Crack front propagation and fracture in a graphite sheet: A molecular-dynamics study on parallel computers

Crack propagation in a graphite sheet is investigated with million atom molecular-dynamics simulations based on Brenner's reactive empirical bond-order potential. For certain crystalline orientations, multiple crack branches with nearly equal spacing sprout as the crack tip reaches a critical speed of 0.6VR, where VR is the Rayleigh wave speed. This results in a fracture surface with secondary branches and overhangs. Within the same branch the crack-front profile is characterized by a roughness exponent, α=0.41±0.05. However, for interbranch fracture surface profiles the return probability yields α=0.71±0.10. Fracture toughness is estimated from Griffith analysis and local-stress distributions. © 1997 The American Physical Society.