分野別セミナー

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.