The mechanical properties of spatial structures constructed of joints and beam members are strongly influenced by both their geometrical configurations and joint rigidities. From the standpoint of joint flexibility, we have formulated the elastic deformation model of a two-dimensional flexibly jointed structure with multi-rotational nodes. The aim of this paper is to make clear the relationship between overall buckling characteristic and local rotations of the flexibly jointed structure. To this end, the structural instability of periodic square cells under equi-biaxial compression is evaluated by applying our proposed model, and it is clarified that the short wave-length buckling modes are determined by the combinations of multi-rotational modes of flexible joints.

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Three-dimensional finite element model of femur and pelvis was prepared and the propagation of impulsive stress wave from the distal femur to the hip joint was analyzed by the dynamic finite element method. The finite element model with no articular cartilage was also used and the influence of cartilage on the impulsive stress was discussed. The stress concentration is mainly found around the femoral neck. The absolute value of minimum principal stress increases in the medial side, and the maximum principal stress increases in the lateral side during the propagation of stress wave. In this case, the absolute value of maximum principal stress is larger than that of minimum one. The stress of pelvis is small compared with that of femur, indicating that the impulsive stress is absorbed by traveling through the cartilage. The stress in the femoral neck and the pelvis becomes large in the case of no cartilage model, therefore it can be said that the hip joint with no cartilage has a higher risk of bone fracture.

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The polymerization shrinkage of a light cure composite resin was studied using artificial cylindrical cavities fabricated in stainless steel plates. The shrinkage force was measured using a load-cell inserted as the bottom of the cavity from the back side of the plate. The resin was filled into the cavities after prepared with a bonding agent and then irradiated with a visible-light curing unit. The shrinkage force was measured as functions of time and the depth of the cavity. The cavities with constrained surfaces were also employed to study the effect of boundary condition, and the following results were obtained. The force increased greatly due to the irradiation and slightly increased with time after the irradiation. The force increased gradually with the cavity depth, and exhibited the maximum value and then decreased gradually. The cavities with constrained surfaces yielded much larger forces than the ones with the free surface condition for the same depths.

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The chondrocyte-agarose construct has been employed as an experimental model in the cartilage tissue engineering context. We studied the influence of L-Ascorbic acid (AsA) concentration in culture medium on mechanical property of regenerated cartilage. Cylindrical chondrocyte-agarose constructs with a diameter of 4mm and a height of 2.5mm were prepared as test specimens. Chondrocytes isolated from metacarpal-phalangeal joint of steers were seeded in 1wt% agarose (type VII, Sigma) to give an initial cell density of 1×10^7 cells/mL, and cultured in sterile culture medium (DMEM+20%FBS) within a humidified tissue culture incubator. We cultured by using levels of five AsA concentrations, 0.64, 2.2, 3.2 and 6.4pmol/10^9 cells and without AsA. Culture medium was exchanged every two days. After culture periods of 1, 8, 15 and 22 days, tangent modulus of the cultured constructs and glycosaminoglycan (GAG) biosynthesis were evaluated by the unconfined compression test and the demethylmethylene blue (DMMB) assay, respectively. The structural organization of the elaborated tissue was also examined morphologically by the confocal laser scanning microscope (CLSM). Results indicated that the tangent modulus of the cultured constructs increased with increasing the AsA concentration in culture medium. In addition, the growth rate of the tangent modulus was proportional to the AsA concentration. The increased amount of AsA would contribute to the accelerated self-assembly of the collagen fiber network and resultant improvement in the mechanical property, since the reduction ability of AsA could enhance the procollagen expression in cultured chondrocytes.

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The aim of this study is to propose a strategy for performing viscoelastic two-scale analyses for fiber-reinforced plastic (FRP) with periodic microstructures (unit cells), based on the assumption that the anisotropic generalized Maxwell model can be employed for the homogenized viscoelastic constitutive law. We first summarize a method of numerical material testing, for which the standard finite element method is applied to solve the extended system of micro-scale governing equations incorporated with external material points, or equivalently control nodes. Secondly, the anisotropic generalized Maxwell model is provided. Thirdly, we propose a method of parameter identification that uses the "measured data" by the numerical relaxation tests conducted with a relevant set of macroscopic strains. Finally, the trains of two-scale viscoelastic analyses is exemplified to demonstrate the validity of the proposed method.

