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1
Marobhe, Nancy. « Water Supply in Tanzania and Performance of Local Plant Materials in Purification of Turbid Water ». Doctoral thesis, KTH, Mark- och vattenteknik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4781.
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Water supply services in urban and rural areas of Tanzania were reviewed and specific studies were carried out on water supply and on purification of turbid water sources using locally available plant materials in rural villages of Singida Rural District. The review showed that large proportions of urban and rural populations in Tanzania face acute water supply problems mainly due to poor planning, implementation and management of water supply projects, including an inability to address social, technical, operation and maintenance and financial issues. Laboratory-scale experiments studied the effectiveness of crude seed extracts (CSEs) and purified proteins of Vigna unguiculata (VUP), Parkinsonia aculeata (PAP) and Voandzeia subterranea (VS) seeds, which are used traditionally for clarification of turbid water. The VUP and PAP were purified from CSEs using simple and straightforward two-step ion exchange chromatography. The coagulant proteins are thermoresistant and have a wide pH range for coagulation activity. Coagulation of turbid waters with CSEs, VUP and PAP produced low sludge volumes and removed turbidity along with other inorganic contaminants in line with Tanzania drinking water quality standards. The PAP also showed antimicrobial effect against river water bacteria. Citrus fruit juice (CF) enhanced the coagulation of turbid water by CSEs and inhibited bacterial growth, rendering it useful for disinfection of water prior to drinking in rural areas. It was concluded that natural coagulants should not be regarded as a panacea for rural water supply problems, but rather a tool in the development of sustainable water supply services in Tanzania.QC 20100825
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Mwaisumo, Marobhe Nancy Jotham. « Water supply in Tanzania and performance of local plant materials in purification of turbid water / ». Stockholm : Mark- och vattenteknik, Land and Water Resource Engineering, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4781.
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Tziraki, Maria. « The development of photorefractive holography through turbid media for application to biomedical imaging ». Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341934.
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Ducay, Rey Nann Mark Abaque. « Direct Detection of Aggregates in Turbid Colloidal Suspensions ». Miami University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=miami1439434385.
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Su, Rong. « Assessment of optical coherence tomography for metrology applications in high-scattering ceramic materials ». Licentiate thesis, KTH, Mätteknik och optik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-98621.
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Large-scale and cost-effective manufacturing of ceramic micro devices based on tape stacking requires the development of inspection systems to perform high-resolution in-process quality control of embedded manufactured cavities, metal structures and defects. In this work, alumina ceramic samples are evaluated by optical coherence tomography (OCT) operating at 1.3μm wavelength and some dimensional data are obtained by dedicated image processing and segmentation. Layer thicknesses can be measured and laser-machined channels can be verified embedded at around 100μm depth. Moreover, detection of internal defects is enabled. Monte Carlo ray tracing simulations are employed to analyze the abilities of OCT in imaging of the embedded channels. The light scattering mechanism is studied for the alumina ceramics, and different scattering origins and models are discussed. The scattering parameters required as input data for simulations are evaluated from the integrating sphere measurements of collimated and diffuse transmittance spectra using a reconstruction algorithm based on refined diffusion approximation approach.QC 20120628
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Temple, Benjamin John. « Advancements of Gas Turbine Engines and Materials ». OpenSIUC, 2020. https://opensiuc.lib.siu.edu/theses/2763.
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This thesis starts out with a brief description of gas turbine engines and information on railroad locomotives being the gas-turbine electric locomotives with some comparison of the diesel-electric locomotives in the introduction. Section 1.1 is the research problem looking at the older gas turbine electric locomotives in the 1950’s that ran on the rail and the problems they suffered. In section 1.2 titled the purpose of the study takes a look at newer gas turbine locomotives that were being consider or has been built with improvements since the 1950’s. The objective of the study being section 1.3 looks at the advantages of new gas turbines engines. Section 1.4 titled the research questions discusses better materials and methods of gas turbine engines. Chapter 2 is the literature review looking at the fuel oil specifications being number 4, number 5, and number 6. This chapter also talks about the used of distillates, types of distillates, composition of distillates, specifications for distillates, residual fuel oil and fuel oil quality dealing with the firing of gas turbine engines. Section 2.3 of chapter 2 being titled power generation looks at power plant gas-turbine engines and the power they produce. Chapter 3, titled the proposed methodology looks at setting up an experiment using a gas-turbine engine and a diesel-electric engine to compare the advantages of along with the disadvantages. Section 3.1 is titled data collected, within this section is discussion on the data collected from the experiment and improvements that could be made to the gas turbine engines. The end of chapter 3, section 3.2 titled data analyzing, talks about possible the results collected, calculations done, improvements made and rerunning another experiment with the improvements made. Chapter 4 discuss the types of materials using in building the compressor and turbine blades. Last, but not least is chapter 5 which discusses the actual experiment using the gas turbine simulator for aircrafts and how to apply it to the railroad locomotives. After the conclusion which discusses the results, is the appendix a being gas tables, appendix b being trial run 1 and appendix c being trial run 2.
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Nowak, William J. « Fatigue stress analysis of turbine blades / ». Online version of thesis, 2007. http://hdl.handle.net/1850/5467.
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Roth, Richard. « Materials substitution in aircraft gas turbine engine applications ». Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/13112.
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Nalin, Laura. « Degradation of environmental protection coatings for gas turbine materials ». Thesis, Cranfield University, 2008. http://dspace.lib.cranfield.ac.uk/handle/1826/4522.
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Nowadays, problems of component materials reliability in gas and oil-fired gas turbines focus on assessing the potential behaviour of commonly employed coatings, in order to avoid expensive and unpredictable failure in service and producing new materials whose performance meets life time and manufacturing/ repairing requirements. This MPhil project has investigated the oxidative and corrosive degradation mechanisms for some of the alloy/coatings systems (CMSX-4, CMSX-4/ RT22, CMSX-4/ CN91 and CMSX-4/ “LCO22”), which are currently used for turbines blades and vanes, in order to achieve a better knowledge of materials behaviour and to improve models for the prediction of turbine components’ lives. To achieve this target the study has made use of realistic simulations of turbine exposure conditions in combined with pre- and post-exposure metrology of bar shape materials samples, while optical microscopy has been applied to describe the microstructural evolution during the exposure and the products of the degradation for the hot corrosion. For high temperature oxidation, over extended periods of time (up to 10,000 hours), the research has allowed to describe the morphological changes in respect of the exposure time and temperature and to determine the oxidation kinetics experienced by the alloy and coatings. A model has been presented for predicting θ- α-Al2O3 growth. Moreover, using NASA COSP spalling model, with rate constants values coming from this study, a comparison between experimental mass change data and prediction has been shown. The hot corrosion study has provided new quantitative metal loss data and observations that extend/validate an existing model for materials life prediction, based on defining the severity of the corrosion conditions through measures of gas composition and contaminant deposition flux.
