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This master thesis was a part of an ongoing project at Research institutes of Sweden (RISE) and Chalmers University of technology, studying the formation of white layers (WLs) upon hard machining AISI 52100 steel. With a focus on the nanocrystalline microstructure of the machined steel, X-ray diffraction (XRD), white light interferometry (WLI), optical microscopy (LOM) and scanning electron microscopy (SEM) was utilized in the analysis of gathering an in-depth understanding of the WL formation mechanism. By introducing varying cutting parameters as part of the machining process, the effect of cutting speed and tool wear could be observed to directly impact the WL formation and could be linked to the thermomechanical contribution to the formation mechanism. Both thermal and mechanical WLs were observed and could be distinguished by the occurrence of dark layers in thermal WLs. The purpose of this thesis was to observe the influence of retained austenite (RA) on WL formation and from the XRD analysis the residual stress for different RA content could not be concluded. Furthermore, SEM concluded differences in the microstructure where a higher abundance of carbides was observed in the case of lower RA, a phenomenon most likely originating in the heat treatment process. Indications of facilitated mechanical WL formation for lower RA was observed but could not be deemed conclusive. The RA content could not be concluded to have an impact on the surface roughness nor the residual stress where variations were rather linked to the cutting parameters.

Increased efficiency and durability of gas turbine components is driven by demands for reduced fuel consumption and increased reliability in aircraft and power generation applications. The complex flow near the endwall of an axial gas turbine has been identified as a significant contributing factor to aerodynamic loss and increased part temperatures. Three-dimensional (non-axisymmetric) contouring of the endwall surface has been shown to reduce aerodynamic losses, but the effect of the contouring on endwall heat transfer is not well understood. This research focused on understanding the general flow physics of contouring and the sensitivity of the contouring to perturbations arising from leakage features present in an engine. Two scaled low-speed cascades were designed for spatially-resolved measurements of endwall heat transfer and film cooling. One cascade was intended for flat and contoured endwall studies without considering typical engine leakage features. The other cascade modeled the gaps present between a stator and rotor and between adjacent blades on a wheel, in addition to the non-axisymmetric endwall contouring. Comparisons between a flat and contoured endwall showed that the contour increased endwall heat transfer and increased turbulence in the forward portion of the passage due to displacement of the horseshoe vortex. However, the contour decreased heat transfer further into the passage, particularly in regions of high heat transfer, due to delayed development of the passage vortex and reduced boundary layer skew. Realistic leakage features such as the stator-rotor rim seal had a significant effect on the endwall heat transfer, although leakage flow from the rim seal only affected the horseshoe vortex. The contours studied were not effective at reducing the impact of secondary flows on endwall heat transfer and loss when realistic leakage features were also considered. The most significant factor in loss generation and high levels of endwall heat transfer was the presence of a platform gap between adjacent airfoils. / Ph. D.

Wall, traditionally an enclosing element in architecture, has been used throughout the ages for functions like privacy, protection, definition of spaces, and also to provide attractive facades. Visually walls can be more than a mere static element. Over time, attempts have been made by various architects to explore and redefine the role of a wall as an architectural element. The wall can enhance, adorn, aggrandize, beautify, embellish...... My thesis aims at exploring the role of a wall in a building and moving beyond the boundaries of its primary functions. The wall in this project is a multi-layered , transparent, clear and lucid enclosure wrapping the inner solids. The idea is to have solid and opaque geometrical planes and volumes as inner cores and masking these with an outer envelope of double-glass and steel. The study delves further into the interaction between the three assemblies. / Master of Architecture

Securing a computer from unwanted intrusion requires astute planning and effort to effectively minimize the security invasions computers are plagued with today. While all of the efforts to secure a computer are needed, it seems that the underlying issue of what is being secured has been overlooked. The operating system is at the core of the security issue. Many applications and devices have been put into place to add layers of protection to an already weak operating system. Security did not used to be such a prominent issue because computers were not connected 24/7, they used dialup and did not experience the effects from connecting to multiple computers. Today computers connect to high speed Internet and seem useless without access to email, chat, Internet, and videos. This interconnectedness of computers has allowed the security of many computers to be compromised because they have not been programmatically secured. The core component of computer security might best be done through security layers protecting the operating system. For this research, those who work in the computer field were asked to complete a survey. The survey was used to gather information such as the security layers and enhancements implemented on Linux computers and networks their surrounding network. This research is a stepping stone for further research as to what can be done to further improve upon security and its current implementations. / Securing a computer from unwanted intrusion requires astute planning and effort to effectively minimize the security invasions computers are plagued with today.