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A fatigue life prediction method for composites which is based on the anisomorphic constant fatigue life (CFL) diagram is further tested on a class of composite laminates that exhibit matrix-dominated fatigue behavior. First, constant-amplitude fatigue tests are performed at room temperature on three kinds of symmetric angle-ply CFRP laminates [±θ]_<3S> (θ=30,45,60°) at different stress ratios, respectively, in order to quantify the effect of stress ratio on the constant amplitude fatigue behavior of the angle-ply CFRP laminates. The experimental results demonstrate that the S-N curve significantly depends on the value of stress ratio. It is also observed that the stress amplitude for a given fatigue life becomes largest under a fatigue condition in which stress ratio is equal to the ratio of compressive strength to tensile one. The full shapes of the CFL diagrams for the angle-ply laminates are identified on the basis of the fatigue test results. The CFL diagrams for the [±30] and [±45] angle-ply lay-ups are favorably predicted using the anisomorphic CFL diagram approach, while for the [±60] lay-up the predictive accuracy was poor due to a significant distortion of the experimental CFL curves for a left neighborhood of the critical stress ratio. To accommodate such a distortion of CFL diagram, the anisomorphic CFL diagram is developed into a connected anisomorphic CFL diagram which consists of three segments: the T-T and C-C dominated segments and a transitional segment in between. It is demonstrated that the extended three-segments anisomorphic CFL diagram approach allows adequately predicting the S-N relationships for different stress ratios as well as accurately describing the CFL diagrams for the angle-ply laminates of different lay-ups.

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In this study, in order to calculate the bending rigidity of a honeycomb, a torsion problem of a board was analyzed by using the generalization variation principle. The analysis was checked by using the numerical analysis of FEM. In the torsion problem of a board, the boundary condition that rotation angle is zero on two edges is fulfilled. Also, the bending rigidity of honeycomb was investigated using board torsion coefficient q_τ, obtained from the analysis of the torsion problem of a board. It is shown that the bending rigidity of honeycomb is mostly proportional to the 3rd power of height h of the honeycomb, and in h/l>0.5, is mostly proportional to thickness t of the cell board, which constitutes the honeycomb.

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The generalized solutions of the macroscopic elastic moduli of the composite material containing many ellipsoidal reinforcements are derived as a function of the geometrical factors defined by the authors in the previous study. In the present study, by assuming the continuous change in the aspect ratios of ellipsoidal reinforcement at a fixed coordinate, the corresponding change in values of the geometrical factors is examined and their expressions are derived to the elliptic flake, elliptic cylinder and spheroid reinforcement. Macroscopic elastic moduli of the composite are calculated by using the expressions of geometrical factors and their values are compared to the results calculated from the Hashin's solution. As a result, these values are good agreement with each other.

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Macroscopic loss factors are derived for a composite material containing many ellipsoidal reinforcements whose semi-axes are different from each other by using the equivalent inclusion method combined with the Mori-Tanaka theorem. Eshelby tensor rearranged as a function of Poisson's ratio of the matrix multiplied by the geometrical factor is used for the reinforcement in the analysis. Since all reinforcements are assumed to align along the same direction in the modeling, the composite material has three perpendicular two-fold rotational symmetries and hence nine components of the macroscopic loss factor of the composite can be expressed in terms of the geometrical factors. Moreover, it can be seen that the imaginally part of the complex Poisson's ratio of the constituent must be equal to zero from the condision that the magnitude of the macroscopic loss factor of a porous material must be equal to that of the matrix.

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The manufacturing method of micro sacrificial plastic mold (SP-mold) insert metal injection molding (MIM) combined LIGA process, namely LIGA/μ-SPiMIM process has been proposed to solve specific problems involving the miniaturization of MIM. Two types of SP-molds with fine structures were used: 1) PMMA resist, 2) PMMA mold injected into Ni-electroform, which is a typical LIGA process. Stainless steel 316L feedstock was injection-molded into the SP-molds with multi-pillar structures. To reduce the defects in plastic injection molding such as weld-line and short filling, which were developed around micro pillar structures of molded parts, the molding conditions for producing the SP-molds were optimized. This study also focused on the effects of metal particle size and processing conditions on the shrinkage, transcription and surface roughness of sintered parts.

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A silica-filled EPDM composite (SCT) was exposed to hydrogen gas at P_H&le;10MPa, and the critical hydrogen pressure at crack initiation P_<H,cr> was evaluated. From observations of cracks by an optical microscope, P_<H,cr> ranged from 4 to 5MPa. It was inferred that these cracks initiated due to the stress concentration of the micrometer-sized bubbles caused by supersaturated hydrogen molecules after decompression. Furthermore, tearing energy of these bubbles, T, was calculated by FEM and theoretically. In this calculation, the SCT was regarded as a hyperelastic material, and so its strain energy density was approximated by a polynominal Mooney-Rivlin model which can express the strain energy density of practical sealing materials more exactly than the Neo-Hookean model. Parallel to the calculation, static crack growth tests were conducted using single edge crack specimens in air and in 0.7MPa hydrogen gas at room temperature. Since the hydrogen gas did not influence the T_<s,th> value, an inner pressure at T&ge;T_<s,th>, Π_F, was estimated using the T_<s,th> value in air. As a result, the critical hydrogen pressure at crack initiation of the SCT was successfully estimated, i.e., P_<H,cr>&ap;Π_F as well as that of an unfilled composite.

