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1
Abdallah, Zakaria. "Creep lifing methods for components under high temperature creep." Thesis, Swansea University, 2010. https://cronfa.swan.ac.uk/Record/cronfa43065.
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Buttram, Jonathan D. "Characterization of high temperature creep in siliconized silicon carbide using ultrasonic techniques." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03122009-040453/.
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Cain, Victoria. "High temperature creep behaviour niobium bearing ferritic stainless steels." Thesis, Cape Peninsula University of Technology, 2005. http://hdl.handle.net/20.500.11838/1249.
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A thesis submitted to the Faculty of Engineering in
fulfilment of the requirements for the degree of Master of
Technology in Mechanical Engineering
2005The objective of this project was to monitor the high temperature creep behaviour of 441 stainless steel. Two different alloys of 441 were investigated; the main difference between them being the Niobium content. Particularly imporlant to the project was how the Niobium content and grain size affected the creep resistance of the material. Creep tests were performed using purpose built constant load creep test rigs. Initially the rigs were not suitable for the testing procedures pertaining to this project. This was due to persistent problems being experienced with regards the reliability and reproducibility of the rigs. After various modifications were made the results produced from the rigs were consistent. Creep test data was used in order to determine the mechanism of creep that is operative within the material (at a predetermined temperature) under a predetermined load. Particular attention was paid to the resulting stress exponents. in order to identify the operative creep mechanism. The identification of the operative creep mechanisms was also aided by microscopical analysis. This analysis was also necessary to monitor how the grain size had altered at various annealing temperatures. Heat treatment was used as a method to alter the high temperature strength and microstructure of the material. Heat treatments were performed at various temperatures in order to determine the ideal temperature to promote optimum creep resistance of 441. All heat treatments were performed in a purpose designed and built high temperature salt bath furnace. The commissioning of the salt bath formed part of the objectives for this project. Sag testing was also conducted, using purpose built sag test rigs. It was necessary to design and manufacture a sag test rig that could be comparable to the industry accepted method of sag testing known as the two-point beam method, as this method is believed to produce inconsistent results. Conclusions have been drawn from the results of the data and from previous research on the subject matter.
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Palmer, C. J. "High temperature creep of copper." Thesis, Swansea University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638403.
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The key observations that have underpinned traditional power law approaches to creep mechanism identification have been re-evaluated using information obtained for pure copper and aluminium, and also for various other metals and alloys. Specifically, data is presented which show stress/creep rate plots for copper and aluminium over extended stress ranges to be well represented by continuous curves, contradicting the common assumption that a transition in mechanisms occurs as the stress is reduced. Data is also presented from a series of stress interruption tests on pure copper, with strain/strain rate responses which also suggest that essentially the same mechanism dominates creep behaviour at high and low stresses. Furthermore, results for copper single crystals and polycrystals are shown which contradict the assumption that dislocation creep processes are grain size independent so the creep rate increases rapidly with decreasing grain diameter only when diffusional mechanisms are dominant at low stresses. Evidence is also introduced to demonstrate that the theoretical and practical limitations of power-law descriptions of steady-state creep rates can be overcome by quantifying the shapes of normal creep curves and the variations in curve shape with changing stress conditions. The superior predictive capabilities of curve shape analysis are then illustrated by results showing accurate predictions of creep behaviour in the low stress region may be obtained from data generated experimentally at far high stresses. Finally, results are presented showing the effects of a range of room temperature prestrains which illustrate the importance of distinguishing between the contributions made by the grain interiors and the grain boundary zones to the overall rates of strain accumulation during creep.
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Everitt, Nicola Mary. "Indentation creep and anisotropy in magnesium oxide and germanium." Thesis, University of Oxford, 1990. http://ora.ox.ac.uk/objects/uuid:91bd9f5d-f6e9-4f8f-8108-e160ae8c500a.
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Hardness tests have the potential to provide a simple means of investigating the mechanical properties of materials, both at room temperature, and at higher temperatures. However, the information gained can not be fully utilized unless the deformation processes and variables are properly understood. Careful consideration of such deformation on single crystals can help to clarify the situation and lead to better understanding. This thesis describes indentation experiments on (001) MgO and Ge at temperatures up to 1175°C and 700°C respectively. Since anisotropy was one of the questions being addressed, the majority of the testing used Knoop indenters, although a few experiments used Vickers indenters. The work was carried out on a specially commissioned high temperature hardness tester (based on an original design by Wilberforce Scientific Developments). A main conclusion of the discussion on the design of high temperature hardness testers is the importance of independent heating of the indenter for accurate hardness results. The indentation behaviour of MgO was shown to include creep, even at room temperature for the Knoop <110> orientation. However a region of no indentation creep was exhibited between 750°C and 1050°C for both Vickers and Knoop indentations. This has not been reported in previous studies. The anisotropy displayed at room temperature between <110> and <100> Knoop decreased with increasing temperature, due to the faster creep rate of the < 110> orientation, and finally reversed. Knoop indentations in the <110> and <100> orientations on Ge also showed hardness anisotropy which changed with temperature. In this case there was no anisotropy at room temperature, but anisotropy developed as the temperature increased due to the faster creep rate of the <110> orientation. The indentation hardness response of both MgO and Ge is explained in terms of the interaction of dislocation arrays which are formed in the first few moments of the indentation. Measurement of the two diagonals of the Knoop indentations showed that the ratio of the diagonal lengths, and also the morphology of the surrounding material, can be used to examine the extent and direction of material displacement. Surface etching, and etching of sections, were used to analyse the disposition of slip around the indentations.
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Staley, James T. "Mechanisms of creep crack growth in a Cu-1 wt.% Sb alloy." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/10098.
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POWERS, LYNN MARIE. "Mechanical Behavior of Ceramics at High Temperatures: Constitutive Modeling and Numerical Implementation." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1149816510.
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Gardiner, Benjamin Robert. "High temperature creep performance of alloy 800H." Thesis, University of Canterbury. Mechanical, 2014. http://hdl.handle.net/10092/9949.
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Investigations on post service material showed that Alloy 800H pigtails from methanol producer Methanex have service lives ranging from 3 to 18 years. Because of this variability in service life, Alloy 800H creep performance was assessed and a new criterion for its procurement developed. The current criterion recommends an ASTM grain size of 5 (72µm) or coarser with no consideration given to grain size distribution, grain boundary types, or grain boundary network topology. Results from the investigation showed that this current criterion may produce variations in steady state creep rates of an order of magnitude between ASTM grain size 1 and 5, and a 2.5 times variation in creep ductility.
The ability to accurately reveal grain boundaries and assess grain boundary types is fundamental to the identification and quantification of coherent twin boundaries, and the measurement of average grain size and grain size distribution. EBSD mapping has the ability to distinguish grain boundary types using crystal orientation measurement. Grain size measurement from optical micrographs relies on morphological indicators to identify coherent twins. However, it is shown that many of the boundaries observed as straight line morphology on 2D sections did not possess {111} (coherent) interfaces.
3D reconstructions of Alloy 800H revealed the deficiencies in classifying geometry from two-dimensional (2D) sections. Σ3 Crystal volumes can be categorized as lamellar or edge structures. Lamellar structures are characterized by the appearance of parallel Σ3 boundary planes while an edge structure contains a single Σ3 interface. Sectioning plane location alters the perception of morphology. For simple twin structures, the tradition 2D classifications of morphology (complete parallel, incomplete parallel and corner Σ3) may all appear on a section plane from a single lamellar structure.
