Jefferson E. Bourdeau
Advisor: Prof. Satish Kumar

will propose a doctoral thesis entitled,

Improving fiber-based materials on the fiber, fiber/matrix interface and composite levels: A multi-material study

On

Tuesday, August 26, 2025 at 10:00 a.m.

Committee
            Prof. Satish Kumar – School of Materi (advisor)

             Prof. Kyriaki Kalaitzidou – School of ME/MSE

            Prof. Meisha Shofner – School of MSE            

            Prof. Donggang Yao – School of MSE

            Dr. Cheol Park – NASA Langley Research Center

Abstract
Our research aims to improve the mechanical performance of fiber-based materials. They are typically applied in lightweight composites where strength-to-weight performance is paramount. Mechanical performance is strongly influenced by the inherent properties of the fiber, the interactions between the fiber and the matrix and the fiber geometry. To improve fiber-based materials, research efforts must focus on improving performance at each of these levels. To that end, we consider three fiber-based materials and explore each of them at a different level. Polyacrylonitrile (PAN)/boron nitride nanotube (BNNT) composite fiber derived BNNT fibers are explored on the fiber level to improve their tensile properties. To date, such BNNT fibers have higher mechanical properties than BNNT fibers made from any other method. We hypothesize that even higher mechanical properties can be achieved by improving BNNT dispersion in the processing solution and increasing BNNT concentration in the PAN/BNNT precursor fiber. We have conducted some studies incorporating additives into PAN/BNNT spinning dopes that resulted in better BNNT fibers. We have also conducted some studies using aromatic polar additives in BNNT dispersions in DMAc. These studies suggest that aromatic polar aprotic additives may improve BNNT dispersion in DMAc. Our results are supported by computational Hansen solubility parameter analyses showing a lower relative energy difference for BNNT dispersion in DMAc /cosolvent systems compared pure DMAc. Herein, future experiments exploring methods of improving BNNT dispersions are proposed. We also propose experiments attempting to use improved BNNT dispersions to increase BNNT concentration in PAN/BNNT fibers and ultimately make better BNNT fibers. Carbon nanotube (CNT) yarn composites are studied on the fiber/matrix interface level to increase the interfacial shear strength (IFSS) of CNT yarns with epoxy and bismaleimide (BMI) resins. Herein, we report a chemical treatment method that can improve the apparent interfacial shear strength (IFSS) of CNT yarn with epoxy by up to 45%. We also report a heat treatment method that increases the specific modulus of CNT yarns by as much as 16%. A combined heat and APM treatment protocol produces 43% and 6% increases in IFSS and specific tensile modulus, respectively. Hollow carbon fiber (HCF) composites are developed to study the effect of fiber geometry on the bulk properties of carbon fiber reinforced epoxy composites. Herein, we build upon previously reported results on the mechanical performance of HCF in general and the mechanical performance of HCF composites under compressive and tensile loadings. We report novel flexural data for HCF composites. Our studies show that HCF/epoxy composites are less dense and more thermally insulative than T300/epoxy composites. Furthermore, HCF/epoxy composites showed 8.6% greater specific flexural strength, and 18.8% greater specific flexural modulus than T300/epoxy composites. We also report thermal conductivity result showing that HCF composites are 20%