A unified strength criterion of diamane grain boundaries

Mechanical failure is one of the fundamental problems in solids, while the strength criterion, a measure of mechanical failure, is usually a phenomenological model that needs to be calibrated case by case. Diamane, a two-dimensional (2D) diamond is synthesized from graphene precursor, and the defect inherited from the graphene precursor is inevitable. Regrettably, the unified strength criterion of diamane is still a challenge due to the complexity of the stress state and defect structure. Here, the atomic configuration and stability of diamane grain boundaries (GBs) are first characterized through ab initio molecular dynamics (AIMD). Then, a unified strength criterion is proposed that can describe the mechanical failure of different diamane GBs under different loading states by using the concept of intrinsic bond strength. It is found the intrinsic bond strength is exclusively dependent on the local chemical environment of the bond and remains independent of loading states, GB structures and diamane thickness. In this regard, the bond fracture is initialized as the bond stretch stress arising from residual stress of defect and external loads exceeding the intrinsic bond strength. This work provides a physical understanding to construct the strength criterion of matter from the viewpoint of bond fracture analysis.