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Davoodi, Mehdi. « High performance repair materials in hydraulic structures and machines ». Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285358.
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Li, Jianing. « Characterization of a Novel Porous Injector for Multi-Lean Direct Injection (M-LDI) Combustor ». University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1530269081550143.
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Chang, Min Carleton University Dissertation Engineering Mechanical. « Damage tolerance of Inconel 718 turbine disc material ». Ottawa, 1991.
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13
Andersen, Niklas. « Wind Turbine End of Life : Characterisation of Waste Material ». Thesis, Högskolan i Gävle, Avdelningen för bygg- energi- och miljöteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-20633.
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Wind power is growing fast all over the world, and in Sweden alone thousands of turbines has been installed the last few decades. Although the number of decommissioned turbines so far is very low, the rapid installation rate indicates that a similar rapid decommissioning rate is to be expected shortly. If the waste material from these turbines is not handled sustainably the whole concept of wind power as a clean energy alternative is challenged. This study aims to present an accurate estimate of the amounts of waste material that will be generated from wind turbines in Sweden during the coming decades, allowing the waste management industry to plan for this and by extension prevent unnecessary energy losses through imperfect waste treatment. It should also present helpful information on how problematic waste can be reduced or avoided. VindStat’s annual report, presenting installation date and other relevant data for most installed turbines in Sweden, has been used as the base for the calculations. Information on material composition in different types and sizes of wind turbines has been extracted from various life cycle assessments, and by using the available parameters in the data base each turbine has been assigned a specific amount of steel, iron, copper, aluminum, blade material and electronics. An average life time of 20 years has been assumed, based on prior research and comparison with empiric data, and the material of each turbine is therefore seen as generated waste 20 years after installation date. To calculate the amount of waste material from replacing faulty components, empiric data over replacement rates in further developed markets has been combined with a prognosis over future development of installed wind capacity in Sweden based on a method described by prior research. As no sufficient way to predict how the future second hand market for turbines and components has been found, three different possible scenarios have been investigated to see how this may affect waste amounts. The results show that annual waste will grow slowly at about 12 % increase per year until around 2026, and then the average increase is 41 % per year until 2034. By then, annual waste amounts are estimated to have reached 237 600 tonne steel and iron (16 % of currently recycled amounts), 2 300 tonne aluminium (4 %), 3 300 tonne copper (5 %), 343 tonne electronics (<1 %) and 28 100 tonne blade material. There is no industrial scale recycling method for commonly used blade materials, and a high strength steel developed by Sandvik is proposed as a fully recyclable material to consider for further research. A well-functioning second hand market is shown to possibly have a major impact on waste amounts, at least in postponing it until better recycling systems are in place.Vindkraft är en snabbt växande energikälla världen över och enbart i Sverige har tusentals vindkraftverk installerats under senaste decennier. Även om antalet nedmonterade verk än så länge är relativt lågt, indikerar det stora antalet årliga installationer att ett liknande antal nedmonteringar är att vänta inom kort. Om avfallsmaterialet från dessa verk inte hanteras på ett hållbart sätt riskeras att syftet med vindkraft som ett miljövänligt alternativ utmanas. Målet med studien är att presentera en noggrann uppskattning om vilka mängder avfallsmaterial som kommer att genereras från vindkraftverk i Sverige under kommande årtionden, vilken kan användas för att planera avfallshantering och på så vis i förlängningen undvika onödiga energiförluster genom felaktiga processer. Information om hur problematiskt avfall kan undvikas eller minskas ska även presenteras. Vindstats årliga rapport, vilken presenterar installationsdatum och annan relevant information för de flesta installerade vindkraftverk, har använts som bas för beräkningar. Information över materialfördelning i olika typer och storlekar av vindkraftverk har extraherats från ett antal livscykelanalyser och genom att använda tillgängliga parametrar i databasen har varje enskilt vindkraftverk tilldelats en specifik mängd stål, järn, koppar, aluminium, bladmaterial och elektronik. En genomsnittlig livslängd på 20 år har antagits, baserat på tidigare forskning och jämförelse med empirisk data, och materialet i vindkraftverken har därför setts som genererat avfall 20 år efter installationsdatum. För att beräkna mängden avfallsmaterial från utbytta komponenter har empirisk data över utbytningsfrekvenser hos mer utvecklade marknader applicerats på en prognos över över möjlig framtida utbyggnad av vindkraftskapacitet i Sverige som skapats enligt en metod beskriven i tidigare forskning. Eftersom ingen fullständig metod har funnits för att förutse hur framtida andrahandsmarknad för vindkraftverk och komponenter så har tre möjliga scenarion undersökts för att se hur detta kan komma att påverka avfallsmängder. Resultaten visar att de årliga avfallsmängderna förväntas växa med ca 12 % per år fram till 2026, och därefter i genomsnitt 41 % per år fram till 2034. Då förväntas avfallsmängderna uppnått 237 600 ton stål och järn (16 % av nuvarande återvunnen mängd), 2 300 ton aluminium (4 %), 3 300 ton koppar (5 %), 343 ton elektronik (<1 %) och 28 100 ton bladmaterial. Det finns ingen metod för att återvinna vanligen använda bladmaterial på industriell skala, och ett extra starkt stål utvecklat av Sandvik föreslås som fullt återvinningsbart alternativ att undersöka. En väl fungerande andrahandsmarknad visar sig kunna ha en betydande inverkan på framtida avfallsmängder, åtminstone genom att skjuta upp behovet av hantering tills ett mer effektivt system finns på plats.
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Romanoski, Glenn Roy. « The fatigue behavior of small cracks in aircraft turbine disk alloys ». Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/32577.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1990.Includes bibliographical references (leaves 245-258).
by Glenn R. Romanoski, Jr.
Ph.D.
15
Verona, Claire L. « Stress corrosion cracking of low pressure steam turbine blade and rotor materials ». Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/10165.
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Stress corrosion cracking of a 14 wt% Cr martensitic stainless steel, with commercial names PH-15Cr5Ni, FV520B or X4CrNiCuMo15-5, used for the manufacture of low pressure turbine blades, has been studied with the intention of gaining a better understanding of the processes involved, how they occur and why. Industrially this is very important as stress corrosion cracking is considered to be a delayed failure process, whereby microscopic cracks can potentially propagate through a metal undetected until catastrophic failure occurs. The aim of this work is to establish links between crack length and external factors, such as exposure time, in order to devise a method of dating stress corrosion cracks and therefore predicting their possible occurrence in-service.
