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Investigation of Friction Stir Back Extrusion

Al-Jarrah, Obadah Mosbah
A Master of Science thesis in Mechanical Engineering by Obadah Mosbah Al-Jarrah entitled, “Investigation of Friction Stir Back Extrusion”, submitted in January 2020. Thesis advisor is Dr. Mohammad Nazzal and thesis co-advisor is Dr. Bassil Darras. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).
Friction Stir Back Extrusion (FSBE) is a new bulk deformation manufacturing process that utilizes severe plastic deformation to force the processed material to produce a tubular shape. To date, most of the research conducted in the field of FSBE investigates the mechanical behavior of the produced tubes without paying enough attention to the temperature history, strain rates or the material flow during deformation. In this work, a multiphysics thermomechanical model based on the coupled Eulerian Lagrangian approach was developed to simulate the FSBE process and investigate the material flow, strains, strains rates, grain size and temperature history in the formed tube during deformation. The numerical model accounts for large plastic deformation, heat generation due to friction and plastic deformation, tool-workpiece and die-workpiece mechanical and thermal interaction to accurately simulate the FSBE process. FSBE experiments for Mg AZ31 alloy were conducted to validate the numerical FSBE model. It is shown that the reactive body force in the principal loading direction and the temperature history in the die obtained from numerical modeling agree well with experiments. The numerical results show that strain rates in the range of 70 s ˉ¹ were attained at the inner surface of the formed tubes. The maximum temperature in the workpiece reaches 600 °C with no signs of material melting. Different material flow patterns were observed in the formed tube during deformation. The material in the central region of the cylindrical workpiece moves in a spiral motion with significant rotation while the material near the outer surface of the workpiece moves in a linear path.
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