Molecular dynamics simulation of fatigue crack propagation in bcc iron under cyclic loading

• The fatigue crack propagation characteristics of iron were analyzed for the crack models of various orientations.
• The influences of classical grain boundary on crack growth was taken into account on ∑3∑3〈1 1 2〉{1 1 1} and ∑5∑5〈3 1 0〉{0 0 1} models.
• Crack grow rate and stress intensity factor were discussed for the crack models of various orientations and grain boundary.

The mechanism of crack propagation under cyclic loading in iron single crystal was investigated using molecular dynamics simulation. The cyclic loading was strain controlled and three typical specimens of pre-existing center crack of [0 0 1](0 1 0), [001¯](1 1 0) and [112¯](1 1 1) models were chosen to study the effect of orientation on fatigue crack propagation. The slip bands, vacancies and voids nucleation were observed during the process of crack growth under cyclic loading, the rate of crack growth and slip direction were different for the three models. No significant slip band was observed in [112¯](1 1 1) model, and the crack propagation was brittleness. In addition, the influences of grain boundary on crack growth were analyzed on ∑3∑3〈1 1 2〉{1 1 1} and ∑5∑5〈3 1 0〉{0 0 1} models. No significant effect was observed for ∑3∑3 on crack propagation, while ∑5∑5 resisted crack growth remarkably and resulted in a decreasing rate of crack growth, during which a little hexagonal close-packed (hcp) slip bands appeared in the plastic deformation zone.