This thesis deals with numerical simulation of a peel test with an Aluminium foil and Low Density Poly-Ethylene (LDPE) laminate. This work investigates the effects of the substrate thickness and studies the influences of interfacial strength and fracture energy of the cohesive zone between the Aluminium and LDPE. This study evaluates the proper guidelines for defining cohesive properties. A numerical cohesive zone model was created in ABAQUS. Continuum tensile tests were performed to extract LDPE material properties. The aluminium properties were found in literature. After acquiring material parameters, the simulation continued with studying the effects of changing interfacial strength, geometric parameters and fracture energy. The results were obtained in the form of root rotations and the force displacement response was studied carefully. It was validated by comparison to the traction separation curve.

Orientador: Vicente Afonso Ventrella / Resumo: O presente trabalho estudou o processo de soldagem laser Nd:YAG pulsado aplicado em lâminas finas da liga de titânio Ti-6Al-4V, utilizado no revestimento de sensores que trabalham em ambiente corrosivo da indústria sucroalcooleira, química, petroquímica e alimentícia. Variou-se a energia de pulso de 1,0 J a 2,00 J, com incrementos de 0,25 J com a velocidade de soldagem de (ν) taxa de repeticao (Rr) fixas de 525mm/min e 39Hz respectivamente e largura temporal de 4 ms. As soldas foram realizadas com proteção gasosa de argônio com vazão de 10 l/min. Os ensaios realizados para a pesquisa foram: análise macrográfica, ensaio de tração e fractografia, ensaio de microdureza e caracterização microestrutural. Para revelação dos detalhes no metal de solda foi utilizado um ataque químico com o reagente Kroll. As medidas de geometria (largura do cordão, largura de união e profundidade) dos cordões de solda, bem como a microestrutura, foram realizadas através de imagens obtidas pelo Microscópio Óptico Neophot 21 e editadas utilizando o software ImageJ. O ensaio de tração foi realizado através de uma Máquina Universal de Ensaios, além do ensaio de microdureza, que foi realizado na escala Vickers. Os resultados obtidos mostraram que o controle da energia do pulso é de fundamental importância para a geração de juntas soldadas adequadas, em processo de soldagem por laser de lâminas finas. Também, os parâmetros geométricos aumentaram em função do aumento da energia de pulso e houve maior formaç... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The present work studied the pulsed Nd: YAG laser welding process applied in thin films of the titanium alloy Ti-6Al-4V, used in the coating of sensors that work in the corrosive environment of the sugar-alcohol, chemical, petrochemical and food industry. The pulse energy was varied from 1.0 J to 2.00 J, with increments of 0.25 J with welding speed (ν) and repetition rate (Rr) fixed in 525 mm / min and 39 Hz respectively and time width of 4 ms. An argon gas protection was used with a flow rate of 10 l / min. The tests carried out for the research were: macrographic analysis, tensile and fracture tests, microhardness test and microstructural characterization. A chemical attack with the Kroll reagent was used to reveal details on the weld bead. Measurements based on bead width, union width and depth of the fusion zone as well as the microstructure were performed using images obtained by the Neophot 21 Optical Microscope and edited using the ImageJ software. The tensile test was performed through a Universal Testing Machine, in addition to the microhardness test, which was performed on the Vickers scale. Results showed that the control of the pulse energy is of fundamental importance for the generation of suitable welded joints, in process of laser welding of thin slides. Also, geometric parameters increased as a function of the increase in pulse energy and there was more formation of the α 'phase (martensite) according to the highest peak energy used. Besides that, microhardnes... (Complete abstract click electronic access below) / Mestre

Increasing insensitivity demands on designing and producing munitions necessitates utilizing primarily insensitive initiation trains specifically in missile systems. Exploding Foil Initiator (EFI) is a high voltage detonator that is used as the initiation elementof rocket motor and warhead initiation trains of modern insensitive missile systems. In this thesis, EFI prototypes are designed and manufactured with the knowledge gained from detailed literature studies. An experimental setup is constructed including firing and testing means for EFI prototypes. That experimental setup is capable of firing EFI prototypes from 500 volts to 3000 volts voltage range. Besides, it allows measuring electrical characteristics like current and voltage traces and average velocity of the flyer plates of these prototypes.Using EFI prototypes,detonation tests of HNS &ndash / IV and PBXN &ndash / 5 explosive pellets are carried out.Function times and detonation outputs of the prototypesare measured with the same experimental setup. A numerical study which predicts electrical performance of EFI prototypes and impact characteristics of flyer plates are carried out. Numerical code is validated with the experimental results.

