▼ Supercapacitors used in conjunction with batteries offer a solution to energy storage and delivery problems in systems where high power output is required, such as in fully electric cars. This project aimed to enhance current supercapacitor technology by fabricating activated carbon on a substrate consisting of carbon nanotubes (CNTs) grown on a carbon fiber fabric (fuzzy fabric). The fuzzy surface of CNTs lowers electrical resistance and increases porosity, resulting in a flexible fabric with high specific capacitance. Experimental results confirm that the capacitance of activated carbon fabricated on the fuzzy fiber composite is significantly higher than when activated carbon is formed simply on a bare carbon fiber substrate, indicating the usefulness of CNTs in supercapacitor technology. The fabrication of the fuzzy fiber based carbon electrode was fairly complex. The processing steps included composite curing, stabilization, carbonization and activation. Ratios of the three basic ingredients for the supercapacitor (fiber, CNT and polymer matrix) were investigated through experimentation and Grey relational analysis. The aim of Grey relational analysis was to examine factors that affect the overall performance of the supercapacitor. It is based on finding relationships in both independent and interrelated data series (parameters). Using this approach, it was determined that the amount of CNTs on the fiber surface plays a major role in the capacitor properties. An increased amount of CNTs increases the surface area and electrical conductivity of the substrate, while also reducing the required time of activation. Technical advances in the field of Materials and Structures are usually focused on attaining superior performance while reducing weight and cost. To achieve such combinations, multi-functionality has become essential; namely, to reduce weight by imparting additional functions simultaneously to a single material. In this study, a structural composite with excellent capacitive energy properties was successfully prepared. Moreover, after carbon nanotube growth the fuzzy fabric gained tangible energy storage properties without any structural degradation to the carbon fiber. These results represent a state-of-the-art advancement for multifunctional structural composites and warrant further development. Advisors/Committee Members: Lafdi, Khalid.

▼ The catalyst nanoparticle is critical to the yield, type, and diameter in the growth and nucleation of carbon nanotubes. The objective of this study is focused on determining what changes take place with the catalyst chemistry under growth conditions typically seen in chemical vapor deposition, CVD, experiments. It is well known that catalyst poisoning can occur and in turn effects the catalytic activity of the nanoparticle. A complete description of this mechanism is as of yet undetermined. In order to elucidate this process iron films were deposited onto Si substrates that contained a support layer of Al2O3 or SiO2. These samples were investigated with various surface chemistry techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and electron energy loss spectroscopy (EELS). In addition, structural characteristics were investigated with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface techniques were used in-situ in order to observe chemistries that might not be observable outside a CVD reactor. Two sets of experiments were performed on the silica and alumina supports. The first consisted of carbon nanotube growth at near atmospheric pressure, while the second was performed under vacuum. The oxide support was shown to have an affect on the type of nanotubes grown under identical conditions. The silica support films produced more MWNT, while the alumina support films produced more SWNT. This difference was due to the amount of ripening that takes place on the oxide supports. Also in-situ XPS revealed differences in the chemistry of iron catalyst during growth and these differences were attributed to substrate interactions between alumina and iron. Finally, in-situ XPS analysis showed no evidence of carbides or oxides acting as a catalyst during the nucleation process. Advisors/Committee Members: Murray, Paul T.

