Date of Award

5-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Committee Chair/Advisor

Dr. Xin Zhao

Committee Member

Dr. Laine Mears

Committee Member

Dr. Huijuan Zhao

Committee Member

Dr. Hongseok Choi

Abstract

Friction element welding (FEW) has been advocated as a solution to weld different materials together, with the ability to join high-strength materials for a range of thicknesses with low input energy and a short processing time. This work develops a coupled thermal-mechanical finite element model to better understand the physical mechanisms involved in the process and to predict temperature and material flow during the process. Furthermore, microstructural analysis is performed for the steel layer using a scanning electron microscope and Vickers microhardness tester to understand the variation in its grain structure and hardness. Results from the finite element model and microstructural analysis are correlated to help understand influence of process parameters on the microstructure and weld strength. The simulation results for sets with varying process parameters show that the friction element's rotational speed has the greatest influence on the amount of friction heat generated, followed by the time for different steps. The experimental results show that grain refinement and improvement in hardness value is observed in the steel layer due to high temperature levels and/or high stress. In addition to investigating the effects of process parameters on the heat generation and resultant weld quality, chipping phenomena during the FEW process is investigated using finite element modeling. The numerical analysis indicates that chipping is severe at the beginning when the friction element contacts the workpiece and tends to reduce as the former advances into the latter. Chipping can be minimized by using high rotational speeds coupled with low feed rates.

Author ORCID Identifier

https://orcid.org/0000-0002-8337-5662

Available for download on Wednesday, April 19, 2023

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