Dissertations / Theses on the topic 'Elevated temperatures'
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1
Mamilla, Amala Kishore. "Ultrasonic Couplants at Elevated Temperatures." Fogler Library, University of Maine, 2004. http://www.library.umaine.edu/theses/pdf/MamillaAK2004.pdf.
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Xu, Lei. "Magnetization Dynamics at Elevated Temperatures." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/311342.
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The area of ultrafast (sub-nanosecond) magnetization dynamics of ferromagnetic elements and thin films, usually driven by a strong femtosecond laser pulse, has experienced intense research interest. In this dissertation, laser-induced demagnetization is theoretically studied by taking into account interactions among electrons, spins, and lattice. We propose a microscopic approach under the three temperature framework and derive the equations that govern the demagnetization at arbitrary temperatures.To address the question of magnetization reversal at high temperatures, the conventional Landau-Lifshitz equation is obviously unsatisfactory, since it fails to describe the longitudinal relaxation. So by using the equation of motion for the quantum density matrix within the instantaneous local relaxation time approximation, we propose an effective equation that is capable of addressing magnetization dynamics for a wide range of temperatures. The longitudinal and transverse relaxations are analyzed, magnetization reversal processes near Curie temperatures is also studied. Furthermore, we compared our derived Self-consistent Bloch equation and Landau-Lifshitz-Bloch equation in detail. Finally, the demagnetzation dynamics for ferromagnetic and ferrimagnetic alloys is studied by solving the Self-consistent Bloch equation.
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Ray, Katherine Leung. "Photovoltaic cell efficiency at elevated temperatures." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59937.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 23).
In order to determine what type of photovoltaic solar cell could best be used in a thermoelectric photovoltaic hybrid power generator, we tested the change in efficiency due to higher temperatures of three types of solar cells: a polymer cell, an amorphous silicon cell and a CIS cell. Using an AM1.5 G solar simulator at 973 W/m2 we took the I-V curve of each of the three cells at increasing temperatures. We used the I-V curve to find the maximum power and determine the efficiency of each cell with respect to temperature. We found that the CIS cell had an efficiency of 10% and the performance decreased with respect to temperature in a non-linear manner. The efficiency at 83*C was a peak and the same efficiency as at 40"C. We found that the amorphous silicon cell tested had an efficiency of 4% at 450C that decreased with respect to temperature in a linear manner such that an 800C increase in temperature resulted in an efficiency of 3%. We further found that the polymer cell efficiency decreased from 1.1% to 1% with a 60*C increase in temperature, but that the polymer cell is destroyed at temperatures higher than 1 00*C. We determined that CIS or amorphous silicon could be suitable materials for the photovoltaic portion of the hybrid system.
by Katherine Leung Ray.
S.B.
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Dike, Shweta Srikant. "Dynamic Deformation of Materials at Elevated Temperatures." Cleveland, Ohio : Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1268337193.
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Thesis (Master of Sciences (Engineering))--Case Western Reserve University, 2010Department of EMC - Mechanical Engineering Title from PDF (viewed on 2010-05-25) Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center
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MacNeil, Dean Delehanty. "Lithium-ion battery reactions at elevated temperatures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ66633.pdf.
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Prajapati, Kamlesh. "Properties of magnetostrictive alloys at elevated temperatures." Thesis, University of Hull, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322348.
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Lakhamraju, Raghava R. "Liquid jets in subsonic airstream at elevated temperatures." Cincinnati, Ohio : University of Cincinnati, 2005. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1116266049.
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Nedukanjirathingal, Santhosh Kumar Yang Charles. "Characterization of adhesives at room and elevated temperatures." Diss., Click here for available full-text of this thesis, 2006. http://library.wichita.edu/digitallibrary/etd/2006/t068.pdf.
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Thesis (M.S.)--Wichita State University, Dept. of Aerospace Engineering."July 2006." Title from PDF title page (viewed on October 29, 2006). Thesis adviser: Charles Yang. Includes bibliographic references (leaves 87-89).
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Christian, Lee Conner. "Thru-thickness bending stress distribution at elevated temperatures." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2315.
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During the bending of flange plate used for dapped girders some highway bridge
fabricators are experiencing cracking of the flange plate particularly when heat is used in
assisting the bending process. Due to the extreme strains experienced during the
fabrication process, investigating this problem requires the use of a finite element
analysis. The fabrication process was broken down into two parts, first the heating of
the plate through the use of either a furnace or an acetylene torch (thermal), and the
second was the bending process (structural). The five different temperatures collected
during the thermal analysis were a uniform temperature of 75oF, a 1100oF uniform
temperature as a result of furnace heating, both five and ten minutes of air-cooling after
the plate had reached a uniform temperature of 1100oF, and the temperature gradient
after heating the flange plate to a surface temperature of 1200oF though the use of an
acetylene torch. After the thermal analysis was completed, the resulting temperatures
were imported into the structural model. The plate thicknesses analyzed were one, one
and a half, and two inches, assuming both 50 and 70 ksi yield strengths. To achieve a 90
degree six-inch radius bend the plate was bent in five separate locations. The result of
this analysis showed that with the introduction of temperature gradients into thefabrication process, the strains along the plate??s extreme fibers increased. The model
further showed that for both a one and a half and two-inch thick plate the extreme fiber
strains exceeded ten percent, which further adds to the increased risk of the flange plate
cracking during fabrication. The highest residual stresses through the plate??s thickness
occurred during cold bending. The residual stresses through the plate??s thickness
decreased when the fabrication process was carried out at elevated temperatures. When
steel exceeds a strain of 10 to 16 percent during the fabrication process, the plate
becomes susceptible to cracking. This strain limit was exceeded for plate thicknesses of
one and a half and two inches.
10
Lu, Chi. "Micro-Fabricated Hydrogen Sensors Operating at Elevated Temperatures." UKnowledge, 2009. http://uknowledge.uky.edu/gradschool_diss/767.
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In this dissertation, three types of microfabricated solid-state sensors had been designed and developed on silicon wafers, aiming to detect hydrogen gas at elevated temperatures. Based on the material properties and sensing mechanisms, they were operated at 140°C, 500°C, and 300°C. The MOS-capacitor device working at 140°C utilized nickel instead of the widely-used expensive palladium, and the performance remained excellent. For very-high temperature sensing (500°C), the conductivity of the thermally oxidized TiO2 thin film based on the anodic aluminum oxide (AAO) substrate changed 25 times in response to 5 ppm H2 and the response transient times were just a few seconds. For medium-high temperatures (~300°C), very high sensitivity (over 100 times’ increment of current for H2 concentration at 10 ppm) was obtained through the reversible reduction of the Schottky barrier height between the Pt electrodes and the SnO2 nano-clusters. Fabrication approaches of these devices included standard silicon wafer processing, thin film deposition, and photolithography. Materials characterization methods, such as scanning electron microscopy (SEM), atomic force microscopy (AFM), surface profilometry, ellipsometry, and X-ray diffractometry (XRD), were involved in order to investigate the fabricated nano-sized structures. Selectivities of the sensors to gases other than H2 (CO and CH4) were also studied. The first chapter reviews and evaluates the detection methodologies and sensing materials in the current research area of H2 sensors and the devices presented this Ph.D. research were designed with regard to the evaluations.