▼ The objective of this research is to determine the ability of several Non-Destructive Inspection (NDI) methods to detect various levels of High Cycle Fatigue fretting fatigue damage induced in simulated Ti-6Al-4V dovetail engine components. To generate various levels of fretting fatigue damage; a specially designed dovetail specimen is utilized which more accuracy simulates the cyclic loading interaction between a compressor blade and disk of an aircraft turbine engine. All fretting fatigue tests were conducted with un-coated Ti-6Al-4V alloy at ambient temperature, at a load ratio of 0.1, and two 30 Hz cyclic load levels (10% and 30% of expected life). In addition, two microstructures (α+β, β-annealed) are utilized to determine their effect on fretting fatigue as well as the NDI signal response. To quantify the extent of fretting fatigue damage; mini-C specimens are extracted from the fretted dovetail specimens and “step-tested” to quantify the debit in fatigue strength. Specimens are heat-tinted after fretting fatigue to help qualify the extent of fretting fatigue damage and aid in crack initiation site identification using both optical microscope and the Scanning Electron Microscope (SEM). Three NDI techniques are used to qualify the extent of fretting fatigue damage in Ti-6Al-4V and relate this damage to the NDI signal response and the debit in fatigue strength. The NDI techniques utilized in this research include: White Light Interference Microscopy (WLIM), Wyle Lab Eddy Current Inspection System (ECIS) and the JENTEK Meandering Winding Magnetometer (MWM) Array. Note: these NDI techniques are used “as is” and were not modified for fretting fatigue detection. However, in the case of the WLIM, a fretting fatigue damage parameter methodology is utilized to specifically quantify the extent of fretting damage. In addition, the Scanning Electron Microscope (SEM), Auger Electron Spectroscopy (AES), and Knoop micro-hardness tester were utilized to investigate the compacted fretting fatigue layer beneath the fretting fatigue scar and determine the existence of either a tribologolically transformed structure (TTS) or hard alpha case (HAC). In general, all three NDI techniques were able to detect various degrees of fretting fatigue damage (i.e., fretting fatigue cracks). However, as fretting fatigue cycles increased, the white light surface measurement technique's ability to discern higher levels of crack damage is suppressed by the modification of the contact fretting surface features (i.e., particle compaction with reduced asperity heights with nano sized contact debris) to include debris filled pits and cracks that help promote the loss of surface fidelity. The WLIM damage parameter and elements of the JENTEK MWM signal did correlate with the Mode I Newman-Raju stress intensity factor. However, the detection of fretting fatigue damage beyond fretting fatigue cracking was not attempted and would require special calibration specimens of a specific damage type (i.e., TTS, HAC, multiple co-linear cracking or perpendicular, slanted or zig-zag cracking, or corrosion effects) to correlate the NDI signal response to that damage. Advisors/Committee Members: Eylon, Dr. Daniel.

▼ Mercury (Hg) transformation under homogeneous (gas-phase oxidation reactions primarily involving chlorine species in flue gases) and heterogeneous (gas-surface oxidation reactions involving surface enhanced Hg oxidation in the presence of flue gases) environments were investigated. Gas phase experiments were performed in the presence of chlorine sources such as Cl2 and HCl. A large body of literature studies indicates that during combustion in coal-fired power plants coal mineral matter components play a major role in Hg transformation. Surface activity of these components with respect to Hg adsorption and overall Hg removal were evaluated using a laboratory-scale, fixed bed flow reactor where initial Hg concentration, temperature, residence time, gas composition, and the metal oxide surface were carefully controlled. The metal oxides of interest were γ-Fe2O3, TiO2, Al2O3, and CaO. These catalytic materials were immobilized between quartz wool in a quartz flow reactor. Homogeneous experiments with different gas compositions, different chlorine sources (HCl or Cl2), and gas-phase residence times of 1 and 2 sec showed no measurable difference in Hg oxidation except at 100°C. Hg removal (oxidation) efficiencies ranged from 2 to 15%. Heterogeneous studies in the presence of metal oxides (with Cl2 and HCl as the chlorine source) indicated that γ-iron oxide showed the highest Hg removal efficiency at 1 sec residence time, compared to other metal oxides under the same experimental conditions. However, the data were highly scattered and occasionally showed inconsistency. A reduction in the surface activity of γ-iron oxide due to aging may have been responsible for the inconsistency in some of the results. TiO2, used in the presence of Cl2 at 100°C, resulted in a 60% Hg removal efficiency which decreased with increasing temperature. TiO2 used in the presence of HCl resulted in a 55% Hg removal efficiency at 400°C. Al2O3 and CaO were ineffective with regard to Hg oxidation in the presence of Cl2 or HCl compared to γ-iron oxide and TiO2. Adsorption and overall Hg removal efficiencies showed the following trend (in descending order of effectiveness): γ- Fe2O3 > TiO2 > Al2O3 > CaO. Advisors/Committee Members: Yamada, Takahiro.

