Small-angle X-ray Scattering

Analysis of Voids and Particles
paper

Disorder of the periodic structure can be estimated by analyzing the X-ray scattering using the Hosemann equation. The long-period structure in polymers, however, often produces so broad small-angle X-ray scattering peak that this equation can not be applied. In the present study, a method for estimating disorder from the small-angle X-ray scattering with a broad peak has been proposed. By applying this method, the structural changes of polyacrylonitrile fibers during the stabilization process for producing carbon fibers have been investigated.



Analysis of Long-period Structure
paper

Disorder of the periodic structure can be estimated by analyzing the X-ray scattering using the Hosemann equation. The long-period structure in polymers, however, often produces so broad small-angle X-ray scattering peak that this equation can not be applied. In the present study, a method for estimating disorder from the small-angle X-ray scattering with a broad peak has been proposed. By applying this method, the structural changes of polyacrylonitrile fibers during the stabilization process for producing carbon fibers have been investigated.



Analysis of Fracture Process of Polymers
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The figure shows the small-angle X-ray scattering pattern of a poly(ethylene terephthalate) (PET) film measured during tensile deformation using a synchrotron radiation and shows the formation of crazes in the film. The PET fibers also produce characteristic small-angle X-ray scattering patterns which change during tensile deformation. The analysis of the fracture process of polymers based on these results has been undertaken.

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Wide-angle X-ray Diffraction

Analysis of Stack of Layer Type Molecules
paper

With the turbostratic carbon structure, the carbon layers are stacked with displacements and rotations in parallel to the layer plane. This type of crystallite produces a peculiar wide-angle X-ray diffraction pattern which differs widely from that of the graphite. In the present study, a method for analyzing the structure of the stack of the layer type molecules which are preferentially oriented in the system from the wide-angle diffraction has been proposed



Mechanical Properties of Fibers

Non-Hookean Stress-Strain Response of Carbon Fibers
paper

Tensile modulus of carbon fibers increases with increasing tensile stress. In order to elucidate the mechanism of non-Hookean stress-strain response, the changes of the crystallite orientation of carbon fibers during tensile deformation have been measured. Stress dependencies of the tensile modulus and the crystallite orientation have been theoretically analyzed based on various models such as undulating ribbon, zigzag ribbon, series elements, series rotatable elements, parallel elements and mosaic model. It was concluded that the increased constraint of the crystallite deformation with increasing tensile stress is responsible for the non-Hookean stress-strain response of carbon fibers



Axial Compressive Behavior of Carbon Fibers
paper

Carbon fibers show extremely low axial compressive strength in comparison to their tensile strength. In the present study, the axial compressive strength of carbon fibers has been determined by compressing directly the single filaments. By considering that the axial compressive strength is determined by the buckling stress of carbon layers, the axial compressive strength has been derived theoretically as a function of the size of microvoids.



Yarns and Composite Materials with Twist Structure
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Variations of longitudinal and transverse moduli with twist for twisted yarns and twisted yarn/resin composite strands composed of fibers covering a wide range of tensile moduli including carbon and aramid fibers have been investigated using a sonic pulse propagation method. The relationship between the longitudinal modulus of twisted yarns and the twist angle has been derived theoretically on the bases of a model that takes into account the anisotropic elasticity of the fibers.



Analysis of Defects in Polymeric Fibers
paper

he figure is the SEM photograph of a polyester fiber with a diameter of about 20 mm on which a notch was introduced using a focused ion beam milling apparatus. From the strength of the fibers having notches with different depths, the defect size and the strength of the fiber attained by eliminating the defects have been estimated. The deflection of the Weibull plots of the tensile strength has been also discussed.

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Structure of Carbon Materials

Temperature-time Superposition
paper

The figure shows the changes in the resistivity of carbon fibers during the heat-treatment at 1400oC for more than 200,000 years, obtained by applying the temperature-time superposition. Theses experiments have been performed using internal resistance heating which allows quick heating at temperatures above 2000oC. The difference in the structure development of pitch-, polyacrylonitrile- and phenol formaldehyde resin-based carbons, the influences of the applied stress, the temperature dependent activation energy of the structure development, and the application of the temperature-time superposition to the physical properties and the structure parameters have been discussed.

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Structure, Properties and Preparation Methods
paper

Structure, properties and preparation methods of carbon fibers and films were investigated with various starting materials such as pitch, polyacrylonitrile, polyoxadiazole, polycarbodiimide and poly(vinylidene fluoride).



Mesopores Carbon
paper

The activated carbon produced through conventional activation process is microporous. In order to produce mesoporous carbon, we have made various attempts including liquid-phase dehydrohalogenation of starting polymer, iodine vapor treatment, supercritical carbon dioxide treatment and gas phase activation. The growing process of pores during activation has been analyzed as well based on the changes of mass, pore volume and surface area.



Composite Materials

Fragmentation Test, Pull-out Test
paper

The figure shows the fiber breaks in a single-fiber composite loaded in tension. By analyzing the fiber fragmentation process, the fiber-matrix interfacial shear strength can be estimated. This method is called fragmentation test. So far the interfacial shear strength has been calculated from the fragment lengths of the fiber and the tensile strength of the fiber determined with the tensile tests. However, the strength determined with the tensile tests or its extrapolation to the fragment length is an average fiber strength which is different from the stress at break of the individual fiber in the single-fiber composite. In addition, the fiber in the composite may be degraded during the fabrication process and by the exposure of the composite to the environments in the case of the durability studies. In order to overcome these problems, a method for estimating the interfacial shear strength, tensile strength of the individual fiber and its distribution from the relation between the number of breaks of the fiber and the tensile strain of the single-fiber composite has been proposed (Composite Interfaces, 4, 379 (1997)). By applying this method to the glass fiber/epoxy resin single-fiber composites, the degradation of the fiber and the interface when the composites were exposed to the hydrothermal conditions was investigated.

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Mechanical Properties
paper

The mechanical properties of carbon fiber reinforced composites have been studied experimentally and theoretically. The tensile strength of unidirectional fiber reinforced composites has been theoretically derived as a function of the distribution of the fiber strength, the number of multiple fiber fracture and interfacial strength (Composite Interfaces, 6, 305 (1999)). The tensile and compressive strengths of woven laminate composites have been theoretically derived as a function of the radius of curvature of yarns (Composites Science and Technology, 64, 2221 (2004)). The compression-after-impact strength of the woven laminate and the felt/resin composites have been uniquely related to the mode I interlaminar fracture toughness and interpreted by applying the analysis given by Ilic and Williams (Composites Science and Technology, 64, 2231 (2004)). The fracture toughness of resins dispersed with carbon nanotubes has also been studied (Oral presentations).



Other Researches (English Papers)

Other Researches (English Papers)
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