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Cowley, Kevin David. "Damage mechanics of polymer composites at elevated temperatures." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337949.
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Haghi, Mehrdad. "Elasto-viscoplasticity of porous metals at elevated temperatures." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/13080.
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Tamer, Fouad G. "Compressive behavior of refractory ceramics at elevated temperatures." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/50281.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1989.Title as it appears in M.I.T. Graduate List, Feb. 1989: Compressive behavior of refractory ceramics at high temperatures.
Includes bibliographical references.
by Fouad George Tamer.
Ph.D.
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Cotton, John. "Finite element modelling of concrete at elevated temperatures." Thesis, Cardiff University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.630477.
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This thesis presents a new plastic damage constitutive model for concrete subjected to elevated temperatures. The proposed Cardiff Concrete Temperature (CARCOT) model combines the original theory presented by Lubliner et al. (1989) with newly derived temperature dependent material parameters developed for normal and high strength concrete. The temperature dependent material parameters have been obtained from a laboratory based experimental study conducted by the author. The CARCOT model has been implemented into the finite element code LUSAS after a successful validation programme using a single point constitutive driver. The overall aim of the CARCOT model is to accurately represent the non-linear behaviour of concrete in both tension and compression for temperatures up to 600· C with a single set of constitutive equations. This is achieved by using the Lubliner yield surface to asses the current stress level and the Mohr Coulomb surface to control the change in volume caused by plastic deformation, i.e. a non associated flow rule is adopted. The proposed model also incorporates the comer indicators proposed by Crisfield (1987) to assess the comers present on the yield surface. Depending on the current stress level and its position on the yield surface a multi vector return algorithm is employed to bring the stress increment back to the yield surface. The thermal damage mechanisms are dealt with in a staged approach in which the temperature damage effects are accounted for at the start of every load increment of finite element computations by a subroutine incorporating the temperature dependent functions.
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Pochopien, Bernadeta Anna. "Interactions of antioxidants with NOx at elevated temperatures." Thesis, University of York, 2012. http://etheses.whiterose.ac.uk/3390/.
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Automotive engines contain aggressive environments where lubricants are degraded by exposure to corrosive combustion by-products such as nitrogen oxides (NO2 and NO), and understanding their interaction is key to the development of long-lived lubricants. Therefore the effect of 1000 ppm of nitrogen oxides on lubricants containing phenolic and aminic antioxidants, individually or in combination, in branched alkane base fluid has been investigated in laboratory reactors at 180 °C, representative of piston conditions. The reaction of the phenolic antioxidant, octadecyl 3-(3,5-di-tert-butyl-4-hydroxy-phenyl) propanoate with 1000 ppm NO2 in N2 resulted in the formation of a quinone methide product (octadecyl3-(3,5-di-tert-butyl-4-oxo-cyclohexa-2,5-dien-1-ylidene)propanoate), in apparent contradiction to previous studies, which observed at room temperature the formation of nitro-phenols. Therefore a novel reaction mechanism is proposed to account for this change in mechanism with the temperature, with the addition of NO2 to phenoxyl radicals being dominant at low temperatures, but reversible at a higher temperature,at which the dominant reaction becomes an abstraction of a hydrogen atom from the α carbon on the alkyl group at the para- position of the phenoxyl radical. The thermochemistry of key intermediates for this mechanism was also investigated using ab-initio calculation, allowing the prediction of the ceiling temperature for the addition of NO2 (1000 ppm) to phenoxyl radicals, and hence of the formation of nitrated phenolics, to be approximately 51 ± 57 °C. The reaction of the aminic antioxidant, 4.4’-dioctyl diphenylamine, with 1000 ppm NO2 was also investigated, with chemical analysis of the reaction products showing the formation of two monomers and five dimers of the starting antioxidant, and possible reaction mechanisms are based on these results. The reaction of NO2 with phenolic and aminic antioxidants when used in conjunction resulted in the identification of two new intermediates formed partially from fragments of aminic and phenolic antioxidants; novel chemical mechanisms for their formation are also suggested.
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Portmann-Orlowski, Michael. "Diffuse neutron scattering of Ni-Au at elevated temperatures /." [S.l.] : [s.n.], 2002. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=14940.
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Omer, Echat. "Failure of composite steel-concrete slabs under elevated temperatures." Thesis, Imperial College London, 2006. http://hdl.handle.net/10044/1/1341.
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The behaviour of composite steel-concrete slabs under fire has attracted considerable attention over recent years and has led researchers to develop performance based models capturing the phenomena observed during fires. However, while the limit load proposed defined corresponds to fracture of the reinforcing mesh, the criterion employed is semi-empirical ignoring fundamental issues such as the bond slip characteristics. A recent model has addressed this issue for lightly reinforced beams, considering the bond slip response of the reinforcement along with other salient problem characteristics, however, it becomes complex for practical application when extended to slabs. In the current work, novel models are developed for the assessment of the failure load of lightly reinforced concrete slabs under fire conditions, considering simply supported rectangular slabs with and without planar edge restraints. In the limit, this load corresponds to the failure load of composite slabs under fire, since fire tests have demonstrated that the steel deck de-bonds leaving a lightly reinforced concrete slab. The developed models account for the temperature effect on the geometric and material properties, and they consider the tensile membrane action developed at large deflections. The deflected shape, used as the basis of model formulation, was observed experimentally to match the failure mode described by yield line theory, and in the developed models, it is assumed that cracks forming along the yield lines, penetrate through the slab depth. The strain concentration in the reinforcement along these cracks is established by considering the bond slip characteristics, and the failure load is determined as that corresponding to a specific rupture mechanical reinforcement strain. Comparisons against the non-linear finite element analysis program ADAPTIC and experimental results are presented along with case studies highlighting the influence of various parameters. Simplified versions of the proposed models are also presented for direct use by designers to assess the failure of composite slabs under elevated temperatures.
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Lee, Seungjea. "Robustness of reinforced concrete framed building at elevated temperatures." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/robustness-of-reinforced-concrete-framed-building-at-elevated-temperatures(db90ad82-86b5-4ba3-9ef1-42e7004b4b34).html.
