past trends. Modeling these changes requires a bottom-up modeling of each contributor to electricity demand. This kind of model is challenging because of the large number of input data required. At the same time, data and information are more and more available. Such availability can be considered both as an asset for modeling and as an important issue because of data heterogeneity. In this context, this dissertation offers an approach to build a bottom-up load curve simulator which enables to simulate prospective scenarii at the scale of France country. Firstly, an assessment, classification, and matching of the large databases explaining the electricity demand have been performed. Then, the electricity demand model has been presented. It has been validated and calibrated on Enedis’ large volumes of electricity demand measurements of medium voltage feeders. Finally, this model has been used to simulate several prospective scenarii in order to improve the electricity distribution network sizing
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Verdade, Lucas Lauer. "Avaliação do uso de um polietileno de alta densidade e baixo peso molecular oxidado como agente de compatibilização em asfalto modificado com copolímero SBS." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/18/18143/tde-01102015-093027/.
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O copolímero SBS é o aditivo mais empregado mundialmente na modificação de ligantes asfálticos, por melhorar diversas de suas características. Um dos principais problemas deste tipo de formulação é a separação de fases, que pode ser minimizada com a incorporação de aditivos. Um novo polietileno de alta densidade e baixo peso molecular oxidado (com denominação comercial TITAN 9686) foi utilizado nesta pesquisa, com o objetivo de testar a hipótese de que a adição de proporções adequadas deste aditivo possa melhorar as características reológicas do asfalto+SBS. O experimento laboratorial foi delineado com base na técnica de experimentos com misturas, englobando um total de nove formulações compostas com asfalto, SBS e TITAN. O teor de SBS variou entre 0 e 5% em peso e o de polietileno variou entre 0 e 2% em peso. Foi utilizado óleo aromático no teor de 4% em peso para todas as nove misturas. As misturas foram analisadas em três condições de envelhecimento: virgem, curto prazo (na estufa RTFO) e longo prazo (na estufa PAV). Foram realizados os seguintes ensaios reológicos: (i) de cisalhamento em regime oscilatório em diferentes condições de temperatura e frequência (para medida do módulo complexo e do ângulo de fase, usados na determinação do grau de desempenho, no cálculo dos parâmetros G*/sen(δ) e G*.sen(δ) e na construção de curvas-mestre), (ii) de viscosidade Brookfield, (iii) de fluência e recuperação sob múltiplas tensões (para medida do percentual de recuperação e da compliância não-recuperável), (iv) de varredura de amplitude linear (para cálculo do parâmetro a f e para ajuste do modelo de fadiga) e (v) de estabilidade à estocagem. Acerca das características escolhidas para mensurar a melhora ou piora das propriedades das misturas asfalto+SBS com a adição de TITAN, podem ser feitas as seguintes observações: (i) a estabilidade à estocagem é melhorada com a adição de TITAN, em particular no teores entre 1 e 2%; (ii) a sensibilidade ao envelhecimento tanto a curto quanto a longo prazos diminui com a adição de TITAN; (iii) a adição de TITAN aumenta a resistência à deformação permanente, à luz dos parâmetros Jnr e R e aumenta a sensibilidade dos ligantes asfálticos modificados com SBS a mudanças bruscas nos níveis de tensão aplicados; e (iv) a adição de TITAN contribui com o aumento da resistência à fadiga, à luz dos parâmetros Nf , a baixos níveis de deformação, e af , e a prejudica reduzindo o parâmetro Nf a altos níveis de deformação e aumentando a temperatura crítica de fadiga ou o parâmetro G*.sen(δ). Tendo por base estas evidências, é possível concluir que a adição de TITAN, em linhas gerais, melhorou a estabilidade dos ligantes asfálticos modificados com até 5,0% de SBS. Com base nas análises realizadas, é possível afirmar que teores da ordem de 1 a 2% de TITAN, para teores de SBS entre 3,0 e 5,0%, são recomendáveis, à luz das propriedades, índices e parâmetros analisados neste trabalho.The SBS copolymer is the most widely used additive in asphalt binder modification, since it enhances many of the properties of the original material. A critical problem that arises from this type of modification is phase separation, which can be minimized by adding other modifiers to the formulation. A new oxidized, high-density polyethylene with low molecular weight (commercial designation of \"TITAN 9686\") was used in the study with the purpose of verifying the hypothesis that the addition of suitable contents of this modifier can improve the rheological properties of the SBS-modified binder. The laboratory matrix of formulations was based on the experiments with mixtures, and nine types of materials were prepared with asphalt binder, SBS and TITAN. The SBS contents ranged from 0 to 5% by weight, whereas the polyethylene contents ranged from 0 to 2% by weight. These formulations also contained 4% of aromatic oil by