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1
Cigas, Saulius. "Standaus apkrovimo ciklinių deformavimo parametrų nustatymas korozijai ir karščiui atsparaus plieno suvirintųjų sujungimų medžiagoms". Master's thesis, Lithuanian Academic Libraries Network (LABT), 2005. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2005~D_20050613_152519-67955.
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Cigas S. Determination of low cycle straining parameters for weld metals of stainless steel: Master thesis of mechanical engineer / research advisor associate professor dr. R. Šniuolis; Šiauliai University, Technological Faculty, Mechanical Engineering Department.–Šiauliai, 2005.-68p.
Strain and stress change during the exploitation depend on the type of material (hardening, softening or cyclically stabile), that is chosen for the constructions in low cycle loading. If we know the type of the material, we can determine the possibility of its application in concrete exploitation conditions. Real working conditions of the most constructions are close to loading with limited strain (hard straining), because elastic and plastic deformation is met in the zones of crack and stress concentration, that are surrounded with elastically deformed material.
Analytical dependences between stress and strain in any semicycle k are expressed by summarized low cyclic stress strain curve. The low cycle loading curves parameters A, and are used for the computation of this curve. These parameters were obtained from the low cycle straining results. The other possible ways for the determination of parameters A, , and statistical methods for the evaluation of these parameters for weld metals of stainless steel at room temperature are presented in this work.
Cyclic characteristics A, and were determined by methods shown in this work. It was determined, that the values of cyclic strain and... [to full text]
2
Karademir, Tanay. "Elevated temperature effects on interface shear behavior". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42764.
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Environmental conditions such as temperature inevitably impact the long term performance, strength and deformation characteristics of most materials in infrastructure applications. The mechanical and durability properties of geosynthetic materials are strongly temperature dependent. The interfaces between geotextiles and geomembranes as well as between granular materials such as sands and geomembranes in landfill applications are subject to temperature changes due to seasonal temperature variations as well as exothermic reactions occurring in the waste body. This can be a critical factor governing the stability of modern waste containment lining systems. Historically, most laboratory geosynthetic interface testing has been performed at room temperature. Information today is emerging that shows how temperatures in the liner systems of landfills can be much higher.
An extensive research study was undertaken in an effort to investigate temperature effects on interface shear behavior between (a) NPNW polypropylene geotextiles and both smooth PVC as well as smooth and textured HDPE geomembranes and (b) sands of different angularity and smooth PVC and HDPE geomembranes. A temperature controlled chamber was designed and developed to simulate elevated temperature field conditions and shear displacement-failure mechanisms at these higher temperatures. The physical laboratory testing program consisted of multiple series of interface shear tests between material combinations found in landfill applications under a range of normal stress levels from 10 to 400 kPa and at a range of test temperatures from 20 to 50 °C.
Complementary geotextile single filament tensile tests were performed at different temperatures using a dynamic thermo-mechanical analyzer (DMA) to evaluate tensile strength properties of geotextile single filaments at elevated temperatures. The single filament studies are important since the interface strength between geotextiles and geomembranes is controlled by the fabric global matrix properties as well as the micro-scale characteristics of the geotextile and how it interacts with the geomembrane macro-topography.
The peak interface strength for sand-geomembrane as well as geotextile-geomembrane interfaces depends on the geomembrane properties such as hardness and micro texture. To this end, the surface hardness of smooth HDPE and PVC geomembrane samples was measured at different temperatures in the temperature controlled chamber to evaluate how temperature changes affect the interface shear behavior and strength of geomembranes in combination with granular materials and/or geotextiles. The focus of this portion of the experimental work was to examine: i) the change in geomembrane hardness with temperature; ii) develop empirical relationships to predict shear strength properties of sand - geomembrane interfaces as a function of temperature; and iii) compare the results of empirically predicted frictional shear strength properties with the results of direct measurements from the interface shear tests performed at different elevated temperatures.
3
borgonovo, cecilia. "Aluminum Nano-composites for Elevated Temperature Applications". Digital WPI, 2010. https://digitalcommons.wpi.edu/etd-theses/962.
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"Conventional manufacturing methods are sub-optimal for nano-composites fabrication. Inhomogeneous dispersion of the secondary phase and scalability issues are the main issues. This work focuses on an innovative method where the reinforcement is formed in-situ in the melt. It involves the reaction of the molten aluminum with a nitrogen- bearing gas injected through the melt at around 1273 K. AlN particles are expected to form through this in situ reaction. A model has been developed to predict the amount of reinforced phase. Experiments have been carried out to confirm the feasibility of the process and the mechanism of AlN formation discussed. The detrimental effect of oxygen in the melt which hinders the nitridation reaction has been proved. The effect of process times and the addition of alloying elements (Mg and Si) have also been investigated."
4
Lind, Jonna. "Tribology of polymer composites for elevated temperature applications". Licentiate thesis, Uppsala universitet, Tillämpad materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-332985.
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Polymers as construction material are common in the industry. Although more recently the use of polymer composites in more demanding applications has increased, requiring more of them mechanically, tribologically and thermally. To enhance the properties various fillers are used, from common glass fibers to more advanced nanoparticles. For this study three types of base polymers have been studied: poly-amide (PA), poly-phenylene-sulphide (PPS) and poly-ether-ether-ketone (PEEK). They have been filled with glass fibers, carbon fibers, poly-tetra-fluoro-ethylene (PTFE), graphite and thermally conductive modifier in various combinations. Fibers are used to increase the mechanical properties, PTFE and graphite are added as lubricating additives to reduce the friction, and the thermally conductive modifier to increase the thermal conductivity. Five general groups of polymer composites were studied. Pure PEEK PPS, PA and PEEK filled with fibers PPS, PA and PEEK filled with fibers and lubricating additives PA filled with lubricating additives PEEK filled with fibers and additives for lubrication and thermal conductivity The polymer composites have been tribologically tested in a reciprocating sliding test set-up. Friction, wear and surface damage have been studied. Three types of counter surfaces have been used: ball bearing steel balls, stainless steel cylinders and anodized aluminum cylinders. Load, surface temperature of the polymer composites and number of cycles were varied to study any changes in friction and wear. The wear marks on the polymer composites were studied using an SEM. Cross sections of some tested samples were prepared to study any subsurface damage. From the tests the polymer composites showed similarities in friction. Lubricating additives gave lower friction, often around 0.05-0.15, while pure and only reinforced gave higher, often around 0.4-0.5. The wear was also less for polymer composites with lubricating additives. There was no clear influence of temperature but for most tests an increase in temperature gave lower friction. The only influence of load was that higher load gave wider wear tracks. Since no cross sections were prepared to compare subsurface damage due to different loads there might be a possibility that there were some differences below the surface as well. Otherwise cross sections showed that polymer composites with only fibers had cracks and cracked fibers below the surface due to the high stresses the polymer composite had been subjected to. With lubricating additives there was no large subsurface damage and it seems as if the lubricating additives formed a protective tribofilm in the wear track, giving both lower friction and wear. The presence of such a tribofilm was confirmed by XPS analysis that showed a surface layer containing F from PTFE. The conclusions are that the tribological properties of a polymer composite are strongly dependent on its fillers. Lubricating additives form a tribofilm that lowers friction and wear. Elevated temperatures might drastically change the tribological behavior of a polymer composite why it is important to do tests at higher temperatures. Cross sections can give information about subsurface damage and might help to understand the wear mechanisms and deformation of polymer composites better. More microscopy and mechanism studies are required in order to further understand the tribological behavior of polymer composites.
