Date of Award

Fall 2023

Access Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Sirish Namilae

First Committee Member

Mandar Kulkarni

Second Committee Member

Alberto Mello

College Dean

James Gregory

Abstract

The carbon fiber/epoxy interface is of great importance in composite design due to its load transfer mechanisms from the weak epoxy to the stronger fiber. Improving the strength of the interface reduces the risk of failure at the interface and improves the load transfer to the fiber. In this study, two types of nano-species ZnO nanowires and nickel-based metal organic frameworks were grown on carbon fibers to improve the interfaces. The interfacial mechanics of the enhanced fibers are evaluated using nanoindentation studies. Composite samples with Aeropoxy matrix and vertically aligned fibers are fabricated for this purpose. A Bruker TI-980 TriboIndenter is used to perform single-fiber push-in tests to analyze the interfacial behavior. The load-displacement curves of these push-in tests denote a clear nonlinearity where debonding occurs, and the debonding loads are used to calculate interfacial shear stress. A 15-20% improvement in interfacial strength was observed with the fiber modification. Along with that, modulus mapping techniques allow for the analysis of the change in moduli along the interface. In conjunction with mechanical analysis, chemical and hydrodynamic perspectives are also investigated for additional reasoning as to why nano-species surface modification positively affects the fiber/matrix interface. These perspectives show that the increase in roughness on the fiber’s surface, increase in surface free energy, and decrease in interfacial tension of the nano-species increases the wettability of the epoxy onto the fiber’s surface. The combined mechanical, chemical, and hydrodynamic analyses lead to the conclusion that the growth of these nano-species enhances the interfacial properties of the carbon fibers and opens promising possibilities for multifunctional applications by harnessing the properties of the nanomaterials.

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