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Mirmasoudi, Sara. "High Temperature Transient Creep Analysis of Metals." Wright State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=wright1452693927.
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Halverson, Howard Gerhard. "Durability of Ceramic Matrix Composites at Elevated Temperatures: Experimental Studies and Predictive Modeling." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/27834.
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In this work, the deformation and strength of an oxide/oxide ceramic matrix composite system under stress-rupture conditions were studied both experimentally and analytically. A rupture model for unidirectional composites which incorporates fiber strength statistics, fiber degradation, and matrix damage was derived. The model is based on a micromechanical analysis of the stress state in a fiber near a matrix crack and includes the effects of fiber pullout and global load sharing from broken to unbroken fibers. The parameters required to produce the deformation and lifetime predictions can all be obtained independently of stress-rupture testing through quasi-static tension tests and tests on the individual composite constituents. Thus the model is truly predictive in nature. The predictions from the model were compared to the results of an extensive experimental program. The model captures the trends in steady-state creep and tertiary creep but the lifetime predictions are extremely conservative. The model was further extended to the behavior of cross-ply or woven materials through the use of numeric representations of the fiber stresses as the fibers bridge matrix cracks. Comparison to experiments on woven materials demonstrated the relationship between the behavior of the unidirectional and cross-ply geometries. Finally, an empirical method for predicting the durability of materials which exhibit multiple damage modes is examined and compared to results of accurate Monte Carlo simulations. Such an empirical method is necessary for the durability analysis of large structural members with varying stress and temperature fields over individual components. These analyses typically require the use of finite element methods, but the extensive computations required in micromechanical models render them impractical. The simple method examined in this work, however, is shown to have applicability only over a narrow range of material properties.Ph. D.
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Jones, J. Nicholas. "Flux creep and magnetization in high temperature superconductors." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307081.
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Swaroop, N. R. Sathya. "Processing And High Temperature Deformation Of Pure And Magnesia Doped Alumina." Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/180.
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Creep resistance is an important design criterion at high temperatures especially when continuous attempts are made to increase the efficiencies by increasing the operating temperatures. Alumina is an important high temperature material and in addition to that it is used in wide variety of applications such as substrates for electronic packaging, spark plugs, envelopes for sodium vapour lamps, cutting tools (when reinforced with silicon carbide) and in artificial joint prostheses.
Studies on creep in alumina. have started as early as 1961. There are differing mechanisms proposed to explain the creep behaviour of alumina in the literature, but until now there is no any unanimous decision as to what the rate controlling mechanism is. Magnesia doped at ppm levels can produce significant changes in the microstructure of alumina, the most important consequence of that being the grain growth inhibition, which renders alumina superplastic. However, in a stoichiometric oxide like alumina, small impurities can create extrinsic defects which would change the diffusivities and creep rates. Therefore the background impurities in alumina should be kept to a minimum, if small dopant effects have to be studied. The present study was undertaken making use of high purity alumina powder and comparing the grain growth and creep properties of pure and magnesia doped alumina, especially since no such investigation was carried out in the recent past with high purity alumina.
Pure alumina was processed by cold compaction followed by cold isostatic pressing (CIP) and pressureless sintering in air at 1773 K for 1 hour. Magnesia doped alumina was prepared by calcining a mixture of alumina and magnesium nitrate at 973 K for 2 hours followed by cold compaction, CIPing and pressureless sintering in air at 1773 K. Both pure and magnesia doped alumina were further annealed at 1873 K for various times to get grain sizes in the ranges of 1-5 μm.
Grain growth kinetics of pure and magnesia doped alumina were studied at 1823 and 1873 K. The parameter Kg which quantifies the mobility of the grain boundary was got. It was found that Kg had decreased in the magnesia doped alumina (in comparison with pure alumina) by a factor of about 3 to 4 which was marginal and insignificant. The grain sizes followed a log normal distribution in both the cases, indicative of normal grain growth.
Creep studies were conducted on pure and magnesia doped alumina in three modes, namely, constant stress, temperature jump and stress jump test. The temperature range used was 1673 to 1773 K and the stress range used was 10 to 100 MPa. The creep parameters were found to be n~1.6, p~3.7 and Q-545 kJ mol"1 for pure alumina and n~l .3, p~3.0 and Q~460 kJ mol-1 for magnesia doped alumina. The creep rates in the case of magnesia doped alumina were found to have increased by a factor of 2 to 3, in comparison with pure alumina. The increase in creep rates were found to be insignificant. The creep data were analyzed and the possibility of the dislocation and interface reaction controlled creep mechanisms were ruled out since they were inconsistent with the data. It was found, from creep parameters and the comparison of theoretical Coble and Nabarro-Herring creep rates with the experimental rates, that Coble creep might be rate controlling. The activation energy values suggested that aluminium ion diffusing along grain boundary might be the rate controlling species. However, when the theoretical creep rates considering various species were compared, the rate controlling species turned out to be oxygen ion diffusing along the grain boundary.
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Srivastava, Vivek. "Low stress creep of copper and some aluminium and magnesium alloys at high and intermediate homologous temperatures." Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398484.
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Deutchman, Hallee Zox. "ON THE CREEP BEHAVIOR AND DEFORMATION MECHANISMS FOUND IN AN ADVANCED POLYCRYSTALLINE NICKEL-BASE SUPERALLOY AT HIGH TEMPERATURES." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374238461.
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Fookes, Anita Janet. "Assessment of crack growth in steels at high temperature." Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271777.
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McAllister, Alexander S. "The high-temperature multiaxial creep behaviour of alloy 800H tubes." Thesis, Loughborough University, 1986. https://dspace.lboro.ac.uk/2134/32248.
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Literature concerning the development of mechanistic and empirical models of creep deformation and failure, under uniaxial and multiaxial stress systems are reviewed. The detailed metallurgy of the alloy is discussed and its specific creep behaviour in the experimental temperature range is reviewed from published experimental data, mostly obtained from the Alloy 800 Data Bank of the EEC Joint Research Centre at Petten.
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Fletcher, Michelle Lynn. "Characterization of creep and microstructure of novel high-temperature magnesium alloys." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42230.
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The desire for fuel efficient, yet high performance, vehicles in the automotive industry has resulted in a high demand for light weight structural materials. Magnesium alloys are one of the lightest structural materials available to engineering designers. Wrought magnesium alloy bars, sections and tubes have been used in the aerospace, electronics and automotive industries, where component weight is of concern. The operating temperature of these components is typically limited to below 100°C, since creep resistance begins to deteriorate above this temperature. Creep deformation in magnesium alloys has been generally contributed to grain boundary sliding and plastic deformation leading to inter-granular failure.
This research investigated the creep resistance of five wrought magnesium alloys (AE42, AJ32, AX30, EZ33 and ZE10) developed for elevated temperature automotive applications. Non-conventional techniques were utilized to study the creep resistance of these alloys on the micro and macro scale at temperatures ranging from 25°C to 175°C. Neutron diffraction techniques were utilized to measure alloy texture, total strain and elastic creep strain. Metallographic techniques were subsequently used to analyze microstructural constituents in each alloy. The alloy microstructure was then correlated to the alloy’s creep resistance.
