Grandes partes dos estudos disponíveis na literatura sobre o comportamento dos materiais com microestruturas martensítica e bainítica relatam que a microestrutura bainítica, comparativamente à martensita revenida, promove melhores propriedades de impacto. No presente trabalho foi proposto o estudo de comportamento ao impacto de aços SAE 4140 e SAE 01 (VND) sob diferentes condições de tratamento térmico. Ao todo foram feitos 57 corpos de prova CHARPY para cada tipo de aço divididos em 3 lotes que foram então: temperados e revenidos, com e sem banho criogênico e austemperados. A dureza final após tratamento térmico foi similar nos diferentes tratamentos térmicos. Os resultados obtidos para os dois tipos de aço mostram que os corpos de provas que passaram pelo tratamento térmico de têmpera, revenido e banho criogênico apresentaram melhor tenacidade ao impacto. / Studies available in the literature about bainitic and martensitic microstructure report that bainitic microstructure compared to tempered martensite has better impact properties. In present work has proposed the study of the impact performance of steel SAE 4140 and SAE 01 (VND) under different conditions of heat treatment. A total 57 CHARPY specimens were divided in 3 sets, which were quenched and tempered, with and without cryogenic bath and austempered. The final hardness after heat treatment was similar in the different heat treatments. The results obtained for the two tipes of steel showed better impact performance for samples submitted to quenching tempering and cryogenie bath.

<p>Within the European space programme, a new upper stage engine (Vinci) for the Ariane 5 launcher is being developed, and the Volvo Aero Corporation (VAC) is contributing with tur-bines for the fuel turbopumps. This MSc thesis investigates the possibility of designing the Turbine Exhaust Duct (TED) of the Vinci-engine in a carbon fibre composite material with adhesively attached titanium flanges. The focus of the project has been on stress analyses of the adhesive joints using Finite Element Methods (FEM), more specifically by using a cohe-sive zone material (CZM) to model the adhesive layer. Analysing adhesive joints is complex and an important part of the work has been to develop and concretise analysis methods for future use within VAC.</p><p>To obtain the specialised material parameters needed for a CZM analysis, FE-models of ten-sile test specimens were analysed and the results compared to those of equivalent experimen-tal tensile tests. These parameters were then used when analysing the TED geometry with load cases specified to simulate the actual operation conditions of the Vinci engine. Both two-dimensional axisymmetric and fully three-dimensional models were analysed and, addition-ally, a study was performed to evaluate the effect of cryogenic temperatures on the strength of the joint.</p><p>The results show that the applied thermal and structural loading causes local stress concentra-tions on the adhesive surface, but the stresses are not high enough to cause damage to the joint if a suitable joint design is used. Cryogenic temperatures (-150 °C) caused a significant strength reduction in the tensile specimens, partially through altered adhesive properties, but no such severe effects were seen in the temperature-dependent FE-analyses of the TED. It should be pointed out however, that some uncertainties about the material parameters exist, since these were obtained in a rather unconventional way. There are also several other impor-tant questions, beside the strength of the adhesive joint, that need to be answered before a metal-composite TED can be realised.</p> / <p>Volvo Aero deltar i utvecklingen av Vinci, en ny motor till det övre steget i den europeiska Ariane 5-raketen. Detta examensarbete behandlar möjligheten att tillverka ett turbinutlopp (TED) till vätgasturbinen i Vinci-motorn i kompositmaterial med flänsar i titan för att på så sätt uppnå en viktbesparing gentemot den tidigare konstruktionen i gjuten Inconel 718. Fokus har legat på att analysera hållfastheten i de limfogar som är tänkta att sammanfoga huvudröret med flänsarna, genom analyser med finita elementmetoden (FEM). Ett viktigt syfte har även varit att, för Volvo Aeros räkning, samla praktiska erfarenheter angående numerisk analys av limfogar, särskilt med användning av kohesiva zon-element för att modellera limfogen.</p><p>FEM-analyser har gjorts av provstavsmodeller, där resultaten sedan jämförts med experimen-tella dragprovsresultat för att ta fram lämpliga material- och modelleringsparametrar för ana-lys med kohesiva zonelement. Därefter tillämpades dessa parametrar i analyser av den verkli-ga TED-geometrin med relevanta lastfall framtagna för att simulera driftsförhållandena i Vin-ci-motorn. Lastfallsanalyser med både tvådimensionellt axisymmetriska och tredimensionella geometrimodeller genomfördes, liksom uppskattningar av limfogens styrka vid kryogena driftstemperaturer.</p><p>Resultaten pekar entydigt mot att en limfog med en ändamålsenlig tvärsnittsgeometri skulle hålla för de angivna lasterna utan att ta skada. De spänningskoncentrationer som uppstår ger lokalt höga spänningar i limmet, men inte på nivåer som skulle kunna orsaka brott. Det finns dock en viss osäkerhet angående riktigheten i materialparametrarna då en något okonventio-nell metod användes för att ta fram dessa. Flera stora frågor finns fortfarande kvar att besvara innan en metall-komposit konstruktion kan realiseras, inte minst hur flödeskammarens kom-plicerade geometri skall kunna tillverkas i kompositmaterial.</p>