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This thesis presents the results of a research programme to investigate the behaviour and robustness of reinforced concrete (RC) frames in fire. The research was carried out through numerical simulations using the commercial finite element analysis package TNO DIANA. The main focus of the project is the large deflection behaviour of restrained reinforced concrete beams, in particular the development of catenary action, because this behaviour is the most important factor that influences the frame response under accidental loading. This research includes four main parts as follows: (1) validation of the simulation model; (2) behaviour of axially and rotationally restrained RC beams at elevated temperatures; (3) derivation of an analytical method to estimate the key quantities of restrained RC beam behaviour at elevated temperatures; (4) response and robustness of RC frame structures with different extents of damage at elevated temperatures. The analytical method has been developed to estimate the following three quantities: when the axial compression force in the restrained beam reaches the maximum; when the RC beams reach bending limits (axial force = 0) and when the beams finally fail. To estimate the time to failure, which is initiated by the fracture of reinforcement steel at the catenary action stage, a regression equation is proposed to calculate the maximum deflections of RC beams, based on an analysis of the reinforcement steel strain distributions at failure for a large number of parametric study results. A comparison between the analytical and simulation results indicates that the analytical method gives reasonably good approximations to the numerical simulation results. Based on the frame simulation results, it has been found that if a member is completely removed from the structure, the structure is unlikely to be able to develop an alternative load carrying mechanism to ensure robustness of the structure. This problem is particularly severe when a corner column is removed. However, it is possible for frames with partially damaged columns to achieve the required robustness in fire, provided the columns still have sufficient resistance to allow the beams to develop some catenary action. This may be possible if the columns are designed as simply supported columns, but have some reserves of strength in the frame due to continuity. Merely increasing the reinforcement steel area or ductility (which is difficult to do) would not be sufficient. However, increasing the cover thickness of the reinforcement steel to slow down the temperature increase is necessary.
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Chen, Ju. "Behaviour of high strength steel columns at elevated temperatures." View the Table of Contents & Abstract, 2007. http://sunzi.lib.hku.hk/hkuto/record/B37206230.
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Britt, James Marcel. "Fracture mechanisms of an alumina ceramic at elevated temperatures." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/9329.
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Harris, Trudy Katherine. "The mechanical properties of ultrahard materials at elevated temperatures." Thesis, University of Hull, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363188.
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Christopoulos, S. "Lasing and BEC of microcavity polaritons at elevated temperatures." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597666.
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We investigate the room temperature polaritons dynamics of wide bandgap semiconductor microcavities. Our efforts are focused on microcavities based on wide bandgap semiconductors, such as GaN and ZnO, which possess large exciton binding energies and consequently exhibit enormous Rabi splittings, ensuring the thermal stability of excitons even at room temperature. In this context, the strong coupling regime is indeed observed for the first time in a hybrid bulk GaN microcavity at room temperature. The polaritonic properties are studied with a range of spectroscopic techniques and reveal the occurrence of a polaritonic lasing transition, characterized by an ultralow threshold. The condensate originated emission exhibits a stochastic change of its polarization state. This result is regarded as evidence of spontaneous symmetry breaking. Our observations thus indicate the realization of the first polaritonic Bose-Einstein condensate at room temperature.
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Chen, Ju, and 陳駒. "Behaviour of high strength steel columns at elevated temperatures." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B37936554.
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Nishida, Kenji. "Creep-fatigue failure of engineering materials at elevated temperatures." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47589.
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Ding, Yuan. "Mechanistic Understanding of CO2 Corrosion Inhibition at Elevated Temperatures." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1547122087551426.
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Zwiklitz, L. von. "Fatigue and fracture behaviour of PVC at elevated temperatures." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/5444.
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Includes abstract.Includes bibliographical references (leaves 133-141).
The research studies revealed that there was a distinct difference in fatigue performance as a result of a temperature increase from 20°C to 45°C, as characterised by both SN and Paris fatigue tests. There was also, but to a lesser degree, an ageing effect. The temperature performance factor for the SN curves was between 1.6 and 4.6, while for the Paris characterisation the temperature performance factor was between 3 and 3.5.
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Von, Zwiklitz L. "Fatigue and fracture behaviour of PVC at elevated temperatures." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/15429.
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Includes bibliographical references.A series of failures in underground water-carrying uPVC piping in a luxury resort in Dubai gave rise to a research opportunity to determine the effect of temperature on fatigue life performance of uPVC piping. Two different modes of testing were used to determine this temperature effect, namely SN and Fracture Mechanics Paris testing. The temperatures tested were 20%C and 45%C. In addition to temperature tests, a potential ageing effect was also investigated by comparing pipes which had been in service in the resort, and previously unused piping. The SN tests consisted of externally and symmetrically stressing, across the diameter, sections of pipe from the luxury Madinat Jumeirah resort in Dubai where the failures had occurred. The Paris equation generating FM tests used Compact Tension specimens and produced an equation relating the crack growth rate to the cyclic stress intensity amplitude. In addition, material properties were measured which could then be used for fatigue lifetime predictions. In addition to the lifetime tests, fracture toughness tests were also completed. These were done with a view to determining the fracture toughness of the material, and also to ascertain if there was an orientation effect for crack growth. The potential ageing effect was also investigated. This was achieved by means of using differently orientated specimens. SENB specimens were used to determine circumferential fracture toughness and C-Shaped specimens for longitudinal cracks (the direction of on-site crack growth). Fracture surfaces were inspected and calculations performed to indicate critical flaw sizes were broadly consistent with linear elastic fracture mechanics (LEFM). Using the material properties garnered from the Paris fatigue and fracture toughness tests, lifetime predictions were made and compared to the SN data for cycles to failure The research studies revealed that there was a distinct difference in fatigue performance as a result of a temperature increase from 20%C to 45%C, as characterised by both SN and Paris fatigue tests. There was also, but to a lesser degree, an ageing effect. The temperature performance factor for the SN curves was between 1.6 and 4.6, while for the Paris characterisation the temperature performance factor was between 3 and 3.5.
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Arbuthnot, Colin Hugh David. "The fatigue performance of nimonic PE16 at elevated temperatures." Thesis, University of Sussex, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359623.
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Moody, Gareth John. "The chemistry of radical scavenging antioxidants at elevated temperatures." Thesis, University of York, 2013. http://etheses.whiterose.ac.uk/4383/.
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In this study, the autoxidation of squalane inhibited by phenolic and aminic antioxidants was analysed between 160 and 220 °C representing piston assembly temperatures of automotive engines. The mechanism of the phenolic antioxidant octadecyl 3-(3,5-di-tert-butyl-4- hydroxyphenyl) (OHPP) in the presence of oxygen at these temperatures was analysed. It was concluded that OHPP autoxidation formed four products; a hydroxyl-substituted phenolic, octadecyl 3-(3,5-ditert-butyl-4-hydroxy-phenyl)-3-hydroxy-propanoate, a hydroxyl-substituted quinone methide (octadecyl 3-(3,5-ditert-butyl-4-oxo-cyclohexa- 2,5-dien-1-ylidene)-2-hydroxy-propanoate), and the previously observed hydroxycinnamate and di-tert-butyl benzoquinone. Quantification of the time development of these products indicates that benzoquinone is formed from hydroxycinnamate and not from the phenoxyl radical as previously thought. Mechanisms are suggested to account for this. In the presence of alkyl hydroperoxide, the aminic antioxidant octylated diphenylamine (ODPA) was found to be less effective at high temperatures with large amounts of ODPA remaining at the end of the induction period where the substrate started to oxidise significantly. This is contrary to most previous studies where all the ODPA was consumed by the end of the induction period. The suggested reason for this is that autoxidation occurs preferentially by abstraction of tertiary hydrogen atoms, forming tertiary alkyl peroxy radicals and hydroperoxides. The difference of the O-H bond strength of tertiary alkyl hydroperoxides and the N-H bond strength of ODPA was relatively small resulting in the abstraction of hydrogen atoms from ODPA by tertiary alkyl peroxy radicals being noticeably reversible at higher temperatures. Aminic antioxidants containing naphthalene rings and heteroatom bridges were found to increase the induction period relative to substituted diphenylamines. The alkylated naphthenic antioxidant N-[4-(1,1,3,3-tetramethylbutyl)phenyl]naphthalen-1-amine could achieve this despite 53% of the reacted antioxidant in the initial stages forming dehydrodimer structures. N-(1-naphthyl)naphthalene-1-amine was investigated and was found to form the product (4E)-4-(1-naphthylimino)-1H-naphthalen-1-ol. Based on the aminic antioxidants used, (1,1,3,3-tetramethylbutyl)-12H-benzo-α-phenothiazine was synthesised and used as an antioxidant in squalane autoxidation.
