Fatigue experiments on copper have shown that vacancy production leads to the evolution of extrusions, which were the preferred sites for fatigue crack initiation. However, experimental, analytical and numerical results for the critical edge-dislocation dipole annihilation distance vastly differ. This study performs molecular statics and molecular dynamics simulations at elevated temperature to investigate the discrepancies in annihilation distance. Vacancy forming edge dislocation dipoles were stable if their spacing exceeds 2 lattice spacings. If the dislocation dipole was perpendicular to the free surface in a thin sheet of material, jogs on edge dislocations lead to dipole annihilation. The main conclusion was that dislocation generation, glide and stable edge dislocation dipoles were sufficient to lead to that extrusion growth, which results in fatigue crack initiation.

On the Formation of Vacancies by Edge Dislocation Dipole Annihilation in Fatigued Copper. S.Brinckmann, R.Sivanesapillai, A.Hartmaier: International Journal of Fatigue, 2011, 33[10], 1369-75