Mechanical Properties of Defective Graphene Sheets

Graphene GBs may have significant effects on the mechanical properties, in particular, on the failure strength of graphene sheets. In this work, the failure strengths of graphene grain boundaries, over a range of misorientation angles from [IMAGE png] to [IMAGE png], were investigated by molecular dynamics simulations. The GB failure strength as the function of GB disorientation angles is displayed in Fig. j. Our simulations revealed that, for GBs with uniformly distributed GB dislocations (red squares and purple triangles in Fig. j), a higher dislocation density yields a counterintuitive higher GB failure strength; this trend is disrupted, however, by GBs having a non-uniform dislocation distribution (blue squares and green circles in Fig. j). Hence, our study indicates that, in addition to the dislocation density, the distribution of GB dislocations also plays an important role in determining the GB failure strength. Figures a-i display the correlation between the level of the initial atomistic stress distribution and onset of bond rupture. From Figs. a,c,h,i, we found that for GBs featuring a uniform dislocation distribution, a higher misorientation angle will yield a higher failure strength as a result of overlapping and mutual cancelation of the strain fields of neighboring dislocations. For GBs with a non-uniform dislocation distribution (Figs. b,d-g), however, local structural inhomogeneity introduces large local tensile stresses and the failure strength decreases significantly. Therefore, a complicated interplay exists between the dislocation density and distribution, and the failure strength of graphene grain boundaries. This work has been published in the journal CARBON (DOI:10.1016/j.carbon.2012.03.012).

Figure: (a-i) (left panel) Initial atomistic stress distribution [namely, the distribution of Tr(r) = [IMAGE png] prior to applying the loading] and (right panel) onset of the rupture process for several representative GBs. In the right panels of (a-i), pentagons, heptagons, and crack regions are colored blue, red, and green, respectively; cleaved bonds are highlighted with dark dashed lines. (j) GB failure strengths plotted with respect to the misorientation angle in the zigzag orientation. The gray dashed line represents the GB dislocation density.