The elliptical particles were added to the RVE until the desired graphene volume fraction was reached. Equation (3) suggests that the center of the ellipse is always located inside the RVE. However, the ellipse may intersect with one or two of the RVE boundaries. Periodic boundary conditions were used in such cases. Note that the implementation of PBCs for elliptical particles has additional steps compared to circular particles [32]. If an ellipse intersects with a single boundary segment, one additional ellipse $(x0i+1,y0i+1,\theta 0i)$ was compensated (Fig. 2(a)). If the ellipse intersects with two boundary lines, on or outside the segments, two additional ellipses $(x0i+1,y0i+1,\theta 0i)$ and $(x0i+2,y0i+2,\theta 0i)$ were compensated (Figs. 2(b) and 2(c)). If one of the RVE corner is located inside the ellipse, three additional ellipses $(x0i+1,y0i+1,\theta 0i)$, $(x0i+2,y0i+2,\theta 0i)$, and $(x0i+3,y0i+3,\theta 0i)$ were compensated (Fig. 2(d)). Figures 2(b) and 2(c) can happen only with radially asymmetric shapes like ellipses. As a modeling constraint, the ellipses are impenetrable, i.e., not allowed to overlap. This constraint is needed to make the 2D model closer to a three-dimensional microstructure.