Hydrogen diffusion and trapping in bodies undergoing rolling contact

Diffusion and trapping of hydrogen (H) in bodies undergoing combined rolling and sliding contact has been evaluated using finite element analysis. The elastic stress-strain conditions of the bodies were calculated in 3D for a single rotation. The stresses were then used to simulate H diffusion in a single plane close to the contact point over large numbers of cycles. The distribution of deformation-induced defects was approximated by relating an isotropic hardening model to the dislocation density. The influence of the defects on H diffusion was evaluated using the McNabb & Foster model assuming local equilibrium as per Oriani. The influence of residual stresses, such as those occurring in bearings after manufacturing, and frictional heating were also considered. The results show that slightly elevated H concentrations occur in the plastic zone conditions and that the increase in H concentration is due to trapping by deformation-induced defects. The influence of stress-assisted diffusion is small due to (i) the short period of time a point on the contact surface spends under load relative to the period of rotation; and (ii) the spatial separation of the hydrostatic and von Mises components of the contact stresses.