Mechanical properties of pristine and nanoporous graphene

Abstract

We present molecular dynamics simulations of monolayer graphene under uniaxial tensile loading. The

Morse, bending angle, torsion and Lennard-Jones potential functions are adopted within the mdFOAM

library in the OpenFOAM software, to describe the molecular interactions in graphene. A well-validated

graphene model using these set of potentials is not yet available. In this work, we investigate the accuracy

of the mechanical properties of graphene when derived using these simpler potentials, compared to

the more commonly used complex potentials such as the Tersoff-Brenner and AIREBO potentials. The

computational speed up of our approach, which scales O(1.5N), where N is the number of carbon atoms,

enabled us to vary a larger number of system parameters, including graphene sheet orientation, size,

temperature and concentration of nanopores. The resultant effect on the elastic modulus, fracture stress

and fracture strain is investigated. Our simulations show that graphene is anisotropic, and its mechanical

properties are dependant on the sheet size. An increase in system temperature results in a significant

reduction in the fracture stress and strain. Simulations of nanoporous graphene were created by distributing

vacancy defects, both randomly and uniformly, across the lattice. We find that the fracture stress decreases

substantially with increasing defect density. The elastic modulus was found to be constant up to around

5% vacancy defects, and decreases for higher defect densities.