Recent experiments have shown that the graphene foam material exhibits a rubber-like constitutive behavior and a near-zero Poisson's ratio. We have performed coarse grain molecular dynamics simulations, which show that these intriguing phenomena can be attributed to the microstructure deformation, rearrangement and compaction in three stages, respectively. The elastic deformation of microstructures leads to the initial linear behavior of the graphene foam material. Microstructure rearrangement, including bending, self-folding and flake-rotation, should be responsible for the second stage with a good performance of deformation but with a low bearing capacity. Microstructure compaction leads to a high bearing capacity at the last stage. A near-zero Poisson's ratio of the material within a certain range of compressive strain is also found to be due to the microstructure rearrangement, which induces soft flakes to fill the empty space without volume expansion in the other directions. Furthermore, it demonstrates that Poisson's ratio of such a type of material can be further tuned by the stiffness of graphene flakes as well as the amplitude of external strain. This study highlights the promise of graphene foam materials for energy absorption and dissipation under extreme conditions.

The work reported here is supported by NSFC through Grants #11532013, #11372317, #11502150 and the 973 Nano-project (2012CB937500).