▼ Silicon nitride and WC-Co cermet tools are used for metal forming processes including extrusion and drawing. These materials are used to make tool dies which are exposed to deformation caused by friction and wear. Surface treatments such as ion implantation, laser blazing and coating have been found to improve surface properties, to optimize tribological behavior between the metal and die, as well as to extend service life of the tool dies. Early detection and continuous monitoring processes by non destructive testing (NDT) methods are needed in order to ensure the functionality of the wear process and extend the tool service life. Acoustic emission is one of the promising NDT methods for this application. The surface treatment chosen for this investigation was ion implantation. Three types of wear resistant materials with and without surface treatment were selected for this project; silicon nitride and two tungsten carbides (6% Cobalt and 10% Cobalt). This investigation was conducted using a pin-on-disk device for wear/friction tests of the selected materials with lubrication and/or without lubrication against both a stainless steel disk and an aluminum disk. The acoustic emissions generated during the experiments were recorded and analyzed. The results of this investigation showed that the ion implantation improved the tribological properties of the materials and reduced acoustic emission and coefficient of friction. A linear relationship between the average amplitude of the acoustic emission and the coefficient of friction of the tested materials was found. The investigation demonstrated that the acoustic emission method could be used to monitor the wear/friction processes. Advisors/Committee Members: Meyendorf, Norbert.

▼ Cholesteric liquid crystals (CLCs) are chiral-structured materials that exhibit selective reflection color. While methods to switch off this color with external stimuli have been established, the use of external stimuli to change the reflection color is currently under development. This work explores processing-structure-property relationships of a polymer-templated CLC system that exhibits large-scale reflection color changes with temperature. The effects of heating rate, curing intensity, and cell geometry on the magnitude of these color changes were investigated by collecting transmission spectra of the system during heating and cooling. The system exhibited a constant color change of 500-600 nm at heating rates up to 10°C/min. Samples cured at intensities below 1.00 mW/cm² displayed larger color changes. The cell geometry was largely unaffected by the cell thickness. However, for cell thicknesses between 10 and 50 μm, as cell thickness increased, the magnitude of the color change decreased. The potential impact of attaching, or "tethering," the chiral-structured polymer/liquid crystal gel to the cell surface was also considered. Both tethered and untethered systems displayed large-scale color changes with temperature. Advisors/Committee Members: Browning, Charles E.

▼ This study explored the use of a high energy electron beam as the only available technique for selective area surface modification of carbon nanofibers through controlled parameters such as radiation dose, sample temperature, and environment. The application of this variable space led to the production of unique morphological features on the nanofiber surfaces. Several analytical techniques were used to establish the mechanism for these surface modifications, including microscopy, spectroscopy, thermal analysis, and gas adsorption. Depending on the exposure parameters, a nanofiber surface rich with some or all of the following was created: i) free radicals, ii) chemisorbed or physisorbed functional groups, iii) surface roughness from peeling and recombination of graphene layers, and iv) activated carbon surface with nano to meso porosity. The demonstrated consequences of these selective modifications were improved dispersion of the nanofibers in liquid and good bonding with epoxy. Ultimately this process will give the user custom control over the surface interaction of carbon nanofibers with other media such as liquids, polymer resins, gas probes, etc. Advisors/Committee Members: Klosterman, Donald.

▼ While polymer based materials oer many benecial properties, they are inherently susceptible to environmental degradation over time. This type of degradation, especially for thermal oxidative aging, occurs predominantly within a thin surface layer often less than 200 μm thick. A nondestructive technique for characterizing this layer has been developed that uses high resolution laser detection of displacements generated by a surface traveling ultrasonic Rayleigh wave. This research evaluates the potential of the technique to quantify the degree and depth of surface degradation caused by thermal aging. Rayleigh surface waves are useful because the measurement parameters depend directly on the mechanical properties of the degraded material, and the frequency of operation determines the ultrasonic depth of penetration. The measurements show sensitivity to polymeric thermal degradation, and feasibility is demonstrated for measuring surface layer depth with a frequency sweep. This research establishes the fundamental relationships between the developed ultrasonic procedures and its potential applications to thermal oxidative polymeric aging through finite element simulation, a representative aging experiment, and appropriate data analyses. Advisors/Committee Members: Brockman, Robert A.