In this work the conditions for which a (0,90,90,0,0,90)s BMI-carbon fiber laminate will initiate transverse microcracking are determined for the fabrication of a cryogenic fuel tank for use in a Reusable Launch Vehicle (RLV). This is accomplished using a quadratic interaction criterion failure analysis on the total stress state at possible launch conditions. There are three major sources of stress, that is, thermal residual stress, internal pressure stress, and applied load stress, that are evaluated at the launch stage to determine the total stress state. To assess the accuracy of the analysis the well known X-33 cryogenic fuel tank failure was analyzed as an example. The results of the X-33 example show that the analysis accurately portrays the failure of the X-33 and provides evidence that the analysis can be used to provide reliable conditions for the initiation of microcracking. The final result of this study is a range of launch conditions that can be used without the initiation of microcracking and a limiting range of conditions that cause complete microcracking throughout the laminate.

One of the greatest mysteries of the universe that, for the present, puzzles the mind of most astronomers, cosmologists and physicists is the question: "What makes up our universe?". This is due to how a certain substance named Dark Matter came under speculation. It is believed this enigmatic substance, of type unknown, accounts for almost three-quarters of the cosmos within the universe, could be the answer to several questions raised by the models of the expanding universe astronomers have created, and even decide the fate of the expansion of the universe. There is strong observational evidence for the dominance of non-baryonic Dark Matter (DM) over baryonic matter in the universe. Such evidence comes from many independent observations over different length scales. The most stringent constraint on the abundance of DM comes from the analysis of the Cosmic Microwave Background (CMB) anisotropies. In particular, the WMAP (Wilkinson Microwave Anisotropy Probe) experiment restricts the abundance of matter and the abundance of baryonic matter in good agreement with predictions from Big Bang Nucleosynthesis. It is commonly believed that such a non-baryonic component could consist of new, as yet undiscovered, particles, usually referred to as WIMPs (Weakly Interacting Massive Particles). Some extensions of the standard model (SM) of particle physics predict the existence of particles that would be excellent DM candidates. In particular great attention has been dedicated to candidates arising in supersymmetric theories: the Lightest Supersymmetric Particle (LSP). In the most supersymmetric scenarios, the so-called neutralino seems to be a natural candidate, being stable in theories with conservation of R-parity and having masses and cross sections of typical WIMPs. The EDELWEISS collaboration is a direct dark matter search experiment, aiming to detect directly a WIMP interaction in a target material, high purity germanium crystal working at cryogenic temperatures. It relies in the measurement of nuclear recoils that produce measurable effects in the crystal such ionization and heat. My PhD thesis is organized as follows. The first chapter aims to provide an introduction to the theoretical framework and the scientific motivation for the following work. The nature of DM has been one of the most challenging topics in contemporary physics since the first evidences of its existence had been found in the 1930s. Cosmologists and astrophysicists on one side, together with particle theorists on the other have put a lot of effort into this field: I will briefly account for their achievements and for the experimental strategies which can be set in this scenario. Since this thesis work was carried out within the EDELWEISS-II direct dark matter experiment, I will focus the next chapter on this topic, describing the main features. The second chapter is related to the set-up of the EDELWEISS-II, the current stage of the EDELWEISS experiment necessary after a first phase that achieved the best upper limit on the WIMP elastic scattering on nucleon as a function of WIMP mass in 2004. [....]

