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1
Ellis, M. "The ductile to brittle transition in BCC metals." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306220.
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Valikova, Irina, and Andrei Nazarov. "Simulation of diffusion under pressure in BCC metals." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-195673.
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Valikova, Irina V., and Andrei V. Nazarov. "Simulation of diffusion under pressure in bcc metals." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194630.
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This work is devoted to simulation of atom configurations in bcc metals near the point defect using the molecular static method. The values of migration and formation volumes are very sensitive to the atomic structure in the vicinity of a defect, which makes it necessary to consider a large number of atoms in the computation cell and to take into account an elastic matrix around the cell. We have developed the new model taking into the consideration these factors. It allows to define “fine structure” of displacement atoms
near the point defect. The atoms of third zone were embedded in an elastic continuum. The displacement of each atom embedded in an elastic continuum was defined as the first and the second terms in solution of elastic equation. In the framework of this model we calculated the formation and migration volumes of defect. Also we take into the consideration that the energy of system (in particular the system with defect) depends on the outer pressure. This dependence gives an addition to the values of migration and formation volumes.
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Valikova, Irina V., and Andrei V. Nazarov. "Simulation of diffusion under pressure in bcc metals." Diffusion fundamentals 3 (2005) 11, S. 1-15, 2005. https://ul.qucosa.de/id/qucosa%3A14298.
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This work is devoted to simulation of atom configurations in bcc metals near the point defect using the molecular static method. The values of migration and formation volumes are very sensitive to the atomic structure in the vicinity of a defect, which makes it necessary to consider a large number of atoms in the computation cell and to take into account an elastic matrix around the cell. We have developed the new model taking into the consideration these factors. It allows to define “fine structure” of displacement atoms
near the point defect. The atoms of third zone were embedded in an elastic continuum. The displacement of each atom embedded in an elastic continuum was defined as the first and the second terms in solution of elastic equation. In the framework of this model we calculated the formation and migration volumes of defect. Also we take into the consideration that the energy of system (in particular the system with defect) depends on the outer pressure. This dependence gives an addition to the values of migration and formation volumes.
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Valikova, Irina, and Andrei Nazarov. "Simulation of diffusion under pressure in BCC metals." Diffusion fundamentals 2 (2005) 39, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14369.
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Nazarov, Andrei V., Alexander A. Mikheev, Irina V. Valikova, Aung Moe, and Alexander G. Zaluzhnyi. "Kinetic of void growth in fcc and bcc metals." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193483.
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Nazarov, Andrei V., Alexander A. Mikheev, Irina V. Valikova, Aung Moe, and Alexander G. Zaluzhnyi. "Kinetic of void growth in fcc and bcc metals." Diffusion fundamentals 6 (2007) 28, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14203.
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Escobedo, Juan Pablo. "Measurement of shear strength and texture evolution in BCC materials subjected to high pressures." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Fall2007/j_escobedo_120507.pdf.
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Tsai, Joshua Jr-Syan. "Micromechanisms of Near-Yield Deformation in BCC Tantalum." BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/8906.
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New materials, optimized for increased strength, ductility, and other desirable properties, have the potential to improve every aspect of modern living. To achieve these optimums, the necessary technological advancements are impeded mainly by the limits of available material models. Innovations in this field rely on research into the nature of material behavior. While a typical model of material behavior in the region near yield involves the initial linear elastic response, followed by yield and isotropic hardening, this fails to explain various important phenomena that manifest in a range of materials, such as pre-yield nonlinearity, anelasticity, yield point phenomena, hardening stagnation, and the Bauschinger effect. These effects have been explained over the past century with the theories of Cottrell atmospheres, the Orowan by-pass mechanism, and back stress. This manuscript compares data from experimental observation in tantalum to these theories to better understand the micromechanisms occurring near yield. Understanding deformation in this region has significant implications in structural and mechanical engineering, as well has having direct applications in the forming of metals. Forty-four dogbone-shaped samples were cut from 99.99% pure tantalum and pulled in load-unload-load and multi-cycle loop tensile tests at room temperature. The specimens were either single crystal, whose orientations were chosen based on desired active slip mode determined by Schmid factors, or bicrystal, based on the orientation of the single grain boundary. Sample behavior was simulated in both crystal plasticity and General Mesoscale finite element models to assist in interpreting results and in suggesting plausible micromechanisms. The experimental results and crystal plasticity simulations suggest alternate explanations to some of the discussed mechanical theories of near-yield deformation. The combined experimental / modeling approach indicates that other slip systems, besides the conventionally assumed {110}, are activated upon yield; particularly the {112} system. The breakaway model traditionally associated with the yield point phenomenon may also be better explained through a different mechanism; back stress development during deformation is shown to result in the observed behavior. Lastly, as is well-known, the Taylor formulation, upon which most crystal plasticity models are based, does not adequately predict yield stress behavior in the presence of grain boundaries; once again, an internal stress mechanism matches much better with the experimental results on single and bicrystals. While not all observations could be fully explained by simply adding internal stress generation to a standard crystal plasticity model, this work anticipates further studies to enable more accurate predictive modeling capabilities and increase understanding of the mechanisms driving the fundamental material properties necessary for future progress.
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Waterton, Michael. "Characterisation and evolution of the grain boundary network in BCC metals." Thesis, Swansea University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678443.
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Gilbert, Mark R. "BCC metals in extreme environments : modelling the structure and evolution of defects." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:d972d28d-5d2d-4392-8cf5-fc5728dc74f6.
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Designing materials for fusion applications is a very challenging problem, requiring detailed understanding of the behaviour of materials under the kinds of extreme conditions expected in a fusion environment. During the lifetime of fusion-reactor components, materials will be subjected to high levels of neutron irradiation, but must still perform effectively at high operating temperatures and under significant loading conditions. Body-centred cubic (bcc) transition metals are some of the most promising candidates for structural materials in fusion because of their relatively high density, which allows for effective neutron-shielding with the minimum volume and mass of material. In this work we perform atomistic simulations on two of the most important of these, Fe and W. In this thesis we describe atomic-scale simulations of defects found in bcc systems. In part I we consider the vacancy and interstitial loop defects that are produced and accumulated as a result of irradiation-induced displacement cascades. We show that vacancy dislocation loops have a critical size below which they are highly unstable relative to planar void defects, and thus offer an explanation as to why they are so rarely seen in TEM observations of irradiated bcc metals. Additionally, we compare the diffusion rates of these vacancy loops to their interstitial counterparts and find that, while interstitial loops are more mobile, the difference in mobility is not as significant as might have been expected. In part II we study screw dislocations, which, as the rate limiting carriers of plastic deformation, are significantly responsible for the strength of materials. We present results from large-scale finite temperature molecular dynamics simulations of screw dislocations under stress and observe the thermally-activated kink-pair formation regime at low stress, which appears to be superseded by a frictional regime at higher stresses. The mobility functions fitted to the results are vital components in simulations of dislocation networks and other large-scale phenomena. Lastly, we develop a multi-string Frenkel-Kontorova model that allows us to study the core structure of screw dislocations. Subtle changes in the form of the interaction laws used in this model demonstrate the difference between the non-degenerate and degenerate core structures. We provide simple criteria to guarantee the correct structure when developing interatomic potentials for bcc metals.
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Valikova, Irina, and Andrei Nazarov. "Simulation of pressure- and temperature dependence of impurity diffusion in BCC metals." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-190167.
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Valikova, Irina, and Andrei Nazarov. "Simulation of pressure- and temperature dependence of impurity diffusion in BCC metals." Diffusion fundamentals 11 (2009) 53, 2009. https://ul.qucosa.de/id/qucosa%3A14015.
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Hyde, Brian. "Effects of Carbon on Fracture Mechanisms in Nanocrystalline BCC Iron - Atomistic Simulations." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/27315.
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Atomistic computer simulations were performed using embedded atom method interatomic potentials in α-Fe with impurities and defects. The effects of intergranular carbon on fracture toughness and the mechanisms of fracture were investigated. It was found that as the average grain size changes the dominant energy release mechanism also changes. Because of this the role of the intergranular carbon changes and these mechanisms compete affecting the fracture toughness differently with changing grain size.
