Small Punch, hereinafter termed SP, creep test has been proposed as a semi destructive testing methodology to examine the residual creep life of high temperature components. A series of SP creep tests were conducted on low alloy steel at 600°C both in air and in high vacuum to investigate influences of testing environment and the radius of the lower die on the SP creep rupture life. The thickness of the oxide scale on the SP creep specimen in air increased with the test duration, e.g., about 30μm in thickness after 400 hours exposure. The SP creep rupture life in air reduced to a half of the life in vacuum due to an increase of both the actual stress in the specimen and the coefficient of friction. In addition, the magnitude of the radius at the lower die shoulder also affected the SP creep rupture life. The influence of this radius on the SP creep rupture life was studied experimentally and numerically. The SP creep rupture life with a smaller die radius had twice longer than that with a larger one. This fact was also demonstrated by the FE analysis.

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Topology optimization for structures has been applied to nonlinear structural problems, however conventional topology optimization methods for structures with geometrical nonlinearity encounter difficulties during nonlinear analysis using the FEM (Finite Element Method), due to the use of a mesh. In this study, we propose a new level set-based topology optimization method considering geometrical nonlinearity using a mesh-free/particle technique, for optimizing elastic structures that undergo large deformation. In the proposed method, the MPS (Moving Particle Semiimplicit) method, a particle method, is used for the response analysis, since it does not rely on a mesh for geometrically nonlinear analysis. In this paper, first, a topology optimization problem is formulated based on the level set method and a method for regularizing the optimization problem by the Tikhonov regularization method is explained. The reactiondiffusion equation that updates the level set function is then derived and an optimization algorithm, which uses the FEM to solve the equilibrium equations and the reaction-diffusion equation when updating the level set function, is constructed. Next, the particle interaction model and the treatment of geometrical nonlinearity in the MPS method are shown, and the implementation of combining the level set-based topology optimization and the MPS methods is explained. Finally, several numerical examples are provided to demonstrate the effectiveness of the proposed method of topology optimization for geometrically nonlinear problems.

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In this research, the equivalent rigidities for the out-of-plane deformation of honeycombs, consisting of triangle cells, were studied theoretically based on the equivalence of strain energy. Honeycombs composed of unsymmetrical cells are anisotropic and the out-of-plane deformation of honeycombs should be expressed by considering six equivalent rigidities. The validity of the analytical results was confirmed by comparing with the results of numerical analysis of FEM. Also, in this research, two kinds of honeycombs composed of the same shape triangle cells are treated. One is such honeycomb where each triangle cell joins mutually at a vertex. And the other is such that a vertex of a triangle is on another triangular base. The former is called type A and latter is called type B. The mean density for two types of honeycombs consisting of same triangles is the same. However, one of the bending rigidities of type B is very low compared with type A, because the load conditions of the cell walls differ.

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In the previous paper, the authors have discussed the effect of the adhesive thickness and material combinations on the strength of adhesive joint under tension. On the basis of the FEM results, it has been explained explicitly that the strength of adhesive joint decreases with increasing of adhesive thickness under arbitrary material combinations. In this paper, an adhesive joint under bending is discussed using the FEM. Then, the effect of adhesive thickness on the strength of adhesive joint is discussed under bending. Comparing the results of tension and bending for the adhesive joint, it is found that the intensity of singular stress for the bending sometimes is larger than the intensity of singular stress for the tension. On the other hand, the intensity of singular stress for the bending is always smaller than the intensity of singular stress for the tension when the adhesive thickness is large enough.

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In hydraulic turbine runner, accidents due to fatigue often occur. In this study, cyclic tension-compression tests and fatigue crack growth tests using compact tension specimens under the stress ratio R-constant were carried out for welding material SUS309, in order to clarify fatigue properties, fracture mechanisms, fatigue crack growth and closure properties. The test results are summarized as follows : (1)The S-N curve of welding material SUS309 used in this study has narrow scatter and the tension-compression fatigue strength was lower than the test data of the stainless cast steel SCS6 used as hydraulic turbine runner material. (2)From SEM observation of the fracture surfaces, crack initiation sites were found to be surface slip, and the casting defect in the bond region. (3) Fatigue crack growth rates of the specimens which is the vertical and the parallel to welded direction could be correlated with the stress intensity factor range ΔK in the Paris's law. (4)It is considered that threshold stress intensity factor range ΔK_th is influenced by plastic zone and grain size, and the ΔK_th of parallel direction specimen is lower than that of vertical direction specimen.

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The effect of the specimen size on tensile and fatigue properties was studied by using thin wires with the grain size of 22μm and the diameter, D_min, of 800μm, 700μm and 500μm (these are named Specimen-800, 700 and 500, respectivly). For tension test results, the yield strength (proof stress) strongly depended on the specimen diameter. All Specimen-800 and Specimen-700 and a part of Specimen-500 show the clear yield phenomena. However, most of Specimen-500 did not show yielding. For all specimens fractured under cyclic loading, the necking was occurred at the final stage of the fatigue process, and the initiation and the propagation of fatigue cracks were not observed. Two kinds of failure processes were observed. One was ratcheting failure and the other was delayed yielding failure. After the delayed yielding, specimens showed the process similar to ratcheting failure. It was concluded that these size effect are caused by the difference in the number of grains at the minimum cross section. Regardless of diameters of specimens, the scatter in fatigue life was very large compared with that of bulk specimen. It was concluded that the main cause of the large scatter in fatigue life was attributed to the scatter in the number of cycles to start ratcheting deformation (delayed yielding).