weight. Three aging conditions were selected: unaged, short-term aged in the rolling thin-film oven (RTFO) and long-term aged in the pressurized aging vessel (PAV). The following tests were carried out: (i) dynamic oscillatory shear at different temperatures and frequencies of loading for the determination of the complex modulus, the phase angles and the master curves, as well as the performance grades and the numerical values of the parameters G*/sin(δ) and G*.sen(δ); (ii) rotational viscosity; (iii) creep and recovery at multiple stress levels for the determination and the percent recovery and the nonrecoverable compliance; (iv) linear amplitude sweep, in order to calculate the parameter a f and fit the fatigue model to the data; and (v) storage stability. With respect to the characteristics used in the evaluation of the properties of the AC+SBS mixtures after the addition of TITAN, the following observations can be made: (i) storage stability is improved when TITAN is added to the formulation, especially at contents ranging from 1 to 2%; (ii) the sensitivity to the short-term and long-term aging processes decreased with the incorporation of TITAN; (iii) the changes in the R and the Jnr values indicate that the addition of TITAN makes the asphalt binder more resistant to rutting, and also increases the sensitivity of the SBS-modified binders to sudden increases in the stress level; and (iv) the presence of TITAN in the material leads to an increase in the fatigue resistance as based on the parameters Nf and af at low strain levels and the increases in the critical fatigue temperature and the parameter G*.sen(δ). With reference to these evidences, it is possible to conclude that the addition of TITAN generally improves the storage stability of the SBS-modified binders with no more than 5% of copolymer by weight. Based on the results of the present study, it is possible to say that percentages between 1 and 2% of TITAN by weight are recommended for SBS contents between 3 and 5% by weight.
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Savioli, Rafael Guimarães. "Estudo experimental do comportamento à fratura frágil em aços estruturais ferríticos e aplicações à determinação da curva mestra." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3135/tde-23062016-074259/.
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Este trabalho apresenta uma investigação experimental sobre o comportamento à fratura frágil de aços estruturais ferríticos, ASTM A285 Gr C e ASTM A515 Gr 65. Os resultados deste trabalho ampliam a base de dados de propriedades mecânicas utilizadas nas análises de integridade de estruturas pressurizadas tais como vasos de pressão e tanques de armazenamento construídos com esta classe de material. O trabalho tem por objetivo também avaliar a aplicabilidade de corpos de prova de dimensões reduzidas, PCVN, na determinação da temperatura de referência, T0, por meio da metodologia da Curva Mestra, a qual define a dependência da tenacidade à fratura do material em função da temperatura. Os ensaios de tenacidade à fratura foram conduzidos utilizando-se corpos de prova solicitados em flexão três pontos com geometria SE(B), PCVN e PCVN com entalhe lateral, extraídos de chapas laminadas. Os resultados dos ensaios foram obtidos em termos de integral J no momento da instabilidade, denotados por Jc. Dados adicionais de resistência à tração e de Impacto Charpy convencional também foram obtidos para caracterizar o comportamento mecânico dos aços utilizados. Os resultados mostraram uma forte influência da geometria dos corpos de prova sobre os valores de Jc, evidenciada pela grande variação nos valores de tenacidade à fratura.This work presents an experimental investigation on the cleavage fracture behavior of structural ferritic steels, ASTM A285 Grade C and ASTM A515 Grade 65. One purpose of this study is to enlarge a previously reported work on mechanical and fracture properties for this class of steel to provide a more definite database for use in structural and defect analyses of pressurized components, including pressure vessels and storage tanks. Another purpose is to address the applicability of Precracked V-notch Charpy specimens to determine the reference temperature, T0, derived from the Master Curve Methodology which defines the dependence of fracture toughness with temperature for the tested material. Fracture toughness testing conducted on single edge bend specimens in three-point loading (SE(B), PCVN Plain Side and PCVN Side Grooved) extracted from laminated plates provides the cleavage fracture resistance data in terms of the J-integral at cleavage instability, Jc. Additional tensile and conventional Charpy tests produce further experimental data which serve to characterize the mechanical behavior of the tested materials. The results reveal a strong effect of specimen geometry on Jc values associated with large scatter in the measured values of cleavage fracture toughness.
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Ribeiro, Margareth Jacobi. "Estudo sobre a implementação do curso de mestrado na Escola de Direito do Rio de Janeiro da Fundação Getulio Vargas." reponame:Repositório Institucional do FGV, 2012. http://hdl.handle.net/10438/10443.
