Atomistic modeling of penny-shaped and through-thickness cracks in bcc iron

Atomistic simulations of penny-shaped embedded cracks in body-centered cubic (bcc) iron are performed using molecular dynamics. The results reveal that the original circular crack geometry can change shape gradually upon loading, depending on the crystallographic orientation. This new geometry generally favors emission of dislocation loops instead of unstable fracture. A comparison is made between through-thickness cracks in six different orientations and penny-shaped cracks on the same crack planes. We find that changes in crack shape and the interaction of events in different directions play an important role in how fracture mechanisms evolve when cracks in full 3D simulations extend, and that dislocation emission and mechanical twins 'win' over unstable crack growth by bond breaking. (paper)