High density polyethylene (HDPE) films having simple and well-defined stacked lamellar morphology, either with or without a distinct presence of row-nucleated fibril structures, have been utilized as <i>model</i> materials to carry out investigations on solid state structure-property relationships. Four different subjects that were addressed are: 1) mechanical properties and deformation morphologies, 2) orientation anisotropy of the dynamic mechanical α relaxation, 3) orientation dependence of creep behavior, and 4) crystalline lamellar thickness and its distribution. For the first three topics, appropriate mechanical tests, including tensile (INSTRON), creep (TMA), and dynamic mechanical (DMTA) tests, were performed at <i>different angles with respect to the original machine direction (MD)</i> of the melt extruded films; morphological changes as a result of these mechanical tests were detected by WAXS, SAXS, and TEM. For the forth topic, crystalline lamellar thickness and its distribution were determined by DSC, SAXS, TEM and AFM experiments. In the <i>large strain deformation</i> study (chapter 4.0), samples were stretched at 00°, 45° and 90° angles with respect to the original MD. A distinct orientation dependence of the tensile behavior was observed and <i>correlated</i> to the corresponding deformation modes and morphological changes, namely 1) lamellar separation and fragmentation by chain slip for the 00° stretch, 2) lamellar break-up via chain pull-out for the 90° stretch, and 3) lamellar shear, rotation and break-up through chain slip and/or tilt for the 45° stretch. A strong strengthening effect was observed for samples with row-nucleated fibril structures at the 00° stretch; whereas for the 90° stretch, the presence of such structures significantly limited deformability of the samples. In the <i>dynamic strain mechanical α relaxation</i> study (chapter 5.0), samples were tested at nine different angles with respect to the original MD, and the morphologies of samples <i>before</i> and </i>after</i> the dynamic tests were also investigated. The mechanical dispersions for the 00° and 90° tests were believed to arise essentially from the crystalline phase, and they contain contributions from two earlier recognized sub-relaxations of α_I and α_II. While for the 45° test, in addition to a high temperature α_II relaxation, a interlamellar shear induced low temperature mechanical relaxation was also observed. It is concluded that the low temperature relaxation is related to the characteristics of the interface between the crystalline lamellae and amorphous layers. In the <i>small strain creep</i> study (chapter 6.0), samples were tested at the 00°, 45° and 90° angles at the original MD. Both creep strain and creep rate for samples at the three angles were very different. An Eyring-rate model was utilized to analysis the observed creep behavior, and structural parameters associated with this model, including population of creep sites, activation energy and volume, were obtained by fitting the experimental data to the Eyring-rate equation. It was concluded that the plateau creep rate in these model materials is primarily controlled by the density and physical state of tie-chains in the amorphous phase. For the lamellar thickness and distribution study, DSC, SAXS, TEM and AFM experiments were conducted for samples having a well-defined stacked lamellar morphology. It was found that the most probable lamellar thickness from SAXS and TEM agreed very well; however, these values did not match with those obtained by DSC and AFM. It was pointed out that the use of DSC to determine lamellar thickness and distribution is so sensitive to heating rate and numerical values for the parameters in the Gibbs-Thomson equation that it is not believed to be suitable for quantitative analysis. / Ph. D.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第17904号 / 農博第2027号 / 新制||農||1018(附属図書館) / 学位論文||H25||N4800(農学部図書室) / 30724 / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 杉山 淳司, 教授 矢野 浩之, 教授 髙部 圭司 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

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Thermal-resistant coatings, based on polysilazane and polysiloxane polymers, were applied onto the glass fiber rovings with the dip-coating method. The coated glass fibers were characterized by performing different experiments to evaluate the effect of coatings on thermomechanical and topographical properties of glass fiber. The effect of temperature on the mechanical properties of the coated rovings were studied and compared with the uncoated rovings. Thermogravimetric analysis was carried out to investigate the thermal stability of coated samples. Scanning electron microscopy and energy-dispersive X-ray analyses were performed to evaluate the surface topographical characteristics of the glass fiber rovings. These analyses showed the changes in surface morphological properties due to modification of glass fiber by coating treatment. The results of tensile testing indicated that thermal-resistant coatings enhanced up to 60% tensile strength and 20% stiffness of uncoated glass fiber roving. Thermomechanical study up to 500°C revealed that polysiloxane coating on glass fiber showed better performance than polysilazane polymeric coating.