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This dissertation proposes to examine the central issues related to the elaboration and implementation of an academic (stricto sensu) master program. The opening of an academic master program in Law by FGV DIREITO RIO, focus on Regulatory Law, represents a trademark in innovation and pioneering, since it will be the first program as such to be offered in Brazil. Moreover, it will assist in meeting demand for training of researchers in the State of Rio de Janeiro, which currently has only nine academic (stricto sensu) master programs accredited by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes). The team responsible for drafting the proposal conducted a research on the nine academic master program available, as well as a detailed examination on the basic premises and required features necessary to submit a formal proposal for the opening of a new academic master program respecting the norms and procedures established by the Capes. The preparation of FGV DIREITO RIO`s academic master program proposal was only possible by adjusting it to the policies of its research centers which confirms the preparation of high-level researchers able to associate solid scientific basis to collaborate in the solution of national and global issues. Thus, to achieve these goals, it was also essential to gather efforts from all research centers to provide FGV DIREITO RIO with their expertise and knowledge resulted from their scientific projects under development.
A presente dissertação tem como objetivo oferecer um estudo sobre as questões centrais para a elaboração e implementação de um curso de pós-graduação stricto sensu nível mestrado. A proposta de abertura de um mestrado acadêmico em Direito, com área de concentração em Direito da Regulação pela FGV DIREITO RIO é marca de inovação e pioneirismo, pois será o primeiro a ser oferecido no Brasil. Além disso, auxiliará no atendimento de demanda de formação de pesquisadores no Estado do Rio de Janeiro, que atualmente possui apenas nove programas stricto sensu credenciados pela Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes). A equipe responsável pela elaboração da proposta realizou uma pesquisa sobre os nove cursos de mestrado oferecidos, bem como um detalhado estudo sobre as premissas básicas e as características necessárias para submissão de uma proposta de abertura de mestrado com base nas normas e procedimentos estabelecidos pela Capes. A elaboração da proposta só foi possível por ajustar-se às políticas dos Centros de Pesquisa da FGV DIREITO RIO que corrobora os objetivos de formação de pesquisadores de alto nível, aptos a associar sólida base científica para colaborar na solução das demandas nacionais e globais. Assim, para consecução destes objetivos, foi fundamental a união de esforços dos quatro centros de pesquisa responsáveis por alimentar a Escola com os diversos projetos em desenvolvimento.
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Альристим, М. Х. А., and M. H. A. Alristim. "Влияние мирового нефтяного рынка на экономику Ирака : магистерская диссертация." Master's thesis, б. и, 2020. http://hdl.handle.net/10995/86612.
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The relevance of the research of the topic master's thesis is due to the increasing impact to the fact that Iraq is a vivid example of a resource-dependent country today, which is affected by the resource curse and which faces many problems. The purpose of the research: to assess the impact of the volatility of the global oil market on the economic development of Iraq and determine the prospects for its development. In accordance with the chosen of the purpose of the research is the following tasks in the work: to consider the theoretical aspects of resource-dependent countries and the features of their development; to study the theory of "resource curse" and ways to overcome it; to analyze the world oil market, especially its development and its factors; consider OPEC and its role in regulating the global oil market; to analyze the economic development of Iraq as a resource-dependent country; conduct a SWOT analysis for the economy of Iraq; develop recommendations for the development of the economy of Iraq. The scientific novelty can be attributed to highlighting the factors that make Iraq a resource-dependent country and is leading to the resource curse, as well as conducting a SWOT analysis and highlighting the weaknesses, strengths, threats and opportunities for the economy of Iraq. The practical significance of the research is determined to develop recommendations to help the country find a way out of its resource dependence. The implementation of these recommendations will help improve the situation in Iraq.Ирак на сегодняшний день является ярким примером ресурснозависимой страны, на которую действует ресурсное проклятие и которая сталкивается со множеством проблем. Целью исследования является оценка влияния волатильности мирового рынка нефти на экономическое развитие Ирака и определение перспектив его развития. В соответствии с выбранной целью в работе были поставлены следующие задачи: рассмотреть теоретические аспекты ресурсозависимых стран и особенности их развития; изучить теорию «ресурсного проклятия» и пути его преодоления; проанализировать мировой рынок нефти, особенности его развития и его факторы; рассмотреть ОПЕК и ее роль в регулировании мирового рынка нефти; проанализировать экономическое развитие Ирака как ресурсозависимой страны; провести SWOT-анализ для экономики Ирака; разработать рекомендаций для развития экономики Ирака. К научной новизне можно отнести выделение факторов делающих Ирак ресурснозависимой страной и способствующих ресурсному проклятию, а также проведение SWOT-анализа и выделение слабых, сильных сторон, угроз и возможностей для экономики Ирака. Практическая значимость магистерской работы состоит в разработки рекомендаций, помогающих стране выйти из ресурсной зависимости. Внедрение данных рекомендаций будет способствовать улучшению ситуации в Ираке.
