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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 39310 (07)
- University: Sharif University of Technology
- Department: Materials Science and Engineering
- Advisor(s): Serajzadeh, Siamak
- Abstract:
- In this work a three-dimensional thermo-mechanical finite element analysis has been utilized to predict the large deformation of workpiece during the friction stir welding process using Arbitrary Lagrangian-Eulerian formulation in commercially finite element code, ABAQUS. The model can consider various process parameters including rotational and longitude speeds of the tool, backing plate and delay time. Ultimately, with optimizing the process parameters by presented model, experimental works carry out to improvement appropriate mechanical parameters of the weld. Comparison between the predicted and the experimental data displays a good consistency between distributions of the equivalent plastic strain and the macrostructure of across the weld. The predictions show that both temperature and strain are not distributed symmetrically. The reason for the locations of the high and low stress values can be explained by the temperature and strain rate dependent behavior of flow stress. The condition for formation of crack and tunnel-like defect is increased with increase of the ratio of the longitude speed to rotation speed from 0.033 mm/rev to 0.1 mm/rev. For a given longitude speed, it has been revealed that there is an optimum rotational speed, which gives the highest tensile strength and elongation for the stir zone. For a given longitude speed, the grain size is reduced with increase of the rotational speed from 1000 rpm to 1300 rpm although heat input is increased. This implies that the recrystallized grain size is far more sensitive to deformation rate than to temperature, at higher rotational speed. Also, at the lower longitude speed of 40 mm min-1 inquired, microstructure were more homogenous and the grain sizes in the nugget zone were very fine, being in the range of 2-8 μm. However, this is increased to 6-14 μm with increase of longitude speed from 40 to 60 mm min-1
- Keywords:
- Friction Stir Welding ; Plastic Strain ; Aluminum Alloy 7075 ; T6 Heat Treatment ; Arbitrary Lagrangian-Eulerian Formulation
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