Grain boundary accommodation mechanisms are seen to be dominant in the fracture of nanocrystalline α-Fe. To supplement this work we investigate grain boundary sliding using the Σ = 5,(310)[001] symmetrical tilt grain boundary. We observe that in this special boundary sliding is governed by grain boundary dislocation activity with Burgers vectors belonging to the DSC lattice. The sliding process was found to occur through the nucleation and glide of partial grain boundary dislocations, with a secondary grain boundary structure playing an important role in the sliding process. Interstitial impurities and vacancies were introduced in the grain boundary to study their role as nucleation sites for the grain boundary dislocations. While vacancies and H interstitials act as preferred nucleation sites, C interstitials do not.<br>Ph. D.
15
Makarow, Irina. "Correlation of the elastic and plastic anisotropy of rolled FCC and BCC sheet." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66250.
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Srivastava, Ashish Kumar Mirshams Reza. "Orientation, microstructure and pile-up effects on nanoindentation measurements of FCC and BCC metals." [Denton, Tex.] : University of North Texas, 2008. http://digital.library.unt.edu/permalink/meta-dc-6050.
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Srivastava, Ashish Kumar. "Orientation, Microstructure and Pile-Up Effects on Nanoindentation Measurements of FCC and BCC Metals." Thesis, University of North Texas, 2008. https://digital.library.unt.edu/ark:/67531/metadc6050/.
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This study deals with crystal orientation effect along with the effects of microstructure on the pile-ups which affect the nanoindentation measurements. Two metal classes, face centered cubic (FCC) and body centered cubic (BCC, are dealt with in the present study. The objective of this study was to find out the degree of inaccuracy induced in nanoindentation measurements by the inherent pile-ups and sink-ins. Also, it was the intention to find out how the formation of pile-ups is dependant upon the crystal structure and orientation of the plane of indentation. Nanoindentation, Nanovision, scanning electron microscopy, electron dispersive spectroscopy and electron backscattered diffraction techniques were used to determine the sample composition and crystal orientation. Surface topographical features like indentation pile-ups and sink-ins were measured and the effect of crystal orientation on them was studied. The results show that pile-up formation is not a random phenomenon, but is quite characteristic of the material. It depends on the type of stress imposed by a specific indenter, the depth of penetration, the microstructure and orientation of the plane of indentation. Pile-ups are formed along specific directions on a plane and this formation as well as the pile-up height and the contact radii with the indenter is dependant on the aforesaid parameters. These pile-ups affect the mechanical properties like elastic modulus and hardness measurements which are pivotal variables for specific applications in micro and nano scale devices.
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Tarleton, Edmund. "Dislocation-dynamics modelling of crack-tip plastic zones and brittle-ductile transitions in BCC metals." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526123.
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Coombes, Matthew. "A Comparative study of two copper(II) based metal-organic frameworks : Cu2¼(OH)½B4C•8H2O and Cu2Na(OH)B4C•7H2O." Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1016245.
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This study focussed on two copper(II)-containing metal-organic frameworks (MOFs): Cu2Na(OH)B4C•7H2O and Cu2¼(OH)½B4C•8H2O (B4C = 1,2,4,5- benzenetetracarboxylate). They are both covalent, three-dimensional metalorganic framework polymers containing voids filled with water molecules. Both were characterised by elemental analysis, infrared spectroscopy, X-ray powder diffractometry (both in situ and regular), thermogravimetric analysis, differential scanning calorimetry and X-ray photoelectron spectroscopy. These two MOFs are essentially identical, with the only difference being the substitution of sodium by copper at every 4th site (disordered throughout the crystal). The guest inclusion properties of both MOFs were studied and compared. Although both structures collapse on dehydration, it was observed that Cu2Na(OH)B4C•7H2O is able to take up signifcant amounts of water, methanol and ethanol. All these processes are fully reversible. Car-Parrinello molecular dynamics studies suggest that it is a strong interaction between the oxygen atoms on these molecules with the sodium cation of the MOF that is responsible for this signifcant uptake. In contrast, Cu2¼ (OH)½ B4C•8H2O, the MOF without a sodium cation, did not demonstrate any methanol or ethanol uptake, but was able to take up some water. The uptake of water, however, is not a fully reversible process. The absence of sodium likely results in insuffcient energy to draw methanol and ethanol into the framework, while a subtle rotation of a carboxylate group on dehydration decreases the ability of the framework to form hydrogen bonds, thus reducing the ability to take up water. A series of hydrothermal syntheses were performed in order to develop a method of synthesis superior to the current gel-based synthesis that requires several months and has poor yields. The hydrothermal products were characterized by elemental analysis, infrared spectroscopy, X-ray powder diffractometry, thermogravimetric analysis and differential scanning calorimetry. It was shown that the MOF Cu2Na(OH)B4C•7H2O may be synthesised in almost 100% yield by using a temperature of 120°C over a period of 72 hours. It was not possible to synthesise Cu2¼ (OH)½ B4C•8H2O in a 100% yield - it was only obtained as a minor product.
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Docherty, Callum James. "Terahertz spectroscopy of graphene and other two-dimensional materials." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:98c03952-dc3f-442b-bbc0-d8397645cc1b.
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In this thesis, two-dimensional materials such as graphene are tested for their suitability for opto-electronic applications using terahertz time domain spectroscopy (THz-TDS). This ultrafast all-optical technique can probe the response of novel materials to photoexcitation, and yield information about the dynamics of the material systems. Graphene grown by chemical vapour deposition (CVD) is studied using optical-pump THz-probe time domain spectroscopy in a variety of gaseous environments in Chapter 4. The photoconductivity response of graphene grown by CVD is found to vary dramatically depending on which atmospheric gases are present. Adsorption of these gases can open a local bandgap in the material, allowing stimulated emission of THz radiation across the gap. Semiconducting equivalents to graphene, molybdenum disulphide (MoS<sub>2</sub>) and tungsten diselenide (WSe<sub>2</sub>), grown by CVD, are investigated in Chapter 5. These members of the transition metal dichalcogenide family show sub-picosecond responses to photoexcitation, suggesting promise for use in high-speed THz devices. In Chapter 6, an alternative production route to CVD is studied. Liquid-phase exfoliation offers fast, easy production of few-layer materials. THz spectroscopy reveals that the dynamics of these materials after photoexcitation are remarkably similar to those in CVD-grown materials, offering the potential of cheaper materials for future devices. Finally in Chapter 7, it is shown that carbon nanotubes can be used to make ultrafast THz devices. Unaligned, semiconducting single walled carbon nanotubes can be photoexcited to produce an ultrafast, dynamic THz polariser. The work in this thesis demonstrates the potential for these novel materials in future opto-electronic applications. THz spectroscopy is shown to be an important tool for the characterisation of new materials, providing information that can be used to understand the dynamics of materials, and improve production methods.
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Gai, Xiao. "Radiation damage and inert gas bubbles in metals." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/17927.
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Inert gases in metals can occur due to ion implantation, from a plasma in a magnetron device or as a result of being by-products of nuclear reactions. Mainly because of the nuclear applications, the properties of the inert gases, helium, argon and xenon in the body centred cubic (bcc) iron crystal are examined theoretically using a combination of molecular dynamics, static energy minimisation and long time scale techniques using empirical potential functions. The same techniques are also used to investigate argon and xenon in aluminium. The primary interest of the work occurred because of He produced in nuclear fission and its effect on the structural materials of a fission reactor. This structure is modelled with perfectly crystalline bcc Fe. In bcc iron, helium is shown to diffuse rapidly forming small bubbles over picosecond time scales, which reach a certain optimum size. In the initial phase of He accumulation, Fe interstitials are ejected. This occurs instantaneously for bubbles containing 5 He atoms and as the more He accumulates, more Fe interstitials are ejected. The most energetically favourable He to vacancy ratios at 0 K, vary from 1 : 1 for 5 vacancies up to about 4 : 1 for larger numbers of vacancies. An existing He bubble can be enlarged by a nearby collision cascade through the ejection of Fe interstitials, allowing more He to be trapped. Ar and Xe in bcc Fe prefer to be substitutional rather than interstitial and there are large barriers to be overcome for the inert gas atoms to diffuse from a substitutional site. Bubbles that form can again be enlarged by the presence of a nearby collision cascade or at very high temperatures. In this case the most energetically favourable vacancy ratios in the bubbles is 1: 1 for Ar and from 0.6: 1 to 0.8: 1 for Xe. For Ar and Xe, bubble formation is more likely as a direct result of radiation or radiation enhanced diffusion rather than diffusion from a substitutional site. Ar in aluminium is also studied. Ar atoms in fcc Al prefer to be substitutional rather than interstitial and evolution into substitutional occurs over picosecond time scales at room temperature. Bubble formation can occur more easily than in bcc iron, mainly because the barriers for vacancy diffusion are much lower but the time scales for bubble accumulation are much longer than those for He. A vacancy assisted mechanism is found which allows Ar to diffuse through the lattice. Finally some preliminary results on the energetics of different geometrical structures of larger Xe bubbles in Al are investigated since experiment has indicated that these can become facetted.