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Yang, Kwan-Ho. "Development of impact testing procedure at elevated temperature /". Thesis, Connect to this title online; UW restricted, 1988. http://hdl.handle.net/1773/7038.
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Cretegny, Laurent. "Fracture toughness behavior of weldments at elevated temperature". Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19957.
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Przydatek, Jan. "The elevated temperature deformation of aluminium alloy 2650". Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287577.
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Tsembelis, Kostantinos. "Elevated temperature measurements during a hypervelocity impact process". Thesis, University of Kent, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285978.
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Zhu, Cuiru. "Elevated temperature liquid chromatography and peak shape analysis". Thesis, University of York, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413172.
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Renshaw, Matthew Peter. "Magnetic resonance studies at elevated temperature and pressure". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709303.
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Braun, Eric. "Elevated temperature stability of gallium arsenide integrated circuits". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38045.
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Poole, Eric L. "Durability of polymeric composites after elevated temperature aging /". Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9963.
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Chiu, Sing-Lok. "Behaviour of normally consolidated clay at elevated temperature". Thesis, The University of Sydney, 1996. http://hdl.handle.net/2123/18126.
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Not much has research work been done so far on temperature-related behaviour of clays. This theme has not received much attention of research workers in this field for a long time until the late 1960s when Campanella and Mitchell published their paper on "Influence of Temperature Variations on Soil Behaviour" in 1968 (Campanella and Mitchell, 1968). What followed was a special conference on this subject held in Washington in 1969, addressing a variety of research results in this field at that time. However, the interest of most research workers in the following two decades has been in soil models and their numerical implementation. Most research funds have been channelled towards studies concerning basic soil properties and the implementation of the results of research than to other topics in the same time. In recent years, rapid industrialization and implementation of many military technologies into civil industries have taken place in many western countries and a few other countries in Asia. This gave rise to a variety of problems related to the disposal of nuclear waste particularly in the late 1980s. A series of studies regarding disposal problems of nuclear waste were then carried out in Italy and the United States (Hueckel et al, 1990). In Australia, the first project related to this topic was awarded in 1991 to the Centre for Geotechnical Research (CGR) at School of Civil and Mining Engineering, University of Sydney. This thesis contains the results obtained from triaxial tests performed at different elevated temperatures using a new triaxial apparatus called HTTA (High Temperature Triaxial Apparatus) specially designed for and forming part of, the work in this research. The thesis also contains a comparison of the experimental results and the predictions by different Cam-clay models including the revised Camclay model developed in this research. Specimens of a remoulded clay, Kaolin CIC, have been tested at various I temperatures ranging from ambient temperature of 22±2°C to 100±5°C with two triaxial apparatuses. The first apparatus for tests at ambient temperature is a Bishop- Wesley-Type hydraulic triaxial apparatus; the other is a modified triaxial apparatus specially tailored and assembled for performing triaxial tests on the specimens at various elevated temperatures. The triaxial tests on the specimens were conducted at room temperature as well as at two elevated temperatures, namely 50°C and 100°C. Stress-strain response of the specimens at different temperatures was observed. Attempts have been made in different ways to investigate whether soil properties of the selected clay would change with temperature. Further, the attempts made were also to see what have been changed in the stress-strain behaviour of the clay at different elevated temperature. Then, the test results from different elevated temperatures were compared with those obtained from the tests at room temperature; and also compared with the predictions by the Cam-clay models.
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Schoech, Alexander. "Quality control of freeform parts at elevated temperature". Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424502.
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Modern industries operate under high cost pressure coupled with ever increasing demands on their processes and products. Production processes are e.g. increasingly complex while the permitted tolerances, batch sizes and time-to-market times decrease. These partly contradictory trends require sophisticated production processes with advanced strategies for quality assurance and process control. The aim of this work is to analyse such a complex, multi-stage production process, the production of turbine blades, in terms of quality, process adjustment for small batch sizes and cost.
In the considered process, turbine blades are manufactured by forging and are cooled down in calm air to ambient temperature for subsequent machining. This significantly impedes quality control during the process due to the prevailing elevated temperature of workpieces and the consequential need for several hours of cooling before measurements can be performed. Due to small batch sizes, forging of one batch is completed within hours, possibly before quality control at the first produced workpiece takes place. This results in late verification of tolerances when all workpieces are already produced and potentially violate their tolerance limits. After forging, the focus is on verification of dimensional forging tolerances. These asymmetric tolerances allow only for additional material that is to be subsequently removed by machining. Equivalent asymmetry is encountered in the incurred cost, positive deviations increase machining cost while negative deviations cause high cost due to classification as defective.
Analysis of the production process indicated substantial process optimisation opportunities by quality control during the process. However, not only measurements at elevated workpiece temperature have to be performed, also the cooling influence on the workpiece must be predicted to make early conformance statements. This is especially crucial for the thin freeform aerofoil of turbine blades that is subject to complex geometrical distortions during cooling. Additionally, if the process parameters shall be adjusted according to measurement results, appropriate methods to account for asymmetric tolerances and cost are necessary. Adjusting process parameters during the ramp-up of a batch is necessary to setup the process for the specific product. Such adjustments slow down the production, can be costly and may require a considerable period of the production time, especially for small batches. Therefore, a method shall be developed to determine when to stop initial adjustments.
In this work, a multisensor light sectioning coordinate measuring system for dimensional measurements at elevated temperature is presented and discussed. For visualisation and measurand evaluation, an existing heuristic surface reconstruction method is adapted for enhanced surface quality on partly concave freeform workpieces as turbine blades. Its low time complexity enables realtime visualisation during measuring, allowing operators to monitor and qualitatively verify measurement results quickly. Main uncertainty contributors on the system are identified, quantified and, where necessary, corrected. In particular for freeform workpieces, the requirement for improved sensor adjustment is demonstrated. A novel method for sensor adjustment and multisensor registration is proposed, yielding a five times improvement in experiments compared to manual methods.
