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A new method for pre-impregnating nickel coated carbon fiber with a thermoplastic polymer to make towpreg, similar to a recently developed coating-line by João P. Nunes et al and a new electrically conductive thermoplastic are developed. A melted bath was used to help mitigate health concerns and waste for dispersion of nickel coated carbon fibers (NCF) in low density polyethylene (LDPE). This towpreg was then mixed with more LDPE or a mixture of LDPE and nickel nanostrands (NiNS) to a desired filler volume fraction to test the electrical conductivity of the composite. Some of these mixtures were then injection molded and tested again for conductivity as well as tensile and impact strength and compared to each other and the non-injection molded samples. It was found that mixing NiNS into the polymer in addition to NCF created a more conductive part than with NCF alone, in a couple orders of magnitude. Also, the shorter the NCF were, the greater the contribution of the NiNS to the electrical properties of the NCF filled material. The tensile strength was increased by adding the NCF and NiNS, while the impact strength (toughness) decreased.

Carbon fiber (CF) is predominantly produced from fossil-based sources and is therefore an area of interest for further development towards a more sustainable society. The purpose of this thesis work was to investigate the possibility of producing precursor fibers (PFs) for CF production from a blend of renewable cellulose andlignin. Cellulose, which is used to some extent for CF production, was chosen, while the possibility of adding lignin was investigated in hope of increasing the gravimetric yield of the CF production. Blends of softwood kraft cellulose pulp (SKP) and softwood kraft lignin (SKL) were dissolved in an alkaline (NaOH) solvent system at different cellulose/lignin ratios. A total of eight dopes were prepared (SKP/SKL ratios of 100/0–60/40 wt./wt.) with total dope concentrations ranging from 4.5 wt.% to 9.2 wt.%. The addition of SKL resulted in dark colored dopes with viscosities of which mainly appeared to depend on the SKP concentration. The dopes were wet spun, resulting in continuously spun PFs. The PFs showed on an increasing pyrolysis yield with increased SKL content but decreasing mechanical properties. However, process optimization was not included in the work, subsequently leading to the assumption that greater values on mechanical properties can be achieved. A pure SKP PF and a SKP-SKL (70/30 wt./wt.) PF were successfully thermally converted into CFs by carbonization at 1000 °C. The PF containing SKL had a total gravimetric yield more than twice as high as the pure SKP PF, 28 wt.% and 12 wt.%, respectively. Thereby, the addition of SKL seems to have a positive impact on the CF yield when utilizing a NaOH(aq) solvent system. This thesis work has become a base for the future work towards the development of CFs from wet spun cellulose-lignin PFs in the NaOH(aq) solvent system.

Experimentation exploring the movement of voids within carbon fiber reinforced plastics was performed using fluorescent dye infused into the laminates observed through a transparent mold under ultraviolet light. In situ photography was used as an inspection method for void content during Resin Transfer Molding for these laminates. This in situ inspection method for determining the void content of composite laminates was compared to more common ex-situ quality inspection methods i.e. ultrasonic inspection and cross-section microscopy. Results for localized and total void count in each of these methods were directly compared to test samples and linear correlations between the three test methods were sought. Test coupons were then cut from these laminates and were used to calculate the interlaminar shear strength at certain locations throughout the laminates. Although this research did not adequately observe correlations between results obtained from ultrasonic C-scans, cross-sectional microscopy and in situ photography of the surface, it was seen that the fluid dynamics of the thermosetting epoxy used in this experimentation correlated to results obtained from previous experimentation performed by students at Brigham Young University using vegetable oil as a substitute for resin.