The results indicate that the aluminum free magnesium alloys (i.e., EZ33 and ZE10) had higher creep resistance compared to aluminum containing alloys (i.e., AE42, AJ32 and AX30). For the aluminum containing alloys, twinning and formation of a large amount of the Mg₁₇Al₁₂ intermetallic compound likely contributed to a decreased creep resistance. Strontium and calcium were both seen to limit Mg₁₇Al₁₂ formation, thus improving creep resistance of the AJ32 and AX30 alloys with respect to the AE42 alloy, respectively. Both the EZ33 and ZE10 alloys contained nanoprecipitates uniformly dispersed throughout the matrix, possibly contributing to dispersion strengthening and improved creep resistance. The results of neutron diffraction studies suggest that the aluminum containing alloys have experienced unique lattice structure changes on different crystallographic planes. In contrast, the aluminum free alloys had very stable crystallographic lattice strains throughout the duration of creep testing.
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Maharaj, Chris. "Researching methods to assess creep damage in high temperature plant components." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506926.
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Barbera, Daniele. "On the evaluation of high temperature creep-fatigue responses of structures." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27917.
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This thesis details the research and development steps undertaken to improve and enhance the Linear Matching Method Framework (LMMF) for high temperature structural integrity assessment. Firstly, a more accurate interpolation method is developed to calculate the revised yield stress, which is necessary to calculate the creep rupture limit. Convergence issues are also investigated to improve the numerical difficulties often suffered by the "fluctuating" revised yield stress. Secondly, the extended Direct Steady Cycle Analysis (eDSCA) is used to solve two complex case studies and a comprehensive theoretical study is undertaken on the effect of combined creep and cyclicplasticity. This subroutine is enhanced by adding many new features, including the possibility to calculate the fatigue damage using only few tensile constants. Multiple creep dwells within the load cycle can be considered and improvements are made to the cyclic loop construction. In order to make the eDSCA more accurate for creep damage assessment, the stress modifed ductility exhaustion method is implemented combining the advantages of both stress and strain based methods. Thirdly, several case studies on creep-fatigue interaction are discussed thanks to the flexibility of the LMMF including the detrimental effect of creep-ratchetting. Furthermore, a new potentially dangerous mechanism involving the sudden accumulation of plastic strain during the creep dwell is identified and studied by numerical means.
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Maclachlan, Duncan Wilmot. "High temperature creep and fatigue of Ni-base blade alloy CMSX4." Thesis, University of Cambridge, 1999. https://www.repository.cam.ac.uk/handle/1810/251669.
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He, Junjing. "High temperature performance of materials for future power plants." Doctoral thesis, KTH, Materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-191547.
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Increasing energy demand leads to two crucial problems for the whole society. One is the economic cost and the other is the pollution of the environment, especially CO2 emissions. Despite efforts to adopt renewable energy sources, fossil fuels will continue to dominate. The temperature and stress are planned to be raised to 700 °C and 35 MPa respectively in the advanced ultra-supercritical (AUSC) power plants to improve the operating efficiency. However, the life of the components is limited by the properties of the materials. The aim of this thesis is to investigate the high temperature properties of materials used for future power plants. This thesis contains two parts. The first part is about developing creep rupture models for austenitic stainless steels. Grain boundary sliding (GBS) models have been proposed that can predict experimental results. Creep cavities are assumed to be generated at intersection of subboundaries with subboundary corners or particles on a sliding grain boundary, the so called double ledge model. For the first time a quantitative prediction of cavity nucleation for different types of commercial austenitic stainless steels has been made. For growth of creep cavities a new model for the interaction between the shape change of cavities and creep deformation has been proposed. In this constrained growth model, the affected zone around the cavities has been calculated with the help of FEM simulation. The new growth model can reproduce experimental cavity growth behavior quantitatively for different kinds of austenitic stainless steels. Based on the cavity nucleation models and the new growth models, the brittle creep rupture of austenitic stainless steels has been determined. By combing the brittle creep rupture with the ductile creep rupture models, the creep rupture strength of austenitic stainless steels has been predicted quantitatively. The accuracy of the creep rupture prediction can be improved significantly with combination of the two models. The second part of the thesis is on the fatigue properties of austenitic stainless steels and nickel based superalloys. Firstly, creep, low cycle fatigue (LCF) and creep-fatigue tests have been conducted for a modified HR3C (25Cr20NiNbN) austenitic stainless steel. The modified HR3C shows good LCF properties, but lower creep and creep-fatigue properties which may due to the low ductility of the material. Secondly, LCF properties of a nickel based superalloy Haynes 282 have been studied. Tests have been performed for a large ingot. The LCF properties of the core and rim positions did not show evident differences. Better LCF properties were observed when compared with two other low γ’ volume fraction nickel based superalloys. Metallography study results demonstrated that the failure mode of the material was transgranular. Both the initiation and growth of the fatigue cracks were transgranular.QC 20160905
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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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Wen, Xingshuo. "Creep Behavior of High Temperature Alloys for Generation IV Nuclear Energy Systems." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397468088.
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Lim, Rattanak. "Numerical and experimental study of creep of Grade 91 steel at high temperature." Paris, ENMP, 2011. https://pastel.hal.science/pastel-00687235.