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Vogiatzoglou, Sotiris. "Deformation and fracture behaviour of polyoxymethylene at elevated temperatures." Thesis, University of Leeds, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503254.
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Batista, Junia Cristina Avelar. "Promising duplex coatings for tribological applications at elevated temperatures." Universidade Federal de Minas Gerais, 2001. http://hdl.handle.net/1843/BUDB-8DNJCJ.
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The world iron ore production boomed by an expanding steel market forced the producers to seek for larger reserves achieved only through the better understanding of their mineral resources. This is possible through a detailed characterization of the natural resource and of the ores to be exploited. In this study it was performed a detailed mineralogical characterization of the Alegrias mines amphibolitic itabiriteswhich represents 36% of the total resources and more than 20% of Samarcos reserves and are mined either as ore and waste. The first purpose of this study was to identify different types of amphibolitic itabirites based on their chemical and mineralogical characteristics as well as on their performance through laboratory tests that simulate Samarcos production processes. The second purpose was to have amore detailed chemical and mineralogical characterization of the several aliquots coming from the products of the laboratory simulating processes tests. It was identified in Alegrias Mines five visual different amphibolitic itabirites and from each one it was taken 400kg to compose the samples. The samples were submitted to size and chemical analysis, x-Ray diffratometry, infrared spectrometry, thermogravimetry, opticaland scanning electron microscopy, microprobe, grinding, desliming and flotation laboratory tests. The products of these laboratory processes tests were also analyzed. More five tons of each sample was taken in order to produce concentrates to generate pellets to be tested in Pot Grate furnace. The five amphibolitic itabirites are not compact and potentially ore. Their iron content are typical of the poor itabirites (<50%), the LOIs are considered high tenures (>3%), the Al2O3, as well as MnO2 and FeO contents are within the typical values presented by the Alegrias ores. The main iron ore minerals are goethite (botryoidal, massive,pseudomorphs of amphibole, product of the alteration of the magnetite and earthy) and the porous martitic hematite. The iron ore minerals alteration and porosity grades are elevated and the size of their particles variable (from few micrometers to millimeters). The goethites loss their hydroxyl content in an abrupt way and around 315°C. The slimes percentages of these itabirites are high and by their weight and metallic global recoveries numbers they can be classified as potential ores. Simple modifications on the ignition Pot Grate furnace parameters leaded to improvements and to pellets within the required specifications. The five amphibolitic itabirites are suitable to be divided into four different types. The mineralogical association of amphiboles, iron oxides, quartzand carbonates present on the fresh amphibolitic itabirites recently found in Alegrias mines reinforce their origin to be the iron ore formations of the silicate or oxide-silicate facies associated with carbonates impurities or layers.O aumento de produção de minério de ferro, demandada por um mercado siderúrgico aquecido e em franco crescimento, tem levado à necessidade das empresas mineradoras de aumentarem suas reservas através do conhecimento melhor de seu recurso mineral. Isso só é possível através da caracterização detalhada de suas jazidas e dos minérios a serem explotados. Neste trabalho, foi proposto fazer-se umestudo de caracterização mineralógica dos itabiritos anfibolíticos das minas de Alegria, que representam 36% do total dos recursos geológicos da Samarco e cerca de 20% de sua reserva total e que ora são lavrados como minério ora são dispostos como estéril. Os objetivos desse trabalho foram o de identificar diferentes tipos de itabiritoanfibolítico nas minas de Alegria, baseando-se em suas características químicas, mineralógicas e de comportamento em testes que simulam o processo produtivo da Samarco Mineração S.A., além de fazer-se uma caracterização química e mineralógica mais detalhada, de diversas alíquotas provenientes dos testes de laboratório. Para tanto, foram identificadas cinco amostras de itabiritos anfibolíticos visualmente distintos e pertencentes às minas de Alegria 3/4/5, Alegria 1/2/6 eAlegria 9. De cada amostra, foram coletados 400kg para serem submetidos às análises granulométricas, químicas, difratometria de raios-X, espectroscopia no infravermelho, termogravimetria, microscopia óptica, microscopia eletrônica de varredura e microanálise EDS, além de testes de laboratório de moagem, deslamagem e de flotação de bancada cujos produtos foram também analisados. Foram aindaamostradas cerca de cinco toneladas de cada itabirito anfibolítico, para a preparação de concentrados em planta piloto e a geração de pelotas para queima em forno de Pot Grate e determinação de suas principais características. Os cinco itabiritos anfibolíticos estudados não são compactos e, portanto, potencialmente minérios. Seus teores de FeT são típicos de itabiritos pobres (<50%), os de P são relativamente altos (>0,050%), os de PPC são elevados (>3%) e os de Al2O3 MnO2 e FeO estão geralmente dentro da faixa média dos minérios das minas deAlegria. Os principais minerais de ferro são a goethita (botrioidal, maciça, pseudomórfica de anfibólio, produto de alteração da magnetita e terrosa) e a hematita martítica porosa. Os graus de alteração e de porosidade dos minerais de ferro são elevados e o tamanho de suas partículas é bem variado (desde poucos micrometros até milímetros). A desidroxilação das goethitas ocorre de forma relativamente abruptae por volta de 315°C. A porcentagem de lama desses itabiritos é relativamente elevada e suas recuperações em massa e metálicas globais os classificam como potencialmente minérios. Simples modificações nos parâmetros de queima levaram a melhores queimas e a pelotas dentro dos parâmetros de especificação. Para os cinco itabiritos anfibolíticos estudados, propõe-se a formação de quatro tipos diferenciados.A associação mineralógica de anfibólios, óxidos de ferro, quartzo e carbonatos, encontrada nos itabiritos anfibolíticos frescos recém-identificados nos furos de sondagem de Alegria, corroboraram sua origem atribuída a formações ferríferas da fácies silicato ou óxido-silicato, contendo intercalações e impurezas carbonáticas.
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Matthews, Jeremy P. "Kinetic behaviour of ion intercalation electrodes at elevated temperatures." Thesis, Queensland University of Technology, 2001. https://eprints.qut.edu.au/15786/1/Jeremy_Matthews_Thesis.pdf.