Clean air is a global health concern. Each year more than seven million people across the globe perish from breathing poor quality air. Development of high efficiency particulate air (HEPA) filters demonstrate an effort to mitigate dangerous aerosol hazards at the point of production. The nuclear power industry installs HEPA filters as a final line of containment of hazardous particles. Advancement air filtration technology is paramount to achieving global clean air. An exploration of analytical, experimental, computational, and machine learning models is presented in this dissertation to advance the science of air filtration technology. This dissertation studies, develops, and analyzes alternative air filtration materials and methods of analysis that optimize filtration efficiency and reduce resistance to air flow. Alternative nonwoven filter materials are considered for use in HEPA filtration. A detailed review of natural and synthetic fibers is presented to compare mechanical, thermal, and chemical properties of fibers to desirable characteristics for air filtration media. An experimental effort is undertaken to produce and evaluate new nanofibrous air filtration materials through electrospinning. Electrospun and stabilized nanofibrous media are visually analyzed through optical imaging and tested for filtration efficiency and air flow resistance. The single fiber efficiency (SFE) analytical model is applied to air filtration media for the prediction of filtration efficiency and air flow resistance. Digital twin replicas of nonwoven nanofibrous media are created using computer scripting and commercial digital geometry software. Digital twin filters are visually compared to melt-blown and electrospun filters. Scanning electron microscopy images are evaluated using a machine learning model. A convolutional neural network is presented as a method to analyze complex geometry. Digital replication of air filtration media enables coordination among experimental, analytical, machine learning, and computational air filtration models. The value of using synthetic data to train and evaluate computational and machine learning models is demonstrated through prediction of air filtration performance, and comparison to analytical results. This dissertation concludes with discussion on potential opportunities and future work needed in the continued effort to advance clean air technologies for the mitigation of a global health and safety challenge.

<p dir="ltr">Computational materials science has emerged as a powerful technique to discover and develop new materials in past decades, primarily because accurate computational modeling can act as guidance before performing experiments that are expensive and time-consuming. However, modeling material behaviors across different scales of length and time poses a challenge, accentuating the importance of choosing appropriate levels of approximations and theories. First principles calculations based on density functional theory (DFT) are essential to predict the electronic structure of periodic crystalline systems. We will discuss a prediction of chemical doping induced metal-to-insulator transition (MIT) of transition metal perovskites owing to the variation of the electronic occupation. Nevertheless, electronic structure predictions based on DFT are not without limitation as it fails when treating strongly correlated electronic system due to the over-delocalization of valence electrons. In principle, adding on-site Hubbard U corrects this error with a low computational cost. Using an example of a two-dimensional rare-earth MXene, we demonstrate the essence of choosing the appropriate U value self-consistently for the prediction of electronic and magnetic configurations. Furthermore, molecular dynamics (MD) can be employed to study the dynamic evolution of complex condensed systems with thousands to millions of atoms at the atomistic and molecular levels. Carbon fiber manufacturing is an established industry, though the fiber produced achieves only 10% of its theoretical tensile strength. Therefore, optimizing the carbon fiber processing is a pressing topic. To achieve this, we study two steps, spinning and stabilization, of polyacrylonitrile (PAN)-based fiber fabrication at the molecular level using MD. We will discuss the realistic molecular structure of the spun PAN and the properties affected by its structural heterogeneity. Moreover, for the following step, we develop a PAN stabilization simulator, an automated workflow that addresses the underlying chemistry and the molecular-level structure-property relationship, often inaccessible through experiments.</p>

