Global ETD Search

421	Solid-Solution Strengthening and Suzuki Segregation in Co- and Ni-based Alloys Dongsheng Wen (12463488) 29 April 2022 (has links) <p>Co and Ni are two major elements in high temperature structural alloys that include superalloys for turbine engines and hard metals for cutting tools. The recent development of complex concentrated alloys (CCAs), loosely defined as alloys without a single principal element (e.g. CoNiFeMn), offers additional opportunities in designing new alloys through extensive composition and structure modifications. Within CCAs and Co- and Ni-based superalloys, solid-solution strengthening and stacking fault energy engineering are two of the most important strengthening mechanisms. While studied for decades, the potency and quantitative materials properties of these mechanisms remain elusive. </p> <p><br></p> <p>Solid-solution strengthening originates from stress field interactions between dislocations and solute of various species in the alloy. These stress fields can be engineered by composition modification in CCAs, and therefore a wide range of alloys with promising mechanical strength may be designed. This thesis initially reports on experimental and computational validation of newly developed theories for solid-solution strengthening in 3d transition metal (MnFeCoNi) alloys. The strengthening effects of Al, Ti, V, Cr, Cu and Mo as alloying elements are quantified by coupling the Labusch-type strengthening model and experimental measurements. With large atomic misfits with the base alloy, Al, Ti, Mo, and Cr present strong strengthening effects comparable to other Cantor alloys. </p> <p> </p> <p>Stacking fault energy engineering can enable novel deformation mechanisms and exceptional strength in face-centered cubic (FCC) materials such as austenitic TRIP/TWIP steels and CoNi-based superalloys exhibiting local phase transformation strengthening via Suzuki segregation. We employed first-principles calculations to investigate the Suzuki segregation and stacking fault energy of the FCC Co-Ni binary alloys at finite temperatures and concentrations. We quantitatively predicted the Co segregation in the innermost plane of the intrinsic stacking fault (ISF). We further quantified the decrease of stacking fault energy due to segregation. </p> <p><br></p> <p>We further investigated the driving force of segregation and the origin of the segregation behaviors of 3d, 4d and 5d elements in the Co- and Ni-alloys. Using first-principles calculations, we calculated the ground-state solute-ISF interaction energies and revealed the trends across the periodic table. We discussed the relationships between the interaction energies and the local lattice distortions, charge density redistribution, density of states and local magnetization of the solutes. </p> <p><br></p> <p>Finally, this thesis reports on new methodologies to accelerate first-principles calculations utilizing active learning techniques, such as Bayesian optimization, to efficiently search for the ground-state energy line of the system with limited computational resources. Based on the expected improvement method, new acquisition strategies were developed and will be compared and presented. </p> Metals and Alloy Materials Theory and Design of Materials Solid-solution strengthening Stacking Fault Energy Dislocation Co-based alloys Ni-based alloys first-principle calculations Integrated Computer Modeling Thermodynamics Bayesian optimization technique Acquisition function Active Learning Methodologies Density funcational theory Grand Canonical Monte Carlo simulations cluster expansion method phase transformation high-entropy alloy complex concentrated alloys tensile properties ground-state atomic-charge distributions interaction energy calculation
422	Assessing foresight to advance management of complex global problems Berze, Ottilia E. 15 April 2019 (has links) Many people do not like thinking about the future. If they do, over 50% of Canadians think “our way of life” (p. 7) will end within 100 years and over 80% of Canadians think “we need to change our worldview and way of life if we are to create a better future for the world” (Randle & Eckersley, 2015, p. 9). There is a good reason for this. Alarms have sounded over global urgent complex problems with potential for catastrophic consequences such as the development of artificial intelligence, climate change, mass extinction, nuclear war and pandemics (Marien & Halal, 2011). Society is also increasingly fragmenting as imminent crises build on lack of understanding, the sense of incapacity to act, fear, distrust, blame and a lack of hope. This struggle for humanity’s survival is complicated by the turbulent global environment in which institutions continue to follow path-dependent trajectories set forth in a different time and context. Governments at various levels face a problem of “fit” between current structures and processes, that have not progressed sufficiently to meet changing needs of a global society mired in complexity and governance challenges. However, hope exists. Incremental progress on many fronts and a massive amount of efforts and resources are being engaged worldwide. There are emerging fields, lenses and tools that can potentially alleviate complex problems and address this emergency. The purpose of this dissertation is to understand and assess dialogue-based foresight practices being applied towards complex problems in Canada to provide insights into how these practices can assist society to alleviate global urgent complex problems and their impacts, within this backdrop of looming crises. Foresight, alternatively known as future studies or scenario-building, is a forward-looking practice recognized and used globally with over 100 research organizations focused on foresight, widespread usage by firms and over 18 countries involved in foresight activities (Berze, 2014b). Overall literature findings suggest foresight is widely and at least incrementally effective with a number of impacts in various areas (Calof, Miller, & Jackson, 2012; March, Therond, & Leenhardt, 2012; Meissner, Gokhberg, & Sokolov, 2013) but the extent of this effectiveness, the mechanisms involved, and the specific foresight benefits per type of project needs further research and evidence. For instance, limited literature exists on whether foresight can transform complex situations and if so, under what conditions. Thus, opportunities exist for assessing and increasing foresight’s impact. This dissertation is a contextualized, systematic empirical study that taps into transdisciplinary literature and practice, case studies of how foresight has been used to address specific types of complex problems in Canada, as well as surveys and interviews with foresight experts and participants. This dissertation uses a foresight community scan and a comparative case study approach to provide practical and theoretical benefits to foresight and complex problem area stakeholders. The research focuses on studying the broad interactions