Molecular simulations of stress wave propagation and perforation of graphene sheets under transverse impact

Transverse impact behaviour of graphene sheet (GS) has been studied using molecular dynamics (MD) simulations. One, two and three layers of GS have been impacted with a fullerene rigid projectile in the impact velocity range: 3.5-7.5 km/s. LAMMPS is used for MD simulations using the AIREBO force field. Kinetic energy, displacement, velocity and perforation resistance force of the projectile have been investigated to understand the perforation mechanics of GS. In-plane axial-wave and out-of-plane cone-wave speeds in the GS are determined. In-plane axial-wave speed is also determined using membrane theory where the modulus and Poisson's ratio used in that formula are derived from the MD simulations. Results show that the energy transmitted to the GS is equal to the work of perforation. At high impact velocities, two to three in-plane crack initiates in the GS along six different preferential crack angles at 60° interval in the form of bond breakage and propagates through the sheet during perforation which matches well with the lower bound of recent Lee et al. (2014) experiments. High axial-wave and cone-wave velocity of the graphene sheet indicates that GS will allow more momentum transfer offering the potential for improved ballistic protection per unit areal-density.