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Costes, Sylvain. "Extension de l'approche par la courbe maitresse de la prédiction des durées de vie de réseaux d'indice complexes inscrits par UV dans les fibres." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00917592.
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L'objectif principal de cette thèse était d'examiner dans quelle mesure il est possible d'étendre l'approche de la courbe maîtresse à des composants complexes afin de déterminer des conditions de déverminage et de réaliser une prédiction de durée de vie en fonction de ces conditions de déverminage. Nous avons considéré la stabilité d'un réseau dit élémentaire (réseau carré, à pas constant et droit) puis le problème de la stabilité (selon des critères spécifiques) des composants complexes: les CDC et les monofiltres GFF. Cette thèse a permis de décrire de façon rigoureuse, puis d'utiliser le cadre de travail VAREPA pour résoudre des problèmes issus de l'industrie de télécoms. A cet effet, des séries d'études de vieillissement accéléré sur des réseaux simples et complexes ont été menées. Un protocole de mesure permettant de déterminer les incertitudes de mesure a été mis au point afin de déterminer de façon fiable des intervalles de confiance sur les prédictions de durée de vie.Nous avons étudié les cinétiques de croissance des réseaux inscrits dans une fibre dédiée à l'inscription des CDC (Coreactive). Cette étude nous a permis de montrer que la réaction prédominante à l'origine des changements d'indice de réfraction est activée par une absorption à 1 photon. D'autre part, nous avons étendu le cadre de travail utilisé pour prédire l'effacement des réseaux (VAREPA) afin de rendre compte de leurs cinétiques d'inscription. Puis nous avons cherché à déterminer les conditions de passivation et à prédire la durée de vie des réseaux déverminés en présence d'hydrogène résiduelle (procédé industriel actuel). Pour cela, nous avons établi la courbe maîtresse de réseaux photoinscrits non déverminés puis nous avons validé les conditions de déverminage et les prédictions de durée de vie en construisant une nouvelle courbe maîtresse sur des réseaux déverminés.Nous avons étudié la stabilité thermique des réseaux inscrits dans une fibre hydrogénée dédiée aux futurs monofiltres GFF dans des conditions d'inscription similaires à celles de ces composants. Nous avons utilisé les courbes maîtresses établies à partir des réseaux élémentaires (mais apodisés) simplement dégazés " à froid " (ici 2jours à 50°C puis 2 jours à 110°C). Puis, nous avons fait vieillir le profil d'indice (cœur et gaine) d'un monofiltre GFF. Puis, nous avons recalculé la réponse spectrale de ce filtre vieilli (e.g. 30jours à 200°C) et nous l'avons comparé à des mesures expérimentales. Cette approche reste générale et permet de changer les conditions de déverminage au besoin. Cette étude nous a permis de mettre en évidence que la stabilité des variations d'indice photo-induites dans le cœur dépend peu de l'amplitude initiale de la modulation pour des valeurs comprises entre quelques 10-5 et 10-3. Du fait de la présence d'une gaine optique fortement photosensible (car fortement dopée en Ge), nous avons établi les courbes maîtresses des variations d'indice photo-inscrites dans le cœur et la gaine optique pour des valeurs allant jusque 10-3 dans le cœur et 3.10-3 dans la gaine. Nous avons ainsi obtenu des courbes maîtresses présentant le même k0 (fréquence d'essai, i.e facteur pré exponentiel) mais dont la forme est légèrement différente. La stabilité des variations d'indice est meilleure dans le cœur (moins dopé en Ge) que dans la gaine photosensible. Dans un second temps, nous avons cherché à déterminer les conditions de passivation et à prédire la durée de vie des réseaux déverminés à partir des réseaux de Bragg qualifiés d'élémentaires. Pour la première fois à notre connaissance, nous avons validé de façon fiable les conditions de passivation et les prédictions de durée de vie en construisant une nouvelle courbe maîtresse sur des monofiltres GFF préalablement déverminés. Conformément à la théorie, cette courbe maîtresse présente le même k0 et une forme similaire à celle établie au moyen de réseaux non déverminés, ce qui valide la fiabilité de nos prédictions.
