haruki okuda - Academia.edu (original) (raw)
Papers by haruki okuda
General. All reactions were carried out under Ar atmosphere using Schlenk technique, whereas the ... more General. All reactions were carried out under Ar atmosphere using Schlenk technique, whereas the workup was performed in air. 1H, 13C and 31P NMR spectra were recorded in acetone-d6 or CDCl3 on JEOL JNM-LA400,-LA600 and Bruker ARX400 spectrometers using SiMe4 as an internal standard for 1H and 13C nuclei, and H3PO4 as an external standard for
Carbon, 2019
A single fibre tensile in-situ microbeam small-angle X-ray scattering study was performed on the ... more A single fibre tensile in-situ microbeam small-angle X-ray scattering study was performed on the polyacrylonitrile-based carbonised fibres. There was no remarkable skin-core difference in the scattering profiles for the fibres tested. Meanwhile, we found that the chord length of the scattering objects shows an immense, yet reversible, increase of as much as 30e35% before the fibre fails at the macroscopic tensile strain of 2e2.5%. We believe this anomalous behaviour in the apparent length of the scattering objects reflect the complicated internal nanostructure of the carbonised fibres.
![Research paper thumbnail of Corrigendum to “Nanocomposite microstructures dominating anisotropic elastic modulus in carbon fibers” [Acta Mater. 166 (2019) 75–84]](https://attachments.academia-assets.com/91478798/thumbnails/1.jpg)
](Acta Materialia, 2019
The authors regret that in the micromechanics calculations using the nanocomposite microstructure... more The authors regret that in the micromechanics calculations using the nanocomposite microstructure model of carbon fibers, the coordinate system in the graphite-crystal inclusions was explained incorrectly. There are incorrect explanations in 5.1 (ii) and (iii). Correctly, in the nanocomposite model calculations, the [10] and [001] directions of the graphite crystals are oriented along the x 0 3 and x 0 1 directions, respectively, as shown in the Supplementary Fig. S1c. Thus, the aspect ratio a 3 /a 1 of the graphite-crystal inclusion corresponds to the ratio of the length along the [10] direction to that along the [001] direction, as shown in the Supplementary Fig. S1d. The aspect ratio a 2 /a 1 also reflects the ratio of the lengths of the graphite-crystal inclusion, defined in the Supplementary Fig. S1d. The orientation relationship between the coordinate system x 0 of a graphite-crystal inclusion and the coordinate system x of carbon fibers is expressed by the Euler angles p=2 À a, b, and f, as shown in the Supplementary Fig. S1e. In the nanocomposite model calculations, the angles b and f for the graphitecrystal inclusions in Supplementary Fig. S1e are isotropically distributed around the x 3 and x 0 3 axes, respectively. The angle a values in the Supplementary Fig. S1e corresponds to the angle a values in the Supplementary Fig. S1b, Supplementary Fig. S3, and Fig. 3, used for the orientation distribution of the [001] direction. The definitions of angles b and f in Supplementary Figs. S1c and S1e are different from those in Supplementary Figs. S1a and S1b. These corrections for the explanation of the coordinate system do not affect the results and conclusions obtained for the elastic properties and microstructures in carbon fibers.
Composites Part A: Applied Science and Manufacturing, 2019
Considering the stress concentration of fiber surfaces in the prediction of the tensile strength ... more Considering the stress concentration of fiber surfaces in the prediction of the tensile strength of unidirectional carbon fiber-reinforced plastic composites, Composites:
Acta Materialia, 2018
Nanocomposite microstructures dominating the anisotropic elastic properties in carbon fibers were... more Nanocomposite microstructures dominating the anisotropic elastic properties in carbon fibers were studied, to construct a micromechanics model that can explain the anisotropic elastic properties of carbon fibers. Aluminum-based composites containing five types of carbon fibers were prepared, and their anisotropic elastic properties were measured using resonant ultrasound spectroscopy combined with electromagnetic acoustic resonance. Then, all the independent elastic stiffness components of the carbon fibers were extracted from those of the composites using a composite model based on Eshelby's inclusion theory, MorieTanaka mean-field theory, and effective-medium approximation. Moreover, we newly developed a nanocomposite microstructure model that can fully reproduce all the anisotropic constants of carbon fibers exhibiting a wide variety of Young's moduli. In the developed model, the microstructures of carbon fibers were approximated as nanocomposites comprised of an amorphous carbon matrix and graphite-crystal inclusions that are aggregations of graphite nanocrystallites. Based on this nanocomposite microstructure model, the shape of the graphite-crystal inclusions and the elastic properties of the amorphous carbon matrix were analyzed, considering the volume fraction and orientation of the graphite nanocrystallites, as determined using X-ray diffraction. The analysis revealed that the shapes of the graphite-crystal inclusions are flat ellipsoids elongated along the fiber axis, and the aspect ratio of the graphite-crystal inclusions dominantly affects the anisotropy in the Young's modulus. This indicates that the graphite nanocrystallites are connected along the in-plane directions of the graphitic layers, and not the shape of nanocrystallites but their two-dimensional connectivity dominates the anisotropic elastic modulus in carbon fibers.