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Schneider, Andreas Simon [Verfasser]. "Mechanical properties of small scale BCC metal structures / vorgelegt von Andreas Simon Schneider." Stuttgart : Max-Planck-Inst. für Metallforschung, 2010. http://d-nb.info/1004952171/34.
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Rashetnikava, Alena, Alexander Germanov, Irina Valikova, and Andrei Nazarov. "Molecular dynamics simulation of atomic structure in the vicinity of point defects in FCC and BCC metals." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-190156.
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Rashetnikava, Alena, Alexander Germanov, Irina Valikova, and Andrei Nazarov. "Molecular dynamics simulation of atomic structure in the vicinity of point defects in FCC and BCC metals." Diffusion fundamentals 11 (2009) 52, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A14014.
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LUCENA, Marcella Auxiliadora de Melo. "Marcadores luminescentes para identificação de resíduos de tiro: síntese, avaliação da toxicidade e aplicação da rede metal-orgânica [Ln(BTC)]." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/18429.
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Previous issue date: 2016-07-26<br>CAPES<br>Resíduos de tiro (GSR) são evidências físicas de grande valor forense em casos envolvendo o uso de armas de fogo. Mas apesar de sua importância, existe uma carência metodológica para a caracterização do GSR proveniente de munição ambiental (NTA). Adicionalmente, o tamanho micrométrico das partículas geradas torna sua detecção em uma cena de crime ou em um suspeito uma tarefa difícil, podendo originar falsos-negativos. Neste sentido, tem sido proposto o uso de materiais luminescentes para a marcação química e óptica de munições. O presente trabalho aborda o desenvolvimento de marcadores luminescentes baseados na rede metal-orgânica (MOF) [Ln(BTC)] (em que BTC = ácido trimésico), desde a sua síntese, aplicação e avaliação da toxicidade, assim como seu uso na codificação de munição e sua caracterização junto aos resíduos orgânicos de disparo (OGSR). Por isto, este trabalho é dividido em cinco capítulos. No primeiro são discutidos aspectos relativos à síntese da MOF [Eu(BTC)] e à sua influência nas propriedades estruturais, térmicas e espectroscópicas dessa rede. Para tal, os métodos de síntese hidrotermal convencional e hidrotermal assistido por micro-ondas (MW), com diferentes tempos de síntese e proporções metal:ligante, são analisados. Com os métodos adotados, a MOF [Eu(BTC)] foi obtida com elevada cristalinidade, estabilidade térmica e luminescência. Adicionalmente, sínteses mais curtas e proporção metal:ligante 1:1 produziram redes com maior pureza de fase. Neste caso, o método assistido por micro-ondas se destacou devido ao rápido tempo de síntese. No segundo capítulo é apresentada a eficiência dessa MOF como marcador luminescente de munições. Com esta rede, além da detecção visual dos resíduos luminescentes (LGSR), técnicas como espectroscopia de emissão e microscopia eletrônica de varredura acoplada a espectroscopia por dispersão de energia (MEV/EDS) foram usadas para caracterizar e confirmar a presença do LGSR nos resíduos coletados, tanto da arma como das mãos do atirador. No terceiro capítulo são apresentados os dados relativos à avaliação da toxicidade oral aguda e subaguda da MOF [Eu(BTC)] em ratos. Para avaliação da toxicidade aguda, o protocolo 423 da OECD (Organisation for Economic Co-operation and Development) foi utilizado. Como resultado, nenhum sinal de
toxicidade foi observado até mesmo para a dosagem mais elevada, e a dose letal média (DL50) foi estimada em 5000 mg/kg. Com isto, a MOF [Eu(BTC)] foi classificada na categoria menos tóxica do GHS (Globally Harmonized System). A toxicidade subaguda foi avaliada através da administração por 7 dias consecutivos de 300 mg/kg e, apesar de observados sinais graves de toxicidade, estes foram atribuídos à aspiração do material particulado para o pulmão, e não a toxicidade do marcador. Estes resultados atribuem a MOF [Eu(BTC)] uma elevada margem de segurança para aplicação como marcador de GSR. No quarto capítulo é proposto um método de codificação de munição baseado no uso de marcadores co-dopados [Y1-xLnx(BTC)] com os íons Eu3+, Sm3+, Tb3+ e/ou Yb3+. Após a realização de disparos, o marcador utilizado em cada munição foi identificado por MEV/EDS em função da composição química dos resíduos em 100% dos casos (sem que o analista tivesse conhecimento do marcador presente em cada munição). Além disso, foi possível estabelecer correlações atirador-arma-local do disparo através da composição dos resíduos em 89% dos casos. E no último capítulo é abordada a caracterização simultânea dos resíduos orgânicos e luminescentes por meio da microscopia Raman. Com a metodologia proposta, através de uma única medida foi possível determinar o tipo de marcador e pólvora utilizados, fornecendo um código muito seguro para caracterização e classificação inequívoca dos resíduos como provenientes de disparo de arma de fogo. Além disso, o LGSR atuou como sonda luminescente ajudando a coletar o OGSR em distâncias acima daquelas normalmente abordadas na literatura.<br>Gunshot residue (GSR) are physical evidences of great forensic value in firearms-related crimes. Despite its importance, there is a methodologic need for the characterization of GSR from non-toxic ammunition (NTA). In addition, the micrometric size of the generated particles makes its detection in a crime scene or on a suspect a hard task, which may produce false-negatives. In this sense, the use of luminescent materials has been proposed for chemical and optical marking of ammunition. This work presents the development of luminescent markers based on the metal-organic framework (MOF) [Ln(BTC)], since its synthesis, application and toxicity evaluation, as well as its ability to encode ammunitions and its simultaneous characterization with the organic gunshot residue (OGSR). Hence, this work is divided in five chapters. In the first chapter, aspects related to the synthesis of the MOF [Eu(BTC)] and its influence on the structural, thermal and spectroscopic properties are discussed. To this end, conventional hydrothermal synthesis and microwave(MW)-assisted hydrothermal synthesis, with different reaction times and metal:ligand proportions are analyzed. With the chosen methods, the MOF [Eu(BTC)] was obtained with high crystallinity, thermal stability and luminescence. However, faster synthesis and 1:1 metal:ligand proportion produced frameworks with higher phase purity. In this case, the MW-assisted method stood out due to the faster reaction time. In the second chapter, the efficiency of the MOF [Eu(BTC)] as a luminescent marker for ammunition is presented. With this framework, besides visual detection of the luminescent residues (LGSR), techniques as emission spectroscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy (MEV/EDS) were used to characterize and confirm the presence of LGSR in the residues collected, both on the gun and in the shooter’s hand. In the third chapter, data related to the evaluation of acute and subacute oral toxicity of the MOF [Eu(BTC)] in rats is presented. For evaluation of acute oral toxicity, the OECD (Organisation for Economic Co-operation and Development) 423 guideline was used. As a result, no signs of toxicity was observed even at the highest dose, and the median lethal dose (LD50) estimated was 5000 mg/Kg. There by, the MOF [Eu(BTC)] was classified in the less toxic category of GHS (Globally Harmonized
System). The subacute toxicity was evaluated by consecutive administration of 300 mg/Kg for 7 days and, despite severe toxicity signs were observed, they were attributed to the aspiration of the particulate material into the lungs, but not to the marker’s toxicity. These results give a high safety margin for application of this MOF as a GSR marker. In the fourth chapter an ammunition encoding method is proposed based on the use of the co-doped markers [Y1-xLnx(BTC)] with the ions Eu3+, Sm3+, Tb3+ and/or Yb3+. After shots, the markers used in each ammunition was identified by SEM/EDS due the chemical composition of the residues, in 100% of the cases (without the analyst’s knowledge of which marker was present in each ammunition). Furthermore, shooter-weapon-location correlations was established by the composition of the residues in 89% of the cases. And in the last chapter the simultaneously characterization of the organic and luminescent residues was performed by Raman microscopy. With the proposed methodology, the type of marker and gunpowder used were identified by a single run, providing a security code for its characterization and the unequivocal classification of the residues as coming from firearm discharge. Furthermore, the LGSR acted as a luminescent probe, helping to collect the OGSR further than those reported in the literature.