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Беляев, А. В., and A. V. Belyaev. "Анализ стохастических моделей живых систем с дискретным временем : магистерская диссертация." Master's thesis, б. и, 2020. http://hdl.handle.net/10995/87578.
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Работа содержит исследования трех моделей живых систем с дискретным временем. В первой главе рассматривается одномерная модель нейронной активности, задаваемая кусочно-гладким отображением. Показывается, что в случае одномерного отображения наличие случайного возмущения приводит к появлению всплесков (спайкингу). Исследуются два механизма генерации спайков, вызванных добавлением случайного возмущения в один из параметров. Иллюстрируется, что сосуществование двух аттракторов является не единственной причиной возникновения спайкинга. Для прогнозирования уровня интенсивности шума, необходимого для генерации спайков, применяется метод доверительных областей, который основан на функции стохастической чувствительности. Также находятся основные характеристики межспайковых интервалов в зависимости от интенсивности шума. Вторая глава работы посвящена применению метода функции стохастической чувствительности к аттракторам кусочно-гладкого одномерного отображения, описывающего динамику численности популяции. Первым этапом исследования является параметрический анализ возможных режимов детерминированной модели: определение зон существования устойчивых равновесий и хаотических аттракторов. Для определения параметрических границ хаотического аттрактора применяется теория критических точек. В случае, когда на систему оказывает влияние случайное воздействие, на основе техники функции стохастической чувствительности дается описание разброса случайных состояний вокруг равновесия и хаотического аттрактора. Проводится сравнительный анализ влияния параметрического и аддитивного шума на аттракторы системы. С помощью техники доверительных интервалов изучаются вероятностные механизмы вымирания популяции под действием шума. Анализируются изменения параметрических границ существования популяции под действием случайного возмущения. В третьей главе проводится анализ возможных динамических режимов детерминированной и стохастической модели Лотки-Вольтерры. В зависимости от двух параметров системы строится карта режимов. Изучаются параметрические зоны существования устойчивых равновесий, циклов, замкнутых инвариантных кривых, а также хаотических аттракторов. Описываются бифуркации удвоения периода, Неймарка--Саккера и кризиса. Демонстрируется сложная форма бассейнов притяжения. Помимо детерминированной системы подробно изучается стохастическая, описывающая влияние внешнего случайного воздействия. В случае хаоса дан алгоритм нахождения критических линий, описывающих границу хаотического аттрактора. Опираясь на найденную чувствительность аттракторов, строятся доверительные полосы и эллипсы, позволяющие описать разброс случайных состояний вокруг детерминированного аттрактора.The work contains study of three models of biological systems with discrete time. In the first chapter a one-dimensional model of neural activity defined by a piecewise-smooth map is considered. It is shown that in the case of a one-dimensional model, the presence of a random disturbance leads to a spike generation. Two mechanisms of spike generation caused by the presence of a random disturbance in one of the parameters are investigated. It is illustrated that the coexistence of two attractors is not the only reason of spiking. To predict the level of noise intensity needed to generate spikes, the confidence-domain method is used, which is based on the stochastic sensitivity function. The main characteristics of interspike intervals depending on the intensity of the noise are also described. The second chapter is devoted to the application of the method of the stochastic sensitivity function to attractors of a piecewise-smooth one-dimensional map, which describes the population dynamics. The first stage of the study is a parametric analysis of the possible regimes of the deterministic model: determining the zones of existence of stable equilibria and chaotic attractors. The theory of critical points is used to determine the parametric boundaries of a chaotic attractor. In the case where the system is affected by a random noise, based on the stochastic sensitivity function, a description of the spread of random states around equilibrium and a chaotic attractor is given. A comparative analysis of the influence of parametric and additive noise on the attractors is carried out. Using the technique of confidence intervals, the probabilistic mechanisms of extinction of a population under the influence of noise are studied. Changes in the parametric boundaries of the existence of population under the influence of random disturbance are analyzed. In the third chapter the possible dynamic modes of the Lotka-Volterra model in determi\-nistic and stochastic cases are analyzed. Depending on the two parameters of the system, bifurcation diagram is constructed. Parametric zones of the existence of stable equilibria, cycles, closed invariant curves, and also chaotic attractors are studied. The bifurcations of the period doubling, Neimark--Sacker and the crisis are described. The complex shape of the basins of attraction is demonstrated. In addition to the deterministic system, the stochastic system is studied in detail, which describes the influence of external random disturbance. In the case of chaos, an algorithm for finding critical lines describing the boundary of a chaotic attractor is given. Based on the stochastic sensitivity function, confidence bands and ellipses are constructed to describe the spread of random states around a deterministic attractor.