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Saari, Henry M. J. « The processing of gas turbine engine hot section materials through directional solidification ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0018/MQ48472.pdf.
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Zhang, P. « Development of next generation high temperature materials for high performance gas turbine ». Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1474017/.
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Thermal barrier coatings (TBCs) are advanced protective coating systems used to protect metallic substrates at high-temperature application. Currently, the state-of-the-art industrial TBC material is 6-8wt% Y2O3 stabilized ZrO2 (6-8YSZ), but it cannot be used over 1200oC for a long time due to sintering behaviour and phase transformation. The purpose of this thesis was to explore new thermal barrier materials that can be used at high temperature for a long time to replace YSZ. Micron lanthanum titanium aluminum oxide (LaTi2Al9O19, LTA) has been proven as a very promising thermal barrier material due to low thermal conductivity, and excellent phase and thermochemical stability. The main drawback of LTA is the low fracture toughness. Therefore, this thesis studied nano-structured LTA, toughened LTA, and ion doped LTA synthesized by sol- gel method, and LTA and toughened LTA coatings on steel substrate prepared by air plasma spray (APS). The experimental results indicate that compared to micron LTA, the nano-structured LTA had higher coefficients of thermal expansion (CTEs) and comparable thermochemical stability. LTA toughened by 10vol% tetragonal zirconia (LTA-4YSZ) was synthesized by a hybrid sol-gel method. The ceramic composite LTA- 4YSZ had lower thermal conductivity of approximately 1.054 W/(m·K) at room temperature, stable CTEs, better sintering resistance, and mechanical properties. Single phase ion doped LTA by gadolinium was obtained with a Gd3+ content of less than 10mol%, La0.9Gd0.1Ti2Al9O19 (L9G1) had higher CTEs around 11.7×10-6 oC-1 at 950oC, lower thermal conductivity circa. 1.404 W/(m·K) at room temperature, and better sintering resistance than LTA. The APS produced LTA-4YSZ coatings were prepared with optimized granulated powders, which were typical APS coatings with five types of defects: cracks, gaps, cavities, voids, and interspace.
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Saari, Henry M. J. Carleton University Dissertation Engineering Mechanical and Aerospace. « The Processing of gas turbine engine hot section materials through directional solidification ». Ottawa, 1999.
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Walsh, Justin M. « Composite material bend-twist coupling for wind turbine blade applications ». Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1965523621&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Carter, Jace A. « EFFECT OF MATERIAL ANOMALIES ON FATIGUE LIFE OF TURBINE DISKS ». Wright State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=wright1316211638.
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Elm, Svensson Erik. « Nanotemplated High-Temperature Materials for Catalytic Combustion ». Doctoral thesis, KTH, Kemiteknik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4800.
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Catalytic combustion is a promising technology for heat and power applications, especially gas turbines. By using catalytic combustion ultra low emissions of nitrogen oxides (NOX), carbon monoxide (CO) and unburned hydrocarbons (UHC) can be reached simultaneously, which is very difficult with conventional combustion technologies. Besides achieving low emission levels, catalytic combustion can stabilize the combustion and thereby be used to obtain stable combustion with low heating-value gases. This thesis is focused on the high-temperature part of the catalytic combustor. The level of performance demanded on this part has proven hard to achieve. In order to make the catalytic combustor an alternative to the conventional flame combustor, more stable catalysts with higher activity have to be developed. The objective of this work was to develop catalysts with higher activity and stability, suitable for the high-temperature part of a catalytic combustor fueled by natural gas. Two template-based preparation methods were developed for this purpose. One method was based on soft templates (microemulsion) and the other on hard templates (carbon). Supports known for their stability, magnesia and hexaaluminate, were prepared using the developed methods. Catalytically active materials, perovskite (LaMnO3) and ceria (CeO2), were added to the supports in order to obtain catalysts with high activities and stabilities. The supports were impregnated with active materials by using a conventional technique as well as by using the microemulsion technique. It was shown that the microemulsion method can be used to prepare catalysts with higher activity compared to the conventional methods. Furthermore, by using a microemulsion to apply active materials onto the support a significantly higher activity was obtained than when using the conventional impregnation technique. Since the catalysts will operate in the catalytic combustor for extended periods of time under harsh conditions, an aging study was performed on selected catalysts prepared by the microemulsion technique. The stability of the catalysts was assessed by measuring the activity before and after aging at 1000 C in humid air for 100 h. One of the most stable catalysts reported in the literature, LMHA (manganese-substituted lanthanum hexaaluminate), was included in the study for comparative purposes. The results showed that LMHA deactivated much more strongly compared to several of the catalysts consisting of ceria supported on lanthanum hexaaluminate prepared by the developed microemulsion method. Carbon templating was shown be a very good technique for the preparation of high-surface-area hexaaluminates with excellent sintering resistance. It was found that the pore size distribution of the carbon used as template was a crucial parameter in the preparation of hexaaluminates. When a carbon with small pores was used as template, the formation of the hexaaluminate crystals was strongly inhibited. This resulted in a material with poor sintering resistance. On the other hand, if a carbon with larger pores was used as template, it was possible to prepare materials with hexaaluminate as the major phase. These materials were, after accelerated aging at 1400 C in humid air, shown to retain surface areas twice as high as reported for conventionally prepared materials.QC 20100719
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Heaton, Mark Edwin. « A laser-machined MEMS axial flow turbine : design, fabrication, testing and materials analysis ». Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/13174.
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This thesis details the design, fabrication and characterisation of a 13 mm-diameter axial flow microturbine with an integrated electromagnetic generator. Axial turbine blades are not amenable to fabrication by traditional MEMS (micro-electromechanical systems) processes because they cannot be produced by machining prismatic shapes into the rotor disc; the direction of machining has to change as material is removed to produce the required blade curvature. This challenge was met by laser machining the blades with a novel moving-mask process so as to produce a step-wise approximation to the desired profile. The chosen material for making the microturbine rotor was the negative photo-resist SU-8. Once properly cured into its solid state, this polymer becomes very durable and dimensionally stable. The SU-8 was readily preformed using lithography and RIE (reactive ion etching), and was also responsive to excimer laser ablation as necessary for finishing the blade profiles. The microturbine was designed to be assembled into a stacked MEMS device comprising a rotor embedded with ten rare earth magnets sandwiched between upper and lower silicon stators carrying electroplated generator coils. Characterisation of the turbine showed that mechanical losses, mainly in the bearings, were significantly reducing the efficiency. A laser scanning vibrometer (Polytec MSA-400) was used to measure the turbine rundown time which was found to be only ~150 ms due to high bearing friction. The in-plane and out-of-plane vibration (wobble) of the rotor as it spun around on its micro roller bearings were also mapped to determine if bearing alignment was reducing power output. The out-of-plane vibration was found to be the main problem, so a new one-piece rotational support holder was constructed for the device. Some microturbine rotors were found to shatter above 100,000 rpm, and this led to interest in the mechanical properties of the cured SU-8. Firstly, PGAA (prompt gamma activation analysis) was used to measure the constituent element percentages and contaminants in a range of SU-8 samples subjected to different heat curing temperatures and UV cross-linking times. It was of interest to see how the O and H percentages changed as these are normally expected to vary depending on temperature and humidity. SANS (small angle neutron scattering) tests were also performed using a 10 MW reactor which measured sub-surface scattering for the same samples to reveal material defects.