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L'acier grade 91 serait un candidat approprié pour des éléments de structures du circuit secondaire et du générateur de vapeur des réacteurs nucléaires de génération IV. Leur durée de vie sera prolongée jusqu'à 60 ans. Cela nécessite de considérer les mécanismes actifs durant de très longs temps de fluage afin de proposer des prédictions de durées de vie plus fiable que de simples extrapolations. La striction est le mécanisme de ruine principal pour des durées de vie jusqu'à 160 kh à 500°C et 94 kh à 600°C. Une simulation de la striction tenant compte de l'adoucissement du matériau conduit à deux lois de bornes qui encadrent les durées de vie expérimentales d'un grand nombre d'aciers martensitiques revenus jusqu'à 200 kh à température 500-700°C. Des cavités intergranulaires observées en FEG-SEM à deux durées de vie longues affectent faiblement la vitesse de déformation. Une prédiction du développement des cavités permettrait d'extrapoler les durées de vie hors du domaine expérimental. Leur germination et croissance, supposées associées à la diffusion des lacunes, sont modélisées grâce à deux modèles classiques. Le premier tient compte d'une germination instantanée (Raj et Ashby) et le second d'une germination continue - Dyson. Le second, plus stable par rapport à ses paramètres que le premier, conduit à des prédictions des tailles finales de cavités en accord raisonnable avec les mesures en FEG-SEM. La vitesse de germination identifiée expérimentalement est requise dans ce modèle. La germination continue des cavités par diffusion est modélisée grâce au modèle classique de Raj. Ce modèle ne permet pas des prédictions de densité de cavités en accord avec les mesures, même en tenant compte de la germination aux interfaces matrice / précipités, observée au MEB-FEG et d'un facteur maximal de concentration de contrainte locale de 2. Ce dernier a été obtenu grâce à des calculs par éléments finis en déformations planes du fluage de microstructures simulées ou réelles, comprenant des points triples ou des précipités/phases de Laves. L'utilisation de la loi de germination de Dyson permet de proposer des prédictions au-delà de 200kh. La durée de vie prédite par le modèle de Riedel d'un essai à basse contrainte semble être en accord avec la durée expérimentale estimée de l'essai (toujours en cours) et actuellement en stade tertiaire, basée sur la fraction de la durée de vie habituellement consommée par le stade tertiaireGrade 91 steel is a suitable candidate for structural components of the secondary and the vapour of generation IV nuclear reactors. Their in-service lifetime will last for 60 years. It is necessary to consider the mechanisms involved during long-term creep to propose reliable predictions of creep lifetimes. Necking is the main failure mode for creep lifetimes up to 160 kh at 500°C and 94 kh at 600°C. Necking modelling including the material creep softening leads to two bound equations including experimental lifetimes of a large number of tempered martensitic steels loaded up to 200 kh at temperature 500-700°C. The observed creep intergranular cavities are shown to affect very weekly creep strain rate. The prediction of the cavity evolution will allow estimating creep lifetimes out of experimental data domain. Their nucleation and growth, supposed to be associated to vacancy diffusion, are modelled using two classical models. The first one considers instantaneous nucleation (Raj and Ashby) and the second one continuous nucleation obeying the Dyson law (Riedel). The second one leads to two bound equations, more stable with respect to the parameter values. It allows predicting final size of cavities in reasonable agreement with measured ones. Yet, the nucleation rate should still be estimated from measured cavity densities. Nucleation of cavities by diffusion is simulated using the Raj model. This model does not allow predicted final cavity densities in agreement with the measured ones, even by considering cavity nucleation at precipitates/ Laves interfaces experimentally observed and the maximum local stress concentration of a factor 2 computed using finite element calculation in a 2D plane strain hypothesis based on either simulated or real microstructures containing triple points or precipitates/Laves phases. The use of the Dyson model allows us to propose predictions of long-term creep lifetimes. Lifetime predicted using the diffusion-induced growth model of one creep test under low stress still in progress is approximately in agreement with the experimental lifetime estimated based on the fraction of tertiary stage
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Yeh, An-Chou. "High temperature phase stability and creep of Ru-bearing Ni-based single crystal superalloys." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615094.
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Wright, Lawrence William. "Creep deformation of CMSX-4 NBSCS during uniaxial and multiaxial loading at high temperature." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619709.
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Tan, Feng. "Development of subroutine library and data transfer interface for high temperature structural integrity-creep." Thesis, University of Huddersfield, 2015. http://eprints.hud.ac.uk/id/eprint/26220/.
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Creep plays a critical role in the research of high temperature materials because it is the major failure form of high temperature devices. In the safety assessment of high temperature devices, creep failure is one of the key factors used to evaluate residual lifetime of metal components; however, creep analysis in practical applications is still a great challenge due to the lack of a unified theory of all materials. A number of researchers are conducting research into creep constitutive model based on either experimental approaches or computational approaches, but multifarious computational tools were used because the constitutive model is still in the exploration stage. Traditional commercial software could reach the required capability based on the development of user-developed codes; moreover, some in-house codes were proposed, but just used in a narrow scope. Therefore, the development of a novel universal creep finite element software needs to be carried out to meet the requirements of future research. This research aims to develop required subroutines and interface for the proposed elastic-creep finite element software called High Temperature Structural Integrity-Creep (HITSI). Basic concepts and situations of creep and its computational tools have been reviewed. General knowledge of programming of finite element method has also been studied. A universal subroutine template of creep constitutive equations has been given to enable users to add their own equations directly. A high order and embedded numerical method called Runge-Kutta-Fehlberg (RKF) method has been applied and discussed in order to enhance the accuracy of traditional methods. A mathematical method used to improve the accuracy and efficiency of constitutive equations subroutine call normalization has been applied and discussed. Formatted input and output of purchased pre- and post-processor has been studied to develop the data transfer interface. Some auxiliary modules such as stress transformation and nodal load arrangement have been developed to satisfy the input conditions of constitutive equations subroutines and data transfer interface.
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Turski, Mark. "High temperature creep cavitation cracking under the action of residual stress in 316H stainless steel." Thesis, University of Manchester, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.680051.
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Li, Shu-Xin. "High temperature creep-fatigue and crack growth behaviour of a single crystal nickel base superalloy." Thesis, University of Bristol, 1993. http://hdl.handle.net/1983/5b2c321c-1c74-450e-be61-a392c419eeb7.
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Lee, Kok Loong. "Deformation behaviour of Cu-Cr in-situ composite." Thesis, University of Leicester, 2004. http://hdl.handle.net/2381/11077.
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With the increasing requirements for higher strength materials with high electrical conductivity, a lot of interest has been paid to develop Cu-based composites in the last 25 years. These composites have superior tensile strength, combined with good electrical conductivity, to that exhibited by pure Cu and conventional Cu alloys. To date, much of the research carried out on this composite has focused on the mechanical and electrical properties of the as processed material. However, there is a basic lack of understanding of the way in which the properties may change or degrade during service. Without this knowledge, these composites cannot be fully and safely exploited. Thus the objective of this study was to investigate the thermo-mechanical behaviour of a Cu-Cr composite, and the nature and extent of any damage mechanisms occurring within the composite over a wide range of experimental conditions. Neutron diffraction was used to investigate the deformation behaviour of the individual phases in the composite and their interaction through elastic and plastic loading at room temperature. For the composite, a fairly good agreement was observed in the phase strains predicted by the Eshelby theory and measured by neutron diffraction. In-situ tensile tests in the SEM were also performed to study the damage mechanism of the composite. Tensile and creep tests were carried out in air and in vacuum over a wide range of temperatures. To provide data for comparison with the composite material, pure Cu specimens were tested whenever possible. Creep resistance increases significantly with the introduction of Cr fibres into Cu. The higher creep rate of the composite in air than in vacuum is due to the gradual decrease of the cross-sectional area of the matrix due to increasing thickness of the oxide layer. Damage characteristics and distributions were found to be similar during tensile and creep testing.
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Mattiello, Adriana. "Visco-plasticity and damage modeling of single crystal superalloys at high temperatures : a tensorial microstructure-sensitive approach." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLN004/document.