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Yang, Michael Yichung. "Development of master design curves for particle impact dampers." 2003. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-376/index.html.
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Chen, Ying-Tien, and 陳英田. "Master Sintering Curves and Their Applications of Some Common Oxides Ceramics." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/95337324906986689528.
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碩士國立臺灣大學
地質學研究所
88
Master sintering curve (MSC) is a recently developed model, and is capable of predicting the density variations of ceramic compacts throughout the sintering process. It had been proved earlier that this model worked for simple ceramic material, i.e., alumina. In this study we discovered that the final equations of several solid state sintering models can be separated into two parts on either side of an equal sign, just like in MSC, the one that comprises all geometric terms is ; and another that comprises only the temperature, time, and an apparent activation energy Qa is . Although these sintering models emphasized on different characteristics of sintering process, they appear to have the similar MSC-like relationships hidden inside the mathematical equations. The main work of this study is to establish the MSC of some common ceramic powders, including α-Al2O3, ZnO and TiO2. Using the MSC to analyze the data of different sintering path, we found the best apparent activation energies of α-Al2O3, ZnO and TiO2 were 481 kJ/mol、331 kJ/mol and 365 kJ/mol respectively. The YTZP (yttria tetragonal zirconia polycrystal) powder was also analyzed in this study, and its activation energy is 662 kJ/mol. Using the unique MSC of YTZP, we designed various sintering paths and predicted the densities of samples, which were later confirmed by experiments. We used the binary Al2O3-YTZP system to further investigate the abilities and limitations of MSC. Multi-component system should be more complex on the mass transportation mechanisms because of the existence of many different crystal surfaces and surface energies. Although the two-phase system obviously did not fit to the assumptions of MSC, surprisingly the results show that the MSC can still be applied. Therefore, it is possible that the MSC is a more general analytical method that can be used in more extensive areas; however, further investigations are needed to confirm this conjecture.
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(6400343), Jinsha Li. "Volume Fraction Dependence of Linear Viscoelasticity of Starch Suspensions." Thesis, 2020.
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When starch granules are gelatinized, many complex structural changes occur as a result of large quantity of water being absorbed. The enlargement of granule sizes and the leaching out water-soluble macromolecules contribute to the viscoelasticity. Starch pasting behavior greatly influences the texture of a variety of food products such as canned soup, sauces, baby foods, batter mixes etc. It is important to characterize the relationship between the structure, composition and architecture of the starch granules with its pasting behavior in order to arrive at a rational methodology to design modified starch of desirable digestion rate and texture. Five types of starch used in this study were waxy maize starch (WMS), normal maize starch (NMS), waxy rice starch (WRS), normal rice starch (NRS) and STMP cross linked normal maize starch. Evolution of volume fraction φ and pasting of 8% w/w starch suspension when heated at 60, 65, 70, 75, 80, 85 and 90 °C were characterized by particle size distribution and G’, G” in the frequency range of 0.01 to 10 Hz respectively. As expected, granule swelling was more pronounced at higher temperatures. At a fixed temperature, most of the swelling occurred within the first 5 min of heating. The pastes exhibited elastic behavior with G’ being much greater than G”. G’ increased with time for waxy maize and rice starch at all times. G’ and G’’ were found to correlated only to the temperature of pasting and not change much with the rate of heating. For WMS, WRS and STMP crosslinked NMS, G’ approached a limiting value for long heating times (30 min and above) especially at heating temperatures of 85°C and above. This behavior is believed to be due to the predominant effect of swelling at small times. For normal maize and rice starch, however, G’ reached a maximum and decreased at longer times for temperatures above 80 °C due to softening of granules as evidenced by peak force measurements. For each starch sample, the experimental data of G’ at different heating temperatures and times could be collapsed into a single curve. The limiting value of G’ at high volume fraction was related to granule size and granule interfacial energy using a foam rheology model. The interfacial free energy of granules were obtained from contact angle measurements and was employed to evaluate the limiting G’. The experimental data of G’ for all starches when subjected to different heating temperatures and times were normalized with respect to the limiting value at high volume fractions. The master curve for normalized G’ was employed to predict the evolution of G’ with time for different starches which was found to agree well with experimental data of storage modulus. A mechanistic model for starch swelling that is based on Flory Huggins polymer swelling theory was employed to predict the evolution of volume fraction of swollen granules. The model accounts for the structure and composition of different types of starches through starch-solvent interaction as quantified by static light scattering, gelatinization temperature and enthalpy of gelatinization, porosity and its variation with swelling and crosslinking of starch molecules within the granule from equilibrium swelling. Consequently, one could predict the evolution of texture of these starch suspension from the knowledge of their swelling behavior. Expressing the limiting storage modulus of complete swelling (volume fraction approaching unity) of starch suspension in terms of foam rheology, we were able to normalize the storage modulus of different types of starches with respect to its limiting value which is found to fall into a master curve. This master curve when employed along with the swelling model resulted in the successful prediction of development of texture for different types of starches. The above methodology can quantify the effects of structure and composition of starch on its pasting behavior and would therefore provide a rational guideline for modification and processing of starch-based material to obtain desirable texture and rheological properties.