<p>This investigation delineates the optimal synthesis and characterization of innovative epoxy-carbon nanotube (CNT) nanocomposite filaments via electrospinning. Electrospinning thermosetting materials such as epoxy resins presents significant challenges due to the polycationic behavior arising from intermolecular noncovalent interactions between epoxide and hydroxyl groups, resulting in a substantial increase in solution surface tension. In this study, electrospinning submicron epoxy filaments was achieved through partial curing of epoxy via a thermal treatment process in an organic polar solvent, circumventing the necessity for plasticizers or thermoplastic binders. The filament diameter can be modulated to as low as 100 nm by adjusting electrospinning parameters.</p> <p><br></p> <p>Integrating a minimal amount of CNT into the epoxy matrix yielded enhanced structural, electrical, and thermal stability. The CNTs were aligned within the epoxy filaments due to the electrostatic field present during electrospinning. The modulus of the epoxy and epoxy-CNT filaments were determined to be 3.24 and 4.84 GPa, respectively, resulting in a 49% improvement. Epoxy-CNT nanofibers were directly deposited onto carbon fiber reinforced polymer (CFRP) prepreg layers, yielding augmented adhesion, interfacial bonding, and significant mechanical property enhancements. The interlaminar shear strength (ILSS) and fatigue resistance demonstrated a 29% and 27% increase, respectively, under intense stress conditions. Up to 45% of the Barely Visible Impact Damage (BVID) energy absorption was increased. In addition, the strategic incorporation of CNT (multi-walled) networks between the layers of CFRP resulted in a significant increase in thermal and electrical conductivities.</p> <p>This study also introduces a scalable fabrication procedure to address large volume processing, reproducibility, accuracy, and electrospinning safety. Electric fields of the experimental multi-nozzle setups were simulated to elucidate the induced surface charges responsible for the Taylor cone formation of the epoxy-CNT solution droplet on the nozzle tips. Electrospinning parameters were subsequently optimized for the multi-nozzle system and analyzed alongside simulated data to improve stability and synthesize fibers with smaller diameters.</p> <p><br></p> <p>Smaller diameter epoxy-CNT nanofibers proved critical as CNTs maintained alignment within the nanofibers when compared to larger diameter nanofibers. This research examines the impact of effective parameters on the diameter of electrospun epoxy-CNT nanofibers using artificial neural networks (ANNs). Consequently, employing a genetic algorithm (GA) and Bayesian optimization (BO) methods enable accurate prediction of epoxy-CNT nanofiber diameters prior to electrospinning. The presented models could aid researchers in fabricating electrospun thermosetting and thermoplastic scaffolds with specified fiber diameters, thereby tailoring these scaffolds for specific applications.</p>

Total hip joint prostheses made of CoCrMo heads versus ultra high molecular weight polyethylene (UHMWPE) cups have a limited lifetime, mainly due to the wear of the UHMWPE cups as a result of high friction between the articulating surfaces leading to osteolysis and implant loosening with revision surgery becoming inevitable in more active patients. Tribology plays an important role in developing the design, minimizing wear and reducing friction of hip joint prostheses in order to improve their long-term performance, with good lubricating properties. Metal-on-metal hip resurfacing prostheses have shown significantly lower wear rates compared with conventional metal-on-polyethylene implants and thus osteolysis is potentially reduced leading to increased lifetime of the prosthesis. Nevertheless, excessive wear of metal-on-metal joints leads to metal ion release, causing pseudo-tumours and osteolysis. An alternative approach to such bearings is the use of newly developed carbon fiber-reinforced poly-ether-ether-ketone (CFR PEEK) acetabular cups articulating against ceramic femoral heads due to their better wear resistance compared to UHMWPE. In this study, therefore, friction and lubrication properties of large diameter, as cast, Co-Cr-Mo metal-on-metal hip resurfacing implants with various diameters and clearances have been investigated and compared to those of the newly developed zirconia toughened alumina (ZTA) ceramic femoral heads articulating against carbon fiber reinforced poly-ether-ether-ketone (CFR PEEK) acetabular cups with different diameters and clearances. Friction hip simulator was used to measure frictional torque and then friction factors were calculated along with Sommerfeld numbers leading to Stribeck analysis and hence the lubricating mode was also investigated. This involved using lubricants based on pure bovine serum (BS) and diluted bovine