Full textAbstract:
Un modèle phénoménologique 3D de visco-plasticité couplée avec les évolutions microstructurales et l'endommagement est proposé pour les superalliages monogranulaires base Nickel, les matériaux des aubes de turbine à haute pression de moteurs d'hélicoptères. L'anisotropie de la mise en radeaux, la croissance et la dissolution de la phase durcissante sont modélisés. Une variable tensorielle et sa loi d'évolution permettent la description de la variation de la largeur des couloirs de matrice. Ce travail s'appuie sur la décomposition en modes de Kelvin du tenseur d'élasticité. Cette décomposition conduit également à une description multi-critère mésoscopique de la visco-plasticité cubique. Une formulation en (visco-)plasticité cristalline a été également proposée. Une loi d'endommagement avec seuil de type dD/dt=... est formulée pour la modélisation du fluage tertiaire et pour la prévision de la ductilité en traction. Une expression originale du seuil d'endommagement rend compte des effets de vitesse sur l'amorçage de l'endommagement par visco-plasticité. Une étude expérimentale a été conduite sur le CMSX-4, l'alliage au centre de cette étude, parallèlement aux travaux de modélisation. Des essais de dissolution ont été réalisés afin de mesurer la variation de la fraction volumique des précipités avec la température. Les mécanismes de déformation du matériau ont été observés en fluage isotherme à 850°C et 1050°C selon les principales directions cristallines du triangle stéréographique standard et constituent une base d'identification pour le modèle, la réponse mécanique du matériau obtenue. Trois essais de traction ont été réalisés selon la direction <111>, deux à vitesse de chargement constante, le troisième à vitesse variable. Des essais cyclés thermiquement de type 150h-moteur ont été réalisées sur le banc MAATRE. Des analyses EBSD et MET ont été réalisés sur les échantillons orientés selon les directions cristallines <011>, <111> et <112> et testés à 850°C. Ces analyses ont montré que le mâclage est le principal mécanisme de déformation pour des déformations supérieures à $1-2%$ selon ces orientations cristallines en fluage à cette température et à haute contrainte (>400 MPa). Enfin, le modèle a été implanté dans le code à élément Finis ZéBuLon, sans ou avec endommagement, et des calculs de structures ont été réalisésA 3D phenomenological model coupling viscoplasticity, microstructural evolutions and damage is proposed for Ni-based single crystal superalloys, which are widely used materials for high pressure turbine blade in helicopter engines. The anisotropy of the gamma'-rafting, the gamma'-coarsening and the dissolution of the hardening gamma' phase are modeled. A tensorial variable and its evolution law allow to describe the variation of the gamma channels. The modeling is based on the Kelvin decomposition of the elasticity tensor. This decomposition leads to a phenomenological multi-criterion description of the cubic visco-plasticity. A formulation based on the single crystal (visco-)plasticity framework is also proposed. A damage law of type dD/dt=… is introduced in order to model the tertiary creep stage and the ductility. A novel rate sensitive damage threshold is introduced in order to account for the rate sensitivity of the damage onset by visco-plasticity. An experimental study has been carried out on the CMSX-4 alloy, which is the material of main interest in this study, in parallel to the modeling work. Dissolution tests have been carried out to measure the gamma'-volume fraction variation with temperature. The deformation mechanisms of the CMSX-4 alloy have been observed by performing tensile creep tests at 1050°C and 850°C. These tests have also constituted a database for the model identification. Three tensile tests have been realized along the <111> crystal direction, two at constant strain rate and the third by varying the strain rate. Non-isothermal creep tests reproducing the 150h-type engine test have been performed on the MAATRE bench. EBSD and TEM analysis have been realized on the specimens oriented along the <011>, <011> and <112> crystal directions and crept at 850° C. These analysis have shown that micro-twinning governs the deformation along these crystal directions during creep at this temperature and at high stresses (> 400 MPa) for deformation in excess of 1-2%. Finally, the model (with and without damage) has been encoded in the ZéBuLoN Finite Element solver and structure computations have been performed
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Maritz, E. J. (Erasmus Jacobus). "Flux creep in pulsed laser deposited superconducting YBa₂Cu₃O₇ thin films." Thesis, Stellenbosch : University of Stellenbosch, 2002. http://hdl.handle.net/10019.1/6394.
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Thesis (PhD (Physics))--University of Stellenbosch, 2002.Includes bibliography.
ENGLISH ABSTRACT: High temperature superconductivity is an important topic in contemporary solid state physics, and an area of very active research. Due to it’s potential for application in low temperature electronic devices, the material has attracted the attention of researchers in the electronic engineering and material science fields alike. Moreover, from a fundamental point of view, several questions remain unanswered, related to the origin of superconductivity of this class of materials and the nature of quantised magnetic flux present in magnetised samples. In this work, flux creep phenomena in a thin superconducting YBa₂Cu₃O₇ film deposited by pulsed laser deposition, is investigated near the critical temperature 0 ≤ Tc – T ≤ 10 K. Creep activation energy U0 and critical current density jc were determined as a function of temperature close to Tc, providing important data to a problem of high-Tc superconductivity which is still a matter of debate. In particular it is still an open question whether restoring the temperature in a creep freezing experiment in fact restores the film to it's original state before the freezing. The most important novel results concern the regime of critical fluctuations in the vicinity Tc - T < 1 K. We studied the isothermal relaxation of trapped magnetic flux, and determined that the long time decay follows a power law, where the exponent is inversely proportional to the creep activation energy. The temperature dependence of the critical current density jc(T) of the YBa₂Cu₃O₇ film close to Tc was obtained during warming runs. It was determined that jc(T) follows a square root dependence on T to high accuracy in the range 0.2 ≤ Tc – T ≤ 1.5 K. During flux creep experiments an interesting phenomenon called creep freezing related to the strong temperature dependence of the relaxation rate was observed. A pronounced slowing of relaxation with only a small drop in temperature from a starting temperature close to Tc was detected. Experiments were conducted by initiating an isothermal flux decay run. At a certain point the temperature was slightly lowered, and the flux decay stopped within experimental accuracy. When the temperature was restored to the initial value, the flux decay resumed at the previous rate before cooling. An argument based on vortex drift velocity was employed to explain the phenomenon qualitatively. During the course of this investigation, a pulsed laser deposition (PLD) system was designed and built from scratch. PLD involves the interaction of a focussed laser pulse with a multielemental solid target material. Material ablated from the target forms a fast moving plume consisting of atomic and molecular particles, directed away from the target, and towards a usually heated substrate on which the particles condense layer by layer to form a thin film. The substrate temperature and background gas are carefully controlled to be conductive to the growth of a desired phase of the multi-elemental compound. The PLD system proved to be quite versatile in the range of materials that could be deposited. It was used to deposit thin films of different materials, most notable were good quality superconducting YBa₂Cu₃O₇, thermochromic VO2, and magnetoresistive LaxCa1-xMnO3. Metallic Au and Ag layers were also successfully deposited on YBa2Cu3O7 thin films, to serve as protective coatings. The critical temperatures of the best superconducting films were 90 K as determined by resistivity measurement. The optimal deposition conditions to deposit high quality superconducting YBa₂Cu₃O₇ thin films was found to be: deposition temperature 780°C, laser energy density 2-3 J/cm2, oxygen partial pressure 0.2 mbar, and target-substrate distance 35 mm. This yields film with Tc ~ 90 K. It was found that deposition temperature plays the predominant role in determining the quality of YBa₂Cu₃O₇ thin films deposited by PLD.
