Nanofracture in graphene under complex mechanical stresses

Nanoscale fracture of graphene under coupled in-plane opening and shear mechanical loading is investigated by extensive molecular dynamics simulations. Under opening-dominant loading, zigzag edge cracks grow self-similarly. Otherwise, complex stresses concentrated around crack-tip can manipulate the direction of crack initiation changing by 30° (or multiples of 30°). Toughness determined by obtained critical stress intensity factors 2.63–3.38 nN Å−3/2 demonstrates that graphene is intrinsically brittle opposite to its exceptional high strength at room temperature. Torn zigzag edges are more energetically and kinetically favorable. Cracking of graphene has dependences on local stresses, edge energy, and dynamic effects, which provides a possible way to regulate graphene edges.