Theses and Dissertations - Department of Physics & Astronomy

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Browsing Theses and Dissertations - Department of Physics & Astronomy by Author "Barkey, Mark E."

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    Production, modification, and characterization of natural bamboo fiber
    (University of Alabama Libraries, 2019) Rocky, AMK Bahrum Prang; Thompson, Amanda J.; University of Alabama Tuscaloosa
    In an effort to extract natural bamboo fiber (NBF) from bamboo for textiles and other uses, four bamboo species Bissetii, Giant Gray, Moso, and Red Margin were chosen for investigation. Conventional fibers such as cotton, polyester, regular rayon, and 12 commercial bamboo viscose were included for comparative study. By using different chemicals and routes, 144 types of NBFs were produced. Assessments on fiber yield percentages (40-77%), average lengths (1.50-37.10 cm), fineness (9.68—93.3 Tex), and overall qualities, determined at least 47 sets were prospective for commercial use. Hand-spinning was executed on three sets of NBFs after blending with cotton fibers. Investigation on moisture regain (M_R) and moisture content (M_C), revealed that bamboo plants and NBFs had M_R=8.0% and M_R=7.5% which was lower than rayon and bamboo viscose fiber (~11% and ~10%) but higher than raw cotton fibers (~5.7% and 5.4%). Among tensile properties, breaking tenacity of longer NBFs (33-37 cm) was 64-140 N/Tex and elongation at break was 2.0-2.5%; these values were 1.50-2.50 N/Tex and 8.0-11.0% respectively for blended yarns. Elemental, chemical, and crystallographic investigations were accomplished by energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), ATR-FTIR (Attenuated Total Reflectance Fourier Transform Infra-Red), Raman spectroscopy (RS) and X-ray diffraction (XRD) techniques. Bamboo plants were estimated to be 70-78% carbon (C) and 20-30% oxygen (O) atoms, and O/C ratio of 0.26-0.33. The NBFs had a higher O/C ratio of 0.58-0.70. Comparisons of the spectra revealed the differences between bamboo-NBF and other fibers. Some distinct lignocellulosic peaks were in NBFs that could be responsible for unique properties. The crystallinity index (CI) of bamboo plants was 63-67% but CI of NBFs was higher 69-73% with crystallite sizes of 35-39 Å (3.5-3.9 nm). Four reflection planes and other properties are also documented. A suitable antibacterial test method was modified for quantitative estimation of bacterial reduction. Results suggest that though 11 out of 12 bamboo viscose products failed to exhibit inhibition against the bacteria, most of the bamboo and NBF specimens successfully showed a bacterial reduction of 8-95% against Klebsiella pneumoniae and 3-50% against Staphylococcus aureus.
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    Structure-property relationships of solid state additive manufactured aluminum alloy 2219 and inconel 625
    (University of Alabama Libraries, 2017) Rivera Almeyda, Oscar Gabriel; Allison, Paul Galon; University of Alabama Tuscaloosa
    In this investigation, the processing-structure-property relations are correlated for solid state additively manufactured (SSAM) Inconel 625 (IN 625) and a SSAM aluminum alloy 2219 (AA2219). This is the first research of these materials processed by a new SSAM method called additive friction stir (AFS). The AFS process results in a refined grain structure by extruding solid rod through a rotating tool generating heat and severe plastic deformation. In the case of the AFS IN625, the IN625 alloy is known for exhibiting oxidation resistance and temperature mechanical stability, including strength and ductility. This study is the first to investigate the beneficial grain refinement and densification produced by AFS in IN625 that results in advantageous mechanical properties (YS, UTS, εf) at both quasi-static and high strain rate. Electron Backscatter Diffraction (EBSD) observed dynamic recrystallization and grain refinement during the layer deposition in the AFS specimens, where the results identified fine equiaxed grain structures formed by dynamic recrystallization (DRX) with even finer grain structures forming at the layer interfaces. The EBSD quantified grains as fine as 0.27 microns in these interface regions while the average grain size was approximately 1 micron. Additionally, this is the first study to report on the strain rate dependence of AFS IN625 through quasi-static (QS) (0.001/s) and high strain rate (HR) (1500/s) tensile experiments using a servo hydraulic frame and a direct tension-Kolsky bar, respectively, which captured both yield and ultimate tensile strengths increasing as strain rate increased. Fractography performed on specimens showed a ductile fracture surface on both QS, and HR. Alternatively, the other AFS material system investigated in this study, AA2219, is mostly used for aerospace applications, specifically for rocket fuel tanks. EBSD was performed in the cross-section of the AA2219, also exhibiting DRX with equiaxed microstructure in the three directions and an average grain size of 2.5 microns. EBSD PFs showed that the material has a strong torsional fiber A texture in the top of the build, and this texture gets weaker in the middle and bottom sections. TEM showed that there are no ’ precipitates in the as-deposited cross-section, therefore no precipitation strengthening should be expected. Strain rate and stress state dependence was study, and in both tension and compression, with an increase in strain rate, the YS increase and the UTS decreased. Ductile fracture surface was observed on specimens tested to failure in both QS and HR. The AFS AA2219 processing-structure-property relations are being studied in this investigation to address the stress-state and strain rate dependence of AFS AA2219 with an internal sate variable (ISV) plasticity-damage model to capture the different yield stress, work hardening and failure strain in the AFS AA2219 for high fidelity modeling of AFS components. The ISV plasticity model successfully captured the material behavior in tension, compression, tension-followed-by-compression and compression-followed-by-tension experiments. Furthermore, the damage parameters of the model were calibrated using the final void density measured from the fracture surfaces.