Full textAbstract:
Electrochromic films undergo a colour change when small ions and electrons are inserted into them, under the influence of an applied electric field. These films are also known as ion-intercalation electrodes, and may be incorporated into glazing structures more commonly known as 'smart windows'. Smart windows are that which may be used to control the amount of heat and light entering a building and may therefore be used to minimise the energy consumption associated with heating, cooling and lighting. The commercial success of smart windows, requires that they operate reproducibly at temperatures up to approximately 70ºC, for many tens of thousands of colouring and bleaching cycles. An understanding of the underlying kinetic processes over a wide temperature range is therefore needed, in order to determine suitable control strategies and switching conditions capable of fulfilling these requirements.
The research detailed in this thesis has involved an investigation into the kinetic behaviour of ion-intercalation electrodes, and simulation of the electrical response as a means of developing a tool for predicting and then optimising electrochromic switching. More specifically, the electrical and optical properties of electrochromic thin films of WO3/TiO2 have been studied over a wide temperature range, appropriate for the operation of electrochromic windows. The magnitude of the voltages required for coloration and bleaching significantly reduces as temperature increases. Some irreversibility was observed at high temperature, as well as a reduction in coloration efficiency. Further investigation revealed that self-bleaching and irreversibility effects were caused by the presence of water, and this problem was exacerbated at high temperature. Post-experiment chemical analysis of a film sample revealed that some trapping of the inserted ions had occurred, however the amount of ions remaining in the film was much smaller than expected. The results suggested that a large quantity of the lithium ions injected into the film were lost to the electrolyte after many cycles, possibly accompanied by some film dissolution.
Experimental work carried out in a dry-box showed that films may be cycled reversibly in a very dry environment, and the optical properties were independent of temperature under these conditions. Unfortunately, the conditions which led to reversible cycling and good electrochromic memory, also resulted in very long response times for film bleaching. This result implies that a good electrochromic memory and a fast response are mutually competitive aims.
Data from high temperature experiments was simulated with a mathematical model and the mobility of lithium ions inside the electrochromic films was estimated in the process. The estimated diffusion coefficients agreed well with published values, and exhibited an Arrhenius dependence on temperature. Activation energies for diffusion were calculated and the results were very reasonable. Some deviation from ideal Arrhenius behaviour was observed for the estimated diffusion coefficients at high temperature. It is likely that the rate limiting mechanism changes from diffusive motion of ions at low temperature, to charge transfer at high temperature.
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Matthews, Jeremy P. "Kinetic behaviour of ion intercalation electrodes at elevated temperatures." Queensland University of Technology, 2001. http://eprints.qut.edu.au/15786/.
Full textAbstract:
Electrochromic films undergo a colour change when small ions and electrons are inserted into them, under the influence of an applied electric field. These films are also known as ion-intercalation electrodes, and may be incorporated into glazing structures more commonly known as 'smart windows'. Smart windows are that which may be used to control the amount of heat and light entering a building and may therefore be used to minimise the energy consumption associated with heating, cooling and lighting. The commercial success of smart windows, requires that they operate reproducibly at temperatures up to approximately 70ºC, for many tens of thousands of colouring and bleaching cycles. An understanding of the underlying kinetic processes over a wide temperature range is therefore needed, in order to determine suitable control strategies and switching conditions capable of fulfilling these requirements. The research detailed in this thesis has involved an investigation into the kinetic behaviour of ion-intercalation electrodes, and simulation of the electrical response as a means of developing a tool for predicting and then optimising electrochromic switching. More specifically, the electrical and optical properties of electrochromic thin films of WO3/TiO2 have been studied over a wide temperature range, appropriate for the operation of electrochromic windows. The magnitude of the voltages required for coloration and bleaching significantly reduces as temperature increases. Some irreversibility was observed at high temperature, as well as a reduction in coloration efficiency. Further investigation revealed that self-bleaching and irreversibility effects were caused by the presence of water, and this problem was exacerbated at high temperature. Post-experiment chemical analysis of a film sample revealed that some trapping of the inserted ions had occurred, however the amount of ions remaining in the film was much smaller than expected. The results suggested that a large quantity of the lithium ions injected into the film were lost to the electrolyte after many cycles, possibly accompanied by some film dissolution. Experimental work carried out in a dry-box showed that films may be cycled reversibly in a very dry environment, and the optical properties were independent of temperature under these conditions. Unfortunately, the conditions which led to reversible cycling and good electrochromic memory, also resulted in very long response times for film bleaching. This result implies that a good electrochromic memory and a fast response are mutually competitive aims. Data from high temperature experiments was simulated with a mathematical model and the mobility of lithium ions inside the electrochromic films was estimated in the process. The estimated diffusion coefficients agreed well with published values, and exhibited an Arrhenius dependence on temperature. Activation energies for diffusion were calculated and the results were very reasonable. Some deviation from ideal Arrhenius behaviour was observed for the estimated diffusion coefficients at high temperature. It is likely that the rate limiting mechanism changes from diffusive motion of ions at low temperature, to charge transfer at high temperature.
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Knox, Joanne Jennefer. "Aspects of modelling plain and reinforced concrete at elevated temperatures." Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/7713.
Full textAbstract:
Extreme events such as the Mont Blanc Tunnel fire in 1999 (Bettelini et al. 2001) or the Windsor Tower fire in 2005 (Calavera et al. 2005) have shown how concrete failure at elevated temperatures can be hazardous to the safety of members of the public. Generally, there is an absence of understanding of the mechanical behaviour of both plain and reinforced concrete at elevated temperatures, which is essential for computational modelling. Since fire is an extreme event, a certain amount of damage within the structure would be seen to be permissible within its performance objectives. This necessitates analysis in the post-peak regime. As a material, concrete has a very low value of thermal conductivity. This means that large thermal gradients often occur within concrete, causing differential expansion of the material. This, coupled with the change in mechanical properties at elevated temperatures, further complicates analytical analysis procedures. This study investigates issues associated with computational modelling of plain and reinforced concrete at elevated temperatures and its residual behaviour (behaviour when tested after the material has been heated, for example in a fire, and then cooled). In order to achieve this, first the constitutive material properties of both plain and reinforced concrete at ambient and elevated temperatures were investigated. The study showed that mesh sensitivity and localisation of strain softening occurs in plain concrete under both tensile and compressive loading. Path dependency of the stress-strain behaviour of plain concrete was also demonstrated, when it was subjected to loading and heating. Tension stiffening was included in the reinforced concrete material model, to represent the interaction between concrete and reinforcing steel. Complex behaviours were seen for simple reinforced concrete benchmark tests, due to changing material properties at elevated temperatures and differential thermal expansion of steel and concrete. Non-linear load-displacement relationships were seen as a result of complex load-sharing between concrete and reinforcement. A hypothesis was proposed – that variation of temperatures during heating and cooling of a specimen will cause damage, and hence material degradation, in plain and reinforced concrete. On investigation, it was seen that damage due to differential thermal expansion plays a small part in the reduction of elastic load-displacement slope and peak strength seen in experimental data on residual tests, indicating that other factors identified in previous research also affect the residual behaviour of plain and reinforced concrete. Indeed, in reinforced concrete, when tension stiffening was included, it was found that damage due to differential thermal expansion and contraction had a negligible effect on the residual response in the pre-peak regime. The study also found that for a simply supported beam pure thermal expansion caused a localised response, while pure thermal gradient gave distributed yield. When both were present, in this study, distributed yield with no mesh sensitivity was seen. Realistic heating of a restrained reinforced concrete plane strain model caused compressive stresses accompanied by tensile longitudinal total strains and tensile longitudinal plastic strains throughout the depth of the slab, with the largest values occurring near to the model supports. Damage and recovery variables were found to have no effect on the response of the model. When a portal frame was exposed to heating, plastic strains were distributed throughout the beam, with column rotation limiting downward thermal bowing due to a uniformly distributed load or thermal gradient present. Application of displacement loading causing plastic damage changed the behaviour of the structure under heating – instead of symmetrical compressive plastic strains being induced, areas of varying tensile and compressive strain were caused within the beam. Throughout, simple, easily reproducible simulations were used so that single parameters could be altered and considered. This was important, so that the important parameters to computational modelling could be identified. These can be used to guide experimental series to ensure that they are investigated, in order to improve computational material models. Not all variations of parameters were investigated in this study, but it is clear where further repetition would be beneficial (e.g. in varying thermal expansion and thermal gradient ratios in heating regimes). This study looks to address experimentalists and people working in structural analysis, who would be interested in the parameters investigated, as well as practitioners who may want to use these results.
