Numerical analysis of the interaction of solute hydrogen atoms with the stress field of a crack

Finite element analysis is used to study the effect of mobile interstitial hydrogen on the deformation of metals and alloys in the case when hydrogen is in equilibrium with local stresses. The effect is studied by calculating the hydrogen atmosphere around a stationary crack tip in a linearly elastic isotropic material loaded in mode I plane strain conditions. Stresses, strains and equilibrium hyclrogen concentrations are determined through an iterative finite element analysis while accounting for stress relaxation due to hydrogen induced local volume and elastic modulus changes. Numerical calculations reveal a zone immediately ahead of the crack tip in which the lattice is saturated with hydrogen. The dimensionless size of the saturation zone is found to be independent of the applied loads. The stiffness derivative method is used to calculate the hydrogen induced change:s in the stress intensity factor. Calculations show that the presence of mobile interstitial hydrogen produces crack tip shielding when hydrogen induced changes in the elastic moduli are considered. The implications of the elastic analysis of the interaction between hydrogen in equilibrium with local stresses near a crack tip on the fracture resistance of materials are discussed. Then results are examined in conjunction with the elastic-plastic deformation at the tip.