Theses and Dissertations

Issuing Body

Mississippi State University


Schneider, Judith A.

Committee Member

Luck, Rogelio

Committee Member

Myers, Oliver J.

Committee Member

Nunes, Arthur C., Jr

Committee Member

Thompson, Scott M.

Date of Degree


Document Type

Dissertation - Open Access


Mechanical Engineering

Degree Name

Doctor of Philosophy


James Worth Bagley College of Engineering


Department of Mechanical Engineering


The study of defect formation and identification is important to the further application of friction stir welding in industry. To better understand the topic, a systematic study was undertaken to describe material flow effects on the formation of defects, to list the various types of defects encountered across a parameter window, and to identify features in the weld force data that can then be used to recognize defects within the weld without destructive testing. Tracer studies were used to determine the impact of the material flow on defect formation with a determination that proper shoulder contact is necessary to obtain sufficient material flow to fully consolidate the weld. A series of welds across a range of rotational speeds was used to identify mechanisms that led to variations in the mechanical properties of the welded panels. A balance between the x- and yorces on the tool is needed to produce robust welds that were defect free. UMF was shown to identify regions of changing material flow conditions; however, the identification of intermittent defects was not as successful.