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Voskoboinikov, Roman E. "Analytical Description of Brittle-to-Ductile Transition in bcc Metals. Nucleation of dislocation loop at the crack tip." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-29522.
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Nucleation of dislocation loop at the crack tip in a material subjected to uniaxial loading is investigated. Analytical expression for the total energy of rectangular dislocation loop at the crack tip is found. Depencence of the nucleation energy barrier on dislocation loop shape and stress intensity factor at the crack tip is determined. It is established that the energetic barrier for nucleation of dislocation loop strongly depends on the stress intensity factor. Nucleation of dislocation loop is very sensitive to stress field modifiers (forest dislocations, precipitates, clusters of point defects, etc.) in the crack tip vicinity.
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Jarmakani, Hussam N. "Quasi-isentropic and shock compression of FCC and BCC metals effects of grain size and stacking-fault energy /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3307166.
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Thesis (Ph. D.)--University of California, San Diego, 2008.<br>Title from first page of PDF file (viewed June 18, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 214-225).
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Voskoboinikov, Roman E. "Analytical Description of Brittle-to-Ductile Transition in bcc Metals. Nucleation of dislocation loop at the crack tip." Forschungszentrum Rossendorf, 2002. https://hzdr.qucosa.de/id/qucosa%3A21779.
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Nucleation of dislocation loop at the crack tip in a material subjected to uniaxial loading is investigated. Analytical expression for the total energy of rectangular dislocation loop at the crack tip is found. Depencence of the nucleation energy barrier on dislocation loop shape and stress intensity factor at the crack tip is determined. It is established that the energetic barrier for nucleation of dislocation loop strongly depends on the stress intensity factor. Nucleation of dislocation loop is very sensitive to stress field modifiers (forest dislocations, precipitates, clusters of point defects, etc.) in the crack tip vicinity.
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Raja, Daniel Selvakumar. "Dependence of Initial Grain Orientation on the Evolution of Anisotropy in FCC and BCC Metals Using Crystal Plasticity and Texture Analysis." Thesis, Southern Illinois University at Edwardsville, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1597933.
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<p>Abundant experimental analyses and theoretical computational analyses that had been performed on metals to understand anisotropy and its evolution and its dependence on initial orientation of grains have failed to provide theories that can be used in macro-scale plasticity. Ductile metals fracture after going through a large amount of plastic deformation, during which the anisotropy of the material changes significantly. Processed metal sheets or slabs possess anisotropy due to textures produced by metal forming processes (such as drawing, bending and press braking). Metals that were initially isotropic possess anisotropy after undergoing forming processes, <i>i.e</i>., through texture formation due to large amount of plastic deformation before fracture. It is therefore essential to consider the effect of anisotropy to predict the characteristics of fracture and plastic flow performances in the simulation of ductile fracture and plastic flow of materials. Crystal plasticity simulations carried out on grains at the meso-scale level with different initial orientations (ensembles) help to derive the evolution of anisotropy at the macro-scale level and its dependence on initial orientation of grains. This paper investigates the evolution of anisotropy in BCC and FCC metals and its dependence on grain orientation using crystal plasticity simulations and texture analysis to reveal the mechanics behind the evolution of anisotropy. A comparison of anisotropy evolution between BCC and FCC metals is made through the simulation, which can be used to propose the theory of anisotropy evolution in macro-scale plasticity. </p><p> <i>Keywords</i>: ensembles; grains; initial orientation; anisotropy; evolution of anisotropy; crystal plasticity; textures; homogeneity; isotropy; inelastic; equivalent strain </p>
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Schultz-Jones, Barbara Schamber Linda. "The intersection of social networks in a public service model a case study /." [Denton, Tex.] : University of North Texas, 2007. http://digital.library.unt.edu/permalink/meta-dc-5124.
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Larsson, Thomas B. "The Bronze Age metalwork in southern Sweden aspects of social and spatial organization 1800-500 B.C. /." Umeå : University of Umeå, 1986. http://catalogue.bnf.fr/ark:/12148/cb357239764.
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Khan, Kirity Bhusan. "Processing And Characterization Of B4C Particle Reinforced Al-5%Mg Alloy Matrix Composites." Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/182.
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Metal matrix composites (MMCs) are emerging as advanced engineering materials for application in aerospace, defence, automotive and consumer industries (sports goods etc.). In MMCs, a metallic base material is reinforced with ceramic fiber, whisker or particulate in order to achieve a combination of properties not attainable by either constituent individually. Aluminium or its alloy is favoured as metallic matrix material because of its low density, easy fabricability and good engineering properties. In general, the benefits of aluminium metal matrix composites (AMCs) over unreinforced aluminium alloy are increased specific stiffness, improved wear resistance and decreased coefficient of thermal expansion. The conventional reinforcement materials for AMCs are SiC and AI2O3.
In the present work, boron carbide (B4C) particles of average size 40μm were chosen as reinforcement because of its higher hardness (very close to diamond) than the conventional reinforcement like SiC, AI2O3 etc. and of its density (2.52 g cm"3) very close to Al alloy matrix. In addition, due to high neutron capture cross-section of 10B isotope, composites containing B4C particle reinforcement have the potential for use in nuclear reactors as neutron shielding and control rod material. Al-5%Mg alloy was chosen as matrix alloy to utilize the beneficial role of Mg in improving wettability between B4C particles and the alloy melt. (Al-5%Mg)-B4C composites containing 10 and 20 vol% B4C particles were fabricated. For the purpose of inter-comparison, unreinforced Al-5%Mg alloy was also prepared and characterized. The Stir Cast technique, commonly utilized for preparation of Al-SiC, was adapted in this investigation.The Composites thus prepared was subsequently hot extruded with the objective of homogenization and healing minor casting defects. Finally the unreinforced alloy and its composites were characterized in terms of their microstructure, mechanical and thermo-physical properties, sliding wear behaviour and neutron absorption characteristics.
The microstructures of the composites were evaluated by both optical microscope and scanning electron microscope (SEM). The micrographs revealed a relatively uniform distribution of B4C particles and good interfacial integrity between matrix and B4C particles.
The hot hardness in the range of 25°C to 500°C and indentation creep data in the range of 300°C to 400°C show that hot hardness and creep resistance of Al-Mg alloy is enhanced by the presence of B4C particles. Measurement of coefficient of thermal expansion (CTE) of composites and unreinforced alloy upto 450°C showed that CTE values decrease with increase in volume fraction of reinforcement.
Compression tests at strain rates, 0.1, 10 and 100 s-1 in the temperature range 25 - 450 °C showed that the flow stress values of composites were, in general, greater than those of unreinforced alloy at all strain rates. These tests also depicted that the compressive strength increases with increase in volume fraction of reinforcements. True stress values of composites and unreinforced alloy has been found to be a strong function of temperature and strain rate. The kinetic analysis of elevated temperature plasticity of composites revealed higher stress exponent values compared to unreinforced alloy. Similarly, apparent activation energy values for hot deformation of composites were found to be higher than that of self-diffusion in Al-Mg alloy.
Tensile test data revealed that the modulus and 0.2% proof stress of composites increase with increase in volume fraction of the reinforcements. Composites containing 10%BUC showed higher ultimate tensile strength values (UTS) compared to unreinforced alloy. However, composites with 20%B4C showed lower UTS compared to that of the unreinforced alloy. This could be attributed to increased level of stress concentration and high level of plastic constraint imposed by the reinforcing jparticles or due to the presence solidification-induced defects (pores and B4C agglomerates ).
Sliding wear characteristics were evaluated at a speed of 1 m/s and at loads ranging from 0.5 to 3.5kg using a pin-on-disc set up. Results show that wear resistance of Al-5%Mg increases with the addition of B4C particles. Significant improvement in wear resistance of Al-5%Mg is achieved with the addition of 20% B4C particles. SEM examination of worn surfaces showed no pull-out of reinforcing particles even at the highest load of 3.5 kg, thus confirming good interfacial bonding between dispersed B4C particles and Al alloy matrix.
The neutron radiography data proved that (Al-5%Mg)-B4C composites possess good neutron absorbing characteristics.