▼ The objective of this study was to improve the accuracy and reliability of nondestructive case depth determination from the current state of the art for application in an industrial environment. In the current state of the art only a single test method is used. In the present study simultaneous measurements were made with four independent electromagnetic test methods. The test methods used were measurement of tangential component of the magnetizing field, magnetic Barkhausen noise analysis, incremental permeability and multi-frequency eddy current measurement. The methods have different penetration depth and sensitivity to microstructure variations, thus complementing each other. The method that measures the tangential component of the magnetizing field is the only method that has a sufficiently deep depth of penetration to be useful for case depth testing. However, measurements with this method can be distorted by material variations other than the case depth. This distortion can be corrected by combining the measurement of the tangential component of the magnetizing field with a method that is mainly sensitive to the distorting effect. Such distorting effects can for example be a thin martensite layer on top of the case or a different quench oil temperature. From the 4 test methods used here 41 parameters were derived that describe the measurement signals. Multiple regression methods were used to select the most suitable parameters and build models from them. This procedure is called calibration. A separate calibration has to be performed for each different material. Models were built and the case depth testing accuracy was evaluated at 2 case hardened specimen groups. For one group the average case depth test error was in a range of ±15µm. For another group the average test error was in a range of ±100µm for case depths ranging from 1 – 2.5mm. The results of the study show that the case depth testing accuracy and robustness could be improved by combining several independent electromagnetic test methods, thus providing industry with an effective quality control method for fast and reliable quality assurance. Advisors/Committee Members: Eylon, Daniel.

▼ A novel multi-element nanoparticle synthesis technique, noted pixel target ablation (PTA) is reported here. In the experiments described here, Iron-Nickel pixel targets were prepared on a transparent disc by sputtering and by photolithography. By irradiating the target materials from the backside, the laser energy breaks the target materials into metal atoms, which then forms nanoparticles by recombination in the gas phase. The nanoparticles were subsequently captured by a substrate. The degree of interaction between the two metals species and the plume dynamics of this method were examined. The average composition and size distribution of synthesized nanoparticles were studied using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) respectively. The results show that this process has congruent transformation of target materials weight ratio to particle composition, and controllable particle size distribution with no agglomeration. Additionally, the structure of the particles was determined by the use of X-ray diffraction (XRD). Samples were prepared by ablation in vacuum and in the presence of a background gas. A mixture of single-metallic and alloyed nanoparticles were collected. The implications of these observations for multi-element nanoparticle synthesis are discussed. Advisors/Committee Members: Murray, Paul.

▼ While open-circuit magnetic measurements are noted to involve distortions related to the image effect and, most significantly, the sample's demagnetizing factor, closed-circuit measurements are generally considered to be free of these distortions. However, it has been reported and observed within this research that for certain sample geometries and materials operating near the magnetic saturation of the electromagnet poles, there are observed distortions of up to 40.7% of the maximum magnetization at a field level of 25 kiloOersteds for a cylindrical sample with an L/D ratio of 0.2. This observed distortion in the magnetic measurement in a closed-circuit has been referred to in the literature as an “apparent image effect” error. The intent of this research is to apply finite element modeling (FEM) to replicate original experimental and published data for cylindrical samples of both hard and soft magnetic material and to observe the phenomenology of the error within the results of the model. The hard magnetic material of interest is NdFeB and the soft magnetic material used is 1018 steel. Additionally, the sample data base is extended to rectangular prisms with data generated both experimentally and with FEM. Using a validated model it is possible to develop a corrective methodology and equations to address the magnetization measurement errors noted at high field levels within both the first and third quadrants of the hysteresis curve. The methodology developed through this research produced corrective surfaces with two dimensional polynomial fits with average adjusted R-values of 0.97. As a fault study secondary to the development of the corrective methodology, this project investigated the significance of the sample's surface mating to the poles of the hysteresigraph. It was determined that a 5 ° partial misalignment air gap has only approximately 0.5% variation in magnetization, 4πMmax, from the baseline of an ungapped sample. It is indicated that the sample gap becomes statistically significant at the t-test risk level of α = 0.05 significance level at approximately a 14 ° gap. The successful use of FEM in determining the closed circuit corrective methodology has led to the identification of the potential for a similar open circuit application. The calculation of the demagnetizing factor, N, required for open circuit measurements is a difficult exercise and, in the past, could only be precisely calculated for an ellipsoidal sample. For other regular geometries N was determined experimentally or calculated using certain assumptions. Either method introduces errors. This application used FEM to calculate the spherical demagnetizing factor of a magnetic sphere within a long solenoid. The FEM results indicated a demagnetizing factor N = 0.333 in all three axis. This result is in agreement with widely published and accepted results for such an arrangement. The hysteresis distortion complicates identifying and developing new magnetic materials. Only a comprehensive understanding of the phenomenon can help to establish effective correction methods, which is important for infrastructure enhancement in scientific research and for development of advanced modern technology to accurately characterize new magnetic materials. Advisors/Committee Members: Kramer, Daniel P.