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Heistermann, Tim. "Stiffness of reverse channel connections at room and elevated temperatures." Doctoral thesis, Luleå tekniska universitet, Byggkonstruktion och -produktion, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16840.
Full textAbstract:
A frame structure exposed to fire undergoes two types of changes due to the resulting temperature fields. The first is the thermal expansion of the structural members and the second is the degradation of the material strength and stiffness as temperature rises. Initially the thermal expansion dominates the response and the structural member (beam) is exposed to compressive forces due to restrained expansion, thus precipitating flexural buckling. At higher temperatures the mechanical material properties degrade. This fact, together with the high compressive forces in the bottom flanges of the beam often results in local buckling, followed by the formation of a plastic hinge close to the support region. The combination of transverse loads and the rising temperature leads to the development of excessive deflections in the beam. When temperature rises enough for the bending resistance of the beam to become insufficient, catenary action is introduced. The result is that the beam transitions to a stage where tensile forces appear due to the catenary action. In these different stages of the response of the structure the beam-to-column connection plays a crucial role and its robustness will determine if the structure will be able to maintain its integrity.The robustness of a structure in a fire situation greatly depends on the rotational capacity of the connection region. High rotational capacity is required at elevated temperatures since the steel beams lose their bending stiffness and exhibit increasingly large deflections under constant load. Beam deflections result in increasing rotations at the supports and may lead to collapse due to connection failure. Other possible failure modes may occur in the structural members, for example due to yielding in tension of the beam. The reverse channel has been proposed as a practical alternative to assemble beams to tubular columns. In a simple implementation, the bending moment generated in the joint due to rotation of the beam may be neglected; however, research efforts are being attempted to quantify the level of constraint. The typical arrangement of the connection type consists of a reverse channel with its flanges welded onto the face of concrete-filled tubular columns and the web bolted to the endplate of a beam. Thicknesses and depths of the reverse channel determine the level of rotational restraint at high temperature. The reverse channel has the ability to undergo catenary deformation in the tensile zone due to the applied rotation at the support and similarly it is relatively ductile in the compression zone. Overall, the reverse channel connection response is rather ductile in terms of its ability to undergo large rotational deformation as long as bolt failure is avoided through proper design.Various tests have been performed to study the behaviour of this type of connection such as full scale buildings, sub-frames, isolated joints and individual sections. The aim of these tests was to capture the connection behaviour in relation to other structural components in fire. This thesis focuses on the tests carried out on the connection components and their finite element modelling. A comprehensive parametric study was performed to assess the influence of different parameters on the behaviour of the connection component at elevated temperatures. The results from the finite element analyses have been utilized to validate analytical models that describe the behaviour of this type of connection at ambient and elevated temperature. Insight into the analytical models provides proper background to a structural designer to estimate the initial stiffness and understand the behaviour of the reverse channel in the connection.En ramkonstruktion utsatt för brand påverkas på två olika sätt av temperaturhöjningen. För det första blir det en längdutvidgning av temperaturhöjningen och för det andra tappar materialet styrka och styvhet med ökande temperatur. Inledningsvis dominerar effekten av temperatur-utvidgningen. Denna leder till tryckande tvångskrafter i konstruktionen vilka kan leda till knäckning.Vid höga temperaturer sjunker materialets styvhet och styrka. Detta kan tillsammans med de höga tryckkrafterna leda till att flytleder bildas vid stöd. De stora tryckkrafterna kan också orsaka knäckning i balken och transversallasterna kan med den minskade styvheten på grund av temperaturhöjning ge upphov till mycket stora deformationer och balkens bärförmåga blir vid tillräckligt höga temperaturer otillräcklig. Vid tillräckligt stora deformationer övergår det statiska verkningssättet från böjning till linverkan. Under denna övergång spelar förbanden mellan balkar och pelare en central roll, och hur dessa klarar att hantera laster och deformationer avgör om hela konstruktionen kan klara belastningen.Hur en konstruktion klarar en brandbelastning beror i hög grad på hur förbanden mellan balkar och pelare klarar rotationer. En stor rotationskapacitet krävs vid höga temperaturer eftersom stålbalkar då har låg bärförmåga och deformationerna kan bli mycket stora även om lasterna är oförändrade. Stora deformationer i balkarna leder till stora rotationer i knutpunkterna vilket kan leda till att förbanden brister och hela konstruktionen kollapsar. Andra möjliga brottmoder kan vara kollaps av balkarna på grund av plasticering under drag. U-profilen har föreslagits som ett praktiskt alternativ för att ansluta balk till pelare. Rotationskapaciteten för ett sådant förband kan bedömas som försumbar, men forskningsinsatser görs för att bestämma den. En föreslagen utformning är att svetsa U-profilens flänsar till den betongfyllda pelaren med slutet tvärsnitt och livet fäst med skruvar i ändplåten på en balk. Rotationsstyvheten vid höga temperaturer kommer att bero på dimensioner på U-profilen. En U-profil har möjligheten att genomgå omvandlingen till linverkan i den dragna delen när den utsätts för ändrotation med den tryckta delen intakt. I allmänhet har ett förband med en U-profil möjlighet att klara stora rotationer under förutsättning att skruvförbandet är utformat på rätt sätt.Ett antal försök har genomförts för att studera hur föreliggande förband kan fungera i en byggnad, en del av en ram, enskilda förband och i tvärsnitt. Försöken har gjorts för att nå förståelse för hur förbandet fungerar tillsammans med andra konstruktionsdetaljer när de utsätts för brandbelastning. Denna avhandling fokuserar på försöken med delar ur förbandet och finit element modellering. En omfattande parameterstudie har gjorts för att förstå hur olika parametrar påverkar förbandets egenskaper vid förhöjd temperatur. Från FE-beräkningarna har analytiska modeller tagits fram som beskriver förbandets egenskaper vid medelhöga och höga temperaturer och dessa ger konstruktören möjlighet att uppskatta den ursprungliga styvheten hos förbandet med U-profil och förståelse för dess uppträdande.
