Here we investigated the fracture and wrinkling in graphene with topological defects using atomistic simulations and continuum models. We first studied the flaw insensitive fracture in nanocrystalline graphene and found the critical size around 20 nm. Our simulations reveal that micro-cracks nucleate randomly at intrinsic defects along grain boundaries and coalesce to form a big crack, eventually leading to catastrophic fracture. The key finding is that the microcrack nucleation and coalescence are not always induced by nor associated with pre-existing geometrical flaws such as a hole or notch in the system. Following the proceeding work, we conducted MD simulations on dislocation and grain boundary interacting with an edge crack. Our work reveals that a single dislocation can increase or decrease the effective stress intensity factor by 30% depending on the orientation of the dislocation with respect to the crack. The MD simulations for crack propagation along grain boundaries also indicate significant effect on the crack nucleation and propagation. We next employ large-scale atomistic simulations and continuum modeling to analyze the defects controlled wrinkling in graphene. Both atomistic and continuum simulations indicate that, due to the atomic thickness of graphene, even a single disclination/dislocation can cause significant out-of-plane wrinkling. Comparison with atomistic simulations indicates that the proposed model, with only three parameters (i.e., bond length, stretching modulus and bending stiffness), is capable of accurately predicting the atomic scale wrinkles near disclination/dislocation cores while also capturing the large scale graphene configurations under specific defect distributions such as those leading to a sinusoidal surface ruga or a catenoid funnel. A great challenge in designing curved graphene with topological defects is that the defect distribution that generates a specific 3D shape of graphene membrane is usually unknown, which is actually an inverse problem involving highly nonlinear deformation. To address this issue, we apply the phase field crystal (PFC) method to search for a triangular lattice pattern with the lowest energy on a given curved surface, which then serves as a good approximation of the graphene lattice structure conforming to that surface.
zhang, teng,
"Fracture and Wrinkling in Graphene with Topological Defects"
(2015).
Mechanics of Solids Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.7301/Z0RN3676