From the experimental data evaluated in the "study, it may be concluded that (Al-5%Mg)-B4C composites could be a candidate material for neutron shielding and control rod application.
The enhanced elevated temperature-strength and favourable neutron absorption characteristics of these composites are strong points in favour of this material.
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Ghorai, Amitava, Tirthankar Choudhury, Arjun Das, Rajesh Dey, and Sourav Ganguly. "Calculation of parameter of Ashcroft’s potential using vacancy formation energy for bcc metals like Cr, Mo, W, V, Nb, Ta, Tl, Eu and Zr." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184513.
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Variation of vacancy formation energy with the parameter of Ashcroft\'s model for nine different exchange and correlation functions show almost similar nature for the bcc metals like Cr, Mo, W, V, Nb, Ta, Tl, Eu and Zr. The mean value of this parameter for these bcc metals are respectively 1.173, 1.383, 1.458, 1.263, 1.478, 1.489, 1.802, 2.222 atomic unit.
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Ghorai, Amitava, Tirthankar Choudhury, Arjun Das, Rajesh Dey, and Sourav Ganguly. "Calculation of parameter of Ashcroft’s potential using vacancy formation energy for bcc metals like Cr, Mo, W, V, Nb, Ta, Tl, Eu and Zr." Diffusion fundamentals 17 (2012) 4, S. 1-11, 2012. https://ul.qucosa.de/id/qucosa%3A13728.
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Variation of vacancy formation energy with the parameter of Ashcroft\''s model for nine different exchange and correlation functions show almost similar nature for the bcc metals like Cr, Mo, W, V, Nb, Ta, Tl, Eu and Zr. The mean value of this parameter for these bcc metals are respectively 1.173, 1.383, 1.458, 1.263, 1.478, 1.489, 1.802, 2.222 atomic unit.
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Jago, Christopher Paul. "Metal- and alteration-zoning, and hydrothermal flow paths at the moderately-tilted, silica-saturated Mt. Milligan copper-gold alkalic porphyry deposit." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/609.
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The Mt. Milligan deposit is a tilted (~45°) Cu-Au alkalic porphyry located 155 km northwest of Prince George, B.C., Canada. It is the youngest of the BC alkalic porphyry deposits, all of which formed between 210 to 180 Ma in an extensive belt of K-enriched rocks related to the accretion of the Quesnellia-Stikinia superterrane to ancestral North America. Mt. Milligan has a measured and indicated resource of 205.9 million tonnes at 0.60 g/t Au and 0.25% Cu containing 3.7 million oz. gold, and 1.12 billion lb. copper.
Shoshonitic volcanic and volcaniclastic andesites host mineralization. These have been intruded by a composite monzonitic stock (MBX stock), and associated sill (Rainbow Dike). Early disseminated chalcopyrite-magnetite and accessory quartz veins are associated with K-feldspar alteration in the MBX stock. A halo of biotite alteration with less extensive magnetite replaces host rocks within a ~150 m zone surrounding the stock, while K-feldpsar alteration extends along the Rainbow Dike and permeable epiclastic horizons. Peripheral albite-actinolite-epidote assemblages surround the K-silicate zone. Albite-actinolite occurs at depth, and epidote dominates laterally. Copper and Au grade are maximal where the albite-actinolite assemblage overprints biotite alteration. Gold grade is moderate in association with epidote, whereas Cu is depleted. The post-mineral Rainbow Fault separates the core Cu-rich zone from a downthrown Au-rich zone. A similar zonation of metals occurs in the hanging-wall (66 zone), where a Cu-bearing, potassically-altered trachytic horizon transitions to a funnel-shaped zone of pyrite-dolomite-sericite-chlorite alteration with elevated gold.
Sulfide S-isotope compositions range from -4.79 δ34S in the central Cu-Au orebody to near-zero values at the system periphery, typical of alkalic porphyries. Sulfur isotope contours reflect the magmatic-hydrothermal fluid evolution, and indicate late-stage ingress of peripheral fluids into the Cu-Au zone. Carbonate C- and O-isotope compositions corroborate the magmatic fluid path from the Cu-Au rich zone to Au-rich zone with decreasing depth. Strontium isotopic compositions of peripheral alteration minerals indicate a laterally increasing meteoric fluid component. Changes in major- and trace element composition of epidote and pyrite across the deposit are also systematic. These provide additional vectors to ore, and confirm the kinematics of the Rainbow Fault.
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Tiwari, Housila. "INVESTIGATION OF THE FEASIBILTY OF METALS, POLYMERIC FOAMS, AND COMPOSITE FOAM FOR ON-BOARD VEHICULAR HYDROGEN STORAGE VIA HYDROSTATIC PRESSURE RETAINMENT (HPR) USING IDEAL BCC MICROSTRUCTURE." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1186967436.
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Gorondy, Novak Sofia Maria. "Etude du comportement de l'hélium dans les structures cubiques centrées pour les nouvelles générations de réacteurs nucléaires : approche expérimentale dans le cadre de matériaux modèles." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066537/document.
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La présence de l’hélium induite par le fonctionnement des futurs réacteurs à neutrons rapides et à fusion dans les matériaux de cœur peut entrainer une dégradation de leurs propriétés mécaniques (durcissement, gonflement, fragilisation). Pour poursuivre le développement des alliages de structure, il est nécessaire d’acquérir une meilleure compréhension de l’interaction entre l’He et les structures métalliques donc le point en commun est de comporter comme métal de base un élément de cristallographie cubique centrée (CC), notamment le fer et le vanadium.L’implantation ionique d’ions 4He a été utilisée pour simuler les effets d’endommagement liés à l’insertion d’He, la création des défauts ponctuels (lacunes, interstitiels) et la formation des amas hélium-lacunes dans les futurs réacteurs. L’évolution du comportement de l’He dans le fer et le vanadium purs a été mise en évidence tant du point de vue de la nature des sites de piégeage que du point de vue des mécanismes de migration de l’He et de germination et croissance de bulles associés, en s'appuyant sur un couplage original de techniques. Les résultats obtenus mettent en avant une différence de comportement entre les deux métaux CC, bien que certains mécanismes impliqués soient similaires. Les défauts microstructuraux, notamment les joints de grains, et la concentration d’He implantée (fluence) joueront des rôles clés sur le comportement de l’He à haute température.Les données expérimentales acquises couplées avec des méthodes de simulation serviront de point de départ pour développer une approche cinétique et thermodynamique du comportement de l’He dans les éléments constitutifs des alliages d’intérêt nucléaire<br>The presence of helium produced during the operation of future fast reactors and fusion reactors in core structural materials induces a deterioration of their mechanical properties (hardening, swelling, embrittlement).In order to pursue the development of the metallic structural alloys, it is necessary to comprehend the He interaction with the metal lattice thus the point in common is the study of the metallic components with body-centered cubic structure (bcc) of future alloys, such as iron and/or vanadium.Ion implantation of ions 4He was employed with the aim of simulating the damaging effects associated with the helium accumulation, the point defects’ creation (vacancies, self-interstitials) and the He cluster formation in future reactors. Helium evolution in pure iron and pure vanadium has been revealed from the point of view of the trapping sites’ nature and well as the helium migration mechanisms and the nucleation/growth of bubbles. These phenomena were studied by coupling different complementary techniques. Despite of the fact that some mechanisms involved seem to be similar for both bcc metals, the comparison between the helium behavior in iron and vanadium shows certain differences. Microstructural defects, including grain boundaries and implanted helium concentration (dose) in both bcc metals will play significant roles on the helium behavior at high temperature.The acquired experimental data coupled with simulation methods contribute to the future development in terms of kinetic and thermodynamic data management of helium behavior in the metal components of the alloys of nuclear interest
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Dan, Mo. "THE PHARMACOKINETICS OF METAL-BASED ENGINEERED NANOMATERIALS, FOCUSING ON THE BLOOD-BRAIN BARRIER." UKnowledge, 2013. http://uknowledge.uky.edu/pharmacy_etds/21.
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Metal-based engineered nanomaterials (ENMs) have potential to revolutionize diagnosis, drug delivery and manufactured products, leading to greater human ENM exposure. It is crucial to understand ENM pharmacokinetics and their association with biological barriers such as the blood-brain barrier (BBB). Physicochemical parameters such as size and surface modification of ENMs play an important role in ENM fate, including their brain association. Multifunctional ENMs showed advantages across the highly regulated BBB. There are limited reports on ENM distribution among the blood in the brain vasculature, the BBB, and brain parenchyma.
