Mechanistic study on mechanical properties of graphene origami/aluminum nanocomposites under nanoindentation

Abstract

Nano-phase (graphene)/Al matrix composites exhibit a trade-off between strength and toughness. In this study, we present a novel approach to achieving synergistic effect between strength and toughness by constructing graphene origami/aluminum nanocomposites (GOri/Al). Molecular dynamics (MD) simulations were applied to investigate the nanoindentation behavior and reveal the strengthening and toughening mechanisms of the GOri/Al. The results show that compared to graphene/aluminum composites (Gra/Al), GOri/Al exhibits a 35 % enhancement in fracture toughness and a 22 % improvement in load-bearing capacity respectively. In the Gra/Al, the graphene fails and fractures at an indentation depth of 49.8 Å, resulting in the loss of reinforcement. In contrast, the GOri in the GOri/Al remains intact at an indentation depth of 55 Å with a unique unfolding process. After the indenter is completely unloaded, the GOri/Al shows significantly reduced dislocations and excellent plastic recovery. In the elastic stage, the speed of dislocation nucleation in different systems is the main factor affecting the indentation force. When the diamond indenter begins to interact with the insertion layer, the C-C bond stretching tension in the graphene causes a significant increase in indentation force, while the GOri is still in its buffering phase. In the plastic stage, stress in the GOri/Al is distributed along the periphery, with the ridges of the folds bearing more stress, effectively relieving stress concentrations. Adding a GOri together with a graphene of the same size to the Al further enhances the composite flexibility, strength, and hardness. Finally, the effects of indenter speed and indenter radius on the mechanical properties of the GOri/Al are also investigated. Our study provides a novel theoretical analysis and approach for the development of new Al nanocomposites.