83 Hydrogen Enhanced Dislocation Emission at a Crack Tip

The influence of hydrogen on plasticity is an essential component of the modeling of H induced damage in structural metallic alloys. In this work, we study an idealized configuration where an atomistically sharp crack is loaded in mixed mode until a straight dislocation is emitted directly at the tip. We calculate, by molecular statics, the critical load for emitting dislocations in mixed I and II modes. It is shown that the model proposed by Rice, which relates the critical stress intensity factor for emission (k_IIe) to the unstable staking fault energy (γ_us), is exact for dislocations moving along the crack plane, provided the influence of mode I is taken into account in the γ_us calculation. We report first results concerning the drop of k_IIe obtained by an EAM model for Al-H and DFT calculations.