Multi-scale modelling of nuclear graphite tensile strength using the Site-Bond lattice model

Failure behaviour of graphite is non-linear with global failure occurring when local micro-failures, initiated at stress-raising pores, coalesce into a critically sized crack. This behaviour can be reproduced by discrete lattices that simulate larger scale constitutive responses, derived from knowledge of microstructure features and failure mechanisms. A multi-scale modelling methodology is presented using a 3D Site-Bond lattice model. Microstructure-informed lattices of both filler and matrix constituents or ‘phases’ in Gilsocarbon nuclear graphite are used to derive their individual responses. These are based on common elastic modulus of “pore-free” graphite, with individual responses emerging from pore distributions in the two phases. The obtained strains compare well with experimentally obtained data and the stress-strain behaviour give insight into the deformation and damage behaviour of each phase. The responses of the filler and matrix are used as inputs to a larger scale composite lattice model of the macroscopic graphite. The calculated stress-strain composite behaviour, including modulus of elasticity and tensile strength, is in acceptable agreement with experimental data reported in the literature, considering the limited microstructure data used for model's construction. The outcome supports the applicability of the proposed deductive approach to the derivation of macroscopic properties