In this study, ceria ENM was used to study the effect of size on its pharmacokinetics. Four sizes of ceria ENMs were studied. Five nm ceria showed a longer half-life in the blood and higher brain association compared with other sizes and 15 and 30 nm ceria had a higher blood cell association than 5 or 55 nm ceria. Because of the long circulation and high brain association of 5 nm ceria compared with other sizes, its distribution between the BBB and brain parenchyma was studied. The in situ brain perfusion technique showed 5 nm ceria (99%) on the luminal surface of the BBB rather than the brain parenchyma.
For biomedical applications in the central nervous system (CNS), it is vital to develop stable and biocompatible ENMs and enhance their uptake by taking advantage of their unique properties. Cross-linked nanoassemblies entrapping iron oxide nanoparticles (CNA-IONPs) showed controlled particle size in biological conditions and less toxicity in comparison to Citrate-IONPs. CNA-IONPs considerably enhanced MRI T2 relaxivities and generated heat at mild hyperthermic temperatures (40 ~ 42°C) in the presence of alternating magnetic field (AMF). Numerous researchers showed mild whole body hyperthermia can increase BBB permeability for potential brain therapeutic application. Compared to conventional hyperthermia, AMF-induced hyperthermia increased BBB permeability with a shorter duration of hyperthermia and lower temperature, providing the potential to enhance IONP flux across the BBB with reduced toxicity.
Overall, ENMs with optimized physicochemical properties can enhance their flux across the BBB into the brain with desirable pharmacokinetics, which provide great potential for diagnosis and therapy in the CNS.
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Fellinger, Michael Richard. "First Principles-Based Interatomic Potentials for Modeling the Body-Centered Cubic Metals V, Nb, Ta, Mo, and W." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365516163.
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Mondani, Lorenzo. "Deployment e scaling automatici di un cluster Kubernetes low cost su architettura Arm." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23132/.
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Realizzazione di un cluster Kubernetes basato su Raspberry Pi 4 B tramite procedure automatiche. Utilizzo degli strumenti Canonical Metal As A Service (MAAS) e Canonical Juju per l’installazione e configurazione automatiche dei sistemi operativi e dei componenti Kubernetes. Adattamento dei Raspberry, per garantire la compatibilità con MAAS, tramite l'implementazione open-source del firmware UEFI TianoCore EDKII per il Raspberry Pi 4 B. Realizzazione di un BMC (Baseboard Management Controller) personalizzato, tramite un ESP32, per permettere a MAAS di gestire da remoto le operazioni di accensione e spegnimento dei vari Raspberry. Definizione di un device di tipo "power button", nelle tabelle ACPI del firmware UEFI, per permettere lo spegnimento del Raspberry, da parte del BMC, attraverso l’interfaccia GPIO. Installazione del servizio di storage distribuito Ceph tramite Juju, per permettere l’allocazione di volumi persistenti su Kubernetes. Estensione del Kubernetes cluster autoscaler per permettergli di aggiungere o rimuovere nodi fisici, automaticamente, sulla base delle risorse disponibili, comunicando con Juju. Utilizzo del software di IaC (Infrastructure as Code) Terraform per effettuare le operazioni di deployment e configurazione delle applicazioni Kubernetes; tra queste, MetalLB, necessaria per allocare servizi di tipo "LoadBalancer". Descrizione delle operazioni compiute e valutazione dei risultati ottenuti.
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Antropov, A., and V. Stegailov. "Bubble diffusivity in BCC metals." 2019. https://ul.qucosa.de/id/qucosa%3A38269.
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Release of gas fission products in nuclear fuels is a practically important phenomenon based on the bubble diffusivity in crystal lattice. The bubble diffusion coefficient can be expressed through the volume and surface self-diffusion coefficients Dvol and Dsurf.
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Wang, Jia-Siang, and 王家祥. "The Effects of Vibration on FCC, BCC and HCP Metals." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/21805326351024426649.
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博士<br>國立中興大學<br>材料科學與工程學系所<br>104<br>The textures and crystallographic orientations beneath the treatment area in AA 6061 aluminum alloy after Vibratory stress relief (VSR) process were investigated by combining the electron backscatter diffraction analysis of the misoriented low- or high-angle boundaries, the (inverse) pole figures, the line scans and the various grain orientations. The relaxation effect caused by compressive residual stress in the intermediate region is superior to that of tensile residual stress on both sides of the cantilever by means of X-ray diffraction techniques. The residual stress relaxation that occurs due to vibrational stress excitation accompanies the “orientation of banding” disintegration, the decreases in the dislocation density, the strain energy, and the fraction of low-angle boundaries within each type of grain orientation, such as Copper {112} <111>, S {123} <634>, Goss {110} <001>, and Brass {110} <112>, excepting the Cube (or near-Cube) {100} <001> grain orientation. The maintained invariance in the Cube texture can be attributed to the maximum number of active primary slip systems, resulting in an interaction that results from hindered slip on intersecting families of the planes. A systematic study of residual stress relaxation and the texture evolution of cold-rolled AZ31 Mg alloys using the vibratory stress relief technique with a simple cantilever beam vibration system was performed using a high-resolution X-ray diffractometer and a portable X-ray residual stress analyzer. The effects of vibrational stress excitation on the surface residual stress distribution and on the texture of pole figures (0002) occurring during the vibratory stress relief were examined. Compared with the effects corresponding to the same alloy under non-vibration condition, it can be observed that the uniform surface residual stress distribution and relaxation of the compressive residual stress in the stress concentration zone were observed rather than all of residual stresses being eliminated. Furthermore, with an increase in the vibrational aging time, the compressive residual stress, texture density, and (0002) preferred orientation increased first and then decreased. It should be underlined that the vibratory stress relief process for the vibrational aging time of more than 10 min is able to weaken the strong basal textures of AZ31 Mg alloys, which is valuable for enhancement of their formability and is responsible for an almost perfect 3D-Debye-Scherrer ring. Non-destructive evaluation techniques can investigate the microstructure and mechanical properties of the fatigue process. However, they cannot associate fatigue with quantized damage variations and evaluate fatigue life. In this work, a systematic study of the FP of DC04 Low-carbon steel was performed using the X-ray diffraction Debye–Scherrer ring technique. We show that the conventional three-stage FP can be divided into a four-stage process that more accurately evaluates the unknown fatigue state of crystalline materials and their regional fatigue in the future according to the evolution of mean full width at half maximum and residual stress.
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Pott, Ute. "Bioindication of atmospheric heavy metals in the lower Fraser Valley, B.C., Canada." Thesis, 1995. http://hdl.handle.net/2429/3675.
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The atmospheric heavy metal content of the Fraser Valley, B.C., Canada was assessed
for 1993 by analyzing lead, cadmium, chromium, nickel, zinc, and manganese content
in 62 samples of the common woodland moss Isothecium stoloniferum Brid. Lead,
cadmium, nickel and zinc showed a correlated regional distribution with high values in
the western more urbanized areas and lower values in the rural eastern areas. Chromium
and manganese exhibited a less distinct distribution pattern. Highest values were
recorded for the North Shore Mountains relating to increased precipitation and pollutant
transport by the local wind pattern from industrial areas in the Port Moody, Burnaby
area, where metal readings reached another maximum. Relationships of these findings
to population density, land use, traffic and industrial activity were investigated.
Historical changes of metal levels in the ambient air of the study area since the early
1960s were examined through analysis of moss specimens from the U.B.C. herbarium.
Metal pollution patterns were established for the periods 1960 - 1966 and 1975 - 1980.
In addition, changes in metal levels in moss samples from three sites with a continuous
collection record since the 1960's are described. A general decline in atmospheric levels
for lead, cadmium, chromium, nickel, and zinc was found. The observed decrease
reflected the reduction of heavy industries in the area, abandonment of leaded gasoline
and the change from oil to gas and elecuicity for space heating. Reduction in
atmospheric metals, as determined by the moss method, reflected the general decline in
particulate .emission, as determined by the GVRD direct air sampling program.
Manganese levels, in contrast, have increased since the 1960s, which might be
attributed to the addition of Methylcyclopentadienyl manganese tricarbonyl (MMT) to
gasoline, replacing the leaded antiknock additives. Comparisons were made to recent
metal levels and historical changes reported from European 'moss method' studies. The
potential of the 'moss method' to be used for general air quality assessments was
investigated, by comparison to direct air quality measurements of various pollutants and
a general air quality index.