Godkänd; 2013; 20131008 (timhei); Tillkännagivande disputation 2013-11-11 Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen, dubbel doktorsexamen LTU och University of Coimbra, Portugal. Namn: Tim Heistermann Ämne: Stålbyggnad/Steel Structures Avhandling: Stiffness of Reverse Channel Connections at Room and Elevated Temperatures Opponent: Professor Darko Beg, Head of Steel Structures, Ljubljana University, Ljubljana, Slovenien Ordförande: Professor Milan Veljkovic, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Vice ordförande: Assistant Professor Rui António Duarte Simões, Civil Engineering Department, University of Coimbra, Coimbra, Portugal Tid: Tisdag den 3 december 2013, kl 09.00 Plats: F1031, Luleå tekniska universitet
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Hakim, Malik. "The copolymerization of butyl acrylate/methyl methacrylate at elevated temperatures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0001/MQ36700.pdf.
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Voyzelle, B. "Hot deformation behaviour of alloys for applications at elevated temperatures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0004/NQ38336.pdf.
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Van, Zeeland Ineke Maria. "Modelling of dimension lumber in axial compression at elevated temperatures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ57752.pdf.
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Davies, Catrin Mair. "Crack initiation and growth at elevated temperatures in engineering steels." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435926.
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Barkby, Campbell Tyrone. "Migration from non-ovenable food contact materials at elevated temperatures." Thesis, De Montfort University, 1995. http://hdl.handle.net/2086/10704.
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A major problem associated with the development of complex polymeric materials for food contact applications is the potential for migration of toxic substances from the polymer to the food. This thesis investigates the transfer of migrants from non-ovenable food contact materials at elevated temperatures, and several applications where migration has occurred have been identified. Boil in the bag applications lead to exposure times of 30 - 120 minutes for complex multilayer laminates, whilst plastic kettles are repeat exposure items, and plastic 'vacuum flasks' have a potential for up to 4 hours exposure. Analytical techniques including, GC-MS, LC-MS, HPLC and UV spectroscopy have been employed to quantify the species migrating from these food contact materials into aqueous and oil simulants, and to ensure that they conform to the implemented EC restrictions. Olive oil is a stipulated EC fatty food simulant, but it is unsuitable for specific migration analyses since it contains many interfering compounds. These could not be eliminated by repeated solvent extraction, and a silicone oil was therefore substituted. In an attempt to identify the species migrating into aqueous and fatty food simulants both the final materials and also the individual components i.e. nylon, adhesive, polyethylene and polypropylene were examined separately. HPLC techniques have been developed to quantify both the known levels of antioxidants present in the polymers and also the anticipated degradation products from these materials. Typical levels of antioxidants in simulants range from <0.1 (aqueous) to 45j..lgdm-2 (oil) and <0.1 (aqueous) to 200j..lgdm" (oil) for antioxidant degradation products. In commercial boil in the bag laminates the major migrants have been shown to be derived principally from the nylon film, and the polyurethane adhesive used to fabricate the laminate. Le-MS investigations have confirmed the presence of the residual monomer Ecaprolactarn and its cyclic oligomers (up to the nonarner) in aqueous food simulants boiled in direct contact with the nylon 6. This technique has also identified the main migrants from the aliphatic and aromatic polyurethane adhesives to be residual oligomers from the polyols. Any residual isocyanates in the adhesive are converted to the corresponding amine, and colourimetric assays have determined levels between 1.1 and O.lj..lgdm". Measured, migration levels into fatty food simulants were found to be greater than in aqueous food simulants. However, none of the material examined showed an overall migration value greater than the EC limit of 10mg dm" for single sided testing. Some instances were found where the consumer was instructed to boil the dry food part of a boil in the bag meal in the same water as that used to heat the pouch containing the meat, and under these circumstances a total migration value for the laminate greater than 10mg dm-2 was measured.
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Zinner, Christopher. "METHANE AND DIMETHYL ETHER OXIDATION AT ELEVATED TEMPERATURES AND PRESSURE." Master's thesis, University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3457.
Full textAbstract:
Autoignition and oxidation of two Methane (CH4) and Dimethyl Ether (CH3OCH3 or DME) mixtures in air were studied in shock tubes over a wide range of equivalence ratios at elevated temperatures and pressures. These experiments were conducted in the reflected shock region with pressures ranging from 0.8 to 35.7 atmospheres, temperatures ranging from 913 to 1650 K, and equivalence ratios of 2.0, 1.0, 0.5, and 0.3. Ignition delay times were obtained from shock-tube endwall pressure traces for fuel mixtures of CH4/CH3OCH3 in ratios of 80/20 percent volume and 60/40 percent volume, respectively. Close examination of the data revealed that energy release from the mixture is occurring in the time between the arrival of the incident shock wave and the ignition event. An adjustment scheme for temperature and pressure was devised to account for this energy release and its effect on the ignition of the mixture. Two separate ignition delay correlations were developed for these pressure- and temperature-adjusted data. These correlations estimate ignition delay from known temperature, pressure, and species mole fractions of methane, dimethyl ether, and air (0.21 O2 + 0.79 N2). The first correlation was developed for ignition delay occurring at temperatures greater than or equal to 1175 K and pressures ranging from 0.8 to 35.3 atm. The second correlation was developed for ignition delay occurring at temperatures less than or equal to 1175 K and pressures ranging from 18.5 to 40.0 atm. Overall good agreement was found to exist between the two correlations and the data of these experiments. Findings of these experiments also include that with pressures at or below ten atm, increased concentrations of dimethyl ether will consistently produce faster ignition times. At pressures greater than ten atmospheres it is possible for fuel rich mixtures with lower concentrations of dimethyl ether to give the fastest ignition times. This work represents the most thorough shock tube investigation for oxidation of methane with high concentration levels of dimethyl ether at gas turbine engine relevant temperatures and pressures. The findings of this study should serve as a validation for detailed chemical kinetics mechanisms.M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering MSME
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Armstrong, Helen Jane. "Enhanced protein gelation using the Maillard reaction and elevated temperatures." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240427.
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Yu, Chaoming. "Three-dimensional analysis of composite structural elements at elevated temperatures." Thesis, University of Sheffield, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443508.
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Share, J. A. "An automated superconducting magnetometer for measuring samples at elevated temperatures." Thesis, Bucks New University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380272.
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Roden, Peter John. "The gas-phase oxidation of unsaturated compounds at elevated temperatures." Thesis, University of York, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338552.