Within the European space programme, a new upper stage engine (Vinci) for the Ariane 5 launcher is being developed, and the Volvo Aero Corporation (VAC) is contributing with tur-bines for the fuel turbopumps. This MSc thesis investigates the possibility of designing the Turbine Exhaust Duct (TED) of the Vinci-engine in a carbon fibre composite material with adhesively attached titanium flanges. The focus of the project has been on stress analyses of the adhesive joints using Finite Element Methods (FEM), more specifically by using a cohe-sive zone material (CZM) to model the adhesive layer. Analysing adhesive joints is complex and an important part of the work has been to develop and concretise analysis methods for future use within VAC. To obtain the specialised material parameters needed for a CZM analysis, FE-models of ten-sile test specimens were analysed and the results compared to those of equivalent experimen-tal tensile tests. These parameters were then used when analysing the TED geometry with load cases specified to simulate the actual operation conditions of the Vinci engine. Both two-dimensional axisymmetric and fully three-dimensional models were analysed and, addition-ally, a study was performed to evaluate the effect of cryogenic temperatures on the strength of the joint. The results show that the applied thermal and structural loading causes local stress concentra-tions on the adhesive surface, but the stresses are not high enough to cause damage to the joint if a suitable joint design is used. Cryogenic temperatures (-150 °C) caused a significant strength reduction in the tensile specimens, partially through altered adhesive properties, but no such severe effects were seen in the temperature-dependent FE-analyses of the TED. It should be pointed out however, that some uncertainties about the material parameters exist, since these were obtained in a rather unconventional way. There are also several other impor-tant questions, beside the strength of the adhesive joint, that need to be answered before a metal-composite TED can be realised. / Volvo Aero deltar i utvecklingen av Vinci, en ny motor till det övre steget i den europeiska Ariane 5-raketen. Detta examensarbete behandlar möjligheten att tillverka ett turbinutlopp (TED) till vätgasturbinen i Vinci-motorn i kompositmaterial med flänsar i titan för att på så sätt uppnå en viktbesparing gentemot den tidigare konstruktionen i gjuten Inconel 718. Fokus har legat på att analysera hållfastheten i de limfogar som är tänkta att sammanfoga huvudröret med flänsarna, genom analyser med finita elementmetoden (FEM). Ett viktigt syfte har även varit att, för Volvo Aeros räkning, samla praktiska erfarenheter angående numerisk analys av limfogar, särskilt med användning av kohesiva zon-element för att modellera limfogen. FEM-analyser har gjorts av provstavsmodeller, där resultaten sedan jämförts med experimen-tella dragprovsresultat för att ta fram lämpliga material- och modelleringsparametrar för ana-lys med kohesiva zonelement. Därefter tillämpades dessa parametrar i analyser av den verkli-ga TED-geometrin med relevanta lastfall framtagna för att simulera driftsförhållandena i Vin-ci-motorn. Lastfallsanalyser med både tvådimensionellt axisymmetriska och tredimensionella geometrimodeller genomfördes, liksom uppskattningar av limfogens styrka vid kryogena driftstemperaturer. Resultaten pekar entydigt mot att en limfog med en ändamålsenlig tvärsnittsgeometri skulle hålla för de angivna lasterna utan att ta skada. De spänningskoncentrationer som uppstår ger lokalt höga spänningar i limmet, men inte på nivåer som skulle kunna orsaka brott. Det finns dock en viss osäkerhet angående riktigheten i materialparametrarna då en något okonventio-nell metod användes för att ta fram dessa. Flera stora frågor finns fortfarande kvar att besvara innan en metall-komposit konstruktion kan realiseras, inte minst hur flödeskammarens kom-plicerade geometri skall kunna tillverkas i kompositmaterial.

A novel transit time based analytical broadband noise model is developed and implemented for high frequency bipolar transistors. This model is applied to a complementary (npn + pnp) silicon germanium (SiGe) heterojunction bipolar transistors (HBT). A complete set of analytical equations are derived using this transit time noise model, to express the four fundamental noise parameters in terms of device parameters. A comprehensive analysis on the ac, dc and broadband noise performance of a 200 GHz SiGe HBT technology, under cryogenic temperatures, is presented. The transit time based noise model is used to analyze the RF noise behavior of the SiGe HBT down to 85 K. Significant performance gain is demonstrated in cryogenic temperatures indicating the suitability of SiGe HBT for extreme environment electronics. A sub-circuit based substrate parasitic modeling methodology, in silicon based processes, is presented. A test case low noise amplifier, operating in the 5 GHz band, is designed in a SiGe HBT process and is used to demonstrate the validity of the design methodology. A dual-band, dual-mode transceiver front end for IEEE802.11a/b/g WLAN applications, is designed in a 0.8 and #956;m SiGe HBT process. The transceiver uses a new architecture which uses an on-chip frequency doubler and a single off-chip frequency synthesizer for both the 2.4 and 5 GHz bands. The performance of the transceiver meets the specification of the IEEE802.11a/b/g standards. The work described in the dissertation significantly advances the state-of-the-art in bipolar broadband noise modeling and RF, microwave circuit design using silicon based processes. The contributions and implications of this work for future research are discussed.