AFRIKAANSE OPSOMMING: Hoë temperatuur supergeleiding is tans ’n aktuele onderwerp van vastetoestandfisika en dit is ’n gebied van baie aktiewe navorsing. Weens die potensiaal vir toepassings van hoë temperatuur supergeleiers in elektronika, het dié klas materiale die aandag van fisici and elektronici getrek. Verskeie fundamentele vraagstukke bly steeds onbeantwoord, veral met betrekking tot die oorsprong van supergeleiding in hierdie materiale en die gedrag van gekwantiseerde magnetiese vloed (“vortekse”) in gemagnetiseerde monsters. In hierdie werk word diffusie van vortekse in dun supergeleidende YBa₂Cu₃O₇ films ondersoek naby die kritieke temperatuur (0 ≤ Tc - T ≤ 10 K). Die temperatuur afhanklikheid van die diffusie aktiveringsenergie U0 en die kritieke stroomdigtheid jc word bepaal naby Tc. Dit verskaf belangrike inligting tot probleme in hoë temperatuur supergeleiding wat tans nog onbeantwoord bly. In die besonder is dit steeds ’n ope vraag of die herstel van die aanvanklike temperatuur in ’n vloedstollings eksperiment waarlik die film tot die oorspronklike toestand herstel. Die belangrikste nuwe resultate hou verband met die gebied van kritieke fluktuasies van die orde parameter in die omgewing 0 < Tc - T < 1 K. Ons het die isotermiese ontspanning van vortekse verstrik in die kristalstruktuur bestudeer, en bepaal dat die lang tydsverval ’n magsverwantskap handhaaf, waar die eksponent omgekeerd eweredig is aan U0. Die temperatuur afhanklikheid van die kritieke stroomdigtheid jc(T) van die YBa₂Cu₃O₇ film naby Tc is bepaal tydens verhittingslopies. Daar is bevind dat naby Tc, jc ’n vierkantswortel verband met T volg, tot hoë noukeurigheid in die gebied 0.2 ≤ Tc – T ≤ 1.5 K. Gedurende vorteksdiffusie eksperimente is ’n interessante verskynsel naamlik vloedstolling (“flux freezing”) waargeneem. Dit hou verband met die sterk temperatuur afhanklikheid van die vervaltempo van die magnetiese moment van ’n gemagnetiseerde film. ’n Skerp daling van die vervaltempo, weens slegs ’n klein temperatuurdaling vanaf die begin temperatuur naby Tc, is waargeneem. Gedurende eksperimente is daar aanvanklik ’n isotermiese vloedontspanning teweeg gebring. Op ’n sekere tydstip is die temperatuur effens verlaag, waarby die vloedontspanning tot stilstand gekom het binne grense van waarneming. Wanneer die temperatuur weer herstel is na die oorspronklike, het die vloedontspanning voortgegaan teen die tempo voor die temperatuurverlaging. ’n Verklaring wat gebaseer is op vorteks dryfsnelheid was aan die hand gedoen om hierdie gedrag te verklaar. ’n Groot komponent van die projek was om die dun YBa₂Cu₃O₇ films self te vervaardig. Tydens hierdie ondersoek, is ’n gepulseerde laser deposisie (“PLD”) sisteem eiehandig ontwerp en gebou. PLD behels die interaksie van ’n gefokuseerde laser puls met ’n teiken bestaande uit ’n multi-element vastestofverbinding. Materiaal wat verdamp (“ablate”) word, vorm ’n snelbewegende pluim bestaande uit atomiese en molekulêre deeltjies. Dit beweeg vanaf die teiken na ’n verhitte substraat, waarop die deeltjies kondenseer om laag vir laag ’n dun film te vorm. Die substraat temperatuur en agtergrond gas word sorgvuldig beheer om die groei van die verlangde fase van die multi-element verbinding teweeg te bring. Die PLD sisteem is baie veeldoelig ten opsigte van die verskeidenheid materiale wat suksesvol neergeslaan kan word. Dit was aangewend om verskillende materiale neer te slaan, onder andere supergeleidende YBa₂Cu₃O₇, termochromiese VO2, en magnetoresistiewe LaxCa1-xMnO3. Geleidende Au en Ag lagies is ook suksesvol neergeslaan op YBa₂Cu₃O₇ dun films, om te dien as beskermingslagies. Die kritieke temperatuur van die beste supergeleidende films was 90 K soos bepaal deur weerstandsmetings. Die optimale neerslaan toestand vir hoë kwaliteit YBa₂Cu₃O₇ dun films was: substraat temperatuur 780°C, laser energiedigtheid 2 - 3 J/cm2, suurstofdruk 0.2 mbar, en teiken-substraat afstand 35 mm. Daar is bevind dat die substraat temperatuur die deurslaggewende rol speel tydens die neerslaan proses om die kwaliteit van die supergeleidende films te bepaal.
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Fisk, Joseph Charles. "Effects of creep and oxidation interaction on high temperature crack growth behaviour of nickel based superalloys." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4572/.
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A complete and comprehensive understanding of dwell crack growth behaviour is required for two compressor and turbine disc alloys, Udimet 720Li and RR1000, both having a fine grain microstructure. The effect of temperature, dwell time and dwell load has been studied in air and vacuum along with detailed fractographic and microstructural analysis to understand the relevant contributions of oxidation, creep and microstructure. The study has been extended to determine the effect of an overload segment in the load waveform, the rationale being that this type of waveform better models real loading cycles on engines in service. In support with extensive modelling carried out within Rolls-Royce plc in order to understand the stress state ahead of the crack tip and its relaxation over dwell time, the effect of overload factor, test temperature and dwell time has also been examined empirically. In good agreement with the findings of others, crack growth rates according to overload cycling are shown to propagate significantly slower than crack growth rates according to (otherwise similar) dwell-only loading, or static loads; even at high temperature and in an oxidising environment. A good agreement between modelled predictions and experimental results has been achieved, indicating that the retardation of crack growth rates is mainly affected by mechanical factors.
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Zhang, Hui. "Influence of High Temperature Creep upon the Structure of ß-NiAl and ß-NiAl(Fe) Single Crystals." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2002. http://nbn-resolving.de/urn:nbn:de:swb:14-1038216865812-53920.
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The principal aim of this thesis is to characterise quantitatively the influence of high temperature creep upon the structure of ß-NiAl and ß-NiAl(Fe) single crystals. A non-destructive procedure is established following the classic line of X-ray structure analysis, namely controlling the chemical composition with the electron probe microanalysis, determining the unit cell contents from the combined lattice parameter and mass density measurements, and refining the structure parameters according to the X-ray reflection intensity. Specifically, two special single crystal X-ray diffraction methods, namely the back reflection Kossel technique and the back reflection Laue method, are applied for the determination of lattice parameter and for the collection of intensity data. All experimental measurements can be performed in non-destructive manner, which allows a direct comparison to be made between the crystal structure determined prior to and after a creep test.
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Zhang, Hui. "Influence of high temperature creep upon the structure of Beta-NiAl and Beta-NiAl(Fe) single crystals." [S.l. : s.n.], 2002. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB10236296.
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Hall, Frank Richard. "Development of continuum damage mechanics models to predict the creep deformation and failure of high temperature structures." Thesis, University of Sheffield, 1990. http://etheses.whiterose.ac.uk/12780/.
