Abstract: The internal stress induced by a porous layer or passive layer can assist the applied stress to promote dislocation emission and crack propagation, e:g: when the pipeline steel is buried in the soil containing water, resulting in stress corrosion cracking (SCC). Molecular dynamics (MD) simulation is performed to study the process of dislocation emission and crack propagation in a slab of Fe crystal with and without a porous layer on the surface of the crack. The results show that when there is a porous layer on the surface of the crack, the tensile stress induced by the porous layer can superimpose on the external applied stress and then assist the applied stress to initiate crack tip dislocation emission under lowered stress intensity K_I, or stress. To respond to
the corrosion accelerated dislocation emission and motion, the crack begins to propagate under lowered stress intensity K_I; resulting in SCC.

Key words: Molecular dynamics simulation, Dislocation emission, Crack propagation, Porous layer, Stress intensity