Deformation and fracture of carbonaceous materials using in situ micro-mechanical testing

The local mechanical properties of vitreous carbon and another three porous graphite materials have been investigated using a novel in situ micro-cantilever bending approach. Vitreous carbon is used for validation of the micro-mechanical measurements. Filter graphite is a single phase material with ∼52 vol% porosity. Gilsocarbon graphite is a nuclear-grade graphite that is currently used in the advanced gas-cooled reactors in the UK with ∼20 vol% porosity in the filler particles and matrix; Pile Grade-A graphite (PGA) was extracted from a fuel brick within a Magnox reactor core with 15% weight loss due to neutron irradiation and CO2 radiolytic oxidation. The 'true' material properties obtained at micro-scale are found to be of much higher value than those measured at the macro-scale due to different failure controlling mechanisms. In particular for the PGA graphite, the micro-mechanical tests allowed the mechanical properties of the filler particles and matrix to be measured separately. The filler particles showed a higher stiffness and flexural strength compared with the matrix indicating the different influence of neutron irradiation on these two constituents. It is demonstrated here that the local mechanical properties of carbonaceous materials with various complex microstructures and even following neutron irradiation can be successfully evaluated.

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