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The use of classical creep continuum damage mechanics, constitutive and damage equations is restricted, to model certain types of creep deformation and fracture mechanisms, under isothermal conditions; and, to extend their predictive capabilities for a wider range of problems they have to be modified. The constitutive and damage equations are modified to represent the bi-linear, log. stress vs. log. rupture, and the log, stress vs. minimum strain rate, characteristics of materials; so that the change in material behaviour, as a mechanism change occurs, is represented in the constitutive model, by a change in the slope of these characteristic lines. Uni-axial creep tests of as-cast (OFHC) Copper have been performed at 150°C, 250°C and 500°C; and, an anisothermal constitutive model has been developed for the temperature range 150°C to 500°C, which highlights how the constitutive equations may be modified, to model creep behaviour under varying temperature conditions. The model predictions are in good agreement with the test results. A compact tension specimen has been studied, which has shown the importance of modelling the effects on rupture, of the high tri-axial stress-state present at the crack-tip, which accelerates void growth. Modified constitutive equations, have been used to model the mechanism of constrained cavity growth, and has enabled improved damage distribution and. lifetime predictions to be obtained for the compact tension specimen, similar to those expected from experimental tests. Non-local damage techniques are developed to model the effects of grain size characteristic dimension, on the failure of large and small cracked tension specimens. Non-local damage techniques are shown to be necessary to give accurate, physically related, finite element solutions. Suitably modified constitutive and damage rate equations are used to model the high temperature failure of a circumferential weld, in a thick steam-pipe, operating at a constant temperature and pressure. The models developed predict, the growth of damage in certain microstructural regions of the weld, and the lifetime of the component; which are observed to be in close agreement with the results from a fullsize pressure vessel tests. It will be shown that it is essential to use creep constitutive and damage equations in computer models, which accurately represent the underlying physics of IX the predominant creep mechanisms present. The implications of the research work on future computer modelling and on design are discussed.
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Kolomazník, Milan. "Predikce koroze trubek pece s využitím provozních dat." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231497.
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The thesis deals with the modeling and prediction of corrosion of radiation tube snake in the heating furnace. Specifically it is focused on vertical cylindrical furnace which is included in the catalytic hydrocracking unit and serves for heating aggressive circulation gas which is the cause of high temperature corrosion. An important basis for the creation of computational models are available records about the operation of the furnace and about the corrosion and degradation mechanisms during the lifetime of the tube system in furnace. Such information enables the creation of a computational model which is based on the prediction of high-temperature corrosive damage of radiation tube snake. The computational model involving all relevant factors may serve as the basis for a predictive life management system of radiation snakes in the heating furnace.
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Wärner, Hugo. "High-Temperature Fatigue Behaviour of Austenitic Stainless Steel : Influence of Ageing on Thermomechanical Fatigue and Creep-Fatigue Interaction." Licentiate thesis, Linköpings universitet, Konstruktionsmaterial, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-153100.
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The global energy consumption is increasing and together with global warming from greenhouse gas emission, create the need for more environmental friendly energy production processes. Higher efficiency of biomass power plants can be achieved by increasing temperature and pressure in the boiler section and this would increase the generation of electricity along with the reduction in emission of greenhouse gases e.g. CO2. The power generation must also be flexible to be able to follow the demands of the energy market, this results in a need for cyclic operating conditions with alternating output and multiple start-ups and shut-downs. Because of the demands of flexibility, higher temperature and higher pressure in the boiler section of future biomass power plants, the demands on improved mechanical properties of the materials of these components are also increased. Properties like creep strength, thermomechanical fatigue resistance and high temperature corrosion resistance are critical for materials used in the next generation biomass power plants. Austenitic stainless steels are known to possess such good high temperature properties and are relatively cheap compared to the nickel-base alloys, which are already operating at high temperature cyclic conditions in other applications. The behaviour of austenitic stainless steels during these widened operating conditions are not yet fully understood. The aim of this licentiate thesis is to increase the knowledge of the mechanical behaviour at high temperature cyclic conditions for austenitic stainless steels. This is done by the use of thermomechanical fatigue- and creepfatigue testing at elevated temperatures. For safety reasons, the effect of prolonged service degradation is investigated by pre-ageing before mechanical testing. Microscopy is used to investigate the microstructural development and resulting damage behaviour of the austenitic stainless steels after testing. The results show that creep-fatigue interaction damage, creep damage and oxidation assisted cracking are present at high temperature cyclic conditions. In addition, simulated service degradation resulted in a detrimental embrittling effect due to the deterioration by the microstructural evolution.
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Phillips, Donald Andrew. "Finite Element Analysis of a Shaft-Rotor System." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/31450.
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The United States Air Force is in the process of developing a more electric aircraft. The development of an aircraft Integrated Power Unit and an Internal Starter/Generator will be instrumental in producing sufficient electrical power to run all non propulsive systems. Iron-cobalt alloys, such as Hiperco alloy 50HS, are high temperature, high strength magnetic materials ideal for these power applications. Design requirements and previous studies indicate that these materials need to survive in temperatures up to 1000F (810K), rotation speeds of about 55,000 rpm, and have strengths in excess of 80 ksi. Research conducted by Fingers provided the material and creep properties used in the analysis presented in this report. The finite element method was used to analyze a spinning rotor mounted to a circular shaft via an interference fit subjected to various operating environments. The power law creep model defined by Fingers was used to analyze three distinct rotor configurations. The first configuration was a constant temperature single lamina, mounted to a shaft of equal thickness, subject to temperatures between 727K and 780K, rotation speeds between 35,000 rpm and 60,000 rpm, and two different interference fits: 0.0015 inches and 0.003 inches. The results yield conservative predictions that indicate that these models could not survive the required operating conditions. The second configuration was a linear radial variation in temperature single lamina, mounted to a shaft of equal thickness, subjected to three temperature ranges, rotation speeds between 30,000 rpm and 55,000 rpm, and two different interference fits; 0.0015 inches and 0.003 inches. These results represent a more realistic model, which indicate that the â coolerâ inner portions of the rotor restrict the creep deformations of the â hotterâ outer portions resulting in higher possible operating temperatures and rotation speeds very near the required operating conditions. The third configuration was a lamina stack comprised of two rotor lamina, with a Coulomb friction surface interaction, and held together by a compressive axial force. These models represent a first step towards understanding the behavior of the entire rotor stack.Master of Science
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Luan, LiKang [Verfasser], and M. [Akademischer Betreuer] Heilmaier. "Micro-tensile creep testing for polycrystalline and single crystalline nickel-based high temperature alloys / LiKang Luan ; Betreuer: M. Heilmaier." Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/1205001905/34.
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Willschütz, H. G., and E. Altstadt. "Generation of a High Temperature Material Data Base and its Application to Creep Tests with French or German RPV-steel." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-29413.
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Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. Numerous experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work /REM 1993/, /THF 1997/, /CHU 1999/. For pre- and post-test calculations of Lower Head Failure experiments like OLHF or FOREVER it is necessary to model creep and plasticity processes. Therefore a Fi-nite Element Model is developed at the FZR using a numerical approach which avoids the use of a single creep law employing constants derived from the data for a limited stress and temperature range. Instead of this a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. A main task for this approach is the generation and validation of the CDB. Additionally the implementation of all relevant temperature dependent material properties has been performed. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied. The validation of the numerical model is performed by the simulation of and com-parison with experiments. This is done in 3 levels: starting with the simulation of sin-gle uniaxial creep tests, which is considered as a 1D-problem. In the next level so called "tube-failure-experiments" are modeled: the RUPTHER-14 and the "MPA-Meppen"-experiment. These experiments are considered as 2D-problems. Finally the numerical model is applied to scaled 3D-experiments, where the lower head of a PWR is represented in its hemispherical shape, like in the FOREVER-experiments. This report deals with the 1D- and 2D-simulations. An interesting question to be solved in this frame is the comparability of the French 16MND5 and the German 20MnMoNi55 RPV-steels, which are chemically nearly identical. Since these 2 steels show a similar behavior, it should be allowed on a lim-ited scale to transfer experimental and numerical data from one to the other.