By the discussed corrections, process adjustment for small batch turbine blade manufacturing becomes feasible. A method to obtain the optimal number of adjustments is available from literature for a specific combination of symmetric cost model and process variation by analytic evaluation of expected cost. A novel formulation and appropriate numerical methods are proposed to evaluate expected cost with arbitrary, possibly asymmetric, cost models and process variation models. Based on this formulation, two generalised criteria when to stop adjustments optimally are presented, each exhibiting distinct advantages for specific application cases. Their performance is compared to a state-of-the-art deadband model for process adjustment, yielding down to 90% lower cost for the evaluated cases if measurements are performed during the adjustment phase only. Eventually, a novel comprehensive framework for process adjustment, incorporating the proposed methods, is discussed.Le moderne industrie manifatturiere si trovano ad operare in una condizione di forte stress economico, ma allo stesso tempo con richieste dal mercato sempre più complesse. Ad esempio, se da un lato i processi produttivi aumentano la proprio complessità, dall’altro, le tolleranze richieste, le dimensioni dei lotti e il “time-to-market” si riducono sempre più. Questo andamento, per certi versi contradditorio, richiede l’adozione di processi produttivi sempre più sofisticati e tecniche avanzate per il controllo della qualità e del processo. L’obbiettivo di questo lavoro è di analizzare, in un processo produttivo complesso come quello delle palette per turbina, il controllo qualità e l’ottimizzazione di processo per lotti ridotti col fine di abbassare i costi legati alla produzione. Nel processo in analisi, le palette per turbina vengono forgiate a caldo e poi raffreddate in aria calma fino al raggiungimento della temperatura ambiente in modo da poter essere successivamente lavorate tramite macchine a controllo numerico. Le attuali tecnologie di misura rendono possibile il primo controllo dimensionale solo a valle del completo raffreddamento, che può richiedere fino a diverse ore. Date le dimensioni dei lotti tipicamente ridotte, spesso, la forgiatura di un intero lotto viene completata prima che sia stato possibile verificare la geometria del primo pezzo; ciò implica che potenzialmente può essere prodotto un intero lotto fuori tolleranza. Dopo la fase di forgiatura, il controllo dimensionale viene focalizzato alla ricerca dei sovrametalli, che, nel caso siano superiori al valore imposto in fase di progetto comporteranno un aumento dei costi di lavorazione a macchina, diversamente, qualora siano inferiori, porteranno a scartare il pezzo appena prodotto. A seguito di queste considerazioni si comprende l’importanza di anticipare la fase di controllo qualità, ma per fare ciò, non solo è importante essere in grado di misura ad elevate temperature occorre anche sviluppare dei modelli per la comprensione degli effetti distorsivi indotti dal raffreddamento così da prevedere la geometria finale. Ciò diventa un punto cruciale per le geometrie sottili e "freeform" che caratterizzano la foglia di una paletta per turbina. Inoltre, per ottimizzare il processo in base ai risultati delle misurazioni, è necessario comprendere le tolleranze e i costi legati all’ottimizzazione. Infatti, l’ottimizzazione dei parametri di processo durante le fasi iniziali di produzione di un lotto, essenziali per la corretta lavorazione di un componente, comportano rallentamenti e conseguenti costi. Lotti di ridotte dimensioni ne vengono maggiormente penalizzati. Di conseguenza è necessario sviluppare una procedura per determinare quando valga la pena fermare il processo di ottimizzazione. In questo lavoro, un sistema di misura basato sulla triangolazione laser per misura dimensionale di pezzi ad elevata temperatura viene presentato e discusso. Per ragioni di visualizzazione e misurazione, un algoritmo euristico, per la ricostruzione di superfici a partire da nuvole di punti, è stato adattato per superfici libere e concave come quelle che caratterizzano le palette per turbina. Data la rapidità dell’algoritmo è possibile visualizzare la geometria in contemporanea alla misura, permettendo all’operatore di monitorare qualitativamente l’andamento della misura. Le cause di incertezza principali del sistema di misura sono state identificate, quantificate e, se necessario, corrette. In particolare, nel caso di geometrie tipo "freeform", è stata dimostrata l’importanza di una miglior procedura di settaggio dei sensori. Un nuovo metodo per la taratura di sistemi multisensore è stato sviluppato ed è in grado di garantire tempi di settaggio cinque volte inferiori rispetto ai metodi manuali. Grazie alle correzioni proposte, l’ottimizzazione di processo per piccoli lotti di palette per turbina diventa possibile. Un metodo per la valutazione del numero ottimale di iterazioni durante il processo di ottimizzazione è disponibile in letteratura per una specifica combinazione di cosi asimmetrici e variabilità del processo tramite la valutazione del costo atteso ("expected cost"). Una nuova formulazione e un appropriato approccio numerico sono proposti per valutare i costi attesi con variabilità di processo e modello di costo arbitrari. A partire da queste considerazioni, due criteri generalizzati per decidere quando fermare l’ottimizzazione sono proposti, ognuno con particolari vantaggi in specifiche applicazioni. Le prestazioni di queste procedure sono comparate ad un esistente modello allo stato dell’arte, portando una riduzione dei costi pari al 90% quando le misurazioni vengono effettuate solamente durante la fase di ottimizzazione. Infine, una procedura complessiva per l’ottimizzazione di processo, incorporando i metodi proposti, verrà discussa.
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Xu, Lei. "Magnetization Dynamics at Elevated Temperatures". Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/311342.
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The area of ultrafast (sub-nanosecond) magnetization dynamics of ferromagnetic elements and thin films, usually driven by a strong femtosecond laser pulse, has experienced intense research interest. In this dissertation, laser-induced demagnetization is theoretically studied by taking into account interactions among electrons, spins, and lattice. We propose a microscopic approach under the three temperature framework and derive the equations that govern the demagnetization at arbitrary temperatures.To address the question of magnetization reversal at high temperatures, the conventional Landau-Lifshitz equation is obviously unsatisfactory, since it fails to describe the longitudinal relaxation. So by using the equation of motion for the quantum density matrix within the instantaneous local relaxation time approximation, we propose an effective equation that is capable of addressing magnetization dynamics for a wide range of temperatures. The longitudinal and transverse relaxations are analyzed, magnetization reversal processes near Curie temperatures is also studied. Furthermore, we compared our derived Self-consistent Bloch equation and Landau-Lifshitz-Bloch equation in detail. Finally, the demagnetzation dynamics for ferromagnetic and ferrimagnetic alloys is studied by solving the Self-consistent Bloch equation.
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Isom, Stephen Clay. "The effects of elevated temperature on preimplantation-stage porcine embryos". Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4385.
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Thesis (Ph.D.)--University of Missouri-Columbia, 2006.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 27, 2007) Vita. Includes bibliographical references.
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Zhang, Zhan. "Development of magnesium-based alloys for elevated temperature applications". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0026/NQ52270.pdf.
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Counts, William Arthur. "Mechanical behavior of bolted composite joints at elevated temperature". Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17315.
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Ratkovich, John. "Processing and elevated temperature ductility of Aluminum alloy 7475". Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27223.
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Harlow, K. S. "The elevated temperature mechanical behaviour of aluminium-lithium alloys". Thesis, University of Nottingham, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374661.
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Sweeney, Deborah May-Katherine. "ELEVATED TEMPERATURE OXIDATION OF BORON MODIFIED Ti-6Al-4V". Wright State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=wright1208285133.
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Chen, Yong-Ching. "Elevated temperature deformation and forming of aluminum-matrix composites /". The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487758178238026.
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Shah, Vishal Sanjay. "Detection of microcracks in concrete cured at elevated temperature". [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0008824.
