| Título: | Theory and simulation of texture formation in mesophase carbon fibers |
| Autores: | Yan, Jun, 1974- |
| Fecha: | 2001 |
| Publicador: | McGill University - MCGILL |
| Fuente: |
 |
| Tipo: | Electronic Thesis or Dissertation |
| Tema: | Engineering, Chemical. |
| Descripción: | Carbonaceous mesophases are discotic nematic liquid crystals that are spun into high performance carbon fibers using the melt spinning process. The spinning process produces a wide range of fiber textures and cross-sectional shapes. The circular planar polar (PP), circular planar radial (PR), ribbon planar radial (RPR), and ribbon planar line (RPL) textures are the most frequently observed in industrial fiber making. This thesis presents, solves, and validates models of mesophase fiber texture formation based on the classical Landau-de Gennes theory of liquid crystals, adapted here to carbonaceous mesophases. The model captures the microstructure and the formation of the four (PP, PR, RPR, RPL) textures. In cylindrical fibers, the computed PP and PR textures phase diagram, given in terms of temperature and fiber radius, establishes the processing conditions and geometric factors that lead to the selection of these textures. The influence of elastic anisotropy to the textures' formation and structure is thoroughly characterized. The multi-stage formation process of the PP texture is reproduced, including defect nucleation, defect migration, and overall texture geometry. The mechanisms that control the PP texture geometry are characterized using analytical methods. The role of elasticity and flow-induced orientation on texture selection mechanism in ribbon-shaped mesophase fibers are characterized using an anisotropic viscoelastic model. The model is able to predict the formation of the commonly observed line defect in the RPL texture, and the fine structure of the line is reproduced and explained in terms of classical liquid crystal defect physics. The results of this thesis provide new knowledge on how to optimize and control mesophase fiber textures. |
| Idioma: | en |
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