▼ This study offers an remarkable example of the ability to synthesize and tune the reactivity of Aluminum nanoparticles. Sonochemical synthesis combined with the application of the particle coating process in situ offers not only the way to stabilize the nano-sized Al but also the capability to alter physical and chemical properties of the material. It was observed in this study that the capping agent can affect nanoparticle formation and control parameters such as morphology and composition of the resulting nanoparticles, while certain agents offer the ability to control size via the concentration. Although no universal standards for measuring stability have been established to date, the sonochemically produced particles demonstrated no major physical and chemical changes when exposed to a variety of solvents for an extended period of time, but completely decomposed in water. This has led to the new, unexplored in the past, properties of catalyzing the hydrogen production from water without the need for any reaction promoters or external energy. In conclusion, the particles studied in this research project were shown to have unusual properties, dictated by their unique structure, with enhanced stability and new catalytic behavior. The results reported in this thesis are believed to contribute to the progress of incorporating nanoscale additives into energetic formulations and advance the overall knowledge in the field of nanoenergetic materials. Further studies will help elucidate mechanisms of particle formation and potentially lead to the development of novel advanced processes and applications on the nanoscale. Advisors/Committee Members: Guliants, Elena A.

▼ Composite structural joints, as observed throughout the natural world, have been systematically altered and proven via lengthy evolutionary processes. Biological fixed joints tend to exhibit unique attributes, including highly optimized fiber paths to minimize stress concentrations. In addition, since the joints consist of continuous, uncut fiber flow patterns, the joint does not inhibit the biological organism in the transportation of information, chemicals and food from one part of the body to the other. To the contrary, large sections of man-made composite material structures are often joined using bolted or bonded joints, which involve low strength and high stress concentrations. These methods are also expensive to achieve. Additional functions such as fluid transport, electrical signal delivery, and electrical and thermal conductivity across the joints typically require parasitic tubes, wires, and clips. By using the biomimetic methods, we seek to overcome the limitations which are present in the conventional methods. In the present work, biomimetic co-cured composite sandwich T-joints were constructed using unidirectional glass fiber, epoxy resin, and structural foam. The joints were fabricated using the wet lay-up vacuum bag resin infusion method. Foam sandwich T-joints with multiple continuous fiber architectures and sandwich foam thickness were prepared. The various joint designs were tested quasi-statically in bending of the T in a calibrated screw-driven load frame. Custom, purpose-designed fixtures were required to support the base of the joint during the bending load. The weight savings using the biomimetic approaches is discussed, as well as a comparison of failure modes versus fiber/core architectures is given. In addition to developing structurally optimized, weight-efficient joints, a tremendous ancillary benefit to the approach is the ability to easily embed wires and micro tubes contiguous across the joined elements. This approach is key to achieving true robust structural multi-functionality. Advisors/Committee Members: Donaldson, Steven.

▼ Dwell loaded components are common in the turbine engine section of gas turbine engines. The turbine components are subjected to high stresses and high loads for up to 2 min during a pilots take-off, cruise and landing. Understanding the mechanisms of crack initiation while the turbine components are subjected to dwell loading is essential for fatigue life predictions. Previously conducted research includes the fatigue testing and life prediction of dwell specimens with an evenly distributed stress that is representative of a smooth location on the turbine disk. However, turbine disks have notches and fillets that change the stress concentration. This thesis utilizes the techniques and testing strategies that have been successful in predicting fatigue life in smooth bar dwell specimens and applies them to dwell notched specimens that are more representative of actual fielded components. The notch fatigue study indicates that the minimum fatigue life prediction method is applicable for various geometries and therefore, its applicability to actual fielded components holds reasonable promise. Advisors/Committee Members: Browning, Charles.

