On the effect of hydrogen on plastic instabilities in metals

Experimental observations and theoretical calculations have demonstrated that hydrogen solute atoms increase the dislocation mobility in metals and alloys, thus promoting highly localized plastic processes which eventually lead to localized ductile rupture. While the underlying mechanism for hydrogen-enhanced dislocation mobility is well understood, little is known on how this mechanism acting at the microscale can lead to macroscopic plastic instability. In this paper, a theoretical investigation is carried out in a specimen under plane-strain tension in an effort to understand how hydrogen-induced softening and lattice dilatation at the microscale can lead to macroscopic i) shear localization (shear banding bifurcation) or ii) necking bifurcation.