THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Monday, September 14, 2020

3:00 PM

via

BlueJeans Video Conferencing

https://bluejeans.com/556188153

will be held the

DISSERTATION PROPOSAL DEFENSE

for

Katarina Adstedt

"Advanced Carbon-Carbon Composites for Extreme Environments: Chemical, Physical, and Mechanical Interfacial Phenomena"

Committee Members:

Prof. Vladimir V. Tsukruk, Advisor, MSE

Dhriti Nepal, Ph.D., Air Force Research Labs

Prof. Satish Kumar, MSE

Prof. Surya Kalidindi, ME/CSE/MSE

Prof. Kyriaki Kalaitzidou, ME/MSE

Abstract:

Carbon-carbon composites are known for their unique mechanical properties, which are often achieved with hierarchical structures. The interphase region of carbon-carbon composites is integral to controlling the overall mechanical performance through interfacial interactions and the interphase adhesion. Carbon-carbon composites have the potential for widespread future use in hypersonic vehicles due to their unique properties; however, they encounter many challenges due to the extreme environment and exhibit failure due to extreme shear forces and oxidation. The proposed research addresses the issues encountered at high temperatures and forces by analyzing the effects of carbon fiber microstructure and introducing new microstructures that can enhance toughness and strength simultaneously while increasing oxidation resistance. The primary hypothesis of this research is that synergistic strengthening and toughening of carbon-carbon composites can be achieved by integrating and co-assembling thermophysically matched nanomaterials with the carbon fiber surface in a tailored, bio-inspired microstructure.

The goal of this research is to elucidate interfacial interactions between carbon and inorganic materials, with different topologies as prospective matrices and binders, in order to understand fundamental principles of interfacial organization at multiple length scales in complex hierarchical nanocomposites.  The ultimate focus of this research is to understand the influence of low dimensional nanostructures and metal nanoparticles on the morphology and the interfacial mechanics of carbon fibers. Accordingly, the first task focuses on elucidating the role of surface defects, nanopores, and varied surface chemistry on carbon fiber interfacial behavior and mechanical performance. The second task elevates the study of carbon fiber microstructures by introducing varied metallic and carbon-based nanostructures that integrate and fill the carbon fiber voids and defects to enhance mechanical interlocking and chemical bonding capabilities. Joint evaluation of these carbon-carbon composites microstructures at highly elevated temperatures will reveal the oxidation effects and interfacial interactions on mechanical performance. The final task incorporates the data from the previous two tasks with regards to intrinsic carbon fiber microstructure and additive material microstructure to develop a bio-inspired microstructure, such as the brick-and-mortar structure of nacre, on the carbon fiber surface to achieve high strength and high toughness in an oxidation resistant composite.

The research proposed here will be instrumental in understanding how the interfacial structure and chemistry of carbon-carbon composites can be tailored to enhance their mechanical performance and reduce thermal oxidation. Numerous characterization techniques, many of which are AFM based, will elucidate the mechanical properties and the relationship between structure-chemistry-mechanics. This knowledge can be leveraged to create stronger carbon-carbon composites capable of withstanding extreme conditions to operate in hypersonic environments.