Trailing edge noise is a common noise source in aerodynamic applications, such as wind turbines, duct fan blades, and propellers. As sound is a nuisance for people near this machinery, methods of reducing trailing edge noise are being investigated. A proven method of trailing edge noise reduction is using a serrated trailing edge. Many prior experiments have shown that a trailing edge with sawtooth serrations can reduce trailing edge noise compared to a straight trailing edge, but the mechanism by which sawtooth serrations reduce noise is not fully understood. Previous theoretical models have assumed that the turbulence field convecting past a serrated trailing edge is unchanged by the presence of the serrations, but experiments have shown that this is not the case in reality. This work attempts to further explore the mechanisms behind why trailing edge serrations reduce trailing edge noise. Additionally, it evaluates the usefulness of a wall jet wind tunnel for use in the study of serrated trailing edges. Experiments were conducted in an anechoic wall jet wind tunnel using a straight trailing edge configuration and a serrated trailing edge configuration. It was found that there may be differences in the unsteady surface pressure over serrated edges in one-sided flows as compared to two-sided flows, like on that of an airfoil, most notably in relation to the magnitude of the unsteady pressure on the serrations. In the wall jet and in agreement with other studies, it was found that the unsteady pressure fluctuations increase towards the tip of the serration in one-sided flows. This is counter to what is found in some studies of two-sided flows. Good agreement was found between some models of the wavenumber-frequency wall pressure spectrum of a turbulent boundary layer and the measured wall pressure spectrum on the straight trailing edge, and these models also produced good predictions of the noise produced by this trailing edge using Amiet's equation. A surface pressure microphone array was used to estimate the zero spanwise wavenumber surface pressure spectrum. This spectrum was used in Amiet's method to predict the measured trailing edge noise. Predictions using the wavenumber-filtered measurement tended to overpredict the measured far field noise most likely due to the inclusion of broader wavenumber content through the array's side lobe response and the breadth of the main lobe. The serrated trailing edge was found to increase coherence between two points on the same serration while reducing coherence between two points on different serrations. It was concluded that the presence of the serrations decorrelates small-scale turbulent eddies. Additionally, it was found that while the serrated trailing edge did reduce the noise produced, its destructive effect on the geometry-based resonance of the straight trailing edge configuration may have amplified the magnitude of the reduction. Finally, it was concluded that the serrations do indeed affect the hydrodynamic field near the trailing edge, and the theoretical models which make the assumption otherwise must be refined. / Master of Science / Trailing edge noise is a common noise source in aerodynamic applications, such as wind turbines, duct fan blades, and propellers. As sound is a nuisance for people near this machinery, methods of reducing trailing edge noise are being investigated. A proven method of trailing edge noise reduction is using a serrated trailing edge. Many prior experiments have shown that a trailing edge with sawtooth serrations can reduce trailing edge noise compared to a straight trailing edge, but the mechanism by which sawtooth serrations reduce noise is not fully understood. This work attempts to further explore the mechanisms behind why trailing edge serrations reduce noise. Experiments were conducted in an anechoic wind tunnel facility. It was found that a one-sided flow over a serrated trailing edge may be significantly different from that over a two-sided flow. Good agreement was found between prediction models and measurements of trailing edge noise. The serrated trailing edge was effective at reducing the coherence of turbulent eddies across the roots of the sawtooth serrations. It was concluded that the serrated trailing edge is effective at reducing noise, and that one means of doing so is decreasing the correlation of small-scale turbulent eddies, and that current models of the flow over serrations may need to be refined.

