SITE-BOND LATTICE MODELLING OF DAMAGE PROCESS IN NUCLEAR GRAPHITE UNDER BENDING

摘要

Graphite is used as neutron moderator and structural material in the core of the UK's fleet of Magnox and Advanced Gas-cooled Reactors (AGRs). The graphite cores are non-replaceable in these two designs and therefore potentially hfe-limiting. Graphite is a multi-phase, aggregated and porous material which could have a non-linear stress-strain response because of distributed damage accumulation within the material prior to rupture: quasi-brittle characteristics. Lattice models provide a way of capturing the resulting nonlinear behaviour by incorporating microstructural features and damage mechanisms within the discrete system. Here, the 3D site-bond model (Jivkov and Yates 2012) is used to simulate a near-isotropic nuclear reactor core Gilsocarbon graphite under bending in a micro-cantilever test (Liu et al 2014). Experimentally measured pore-size distributions and volume densities are used for model construction. Previous work on graphite site-bond modelling (Morrison et al 2014b) is further developed to consider pore effect on the deformation and failure behaviour of the bonds. Damage evolution and accumulation with increasing load is simulated by the consecutive removal of bonds subject to failure criterion. The simulated mechanical properties and force-deflection relationship were validated by experimental results.