Dynamic microcrack initiation in alpha-iron

The results of molecular dynamic simulations of microcrack initiation in the b.c.c. lattice of alpha-iron are presented. In a relatively large sample under quasistatic loading in mode I, the shielding edge dislocations are emitted in [111]{11(2) over bar} slip systems and the initiation of the (001)[<(1)over bar 10>] microcrack requires higher external forces than correspond to the Griffith stress sigma(G). Under fast loading, the shielding dislocations are not observed at the initiation, and due to elastodynamic effects, microcrack extension occurs under lower external forces than for quasistatic loading. Crack tip opening and crack tip healing can be characterized by k(I)(tip). The fracture parameters G(Id) > 2 gamma and K-Id > K-G can be introduced to describe the microcrack initiation according to fracture mechanics.