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Tu, Chien-Hung, and 杜建宏. "Synthesis and Physicochemical Characterization of Metal complexes with TTDA-BBA." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/40232546095083639648.
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碩士<br>高雄醫學大學<br>藥學研究所碩士在職專班<br>94<br>The derivative of 3,6,10-tri(carboxymethyl)-3,6,10-triazadodecanedioic acid (TTDA), TTDA-BBA(1,12-bis(benzylamide)-1,12-dioxo-3,6,10-triaza-3,6,10- tris(carboxymethyl) dodecanedioic acid), was synthesized. The observed longitudinal relaxivity (r1) of [Gd(TTDA-BBA)(H2O)] at 37.0 ± 0.1�aC was 4.41 mM�{1s�{1. The 17O NMR transverse and longitudinal relaxation time and angular frequencies of the Gd(III) complex at variable temperature were investigated in order to obtain water-exchange rate. The residence lifetime of bound water (�鄝298) for [Gd(TTDA-BBA)(H2O)] is longer than that of [Gd(TTDA)(H2O)]2�{. The rotational correlation time (�酺298) of [Gd(TTDA -BBA)(H2O)] (�酺298＝203 ps ) is also longer than that of [Gd(TTDA)(H2O)]2�{ (104 ps). Moreover, the binding constant of [Gd(TTDA-BBA)(H2O)] with human serum albumin(HSA) (KA=1.0×104 M�{�{1) was investigated.
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Hamelin, Cory. "Multi-Scale Modelling of Texture Evolution and Surface Roughening of BCC Metals During Sheet Forming." Thesis, 2009. http://hdl.handle.net/1974/1743.
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This thesis examines the qualitative and quantitative variation in local plastic deformation and surface roughening due to crystallographic texture in body-centered cubic materials, specifically interstitial-free steel sheet and molybdenum foil and sheet. Complex forming operations currently used in industrial manufacturing lead to high material failure rates, due in part to the severity of the applied strain path.
A multi-scale model was developed to examine the contribution of mesoscopic and local microscopic behaviour to the macroscopic constitutive response of bcc metals during deformation. The model integrated a dislocation-based hardening scheme and a Taylor-based crystal-plasticity formulation into the subroutine of an explicit dynamic FEM code, LS-DYNA.
Numerical analyses using this model were able to predict not only correct grain rotation during deformation, but variations in plastic anisotropy due to initial crystallographic orientation. Simulations of molybdenum foil under uniaxial tension supported the existence of bending due to local variations in plastic anisotropy, confirmed with good quantitative agreement by experimental measurements of surface roughening.
A series of two-stage strain-path tests were performed, revealing a prestrain-dependent softening of both the steel and molybdenum samples when an orthogonal secondary strain path is applied. Numerical analyses of these tests overestimate macroscopic hardening during complex loading, due in part to the dynamic nature of the FEM code used.<br>Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2009-04-15 11:51:04.518
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Chen, Yi-Ting, and 陳奕廷. "First-Principles Study of Interface between bcc Fe and Transition Metal Carbides." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/26505215326285026654.
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碩士<br>國立臺灣大學<br>材料科學與工程學研究所<br>105<br>The aim of this thesis is to reveal the role of Mo addition to the Ti-based steel using first-principles calculations based on density functional theory. In the first part of this thesis, we calculated the chemical interface energy and strain interface energy (chemical interface energy including elastic strain) to investigate the effect of the addition of different composition Mo,W and Nb to the Ti-based interface system Fe/Ti1-xMxC. We built the interface system following Baker-Nutting orientation relationship. Our results of interface enrgy calculation shows that Mo and W addition can significantly decrease interface energy. The Fe/(Ti0.5Mo0.5)C interface system, which has Mo present at interface, has been found to be having the lowest chemical and strain interface energy in all the complex interface system. Furthermore, we found that interface energy isn’t a constant but decreases as particle size increases. We then employed density of state calculation to the different interface systems, the results shows that the interaction between segregated transition metal and its first nearest neighbor Fe has increasedfor the interface system that has the lowest interface energy. Moreover, from the analysis of charge difference calculation, the Mo addition to the interface can cause more ssignificant electron redistribution when the interface formed, and eventually induced stronger interface dipole to help stabilizing the interface.
In the second part of the thesis, we investigated the formation energy of the Fe/(Ti1-xMx)C interface system in the viewpoints of thermodynamics. For the dependence of atomic configuration of the TMCs, various stacking sequences have been considered at different composition. We discovered that the complex carbide of (Ti1-xMx)C which has M present at the interface were the most stable. For the Fe/(Ti1-xMox)C precipitation, our results show that there is a turnig point of formation energy at x=0.352 in Fe/Ti1-xMoxC system and x=0.292 for Fe/Ti1-xWxC ststem. Our results suggest that the substitution composition between x=0.352 to x=0.5 can possibly lead to ultimate precipitation hardening enhancement because the formation energy of the interface system in this composition range is low enough for TMC to nucleate,meanwhile, the formation energy increases as precipitation size increases.The results will lead to large amount of extreamly fine precipitations .For the Fe/(Ti1-xWx)C precipitation, our results shows that the substitution composition between x=0.292 to x=0.5 will have same effect.
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Wu, Yi-Ju, and 吳宜洳. "Catalytic Effects of Open Metal Sites in Copper Type Metal-Organic Frameworks (Cu-BDC) on Ammonia Borane Dehydrogenation." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/vm9y97.
Full textAbstract:
碩士<br>國立交通大學<br>材料科學與工程學系所<br>107<br>Ammonia borane (AB) has high hydrogen capacity of 19.6 wt%, which makes it as a promising hydrogen storage material. However, its high dehydrogenation temperature and slow kinetics hinder practical applications. It has been reported that confining AB in the pores of metal organic frameworks (MOF) improves dehydrogenation behavior. However, there’s still a doubt on the
nanoconfinement mechanism due to size or catalytic effect. In this study, Cu-BDC was used as a microporous support to form a nanocomposite with AB via physical mixing. Cu-BDC has two structures, in which the catalytic environment can be adjusted by coordinated solvent while keeping similar porosity to fix nanoconfinement condition. The dehydrogenation temperatures of both AB@Cu-BDCs are reduced by 20 degrees. Due to their similar pore size, it indicates that the factor of decreasing dehydrogenation temperature is size effect of nanoconfinement instead of catalytic environment. Open metal sites have catalytic effect over dehydrogenation kinetics to decrease activation energy, and also reduce byproduct generation and hence increase hydrogen yield. However, catalytic efficiency gets lower over cycles, and open metal sites capped by solvent maintain structural integrity and can reproduce low dehydrogenation temperature over heating cycles.
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Guo, Jun Feng. "Joining of Al-B4C metal matrix composites by laser welding and friction stir welding." Thèse, 2012. http://constellation.uqac.ca/2540/1/030325322.pdf.
Full textAbstract:
Les composites Al-B4C à matrice métallique sont des matériaux importants comme absorbeurs de neutrons dans le stockage et le transport du combustible nucléaire en raison de leur concentration élevée en bore et donc de leur haute capacité d'absorption des neutrons. Toutefois, l'application de ces matériaux est encore limitée en raison, entre autres, de l'absence de techniques d'assemblage appropriées pour bénéficier pleinement des avantages des matériaux. Des problèmes tels que la porosité, la réaction chimique entre la matrice Al et des particules B4C peuvent se produire pendant le soudage par fusion. Par conséquent, la présente étude vise à trouver des techniques de soudage efficaces et fiables pour des composites Al-B4C à matrice métallique. La soudabilité des composites à matrice métallique AA1100-16% B4C (taille moyenne des particules: 11 um) et AA1100-30% B4C (taille moyenne des particules: 15 um) a été évaluée à l'aide du soudage au laser et du soudage par friction malaxage. En comparaison avec les techniques classiques de soudage à l'arc, les zones de fusion pénétrantes et étroites associées au soudage au laser peuvent entraîner des zones affectées par chaleur plus petites, et donc moins de distorsion thermique et de dégradation des propriétés mécaniques. D'autre part, le soudage par friction malaxage, étant un procédé de soudage à l'état solide, est prometteur car il permet d'éviter divers problèmes qui pourraient autrement être rencontrés au cours de soudage par fusion.