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Willschütz, H. G., and E. Altstadt. "Generation of a High Temperature Material Data Base and its Application to Creep Tests with French or German RPV-steel." Forschungszentrum Rossendorf, 2002. https://hzdr.qucosa.de/id/qucosa%3A21768.
Full textAbstract:
Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. Numerous experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work /REM 1993/, /THF 1997/, /CHU 1999/. For pre- and post-test calculations of Lower Head Failure experiments like OLHF or FOREVER it is necessary to model creep and plasticity processes. Therefore a Fi-nite Element Model is developed at the FZR using a numerical approach which avoids the use of a single creep law employing constants derived from the data for a limited stress and temperature range. Instead of this a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. A main task for this approach is the generation and validation of the CDB. Additionally the implementation of all relevant temperature dependent material properties has been performed. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied. The validation of the numerical model is performed by the simulation of and com-parison with experiments. This is done in 3 levels: starting with the simulation of sin-gle uniaxial creep tests, which is considered as a 1D-problem. In the next level so called "tube-failure-experiments" are modeled: the RUPTHER-14 and the "MPA-Meppen"-experiment. These experiments are considered as 2D-problems. Finally the numerical model is applied to scaled 3D-experiments, where the lower head of a PWR is represented in its hemispherical shape, like in the FOREVER-experiments. This report deals with the 1D- and 2D-simulations. An interesting question to be solved in this frame is the comparability of the French 16MND5 and the German 20MnMoNi55 RPV-steels, which are chemically nearly identical. Since these 2 steels show a similar behavior, it should be allowed on a lim-ited scale to transfer experimental and numerical data from one to the other.
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Balos, Daniel [Verfasser], and Jens [Akademischer Betreuer] Strackeljan. "Application of data mining for assessment of material properties : creep behavior of high-temperature steels / Daniel Balos. Betreuer: Jens Strackeljan." Magdeburg : Universitätsbibliothek, 2009. http://d-nb.info/1054419671/34.
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Balos, Daniel Verfasser], and Jens [Akademischer Betreuer] [Strackeljan. "Application of data mining for assessment of material properties : creep behavior of high-temperature steels / Daniel Balos. Betreuer: Jens Strackeljan." Magdeburg : Universitätsbibliothek, 2009. http://d-nb.info/1054419671/34.
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Subramanian, Karthikeyan. "Mechanisms and Effect of Microstructure on High Temperature Deformation of Gamma-TiAl Based Alloys." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1047500481.
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Volf, Milan. "Hodnocení mikrostruktury niklových superslitin s využitím obrazové analýzy." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229721.
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During operational conditions of internal combustion turbines of turbojet engines, the impeller are stressed by load cycles which vary in time, temperature and stress. In the course of operation, the blades are exposed to a considerable number of degradation effects, particularly high-temperature corrosion, fatigue processes and creep. The presented work is aimed at the study of the structure cast nickel-base superalloy INCONEL 713 LC, creep tests exposured. The structural changes (degradation) was clasification by the help of image analyses. Operational conditions of heat parts, used in gas turbines and turbo-compressors, were simulated by creep tests of Inconel 713 LC nickel superalloy during a constant load of temperatures ranging from 750 up to 950°C. Changes in the structure dependent upon time, temperature and stress applied were analysed by means of light and electron microscopy methods and image analyses after the fracture of test bars.
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Fahimi, Shirin [Verfasser]. "Quantitative SEM Analysis of the Evolution of Microstructure in Tempered Martensite Ferritic Steels during Creep and High Temperature Fracture / Shirin Fahimi." Aachen : Shaker, 2016. http://d-nb.info/1120864461/34.
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Kölzow, Felix [Verfasser], Matthias [Akademischer Betreuer] Oechsner, and Hanno [Akademischer Betreuer] Gottschalk. "Application of Probabilistic Methods for Lifetime Prediction of High Temperature Components under Creep-Fatigue Loading / Felix Kölzow ; Matthias Oechsner, Hanno Gottschalk." Darmstadt : Universitäts- und Landesbibliothek, 2021. http://d-nb.info/123566788X/34.
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Dornelas, Dante Antonucci. "Caracterização mecânica em temperaturas elevadas da Superliga MAR-M247." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-01102013-105701/.
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A necessidade de trabalhos em altas temperaturas exige o desenvolvimento de materiais com elevada resistência química e mecânica em temperaturas que podem chegar próximas ao seu ponto de fusão. Em especial, os materiais empregados devem apresentar bom comportamento em fluência, de modo a suportar a combinação de altas tensões e altas temperaturas com o mínimo de deformação. O presente trabalho visa caracterizar a superliga MAR-M247, fornecida pela empresa Açotécnica, em condições de fluência para a produção de rotores empregados em turbocompressores automotivos. Os trabalhos são divididos em duas etapas. Na primeira estuda-se a melhor combinação de tratamentos térmicos de solubilização e envelhecimento, chegando à condição de solubilização por 5 horas a 1250?C e envelhecimento por 20 horas a 980?C. Um trabalho de outro aluno (SILVA, 2011) realiza o mesmo estudo para uma variação da superliga MAR-M247 em que o tântalo é totalmente substituído por nióbio. Neste caso, a melhor condição de tratamento é solubilização a 1260?C por 8 h seguida de envelhecimento duplo por 5 h a 880?C e 20 h a 780?C. Na segunda etapa, os materiais dos dois trabalhos, nas melhores condições de tratamento para cada um, são testados em condições de fluência a 850?C a 370, 390, 410 e 430 MPa. A superliga convencional apresenta os maiores valores de vida em fluência enquanto a modificada apresenta os maiores valores de ductilidade. A análise de fratura dos materiais ensaiados a 390 e 430 MPa mostra a presença massiva de carbonetos em toda a extensão da microestrutura, apresentando, em muitos casos, uma morfologia de \"escrita chinesa\". Apesar disso, todas as amostras apresentam grande quantidade de vazios, indicando que sua nucleação e crescimento são os responsáveis pela fratura do material.The needing for high temperature work claim for new materials capable of maintain high strength and good corrosion resistance at temperatures that could reach values near their melting point. Such materials must be creep resistant to withstand high levels of tension and temperature. The aim of this work is the characterization of MAR-M247 under creep conditions for the production of automotive turbocharger rotors made by Açotécnica. The work is split in two steps. In the first one, the material is studied to find the best conditions for solution and ageing heat treatments. The result is a solution treatment at 1250?C for 5 h followed by aging at 980?C for 20 h. A work made by another student (SILVA, 2011) makes the same with a modification of MAR-M247 in which tantalum is completely substituted for niobium. The best condition for this case is a solution treatment at 1260?C for 8 h and a double aging treatment at 880?C for 5 h and 780?C for 20 h. At the second part of the work, both the materials are tested under creep conditions at 850?C with 370, 390, 410 and 430 MPa. The conventional superalloy shows the highest values for creep strength and the modified superalloy shows the highest ductility. Fracture surfaces for 390 and 430 MPa showed brittle carbides with \"chinese script\" morphology. Conversely, holes are present on all four materials what shall mean that its nucleation and growth was the most probably fracture path.
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Almansour, Amjad Saleh Ali. "USE OF SINGLE TOW CERAMIC MATRIX MINICOMPOSITES TO DETERMINE FUNDAMENTAL ROOM AND ELEVATED TEMPERATURE PROPERTIES." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron148640184494135.
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