Abnormal crack coalescence and ductility in graphene

Abstract

Crack coalescence is a critical component in the study of mechanical resistance and the stability of materials. In the particular case of graphene, despite the extensive investigation of the formation and behavior of individual cracks in graphene, the study of crack coalescence within its structure remains unexplored. In this study, we investigate the interaction between two preexisting cracks and their effect on the mechanical properties of graphene using molecular dynamics simulations. The behavior of zigzag and armchair graphene structures with cracks separated by distances (Wgap) is analyzed under tensile loading. The findings reveal that crack coalescence, defined as the formation of a new crack from two existing crack tips, occurs for lower values of the distance between cracks, Wgap, resulting in a decline in the strength of structures. As Wgap increases, the stress-strain curves shift upward, with the peak stress rising in the absence of crack coalescence. The effective stress intensity factor formulated in this study exhibits a clear upward trend with increasing Wgap. Furthermore, an increase in Wgap induces a transition in fracture behavior from crack coalescence to independent propagation with intercrack undulation. This shift in fracture behavior demonstrates a brittle-to-ductile transition, as evidenced by increased energy absorption and delayed failure. A design guideline for the initial crack geometry is suggested by correlating peak stress with Wgap, within a certain range. The findings offer insights into the fracture mechanics of graphene, emphasizing the impact of crack interaction and geometry on strength. This provides design guidelines for graphene-based structures with enhanced mechanical performance.