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Evangelou, Angelos. « Oxidation-fatigue mechanisms at moderate service temperatures in single crystal turbine blade materials ». Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/420749/.
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The shortage of fossil fuels and the emergence of renewable energy technologies have increased the demand for a more variable and efficient power output from conventional gas turbine units. Single crystal Ni-based superalloys have long been the materials of choice for high temperature, gas turbine blade, applications due to their excellent fatigue, creep and oxidation resistance. However, the increased number of start-ups and shut downs, produce complex, unpredictable, cyclic loadings even at moderate temperatures, where the fatigue - oxidation behaviour of such materials is less well understood. The gas turbine industry has significant economic incentives to optimise maintenance scheduling and determine the useful lifetime of such components and thus a substantial effort is put in the development of damage tolerant, life assessment methods. This thesis aims to elucidate the mechanisms of oxidation - fatigue damage at moderate service temperatures, in single crystal, Ni-based superalloy turbine blade materials, in order to provide the basis for a physics based lifing model accounting for fatigue oxidation interactions. The oxidation behaviour of two commercially available single crystal nickel based superalloys (in CMSX-4 and MD-2) has been investigated at the lower operating temperature range (450-550°C) of an industrial gas turbine blade. Isothermal oxidation was carried out for varying times up to 640h and it was found that exposure resulted in a sub-micron thick oxide. The external and internal oxide kinetics were studied via high resolution image analysis and both showed sub-parabolic growth rates. Thermogravimetric tests indicated that the overall oxidation growth obeys a near quartic power law while parabolic kinetics can describe the transient oxidation period. Characterisation of the resulting oxides was carried out using field emission gun scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Results from thermodynamic modelling (Thermo-Calc) of the oxide formation are also presented. Low temperature oxidation in these Ni-based superalloys begins with the formation of porous NiO protrusions over the γ matrix. As the oxygen partial pressure drops in the substrate, a transition alumina forms near the surface within the γ’. The oxygen anions that diffuse into the alloy, preferentially through the γ/γ’ interface and come in contact with the internal Al-rich γ’ phase. This leads to the preferential oxidation of the γ’ particles internally while the γ matrix remains relatively unaffected. The notch fatigue initiation process has been studied at 450-550oC in CMSX-4 in both air and vacuum (low oxygen partial pressure) environments, to assess the effect of oxidation. Detailed, electron microscopy, fractography indicated that crack initiation in an oxidising environment at 450°C and 550°C, is dominated by subsurface porosity while initiation at lower temperatures and low oxygen partial pressure environments result in crystallographic cracking promoted by surface defects. At these temperatures, oxidation acted as a retardation mechanism to surface initiation processes by plugging porosity and interfering with the resulting strain levels. Porosity not only controlled initiation but also produced significant scatter in the fatigue lives obtained thus constituting an inherent feature of service conditions and should be considered in lifing approaches. Dwell-fatigue testing was conducted on CMSX-4 samples at 450°C and 550°C in air and vacuum (low oxygen partial pressure). The effects of frequency (dwell) on the fatigue crack growth behaviour were studied using a constant stress intensity range test and blocks of alternating frequencies. It was found that at 550oC, a dwell time of 20s or higher (< 0.04Hz) promotes a mixed time/cycle dependent crack growth rate. In order to further investigate the effect of dwell on the crack tip damage, pre-cracked samples were held under sustained loads for 12h. The resulting crack tips were examined using transmission electron microscopy and the resulting oxides using high resolution energy dispersive spectroscopy. Cracks forming under long dwell fatigue conditions had a complex morphology and formed several sub-branches that resulted in rougher fracture surfaces. During dwell fatigue crack propagation at intermediate temperatures, several competing mechanisms contribute synergistically to damage. In addition, the effects of oxidation were found to be two-fold. Strain assisted oxygen diffusion at small distances ahead of the crack tip can promote fracture at the γ/γ’ interface while oxide formation on the crack tip surfaces can bridge the crack tip opening and reduce the effective driving force.
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Naicker, Leebashen. « Influence of heat treatment condition on the stress corrosion cracking properties of low pressure turbine blade steel FV520B ». Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25377.
Texte intégralRésumé :
Stress corrosion cracking (SCC) is a corrosion phenomenon which continues to plague the power generating industry especially in low pressure (LP) steam turbine blades operating in the phase transition zone. An investigation has therefore been conducted to examine the effect of heat treatment condition on the microstructure, mechanical properties and SCC properties of one such LP turbine blade material, FV520B, used in the steam turbines of coal-fired power stations in South Africa. The three stage heat treatment cycle of the FV520B turbine blades consists of homogenisation at 1020°C for 30 minutes, solution treatment at 790°C for two hours and precipitation hardening at 545°C for six hours. In this study, the precipitation hardening temperature was varied in the range 430-600°C to investigate how this variation would affect the material and SCC properties. Hardness and tensile testing were performed to obtain mechanical properties while the investigative techniques used to characterise the microstructures were light microscopy, dilatometry, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Stress corrosion susceptibility for the different heat treatment conditions was quantified using U-bend specimens while crack growth rates and threshold stress intensities for SCC (KISCC) were measured using fatigue precracked wedge open loaded (WOL) specimens. Both SCC tests were conducted in a 3.5% NaCl environment maintained at 90°C. XRD results revealed the presence of reverted austenite in the higher tempered specimens due to the precipitation hardening temperature being close to the Ac1 temperature for the material. The presence of reverted austenite was shown to adversely affect mechanical strength and hardness which decreased with increasing precipitation hardening temperature. Light and electron microscopy (SEM and TEM) revealed the presence of Cr-rich precipitates along the prior austenite grain boundaries in all tested heat treatment conditions. The propensity, quantity and size of the Cr-rich precipitates increased as the specimen temper temperature increased. SCC susceptibility was shown to be dependent upon yield strength and decreased as precipitation hardening temperature increased with specimens in the overaged condition showing no cracking after more than 5000 hours in the test environment. WOL testing only produced cracking in the three highest strength specimens after 2000 hours. Crack growth rates and threshold stress intensities were found to be dependent on yield strength and decreased with increasing precipitation hardening temperature. Analysis of fracture surfaces revealed crack propagation along prior austenite grain boundaries in all test heat treatment conditions indicating intergranular stress corrosion cracking (IGSCC) as the dominant cracking mechanism.
