THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Friday, November 30th, 2018

3:30 PM

in MRDC 3403

will be held the

DISSERTATION DEFENSE

for

Emily R. Fitzharris

"Semicrystalline Polymers in Material Extrusion Additive Manufacturing"

Committee Members:

Prof. Meisha L. Shofner, Advisor, MSE

Prof. David Rosen, Advisor, ME

Prof. Donggang Yao, MSE

Prof. Seung Soon Jang, MSE

Prof. H. Jerry Qi, ME

Abstract:

Material extrusion (MEX) additive manufacturing is one of the most widely used additive manufacturing techniques in which a polymer filament is liquefied and extruded through a nozzle to fabricate a three-dimensional part in a layer-by-layer deposition technique. While MEX offers many advantages over traditional manufacturing methods, the shift of MEX from a prototyping method to a manufacturing technique is limited by the inferior mechanical properties of the produced parts compared to bulk parts and the limited number of MEX feedstock materials. The objective of this research was to provide insights into the molecular behavior specific to semicrystalline MEX materials that influence the resulting MEX part behavior. Polyphenylene sulfide (PPS) was used as a case study material in this research. Process simulation models were developed that predicted the temperature evolution of MEX parts during fabrication and determined correlations between material properties and deformation characteristics of MEX parts. Fast scanning calorimetry showed that the cooling rates experienced during MEX hindered the crystallization of PPS. In addition, a process optimization of material dependent thermal history parameters reduced the disparities between bulk and MEX parts. The combination of process simulation models, thermal and mechanical characterization, and process optimization techniques studied in this research developed a methodology for successfully printing high quality MEX parts using semicrystalline materials.