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Dike, Shweta Srikant. "Dynamic Deformation of Materials at Elevated Temperatures". Cleveland, Ohio : Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1268337193.
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Thesis (Master of Sciences (Engineering))--Case Western Reserve University, 2010Department of EMC - Mechanical Engineering Title from PDF (viewed on 2010-05-25) Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center
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Legrand, Pierre. "Structural assement and design of concrete structures under fire conditions". Thesis, KTH, Betongbyggnad, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-187886.
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Behaviour under fire circumstances is becoming more and more crucial for designing a concrete structureand authorities require more often a fire-resistance time. In fact, engineers need a powerful, user-friendly,accurate and non time-consuming method that can be used to design reinforced concrete structures. Inthis study, the author has developed a method to design any fire-exposed reinforced concrete crosssections under flexure that takes into account second order effect. The first part focuses on the thermal analysis of the reinforced concrete cross section. Fourier'sequation is solved using finite differences method and the development tool of Excel: Virtual BasicAdvanced macro. Thus, it could easily be used on every personal computer (reasonably powerful) andneeds no extra investment. The accuracy of this thermal analysis is checked by comparison with resultsfrom commercial softwares (FAGUS edited by Cubus and SAFIR developed by the university of Liege). The second part deals with the mechanical analysis. Indeed, the concrete compressive strengthtogether with the yield strength of the steel reinforcement bars will decrease when the temperature willraise inside the concrete cross section. This loss of characteristic will be regarded as a loss of area andnew dimensions are set up. Finally a classic analysis (as it can be done at ambient temperature) isperformed. The mechanical analysis which takes into account second order effect is based on the Eulerbuckling load. The last chapter presents a comparison study between this new method and the two commercialsoftwares FAGUS and SAFIR, both of them are using finite element method. Several cross sections havebeen modelled, T-shaped ones with various dimensions and rectangular ones with various dimensionsand various steel areas. The two aspects (mechanical and thermal) have been studied and the resultsshowed good correspondance.Master thesis
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Huang, Ming Jun. "The application of computational fluid dynamics (CFD) to predict the thermal performance of phase change materials for the control of photovoltaic cell temperatures in buildings". Thesis, Ulster University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248684.
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Gunda, Rahul. "Performance analysis of high power photoconductive switch at elevated temperature". Diss., Columbia, Mo. : University of Missouri-Columbia, 2005. http://hdl.handle.net/10355/4310.
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Thesis (M.S.)--University of Missouri-Columbia, 2005.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (July 13, 2006) Includes bibliographical references.
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Leggett, Jonathan. "Elevated temperature oxidation and corrosion of a titanium aluminide alloy". Thesis, Cranfield University, 1997. http://dspace.lib.cranfield.ac.uk/handle/1826/3584.
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Titanium aluminides are being developed to expand the temperature capability of titanium alloys with maximum service temperatures around 700°C. These materials also have the ability to replace nickel superalloys with potential applications in the high pressure compressor, and in the 4th stages of the low pressure turbine. The above applications place these alloys in environments not previously considered. Within the compressor hot salt corrosion may be a problem with salt ingested from the atmospheric aerosol. While in the turbine the combination of salt ingestion, and SO, from the burning of fossil fuels, results in hot corrosion being a potential problem. In this study the individual effects of salt and So2 were investigated, with corrosion mechanisms being proposed using kinetic, metallographic and thermodynamic data. Understanding these effects enabled both the hot salt corrosion and hot corrosion behaviour of TiAl alloys to be evaluated. In air alone continuous alumina layers, within a mixed alumina/rutile scale, provide the oxidation resistance of TiAlNb alloys. Logarithmic kinetics operated for 100 hours at 700°C and for 13 hours at 750°C. Parabolic kinetics then operated out to 100 hours at 900°C. Mass gains ranged from 0.06 to 2.1mg/cO after 100 hours at 700 and 900°C respectively. This situation changes in bi-oxidant, air/S02, atmospheres where increased growth rates are linked to the formation of a continuous sulphide layer at the scale/substratien terface. Below 800°C logarithmic/parabolic kinetics operate. At and above 800°C initial logarithmic kinetics change to near linear/breakaway kinetics with spallation becoming a problem. Mass gains, after 100 hours, ranged from 0.2 mg/cM2 at 700°C up to 6.4 mg/cm2 at 900°C. The presence of low salt concentrations [<0.05mg/cm²] resulted in severe substrate degradation, with preferential attack down a2 lathes.The first 10-20 hours were shown to be the most important with low melting point salt mixtures spreading across the surface, increasing the rate of attack. The evolution of HCI/Cl2 during initial substrate attack leads to the Vapour Phase Transport of aluminium and manganes chlorides resulting in whisker growth over a porous rutile scale. The presence of salt modified the diffusion controlled kinetics under purely oxidising conditions. Chlorine was shown to promote the vapour phase transport mechanism which resulted in the initial accelerated logarithmic kinetics. A change to parabolic type kinetics occurred due to the loss of chlorine to the atmosphere. The mass gains, after 100 hours, ranged from 0.06 to 1.1rn g/cm² between 500 and 800°C. The combination of salt deposits and S02 bearing environments resulted in severe substrate degradation. Salt played a dominant role during the early stages of corrosion, whilst low partial pressures of S02 affected the later stages of corrosion. Non protective oxide scales were developed with low melting point MnSO4-Na2SO4 mixtures forming at salt deposits and a continuous sulphide layer at the scale/substrate interface. Rapid scale growth resulted in severe scale spallation. The initial stages of hot corrosion followed rapid logarithmic type kinetics. Further increases in the corrosion rate where promoted by the formation of continuous sulphide layers at the scale/substrate interface. Parabolic kinetics, at this stage, were followed by linear growth rates once scale spalling occurred. Mass gains, after 100 hours, ranged from 0.52 to 3.89 mg/cm² between 650 and 800°C.
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Malm, Chistorpher. "The Flexural Response of Bolted Composite Panels at Elevated Temperature". Fogler Library, University of Maine, 2001. http://www.library.umaine.edu/theses/pdf/MalmCG2001.pdf.
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Yatomi, Masataka. "Factors affecting the failure of cracked components at elevated temperature". Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405783.
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Barrow, A. T. W. "Strong, tough and fatigue-resistant steel for elevated temperature applications". Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596428.
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The work described in this thesis details the design and characteristics of low-Ni maraging steels suitable for use at elevated temperatures. In addition to having a stable microstructure, they require strength, ductility, fatigue- and creep-resistance with low impurity levels suitable for use in aeroengine shafts. Two chemical compositions have been designed based on thermodynamic calculations which independently investigate the suitability of the matrix and the strengthening phases for use at elevated temperatures. It is believed that substituting Ni with Cr will increase the austenite-start temperature, thus retarding the formation of austenite during manufacture and simulated service at 450°C. Avoiding the formation austenite concomitantly with precipitate coarsening is important when designing a suitable shaft material. The designed alloys have exhibited an excellent combination of strength and ductility in the hardened condition achieved through a non-scale distribution of Ni-rich particles. These particles resist growth at 450°C while largely maintaining the mechanical properties. The austenite observed in one alloy transformed to martensite at room temperature during plastic deformation increasing the elongation. However, the increased thermodynamic stability of austenite at 450°C does not permit the martensitic transformation, thus it must be avoided in shaft alloys. The alloy which resisted the formation of austenite displayed excellent fatigue- and creep-resistance in the hardened condition. These properties are attributed to the size and dispersion of the strengthening phases and the level of inclusions within the microstructures. Neither of the designed alloys meets all the mechanical property requirements of the shaft. However, by combining the desirable features of both alloys it is believed that these properties can be achieved though a low-Ni maraging steel.