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Hu, Dawei. « Development of the epoxy composite complex permittivity and its application in wind turbine blades ». Thesis, Queen Mary, University of London, 2010. http://qmro.qmul.ac.uk/xmlui/handle/123456789/540.
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Offshore wind farm structures may have the potential to affect marine navigation and communication systems by reflecting radar signals. With ever increasing size of wind turbines it is necessary to better understand the influence of radar signals on wind turbine blades in order to minimise the radar reflecting potential. One possible way of reducing radar reflection is to use radar absorbing materials. In this thesis, epoxy composite materials reinforced with five different types of nano-size additives: carbon nanotubes (CNTs), carbon blacks (CBs), silver, tungsten carbide and titanium oxide are manufactured and tested to investigated their potential as wind turbine blade material that absorb radar signals. Nanoadditives/epoxy composites with additives content ranging from 0.05-1 wt. % were fabricated by a simple cast moulding process. The nanoadditives were dispersed in the epoxy resin by sonication method. The degree of nanoadditives dispersion was observed by examining the surface of the composite materials using scanning electron microscope (SEM). Complex permittivity of the nanoadditives/epoxy composites was studied using a free wave transmittance only method at a frequency range of 6.5-10.5 GHz. The effect of the percolation threshold of the direct current conductivity on the composite permittivity was analysed and discussion. In order to get a better insight in the importance of the results they were compared to existing models (Maxwell- Garnett, Bruggeman, Bottcher, Lichtenecker and Lichtenecker-Rother). A new model based rule of mixtures is developed to predict the complex permittivity of the composite. A model of wind turbine rotor blade made of the nanoadditives/epoxy composite was developed using Comsol-multiphysics software. The data obtained from the experimental work was inputted in to the model to generate result of backscattered energy verses composite permittivity as a function of nanoadditives content. A decrease in backscattered energy was noticed with increasing nanoadditives content. The results demonstrate that radar reflecting signals will be significantly reduced by incorporating nanoadditives in the composite materials.
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Caley, Thomas. « Numerical Modeling of Gas Turbine Combustor Utilizing One-Dimensional Acoustics ». University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1491562189178949.
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Seumangal, Nicole. « Influence of the heat treatment procedure on the stress corrosion cracking behaviour of low pressure turbine blade material FV566 ». Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27427.
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Stress corrosion cracking is one of the leading damage mechanisms in low-pressure turbines in the power generation industry; in LP turbine blades it primarily occurs in the last stage blades. The research investigated the influence of tempering temperature on the microstructure, mechanical properties, and stress corrosion cracking properties of 12% chromium FV566 stainless steel, which is used to manufacture LP turbine blades. The standard heat treatment of the steel comprises of austenitising, quenching and double tempering. Austenitising is carried out at 1050°C for one hour - which is sufficiently long to generate a fully austenitic matrix and to dissolve carbon completely. Subsequently, the material is quenched in air. The high level of alloying elements ensures the complete martensitic transformation, with carbon atoms trapped in the matrix and distributed homogeneously. Thereafter, tempering of the material at 580-600°C enhances the ductility and toughness. Tempering replaces the solid solution strengthening of the dissolved carbon with precipitation strengthening by carbides. The final microstructure of the FV566 steel blades is referred to as tempered martensite. van Rooyen showed that for 12% chromium steel tempering at and above 600°C induces passivity of the material against SCC, while tempering of 12% chromium steels at 450-550°C causes sensitisation of the material and the material exhibits intergranular SCC. From such studies, the motivation arises to investigate the impact of heat-treatment parameters - specifically the impact of tempering temperature on the stress corrosion behaviour of the material. The testing methodology comprises heat treatment of FV566 samples at 1050°C for 1 hour, at 350°C for 1 hour, and thereafter tempering for 1 hour at various tempering temperatures. Each stage of heat treatment is followed by air cooling - followed by analysis of the microstructure, mechanical testing and stress corrosion cracking testing of the specimens at the different temper conditions. Stress corrosion testing was divided into two categories. The first set of tests was carried out with U-bend specimens to determine the susceptibility of materials at different heat treatments to SCC, the time taken for SCC to initiate, and the mode of cracking. The second set of tests was conducted to determine the threshold stress intensity, as a function of crack growth rate, for each heat treatment. The SCC failure mechanism observed was intergranular SCC (IGSCC) by anodic dissolution for the 550°C, 560°C, 570°C, 580°C, 590°C, 600°C and 620°C specimens. The material's resistance to SCC improved with increasing tempering temperature. Specimens tempered at 480°C and 550°C were most susceptible to SCC, while specimens tempered at 600°C The material's resistance to SCC improved with increasing tempering temperature. Specimens tempered at 480°C and 550°C were most susceptible to SCC, while specimens tempered at 600°C were immune to SCC in a 4000-hour period. A change in tempering temperature results in a change in the quantity and type of precipitates formed which results in changes in SCC properties of FV566.
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Hartigan, Timothy James. « Effects of notches and fretting on fatigue of steam turbine materials at 524°C ». Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/16726.
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Agnese, Fabio. « Enhanced vibration damping materials and structures for wind turbine blades inspired from auxetic configurations ». Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.653091.
Texte intégralRésumé :
An extensive analysis of the current applications and possible employments of auxetic materials and configurations is presented. These novel materials show a negative Poisson's ratio and, potentially, enhanced mechanical properties. Despite a substantial amount of publications can be found in literature about auxetic material properties, not many of these consider practical applications for them. Objective and novelty of this project is therefore the application of auxetic material and/ or auxetic inspired configurations to existing structures and in particular to wind turbine blades to modify their dynamic characteristics. Wind turbine blades are complex systems manufactured using polymer matrix composite materials and at present made of a combination of glass and carbon fibre · reinforced plastic (GFRP-CFRP). Total damping in a blade is a combination of aerodynamic and structural loss factors, the latter being related to the inherent damping of the material. The two fundamental modes of vibration related to bending are of flapwise and edgewise type. The structural damping is material dependent, therefore the amount of structural damping available for these two vibration modes is the same. However, for the flapwise mode, the aerodynamic damping plays a very important role for the overall modal damping r.atio, whereas for the edgewise mode the only damping mechanism present is the str.uctural one. As a consequence, only a low value of loss factor can be achieved in the edgewise direction. The first aim of this project is then to demonstrate how auxetic inspired structure can be successfully applied to increase the loss factor of the blade in the edgewise direction of vibration. To this end several solutions have been investigated starting from the utilisation of 3D auxetic foams. They showed an effective increase in loss factor but limited by the fact that at present these foams present a low stiffness. Other solutions considered macro composites with shaped fibres and a novel damper design. Both these solutions have been analysed and characterised either by FE analysis and laboratory testing.
