Date of Award

8-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Automotive Engineering

Committee Member

Dr. Laine Mears, Committee Chair

Committee Member

Dr. Gregory Mocko

Committee Member

Dr. Srikanth Pilla

Committee Member

Dr. David Schmueser

Abstract

Automakers have adopted a heavy focus towards lightweighting their fleets due to the stringent emission standards placed upon them. Lightweighting can be done using several methods but material substitution is proven to be most effective considering the traditional powertrains are on the border of theoretical limits. Designing multi-material body structures is a recognized strategy, replacing steels with lightweight metals such as aluminum, magnesium, and fiber-reinforced composites. The issue now arises on how to join these materials that possess such varied thermo-mechanical properties, with resistance spot welding (RSW) currently not an option. One of the newly-adopted joining technologies is Flow Drill Screwing (FDS) which is currently the only structurally viable joining technology that does not require access to the back side of the joint. FDS is a coupled thermo-mechanical process due to the frictional behavior between the rotating screw and stationary workpiece. An understanding of the process is limited to empirical methods mainly based on experimental findings with little known about the frictional behavior at the screw-workpiece interface. This lack of understanding not only inhibits the potential of the process, but more importantly, whether its application borders on the edge of reliability; and without an understanding to the transient contact conditions, accurate torque and temperature modeling is not feasible. Current models have limited accuracy as their methodology couples a friction coefficient and material strength term. A modeling approach that incorporates both a slipping and sticking condition is theorized to be more appropriate for frictional processes of this nature, but no coupled models currently exist. The following research aims at integrating these two conditions under a single model to enable more accurate modeling and prediction of the FDS process performance. A secondary objective presented in this research is to determine whether FDS processing time could benefit from the assistance of supplementary energy sources. Replacing RSW with these alternate joining technologies, such as FDS, comes at the expense of an increased process time. This research aims at augmenting FDS with heat to lower the impact of this decreased process efficiency while also testing the potential to open the design space to thicker/stronger materials.

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