Grain misorientation and grain-boundary rotation dependent mechanical properties in polycrystalline graphene

In two-dimensional polycrystalline graphene, two angular degrees of freedom (DOF) are needed to define a general grain boundary (GB): the misorientation of two grains and the rotation of the boundary line. Via both molecular dynamics simulations and theoretical analysis, we see that the density of GB defects strongly depends on grain misorientation but is insensitive to GB rotation. And reveal the dependence of mechanical properties on grain misorientation and GB rotation in polycrystalline graphene. We find that the dependence of GB normal strength on grain misorientation and GB rotation in graphene stems from the superposition of the stress field induced by a pentagon-heptagon pair itself to that from the interaction between the other defects and the one under consideration. Based on MD simulations and ab initio calculations, we show that failure starts from the bond shared by hexagon-heptagon rings. We then apply continuum mechanics to explain the dependence of GB normal strength on the two angular DOF in graphene with pentagon-heptagon rings. The investigation showed here supplies valuable guidance to develop multiscale and multiphysics models for graphene.