Lattice weakening by edge dislocation core under tension

Abstract

Molecular dynamics simulations are carried out to investigate the influence of edge dislocations on the lattice strength in iron single crystals under tension perpendicular to the dislocation slip plane. Simulations are performed at different temperatures and with different densities of edge dislocations on the [1 1 1] slip system. It is found that cracks nucleate at dislocation cores in dislocation-containing systems at lower critical stresses compared with a perfect lattice, indicating a weakening caused by edge dislocations. Lattice thermal vibration plays an important role during the tensile deformation, resulting in a monotonic decrease in the yield strength as the temperature increases. There exists a critical temperature above which the lattice transforms from brittle to ductile, where dislocation nucleation and glide are favored instead of crack nucleation, and the critical temperature for the dislocated system is lower than that for the perfect lattice. The present simulation shows that higher dislocation density results in lower fracture strength, suggesting that the accumulation of dislocations during cyclic deformation may be the cause of lower strength under fatigue.