Grain boundaries orientation effects on tensile mechanics of polycrystalline graphene

Molecular dynamics simulations were performed to investigate how the orientation of grain boundary (GB) affects the tensile mechanics of polycrystalline graphene, where two opposite GB groups, i.e., armchair (AC) and zigzag (ZZ)-oriented tilted GBs were considered for the anisotropic study. We found very close mechanical similarities between the two groups in misorientation angle effect and critical bond length effect to determine the tensile strength. Mono-atomic carbon chains (MACCs) were commonly generated at tensile failure in both groups, as bridged between fractured sections, yielding the considerably higher population density and achievable length (4.51 nm ^-2 and 1.47 nm, maximally) compared to pristine graphene. Notably, we found that polycrystalline graphene exhibited distinctly different behaviors in this MACC production depending on GB orientation, being 1.2-3.0 times denser and 1.6-5.0 times longer for ZZ-oriented GBs. Atomic stress analyses indicated that all key reactions emerging before tensile failure would not be affected by the GB orientation of polycrystalline graphene since the reactions only occurred along GBs, explaining why anisotropic mechanical GB response has not been observed so far, in contrast to the MACC dynamics occurring after tensile failure.