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Title: Friction stir welding simulation, optimization and design
Author: Zhou, Xingguo
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2013
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Friction stir welding is an advanced welding technology mainly used to join aluminum alloys but with potential for other materials like steel, titanium and its alloys. The aim of this work is to provide a combination of numerical and experiment tools to understand the mechanisms of friction stir welding, optimizing the friction stir welds and characterizing the material properties for welds. The thesis is broadly divided into three themes. In the first theme, an automatic procedure to estimate friction stir welding model parameters, particularly those difficult to measure directly, is proposed and developed. The proposed methodology is seen to predict heat input power from the welding tool and contact conductivity between the workpiece and its supporting plate in good agreement with experimental temperature history data. In the second theme, discontinuous and distributed cooling methods, which use periodical and non-uniformly distributed cooling medium flow to cool the welding workpieces, are proposed to reduce the residual stress of friction stir welds and investigated using multi-physics numerical simulation to predict transient temperature field, residual stress and mechanical performance of welds. The discontinuous cooling method is found to be more effective than conventional active cooling, leading to a lower drop in induced welding temperature and reduced residual stress. The distributed cooling provides another method to balance residual stress and welding temperature for butt welding. The effect of discontinuous cooling on microstructure is evaluated using the multi-physics model. The third part presents small punch beam testing method to characterize material properties of base material, welded material and material property distribution. The small punch beam test utilizes miniaturized specimen and is therefore suited to measuring material properties in local regions of structure, such as the friction stir welding nugget.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral