The stress corrosion cracking (SCC) condition for Alloy 600 was determined for various stress modes: constant-strain standard C-ring, and indentation, used to localize cracks for interrogation with x-ray techniques such as micro Laue diffraction (MLD). The SCC cracks nucleated on both the indentation edge, where finite element analysis showed that the maximum residual tensile stresses lie, and the surface in tension (bulge) on 150-kgf conically indented mill-annealed specimens (0.02 wt% C) in de-aerated solution of 10% caustic at 150 mVRE (pseudo-reference: A600), 315 OC for 48 hr. On the C-rings, the cracks nucleated at the lateral outer surface of apex, where maximum tensile stresses lie, in less than 12 hours, and propagated into the cross section. Also, corrosion tests on as-received A600 30-min ZrO2 surface mechanical attrition treated (SMAT) specimens suggested an intergranular attack type of behavior in 50% caustic at 210 mVRE (pseudo-reference: A600), 280°C for 24 hr.

The stress corrosion cracking (SCC) condition for Alloy 600 was determined for various stress modes: constant-strain standard C-ring, and indentation, used to localize cracks for interrogation with x-ray techniques such as micro Laue diffraction (MLD). The SCC cracks nucleated on both the indentation edge, where finite element analysis showed that the maximum residual tensile stresses lie, and the surface in tension (bulge) on 150-kgf conically indented mill-annealed specimens (0.02 wt% C) in de-aerated solution of 10% caustic at 150 mVRE (pseudo-reference: A600), 315 OC for 48 hr. On the C-rings, the cracks nucleated at the lateral outer surface of apex, where maximum tensile stresses lie, in less than 12 hours, and propagated into the cross section. Also, corrosion tests on as-received A600 30-min ZrO2 surface mechanical attrition treated (SMAT) specimens suggested an intergranular attack type of behavior in 50% caustic at 210 mVRE (pseudo-reference: A600), 280°C for 24 hr.

Internet security (Network security) is a big topic that is very important in our society communication system, but it is extremely dynamic and wide in scope. This is the reason that many companies and organizations invest heavily in a dedicated infrastructure security and highly trained specialists.The aim of security monitoring and preventing the network from cyber threats requires vigilance over the network equipment. The case study of this thesis is to provide the possible solution to the problems encountered by the namely network users such as: Internet Game Center (Centrum Halmstad, Sweden) and, the Blueville Internet Cafe (Ede, Nigeria).Our research and information collected over the telephone and a visit at the nearest office. We concluded that both companies mentioned above experienced similar cyber threats. The two companies have internal and external threats such as accessing the network via ssh by using it brute force attack, network war-driver, the installation of spyware, password sniffer, viruses, SQL injection and PHP attacks (web attacks) on the networks. The cyber threats virus and spyware are among the big internet threat to users, organization and companies.We carry out experiments in the lab to tests for threats such as brute force (ssh) attack, password sniffer and war-driver in the Wireless environment. From the results, we are able to the select WPA2 using 802.1x as the best possible way to limit and reduce the strength of cyber-attacks, and as a suggested solution to the namely café problems in our report. We also list different suggestion and solution to the cyber café attacks from our research papers and information gathers from different sources such as library, internet, seminar and textbooks.

Rutting is one of the major distresses in asphalt pavements and it increases road roughness and traps water, which leads to wet-weather accidents due to the loss of tire-pavement friction and hydroplaning. The fundamental mechanisms of rutting have not been well addressed because of the complexity of asphalt mixtures. A comprehensive characterization of the asphalt mixtures in compression was accomplished by mechanistically modeling the inherent anisotropy, viscoelasticity, viscoplasticity and viscofracture of the material. The inherent anisotropy due to preferentially oriented aggregates was characterized by a microstructural parameter (i.e., modified vector magnitudes) which could be rapidly and accurately measured by lateral surface scanning tests and physically related to anisotropic modulus ratio. The anisotropic viscoelasticity was represented by complex moduli and Poisson's ratios in separate orthogonal directions that were determined by an efficient testing protocol. Master curve models were proposed for the magnitude and phase angle of these complex variables. The viscoplasticity were intensively modeled by an anisotropic viscoplastic model which incorporated 1) modified effective stresses to account for the inherent and stress-induced anisotropy; 2) a new model to provide a smooth and convex yield surface and address the material cohesion and internal friction; 3) a non-associated flow rule to consider the volumetric dilation; and 4) a temperature and strain rate dependent strain hardening function. The viscofracture resulting from the crack growth in compression led to the stress-induced anisotropy and was characterized by anisotropic damage densities, the evolution of which was modeled by the anisotropic pseudo J-integral Paris' laws. Results indicated that the undamaged asphalt mixtures were inherently anisotropic and had vertical to horizontal modulus ratios from 1.2 to 2.0 corresponding to the modified vector magnitudes from 0.2 and 0.5. The rutting would be underestimated without including the inherent anisotropy in the constitutive modeling. Viscoelastic and viscoplastic deformation developed simultaneously while the viscofracture deformation occurred only during the tertiary flow, which was signaled by the increase of phase angle. Axial and radial strain decomposition methods were proposed to efficiently separate the viscoplasticity and viscofracture from the viscoelasticity. Rutting was accelerated by the occurrence of cracks in tertiary flow. The asphalt mixture had a brittle (splitting cracks) or ductile (diagonal cracks) fracture when the air void content was 4% and 7%, respecitvely. The testing protocol that produced the material properties is efficient and can be completed in one day with simple and affordable testing equipment. The developed constitutive models can be effectively implemented for the prediction of the rutting in asphalt pavements under varieties of traffic, structural, and environmental conditions.

