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Title: Numerical optimisation of low alloy steel friction stir welding
Author: Ahmad, Bilal
ISNI:       0000 0004 8502 7578
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2018
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The development of advanced joining processes such as friction stir welding (FSW) is necessary to maintain manufacturing competitiveness in any industrial nation. Substantial research that has been carried out on FSW of aluminium alloys has demonstrated considerable benefits; this has led to greater interest in FSW of steel and other high melting temperature alloys. In this context, numerical modelling can provide cost-effective development of steel FSW. This thesis is focussed on a three dimensional thermomechanical simulation of FSW in Abaqus/Explicit, featuring low alloy steel with previously generated experimental temperature dependant properties. Unlike any previous numerical research in which either the workpiece is assumed as a highly viscous body or the tool is modelled as a moving heating source, the Coupled Eulerian Lagrangian approach has been innovatively applied to model the FSW process on steel. All stages of FSW (plunge, dwell and traverse) have been modelled for slow and fast process parameters and their results compared with previous experimental work on the same grade of steel. Various numerical results, such as temperature distribution, plastic strain, reaction forces, material flow and flash generation, were analysed for both models. In each model, the weld shape and weld surface flash were found to be in exceptionally close alignment with previous experimental results. To optimise the FSW process and reduce the forces on the tool, laser assisted FSW (LAFSW) on steel has been numerically developed and analysed as a viable process amendment. LAFSW increased the traverse speed from 5 00 mm/min to 1500 mm/min, significantly higher than conventional steel FSW. The application of laser assistance with a distance of 20 mm from the rotating tool reduced the reaction forces on the tool probe tip up to 55% as compared to standard FSW during the plunge stage.
Supervisor: Galloway, Alexander M. ; Toumpis, Athanasios I. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral