Hold Date

2010-06-01 15:30〜2010-06-01 17:00

Place

Ito Campus Open Learning Plaza 1st floor Room 10

Object person

　

Speaker

Reza Miresmaeili (Faculty of Engineering, Kyushu University)

summary :
       Uncoupled analyses have been implemented, in which the code
        Zebulon is used for crystal plasticity analyses including a
        fully anisotropic elasticity tensor and an in-house finite
        element code is written for the hydrogen advection diffusion
        computations. After completion of the structural analysis, the
        diffusion code utilizing a Mass-Conservative Characteristic
        Finite Element (MCC FE) scheme is programmed. The required
        structural parameters - displacements, hydrostatic stresses
        and equivalent plastic strains - are transferred step by step
        from the previously completed structural analysis to the
        hydrogen code.

        This work indicates that even without assuming some special
        properties for grain boundaries, which is usually the case in
        research on grain boundary engineering, the non-homogeneous
        stress field itself results in either depletion or enrichment
        of hydrogen, depending on the direction of stress driven flux
        produced by grain misorientation during straining. The
        segregation of hydrogen is observed mainly at the grain
        boundaries and some hydrogen perturbations appear. Results
        show that the grain size has a significant effect not only on
        the amount of hydrogen perturbation but also on the span of
        region under perturbation. A decrease in the grain size by a
        factor of 1.5 times induces an increase in maximum NILS
        concentration by a factor of 1.76. Results of similar analyses
        indicate that an increase in maximum NILS concentration occurs
        by a factor of 3.13 in the case of a decrease in the grain
        size by a factor of 2.

        Moreover, the effect of crystallographic orientations on the
        hydrogen redistributions has been investigated. Different
        hydrogen redistributions have evolved from the uniform initial
        concentration due to dissimilar hydrogen fluxes resulted from
        different crystallographic orientations. The contour of trap
        site concentration changes due to variations in the contour of
        equivalent plastic strain at different crystallographic
        orientations. Progress has been made in that a one-way
        coupled crystal plasticity-transient hydrogen diffusion
        analysis is employed to solve a boundary value problem of an
        elasto-plastic deformation in meso-scale. The hydrogen
        distributions all over the polycrystal, including the hydrogen
        concentration within the grains and close to the grain
        boundaries, are determined. The results of this work may be
        useful for controlling and optimizing the material
        microstructure, eventually providing safe and reliable
        hydrogen transport and storage systems.