Production of hydrogen is primarily achieved via catalytic steam reforming, partial oxidation,and auto-thermal reforming of natural gas. Although these processes are mature technologies, they are somewhat complex and CO is formed as a by-product, therefore requiring a separation process if a pure or hydrogen-rich stream is needed. As an alternative method, supported metal catalysts can be used to catalytically decompose hydrocarbons to produce hydrogen. The process is known as catalytic cracking of hydrocarbons. Methane, the hydrocarbon containing the highest percentage of hydrogen, can be used in such a process to produce a hydrogen-rich stream. The decomposition of methane occurs on the surface of the active metal to produce hydrogen and filamentous carbon. As a result, only hydrogen is produced as a gaseous product, which eliminates the need of further separation processes to separate CO2 or CO. Nickel is commonly used in research as a catalyst for methane cracking in the 500-700C temperature range. To conduct methane catalytic cracking in a continuous manner, regeneration of the deactivated catalyst is required and circulation of the catalysts between cracking and regeneration cycles must be achieved. Different reactor designs have been successfully used in cyclic operation, such as a set of parallel fixed-bed reactors alternating between cracking and regeneration, but catalyst agglomeration due to carbon deposition may lead to blockage of the reactor and elevated pressure drop through the fixed bed. Also poor heat transfer in the fixed bed may lead to elevated temperature during the regeneration step when carbon is burned in air, which may cause catalyst sintering. A fluidized bed reactor appears as a viable option for methane catalytic cracking, since it would permit cyclic operation by moving the catalyst between a cracker and a regenerator. In addition, there is the possibility of using fine catalyst particles, which improves catalyst effectiveness. The aims of this project were 1) to develop and characterize a suitable nickel-based catalyst and 2) to develop a model for thermal catalytic decomposition of methane in a fluidized bed.

This thesis presents the results of a research project that tested five friction reducing techniques on the bearing ends of precast prestressed concrete bridge girders. The five techniques were the following: an oil coated surface, embedded steel plate with an oil coated surface, embedded steel angle with an oil coated surface, teflon pad, and a wax lubricant.

Hydrogenation and dehydrogenation on Pd- and Pt- catalysts are encountered in many industrial hydrocarbon processes. The present work considers the development of catalysts and their kinetic modeling along a general and rigorous approach. The first part deals with the kinetics of selective hydrogenation, more particularly of the C3 cut of a thermal cracking unit for olefins production. The kinetics of the gas phase selective hydrogenation of methyl-acetylene (MA) and propadiene (PD) over a Pd/γ-alumina catalyst were investigated in a fixed bed tubular reactor at temperatures 60 - 80 oC and a pressure of 20 bara. Hougen-Watson type kinetic equations were derived. The formation of higher oligomers slowly deactivated the catalyst. The effect of the deactivating agent on the rates of the main reactions as well as on the deactivating agent formation itself was expressed in terms of a deactivation function multiplying the corresponding rates at zero deactivation. Then, the kinetic model was plugged into the reactor model to simulate an industrial adiabatic reactor. In the second part the production of hydrogen from hydrocarbons was investigated. In both cyclohexane and decalin dehydrogenations, conversions higher than 98% could be obtained over Pt/γ-alumina catalyst at temperature of 320 and 340 oC, respectively, with no apparent deactivation for 30 h and with co-feed of H2 in the feed. Except for H2 and trace amounts of side cracking products, less than 0.01%, benzene was the only dehydrogenated product in cyclohexane dehydrogenation. In the case of decalin dehydrogenation, partially dehydrogenated product, tetralin, was also formed with selectivity lower than 5%, depending on operating conditions. A rigorous Hougen-Watson type kinetic model was derived, which accounted for both the dehydrogenation of cis- and trans- decalin in the feed and also the isomerization of the two isomers. Jet A is the logic fuel in the battlefields. The dehydrogenation of Jet A can produce H2 for military fuel cell application. Although the H2 production is lower than that of steam/autothermal reforming, it eliminates the needs of high temperature and product separation operation.