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Cromey, Tyler. "Effect of elevated temperature on ceramic ultrafiltration of colloidal suspensions". Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51778.
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The inherent thermal resistance of ceramic membranes allows for treatment of industrial waters at elevated temperatures. Traditionally, the high temperature of wastewater has been an issue compromising the integrity of polymeric membrane systems or requiring the temperature to be lowered for further treatments. In ceramic membrane systems, a decrease in viscosity with increasing temperature, however, can be utilized, which increases the permeate flux. In this study, the fouling of ceramic ultrafiltration by feed solutions containing colloidal silica was evaluated at temperatures between 25 – 90 °C seen in various industries. Ceramic membranes were able to perform well at elevated temperatures up to 90 ºC with sustained mechanical and chemical integrity. Results showed net benefit of filtration at elevated temperatures on permeate flux in spite of increasing total fouling resistance with temperature. When the temperature increased from 25 to 90 °C, there was a 90% increase in steady-state permeate flux. The dominant resistance was physically removable fouling, and the increase in fouling with feed temperature was supported by force balance analyses. This study provides a foundation from which further studies can be developed including pilot-scale testing, use of real wastewater, and the effects of operating conditions.
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Agyakwa, Pearl. "Creep and microstructural development in P91 weldments at elevated temperature". Thesis, University of Nottingham, 2004. http://eprints.nottingham.ac.uk/11759/.
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This research concerns weldments in P91 steel and their creep behaviour. Its scope covers three main topics: the microstructure and creep response of the (i) weld metal, (ii) parent metal, and (iii) the effect of extended thermal exposure and creep on the weldments. Microstructural examination of the weld metal revealed an inhomogeneous structure, with each bead consisting of a columnar region, a coarse-grained region and a fine-grained region (the latter two regions resulting from heat-treatment of the weld bead by deposition of subsequent beads). The columnar regions exhibited high hardness whereas the coarse and fine grained regions exhibited lower hardnesses. SEM imaging revealed that the precipitate distribution throughout the weld was somewhat inhomogeneous, due to inadequate mixing in the weld pool during welding, leading to segregation and liquation effects. Examination by TEM revealed a fine martensitic structure with a distribution of chromium carbides, in addition to Mn-rich inclusions. Anisotropy of microstructure was assessed by metallographic examination on planes with normals parallel to and perpendicular to the welding direction. Creep tests on this material were performed, with the stress axis both parallel and perpendicular to the welding direction. Anisotropic creep behaviour was observed and correlated with the microstructural anisotropy. Failure life is significantly longer when uniaxial creep stress is parallel to the welding direction. The columnar regions of the weld were observed to be creep-strong with a low strain to failure whereas the coarse and fine grained regions were observed to be creep-weak with a higher strain to failure. Microstructural variations within weldments as a function of time and temperature have also been investigated. Specimens were aged at five temperatures between 760°C and 650°C for up to 12000 hours. At all exposure temperatures, the parent metal showed little change in terms of fine (subgrain) microstructure and hardness. Significant degradation of the weld metal microstructure was observed. This consisted of recrystallisation, emanating from the weld bead boundaries; in some cases, the recrystallised areas made up approximately 40 % of the metallographic section. The hardness of the recrystallised regions was typically 170 kgf mm-2, whereas that of the non-recrystallised areas was 240 kgf mm-2. TEM examination of the weld metal showed significant change, in the form of transformation of fine martensitic lath structure to larger, more equi-axed subgrains. Creep tests of aged crossweld samples showed accelerated minimum strain rates and reduced failure lives. It was also observed in crossweld specimens creep-tested at three stress levels between 70 MPa and 93 MPa that the failure location moved from the fine-grained HAZ to the parent at the highest test stress. The HAZ failures exhibited extensive cavitation restricted to the HAZ, and low failure ductility. The high stress parent metal failure, on the other hand, showed high ductility and extensive voiding and grain deformation within the parent metal microstructure. An assessment of the effect of strain on microstructural evolution has been made. This is deemed significant, and strain is believed to accelerate precipitate coarsening and martensite recovery processes.
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Holmström, Marcus. "Design of a Carbon Fiber Thermocouple for Elevated Temperature Measurements". Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-279105.
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Thermocouples are one of the most commonly used instruments for thermometry at elevated temperatures. As of today, there are only a few types of thermocouples that are built to withstand a temperature beyond 1600 °C,however they usually have a temperature measurement uncertainty of around 1% at these high temperatures. Beyond the 1600 °C temperature span, most high temperature thermocouples tend to drift in the measurements, causing it to output a faulty and inaccurate read of the actual temperature. This thesis explores the usage of carbon fibers as a material to be used in thermocouples, by the combination of two dissimilar carbon fibers. Polyacrylonitrile (PAN) and rayon based fibers were used up to a temperature of 200 °C, where the output voltage of the thermocouple was logged. The study shows a promising and stable linear output of the electromotive force for this type of thermocouple using commercially available carbon fibers at lower temperatures. A comparison is made between the commonly used thermocouples type K and S, results shows that the carbon thermocouple have around 21% of the thermoelectrical efficiency of that of a type K or S thermocouple at 25 °C. For the case of its functionality at higher temperatures, similar graphite material has been studied through literature and found a potential increase in the thermoelectrical stability at higher temperatures beyond 2000 °C, which show that carbon-based thermocouples are well suited for high temperature measurements.Termoelement är ett av de mest använda instrumenten för temperaturavläsning vid upphöjda temperaturer. Idag finns det bara några få typer av termoelement som är byggda för temperaturer över 1600 ℃, däremot innehar dom vanligtvis en temperaturmätnings osäkerhet på cirka 1% vid dessa höga temperaturer. Över 1600 ℃ temperaturintervallet har de flesta högtemperatur termoelement en tendens att skifta i mätningarna vilket orsakar en felaktig och inexakt mätning av den faktiska temperaturen. Denna avhandling undersöker användningen av kolfiber som ett material för användning i termoelement, genom kombinationen av två olika grafitfibrer. Polyacrylonitrile- (PAN) och Rayon-baserade fibrer användes i en sammansatt kombination upp till en temperatur av 200 ℃, där spänningen mättes mot temperaturen. Studien visar en lovande och stabil linjär effekt av dess elektromotoriska spänning för denna typ av termoelement med kommersiellt tillgängliga kolfibrer vid lägre temperaturer. En jämförelse görs mellan de vanliga termoelementen av typ K och S vid rumstemperaturer, resultaten visar att grafittermoelementen har cirka 21% av den termoelektriska effektiviteten hos den för en typ K eller S termoelement vid 25 ℃. När det gäller dess funktionalitet vid högre temperaturer har liknande grafitmaterial studerats och funnit en potentiell ökning av den termoelektriska stabiliteten vid högre temperaturer över 2000 ℃, vilket visar att grafitbaserade termoelement gör sig väl lämpade för högtemperaturmätningar.
