Browsing by Subject "Carbon fiber"

Now showing 1 - 3 of 3

Advanced manufacturing of carbon fiber reinforced PAEK composites : bonding and fracture mechanisms
(2023-08) Heathman, Nathaniel Thomas; Tehrani, Mehran; Seepersad, Carolyn; Kim, Hyonny; Kovar, Desiderio
Fiber reinforced composites are used in applications where lightweight, strength, stiffness, fatigue life, and corrosion resistance are critical. Thermoplastic composites (TPC) offer several advantages over thermosetting ones, including higher toughness, recyclability, weldability, and ease of repair. Over the last decade, the interest in in situ consolidation additive manufacturing (AM) of TPCs has increased exponentially due to their potential for rapid cycle out-of-autoclave processes. To this end, several limitations need to be resolved. Specifically in situ consolidation of TPCs usually result in low interlaminar bonding, weak matrix/fiber adhesion, high void content, and low crystallinity. This dissertation aims to provide a new understanding and solutions to these issues. The material system used in this work is carbon fiber reinforced low-melt polyarlyletherketone (LM-PAEK), processed via two AM methods: fused filament fabrication (FFF) and directed energy deposition (DED) in the form of laser-assisted automated fiber placement (AFP). By combining experiments and modeling, this work aims to develop an understanding of how processing parameters affect interlaminar bonding, void development, and crystallinity for both processes. This dissertation also investigates in situ consolidation of TPCs by examining the underlying physics that control bond strength and fracture toughness at inter-layer interfaces. Overall, this dissertation contributes to the knowledge base in the field, toward the adoption of low-energy and high-rate processes for manufacturing high-performance TPC structures.
Monitoring of an outdoor exposure site : evaluating different treatment methods for mitigation of alkali-silica reactivity in hardened concrete
(2011-05) Resendez, Yadhira Aracely; Folliard, Kevin J.; Drimalas, Thano
This research project, funded by the Federal Highway Administration, entails the construction of an outdoor exposure site in order to evaluate various methods for mitigating alkali-silica reaction (ASR) in hardened concrete. The exposure site, built at the Concrete Durability Center at the University of Texas at Austin J.J. Pickle Research campus, included a series of bridge deck, column and slab elements. The specimens were cast in 2008, allowed to expand to predetermined expansion levels and then treated with various mitigation measures, after which the specimens were monitored for expansion, humidity, and deterioration.
Processing and applications of carbon-based electrical conductors
(2021-12-03) Khanbolouki, Pouria; Tehrani, Mehran; Mangolini, Filippo; Warner, Jamie; Korgel, Brian
The next generation of power-dense and efficient machines used in the aerospace, marine, transportation, energy, electronics, and electrical power industries will require superior electrical conductors. To this end, this dissertation investigates i) new post-processing (purification and intercalation) approaches for advanced carbon-based conductors and ii) numerical modeling of advanced conductors for practical applications. Most synthesis approaches leave impurities, catalyst particles and reaction by-products, in carbon nanotubes (CNT) that are not easy to remove. This dissertation investigates a fast and energy-efficient post-processing method for the purification and annealing of CNT yarns. The approach utilizes joule heating under high vacuum for the incandescent annealing process (IAP) of CNT yarns. Electrical properties of CNT yarns, spun directly from a floating catalyst chemical vapor deposition reactor, are correlated with the morphological changes of their structure resulting from the IAP. The correlations between the yarns’ chemical composition, structure, and electrical conductivity provide new insight into doping mechanisms and the stability of CNT conductors. Next, the effect of IAP is extended to other types of CNT yarns fabricated via dry spinning from vertically aligned CNT yarns and wet spinning from super-acid CNT solutions. A potential advantage of advanced electrical conductors is their relatively low density, thermal coefficient of resistance, and high thermal conductivity. This dissertation investigates the elevated temperature performance of advanced electrical conductors by developing, verifying, and validating a one-dimensional ampacity prediction model. Copper (as the reference) is subsequently compared with carbon-based conductors and copper nanocomposites on the basis of equivalent volume and equivalent weight. The performance of advanced carbon-based conductors improves drastically with nano-additives, however, they don’t readily integrate with carbonaceous materials. This dissertation explores gas-phase metal-halide intercalation of carbon-based conductors. Specifically, copper chloride is used as an intercalant with different CNT yarns and carbon fibers as host materials. A chemical vapor transport reactor was designed and constructed for intercalation studies. Dynamic of the process and chemical composition/structure of the intercalated compounds in different carbon hosts are correlated with physical properties of resulting advanced conductors. Advanced carbon-based conductors can survive the harsh space environment. This work investigates the electron irradiation and IAP damage recovery of CNT yarns.