Mechanical and Fracture Properties of Polycrystalline Graphene with Hydrogenated Grain Boundaries

Molecular dynamics (MD) is employed to study the mechanical and fracture properties of polycrystalline graphene with hydrogenated grain boundaries. Polycrystalline graphene sheets with an average grain size of 4, 6, and 8 nm are considered. The impact of hydrogenation percentage on the mechanical strength and fracture toughness of polycrystalline graphene sheets is investigated. Polycrystalline graphene with and without an initial crack are considered. The results show that due to the hydrogenation the strength of polycrystalline graphene sheets reduces. The impact of hydrogenation is significantly greater on the strength of polycrystalline graphene without an initial crack. The strength of polycrystalline graphene sheets with hydrogenated grain boundaries decreases with increase in temperature. The impact of temperature on the strength increases with increase in hydrogenation percentage at the grain boundaries. The results also show that the hydrogenation of the polycrystalline graphene affects the crack propagation path. As the hydrogenation percentage of grain boundaries increases, the crack path changes from intragranular to intergranular. Furthermore, the increase in the hydrogenation reduces the critical stress intensity factor of polycrystalline graphene. Such changes in the strength, fracture toughness, and crack path are due to the hydrogen embrittlement of grain boundaries which reduces their fracture energy.