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Crack propagation tests of lead-free solder were conducted using center-cracked plates (CCP) for tension-compression loading (mode I loading) and thin-walled tubular specimens for torsional loading (mode II loading). Both specimens have an initial slit as a crack starter. The path of crack propagation under mode I loading was macroscopically straight, and perpendicular to the maximum principal stress direction. In tubular specimens under mode II loading, at the high strain amplitude, the crack propagate in shear mode along the maximum shear direction. At low strain amplitude, four cracks are formed from the initial silt and propagate showing macroscopically tensile-mode propagation. The crack propagation rate is expressed as a power function of the J-integral range for both mode I and II loadings. The relation was not much different between mode I and II loadings. Fatigue crack propagation takes place by joining microcracks formed along the maximum shear planes ahead of the crack tip. At high strain ranges of mode II loading, microcracks ahead of the main crack tip were long and abundant, and their connection with the main crack gave rise shear-mode crack propagation.

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In order to clarify the loading frequency effect on fatigue crack growth rate in hydrogen gas environment, fatigue crack growth tests were carried out on a 6061-T6 aluminum alloy at several loading frequency levels in a pure dry hydrogen gas, in air and in a pure dry nitrogen gas. Hydrogen enhances the fatigue crack growth rate. Moreover, the growth rate increases as the loading frequency decreases not only in hydrogen but also in nitrogen. The main cause of the loading frequency effect relate to thermal activation in plastic zone at the tip of a crack growing across grains by slipoff. The loading frequency effect concerning hydrogen itself could not be revealed. There exists a transition loading frequency below which the crack growth rate is practically independent of loading frequency.

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In order to investigate the mechanism for the intergranular fatigue crack propagation of a low carbon steel in a low pressure hydrogen gas environment, two kinds of examinations were carried out. One was the examination on the effect of cyclic prestrain on the crack growth behavior. The other was the in-situ observation of intergranular fatigue crack propagation in hydrogen gas environment. The main results are as follows. (1) SEM observation on the surface morphology of a plain specimen fatigued in a hydrogen gas showed that a gap at the grain boundary induced by slip behavior but not in nitrogen gas. (2) A specimen cyclic-prestrained in hydrogen gas showed the light influences on the increase in crack propagation rate. (3) Mating intergranular facets on the fatigue fracture surfaces showed the matching of striation-like pattern in the manner anticipated from the damaging mechanism of (1). (4) Environment-change test from hydrogen to nitrogen during the fatigue test showed that intergranular facets appeared even in nitrogen. The results (3) and (4) means the damaging process of (1) is valid in actual fatigue crack. (5) In-situ observation of a crack propagation behavior in hydrogen gas showed that a crack propagated faster when along the grain boundary. However, no visible discontinuous crack advance appeared, a large number of load repetitions were required. Phenomena considered to be damage process (1) appeared ahead of a crack tip. From the results, a convincing mechanism for the intergranular fatigue crack propagation process is as follows. Grain boundaries just ahead of a crack tip are damaged due to a large number of hydrogen-enhanced slip repetition, therefore the fatigue crack becomes easier to propagate along the grain boundary in hydrogen.

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In order to establish strength evaluation method of the high strength notch material which has an inclusion, tensile tests of material which have various notch radius and fracture toughness tests about high strength casting high speed steel materials were performed. The validity of considering that an inclusion is equivalent to a crack and considering the influence which the interference between an inclusion and a notch has on tensile strength in fracture mechanics using stress intensity factor were examined. Tensile fracture conditions were evaluated by defining one formulas which calculate the stress intensity factor which used √<area> parameter model as the tensile fracture conditions K_<IB>(ρ). As a result of the test, as for the high strength notch material containing many inclusions, the notch root maximum elastic stress at the time of the fracture varied, and it was shown clearly that the cause was because an inclusion size varies. Moreover, a strength evaluation with little scatter was possible by making K_<IB>(ρ) into fracture conditions. That is, it was shown clearly by considering that an inclusion is equivalent to a crack that it is effective to consider the influence which the interference between an inclusion and a notch has on tensile strength in fracture mechanics using a stress intensity factor.

