Mechanical properties of crumpled graphene under hydrostatic and uniaxial compression

A molecular dynamics study is undertaken to estimate the mechanical responses of crumpled graphene subjected to hydrostatic compression and uniaxial compression, respectively. The crumpled graphene is found to be a non-Hookean medium showing a non-linear stress-strain relation even for small strain and this is explained by structural changes that start to occur when a small stress is applied. Analysis of the unloading curves suggests that the elasticity limit is achieved at smaller densities under hydrostatic compression rather than under uniaxial compression. Corners of double-folded graphene flakes are formed under hydrostatic compression, while uniaxial compression results mainly in formation of single folds with less damage of the graphene lattice.