Failure in Two-Dimensional Materials: Defect Sensitivity and Failure Criteria

Two-dimensional (2D) materials have attracted a great deal of attention recently owing to their fascinating structural, mechanical, and electronic properties. The failure phenomena in 2D materials can be diverse and manifested in different forms due to the presence of defects. Here, we review the structural features of seven types of defects, including vacancies, dislocations, Stone-Wales (S-W) defects, chemical functionalization, grain boundary, holes, and cracks in 2D materials, as well as their diverse mechanical failure mechanisms. It is shown that in general, the failure behaviors of 2D materials are highly sensitive to the presence of defects, and their size, shape, and orientation also matter. It is also shown that the failure behaviors originated from these defects can be captured by the maximum bond-stretching criterion, where structural mechanics is suitable to describe the deformation and failure of 2D materials. While for a well-established crack, fracture mechanics-based failure criteria are still valid. It is expected that these findings may also hold for other nanomaterials. This overview presents a useful reference for the defect manipulation and design of 2D materials toward engineering applications.