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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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Studies on bonding mechanisms of the FSSW for low-carbon steel plates using a novel assembled-type toolLi, Ming-Jie 12 September 2012 (has links)
In this study, a novel assembled-type tool was used to weld SS400 low-carbon steel plate using the friction stir spot welding. The welding tool was made of tungsten carbide embedded a circular rod made of the low-carbon steel. The superiority of this embedded material not only could effectively promote the interface temperature of the joint, but also the thickness of stir zone. Compared to previous studies, this novel tool can significantly improve the manufacturing cost and the trimming time. The welding apparatus composed of a vertical milling machine and a welding platform. The operating conditions of welding were as followings: the diameter of embedded material, the welding speed, and the vertical load. During the welding process, the interface temperature of the joint, the tool plunge depth, and the vertical load were simultaneously measured by the K-type thermocouple, a displacement sensor, and a load cell.
Experimental results revealed that the interface temperature, the thickness of the stir zone, and the tensile strength of the welding joint was proportional to the diameter of the embedded material. The best welding condition is the embedded material diameter of 10mm, the vertical load of 8kN, the welding speed of 1200rpm, and the welding time of 100 seconds.
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An Analysis of Microstructure and Corrosion Resistance in Underwater Friction Stir Welded 304L Stainless SteelClark, Tad Dee 30 June 2005 (has links) (PDF)
An effective procedure and parameter window was developed for underwater friction stir welding (UWFSW) 304L stainless steel with a PCBN tool. UWFSW produced statistically significant: increases in yield strengths, decreases in percent elongation. The ultimate tensile strength was found to be significantly higher at certain parameters. Although sigma was identified in the UWFSWs, a significant reduction of sigma was found in UWFSWs compared to ambient FSWs. The degree of sensitization in UWFSWs was evaluated using double loop EPR testing and oxalic acid electro-etched metallography. Results were compared to base metal, ambient FSW, and arc welds. Upper and lower sensitization localization bands were identified in the UWFSWs. Although higher sensitization levels were present in UWFSWs compared to the arc weld, ambient FSW, and heat treated base metals, the UWFSWs were found less susceptible to corrosion than arc welds due to the subsurface location of the sensitization bands. A SCC analysis of UWFSWs relative to base metal and arc weldments was performed. U-bends were exposed to two 3.5% NaCl cyclic immersion experiments at 21 °C and 63 °C for 1000 hours each. A tertiary test was conducted in a 25% NaCl boiling solution. The UWFSW u-bends were no more susceptible to SCC than base metal in the cyclic immersion tests. In the boiling NaCl test, the SCC of the UWFSWs showed significant improvement over the SCC of arc welds. Arc u-bends cracked entirely within the weld bead and HAZ, while SCC in the UWFSWs showed no cracking localization.
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