3D atomistic studies of fatigue behaviour of edge crack (0 0 1) in bcc iron loaded in mode I and II

•Edge crack (0 0 1)[1 1 0] in bcc Fe loaded cyclically in mode I and II is studied via MD.•Fatigue behaviour of the crack (0 0 1) is compared with the crack (1¯10) studied before.•Growth in mode I is faster for (0 0 1) crack (Paris exponent n = 2.8) due to twinning.•Under pure mode II conditions the crack (0 0 1) deflects along {1 1 2} planes.•In all cases, fatigue crack growth has been monitored well below static Griffith level.

We present new results of 3D molecular dynamic simulations of a mechanical response of an edge crack (0 0 1)[1 1 0] (crack plane/crack front) in a single crystal of bcc iron cyclically loaded in tension mode I and shear mode II at room temperature. Different boundary conditions were tested for mode II. We compare fatigue behaviour of the crack (0 0 1) loaded in mode II and I with behaviour of a ductile crack (1¯10)[1 1 0] recently studied. The paper brings new information on micromechanism of fatigue crack growth.