Pour le soudage au laser sans matériau d'apport, il a été constaté que le plupart de particules B4C ont été décomposées lors du soudage conduisant à la formation de phases AIB2 et AI3BC en forme d'aiguille dans la soudure. Dans ce cas, une efficacité de joint à 63% (UTS) a été obtenue après essai de traction. La variation de puissance de laser de 2 à 4 kW et de la vitesse de soudage de 1 à 2.5 m/min n'a pas d'incidence sur la morphologie en forme d'aiguille. Sur la base de calculs thermodynamiques, le titane a été utilisé comme matériau d'ajout visant à améliorer les propriétés des assemblages. Il a été constaté que l'ajout de Ti avec une feuille de 150 um d'épaisseur a augmenté l'efficacité de joint à 75% en raison de la diminution de la taille et la quantité des phases en forme d'aiguille. L'ajout de Ti sous forme de fil d'apport n'a pas montré une amélioration significative des propriétés mécaniques en raison de la ségrégation du titane et l'inhomogénéité microstructurale dans la zone soudée.
D'autre part, la faisabilité du soudage par friction malaxage pour assmebler les composites à matrice métallique AA1100 renforcées par des particules B4C est étudiée pour des concentrations en volume de 16 et de 30% B4C. Pour les deux composites, le soudage par friction malaxage a une influence significative sur la distribution de la taille des particules et celle des grains de la matrice. Pour le composite AA1100-16% B4C, la taille moyenne des particules diminue après le soudage de ~ 20% et la taille de grain de 15 à 5 um telle que mesurée dans la zone soudée. Les essais de traction des joints soudés a montré une efficacité allant jusqu'à 100% pour les matériaux composites à l'état recuit AA1100-16 % B4C et AA1100-30% B4C. Toutefois, si les résistances ultimes en traction de tous les composites étudiés sont similaires à ~ 130 MPa, la ductilité des joints soudés est plus élevée pour les matériaux recuits. En outre, il a été observé que la variation de la vitesse de soudage entre 100 et 275 mm/min n'influence pas les propriétés de traction et la distribution de tailles des particules. En outre, l'outil de soudage en WC-Co a montré une durabilité bien meilleure que l'outil en acier pour lequel l'usure a eu lieu principalement sur les bords de l'épaulement. Les surfaces du joint FSW produits en utilisant les deux outils ont présenté une résistance à la corrosion inférieure par rapport au matériau de base. Par contre, les assemblages réalisés par l'outil de WC-Co 15 wt.% ont montré une meilleure résistance à la corrosion que celles faites par l'outil en acier.
Des assemblages dissimilaires formés des composites AA1100-16 vol.% B4C avec un alliage d'aluminium AA6063 ont été produits avec succès par FSW. Tous les assemblages produits dans les conditions de soudage étudiées étaient plus forts que les matériaux de base d'Al-B4C et ont donné une résistance ultime élevée de ~ 126 MPa et un allongement de ~ 8%. L'analyse de la concentration de Mg et la distribution des particules B4C indique qu'un bon mélange du matériau a été réalisé pendant le soudage par friction malaxage, autour de l'interface entre le composite AI-B4C et l'alliage AA6063. L'analyse EBSD a montré que pendant le soudage, il y avait une évolution progressive de la microstructure sur les deux côtés des matériaux, résultant en une variété de structures de grain dans les zones de soudure différentes. Dans les zones de soudure, les matériaux ont été dynamiquement recristallisés à des degrés différents en fonction de leur histoire thermo-mécanique. Le raffinement des grains des deux matériaux dans la zone du noyau a été observé (côté MMC : 15 vs 8 um, côté AA6063 : 76 vs 20um). Il est recommandé que l'alliage AA6063 soit positionné sur le côté avançant et l'utilisation d'un 'offset' approprié sur le côté AA6063 est préféré.
Une comparaison de toutes les données des tests de traction ont révélé que le soudage au laser peut être une bonne alternative pour l'assemblage des composites AI-B4C et que l'efficacité du joint peut atteindre jusqu'à 75% (UTS). Une plus grande amélioration des propriétés mécaniques peut être atteint si une quantité optimale de titane est apportée lors du soudage et que le titane est uniformément réparti dans la soudure. D'autre part, le soudage par friction malaxage a été considéré comme un choix judicieux pour assembler des composites AI-B4C car il permet d'éviter les réactions chimiques et conduit à d'excellentes propriétés mécaniques. Il est recommandé que le soudage par friction malaxage soit utilisé pour des matériaux à l'état recuit parce que l'efficacité du joint et la ductilité sont plus élevés que celles des matériaux dans l'état laminé. Il est intéressant de souligner le fait que dans des conditions à l'état recuit la plupart des échantillons soudés entre composites AA1100-16vol.% B4C ont fracturé dans le matériau de base. Cela indique que des composites soudés par friction malaxage étaient plus forts que les matériaux de base, ce qui est très prometteur pour l'assemblage des composites à matrice d'aluminium.
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Peksa, Mikuláš. "Uspořádání, transport a rotační dynamika adsorbovaného oxidu uhličitého v metalo-organické síti Zn2(BDC)2(DABCO)." Doctoral thesis, 2019. http://www.nusl.cz/ntk/nusl-408783.
Full textAbstract:
The work analyzes the dynamics of carbon dioxide adsorbed in crystals of anisotropic metalo-organic frameworks Zn2(BDC)2(DABCO). It utilizes nuclear magnetic resonance methods, namely, the 13 C spetroscopy, the PFG method and the measurement of longitudinal relaxation times. Experimental data are compared with calculation of molecular dynamics. The thesis provides a theoretical model for explaining the temperature dependence of the residual anisotropy of the chemical shift observed in the spectra. The method of measuring diffusion anistropy based on the change of the shape of the 13 C spectra is described. The work determines the theoretical course of dependence of the longitudinal relaxation time on temperature using Redfield's theory. Times characterizing dynamic processes running on a picosecond scale that determine the dynamics of the fluid as a whole are evaluated from the data. 2
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Golub, Michael. "Characterization of tensile and hardness properties and microstructure of 3D printed bronze metal clay." Thesis, 2017. https://doi.org/10.7912/C2QS8X.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)<br>Bronze is a popular metal for many important uses. Currently, there are no economical 3D printers that can print Bronze powders. A recent product, Bronze Metal Clay (BMC) has arrived. Additionally, commercial metal 3D printers require laser or electron beam sources, which are expensive and not easily accessible. The objective of this research is to develop a new two-step processing technique to produce 3D printed metallic component. The processing step includes room temperature 3D printing followed by high-temperature sintering. Since no material data exists for this clay, the tensile strength and hardness properties of BMC are compared to wrought counterpart. In this research tests are completed to determine the mechanical properties of Cu89Sn11 Bronze Metal Clay. The author of this thesis compares the physical properties of the same material in two different formats: 3D printed clay and molded clay. Using measured stress-strain curves and derived mechanical properties, including Young's modulus, yield strength, and ultimate tensile strength, the two formats demonstrate inherit differences.
The Ultimate tensile strength for molded BMC and 3D-printed specimens sintered at 960 C was 161.94 MPa and 157 MPa, respectively. A 3D printed specimen which was red at 843 C had 104.32 MPa tensile strength. Factory acquired C90700 specimen had an ultimate stress of 209.29 MPa. The Young's modulus for molded BMC and 3D-printed specimens sintered at 960 C was 36.41 GPa and 37.05 GPa, respectively. The 843 C 3D-printed specimen had a modulus of 22.12 GPa. C90700 had the highest modulus of 76.81 GPa. The Yield stress values for molded BMC and 3D-printed specimens sintered at 960 C was 77.81 MPa and 72.82 MPa, respectively.
The 3D-printed specimen had 46.44 MPa. C90700 specimen had 115.21 MPa. Hand molded specimens had a Rockwell hardness HRB85, while printed samples had a mean of HRB69. Also, molded samples recorded a higher Young's Modulus of 43 GPa vs. 33 GPa for the printed specimens. Both samples were weaker than the wrought Cu88:8Sn11P0:2 which had a 72 GPa. Cu88:8Sn11P0:2 also was a harder material with an HRC45. The property di erence between 3D printed, molded, and wrought samples was explained by examining their micro structures. It shows that 3D printed sample had more pores than the molded one due to printing process. This study demonstrates the flexibility and feasibility of using 3D printing to produce metallic components, without laser or electron beam source.