In situ indentation behavior of bulk multi-layer graphene flakes with respect to orientation

In situ indentation is performed on bulk multi-layer graphene flakes (MLG) consolidated by spark plasma sintering to study the effect of orientation on the deformation behavior and associated energy dissipation capabilities of MLG. Spark plasma sintering of MLG aligns them into a uniformly oriented, densely packed pellet. With respect to the 2D surface of consolidated MLG, indentation is carried out on the surface (out-of-plane MLG orientation) and in the orthogonal direction (in-plane MLG orientation). The combination of instrumented indentation and imaging provided evidence of deformation and failure mechanisms in real-time, as well as a quantitative comparison of energy dissipation. Indentation performed in the orthogonal direction resulted in a work of indentation 270% greater than indentation performed on the surface. The prevalent energy dissipation mechanisms observed when indenting in the orthogonal direction are compressive reinforcement, bending, push-out, and pop-out while the prevalent mechanisms observed in the surface indent are sliding, bending, kinking, and MLG pull-out.