serum (25 vol. %BS+75 vol. %distilled water) with and without carboxymethyl cellulose (CMC) (as gelling agent). Standard Rheometer was used to measure lubricant viscosity ranged from 0.0014 to 0.236 Pas at a shear rate of 3000 . Pure bovine serum, diluted bovine serum without CMC and with CMC (25BS+75DW+0.5gCMC and +1gCMC) showed pseudoplastic flow behaviour up to shear rate of ¿139 above which a Newtonian flow with significant increase in shear stress was observed. The viscosity flow curves for the 25BS+75DW+2gCMC, +3.5gCMC and +5gCMC showed only shear thinning up to a shear rate of 3000 . The shear rate application modified the flow behaviour of bovine serum from a pseudoplastic to a Newtonian flow depending on its purity and CMC content. This will cause a different frictional behaviour depending on joint diameter and clearance, as seen in this work. The experimental data were compared with theoretical iv predictions of the lubricating regimes by calculating theoretical film thickness and lambda ratio. The metal-on-metal Biomet ReCaps showed similar trends of Stribeck curves, i.e. friction factors decreased from ~0.12 to ~0.05 as Sommerfeld numbers increased in the range of viscosities ~0.001-0.04Pas indicating mixed lubrication regimes above which the friction factor increased to ~0.13 at a viscosity of 0.236Pas. The Stribeck analyses suggested mixed lubrication as the dominant mode with the lowest friction factor in the range ~0.09 - ~0.05 at the physiological viscosities of ~0.01 to ~0.04 Pas and that such joints can be used for more active patients as compared to the conventional total hip replacement joints with 28mm diameter. The Stribeck curves for all ZTA ceramic-on-CFR PEEK components illustrated a similar trend with BS fluids showing higher friction factors (in the range 0.22-0.13) than the diluted BS+CMC fluids (in the range 0.24-0.05). The friction tests revealed boundary-mixed lubrication regimes for the ZTA ceramic-on-CFR-PEEK joints. The results, so far, are promising and suggest clearly that the newly developed ZTA ceramic femoral heads articulating against CFR PEEK cups have similar friction and lubrication behaviour at optimum clearances to those of currently used metal-onmetal hip resurfacing implants at the range of viscosities 0.00612 to 0.155Pas. These results clearly suggest that the ZTA ceramic-on-CFR-PEEK joints showed low friction at the physiological viscosities of ~0.01Pas in the range ~0.1-0.05, suggesting that these novel joints may be used as an alternative material choice for the reduction of osteolysis. The result of this investigation has suggested that the optimum clearance for the 52mm diameter MOM Biomet ReCaps could be ~170¿m. However, 48 and 54mm joints showed lower friction due to clearances to be >200¿m. For the 52mm ZTA ceramic-on-CFR-PEEK joints the optimum clearance seems to be ¿ 630¿m radial clearance. These results suggested that increased clearance bearings have the potential to generate low friction and hence no risk of micro- or even macro-motion for the ceramic-on-CFR-PEEK joints. This study found no correlation between theoretical predictions and experimental data for all metal-onmetal and ZTA ceramic-on-CFR PEEK bearings at the physiological viscosity (0.0127Pas). However, at lubricant viscosity of 0.00157Pas, the theoretical prediction of lubrication regime correlated well with the experimental data, both illustrating boundary lubrication. As expected, a decrease in viscosity resulted decrease in the film thickness.

Carbon concrete composites (C³) hold promise as a material class for constructing lightweight, durable, and sustainable structures. State-of-the-art carbon fiber-reinforced polymer (CFRP) reinforcement comprises infinite multifilament bundles embedded in a polymeric matrix, en-suring adequate load transfer and process robustness, yet it undergoes considerable degrada-tion under elevated temperatures or harsh service conditions. Instead, the success of mineral-impregnated carbon fibers (MCFs) stems from their structural flexibility, inherent heat re-sistance, and outstanding compatibility with cementitious substrates. Geopolymers (GPs) have recently emerged as a viable coating alternative due to a unique combination of many advantages, e.g., sustainability, source diversity, long early-age processing time, synthesis by controlled low-temperature activation and a wide range of temperature resistance. This work aims to develop and test fast-setting MCF composites and associated processing technologies, which hold significant importance for industrial applications and structural fire safety. As a result of the novelty of mineral impregnation technology, challenges regarding the process chain and mixture must be mastered to explore the full material