[in Japanese]

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[in Japanese]

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This paper describes the polycrystal elasto-viscoplastic analyses of a modified 9Cr-lMo steel at 823K in air by using an FEM program developed by the present authors. The analyses used a 2D polycrystal model of a welded joint in the high Cr steel having different aggregates of crystal orientations. The results were compared with creep rupture diagrams experimentally obtained by the creep tests of the high Cr steel at 823K in air. It was shown that the analyses successfully reproduced the creep rupture diagram which agreeds well with the experimental ones. It was also shown that the present analyses reproduced creep deformation behavior of the welded joints and formation of crystal texture in the HAZ largely affected by the crystal orientations of the steel.

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Nonmetallic inclusions and precipitates unusually grown-up inside often bring about fatigue fracture of metallic material. Crystals and their aggregates that are in a situation weakened by mutual interaction with crystallographic orientation, a particle size, a grain-boundary and surrounding crystals, also behave in a similar manner, even though they are the same phase as a matrix. In such a case, it is more appropriate to assume a notched material with a certain stress concentration factor by an internal defect or a cracked material with a certain small crack length, although a material is geometrically smooth. Accordingly, it is required inevitably that a size effect should be taken into consideration because of the minute nature of a scale. From such a viewpoint, influence of metallurgical stress concentration on characteristics of a fatigue strength diagram is discussed.

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[in Japanese]

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In this study, the elastic-viscoplastic properties of aluminum honeycomb sandwich panels are investigated using a homogenization theory. For this, the mathematical homogenization theory is reconstructed for elastic-viscoplastic analysis of honeycomb sandwich panels by introducing traction free and uniform deformation boundary conditions. Moreover, the domain of analysis is reduced to a quarter using point-symmetry of internal structures of honeycomb sandwich panels. The present method is then applied to the analysis of macroscopic elastic-viscoplastic behavior and microscopic stress distribution of an aluminum honeycomb sandwich panel subjected to in-plane uniaxial compression or out-of-plane pure shear. It is shown that for the in-plane uniaxial compression, the stress concentration arises at face/core interfaces, especially at intersections of core walls. On the other hand, for the out-of-plane pure shear, the stress concentration arises at intersections of core walls away from face/core interfaces.

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A disclinations is a line defect which can be regarded as a dense configuration of many dislocations. Because the wedge-shape discontinuity of disclination makes a high stress field, the disclination essentially has a high strain-energy. However some configuration, such as disclination dipoles, can reduce the strain energy, and this structure can be a promising model of description of grain boundary and other inelastic deformation. And the Generalized force is considered as one of the important evaluation standards of mechanical properties of disclinations in solids. We will focus on the estimation of a generalized Peach Koehler force of each disclination, and discuss the possibility of evolution of disclination structure.

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[in Japanese]

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Dissociation of methane molecules on the nickel(lll) surface is examined by way of the ab initio molecular dynamics simulation to discuss the initial stage of graphene growth via a chemical vapor deposition (CVD) technique. Methane molecules are dissociated into isolated carbon and hydrogen atoms via CH3 and CH fragments with chemisorbing the nickel surface. Dissociated carbon atoms are buried into the subsurface space between first and second nickel layers via diffusion through hollow sites between the nickel layers.

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The dissociation of ethanol molecules as the carbon-source molecules on a nickel cluster was investigated by ab initio molecular dynamics (MD) simulation to unravel the initial stage of growth of carbon nanotubes with an alcohol catalytic chemical vapor deposition (CCVD) technique. As results, it has been observed that both C-C and C-0 bonds in ethanol molecules are dissociated on the nickel cluster, which is followed by the formation of various reaction products.

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