In this work, we examined the simulation method, which involves the discontinuities propagation owing to the ductile failures. Estimating the final state of structures and materials is basic interests in many fields of engineering. In nowadays, the simulations play important roles to predict the ductile behavior of materials and structures. However, the ductile failure under the large and plastic deformation is one of the unsolved the problems in the computational mechanics. The continuum damage mechanics, for instance damage model has been developed for predicting the material behavior. Moreover, the damage model describes the discontinuities by immersed boundaries. The FCM is one of the candidate for the implementation to generate the discontinuous surfaces. In order to describe the newly generated discontinuous surfaces, we employ the damage model to our FCM codes. Tensile testing simulation for ductile fractures is demonstrated, in which, the well-known damage model is used to define the material failure, the birth of discontinuity.

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The sintering of nickel in the nickel and yttria-stabilized zirconia (YSZ) anode of a solid oxide full cell (SOFC) is investigated by molecular dynamics (MD) simulation. Low values of the work of separation (up to 500 mJ/m^2) between nickel and YSZ allows sliding of nickel nanoparticles. The sliding is significantly hindered when the work of separation increases up to 2500 mJ/m^2, which implies that the Ni surface diffusion and Ni(OH)_2 vaporization-deposition are supposed to be the main sintering mechanisms. Our MD simulations employing the reactive force field (ReaxFF) method indicate the possibility of the Ni(OH)_2 vaporization-deposition.

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Nucleation of tetragonal phase from cubic phase matrix has been analyzed by phase field calculation including thermal fluctuations. The frequency distribution of the magnitude of the thermal fluctuation was taken into account. The nucleation rates were quantified by calculating the time to form tetragonal phase. The effects of magnetic field and transformation strain also have been analyzed. The nucleation rate well agreed with the classical nucleation theory. Introducing transformation strain led multiple nucleations of variants. This result indicates that fine and uniform tetragonal variants will be obtained when transformation strain taken into account.

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[in Japanese]

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[in Japanese]

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A pressure tank is widely used in many equipment of the social infrastructure. We have been developing the protective cover for the metal pressure tank in order to enhance the safety of it. The cover is made of synthetic fiber and resin. The fracture analysis of the tank failure process has been carried out using the finite-element method under the different thickness of the cover and the surface condition. The physical properties of the cast metal and the cover are determined by measured data from the tensile tests with attention to their variation. The simulation result shows that the tank bursts in form of the brittle failure when an internal pressure reaches the withstanding pressure of it. Furthermore it shows that fragments fly outside the tank and that the protective cover catches the fragments. We confirmed that the cover with thickness in more than 2 [P.U.] has the effect of the prevention of scattering the fragments of the pressure tank.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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A coronary stent is a tube-shaped device, which needs a vascular wall crimp power and bending stiffness reduction, so that a stent matches the blood vessel without any damage. But, in a stent end, its radius increases locally (Dog-Boning), which has an effect to fix a stent to the vascular wall, but an uniform crimp pressure distribution is more desirable. With this background, the balloon for stent expansion is modeled by SHELL elements with contact detection, and after the nonlinear FEM analysis, the Dog-Boning behavior is replicated. The results of analysis is described here in after.

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A simulation result of the single-turn coil method known as one of the electromagnetic field generation techniques is presented in this paper. The simulation result successfully predicts the time history of generation of magnetic field at the center of the single-turn coil until 3.2 micro second as well as the peak value of the magnetic field at 2.2 micro second. A discussion of the importance of electric resistivity as a function of hydrostatic pressure is given comparing the analysis results between the single-turn coil method presented here and the electromagnetic flux compression method which had already been reported by the author.

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In this study, tensile tests of plate-fin structures with a digital image correlation (DIC) measurement system are conducted to investigate validity of the homogenization analysis method developed by our research group. For this, tensile tests using plate-fin test specimens made of an epoxy are performed, and their microscopic deformations are measured by a DIC measurement system. Then, corresponding elastic-viscoplastic analysis of plate- fin structures is carried out using the homogenization theory for nonlinear time-dependent materials. The analysis results obtained are compared with the experimental results to validate the present method.

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Nonlinear FEM analysis is necessary for analyzing the concentrated shear strain at the end of a Footing, which is put on elasto-plastic soil. An application of Particle method is evaluated by the comparison with nonlinear FEM analysis under the Drucker-Prager model.

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In this study, thermal properties of plain-woven laminates are analyzed using a triple-scale homogenization method. For this, thermal strain of fibers and matrix materials is incorporated into the elastic-viscoplastic homogenization theory developed by our research group. This method enables us to analyze thermal properties in not only fiber bundles but also fibers and matrix materials in fiber bundles, as well as macroscopic thermal properties. This method is then applied to the thermal property analysis of plain-woven carbon fiber/epoxy laminates subjected to a macroscopic temperature change from 180℃ to 20℃. Two types of carbon fibers are considered in the analysis. It is shown that quite high thermal residual stress can occur in fiber bundles, fibers and a matrix. It is also shown that the present method can analyze the change of thermal residual stress in the laminates depending on the difference of fibers.

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[in Japanese]

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This paper reports the experimental and polycrystal plasticity analysis of microstructural changes in coarse-grained Al-Mg alloy plates caused by large deformation. An intermittent tensile test was performed on an Al-Mg alloy plate specimen having large crystal grains with the average diameter of 14 mm. The SEM/EBSD analyses were performed before and during the intermittent tensile test to clarify the changes in the configurations and crystal properties of the grains in the plate specimen. The polycrystal elastoplastic simulations of the tensile test were also made on the Al-Mg alloy specimen having the observed initial crystallographic properties by using an FEM code the present authors have been developing. Changes in the configurations and crystal properties of the grains obtained by experimentally and computationally were compared and discussed. It was revealed that texturization and refinement of the crystal grains experimentally observed in the specimen were reproduced by the present polycrystal elastoplastic simulations.

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This study has proposed new methods for reconstructing 3D mandible models with teeth from in vivo CT images and changing the CT values on the CT images on commercial FEM software such as ANSYS. By using the methods proposed, various 3D mandible models with teeth and with implant have been reconstructed on ANSYS software: e.g., a healthy mandible model, osteoporotic mandible models, and osseointegration models, etc. Stress analyses have been performed on the 3D mandible models reconstructed where static inclined biting forces are applied to the Straumann implant in the left second molar position and revealed that the maximum von Mises equivalent stress becomes higher around the implants in the osteoporotic mandible models whereas lower in the osseointegration models than in the healthy mandible model.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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