Atomic behaviors of crack propagation in bcc iron under dynamic loading rate with rectangular fluctuation

This work carries out molecular dynamics simulations to identify the atomic behaviors of the crack initiation and propagation in bcc iron under dynamic loading rate with rectangular fluctuation, where the effects of the upload ratio and contact ratio are revealed. With an increase in upload ratio or a decrease in contact ratio, the plastic behaviors of the crack initiation can transform from only the nucleation of the dislocations to both the dislocation nucleation and the phase transitions. The corresponding behaviors of the crack propagation can transform from only the dislocation emission to both of the emission of the dislocations and the expansions of the stacking faults and twins. The plastic behaviors of the crack initiation and propagation are determined by the stress field around the crack tip. To describe the stress field, the Virial stress tensor and Voronoi volume are introduced. Besides, the simulations and Virial stress are verified through comparing with the results obtained by the continuum mechanics. Since the rectangular loading rate is the typical characteristic of the load applied on the upper part of the tooth root with gear transmission, this work can be used to analyze the atomic mechanisms of the initiation of the gear tooth breakage.