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Ahlbäck, Rasmus. "Elevated temperature tests of SiC experiment for MIST : KTH Student Satellite MIST". Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-275715.
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Electronics today rely heavily on silicon transistors which are unsuitable for extreme environments where temperatures potentially could reach up to 500◦C. Materials other than silicon has been proposed to solve this problem, one of which is silicon carbide. Transistors made of silicon carbide can with-stand higher temperatures than its silicon counterparts and could potentially be used for exploring hostile planets such as Venus or in high temperature applications such as sensors for engines. This project is a part of KTHs student satellite initiative which will send a satellite into orbit containing several experiments. One of the experiments is the SiC in space project which is described in this thesis and is largely based on previous works in this particular project. The goal for this thesis is to ensure that the SiC in space experiment is ready for launch into orbit. This was done by conducting tests in differ-ent temperatures as well as developing software for analyzing data from the experiment as well as modifying already existing software. Based on these tests, it is concluded that the silicon carbide transistors behaves in an ex-pected way and that the platform which operates the experiment is capable of withstanding temperatures up to 100◦C. If the satellite survives launch it is most likely that the data generated by the SiC in space project will be of use for determining the suitability of silicon carbide for space applications.Elektronik idag förlitar sig på kiseltransistorer som är olämpliga för extrema miljöer där temperaturer kan nå upp till 500◦C. Andra material än kisel har föreslagits för att lösa detta problem, där kiselkarbid är en av dem. Transistorer gjorda av kiselkarbid klarar av högre temperaturer än kiseltransistorer och kan potentiellt användas för utforskning av planeter med extrema klimat eller för applikationer vid höga temperaturer så som sensorer inne i motorer. Detta projekt är en del av KTHs student satellit som kommer sändas ut i omloppsbana runt jorden bärandes på ett antal olika experiment, däribland dem finns ”SiC in space” projektet som beskrivs i denna uppsats. Målet med arbetet i denna rapport är att säkerställa att ”SiC in space” experimentet är redo för uppskjutning till rymden. Detta gjordes genom att testa vid olika temperaturer och genom att utveckla mjukvara för analysering av experimentdata samt genom små modifieringar av mjukvara skriven i tidigare arbeten. Baserat på de tester som har genomförts dras slutsatsen att kiselkarbidtransistorn har en acceptabel karaktäristik och att plattformen som kör experimentet klarar av temperaturer upp till 100◦C. Om satelliten överlever uppskjutning ut i rymden kommer med största sannolikhet experimentet att fungera som önskat och generera data som kan påvisa ifall kiselkarbid är lämpligt för applikationer i rymden.
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Knox, Joanne Jennefer. "Aspects of modelling plain and reinforced concrete at elevated temperatures". Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/7713.
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Extreme events such as the Mont Blanc Tunnel fire in 1999 (Bettelini et al. 2001) or the Windsor Tower fire in 2005 (Calavera et al. 2005) have shown how concrete failure at elevated temperatures can be hazardous to the safety of members of the public. Generally, there is an absence of understanding of the mechanical behaviour of both plain and reinforced concrete at elevated temperatures, which is essential for computational modelling. Since fire is an extreme event, a certain amount of damage within the structure would be seen to be permissible within its performance objectives. This necessitates analysis in the post-peak regime. As a material, concrete has a very low value of thermal conductivity. This means that large thermal gradients often occur within concrete, causing differential expansion of the material. This, coupled with the change in mechanical properties at elevated temperatures, further complicates analytical analysis procedures. This study investigates issues associated with computational modelling of plain and reinforced concrete at elevated temperatures and its residual behaviour (behaviour when tested after the material has been heated, for example in a fire, and then cooled). In order to achieve this, first the constitutive material properties of both plain and reinforced concrete at ambient and elevated temperatures were investigated. The study showed that mesh sensitivity and localisation of strain softening occurs in plain concrete under both tensile and compressive loading. Path dependency of the stress-strain behaviour of plain concrete was also demonstrated, when it was subjected to loading and heating. Tension stiffening was included in the reinforced concrete material model, to represent the interaction between concrete and reinforcing steel. Complex behaviours were seen for simple reinforced concrete benchmark tests, due to changing material properties at elevated temperatures and differential thermal expansion of steel and concrete. Non-linear load-displacement relationships were seen as a result of complex load-sharing between concrete and reinforcement. A hypothesis was proposed – that variation of temperatures during heating and cooling of a specimen will cause damage, and hence material degradation, in plain and reinforced concrete. On investigation, it was seen that damage due to differential thermal expansion plays a small part in the reduction of elastic load-displacement slope and peak strength seen in experimental data on residual tests, indicating that other factors identified in previous research also affect the residual behaviour of plain and reinforced concrete. Indeed, in reinforced concrete, when tension stiffening was included, it was found that damage due to differential thermal expansion and contraction had a negligible effect on the residual response in the pre-peak regime. The study also found that for a simply supported beam pure thermal expansion caused a localised response, while pure thermal gradient gave distributed yield. When both were present, in this study, distributed yield with no mesh sensitivity was seen. Realistic heating of a restrained reinforced concrete plane strain model caused compressive stresses accompanied by tensile longitudinal total strains and tensile longitudinal plastic strains throughout the depth of the slab, with the largest values occurring near to the model supports. Damage and recovery variables were found to have no effect on the response of the model. When a portal frame was exposed to heating, plastic strains were distributed throughout the beam, with column rotation limiting downward thermal bowing due to a uniformly distributed load or thermal gradient present. Application of displacement loading causing plastic damage changed the behaviour of the structure under heating – instead of symmetrical compressive plastic strains being induced, areas of varying tensile and compressive strain were caused within the beam. Throughout, simple, easily reproducible simulations were used so that single parameters could be altered and considered. This was important, so that the important parameters to computational modelling could be identified. These can be used to guide experimental series to ensure that they are investigated, in order to improve computational material models. Not all variations of parameters were investigated in this study, but it is clear where further repetition would be beneficial (e.g. in varying thermal expansion and thermal gradient ratios in heating regimes). This study looks to address experimentalists and people working in structural analysis, who would be interested in the parameters investigated, as well as practitioners who may want to use these results.
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Prajapati, Kamlesh. "Properties of magnetostrictive alloys at elevated temperatures". Thesis, University of Hull, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322348.
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Lu, Chi. "Micro-Fabricated Hydrogen Sensors Operating at Elevated Temperatures". UKnowledge, 2009. http://uknowledge.uky.edu/gradschool_diss/767.
