Molecular Simulation of Fracture Dynamics of Symmetric Tilt Grain Boundaries in Graphene

TL;DR

This study uses atomistic simulations to explore how symmetric tilt grain boundaries in graphene influence fracture behavior, revealing unique crack patterns, the formation of monoatomic carbon chains, and differences based on grain boundary orientation and misorientation angle.

Contribution

It provides new insights into the fracture dynamics of graphene with symmetric tilt grain boundaries, highlighting the role of grain boundary orientation and misorientation in crack propagation and chain formation.

Findings

Grain boundaries fracture differently than pristine graphene under tension.

Monoatomic carbon chains form during fracture, with their length and density depending on boundary orientation.

Maximum stress increases with misorientation angle, ranging from 32 to 80 GPa.

Abstract

Atomistic simulations were utilized to obtain microscopic information of the elongation process in graphene sheets consisting of various embedded symmetric tilt grain boundaries (GBs). In contrast to pristine graphene, these GBs fractured in an extraordinary pattern under transverse uniaxial elongation in all but the largest misorientation angle case, which exhibited intermittent crack propagation and formed many stringy residual connections after quasi mechanical failure. The strings known as monoatomic carbon chains (MACCs), whose importance was recently highlighted, gradually extended to a maximum of a few nanometers as the elongation proceeded. These features, which critically affect the tensile stress and the shape of stress-strain curve, were observed in both armchair and zigzag-oriented symmetric tilt GBs. However, there exist remarkable differences in the population density and the achievable length of MACCs appearing after quasi mechanical failure which were higher in the zigzag-oriented GBs. In addition, the maximum stress and ultimate strain for armchair-oriented GBs were significantly greater than those of zigzag-oriented GBs in case of the largest misorientation angle while they were slightly smaller in other cases. The maximum stress was larger as the misorientation angle increased for both armchair and zigzag-oriented GBs ranging between 32~80 GPa, and the ultimate strains were between 0.06~0.11, the lower limit of which agrees very well with the experimental value of threshold strain beyond which mechanical failure often occurred in polycrystalline graphene.