▼ A laser-based nanoparticle synthesis technique, noted through thin film ablation (TTFA), is reported here. In this process, the laser beam strikes the target from the back side and then vaporizes the target material into metal atoms, which then recombine and form nanoparticles. The nanoparticles were captured by a substrate afterwards. In this paper, copper and nickel thin film prepared on a transparent silica disc by sputtering were used as targets. Nanoparticle samples were prepared by ablation in vacuum and in the presence of an inert background gas. The plume dynamics of TTFA method were examined and the nanoparticles were characterized by transmission electron microscopy (TEM). The result shows no evidence of the anomalous large size (micrometer-sized) particles that are typically seen by conventional laser deposition. The TTFA method has the potential for fabricating a wide variety of metallic nanoparticles and nanocomposites. This report provides a deeper comprehension of the TTFA technique. Advisors/Committee Members: Murray, P. Terrence.

▼ The interface between carbon fibers (CFs) and the resin matrix in traditional high performance composites is characterized by a large discontinuity in mechanical, electrical, and thermal properties which can cause inefficient energy transfer. Due to the exceptional properties of carbon nanotubes (CNTs), their growth at the surface of carbon fibers is a promising approach to controlling interfacial interactions and achieving the enhanced bulk properties. However, the reactive conditions used to grow carbon nanotubes also have the potential to introduce defects that can degrade the mechanical properties of the carbon fiber (CF) substrate. In this study, using thermal chemical vapor deposition (CVD) method, high density multi-wall carbon nanotubes have been successfully synthesized directly on PAN-based CF surface without significantly compromising tensile properties. The influence of CVD growth conditions on the single CF tensile properties and carbon nanotube (CNT) morphology was investigated. The experimental results revealed that under high temperature growth conditions, the tensile strength of CF was greatly decreased at the beginning of CNT growth process with the largest decrease observed for sized CFs. However, the tensile strength of unsized CFs with CNT was approximately the same as the initial CF at lower growth temperature. The interfacial shear strength of CNT coated CF (CNT/CF) in epoxy was studied by means of the single-fiber fragmentation test. Results of the test indicate an improvement in interfacial shear strength with the addition of a CNT coating. This improvement can most likely be attributed to an increase in the interphase yield strength as well as an improvement in interfacial adhesion due to the presence of the nanotubes. CNT/CF also offers promise as stress and strain sensors in CF reinforced composite materials. This study investigates fundamental mechanical and electrical properties of CNT/CF using nanoindentation method by designed localized transverse compression at low loads (μN to mN) and small displacements (nm to a few μm). Force, strain, stiffness, and electrical resistance were monitored simultaneously during compression experiments. The results showed that CNT/CF possess a high sensing capability between force and resistance. Hysteresis in both force-displacement and resistance-displacement curves was observed with CNT/CF, but was more evident as maximum strain increased and did not depend on strain rate. Force was higher and resistance was lower during compression as compared to decompression. A model is proposed to explain hysteresis where van der Waals forces between deformed and entangled nanotubes hinder decompression of some of the compressed tubes that are in contact with each other. This study provides a new understanding of the mechanical and electrical behavior of CNT/CF that will facilitate usage as stress and strain sensors in both stand-alone and composite materials applications. A novel method for in situ observation of nano-micro scale CNT/CF mechanical behavior by SEM has been developed in this study. The results indicated that deformation of vertical aligned CNT (VACNT) forest followed a column-like bending mechanism under localized radial (axial) compression. No fracture was observed even at very high compression strain on a VACNT forest. In order to fully understand CNT forest properties, the viscous creep behavior of VACNT arrays grown on flat Si substrate has also been characterized using a nanoindentation method. Resulting creep response was observed to consist of a short transient stage and a steady state stage in which the rate of displacement was constant. The strain rate sensitivity depended on the density of the nanotube arrays, but it was independent of the ramping (compression) rate of the indenter. Advisors/Committee Members: Dai, Liming.