This thesis presents further experimentation and modeling for bump-type gas foil bearings used in oil-free turbomachinery. The effect of shaft temperature on the measured structural force response of foil bearings is of importance for reliable high temperature applications. During actual operation with shaft rotation, the bearing structural parameters are coupled to the effects of a hydrodynamic gas film layer, thus determining the overall bearing load performance. A 38.17 mm inner diameter foil bearing, Generation II, is mounted on an affixed non-rotating hollow shaft with an outer diameter of 38.125 mm. A cartridge heater inserted into the shaft provides a controllable heat source. The clearance between the shaft and the foil bearing increases with increasing shaft temperatures (up to 188°C). A static load (ranging from 0 N to 133 N) is applied to the bearing housing, while measuring the resulting bearing displacement, which represents the compliant structure deflection. Static load versus displacement tests render the bearing static structural stiffness. As the shaft temperature increases, the static test results indicate that the bearing structural stiffness decreases by as much as 70% depending on the bearing orientation. A dynamic load test setup includes a rigid shaft support structure and a suspended electromagnetic shaker. Dynamic load (from 13 N to 31 N) test results show that the test foil bearing stiffness increases by as much as 50% with amplitude of dynamic load above a lightly loaded region, nearly doubles with frequency up to 200 Hz, and decreases by a third as shaft temperature increases. A stick slip phenomenon increases the bearing stiffness at higher frequencies for all the amplitudes of dynamic load tested. The test derived equivalent viscous damping is inversely proportional to amplitude of dynamic load, excitation frequency, and shaft temperature. Further, the estimated bearing dry friction coefficient decreases from 0.52 to 0.36 with amplitude of dynamic load and stays nearly constant as shaft temperature increases. Test results identify static and dynamic bearing parameters for increasing shaft temperature. These experimental results provide a benchmark for predictions from analytical models in current development and are essential to establish sound design practices of the compliant bearing structure.

Metal mesh foil bearings (MMFBs) are a promising low cost gas bearing technology for support of high speed oil-free microturbomachinery. Elimination of complex oil lubrication and sealing system by installing MMFBs in oil free rotating machinery offer distinctive advantages such as reduced system overall weight, enhanced reliability at high rotational speeds and extreme temperatures, and extended maintenance intervals compared to conventional turbo machines. MMFBs for oil-free turbomachinery must demonstrate adequate load capacity, reliable rotordynamic performance, and low frictional losses in a high temperature environment. The thesis presents the measurements of MMFB break-away torque, rotor lift off and touchdown speeds, temperature at increasing static load conditions, and identified stiffness and equivalent viscous damping coefficients. The experiments, conducted in a test rig driven by an automotive turbocharger turbine, demonstrate the airborne operation (hydrodynamic gas film) of the floating test MMFB with little frictional loses at increasing loads. The measured drag torque peaks when the rotor starts and stops, and drops significantly once the bearing is airborne. The estimated rotor speed for lift-off increases linearly with increasing applied loads. During continuous operation, the MMFB temperature measured at one end of the back surface of the top foil increases both with rotor speed and static load. Nonetheless, the temperature rise is only nominal ensuring reliable bearing performance. Application of a sacrificial layer of solid lubricant on the top foil surface aids to reduce the rotor break-away torque. The measurements give confidence on this simple bearing technology for ready application into oil-free turbomachinery. Impact loads delivered (with a soft tip) to the test bearing, while resting on the (stationary) drive shaft, evidence a system with large damping and a structural stiffness that increases with frequency (max. 200 Hz). The system equivalent viscous damping ratio decreases from ~ 0.7 to 0.2 as the frequency increases. In general, the viscous damping in a metal mesh structure is of structural type and inversely proportional to the frequency and amplitude of bearing motion relative to the shaft. Impact load tests, conducted while the shaft rotates at 50 krpm, show that the bearing direct stiffness is lower (~25% at 200 Hz) than the bearing structural stiffness identified from impact load tests without shaft rotation. However, the identified equivalent viscous damping coefficients from tests with and without shaft rotation are nearly identical. The orbits of bearing motion relative to the rotating shaft show subsynchronous motion amplitudes and also backward synchronous whirl. The subsynchronous vibration amplitudes are locked at a frequency, nearly identical to a rotor natural frequency. A backward synchronous whirl occurs while the rotor speed is between any two natural frequencies, arising due to bearing stiffness asymmetry.