The objective of this work is to investigate the suitability of applying silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) bipolar complementary metal oxide semiconductor (BiCMOS) technology to extreme environments and to design high-speed circuits in this technology to demonstrate their reliable operation under these conditions. This research focuses on exploring techniques for hardening SiGe HBT digital logic for single event upset (SEU) based on principles of radiation hardening by design (RHBD) as well as on the cryogenic characterization of SiGe HBTs and designing broadband amplifiers for operation at cryogenic temperatures. Representative circuits ranging from shift registers featuring multiple architectures to broadband analog circuits have been implemented in various generations of this technology to enable this effort.

This research studies individual and combined effects of hydrogen gas exposure and low temperature on the tribological characteristics of Ti-6Al-4V. Experimental approaches include test system modification and tribological analysis. An existing ballon- disk tribometer was modified to allow liquid nitrogen to be constantly injected into an insulated test chamber to enable testing at low temperature. Twelve 3.8 cm diameter Ti-6Al-4V disks were manufactured and polished, then half were exposed to pure hydrogen gas at elevated temperature and pressure and the remaining disks were untreated. The testing was split in to four groups of three disks based on testing temperature and previous hydrogen exposure. A silicon nitride ball was used for all tests. Each group was tested at two normal loads, 10N and 20N, at the same linear speed. Group 1 was unexposed and tested at room temperature, Group 2 was unexposed and tested at low temperature, Group 3 was exposed and tested at room temperature and Group 4 was exposed and tested at low temperature. Average friction coefficients and the specific wear rate were calculated from the test data. Also high-resolution digital microscope imaging was used to observe and characterize the wear mechanisms of the four groups of samples. Results show that hydrogen exposure facilitated adhesive wear of the surface and that low temperature induced a slip-stick wear mechanism under higher loads, but not at lower loads and regardless of exposure to hydrogen gas. This research opens avenues for future investigation in effects of hydrogen and low temperature embrittlement on the tribological performance of materials. With the increasing interests in hydrogen energy, the present work established a foundation for future study.

In this work the conditions for which a (0,90,90,0,0,90)s BMI-carbon fiber laminate will initiate transverse microcracking are determined for the fabrication of a cryogenic fuel tank for use in a Reusable Launch Vehicle (RLV). This is accomplished using a quadratic interaction criterion failure analysis on the total stress state at possible launch conditions. There are three major sources of stress, that is, thermal residual stress, internal pressure stress, and applied load stress, that are evaluated at the launch stage to determine the total stress state. To assess the accuracy of the analysis the well known X-33 cryogenic fuel tank failure was analyzed as an example. The results of the X-33 example show that the analysis accurately portrays the failure of the X-33 and provides evidence that the analysis can be used to provide reliable conditions for the initiation of microcracking. The final result of this study is a range of launch conditions that can be used without the initiation of microcracking and a limiting range of conditions that cause complete microcracking throughout the laminate.

A need was identified to test multi–layer vacuum super insulation (MLVSI) used in cryogenic applications for hydrogen storage. The study focuses on the application of commercially available MLVSI to a locally patented liquid hydrogen cryogenic storage system. This led to an investigation of different types of multi–layer vacuum insulation configurations, as well as further research on tank inlet coupling configurations. It includes the manufacturing of a liquid nitrogen testing cryostat to be able to test and evaluate the system performance. The first set of tests was based on the development of an inlet coupling configuration to limit heat transfer through the inner tank inlet, of a double cryogenic tank system in order to reduce gas boil–off. The couplings were manufactured in the form of a bellow to handle cryogenic vacuum levels, while ensuring low heat transfer rates between inner and outer tanks. It was found that various coupling designs can be considered to limit gas boil–off. The second set of tests was conducted on a specific MLVSI configuration to determine its effectiveness to insulate the spherical header surface of a typical hydrogen storage vessel. The installation procedure, to limit heat transfer and boil–off due to edge effects in this configuration was investigated. It was found that insulation–overlap–edge effects will always have an impact on insulation performance when a spherical header of a storage vessel is insulated, due to its specific geometry. A time efficient way to install MLVSI on such a spherical header is presented and evaluated. Further investigations were carried out by combining findings into one single system to determine the performance of an optimised insulated cryogenic system. It was found that copper plate discs installed between the vanes of a bellowed inlet/outlet nozzle is the most promising to limit heat transfer to the cryogenic fluid. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.