Size effects of graphene sheets on the strengthening mechanism of Al-graphene composites: A molecular dynamics study

Molecular dynamics simulations are performed to investigate the effects of graphene sheet size on the strengthening mechanism in Al-graphene composites during nanoindentation. In all cases, the graphene sheets block the dislocations, and thus the dislocations pile up near the graphene-matrix interface, strengthening the Al matrix. What is of particular interest is that strengthening mechanism is highly dependent on the size of the graphene sheet. If the indenter is not in contact with the graphene sheets, the nanoindentation force tends to increase with a decrease in the graphene sheet size and reaches a maximum value for a graphene sheet size of 30 Å. The trend in force with graphene sheet size is because the larger graphene sheets more effectively dissipate the force and lead to the emission of more dislocations from the Al-graphene interface. On the other hand, when the indenter contacts the graphene sheets, the force decreases with increasing graphene sheet size due to the superior strength of the graphene sheets. The composite containing the graphene sheet with the maximum size that covers the entire matrix shows the highest force that is almost 1.5 times of the value of other Al-graphene composites.