A unified strength criterion for two-dimensional materials via bond failure analysis

The family of two-dimensional (2D) materials, including graphene, hexagonal boron nitride, transition metal dichalcogenides, and others, exhibits a wide range of lattice structures and defect configurations, leading to complex deformation mechanisms and mechanical failure behaviors. However, there is currently no universally accepted criterion that accurately describes the mechanical failures of these materials. In this study, we aim to address this issue by introducing the concept of intrinsic bond strength, which is solely dependent on the local chemical environment of the bond and is independent of loading states, defect types, and fracture bonds. We demonstrate the existence of this intrinsic bond strength and propose a unified strength criterion that considers the balance between the intrinsic bond strength and local stress state for any 2D material. By employing this unified strength criterion, we are able to accurately predict the failure of various 2D materials with different types of defects, including voids, cracks, grain boundaries, and hydrogenation. This work resolves a longstanding issue in predicting the mechanical failure of 2D materials via bond failure analysis, and carries important implications for the design and development of 2D materials with enhanced mechanical properties.