An Atomistic Study of the Stress Corrosion Cracking in Graphene

Using molecular dynamics (MD) simulations, we study the mechanism of stress corrosion cracking in graphene. Two sets of modelings are conducted. In the first one, large graphene sheets with cracks in the armchair and zigzag directions are exposed to oxygen molecules. The crack growth as a result of chemical reactions between carbon radicals and oxygen molecules at different mechanical tensile stress levels is studied. In the second set of simulations, MD simulations are combined with the density functional-based tight bonding method to enhance the accuracy. This set of modelings focuses on a smaller zone in the vicinity of the crack tip. The impact of initial crack orientation on corrosion is studied by investigating corrosion of cracks in both armchair and zigzag directions. We investigate the subcritical crack propagation occurring as a result of the combined effects of both mechanical loading and chemical reactions. Our results show that cracks in graphene can grow due to chemical reactions with the environmental molecules. The MD modelings also predict that reaction of carbon atoms with oxygen molecules might lead to a stress relaxation at the crack tip, hence preventing further crack propagation. The results show that subcritical crack growth can happen by two mechanisms, which include the failure of C-C bonds or by removing the carbon atoms from graphene sheets in the form of CO or CO₂ molecules.