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Ching-Fenq, Wu, and 吳慶豐. "Master sintering curve study of alumina-based ceramics." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/64386206085423752520.
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碩士國立臺灣大學
地質學研究所
87
Master sintering curve (MSC) model, which circumvents the complicated particle geometric assumptions, is capable of predicting the density of a sintered compact for a given powder and green-body process, regardless of its sintering temperature or rate. When the sintering time-temperature profiles and activation energy are known, the sintered density can be predicted through arbitrary time-temperature path. Once had done two or three preliminary experiments that were used to generate the MSC, then by which one can use as a reference to predict the future sintering results. In this study, three systems — pure -alumina, -alumina doped with 300 ppm MgO, and -alumina doped with 500 ppm TiO2 were used. A set of constant heating rate experiments for each system were carried out, and the results were successfully merged into three distinct MSC’s, each with its sintering activation energy 490 kJ/mol, 680 kJ/mol, and 595 kJ/mol respectively. To further test these MSC’s, five sintering experiments with peculiar heating profile were designed and run. The results showed reasonably match with their corresponding MSC, and proved that indeed the sintering experiments will follow a single MSC, independent of their thermal history. On the effect of the error of the density measurement to MSC, analysis showed the error will not affect activation energy, but will shift the MSC to a parallel new position. Furthermore, using sigmoid curve fitting technique in MSC construction is simpler and more reasonable than the polynomial one used in previous studies.
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Wang, Shao-Yu, and 王紹宇. "Comparison Study of Master Kinetics Curve and Three Kinetic models." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/31888643406368297377.
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碩士國立臺灣大學
地質科學研究所
99
Master kinetics curve (MKC) is a new kinetic model derived from general chemical reaction rate equations and has only been studied for several years. The major difference between the MKC and other kinetic models is that it needs no assumptions regarding kinetic parameters. Instead, the establishment of the MKC is based on real experimental data. Thus, the MKC has several advantages, such as convenient to use, accurate to predict and a variety of potential applications. Previous researches have proved that MKC is capable of studying the kinetics of crystallization, thermal decomposition and sintering. However, some of the researches also showed that the predictions of the MKC, and in particular the parameter “apparent activation energy”, are not identical with the values determined by other kinetic methods. Therefore, it is necessary to study and understand these differences to make MKC into a universal kinetic model. To compare the differences between the MKC and other kinetic models, three different kinetic models were chosen. The three models are the master sintering model (MSC), the Ozawa method and the Avrami equation. MSC is a well-established sintering model in the sintering field; it describes the whole densification process of a sintering. The Ozawa method is a kinetic model which greatly simplifies the determination procedure of kinetic parameters from thermogravimetric research. The Avrami equation is a phase transformation kinetic model which describes the relationship between reaction time and the extent of phase transformation; it is capable of determining the mechanism. In order to acquire enough data and reduce experimental errors, synthetic data and real data from early research are used for comparisons of the different models in this research. The results showed that MKC and MSC have similar behavior in regard to prediction. The term 1/T of MSC introduces small deviations between these two models. If the reaction temperature increases, the deviations become slightly larger; however, these differences do not significantly change the predicted results. The comparison between the MKC and the Ozawa method showed that the data from the 0th order and 1st order reactions can be perfectly merged by MKC’s fitting. However, the 2nd order and 3rd order reactions can only be partially merged by MKC analysis. These results can be explained by the reaction rates: 0th order and 1st order reactions have a slower reaction rate at the initial stage of reaction, and they are the same as an S-curve’s behavior (the S-curve has a slow reaction rate at the initial and final stages of reaction). However, the 2nd and 3rd order reactions have the highest reaction rate at the initial stage of reaction; they obviously differ from the characteristic of an S-curve. Consequently, the MKC cannot analyze all types of reactions by only using an S-shaped curve. Nevertheless, it is possible to merge these reaction data by other shaped curves. The comparison between the MKC and the Avrami equation showed that the data only merged in the middle section of reactions. Predictions made by the MKC at both low and high temperatures are impossible. Data errors, especially the errors of reaction extent, might be the reason for the erroneous predictions. Due