The objective of this study is to investigate the relationship among process, structure, and property of the UTSI pitch-based carbon fibers and optimize carbon fiber’s mechanical properties through the stabilization process. Various analysis techniques were employed throughout these investigations which include the Scanning Electron Microscope (SEM), optical microscope, Dia-stron system, MTS, and ImageJ. Several fiber process techniques including fiber spinning, stabilization, and carbonization were explored to determine the effect of the thermal process on the fiber yield, fiber diameter, the sheath-core structure of stabilized fibers, the pac-man and hollow core structures of carbonized fibers, and the resulting mechanical properties of the carbon fibers. It was found that stabilization time and the temperature stepping had a great deal on influence on the resulting carbon fibers. Larger diameter fiber is easy to form sheath-core structure in the stabilization process. Pac-man structure was developed at 600°C during the carbonization. Both stabilization duration and the carbonization temperature control the resulting carbon fiber diameter and fiber structure defects such as the pac-man and hollow core defects. Multi-step stabilization can reduce the total stabilization duration and improve the mechanical properties of the resulting carbon fibers. Fiber structure non-uniformities including fiber diameter distributions for a bundle fiber or along a single fiber, and pac-man angles were determined. Statistical analysis revealed the distribution of the carbon fiber cross-sectional areas and the result is compared against commercial available carbon fibers. Carbon fiber sandwiched composites (CFSCs) were fabricated with UTSI carbon fiber and commercial PAN-based carbon fibers. Several configurations of sandwich structured composites were explored to test the flexural properties with varying sandwich thickness.

The moisture absorption behavior of Zylon fibers was characterized in various high temperature and high humidity conditions in a controlled environment. The results of these thermal cycling tests show that PBO fibers not only absorb, but also retain moisture (approximately 0.5-3%) when exposed to elevated temperature and humidity cycles. Also, the impurities of Zylon fibers were characterized through the use of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and solid state Nuclear Magnetic Resonance (NMR). These tests demonstrated that, in addition to other impurities, PBO fibers may contain up to 0.55 weight percent phosphorus, and that this phosphorus is present in the form of phosphoric acid. It was also shown through accelerated hydrolytic degradation tests that production procedures used to neutralize the acid present in the fibers have a beneficial effect on the hydrolytic performance of the fiber. The data collected in this study was then compared and contrasted to known Kevlar studies, identifying similarities, differences, and potential trends. The results of these tests seem to indicate that there is accelerated acid catalyzed hydrolysis occurring in the fiber which is causing these fibers to degrade at an increased rate. This condition is further accelerated by heat and humidity induced permanent fiber swelling.

Conventional stainless steel - water and ceramic fabric composite water heat pipes have been built and tested. The tests have been conducted to compare the performance characteristics between conventional and fabric composite heat pipe radiators for space nuclear power heat rejection systems. The fabric composite concept combines a strong ceramic fabric with a thin metal liner to form a very lightweight heat pipe. The heat pipes tested have used identical, homogeneous fabric wicks and water as the working fluid. One fabric composite heat pipe has been constructed by fitting a braided aluminoborosilicate fabric tube over the outside of the conventional stainless steel heat pipe. A more advanced fabric composite design combines the woven fabric with a 0.25 mm (10 mil) stainless steel tube as the liner, and reduces the mass of the heat pipe by a factor of three. A heat pipe testing facility was designed and built for the purpose of testing various conventional and fabric composite heat pipes. This facility allows the testing of heat pipes in a vacuum, at low temperatures, and can accommodate a variety of heat pipe designs. Instrumentation and computer interfacing provide for continuous monitoring and evaluation of heat pipe performance. Tests show that heat pipe radiator capacity can be significantly enhanced by using the fabric composite design. Tests comparing a conventional heat pipe with fabric composite heat pipes achieved a 100% increase in the emissivity and heat rejection capacity of the radiator. Since the ceramic fabric is strong enough to withstand the internal pressure of the heat pipe, a very thin metal foil can be used to contain the working fluid. The increase in heat rejection capacity, combined with the significant reduction in the heat pipe mass, translates into a substantial savings for space power systems employing fabric composite heat pipe radiators. / Graduation date: 1993

This thesis concerns polarization mode dispersion (PMD) in optical fiber communications. Specifically, we study fiber birefringence, PMD stochastic properties, PMD mitigation and the interaction of fiber birefringence and fiber nonlinearity. Fiber birefringence is the physical origin of polarization mode dispersion. Current models of birefringence in optical fibers assume that the birefringence vector varies randomly either in orientation with a fixed magnitude or simultaneously in both magnitude and direction. These models are applicable only to certain birefringence profiles. For a broader range of birefringence profiles, we propose and investigate four general models in which the stochastically varying amplitude is restricted to a limited range. In addition, mathematical algorithms are introduced for the numerical implementation of these models. To investigate polarization mode dispersion, we first apply these models to single mode fibers. In particular, two existing models and our four more general models are employed for the evolution of optical fiber birefringence with longitudinal distance to analyze, both theoretically and numerically, the behavior of the polarization mode dispersion. We find that while the probability distribution function of the differential group delay (DGD) varies along the fiber length as in existing models, the dependence of the mean DGD on fiber length differs noticeably from earlier predictions. Fiber spinning reduces polarization mode dispersion effects in optical fibers. Since relatively few studies have been performed of the dependence of the reduction factor on the strength of random background birefringence fluctuations, we here apply a general birefringence model to sinusoidal spun fibers. We find that while, as expected, the phase matching condition is not affected by random perturbations, the degree of PMD reduction as well as the probability distribution function of the DGD are both influenced by the random components of the birefringence. Together with other researchers, I have also examined a series of experimentally realizable procedures to compensate for PMD in optical fiber systems. This work demonstrates that a symmetric ordering of compensator elements combined with Taylor and Chebyshev approximations to the transfer matrix for the light polarization in optical fibers can significantly widen the compensation bandwidth. In the last part of the thesis, we applied the Manakov-PMD equation and a general model of fiber birefringence to investigate pulse distortion induced by the interaction of fiber birefringence and fiber nonlinearity. We find that the effect of nonlinearity on the pulse distortion differs markedly with the birefringence profile.

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