A heavily filtered fast neutron irradiation system (FNIS) was developed for a variety of applications, including the study of long-term health effects of fast neutrons by evaluating the biological mechanisms of damage in cultured cells and living animals such as rats or mice. This irradiation system includes an exposure cave made with a lead-bismuth alloy, a cave positioning system, a gamma and neutron monitoring system, a sample transfer system, and interchangeable filters. This system was installed in the irradiation cell of the Texas A&M University Nuclear Science Center Reactor (NSCR). By increasing the thickness of the lead-bismuth alloy, the neutron spectra were shifted into lower energies by the scattering interactions of fast neutrons with the alloy. It is possible, therefore, by changing the alloy thickness, to produce distinctly different dose weighted neutron spectra inside the exposure cave of the FNIS. The calculated neutron spectra showed close agreement with the results of activation foil measurements, unfolded by SAND-II close to the cell window. However, there was a considerable less agreement for locations far away from the cell window. Even though the magnitude of values such as neutron flux and tissue kerma rates in air differed, the weighted average neutron energies showed close agreement between the MCNP and SAND-II since the normalized neutron spectra were in a good agreement each other. A paired ion chamber system was constructed, one with a tissue equivalent plastic (A-150) and propane gas for total dose monitoring, and another with graphite and argon for photon dose monitoring. Using the pair of detectors, the neutron to gamma ratio can be inferred. With the 20 cm-thick FNIS, the absorbed dose rates of neutrons measured with the paired ion chamber method and calculated with the SAND-II results were 13.7 ?? 0.02 Gy/min and 15.5 Gy/min, respectively. The absorbed dose rate of photons and the gamma contribution to total dose were 6.7??10-1 ?? 1.3??10-1 Gy/min and 4.7%, respectively. However, the estimated gamma contribution to total dose varied between 3.6 % to 6.6 % as the assumed neutron sensitivity to the graphite detector was changed from 0.01 to 0.03.

The beam-foil method was used to determine mean-lives of excited atomic states. Initial studies were done on states. Initial studies were done on states of the helium- and hydrogen-like ions B IV and B V, with the mean-lives determined by fitting the decay curves to sums of exponential terms. Since theoretical values of the mean-lives are very precise in these simple atomic systems, our results indicate the accuracy of the experimental method. A series of measurements was made of the low lying 2s 2p⁴ states in nitrogen-like Ne IV, Na V, Mg VI, Al VII, and Si VIII. The experimental results were compared to theoretical calculations of Fawcett and Sinanoglu, and showed excellent agreement with Sinanolu's nonclosed-shell many electron theory. The lifetimes of the 4p ²P₁/₂ and 4p ²P₃/₂ states in copper-like Br VII were determined by measuring decay curves for both the primary and cascade decays and then analyzing the curves jointly. Our resulting mean-life values are considerbly shorter than those of previous experiments which analyzed only the primary decay curve. Comparison with theoretical calculations showed excellent agreement with those which include core polarization effects.

