Mechanical properties of polycrystalline graphene based on a realistic atomistic model

TL;DR

This study develops a realistic atomistic model for polycrystalline graphene, revealing that its mechanical failure is influenced by grain boundary meeting points and that strength and strain are independent of grain misorientation.

Contribution

It introduces a new method for constructing realistic polycrystalline graphene models and investigates their mechanical properties through atomistic simulations.

Findings

Cracks initiate at grain boundary meeting points and propagate through grains.

Intrinsic strength is normally distributed and about 50% of monocrystalline graphene.

Failure strain and strength are independent of grain misorientation angles.

Abstract

Graphene can at present be grown at large quantities only by the chemical vapor deposition method, which produces polycrystalline samples. Here, we describe a method for constructing realistic polycrystalline graphene samples for atomistic simulations, and apply it for studying their mechanical properties. We show that cracks initiate at points where grain boundaries meet and then propagate through grains predominantly in zigzag or armchair directions, in agreement with recent experimental work. Contrary to earlier theoretical predictions, we observe normally distributed intrinsic strength (~ 50% of that of the mono-crystalline graphene) and failure strain which do not depend on the misorientation angles between the grains. Extrapolating for grain sizes above 15 nm results in a failure strain of ~ 0.09 and a Young's modulus of ~ 600 GPa. The decreased strength can be adequately explained with a conventional continuum model when the grain boundary meeting points are identified as Griffith cracks.