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Researches on the natural fiber reinforced “green” composites have been increasing in recent years due to concern over exhaustible petroleum resources and environmental destruction, and demands for energy saving and carbon dioxide reduction. Green composites are also expected as alternative materials for traditional fiber reinforced composites. Although green composites comprised of plant-derived natural fibers have been investigated by many researchers, use of animal-based natural fibers such as silk fiber (SF) in green composites has been rarely reported. In this regard, the mechanical properties and stress-strain relationships of silk fiber reinforced poly(butylene succinate) (PBS) biodegradable composites (SF/PBS) are evaluated in the present study. In order to investigate the effects of surface treatment of the silk fiber on the mechanical properties of SF/PBS, four types of surface treatment has been applied to the silk fiber. Tensile tests are conducted on the single silk fiber and unidirectional SF/PBS laminates. From the experimental results it has been found that removal of sericin in the silk fiber by the surface treatment improves Young's modulus but decreases fracture strain of the silk fiber. Predictions by generalized method of cells (GMC) micromechanics have shown good agreement with experimental results of the stress-strain relationship of 0° unidirectional laminates. However, nonlinear behavior in high stress region of 45° and 90° unidirectional laminates have not been predicted precisely due to internal damages such as interfacial debonding in the plates.

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In the recent years, natural fiber reinforced composites are expected as alternative materials for traditional fiber reinforced composites. Though many experimental studies on mechanical properties of biodegradable composites have been presented in literature, analytical investigations are rarely reported. In this regard, mechanical properties of silk fiber reinforced poly(butylene succinate) (PBS) biodegradable composite (SF/PBS) laminates are investigated in the present study. In order to investigate the effects of surface treatment of the silk fiber on the mechanical properties of the SF/PBS laminates, four types of surface treatment has been applied to the silk fiber. Tensile tests are conducted on cross-ply laminates and angle-ply laminates. When the silk fibers without sericin are used, tensile strengths and Young's modulus are the highest in all laminate configurations. Stress-strain relations of both cross-ply and angle-ply laminates are predicted by combining the three-parameter plasticity model and the classical laminated plate theory. In the analysis, the properties in unidirectional composite from the generalized method of cells (GMC) micromechanics or experimental results are used. It has been found that it is possible to predict the stress-strain relations for both laminates when the experimentally-obtained properties of unidirectional laminates are used. This implies that nonlinearity caused by damages such as debondings in the unidirectional laminates under off-axis loading should be incorporated in the analysis. It has been also found that it is necessary to consider changes in fiber orientation angle due to deformation of the plates in predicting the stress-strain relation for the angle-ply laminates.

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In this study, analytical solutions for the three-dimensional transient temperature fields and the resulting thermal stress fields in a space plane's nose cone composed of a functionally graded material (FGM) are derived by treating the nose cone as a multi-layered hollow hemisphere with distinct thermal and mechanical properties in each layer. The three-dimensional transient heat conduction problem can be solved by applying Fourier-cosine transform, Legendre transform, and Vodicka's method which is a type of integral transform for the one-dimensional multi-layer regions. The associated thermal stress problem can be analyzed by using thermoelastic displacement potential and Papkovich-Neuber's displacement functions. Numerical calculations for the thermal deformations and the thermal stresses are carried out for the FGM hollow hemisphere composed of SiC and Al-Alloy, which has a graded material composition of a power function expression. It is clarified that there is a specific thermal stress behavior in the FGM hollow hemisphere subjected to the three-dimensional transient temperature field, and the effects of the graded composition and number of layers on relaxation characteristics of thermal stress are quantitatively discussed.

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In order to improve the biocompatibility of a Ni-Ti alloy, mechanically polished Ni-Ti samples were subjected to isothermal oxidation (TO) in N₂-20vol%O₂ at temperatures of 573 and 773K. We conducted cell culture tests with L929 fibroblast cells to examine the cell proliferation. Amount of Ni ions elusion in culture medium used during cell proliferation test was analyzed by atomic absorption photometer. As a results, all TO-treated samples showed good biocompatibility after 3 days of immersion tests, and released Ni ions were significantly reduced by TO-treatment. These are because the TOtreatment generated thick and stable surface modified layer at the alloy surface. In addition, wear resistance of the Ni-Ti alloy was also improved by TO-treatment. After the wear tests, biocompatibility was evaluated by cell proliferation tests, and its results showed that the surface damage on the TO-treated sample did not affect the attachment cells. From these results we can conclude that the isothermal oxidation treatment is effective as a surface modification method for Ni-Ti alloy.

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