potential before the technology is translated to key markets. The introductory chapter offers a comprehensive review of fiber-reinforced geopolymer (FRG) systems in response to temperature influences. The concept development is grounded in a systematic investigation of several interrelated, critical processing aspects of GP impregnation, focusing on processing quality and strength evolution. This investigation is conducted alongside an automated and continuous impregna-tion technology. Findings from numerous experiments revealed that targeted thermal curing profoundly influ-enced the mechanical properties and microstructure of the GP matrices and resulting MCFs. Hereby, rapid setting and high early-age strength of MCF, comparable to conventional CFRPs, were achieved within the first several hours of heat curing. The ability of aluminosili-cate particles to penetrate a dense fiber bundle was studied by applying fly ash (FA) with a systematically varied particle size distribution. Thereby, the max. particle size close to the same range of diameter of individual filament proved to be the most efficient, improving both the mechanical performance of MCF and its bond to concrete. Furthermore, an experimental campaign on the role of fiber sizing agents in processing quality and final composite perfor-mance was conducted. The respective impregnation quality and quantity were comprehen-sively explained by varied yarn spreading behavior and wettability, resulting in apparent dif-ferences in filament-matrix morphology and mechanical performance of MCF. To achieve high shape stability, packing density, and tailor-bond characteristics, the effect of surface pro-filing and prototypical winding technology on MCF was investigated. Finally, the bond quality of the MCF was validated through yarn pull-out tests in GP concrete at elevated temperatures and compared with available CFRP. These tests generated parame-ters related to bond behavior, which were then used to construct a three-dimensional numeri-cal model. Based on proper parametric calibrations, good agreement between numerical and experimental characterizations was achieved to predict the material's performance for future applications.:1 Introduction 1 1.1 Motivation 1 1.2 Objectives of the thesis 5 1.3 Thesis structure 7 2 Publications 11 2.1 A review of the role of elevated temperatures on the mechanical properties of fiber-reinforced geopolymer (FRG) composites 12 2.2 Development and testing of fast curing, mineral-impregnated carbon fiber (MCF) reinforcements based on metakaolin-made geopolymers 37 2.3 Mineral-impregnated carbon-fiber (MCF) composites made with differently sized fly-ash geopolymers for durable light weight and high temperature applications. 50 2.4 Role of sizing agent on the microstructure morphology and mechanical properties of mineral-impregnated carbon-fiber (MCF) reinforcement made with geopolymers 66 2.5 Effect of surface profiling on the mechanical properties and bond behaviour of mineral-impregnated, carbon-fibre (MCF) reinforcement based on geopolymer 80 2.6 Temperature-dependent pull-out behavior of geopolymer concrete reinforced with polymer- or mineral-impregnated carbon fiber composites: an experimental and numerical study. 94 3 Summary and Outlook 108 3.1 Summary of the research work 108 3.2 Outlook 113 References 119 Appendix A IV Appendix B VI / Der Verbundwerkstoff Carbonbeton ist eine vielversprechende Materialklasse für den Bau von leichtgewichtigen, langlebigen und nachhaltigen Strukturen. Hochmoderne Bewehrungen aus Carbonfaser-verstärkte Kunststoffen (CFK) werden durch die Imprägnierung von Endlos-faserbündeln mit einer Polymermatrix hergestellt, was ausreichende Lastübertragungskapazi-tät und Prozessrobustheit gewährleistet, und jedoch durch hohe Temperaturen oder raue Um-gebungen erheblich zerstört wird. Stattdessen resultiert der Erfolg mineralimprägnierter Car-bonfasern (MCFs) aus ihrer strukturellen Flexibilität, inhärenten Wärmebeständigkeit und hervorragenden Kompatibilität mit zementären Substraten. Geopolymere (GPs) haben sich kürzlich als praktikable Beschichtungsalternative herausgestellt, aufgrund einer einzigartigen Kombination vieler Vorteile, wie Nachhaltigkeit, Quellenvielfalt, ausreichendes Verarbei-tungsfenster, Synthese durch kontrollierte thermische Aktivierung bei niedrigen Temperatu-ren und Hitzebeständigkeit. Die vorliegende Arbeit zielt auf die Entwicklung und Erprobung schnell abbindender MCF-Verbundwerkstoffe und zugehöriger Verarbeitungstechnologien ab, was für industrielle An-wendungen und den baulichen Brandschutz von großer Bedeutung ist. Aufgrund der Neuar-tigkeit der mineralischen Imprägnierungstechnologie müssen Herausforderungen in Bezug auf die Prozesskette und Mischung gemeistert werden, um das volle