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Thiruchelvam, Chellathurai. "Deterioration and spalling of high strength concrete at elevated temperatures." Thesis, City University London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274476.
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LIMA, EDUARDO HENRIQUE DE BARROS. "RESIDUAL STRENGTH OF REINFORCED CONCRETE COLUMNS SUBJECT TO ELEVATED TEMPERATURES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36742@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
O concreto é conhecido por ter um bom desempenho quando exposto a altas temperaturas pelo fato de apresentar baixa condutividade térmica, ser incombustível e não exalar gases tóxicos. Entretanto, devido à sua composição heterogênea, o concreto sofre alterações físicas, químicas e mecânicas que podem comprometer sua integridade estrutural. Em estruturas de concreto armado, deve-se ter atenção especial aos pilares, cuja capacidade portante é reduzida significativamente em altas temperaturas e seu colapso, de natureza brusca, pode resultar na instabilidade global da estrutura. As reduções nas propriedades mecânicas dos materiais aliadas a lascamentos, fissuras e deformações excessivas podem comprometer seu desempenho, tornando-se necessária a verificação da segurança em situações de incêndio. Com o objetivo de analisar a resistência residual de colunas de concreto armado submetidas a altas temperaturas, foram realizados ensaios de compressão em corpos-de-prova cilíndricos de concreto simples de 5x10 cm submetidos a diferentes temperaturas (200, 400, 600, 800 e 1000 graus Celsius) e de concreto armado de 15x30 cm com diferentes configurações de estribos e submetidos a distintos tempos de exposição (30, 60, 90 e 120 minutos). Em ambos os ensaios, os corpos-de-prova foram resfriados em temperatura ambiente. Os resultados do programa experimental comprovam a perda de resistência à compressão e seus valores foram comparados a modelos numéricos e ao Método da Isoterma de 500 graus Celsius constante na ABNT NBR 15200 de 2004 e no EUROCODE 2.
Concrete is well-known for exhibiting good performance when exposed to elevated temperatures because its low thermal conductivity coefficient, noncombustible properties and reduced emission of toxic gases. However, due to its heterogeneous composition, concrete undergoes physical, chemical and mechanical alterations that can compromise its structural integrity. In reinforced concrete structures, special attention should be paid to the columns, in bearing capacity is reduced significantly at elevated temperatures and their collapse, naturally brittle, may result in overall instability of structure. Reductions in the mechanical properties of the steel and concrete combined with spalling, cracking and excessive deformation compromise its performance, making it necessary to verify the safety in fire situations. In order to analyze the residual strength of reinforced concrete columns submitted to elevated temperatures, compression tests were carried out on plain concrete cylindrical specimens of 5x10 cm exposed to different temperatures (200, 400, 600, 800 and 1000 degrees Celsius) and on reinforced concrete of 15x30 cm considering different stirrups configuration and exposure times (30, 60, 90 and 120 minutes). In both tests, the specimens were cooled to room temperature. The results of the experimental program demonstrate the loss of compression strength and their values were compared to those obtained numerical models and to the Isotherm Method of 500 degrees Celsius, recommended in ABNT NBR 15200 of 2004 and in EUROCODE 2.
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Packard, Corinne E. "Nanomechanical studies of metallic glasses at ambient and elevated temperatures." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/46663.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Includes bibliographical references (p. 116-127).
Bulk metallic glasses, though attractive for use in structural applications for their high strength and elastic limit, display several unacceptable features upon deformation, including quasi-brittle failure along shear bands, extremely limited tensile ductility, and propensity for fatigue under cyclic loading. Though researchers have studied metallic glasses for the last fifty years, several fundamental aspects of the mechanical deformation process in these materials have not been conclusively established. In this thesis, new instrumentation and techniques were developed to study the deformation mechanism of metallic glasses, enabling a focused, high-resolution method for probing nanomechanical behavior. A nanoindenter capable of sub-nanometer and sub-microNewton resolution was outfitted with a custom heating stage and installed in a controlled atmosphere chamber to allow for high fidelity testing in a non-oxidizing environment across a range of deformation regimes. Using this system, the process of shear band initiation near a stress concentration was investigated using a low load indentation technique, revealing that high stresses at a point directly beneath the contact are not sufficient to cause shear band release to the free surface, but instead the potential for material flow along a slip line to relieve stress must be considered. Additionally, the distribution of strengths associated with the yield event was identified and its origins were determined to be mainly structural by using a variety of specially designed loading functions to examine rate, stress, and dynamic loading dependencies.
(cont.) Elevated temperature testing in the custom indentation system allowed in situ observation of the transition from discrete accommodation of strain in shear bands to homogeneous flow as well as characterization of the main features of viscous flow above the glass transition temperature. With the development of these new high-resolution testing methods, new avenues of experimental investigation have been opened, allowing insight into the fundamentals of plastic flow in metallic glasses across a spectrum of conditions.
by Corinne E. Packard.
Ph.D.
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Rai, Purnima. "Effect of elevated temperatures on Trogerma variabile Ballion life stages." Thesis, Kansas State University, 2014. http://hdl.handle.net/2097/18714.
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Master of ScienceDepartment of Grain Science and Industry
Bhadriraju Subramanyam
Heat treatment of grain-processing facilities involves using elevated temperatures of 50- 60˚C for 24 h or less to manage stored-product insects. Heat is an alternative to a non-ozone depleting fumigant sulfuryl fluoride, which was registered in the United States in 2004 for disinfestation of grain-processing facilities. In this study, life history traits of the warehouse beetle, Trogoderma variabile Ballion, were characterized on ground cat food at 28°C and 65% RH to facilitate harvesting life stages of a specific age for bioassays with heat. Eggs laid by females were observed for daily eclosion. Eggs hatched on days 6 through 10, and the mean proportion for egg hatching was 87%. Larvae hatching from eggs (first instars) were reared on ground cat food and their head capsule widths were measured every 2 d until all larvae became pupae. Head capsule widths indicated six instars and the total larval duration ranged from 28-40 d. Pupae became adults in 3-9 d. Newly eclosed unmated female adults lived 7 d longer than unmated males (16 d), whereas mated males lived 2 d longer than mated females (8 d). Eggs were not observed when food was not provided to male and female pairs. Females started laying eggs 2 d after pairing until the fifth day. The total number of eggs laid by mating pairs in the presence of food ranged from 30 to 135. Exposure of eggs, young larvae, old larvae, pupae, and adults of T. variabile at 46, 50, and 54°C and 15-20% RH for four fixed time periods showed pupae to be generally more heat tolerant than other life stages. At 46, 50, and 54°C, complete mortality of all stages occurred at 1440, 120, and 30 min, respectively. Pupae also were generally more heat tolerant than other life stages during tests in pilot flour and feed mills at Kansas State University and in a commercial grain-processing facility. However, results from pilot and commercial mills were not as conclusive as the results at fixed temperatures in the laboratory.
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LAKHAMRAJU, RAGHAVA RAJU. "LIQUID JET BREAKUP STUDIES IN SUBSONIC AIRSTREAM AT ELEVATED TEMPERATURES." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1116266049.
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