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Han, Songlin. « High temperature deformation modelling and finite element implementation for single crystal turbine blade materials ». Thesis, University of Bristol, 2000. http://hdl.handle.net/1983/943aaa75-6406-4a06-9250-9b0ae85a5eae.
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Ketcham, Jerod W. « Design, build and test of an axial flow hydrokinetic turbine with fatigue analysis ». Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/10945/4943.
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CIVINSApproved for public release; distribution is unlimited
OpenProp is an open source propeller and turbine design and analysis code that has been in development since 2007 by MIT graduate students under the supervision of Professor Richard Kimball. In order to test the performance predictions of OpenProp for axial flow hydrokinetic turbines, a test fixture was designed and constructed, and a model scale turbine was tested. Tests were conducted in the MIT water tunnel for tip speed ratios ranging from 1.55 to 7.73. Additional code was also written and added to OpenProp in order to implement ABS steel vessels rules for propellers and calculate blade stress. The blade stress code was used to conduct a fatigue analysis for a model scale propeller using a quasi-steady approach. Turbine test results showed that OpenProp provides good performance predictions for the ondesign operational condition but that further work is needed to improve performance predictions for the off-design operational condition. Fatigue analysis results show that reasonable estimates of propeller blade fatigue life can be obtained using a relatively simple method.
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Vick, Andrew W. « Genetic Fuzzy Controller for a Gas Turbine Fuel System ». University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1291053513.
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Gouni, Rajkiran. « A New Technique to Study Temperature Effects on Ice Adhesion Strength for Wind Turbine Materials ». Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1283536362.
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Cramer, Klaron Nathanael. « Design, Construction, and Preliminary Validation of the Turbine Reacting Flow Rig ». The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243987343.
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Swar, Rohan. « Particle Erosion of Gas Turbine Thermal Barrier Coating ». University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1259075518.
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Cortelini, Euzineri de Menezes. « Resposta e controle das vibrações de uma torre eólica usando MR-TLCD (magneto reológico-amortecedor de coluna liquida sintonizada) ». Universidade Federal do Pampa, 2014. http://dspace.unipampa.edu.br:8080/xmlui/handle/riu/771.
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As torres eólicas são estruturas esbeltas projetadas para resistir a efeitos dinâmicos da ação do vento. Uma vez excitada, a torre pode entrar em ressonância ocasionando ruptura e falhas em sua estrutura, pás e rotores. Além de evitar possíveis falhas catastróficas, o sistema de amortecimento pode prevenir fadiga prematura de componentes estruturais da torre, entre eles, o gerador e as pás. A presença de amortecimento limita a amplitude de vibração quando o sistema, que sofre vibração forçada, aproxima-se da ressonância. Dentro desse contexto, foi elaborado um modelo numérico de uma torre eólica que determina a resposta da mesma sob uma excitação forçada. A excitação se deu por meio de um motor de corrente contínua desbalanceado, localizado no topo da torre. A estrutura analisada é composta por uma coluna metálica com um motor elétrico de corrente contínua desbalanceado e acoplado a um amortecedor do tipo MR-TLCD (Tuned Liquid Column Dampers with magnetorheological). Neste trabalho, foi utilizado um amortecedor semiativo, no qual consiste de um tubo em formato de ‘U’ e utiliza o fluido magneto-reológico, onde este impede o movimento de grandes amplitudes sujeito à ação de forças externas. No MR-TLCD é possível diminuir a energia cinética do fluido através da válvula de controle. O Magneto Reológico, quando submetido a um campo magnético, aumenta significativamente a sua viscosidade aparente. A equação de movimento do sistema acoplado entre a torre, motor elétrico e MRTLCD foi formulado através das equações de Lagrange. Nesta dissertação, apresentam-se as respostas dinâmicas regulares e caóticas de uma torre eólica com um amortecedor do tipo MR-TLCD através do método numérico da dinâmica não linear, utilizando-se da série temporal, do retrato de fase, do espectro de Fourier (FFT) e das curvas de ressonância. Com ensaios experimentais foram obtidos os valores dos parâmetros das configurações físicas e geométricas da estrutura a serem utilizados nas experiências numéricas.
The wind towers are slender structures designed to handle the dynamic effects of wind action. A once excited, the tower can resonate causing rupture and failures in structure, blades and rotors. Besides preventing possible catastrophic failure the damping system could prevent premature fatigue in structural components of the tower between them the rotor and blades. The presence of damping vibration is limited when the system suffer forced vibration approaches of the resonance. In this context was developed a numerical model of a wind tower which determines the response of the structure under a forced excitation. The excitation was done by a dc motor unbalanced situated on the top of the tower. The structure consists of a metallic column with an electric unbalanced dc motor attached to a MR-TLCD damper. This dissertation was presented a Semi-active damper in which consists in U-tube format using magneto rheological fluid (Tuned Liquid Column Dampers with magneto rheological, MR-TLCD). The fluid existing inside the U-tube prevents the movement of large amplitude subject to the actions of external loads. In MR-TLCD is possible to reduce the kinetic energy of the fluid through the control valve. The fluid used in this work, when exposed in a magnetic field significantly increases its apparent viscosity. The motion equation of coupled system between the tower, electric motor and MRTLCD was formulated using the Lagrange equations. This dissertation was presented the regular and chaotic dynamic of a tower using a MR-TLCD damper through the numerical method of nonlinear dynamics, utilizing a time series, phase portrait, Fourier spectrum (FFT) and resonance curves. The characteristic of experimental model was used for developed the numerical model. Also the free vibration tests were utilized for determine the structural parameters of the system.
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Everitt, Stewart. « Developments in advanced high temperature disc and blade materials for aero-engine gas turbine applications ». Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/348897/.
