Graphene-based papers attract particular interests recently owing to their outstanding properties, the key of which is their layer-by-layer hierarchical structures similar to the biomaterials such as bone, teeth and nacre, combining intralayer strong sp 2 bonds and interlayer crosslinks for efficient load transfer. Here we firstly study the mechanical properties of various interlayer and intralayer crosslinks via first-principles calculations and then perform continuum model analysis for the overall mechanical properties of graphene-based papers. We find that there is a characteristic length scale l 0 , defined as 0 / 4 Dh G , where D is the stiffness of the graphene sheet, h 0 and G are the height of interlayer crosslink and shear modulus respectively. When the size of the graphene sheets exceeds 3l 0 , the tension-shear (TS) chain model that are widely used for nanocomposites fails to predict the overall mechanical properties of the graphene-based papers. Instead we proposed here a deformable tension-shear (DTS) model by considering the elastic deformation of the graphene sheets, also the interlayer and intralayer crosslinks. The DTS is then applied to predict the mechanics of graphene-based paper materials under tensile loading. According to the results we thus obtain, optimal design strategies are provided for designing graphene papers with ultrahigh stiffness, strength and toughness.

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Carbon nanotube networks feature outstanding mechanical performance, and also hierarchical structures and network topologies. In this paper we investigate their structure-property relationship through mesoscale molecular dynamics simulations. We find that their microstructures undergo remarkable evolution under mechanical loads. The correlation between applied strain, microstructural evolution and failure mechanism, especially the bundling process and evolution of bridging carbon nanotubes, is discussed based on the simulation results. Based on the insights of the underlying mechanisms, further engineering approaches on the carbon nanotube networks towards enhanced mechanical properties are proposed and validated, e.g., by including intertube cross-links that resist shear, maintain the network topology and improve strain affinity.

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