Reflection cracking is one of the main distresses in hot-mix asphalt (HMA) overlays. It has been a serious concern since early in the 20th century. Since then, several models have been developed to predict the extent and severity of reflection cracking in HMA overlays. However, only limited research has been performed to evaluate and calibrate these models. In this dissertation, mechanistic-based models are calibrated to field data of over 400 overlay test sections to produce a design process for predicting reflection cracks. Three cracking mechanisms: bending, shearing traffic stresses, and thermal stress are taken into account to evaluate the rate of growth of the three increasing levels of distress severity: low, medium, and high. The cumulative damage done by all three cracking mechanisms is used to predict the number of days for the reflection crack to reach the surface of the overlay. The result of this calculation is calibrated to the observed field data (severity and extent) which has been fitted with an S-shaped curve. In the mechanistic computations, material properties and fracture-related stress intensity factors are generated using efficient Artificial Neural Network (ANN) algorithms. In the bending and shearing traffic stress models, the traffic was represented by axle load spectra. In the thermal stress model, a recently developed temperature model was used to predict the temperature at the crack tips. This process was developed to analyze various overlay structures. HMA overlays over either asphalt pavement or jointed concrete pavement in all four major climatic zones are discussed in this dissertation. The results of this calculated mechanistic approach showed its ability to efficiently reproduce field observations of the growth, extent, and severity of reflection cracking. The most important contribution to crack growth was found to be thermal stress. The computer running time for a twenty-year prediction of a typical overlay was between one and four minutes.

During the bending of flange plate used for dapped girders some highway bridge fabricators are experiencing cracking of the flange plate particularly when heat is used in assisting the bending process. Due to the extreme strains experienced during the fabrication process, investigating this problem requires the use of a finite element analysis. The fabrication process was broken down into two parts, first the heating of the plate through the use of either a furnace or an acetylene torch (thermal), and the second was the bending process (structural). The five different temperatures collected during the thermal analysis were a uniform temperature of 75oF, a 1100oF uniform temperature as a result of furnace heating, both five and ten minutes of air-cooling after the plate had reached a uniform temperature of 1100oF, and the temperature gradient after heating the flange plate to a surface temperature of 1200oF though the use of an acetylene torch. After the thermal analysis was completed, the resulting temperatures were imported into the structural model. The plate thicknesses analyzed were one, one and a half, and two inches, assuming both 50 and 70 ksi yield strengths. To achieve a 90 degree six-inch radius bend the plate was bent in five separate locations. The result of this analysis showed that with the introduction of temperature gradients into thefabrication process, the strains along the plate??s extreme fibers increased. The model further showed that for both a one and a half and two-inch thick plate the extreme fiber strains exceeded ten percent, which further adds to the increased risk of the flange plate cracking during fabrication. The highest residual stresses through the plate??s thickness occurred during cold bending. The residual stresses through the plate??s thickness decreased when the fabrication process was carried out at elevated temperatures. When steel exceeds a strain of 10 to 16 percent during the fabrication process, the plate becomes susceptible to cracking. This strain limit was exceeded for plate thicknesses of one and a half and two inches.

Cracking is a major pavement distress that jeopardizes road serviceability and traffic safety. Automated pavement distress survey (APDS) systems have been developed using digital imaging technology to replace human surveys for more timely and accurate inspections. Most APDS systems require special lighting devices to illuminate pavements and prevent shadows of roadside objects that distort cracks in the image. Most of the artificial lighting devices are laser based, which are either hazardous to unprotected people, or require dedicated power supplies on the vehicle. This study is aimed to develop a new imaging system that can scan pavement surface at highway speed and determine the severity level of pavement cracking without using any artificial lighting. The new system consists of dual line-scan cameras that are installed side by side to scan the same pavement area as the vehicle moves. Cameras are controlled with different exposure settings so that both sunlit and shadowed areas can be visible in two separate images. The paired images contain complementary details useful for reconstructing an image in which the shadows are eliminated. This paper intends to presents (1) the design of the dual line-scan camera system for a high-speed pavement imaging system that does not require artificial lighting, (2) a new calibration method for line-scan cameras to rectify and register paired images, which does not need mechanical assistance for dynamical scan, (3) a customized image-fusion algorithm that merges the multi-exposure images into one shadow-free image for crack detection, and (4) the results of the field tests on a selected road over a long period. / text