Materialpotenzial zu erkunden, bevor die Technologie auf Schlüsselmärkte übertragen wird. Dementsprechend gibt das einleitende Kapitel einen umfassenden Überblick über faserverstärkte Geopolymer (FRG)-Systeme unter Temperatureinwirkung. Das Entwicklungskonzept baut auf einer sy-stematischen Untersuchung mehrerer zusammenhängender, wichtiger Verarbeitungsaspekte der GP-Imprägnierung in Bezug auf Verarbeitungsqualität und Festigkeitsentwicklung von der Mikro- bis zur Makroskala und in Verbindung mit einer automatisierten und kontinuierli-chen Fertigungstechnologie auf. Ergebnisse zahlreicher Experimente zeigten, dass gezielte Wärmehärtung die mechanischen Eigenschaften und Mikrostruktur der GP-Matrizen und resultierenden MCFs nachhaltig be-einflußt. Hierdurch wurde eine schnelle Aushärtung und hohe Festigkeit von MCF innerhalb der ersten Stunden der Wärmebehandlung erreicht, und zwar vergleichbar mit konventionel-len CFRPs. Die Eindringfähigkeit von Aluminosilikatpartikeln in ein dichtes Faserbündel wurde durch die Anwendung von Flugasche (FA) mit systematisch variierter Partikelgrößen-verteilung untersucht. Dabei erwies sich die maximale Partikelgröße, die nahe dem Durch-messer einzelner Filamente liegt, als am effizientesten. Sie verbesserte sowohl die mechani-sche Leistung von MCF als auch seine Bindung an Beton. Darüber hinaus wurde eine expe-rimentelle Kampagne zur Rolle der Faserschlichte auf die Verarbeitungsqualität und die end-gültige Verbundleistung durchgeführt. Die jeweilige Imprägnierungsqualität wurde umfas-send durch ein unterschiedliches Spreizungsverhalten und Benetzbarkeit des Garns erklärt, was zu deutlichen Unterschieden in der Filament-Matrix-Verteilung und mechanischen Ei-genschaften von MCF führte. Zur Verbesserung der Formstabilität, Packungsdichte und ge-zielten Abstimmung der Verbundeigenschaften im Beton wurde der Effekt der Oberflächen-profilierung und prototypischen Wickeltechnik auf MCF untersucht. Schließlich wurde die Verbundqualität der MCF durch den Garnauszugversuch in GP-Beton bei erhöhten Temperaturen validiert und mit einer verfügbaren CFK-Bewehrung verglichen. Diese Tests generierten auf das Verbundverhalten bezogene Parameter, die dann zur Formu-lierung eines dreidimensionalen numerischen Modells verwendet wurden. Durch angemesse-ne parametrische Kalibrierungen wurde eine gute Übereinstimmung zwischen numerischen und experimentellen Charakterisierungen erreicht, um die Leistung des Materials für zukünf-tige Anwendungen vorherzusagen.:1 Introduction 1 1.1 Motivation 1 1.2 Objectives of the thesis 5 1.3 Thesis structure 7 2 Publications 11 2.1 A review of the role of elevated temperatures on the mechanical properties of fiber-reinforced geopolymer (FRG) composites 12 2.2 Development and testing of fast curing, mineral-impregnated carbon fiber (MCF) reinforcements based on metakaolin-made geopolymers 37 2.3 Mineral-impregnated carbon-fiber (MCF) composites made with differently sized fly-ash geopolymers for durable light weight and high temperature applications. 50 2.4 Role of sizing agent on the microstructure morphology and mechanical properties of mineral-impregnated carbon-fiber (MCF) reinforcement made with geopolymers 66 2.5 Effect of surface profiling on the mechanical properties and bond behaviour of mineral-impregnated, carbon-fibre (MCF) reinforcement based on geopolymer 80 2.6 Temperature-dependent pull-out behavior of geopolymer concrete reinforced with polymer- or mineral-impregnated carbon fiber composites: an experimental and numerical study. 94 3 Summary and Outlook 108 3.1 Summary of the research work 108 3.2 Outlook 113 References 119 Appendix A IV Appendix B VI

The Joule heating of carbon fiber-based textiles enables an energy- and cost-efficient processing of carbon fiber reinforced thermoplastic parts. This article introduces a new method to pass direct current into a dry, not pre-consolidated hybrid yarn textile based on recycled carbon fibers and polyamide 6 fibers. The aim is to melt polyamide fibers, subsequently impregnate carbon fibers, and finally consolidate the material to form a composite part in a single process step. To increase the reliability of this technology, the electrical properties and the behavior of the material during the heating process must be thoroughly investigated. It will be addressed how the material is characterized during the process and how the changing resistivity of the textile affects the current flow between the electrodes to generate intrinsic heat. Moreover, a method to determine the effective material resistivity by finite element simulation on the fiber scale based on a CT scan is presented. Thus, a validated material model with respect to the temperature development in the textile based on ρ = ρ (T) was established.