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In this dissertation, three types of microfabricated solid-state sensors had been designed and developed on silicon wafers, aiming to detect hydrogen gas at elevated temperatures. Based on the material properties and sensing mechanisms, they were operated at 140°C, 500°C, and 300°C. The MOS-capacitor device working at 140°C utilized nickel instead of the widely-used expensive palladium, and the performance remained excellent. For very-high temperature sensing (500°C), the conductivity of the thermally oxidized TiO2 thin film based on the anodic aluminum oxide (AAO) substrate changed 25 times in response to 5 ppm H2 and the response transient times were just a few seconds. For medium-high temperatures (~300°C), very high sensitivity (over 100 times’ increment of current for H2 concentration at 10 ppm) was obtained through the reversible reduction of the Schottky barrier height between the Pt electrodes and the SnO2 nano-clusters. Fabrication approaches of these devices included standard silicon wafer processing, thin film deposition, and photolithography. Materials characterization methods, such as scanning electron microscopy (SEM), atomic force microscopy (AFM), surface profilometry, ellipsometry, and X-ray diffractometry (XRD), were involved in order to investigate the fabricated nano-sized structures. Selectivities of the sensors to gases other than H2 (CO and CH4) were also studied. The first chapter reviews and evaluates the detection methodologies and sensing materials in the current research area of H2 sensors and the devices presented this Ph.D. research were designed with regard to the evaluations.
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Farooq, Muhammad. "Strengthening and degradation mechanisms in austenitic stainless steels at elevated temperature". Doctoral thesis, KTH, Materialteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-122158.
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With rapid economic developments and rising living standards, the demand for electricity all over the world is greatly increased. Due to high fuel costs, the steam boilers with higher steam temperature and pressure are needed to decrease the cost of power generation throughout the world extensively. In recent years, human awareness of the gradual strengthening of environmental protection increases, therefore to reduce the CO2 emissions the power generation efficiency needs to be improved. The development of high temperature materials with improved creep rupture strength and oxidation resistance is critically needed. Materials for these demanding conditions are austenitic stainless steels such as 310, 310NbN and Sanicro 25. Fundamental models have been developed for the precipitation of coarse particles during long time ageing of austenitic stainless steels and the influence of the particles on the mechanical properties. The models have been verified by ageing experiments. The austenitic stainless steel 310 was aged for up to 5000 h at 800 ºC. The precipitation models could satisfactorily describe the influence of ageing time on the radii and the volume fractions of particles. Models for the influence of the coarse precipitates on the tensile properties and the toughness were developed and reproduce the measured mechanical properties without the use of any fitting parameters. These developed models were utilised to investigate the influence of bands on ductility and toughness at room temperature. Up to 10 % σ-phase was observed to precipitate, which has a pronounced influence of the mechanical properties. Thermodynamic analysis demonstrated that the amount of precipitates due to ageing can significantly be reduced if the nitrogen or the carbon content is increased. Microstructure investigations of austenitic stainless steel 310NbN and Sanicro 25 were carried out by light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The austenitic stainless steel 310NbN was aged for up to 10000 h at 650 and 750 ºC. The austenitic stainless steel Sanicro 25 was also aged for up to 10000 h at 650 and 700 ºC. Phase fractions and mean radii evolution of precipitates were calculated and compared to the experimental results. Size distributions of the precipitates in these steels were determined. Models for the different contributions to the creep strength have been applied: i) a recovery creep model for the dislocation hardening; ii) a climb controlled model for the precipitation hardening; iii) solid solution hardening from Cottrell clouds of solutes around the dislocations, and iv) A modified Dobes model for the effective stress. The total contributions can describe the experimental creep strength satisfactorily without the use of adjustable parameters.QC 20130517
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Antolovich, Bruce F. "Fatigue crack propagation in single crystal CMSX-2 at elevated temperature". Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/14880.
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Muggelberg, Christiane. "The surface structures of uranium dioxide studied by elevated temperature STM". Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389177.
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Zong, Bernie Yaping. "Strength and fracture of a metal matrix composite at elevated temperature". Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260733.
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Mansour, Morkous Shoukry. "Fundamental study of premixed combustion rates at elevated pressure and temperature". Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535670.
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Moon, Hyung-Soo 1969. "Design of Si/SiC hybrid structures for elevated temperature micro-turbomachinery". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29222.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references.
thermal softening behavior at temperatures above 900 K. This thermal softening behavior limits the turbine inlet temperature, which in turn significantly degrades the overall engine efficiency. Previous studies have shown that hybrid structures of silicon and silicon carbide have good potential for improved engine performance. Detailed design of Si/SiC hybrid structures for high temperature micro-turbomachinery, however, has been hampered by the relatively poor performance of single crystal Si at elevated temperatures and high stresses and by the unavailability of accurate material properties data for both Si and SiC at the temperatures of interest. From previous work, the critical structures and materials issues to be resolved, in order to proceed with the design of high temperature Si/SiC hybrid structures, were identified as follows: 1. the safety margin of the Si/SiC hybrid structures based on the upper yield strength of Si 2. reliable estimation of the service life of the Si/SiC hybrid structures 3. structural instabilities caused by the combination of stress concentrations and strain softening. In the course of this thesis, these issues provided the key motivations of the work, and have been substantially resolved. As a first step, it is critical to obtain a better understanding of the mechanical behavior of this material at elevated temperatures in order to properly exploit its capabilities as a structural material. Creep tests in simple compression with n-type single crystal silicon, with low initial dislocation density, were conducted over a temperature range of 900 K to 1200 K and a stress range of 10 MPa to 120 MPa. The compression specimens were machined such that the multi-slip <100> or <111> orientations were coincident with the compression axis.
(cont.) The creep tests reveal that the response can be delineated into two broad regimes: (a) in the first regime rapid dislocation multiplication is responsible for accelerating creep rates, and (b) in the second regime an increasing resistance to dislocation motion is responsible for the decelerating creep rates, as is typically observed for creep in metals. An isotropic elasto-viscoplastic constitutive model that accounts for these two mechanisms has been developed in support of the design of the high temperature turbine structure of the MIT microengine. From the experimental observations and model validation, basic guidelines for the design of Si/SiC hot structures have been provided. First, the use of the upper yield strength of single crystal Si for design purpose is non-conservative. Also from the perspective of the design of Si hot structures, the lower yield strength is insufficient, particularly for micro-turbomachinery operating at elevated temperatures and high stresses. The recommended approach to the design of Si hot structures is to use the Si model for extracting appropriate operating conditions, and to reinforce the Si structures with SiC in strategic locations. Second, at high temperatures, the effect of stress concentrations is not crucial ...
by Hyung-Soo Moon.
Ph.D.
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Darr, Shehla. "Compression recovery of rigid polymer foams following confinement at elevated temperature". Thesis, Kingston University, 2007. http://eprints.kingston.ac.uk/20383/.
