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A Coupled Elastoplastic-Transient Hydrogen Diffusion Analysis to Simulate the Onset of Necking in Tension by Using the Finite Element Method

Hold Date
2009-12-01 15:30〜2009-12-01 17:00
Ito Campus, Open Learning Plaza, 1st floor, Room 10
Object person
Reza Miresmaeili (Graduate School of Engineering, Kyushu Univ.)

        Hydrogen-enhanced localized plasticity (HELP) is an acceptable
        mechanism for hydrogen embrittlement which is based on the
        experimental observations and the theoretical
        computations. The underlying principle in the HELP theory is
        that the presence of hydrogen causes the localization of the
        slip bands which results in the decrease of the fracture
        strength. In a sample under plane-strain tensile stress,
        plastic instability can lead to either the concentration of
        plastic flow in a narrow neck or bifurcation from homogeneous
        deformation into a mode of an exclusively localized narrow
        band of intense shear. Recently, it has been demonstrated that
        the presence of hydrogen can indeed induce shear banding
        bifurcation at macroscopic strains. By using a steady-state
        equilibrium equation for hydrogen diffusion analysis, the
        effect of hydrogen on the bifurcation of a homogeneous
        deformation in a plane-strain tension specimen into a necking
        or a shear localization mode of deformation has already been
        studied. In the present research, using a transient hydrogen
        diffusion analysis and introducing a new constitutive equation
        accompanied by considering the reduction in the local flow
        stress upon hydrogen dissolution into the lattice, the effect
        of hydrogen on shear localization is investigated. In
        addition, progress has been made in that, the changes in the
        distribution of the total and trapping hydrogen concentrations
        through the loading time and particularly during the
        development of the necking event have been determined.