of foresight and identifying the impacts of dialogue-based foresight projects on people and the outcomes of complex problems. The dissertation concludes that dialogue-based foresight is a valuable and unique practice for ameliorating complex problems and their consequences. Insights are offered towards dialogue-based foresight’s potential contributions within the context of other efforts directed at humanity’s struggle for survival and global complex problems. These insights can then foster the further development and application of dialogue-based foresight on a global scale to alleviate complex problems and their effects. The dissertation outlines recommendations on key next steps to realize these potential contributions. / Graduate foresight dialogue-based complex global problems empirical transdisciplinary crisis comparative cases comparative case study hope practice community Canada projects impact value futures scenario future role wicked problems transformative complexity interviews urgent lens mechanisms assessment well-being strengthening improving concepts types foresight benefits contribution analysis tools approaches mainstream barriers Fore-CAN Georgia Basin Global Energy Landscape Agricultural Adaptation Canadian Payment System 2020 Media Futures systems digital climate change infectious diseases sustainability coping transitioning recommendations multi-perspective dialogue conflict resolution collaboration diversity outcomes invest context contributions efforts innovation cognitive social understanding foresight literacy anticipation futures literacy
423	Navrhování konstrukcí s FRP výztuží / Design of structures with FRP reinforcement Matušíková, Anna January 2012 (has links) This diploma thesis presents available FRP software for calculating load bearing capacity of the structures reinforced with FRP and compares them between each other. Furthermore theory and algorithm of my own software is presented here. Load bearing capacity of structures which are reinforced with non-metallic reinforcement and loaded by combination of normal force and bending moment can be solved by my programme. Effects of high temperatures on the concrete structures can be included in the calculation. In the second part of the thesis is calculated load-bearing capacity and deflection of the real beam reinforced with FRP reinforcement and load-bearing capacity of member with FRP reinforcement with effect of elevated temperature. This has been done using my software. Comparison of results from hand calculation and laboratory load-bearing testing is done at the end. This laboratory testing was accomplished by Institute of Concrete and Mansory Structures at our faculty.
424	Rehabilitation of Exterior RC Beam-Column Joints using Web-Bonded FRP Sheets Mahini, Seyed Saeid Unknown Date (has links) In a Reinforced Concrete (RC) building subjected to lateral loads such as earthquake and wind pressure, the beam to column joints constitute one of the critical regions, especially the exterior ones, and they must be designed and detailed to dissipate large amounts of energy without a significant loss of, strength, stiffness and ductility. This would be achieved when the beam-column joints are designed in such a way that the plastic hinges form at a distance away from the column face and the joint region remain elastic. In existing frames, an easy and practical way to implement this behaviour following the accepted design philosophy of the strong-column weak-beam concept is the use a Fibre Reinforced Plastic (FRP) retrofitting system. In the case of damaged buildings, this can be achieved through a FRP repairing system. In the experimental part of this study, seven scaled down exterior subassemblies were tested under monotonic or cyclic loads. All specimens were designed following the strong-column weak-beam principal. The three categories selected for this investigation included the FRP-repaired and FRP-retrofitted specimens under monotonic loads and FRP-retrofitted specimen under cyclic loads. All repairing/retrofitting was performed using a new technique called a web-bonded FRP system, which was developed for the first time in the current study. On the basis of test results, it was concluded that the FRP repairing/retrofitting system can restore/upgrade the integrity of the joint, keeping/upgrading its strength, stiffness and ductility, and shifting the plastic hinges from the column face toward the beam in such a way that the joint remains elastic. In the analytical part of this study, a closed-form solution was developed in order to predict the physical behaviour of the repaired/retrofitted specimens. Firstly, an analytical model was developed to calculate the ultimate moment capacity of the web-bonded FRP sections considering two failure modes, FRP rupture and tension failure, followed by an extended formulation for estimating the beam-tip displacement. Based on the analytical model and the extended formulation, failure mechanisms of the test specimens were implemented into a computer program to facilitate the calculations. All seven subassemblies were analysed using this program, and the results were found to be in good agreement with those obtained from experimental study. Design curves were also developed to be used by practicing engineers. In the numerical part of this study, all specimens were analysed by a nonlinear finite element method using ANSYS software. Numerical analysis was performed for three purposes: to calculate the first yield load of the specimens in order to manage the tests; to investigate the ability of the web-bonded FRP system to relocate the plastic hinge from the column face toward the beam; and to calibrate and confirm the results obtained from the experiments. It was concluded that numerical analysis using ANSYS could be considered as a practical tool in the design of the web-bonded FRP beam-column joints. Reinforced concrete Reinforcement Bar strong-column weak-beam principal Exterior Beam-Column Joints Core Small scale modelling Experimental Test set-up Control Plain specimen Rehabilitation Retrofitting retrofitted Repair Repaired Repairing Strengthening Controlling Relocating Plastic hinge Pre-cracking Cracking Crushing Post-cracking Crack Cracked Penetration Damaged Pre-cracked Web-Bonded Wrapping De-bonding Fibre Reinforced Plastic FRP Sheets Composite Confinement Monotonic loads Cyclic loading Loads Displacement control Load control Regime Phase Loading sequence Procedure Available ductility factor Curvature ductility factor Ultimate First yield Flexural yielding Strength Moment Stiffness Failure mechanism Modes Sudden Brittle failure Measured beam-tip displacement Deflection Numerical analysis ANSYS Solid65 Solid45 Link8 Non-linear Finite Element (FE) Convergence criteria Analytical Closed from FRP rupture tension failure Compression failure Minimum thickness Maximum thickness Compressive Tensile Steel Ratio Design charts Effective Moment of Inertia Compatibility Strain Stress

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