TANSO, 2018
The nanostructure of PAN-based carbon fibers was comprehensively investigated, with an emphasis o... more The nanostructure of PAN-based carbon fibers was comprehensively investigated, with an emphasis on amorphous carbon. In-situ measurement of the crystallite deformation and micromechanical analysis revealed that the amount of amorphous carbon in PAN-based carbon fibers was approximately 50%. In addition, the mechanical properties of the amorphous carbon could be obtained through the analysis, which helped to identify the structure. The weight fraction of sp 2 carbon layers calculated from an analytical model based on the rule-of-mixtures using Raman spectroscopy data and the crystallinity calculated by the micromechanical model indicated the differences in intermediate modulus and high modulus carbon fibers, which were affected by the measuring method. Radial distribution analysis using neutron scattering allows one to obtain a detailed structural analysis of the amorphous carbon in PAN-based carbon fibers. The analysis results suggest that the number of lattice defects in intermediate modulus carbon fibers is 20% larger than in the high modulus type and these lattice defects are present in the amorphous component. These new findings, based on extensive analysis, suggest that controlling the ratio of amorphous to crystalline carbon is one of the key factors determining the mechanical properties of PAN-based carbon fibers.
Journal of the Japan Society for Composite Materials, 2016
Advanced Composite Materials, 2014
In this study, we determined the strength distribution of high-strength polyacrylonitrile-based c... more In this study, we determined the strength distribution of high-strength polyacrylonitrile-based carbon fibers of different short gauge lengths (~1 mm) using both the single-fiber-composite four-point bending test and the single-fiber tensile test. We employed the bimodal Weibull model to explain the experimental data. We found that the value of the Weibull shape parameter for short gauge lengths was higher than that for long gauge lengths. This implies that the tensile strength distribution of carbon fibers is governed by two different flaw populations. The tensile strength of resin-impregnated fiber bundles predicted on the basis of the bimodal Weibull distribution was in better agreement with the experimental result than the tensile strength of those predicted on the basis of the unimodal Weibull distribution.
Journal of Materials Science, 2012
ABSTRACT
Composites Part A: Applied Science and Manufacturing, 2014
We have investigated the fracture mechanisms of different types of carbon fibres, in terms of ski... more We have investigated the fracture mechanisms of different types of carbon fibres, in terms of skin-core differences in single fibres, flaw size and fracture toughness. The fibre strength distribution was measured precisely using the fragmentation test for single-fibre composites. The failure probability for intermediate/high modulus types fibres was found to be constant with fibre strength in the range 2-4 GPa, but in contrast the strength scatter for high modulus type fibres was reduced. The fracture toughness of the carbon fibres, determined by introducing notches with lengths in range 60-200 nm, was found to be about 1.1 MPa m 1/2. The average flaw size of the carbon fibres increased with increasing fibre modulus, suggesting that the crack growth of surface flaws on the tens-of-nm scale occurred. This appears to be the main reason for the reduction in tensile strength during the carbonisation treatment.
Carbon, 2013
We have introduced the Mori-Tanaka theory as a new micromechanical model to predict the Young's m... more We have introduced the Mori-Tanaka theory as a new micromechanical model to predict the Young's modulus for carbon fibres, that takes into account both the crystallites and amorphous components of the carbon fibre structure. The axial elastic constants of the bulk carbon fibres were measured directly by X-ray diffraction (XRD) and an axial shear modulus of about 20 GPa was calculated. The elastic constants of the amorphous carbon in the fibres and the volume fractions of crystallites were estimated using micromechanical models. It was found that the amorphous modulus was approximately 200 GPa and the volume fractions of crystallites were 0.4 to 0.8, depending upon the nanostructure of the carbon fibres. Also, as it is known that the Raman G band shift rate per unit strain is related to the crystallite modulus, the data indicated a nearly constant value of 1.1 TPa, consistent with direct measurements upon graphene. The results show clearly that the behavior of carbon fibres can be expressed through a composite mechanical model that assumes they consist of both crystalline and amorphous carbon components.