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The author suggested that fatigue lives of the sharp notched specimens of high strength steels the tensile strength of which was higher than 1000MPa, could be estimated only by the stress intensity factor and did not depend on the tensile strength. This result indicates that the fatigue life of the sharp notched specimen is controlled by macro fatigue crack growth rate under small scale yielding. It is well known that macro fatigue crack growth rate under small scale yielding depend on Young's modulus. Therefore, the relationship between the fatigue life and the stress intensity factor of the sharp notched specimen is thought to depend on Young's modulus. In this study, K-N curve of metallic glass and non-ferrous alloys were compared with that of high strength steels and E dependent fatigue of sharp notched specimen was experimentally verified. Its importance on fatigue design of machine and structure using high strength light alloys was discussed and future development was suggested.

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Ni base alloys are widely used as the materials of high temperature components for nuclear power plants because of their high mechanical strength, heat resistance and corrosion resistance. Intergranular Stress Corrosion Cracking (IGSCC) is one of serious problems for this material. Because the sensitization of Ni base alloys is one of the main factors of IGSCC, the establishment of nondestructive evaluation of sensitization is highly required. It is well known that alloy 600, one of Ni base alloys, is paramagnetic after solution heat treatment, but as sensitization increases, its magnetic properties change. In this study, feasibility of nondestructive evaluation of sensitization of alloy 600 is discussed focusing on its magnetic properties. To investigate the relationship between magnetic properties and sensitization, alloy 600 were heated in different temperatures and durations. Then, the relationship between magnetic properties and sensitization is discussed based on hysteresis curves, and microstructure observed by TEM (Transmission Electron Microscope) and numerical analysis. Finally, nonlinear eddy current method is applied and the feasibility of nondestructive evaluation of sensitization is discussed.

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This paper discusses a structural optimization method that optimizes shape and topology based on the phase field method. The proposed method has the same functional capabilities as a structural optimization method based on the level set method incorporating perimeter control functions. Since the proposed method does not require extra operations such as re-initialization of the level set function or smoothing of sensitivities, the computational cost is lower than that of typical level set methods. Structural shapes are represented by the phase field function defined in the design domain, and optimization of this function is performed by solving a time-dependent reaction diffusion equation. The artificial double-well potential function used in the equation is derived from sensitivity analysis. The proposed method is applied to two-dimensional linear elastic and vibration optimization problems such as the minimum compliance problem, a compliant mechanism design problem and the eigenfrequency maximization problem. The numerical examples provided illustrate the convergence of the various objective function and the effect that perimeter control has on the optimal configurations.

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In this study, a new crystal plasticity phase-field model is developed by coupling the phase-field microelasticity theory and the crystal plasticity theory. We first conduct the simulation of uniaxial tensile loading of a single crystal and confirm the developed model can describe the elastic and plastic deformation behaviors depending on crystal orientation. Then, the present model is applied to the simulation of the growth of single and multiple precipitates with dilatational transformation strain. The simulation results show that the high stress region near the interface migrates with the growth of the precipitates. In the growth of precipitates with plastic deformation, the high stress near the interface decreases by the plastic deformation. Furthermore, it is revealed that the plastic deformation concentrates along the direction that shear stress on the slip plane becomes maximum. Thus, the distribution of the plastic strain depends on the crystal orientation of the parent phase. The simulation of the growth of multiple precipitates also demonstrates that the plastic strain produces the residual stress in the final polycrystalline structure. According to these simulation results, the developed phase-field model offers advantage to describe not only the microstructure evolution during the phase transformation, but also the elastic and plastic deformation behaviors on the basis of the crystal plasticity theory.

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Axial enlarging work method, which has been developed on the basis of mechanical ratchet phenomenon over long years, has great merits of being green for environment as well as saving energy and resources. The plastic forming works to enlarge partially a long round bar at nearer position from the bar end would be expected as one of novel axial enlarging technologies. Some difficult matters of how to apply axial compressive force to a long round bar and how to avoid buckling deformation occuring during axial enlarging process could be resolved theoretically considering a significant model analysis, which could determine a suitable process loading condition for axial partial enlarging plastic working without occurring some buckling plastic bends, and so a new axial enlarging machine for a long shaft was successfully developed to form a near net shape of a long round shaft with a boss, which can be manufactured into a ball screw part.

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A composite material was produced using bamboo fiber soaked into biodegradable poly (vinyl alcohol). To enhance the wettability of specimen, corona discharge was conducted as pre-treatments. The pre-treated specimen was soaked into the poly (vinyl alcohol), then it was compressed and fixed in a airtight atmosphere. Young's modulus in the length direction and flatwise and edgewise shear moduli of the composite material were measured by flexural vibration method, whereas Young's modulus and bending strength were measured by static bending tests. The bending strength of the composite satisfied that of sheathing board, which is determined in the Japanese Industrial Standards as JIS A 5905. Nevertheless, the shear modulus in the thickness direction was so small that it should be improved.

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