IN SITU CHARACTERISATION OF UNIRRADIATED GILSOCARBON GRAPHITE AT MULTIPLE LENGTH-SCALES

The evolution of the deformation and fracture of a Gilsocarbon nuclear grade graphite has been investigated in situ at three length-scales (nano-, micro- and macro-scale): (i) Neutron diffraction was used to quantify the lattice spacing changes with externally applied bulk strain. It was found that the lattice strain changes linearly with applied bulk strain but the magnitude is approximately
one order of magnitude less. This relationship deviated from linearity when the applied deformation exceeded about two-thirds of the peak strain. (ii) Micro-scale tests that are capable of isolating a selected volume of material, typically 2 µm x 2 µm x10 µm, were used to observe the propagation of damage at this length-scale. These results are typical of the damage and micro-scale fracture that occurs within an individual process zone. (iii) In situ tests under a scanning electron microscope traced the fracture characteristics of macro-cracking. The results obtained from these approaches are discussed with respect to the characteristics of the elastic and inelastic strain accumulation within individual process zones and the formation of macro-cracks in this quasi-brittle nuclear graphite.