Research progress on enhancement mechanism and mechanical properties of FRP composites reinforced with graphene and carbon nanotubes

This review summarizes the recent advancements in the mechanical properties of fiber-reinforced polymer (FRP) composites reinforced with graphene and carbon nanotubes (CNTs). Different synthesis methods for incorporating graphene and CNTs into the FRP structure are reviewed and discussed. The enhancement of graphene and CNTs on the improvement of the interfacial shear strength (IFSS), interlaminar shear strength (ILSS), interlaminar fracture toughness (ILFT), tensile strength, tensile modulus, flexural strength, flexural modulus, impact resistance and fatigue characteristics of FRP composites is emphatically reviewed, especially the discussion of various performance related reinforcement mechanisms. These enhancement mechanisms are a complex project, in which the key is the interface problem between fiber and matrix caused by graphene and CNTs. This review provides an in-depth review of the improvement of each mechanical property due to the modification of interfacial properties between fibers and a nanofiller-reinforced matrix. In the selected representative papers, the addition process and strengthening mechanism of CNTs and graphene are reviewed in detail, and four enhancement mechanisms and synergistic effects are analyzed, including wettability, mechanical interlocking, chemical bonding and transition layer. Aiming at the improvement of ILFT of composite laminates, various nano strengthening strategies caused by graphene and CNTs and the toughening principle to prevent delamination failure are discussed in detail. The modeling and analysis tools for mechanical properties of graphene and carbon nanotube reinforced composites, including molecular dynamics method, finite element method and multi-scale modeling method, are reviewed. Finally, some problems in the enhancement mechanism of graphene and carbon nanotubes are discussed.