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Cellular materials are all around us. They can be found in nature as in bone, wood, leaves and even in our food. In the last fifty years, man has produced many synthetic cellular materials: firstly with polymeric foams and more recently with foamed metals, ceramics and glass. Polymer foams are used in a variety of applications ranging from coffee mugs to the feet of the Apollo Lunar Module, for which they were used as shock absorbers. This project was aimed at understanding the recovery from long-term compression of rigid polymer foams. Understanding the dynamics involved in the recovery process of foams is very important, especially in the automotive industry where it determines safety of the driver, passengers and pedestrians, for example, in car bumpers. In this study, foam samples were compressed by strains which spanned their linear elastic and stress plateau regions, i.e. 2.5% - 35% for one month at various temperatures. Recovery occurred in two stages, designated phase 1 and phase 2. Phase 1 is the initial recovery, which dominates the full recovery process and is complete within hours or days. Phase 2 is a lesser recovery occurring over a much longer period of approximately 100 days. The initial recovery is associated with the polymer itself, whilst phase 2 recovery is associated with the cellular structure. Recovery of all samples was monitored for a minimum of 100 days at ambient temperature. Tests were also carried out to see how the environmental surroundings affect the polymer recovery. The different polymer foams which were investigated were: • Polyethylene • Polyetherimide • Polyurethane • Polysulphone The polymers tested all showed very different responses to the changes in temperature. All polymers investigated at different compressive strains demonstrated reproducible Arrhenius plot slopes under different conditions and hence a reasonably reproducible set of values of recovery process. Analyses were based on the final total recovery of the thickness as the most reliable parameter of recovery. It has been demonstrated that the mechanism of polymer deformation and recovery probably does not involve chain scission but backbone vibration; that the best parameter for characterising the recovery process is the final total dimensional recovery of the sample; and that subtle environmental changes have a large effect on the recovery from compression, although temperature and humidity are not responsible.
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Rounthwaite, Nicholas James. "Development of bulk nanoquasicrystalline alloys for high strength elevated temperature applications". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:47bdc219-1733-40c1-ac6b-dbd5fc08f175.
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Al93Fe3Cr2Nb2 (at.%) nanoquasicrystalline alloys have been shown to have the potential to push the applications of aluminium alloys to more elevated temperatures, by maintaining a high strength. They also have more thermally stable microstructures than previous nanoquasicrystalline alloys from similar systems (the most studied of which is Al93Fe3Cr2Ti2 (at.%)). Al93Fe3Cr2Nb2 (at.%) alloys have never previously been produced in samples on a scale larger than melt-spun ribbon. This study examines the production parameters of bulk nanoquasicrystalline Al-Fe-Cr-Nb alloys. Firstly an attempt was made to reduce the melting temperatures of thermally stable nanoquasicrystalline alloys through additional alloying. The melting processes of binary, ternary, quaternary and quinary nanoquasicrystalline alloys was analysed though DTA, with endothermic reactions up to 1034oC observed. Rapidly solidified Al-Fe-Cr-Nb alloys were then produced in kilogram quantities through gas atomisation at an industrial scale. The smallest atomised powder particles contained fine scale microstructures consisting of nano-scale quasicrystals embedded in an aluminium matrix. As the cooling rate of the powder particles decreased new phases, including the theta phase (Al13(Fe,Cr)2-4) and Al3Nb were produced. 0-25μm, 25-50μm and 50-75μm (diameter) size fractions of atomised powder were each consolidated through extrusion to produce nanoquasicrystalline Al-Fe-Cr-Nb bars. Composite bars of the nanoquasicrystalline alloy mixed with 10(vol.)% and 20(vol.)% pure aluminium were also produced. The consolidation of the nanoquasicrystalline atomised powders through extrusion led to precipitation of intermetallics including (Al13(Fe,Cr)2-4) and Al3Nb, particularly in the smallest powder size fractions with the most metastable microstructures. Finally the effects of the atomisation and extrusion conditions on the microstructure and its mechanical properties were studied. Improved strength, coupled with reduced ductility was observed with decreases in the elemental aluminium composition of the Al-Fe-Cr-Nb bars and the powder size fraction they were produced from. There was however improvements in toughness of the extruded composite bars, over the nanoquasicrystalline alloy bars.
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Allen, Benjamin William. "Creep and Elevated Temperature Mechanical Properties of 5083 and 6061 Aluminum". Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/52630.
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With the increasing use of aluminum in naval vessels and the ever-present danger of fires, it is important to have a good understanding of the behavior of aluminum at elevated temperatures. The aluminum samples 5083-H116 and 6061-T651 were examined under a variety of loading conditions and temperatures. Tensile testing was completed on both materials to measure strength properties of elastic modulus, yield strength, and ultimate strength as well as reduction of area from room temperature to 500 deg C taking measurements every 50 deg C. These tests showed how much the material weakened as temperature increases. Low temperatures had a minimal effect on strength while exposure to temperatures between 200 and 300 deg C had the most significant impact. Creep testing was also completed for these materials. These tests were completed at temperatures between 200 and 400 deg C in 50 deg C increments. Stresses for these tests were in the range of 13 to 160MPa for 5083 aluminum and between 13 to 220MPa for 6061 aluminum. These tests showed a significant relationship between stress and temperature and how changes to one can cause a very different resulting behavior. In addition to the creep testing, three creep models were examined as a means of predicting creep behavior. These models included a power law, exponential, and hyperbolic-sine versions and were able to predict creep results with decent accuracy depending on the stress used in the model.Master of Science
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Goodrich, Thomas William. "Thermophysical Properties and Microstructural Changes of Composite Materials at Elevated Temperature". Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/35900.
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Experimental methods were developed and used to quantify the behavior of composite materials during heating to support development of heat and mass transfer pyrolysis models. Methods were developed to measure specific heat capacity, kinetic parameters, microstructure changes, porosity, and permeability. Specific heat and gravimetric data for kinetic parameters were measured with a simultaneous differential scanning calorimeter (DSC) / thermogravimetric analyzer (TGA). Experimental techniques were developed for quantitative specific heat measurement based on ASTM standards with modifications for accurate measurements of decomposing materials. An environmental scanning electron microscope (ESEM) was used in conjunction with a heating platform to record real-time video of microstructural changes of materials during decomposition and cooling following decomposition. A gas infusion technique was devised to measure porosity, in which nitrogen was infused into the pores of permeable material samples and used to determine the open-pore porosity of the material. Permeability was measured using a standard pressure differential gas flow technique with improvements over past sealing techniques and modifications to allow for potential high temperature use.
Experimental techniques were used to measure the properties of composite construction materials commonly used in naval applications: E-glass vinyl ester laminates and end-grain balsa wood core. The simultaneous DSC/TGA was used to measure the apparent specific heat required to heat the decomposing sample. ESEM experiments captured microstructural changes during decomposition for both E-glass vinyl ester laminate and balsa wood samples. Permeability and porosity changes during decomposition appeared to depend on microstructural changes in addition to mass fraction.Master of Science
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Shah, Manan Kanti. "Material Characterization and Forming of Light Weight Alloys at Elevated Temperature". The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1306939665.
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Sun, Maoye. "On the burst of pipes under internal pressure and elevated temperature /". Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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