General. All reactions were carried out under Ar atmosphere using Schlenk technique, whereas the ... more General. All reactions were carried out under Ar atmosphere using Schlenk technique, whereas the workup was performed in air. 1H, 13C and 31P NMR spectra were recorded in acetone-d6 or CDCl3 on JEOL JNM-LA400,-LA600 and Bruker ARX400 spectrometers using SiMe4 as an internal standard for 1H and 13C nuclei, and H3PO4 as an external standard for
Carbon, 2019
A single fibre tensile in-situ microbeam small-angle X-ray scattering study was performed on the ... more A single fibre tensile in-situ microbeam small-angle X-ray scattering study was performed on the polyacrylonitrile-based carbonised fibres. There was no remarkable skin-core difference in the scattering profiles for the fibres tested. Meanwhile, we found that the chord length of the scattering objects shows an immense, yet reversible, increase of as much as 30e35% before the fibre fails at the macroscopic tensile strain of 2e2.5%. We believe this anomalous behaviour in the apparent length of the scattering objects reflect the complicated internal nanostructure of the carbonised fibres.
Acta Materialia, 2019
The authors regret that in the micromechanics calculations using the nanocomposite microstructure... more The authors regret that in the micromechanics calculations using the nanocomposite microstructure model of carbon fibers, the coordinate system in the graphite-crystal inclusions was explained incorrectly. There are incorrect explanations in 5.1 (ii) and (iii). Correctly, in the nanocomposite model calculations, the [10] and [001] directions of the graphite crystals are oriented along the x 0 3 and x 0 1 directions, respectively, as shown in the Supplementary Fig. S1c. Thus, the aspect ratio a 3 /a 1 of the graphite-crystal inclusion corresponds to the ratio of the length along the [10] direction to that along the [001] direction, as shown in the Supplementary Fig. S1d. The aspect ratio a 2 /a 1 also reflects the ratio of the lengths of the graphite-crystal inclusion, defined in the Supplementary Fig. S1d. The orientation relationship between the coordinate system x 0 of a graphite-crystal inclusion and the coordinate system x of carbon fibers is expressed by the Euler angles p=2 À a, b, and f, as shown in the Supplementary Fig. S1e. In the nanocomposite model calculations, the angles b and f for the graphitecrystal inclusions in Supplementary Fig. S1e are isotropically distributed around the x 3 and x 0 3 axes, respectively. The angle a values in the Supplementary Fig. S1e corresponds to the angle a values in the Supplementary Fig. S1b, Supplementary Fig. S3, and Fig. 3, used for the orientation distribution of the [001] direction. The definitions of angles b and f in Supplementary Figs. S1c and S1e are different from those in Supplementary Figs. S1a and S1b. These corrections for the explanation of the coordinate system do not affect the results and conclusions obtained for the elastic properties and microstructures in carbon fibers.
Composites Part A: Applied Science and Manufacturing, 2019
Considering the stress concentration of fiber surfaces in the prediction of the tensile strength ... more Considering the stress concentration of fiber surfaces in the prediction of the tensile strength of unidirectional carbon fiber-reinforced plastic composites, Composites:
Acta Materialia, 2018
Nanocomposite microstructures dominating the anisotropic elastic properties in carbon fibers were... more Nanocomposite microstructures dominating the anisotropic elastic properties in carbon fibers were studied, to construct a micromechanics model that can explain the anisotropic elastic properties of carbon fibers. Aluminum-based composites containing five types of carbon fibers were prepared, and their anisotropic elastic properties were measured using resonant ultrasound spectroscopy combined with electromagnetic acoustic resonance. Then, all the independent elastic stiffness components of the carbon fibers were extracted from those of the composites using a composite model based on Eshelby's inclusion theory, MorieTanaka mean-field theory, and effective-medium approximation. Moreover, we newly developed a nanocomposite microstructure model that can fully reproduce all the anisotropic constants of carbon fibers exhibiting a wide variety of Young's moduli. In the developed model, the microstructures of carbon fibers were approximated as nanocomposites comprised of an amorphous carbon matrix and graphite-crystal inclusions that are aggregations of graphite nanocrystallites. Based on this nanocomposite microstructure model, the shape of the graphite-crystal inclusions and the elastic properties of the amorphous carbon matrix were analyzed, considering the volume fraction and orientation of the graphite nanocrystallites, as determined using X-ray diffraction. The analysis revealed that the shapes of the graphite-crystal inclusions are flat ellipsoids elongated along the fiber axis, and the aspect ratio of the graphite-crystal inclusions dominantly affects the anisotropy in the Young's modulus. This indicates that the graphite nanocrystallites are connected along the in-plane directions of the graphitic layers, and not the shape of nanocrystallites but their two-dimensional connectivity dominates the anisotropic elastic modulus in carbon fibers.
