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The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
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Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Joining Polycrystalline Cubic Boron Nitride and Tungsten Carbide by Partial Transient Liquid Phase BondingCook, Grant O., III 16 December 2010 (has links) (PDF)
Friction stir welding (FSW) of steel is often performed with an insert made of polycrystalline cubic boron nitride (PCBN). Specifically, MS80 is a grade of PCBN made by Smith MegaDiamond that has been optimized for the FSW process. The PCBN insert is attached to a tungsten carbide (WC) shank by a compression fitting. However, FSW tools manufactured by this method inevitably fail by fracture in the PCBN. Permanently bonding PCBN to WC would likely solve the fracturing problem and increase the life of PCBN FSW tools to be economically viable. Partial transient liquid phase (PTLP) bonding, a process used to join ceramics with thin metallic interlayers, was proposed as a method to permanently bond PCBN to WC. PTLP bonding is often performed using three layers of pure elements. On heating, the two thin outer interlayers melt and bond to the ceramics. Concurrently, these liquid layers diffuse into the thicker refractory core until solidification has occurred isothermally. A procedure was developed to reduce the number of possible three-layer PTLP bonding setups to a small set of ideal setups using logical filters. Steps in this filtering method include a database of all existing binary systems, sessile drop testing of 20 elements, and a routine that calculates maximum interlayer thicknesses. Results of sessile drop testing showed that the PCBN grade required for this research could only be bonded with an alloy of Ti, Cu, Mg, and Sb. Two PTLP bond setups were tested using this special coating on the PCBN, but a successful bond could not be achieved. However, a PTLP bond of WC to WC was successful and proved the usefulness of the filtering procedure for determining PTLP bond setups. This filtering procedure is then set forth in generalized terms that can be used to PTLP bond any material. Also, recommendations for future research to bond this grade of PCBN, or some other grade, to WC are presented.
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Rehabilitation of Exterior RC Beam-Column Joints using Web-Bonded FRP SheetsMahini, 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.
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