Texte intégralRésumé :
The research carried out as part of this EngD is aimed at understanding the high temperature materials used in modern gas turbine applications and providing QinetiQ with the information required to assess component performance in new propulsion systems. Performance gains are achieved through increased turbine gas temperatures which lead to hotter turbine disc rims and blades. The work has focussed on two key areas: (1) Disc Alloy Assessment of High Temperature Properties; and (2) Thermal Barrier Coating Life Assessment; which are drawn together by the overarching theme of the EngD: Lifing of Critical Components in Gas Turbine Engines. Performance of sub-solvus heat treated N18 alloy in the temperature range of 650°C to 725°C has been examined via monotonic and cyclically stabilised tensile, creep and strain controlled low cycle fatigue (LCF) tests including LCF behaviour in the presence of a stress concentration under load-control. Crack propagation studies have been undertaken on N18 and a particular super-solvus heat treatment variant of the alloy LSHR at the same temperatures, in air and vacuum with 1s and 20s dwell times. Comparisons between the results of this testing and microstructural characterisation with RR1000, UDIMET® 720 Low Interstitial (U720Li) and a large grain variant of U720Li have been carried out. In all alloys, strength is linked to a combination of γ' content and grain size as well as slow diffusing atoms in solid solution. High temperature strength improves creep performance which is also dependent on grain size and grain boundary character. Fatigue testing revealed that N18 had the most transgranular crack propagation with a good resistance to intergranular failure modes, with U720Li the most intergranular. Under vacuum conditions transgranular failure modes are evident to higher temperature and ΔK, with LSHR failing almost completely by intergranular crack propagation in air. For N18 significant cyclic softening occurs at 725°C with LCF initiation occurring at pores and oxidised particles. An apparent activation energy technique was used to provide further insights into the failure modes of these alloys, this indicating that, for N18 with 1s dwell, changes in fatigue crack growth rates were attributed to static properties and for LSHR, with 20s dwell in air, that changes were attributed to the detrimental synergistic combination of creep and oxidation at 725°C. Microchemistry at grain boundaries, especially M23C6 carbides, plays an important role in these alloys. Failure mechanisms within a thermal barrier coating (TBC) system consisting of a CMSX4 substrate, PtAl bond coat, thermally grown oxide (TGO) layer and a top coat applied using electron beam physical vapour deposition have been considered. TGO growth has been quantified under isothermal, two stage temperature and thermal cyclic exposures. An Arrhenius relation was used to describe the TGO growth and produce an isothermal TGO growth model. The output from this was used in the QinetiQ TBC Lifing Model. Thermo-mechanical fatigue test methods were also developed including a novel thermocouple placement permitting substrate temperature to be monitored without disturbing the top coat such that the QinetiQ TBC Lifing Model could be validated. The importance of material, system specific knowledge and performance data with respect to a particular design space for critical components in gas turbine engines has been highlighted. Data and knowledge regarding N18, LSHR and TBC systems has been added to the QinetiQ’s databank enhancing their capability for providing independent advice regarding high temperature materials particularly in new gas turbine engines.
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Liu, Zhimin. « A methodology for probabilistic remaining creep life assessment of gas turbine components ». Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/13004.
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Khoramzad, Elham. « Fretting fatigue life analysis for a gas turbine compressor blade-disk material combination ». Thesis, KTH, Hållfasthetslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-284357.
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In order to analyse fretting fatigue life of dove-tail joints used in the compressor stage of a gas turbine, experimental study of different material combinations was conducted using rectangular fatigue specimen and bridge type pads. Specimen and pad interaction was simulated numerically and obtained results was used as input for 2 different crack propagation life prediction methods. The combined effect of stress and fretting damage which was characterised by means of Ruiz parameter was used in order to estimate the crack initiation and finally numerical results were compared to experimental fretting fatigue life. The aim of this thesis was to study the contact fatigue behaviour of titanium alloy (Ti-6Al-4V) in combination with steel alloy (22NiCrMoV12-7).
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Pang, Hon Tong. « Effect of microstructure variation on turbine disc fatigue lives ». Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274024.
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Prajapati, Seezan. « Numerical Investigation of Power Generated by Turbine Farms ». University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin159216993609908.
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LEE, Tung-Ying. « THE EFECT OF IMPURITIES IN WATER FROM LAKE ERIE ON THE ADHESIVE STRENGTH OF ICE TO WIND TURBINE MATERIALS ». Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1310744454.
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Veldkamp, Herman Frederik. « Chances in wind energy : a probabilistic approach to wind turbine fatigue design / ». [Delft] : DUWIND Delft Univ. Wind Energy Research Inst, 2006. http://www.gbv.de/dms/bs/toc/520167805.pdf.
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Crudden, D. J. « Alloys-by-design : applications to polycrystalline nickel superalloys for turbine disc applications ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:b60e1854-cae4-4dd3-8d6f-cec1351e4c17.
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The nickel-based superalloys have been a key enabler to the development of modern gas turbine engines. Since their introduction the chemical complexity of these alloys has increased significantly, with current generation nickel-based superalloys usually containing over 10 different elements. It is this combination of alloying additions that is responsible for the superior high temperature properties these alloys exhibit. Traditionally, alloy design has invoked considerable use of trial-and-error based approaches involving costly and exhaustive processing backed up by empirical property testing. In this work a computational materials design approach is developed. This method links physically-faithful composition-dependent models with thermodynamic calculations to understand material behaviour. By doing this it is possible to consider large compositional design spaces and isolate alloys expected to have optimal performance for specific applications. The scope of this research has been to apply the computational model to the design of a polycrystalline nickel-based superalloy for turbine disc applications in next generation jet engines. The design trade-offs encountered when developing the new alloy are highlighted. Alloy compositions which are predicted to be optimal for turbine disc applications are isolated. These alloys have been manufactured using a scaled down version of the commercial production method. The newly manufactured alloys have been characterised using microstructural evaluation, mechanical testing and corrosion testing. The experimental results have been compared with modelling predictions in order to determine the capability of the computational approach.
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Von, Hagen William J. « Analysis of the L1A, L1M, L2A, and L2F Low-Pressure Turbine Blades Using Large-Eddy Simulation ». University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470045392.
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Woggon, Nathanial R. « Particle Erosion of a Turbine with Restitution Analysis (PETRA) ». University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1329935606.
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Thamburaj, Rajkumar Carleton University Dissertation Engineering Mechanical. « Environmental and service exposure effects on the fatigue and fracture behaviour of aircraft gas turbine materials ». Ottawa, 1986.
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Mohan, Prabhakar. « Environmental Degradation of Oxidation Resistant and Thermal Barrier Coatings for Fuel-Flexible Gas Turbine Applications ». Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3013.