O desenvolvimento de novos revestimentos ou métodos de proteção considerados ambientalmente amigáveis é extremamente importante para a substituição das eficientes camadas de conversão do cromo, as quais são amplamente utilizadas para proteção anticorrosiva do alumínio e suas ligas. Entre as alternativas relatadas na literatura, podemos destacar a aplicação de filmes de polianilina (PAni) e o uso de camadas de conversão de cério. Neste trabalho é proposta a utilização de revestimentos do tipo bicamadas formada pela combinação de: 1) duas camadas de polianilina ou 2) camadas de conversão de cério (depositadas pelo método electroless ou catodicamente) e filmes de PAni para proteção contra a corrosão das ligas de alumínio AA7075-T6 e AA8006-F em meio aquoso contendo íons cloreto. Nos ensaios de corrosão foram utilizados o monitoramento do potencial de circuito aberto e a polarização potenciodinâmica em meio de NaCl 0,6 mol L-1. A superfície das ligas com e sem os recobrimentos foram analisadas por microscopia óptica e microscopia eletrônica de varredura. Também foi realizado o teste de aderência dos filmes de PAni presentes nas bicamadas sobre as ligas estudadas. O revestimento bicamada composto por uma camada de filme de PAni quimicamente depositada e um filme casting de PAni apresenta excelente aderência sobre as ligas AA7075-T6 e AA8006-F e combina a proteção oferecida pelos filmes casting com a boa aderência dos filmes de PAni depositados quimicamente. O uso da bicamada de cerato electroless e PAni apresenta propriedades anticorrosivas inferiores quando comparadas ao filme de PAni aplicado diretamente sobre o substrato metálico, entretanto, o uso de cerato electroless melhora a aderência dos filmes casting de PAni sobre as ligas estudas. O uso de bicamadas formadas por cerato depositado catodicamente e PAni sobre a liga AA8006-F apresenta valores de potencial de corrosão e potencial de pite inferiores ao do filme casting de PAni aplicado diretamente sobre o substrato metálico, enquanto que para a liga AA7075-T6 foram obtidas melhores propriedades anticorrosivas quando utilizada uma camada de cerato espessa (obtida utilizando uma solução de cério contendo 8 ou 25 µL mL-1 de H2O2). / The development of new coatings or protection methods considered environmentally friendly is extremely important to replace the efficient conversion layers of chromium, which are widely used for corrosion protection of aluminum and its alloys. Among the alternative methods reported in the literature, it can be highlighted the application of polyaniline (PAni) films and the use of cerium conversion layers. This work proposes the use of bi-layers based on: 1) two layers of polyanilines or 2) combination cerium conversion layers (deposited by electroless or cathodic electrodeposition) and PAni films for corrosion protection of AA7075-T6 and AA8006-F alloys in aqueous solutions containing chloride ions. Open circuit potential and potentiodynamic polarization curves were used for the corrosion tests, which were performed in 0.6 mol L-1 NaCl solution. The surface of the alloys with and without the coatings were characterized by optical microscopy and scanning electronic microscopy. It was also performed the adhesion test of the PAni films present in the bi-layers on the studied alloys. The bi-layers formed by a layer of PAni chemically deposited and a layer of PAni film exhibited excellent adhesion to the AA7075-T6 and AA8006-F alloys and combined the protection offered by the cast film of PAni with the good adhesion of PAni chemically deposited. The use of a bi-layer formed by cerium oxides (deposited by electroless) with PAni film as coating presented lower anticorrosive properties compared to the PAni films applied directly on the substrate, however, the use of the cerium layer improves the adhesion of the PAni films on the alloys. The use of bi-layers formed by electrodeposited cerium oxides and PAni films on AA8006-F showed corrosion potential and pitting potential lower when compared with the PAni film directly applied on the substrate, whereas for AA7075-T6, the best anticorrosive properties was obtained using a thick cerium layer (cerium solution containing 8 or 25 µL mL-1 of H2O2).

