Figure 4. Fracture simulations in polycrystalline graphene.

(a) A schematic representation of the simulation of initial crack advance in nanocrystalline graphene. A prescribed K_I-field is applied by holding the atoms outside the circular region of radius 100 Å fixed at the positions given by the LEFM solution. The atoms inside the circular region are allowed to relax with NVT dynamics. Initial crack advance occurs when the stress intensity K_I is sufficiently large. (b) The stress field in a polycrystal where the atoms outside a 100 Å radius from the crack tip are held fixed at the LEFM displacement field for K_I=4 MPa·m^1/2. The black arrows show the enhancement of the crack-tip stress concentration by the GB defects. (c) The crack extends along the GB as indicated by the black arrow. The stress concentration is relieved after crack extension.