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The development of thermal barrier coatings (TBCs) has been undoubtedly the most critical advancement in materials technology for modern gas turbine engines. TBCs are widely used in gas turbine engines for both power-generation and propulsion applications. Metallic oxidation-resistant coatings (ORCs) are also widely employed as a stand-alone protective coating or bond coat for TBCs in many high-temperature applications. Among the widely studied durability issues in these high-temperature protective coatings, one critical challenge that received greater attention in recent years is their resistance to high-temperature degradation due to corrosive deposits arising from fuel impurities and CMAS (calcium-magnesium-alumino-silicate) sand deposits from air ingestion. The presence of vanadium, sulfur, phosphorus, sodium and calcium impurities in alternative fuels warrants a clear understanding of high-temperature materials degradation for the development of fuel-flexible gas turbine engines. Degradation due to CMAS is a critical problem for gas turbine components operating in a dust-laden environment. In this study, high-temperature degradation due to aggressive deposits such as V2O5, P2O5, Na2SO4, NaVO3, CaSO4 and a laboratory-synthesized CMAS sand for free-standing air plasma sprayed (APS) yttria stabilized zirconia (YSZ), the topcoat of the TBC system, and APS CoNiCrAlY, the bond coat of the TBC system or a stand-alone ORC, is examined. Phase transformations and microstructural development were examined by using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. This study demonstrated that the V2O5 melt degrades the APS YSZ through the formation of ZrV2O7 and YVO4 at temperatures below 747°C and above 747°C, respectively. Formation of YVO4 leads to the depletion of the Y2O3 stabilizer and the deleterious transformation of the YSZ to the monoclinic ZrO2 phase. The investigation on the YSZ degradation by Na2SO4 and a Na2SO4 + V2O5 mixture (50-50 mol. %) demonstrated that Na2SO4 itself did not degrade the YSZ, however, in the presence of V2O5, Na2SO4 formed vanadates such as NaVO3 that degraded the YSZ through YVO4 formation at temperature as low as 700°C. The APS YSZ was found to react with the P2O5 melt by forming ZrP2O7 at all temperatures. This interaction led to the depletion of ZrO2 in the YSZ (i.e., enrichment of Y2O3 in t' -YSZ) and promoted the formation of the fluorite-cubic ZrO2 phase. Above 1250°C, CMAS deposits were observed to readily infiltrate and significantly dissolve the YSZ coating via thermochemical interactions. Upon cooling, zirconia reprecipitated with a spherical morphology and a composition that depended on the local melt chemistry. The molten CMAS attack destabilized the YSZ through the detrimental phase transformation (t -> t -> f + m). Free standing APS CoNiCrAlY was also prone to degradation by corrosive molten deposits. The V2O5 melt degraded the APS CoNiCrAlY through various reactions involving acidic dissolution of the protective oxide scale, which yielded substitutional-solid solution vanadates such as (Co,Ni)3(VO4)2 and (Cr,Al)VO4. The molten P2O5, on the other hand, was found to consume the bond coat constituents significantly via reactions that formed both Ni/Co rich phosphates and Cr/Al rich phosphates. Sulfate deposits such as Na2SO4, when tested in encapsulation, damaged the CoNiCrAlY by Type I acidic fluxing hot corrosion mechanisms at 1000°C that resulted in accelerated oxidation and sulfidation. The formation of a protective continuous Al2O3 oxide scale by preoxidation treatment significantly delayed the hot corrosion of CoNiCrAlY by sulfates. However, CoNiCrAlY in both as-sprayed and preoxidized condition suffered a significant damage by CaSO4 deposits via a basic fluxing mechanism that yielded CaCrO4 and CaAl2O4. The CMAS melt also dissolved the protective Al2O3 oxide scale developed on CoNiCrAlY by forming anorthite platelets and spinel oxides. Based on the detailed investigation on degradation of the APS YSZ and CoNiCrAlY by various corrosive deposits, an experimental attempt was carried out to mitigate the melt-induced deposit attack. Experimental results from this study demonstrate, for the first time, that an oxide overlay produced by electrophoretic deposition (EPD) can effectively perform as an environmental barrier overlay for APS TBCs. The EPD protective overlay has a uniform and easily-controllable thickness, uniformly distributed closed pores and tailored chemistry. The EPD Al2O3 and MgO overlays were successful in protecting the APS YSZ TBCs against CMAS attack and hot corrosion attack (e.g., sulfate and vanadate), respectively. Furnace thermal cyclic oxidation testing of overlay-modified TBCs on bond-coated superalloy also demonstrated the good adhesive durability of the EPD Al2O3 overlay.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Materials Science & Engr PhD
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Ghulam, Mohamad. « Characterization of Swirling Flow in a Gas Turbine Fuel Injector ». University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563877023803877.
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Shen, Xiang. « Experimental and numerical study of surface curvature effects on the performance of the aerofoils used in small wind turbines ». Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/24739.
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The effects of surface curvature and slope-of-curvature on the performance of aerofoils used in small wind turbines are studied experimentally and numerically. A symmetric aerofoil NACA0012 and an asymmetric aerofoil E387 are judiciously selected as an example of an aerofoil with a surface curvature discontinuity and an example of an aerofoil with slope-of-curvature discontinuities respectively. The prescribed surface curvature distribution blade design (CIRCLE) method is applied to both aerofoils to remove the curvature and slope-ofcurvature discontinuities. The newly designed aerofoils have continuous curvature and slope-of-curvature distributions and have nearly identical geometry compared to the original aerofoils, denoted as QM13F and A7. Low-speed wind tunnel experiments, together with two numerical methods, are conducted to aerofoil E387 and A7 to investigate the effects of slope-of-curvature. The slope-of-curvature discontinuities of E387 result in a larger LSB, which causes higher drag at low angles of attack, and result in premature LSB bursting process at higher angles of attack, causing earlier stall. The impact of the slope-ofcurvature distribution on aerodynamic performance is more profound at higher angles of attack and lower Reynolds number. The aerodynamic improvements are estimated over a 3 kW small HAWT, resulting in up to 10% increase in instantaneous power and 1.6% increase in annual energy production. In terms of the effects of surface curvature, the curvature discontinuity at the leading edge affects aerofoil lift and drag performance near the stalling angle in the steady flow, and it is estimated in a 5 kW small VAWT that the power coefficient can be increased by 9.7% by removing the curvature discontinuity. Acoustic experimental measurements were performed on aerofoil E387 and A7 in an anechoic wind tunnel to investigate effects of slope-of-curvature on aerofoil acoustic performance. The in-house CFD code Cgles was modified to perform large eddy simulation (LES) the 3D aerofoil sections to further investigate the experimental phenomenon. The tonal noise of E387 at different angles of attack is reduced by removing slope-of-curvature discontinuities. It is experimentally and numerically concluded that continuous curvature and slope-of-curvature distributions can result in better aerodynamic performance of the aerofoil used in small wind turbines, leading to lower aerofoil self-noise and higher energy output efficiency.