Strain Hardening in Graphene Foams under Shear

Strain hardening is an important issue for the design and application of materials. The strain hardening of graphene foams has been widely observed but poorly understood. Here, by adopting the coarse-grained molecular dynamics method, we systematically investigated the microscopic mechanism and influencing factors of strain hardening and related mechanical properties of graphene foams under shear loading. We found that the strain hardening is induced by cumulative nonlocalized bond-breakings and rearrangements of microstructures. Furthermore, it can be effectively tuned by the number of graphene layers and cross-link densities, i.e., the strain hardening would emerge at a smaller shear strain for the graphene foams with thicker sheets and/or more cross-links. In addition, the shear stiffness G of graphene foams increases linearly with the cross-link density and exponentially with the number of graphene layers n by G ∼ n ^1.95. These findings not only improve our understanding of the promising bulk materials but also pave the way for optimizing structural design in wide applications based on their mechanical properties.