O desenvolvimento de novos revestimentos ou métodos de proteção considerados ambientalmente amigáveis é extremamente importante para a substituição das eficientes camadas de conversão do cromo, as quais são amplamente utilizadas para proteção anticorrosiva do alumínio e suas ligas. Entre as alternativas relatadas na literatura, podemos destacar a aplicação de filmes de polianilina (PAni) e o uso de camadas de conversão de cério. Neste trabalho é proposta a utilização de revestimentos do tipo bicamadas formada pela combinação de: 1) duas camadas de polianilina ou 2) camadas de conversão de cério (depositadas pelo método electroless ou catodicamente) e filmes de PAni para proteção contra a corrosão das ligas de alumínio AA7075-T6 e AA8006-F em meio aquoso contendo íons cloreto. Nos ensaios de corrosão foram utilizados o monitoramento do potencial de circuito aberto e a polarização potenciodinâmica em meio de NaCl 0,6 mol L-1. A superfície das ligas com e sem os recobrimentos foram analisadas por microscopia óptica e microscopia eletrônica de varredura. Também foi realizado o teste de aderência dos filmes de PAni presentes nas bicamadas sobre as ligas estudadas. O revestimento bicamada composto por uma camada de filme de PAni quimicamente depositada e um filme casting de PAni apresenta excelente aderência sobre as ligas AA7075-T6 e AA8006-F e combina a proteção oferecida pelos filmes casting com a boa aderência dos filmes de PAni depositados quimicamente. O uso da bicamada de cerato electroless e PAni apresenta propriedades anticorrosivas inferiores quando comparadas ao filme de PAni aplicado diretamente sobre o substrato metálico, entretanto, o uso de cerato electroless melhora a aderência dos filmes casting de PAni sobre as ligas estudas. O uso de bicamadas formadas por cerato depositado catodicamente e PAni sobre a liga AA8006-F apresenta valores de potencial de corrosão e potencial de pite inferiores ao do filme casting de PAni aplicado diretamente sobre o substrato metálico, enquanto que para a liga AA7075-T6 foram obtidas melhores propriedades anticorrosivas quando utilizada uma camada de cerato espessa (obtida utilizando uma solução de cério contendo 8 ou 25 µL mL-1 de H2O2). / The development of new coatings or protection methods considered environmentally friendly is extremely important to replace the efficient conversion layers of chromium, which are widely used for corrosion protection of aluminum and its alloys. Among the alternative methods reported in the literature, it can be highlighted the application of polyaniline (PAni) films and the use of cerium conversion layers. This work proposes the use of bi-layers based on: 1) two layers of polyanilines or 2) combination cerium conversion layers (deposited by electroless or cathodic electrodeposition) and PAni films for corrosion protection of AA7075-T6 and AA8006-F alloys in aqueous solutions containing chloride ions. Open circuit potential and potentiodynamic polarization curves were used for the corrosion tests, which were performed in 0.6 mol L-1 NaCl solution. The surface of the alloys with and without the coatings were characterized by optical microscopy and scanning electronic microscopy. It was also performed the adhesion test of the PAni films present in the bi-layers on the studied alloys. The bi-layers formed by a layer of PAni chemically deposited and a layer of PAni film exhibited excellent adhesion to the AA7075-T6 and AA8006-F alloys and combined the protection offered by the cast film of PAni with the good adhesion of PAni chemically deposited. The use of a bi-layer formed by cerium oxides (deposited by electroless) with PAni film as coating presented lower anticorrosive properties compared to the PAni films applied directly on the substrate, however, the use of the cerium layer improves the adhesion of the PAni films on the alloys. The use of bi-layers formed by electrodeposited cerium oxides and PAni films on AA8006-F showed corrosion potential and pitting potential lower when compared with the PAni film directly applied on the substrate, whereas for AA7075-T6, the best anticorrosive properties was obtained using a thick cerium layer (cerium solution containing 8 or 25 µL mL-1 of H2O2).