Ce travail de thèse porte sur l’extraction et la caractérisation mécanique des fibres de canne à sucre. A partir de la bagasse de canne à sucre, résidu fibreux de l’industrie sucrière, des techniques d’extractions sont mises en place afin d’extraire des fibres techniques, dont l’analyse des propriétés chimiques et physico-mécaniques définira par la suite, les domaines d’application textile possibles. Les fibres de canne obtenues ont d’abord été étudiées d’un point de vue physique et morphologique, à partir de mesures et d’observations de leurs sections et de leurs profils. Ainsi, l’analyse de la distribution en diamètre et en longueur des fibres ont été étudiés avec l’établissement de paramètres de centrage barbe et hauteur (longueur pondérée à la masse), ont permis de déterminer leurs tailles moyennes, leurs finesses et leurs dispersions tout en vérifiant l’effet des conditions de traitement. Ont ainsi été obtenus différents types de fibres, présentant des propriétés mécaniques (en flexion et en traction) variées en relation avec les changements de structure dus à l’extraction. Les performances mécaniques de ces fibres restent comparables aux autres fibres naturelles, confirmant ainsi leur potentiel textile. Une première piste de valorisation de ces fibres a été envisagée lors de la fabrication d’un fil de canne à sucre. Des essais de filature ont ainsi été menés sur micro-filature, en 100% fibres de canne mais aussi en mélange 30-70% coton/bagasse.Enfin, une introduction à l’approche environnementale basée sur l’analyse de cycle de vie, a été succinctement abordée, ouvrant le champ à d’autres études. Les résultats montrent que le potentiel textile de la canne à sucre est quantifiable, et que ses fibres extractibles, sont comparables à d’autres fibres naturelles non conventionnelles utilisés dans le domaine textile. / This doctoral dissertation deals with extraction and mechanical characterization of sugarcane fibers. From bagasse, the fibrous residue left from the sugar mill, several extraction conditions were investigated in order to extract technical sugarcane fibers. At first, morphological and physical characterization were analyzed, based on their sections and longitudinal profiles. Thus, mean size, fiber fineness and scattering were studied regarding adjusting parameters barbe and hauteur, for the fiber length distribution as weighted mean. Different types of technical fibers were obtained and their mechanical characterization as bending and tensile properties linked with the extraction conditions. Mechanical performances of the extracted fibers are common to other natural fibers that confirm their textile potential. To valorize these fibers, some experiments were conducted by producing sugarcane yarn. A micro-spinning were piloted for a 100% bagasse and 30/70% cotton/bagasse yarn made. Finally, an introduction to an environmental approach was analyzed, based on the lifecycle analysis from the sugarcane culture to the fiber extraction, opening new perspectives to study. The results show that good fibers can be extracted from sugarcane, thanks to its chemical and physical composition, but also can be characterized for textile application.

Materials for extreme electrical contacts need to have high electrical conductivity coupled with good structural properties. Potential applications include motor contacts, high power switches, and the components of electromagnetic launch (EML) systems. In particular, the lack of durability of these materials in rail components limits practical EML implementation. These rails experience significant amounts of Joule heating, due to extreme current densities, and subsequent thermally-assisted wear. New more durable materials solutions are needed for these components. A systematic materials selection study was executed to identify and compare candidate materials solutions. Several possible candidate non-dominated materials as well as hybrid materials that could potential fill the "white spaces" on the Ashby charts were identified. A couple potential candidate materials were obtained and evaluated. These included copper-tungsten W-Cu, "self-lubricating" graphite-impregnated Cu, and Gr-W-Cu composites with different volume fractions of the constituents. The structure-property relations were determined through mechanical and electrical resistivity testing. A unique test protocol for exposing mechanical test specimens to extreme current densities up to 1.2 GA/m2 was developed and used to evaluate these candidate materials. The systematic design of multi-functional materials for these extreme electrical contacts requires more than an empirical approach. Without a good understanding of both the tribological and structural performance, the optimization of the microstructure will not be quickly realized. By using micromechanics modeling and other materials design modeling tools coupled with systematic mechanical and tribological experiments, the design of materials for these applications can potentially be accelerated. In addition, using these tools, more complex functionally-graded materials tailored to the application can be systematically designed. In this study, physics- and micromechanics-based models were used to correlate properties to the volume fraction of the constituents of the evaluated candidate materials. Properties correlated included density, elastic modulus, hardness, strength, and electrical resistivity of the W-Cu materials.

Due to their excellent strength, rigidity, and damping properties, as well as low weight, carbon fiber reinforced composites (CFRCs) are being widely used for load bearing structures. On the other hand, with an increased demand and usage of CFRCs, effective methods to re-use waste carbon fiber (CF) materials, which are recoverable either from process scraps or from end-of-life components, are attracting increased attention. In this paper, hybrid yarns consisting of waste staple CF (40 and 60 mm) and polyamide 6 staple fibers (60 mm) are manufactured on a DREF-3000 friction spinning machine with various process parameters, such as spinning drum speed, suction air pressure, and core–sheath ratio. The relationship between different textile physical properties of the hybrid yarns, such as tensile strength, elongation, and evenness with different spinning parameters, core–sheath ratio, and input CF length is revealed.

Parts made out of titanium alloys demonstrate anisotropic mechanical properties when manufactured by electron beam melting, an emerging additive manufacturing technique. Understanding the process history dependent heterogeneous microstructure, and its effect on mechanical properties is crucial in determining the performance of additively manufactured titanium alloys as the mechanical behavior heavily relies on the underlying microstructural features. This thesis work focuses on combined experimental and computational techniques for microstructure characterization, synthetic microstructure generation, mechanical property measurement, and mechanical behavior modeling of polycrystalline materials, with special focus on dual phase titanium alloys. Macroscopic mechanical property measurements and multi-modal microstructure characterizations (high energy X-ray diffraction, computed tomography and optical microscopy) are performed on additively manufactured Ti-6Al-4V parts, revealing the heterogeneity of the microstructure and properties with respect to the build height. Because characterizing and testing every location within a build is not practical, a computational methodology is established in order to reduce the time and cost spent on microstructure-property database creation. First a statistical volume element size is determined for the Fast Fourier Transform based micromechanical modeling technique through a sensitivity study performed on an experimental Ni-based superalloy and syntheticW, Cu, Ni and Ti structures, showing that as the contrast of properties (e.g., texture, field localization, anisotropy, rate-sensitivity) increases, so does the minimum simulation domain size requirement. In all deformation regimes a minimum volume element is defined for both single and dual phase materials. The database is then expanded by generating statistically representative Ti structures which are modified for features of interest, e.g., lath thickness, grain size and orientation distribution, to be used in spectral full-field micromechanical modeling. The relative effect of the chosen microstructural features is quantified through comparisons of average and local field distributions. Fast Fourier transform based technique, being a spectral, full-field deformation modeling tool, is shown to be capable of capturing the relative contribution from varying microstructural features such as phase fractions, grain morphology/ size and texture on the overall mechanical properties as the results indicate that the mean field behavior is predominantly controlled by the alpha phase fraction and the prior beta phase orientation.