Building envelopes are elements with a long lifetime, which provide a barrier between internal and external space and contribute to the internal environmental conditions provision. Their complex role ensures a large impact on the environmental and energy performance of a building and the occupant perception of a space. This study looks at the use of novel materials and processes to help reduce the environmental impact of buildings by improving facade and transparent roof design. There are three main strands to the work. First, novel building components, ETFE foil cushions were examined. Physical testing has shown that ETFE foil cushions compare favourably to double glazing in terms of thermal and daylighting performance which was also noted as one of the most likeable feature by occupants. Environmental impact analysis has indicated that ETFE foils can reduce the environmental impact of a building through reduced environmental burden of both the construction and operation of the building. Secondly, a cradle-to-gate Life Cycle Analysis (LCA) was carried out for float glass, which considered the environmental impacts of glass manufacture. The embodied energy was calculated to be 13.4 ± 0.5 GJ per tonne while the total number of eco-points 243 ± 11 per tonne. It is shown that float glass is comparable to the use of steel, and highly preferable to the use of aluminium as a cladding panel. Finally, a concept design tool (FACADE) was developed by defining a large number of office facade models and employing dynamic thermal, daylighting and environmental impact modelling to create a database which can be accessed through a user friendly interface application. A parametric analysis has indicated that using natural ventilation where possible can reduce the environmental impact of offices by up to 16%. Improving the standard of the facade and reducing the internal heat loads from lighting and equipment can reduce environmental impact up to 22%. This study makes a significant contribution to understanding the environmental impact of building envelope individual and integrated components.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Douglas S. McGregor / The low natural abundance and supply shortage of ³He has resulted in an increase in the cost of ³He. The increase in cost of ³He proportional counters has motived the development of low cost, high efficiency, low gamma-ray sensitivity alternative technologies. A recently developed alternative technology is the ⁶Li-based suspended foil microstrip neutron detector (SFMND) that combines the neutron-conversion and gamma-ray discrimination capabilities of ⁶Li foils with the mechanical robustness and electrical capabilities of microstrip electrodes. SFMNDs differ from Li-foil multi-wire proportional counters because the anode wires are replaced by a single microstrip electrode that improves the mechanical robustness, reduces the microphonic sensitivity, and allows for more ⁶Li foils to be incorporated within a smaller form factor. The first-ever SFMNDs containing one and five 96%-enriched, 75-µm thick ⁶Li foils were fabricated using a silicon microstrip electrode. Neutron-sensitivity testing was performed yielding measured intrinsic thermal-neutron detection efficiencies, εth, of 4.02 ± 0.04% and 14.58 ± 0.11%, respectively. High electrode capacitance and gain instability were exhibited by the silicon microstrip electrode during neutron-sensitivity testing that led to the search for an electrically-stable microstrip-electrode substrate. Schott Borofloat® 33 glass was identified as an electrically-stable substrate and microstrip electrodes were fabricated and characterized. The Schott Borofloat® 33 microstrip electrodes were electrically-stable for a minimum duration of time of approximately 23 hours and had capacitances over an order of magnitude less than the identically sized silicon microstrip electrodes. One- and five-foil SFMNDs were fabricated with a Schott Borofloat® 33 microstrip electrode. Using 96%-enriched, 75-µm thick ⁶Li foils, the one- and five-foil devices had maximum measured εth of 12.58 ± 0.15% and 29.75 ± 0.26%, respectively, with measured gamma-ray rejection ratios of 6.46 x 10⁻⁵ ± 4.32 x 10⁻⁷ and 7.96 x 10-5 ± 4.65 x 10-7 for a ¹³⁷Cs exposure rate of 50 mR hr⁻¹. Devices containing one, five, ten, and twenty 96%-enriched, 75-µm thick ⁶Li foils were simulated using MCNP6 and are theoretically capable of having εth of 18.36%, 54.08%, 65.43%, and 68.36%, respectively. The deviation between measured and simulated εth is suspected to occur due to the electric field strength distribution, electron attachment, microstrip-electrode capacitance, or any combination thereof and solutions for each of these suspected concerns are described.

The theme of this thesis is a "Testing of reflective systems for distance measuring." Within the work was created reflective device of aluminum sheet and reflective foil. This device was tested with another reflective device that operates on the same principle. The aim of this study was to test devices under different climatic conditions. Standard deviations of the measured values and the values of additive constants for each total station and reflective devices were evaluated. In conclusion, it was suggested the use of these devices in geodetic work under land adjustment.