to the characteristic of an S-curve, errors of reaction extent might cause significant deviations to both ends of the curve rather than to the middle section. Likewise, these deviations give poor predictions at both low and high temperatures. In this research, 1% to 5% errors were randomly added to three different variables of a MKC, i.e., time, temperature and reaction extent, in order to determine the relative influence of the variables on the models. From the results, we found that reaction extent affects MKC the most because the reaction extent is a parameter directly affecting the data fitting at the y axis. In comparison, time and temperature have to be integrated into the function log(Σ) at the x axis to affect the fitting. Therefore, the reaction extent requires greater accuracy than the other two variables. In addition, we also used a different number of sets of data for the analysis of MKC in order to determine the minimum sets of data required to obtain a reasonable result. It shows that MKC can obtain a reasonable fitting curve by only three sets of data. This result also implies that, regardless of the accuracy of the data, MKC has the capability to describe the general trend of data. Thus it is important to ensure the accuracy of the data. In conclusion, since MKC does not have to determine kinetic parameters and can analyze different reactions by different shaped curves, MKC definitely has the potential to become a universal kinetic model with a variety of applications and still remain convenient to use.
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Chen, Mong-Hsia, and 陳孟霞. "Using Master Curve on the Sintering of Nanocrystalline Alumina and Titania Ceramic Powders." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/47376157366570849658.
Full textAbstract:
碩士國立臺灣大學
地質科學研究所
92
“Master Curve Model” was originally derived from the general equation of kinetic reactions by our group. It can be used in several fields, including crystallization kinetics and chemical kinetics, to adequately describe the variations of each reaction systems. It has also been proved that the model can describe and predict the densification behaviors of micron- and submicron-sized ceramic sintering in our preliminary study earlier. But there are no any experimental evidence yet whether it can be used in the sintering of nanocrystalline ceramic powders. Furthermore, the sintering of nanocrystalline ceramic powders involves more complicated mechanisms than the sintering of conventional ceramic powders, so the conventional sintering models cannot be applied to the sintering of nanocrystalline ceramic powders. To date no practical model has been developed to describe the sintering of nanoceramics. This study explores the feasibility of using the master curve model to quantitatively describe the densification behaviors of nanocrystalline ceramic powders in sintering. We believe the results will contribute not only to the sintering practice in industry but also to the understanding of the basic science of sintering. Five powders were used in this study. They are ?Al2O3 (average diameter~50 nm)、γ-Al2O3 (~15 nm)、rutile-TiO2 (~35 nm)、anatase-TiO2 (~10 nm) and Degussa P25-TiO2 (~45 nm). The sintering is conducted in air at designed heating paths. The densities of the sintered specimens are measured by the Archimedes method. The phases and microstructure of the samples are determined by XRD and SEM, respectively. Because the particle size effect, the nanocrystalline ceramic powders usually contain metastable phases. Therefore, phase transformation may occur during sintering. I summarize the experimental results into two parts： (1) Only a small fraction of the powders experiences phase transformation during the sintering. In this case, the densification behaviors of the powders show a clear master curve relationship, which is independent of heating path. (2) A large fraction of the powders experiences phase transformation during the sintering. That is when an unmistakable two-stage densification behavior is observed. The 1st stage is the results of both the volume shrinkage due to the phase transformation and the elimination of porosity during the early period of the sintering. The data of this stage cannot be merged into a single curve. The 2nd stage is the results of the sintering after the phase transformation has been completed, and again we observe a clear master curve relationship. The values of the apparent sintering activation energy, which were derived from both the alumina and the titania, are greater than that of the conventional ceramic powders. In particular, we find that the starting powders with a smaller size will give a relatively greater value. The relationship indicates not only the complexity in nanosintering, but also that we cannon use the conventional sintering mechanisms to explain the densification behaviors of nanoceramics. The higher values of the apparent sintering activation energy might due to the predominant surface diffusion during the early stage sintering of nanoceramics. The surface diffusion quickly consumes the sintering driving forces by the shape-change of the grains (into the shape of rod or column), which in term makes the densification process harder in the later sintering stage and effectively makes the sintering apparent activation energies higher than their conventional counterparts.