Mixed-mode (I/II) Cracks In Crystal Diamond: A Molecular Dynamics Study

The evolution of the atomic structure, lattice slip, dislocation and bond breaking etc. around the crack tip in the single-crystal diamond, were investigated by use of molecular dynamics simulation based on the second-generation Brenner potential, where mixed-mode (I/II) displacement loading was applied by boundary layer disk model.Part I: The evolution of the atomic structure of the crack tip in the single-crystal diamond with (001)[100] crack embedded was investigated, and I/II mixed mode displacement loading was applied on the boudary. The critical stress intensity factor was obtained, and lattice slip, dislocation, bond breaking etc. were investigated by setting loading angle as 0°, 30°, 45°, 60°and 90°. It was found that atom bonds around the crack tip were broken, and new carbon rings were formed. The crack entered the trapping lattice and propagated when KⅠand KⅡincreased gradually to the critical values. The propagation of crack tip and lattice slip are all related to the loading angles.Part II: The evolution of the atomic structure of the crack tip in the single-crystal diamond with (110)[110] crack embedded was investigated, and I/II mixed mode displacement loading was applied on the boudary. The critical stress intensity factor was obtained and lattice slip, dislocation, bond breaking etc. were investigated by setting loading angle as 0°, 30°, 45°, 60°and 90°. It was found that crack opening due to the passivation of the crack tip, crack face widened accompanied by the child cracks when KⅠand KⅡincreased gradually to the critical values. Crack cutting-edge slip, fracture modes and the critical K values were different due to the crack orientation.Part III: The the critical stress intensity factors of embedded (001)[100] and (110) [110] cracks in single crystal diamond were compared,where I/II mixed mode displacement loading were applied, the influences of the orientations on the propagation of cracks were also analyzed. It was found that fracture modes and the critical K values were anisotropic for the (001)[100] and (110) [110] cracks.