Atomistic Modelling of Nano-Indentation and Scratching of Nuclear Graphite*

Nuclear graphite, is a synthetic graphite typically manufactured by isostatic pressure moulding. It is used in the core structural components of the UK's nuclear reactors. This material contains many interesting atomic and mesoscale features. Recent TEM imaging shows that in-plane boundaries between misaligned basal planes within the graphite crystallites occur. Our previous work describes this “crazy paving” structure, which consists of nearly perfect slabs of graphite laminae, with nearly parallel c-axis. These slabs range in size from 100-1000 nm, with a thickness of ∼30 nm.

Dynamical MD simulations are performed using a recent ReaxFF potential fitting, as well as, the AIREBO potential model. A geometric relaxation method is used to construct these graphite “crazy paving” structures. The optimised structures show that the lowest energy interfaces comprise of 5, 6 and 7 carbon atom rings, with formation energies in the region of 0.5-1.0 eV.

The mechanical properties of these structures are investigated by performing MD simulations of nano-indentation and scratching. The simulated indenter tips are controlled by spring constraints, instead of a rigid moving surface, in order to more closely model the experimental procedure.