TANSO, 2018
The nanostructure of PAN-based carbon fibers was comprehensively investigated, with an emphasis o... more The nanostructure of PAN-based carbon fibers was comprehensively investigated, with an emphasis on amorphous carbon. In-situ measurement of the crystallite deformation and micromechanical analysis revealed that the amount of amorphous carbon in PAN-based carbon fibers was approximately 50%. In addition, the mechanical properties of the amorphous carbon could be obtained through the analysis, which helped to identify the structure. The weight fraction of sp 2 carbon layers calculated from an analytical model based on the rule-of-mixtures using Raman spectroscopy data and the crystallinity calculated by the micromechanical model indicated the differences in intermediate modulus and high modulus carbon fibers, which were affected by the measuring method. Radial distribution analysis using neutron scattering allows one to obtain a detailed structural analysis of the amorphous carbon in PAN-based carbon fibers. The analysis results suggest that the number of lattice defects in intermediate modulus carbon fibers is 20% larger than in the high modulus type and these lattice defects are present in the amorphous component. These new findings, based on extensive analysis, suggest that controlling the ratio of amorphous to crystalline carbon is one of the key factors determining the mechanical properties of PAN-based carbon fibers.
Journal of the Japan Society for Composite Materials, 2016
Advanced Composite Materials, 2014
In this study, we determined the strength distribution of high-strength polyacrylonitrile-based c... more In this study, we determined the strength distribution of high-strength polyacrylonitrile-based carbon fibers of different short gauge lengths (~1 mm) using both the single-fiber-composite four-point bending test and the single-fiber tensile test. We employed the bimodal Weibull model to explain the experimental data. We found that the value of the Weibull shape parameter for short gauge lengths was higher than that for long gauge lengths. This implies that the tensile strength distribution of carbon fibers is governed by two different flaw populations. The tensile strength of resin-impregnated fiber bundles predicted on the basis of the bimodal Weibull distribution was in better agreement with the experimental result than the tensile strength of those predicted on the basis of the unimodal Weibull distribution.
Journal of Materials Science, 2012
ABSTRACT
Composites Part A: Applied Science and Manufacturing, 2014
We have investigated the fracture mechanisms of different types of carbon fibres, in terms of ski... more We have investigated the fracture mechanisms of different types of carbon fibres, in terms of skin-core differences in single fibres, flaw size and fracture toughness. The fibre strength distribution was measured precisely using the fragmentation test for single-fibre composites. The failure probability for intermediate/high modulus types fibres was found to be constant with fibre strength in the range 2-4 GPa, but in contrast the strength scatter for high modulus type fibres was reduced. The fracture toughness of the carbon fibres, determined by introducing notches with lengths in range 60-200 nm, was found to be about 1.1 MPa m 1/2. The average flaw size of the carbon fibres increased with increasing fibre modulus, suggesting that the crack growth of surface flaws on the tens-of-nm scale occurred. This appears to be the main reason for the reduction in tensile strength during the carbonisation treatment.
Carbon, 2013
We have introduced the Mori-Tanaka theory as a new micromechanical model to predict the Young's m... more We have introduced the Mori-Tanaka theory as a new micromechanical model to predict the Young's modulus for carbon fibres, that takes into account both the crystallites and amorphous components of the carbon fibre structure. The axial elastic constants of the bulk carbon fibres were measured directly by X-ray diffraction (XRD) and an axial shear modulus of about 20 GPa was calculated. The elastic constants of the amorphous carbon in the fibres and the volume fractions of crystallites were estimated using micromechanical models. It was found that the amorphous modulus was approximately 200 GPa and the volume fractions of crystallites were 0.4 to 0.8, depending upon the nanostructure of the carbon fibres. Also, as it is known that the Raman G band shift rate per unit strain is related to the crystallite modulus, the data indicated a nearly constant value of 1.1 TPa, consistent with direct measurements upon graphene. The results show clearly that the behavior of carbon fibres can be expressed through a composite mechanical model that assumes they consist of both crystalline and amorphous carbon components.