Fracture and microstructure of graphites

This review surveys the behaviour of graphite under loading conditions in which the stressing is on the whole tensile. The performance of a recently introduced model of graphite failure is reviewed in relation to the models from which it was developed, and against data obtained from a wide range of experiments on the failure and deformation properties of graphite in tension and bend. The new model represents, to some extent, an amalgamation of two earlier models, which in themselves are only capable of describing graphite behaviour to a limited extent. It is demonstrated to be very successful in describing a wide range of experimental failure behaviour of VFT pitch coke and IM1-24 graphites in tensile and three-and four-point bend stress states. The introduction of non-conservative microstructural processes allows strain hysteresis to be predicted. Furthermore, it is demonstrated that such processes may be associated with a component of acoustic emission which, together with a further component attributed to pore extension by cracking, account for the experimentally observed frequency and energy of events from tensile stressed specimens. The possible extension of the new model, for instance to include the effects of fast neutron irradiation and radiolytic oxidation experienced in a nuclear reactor environment or to allow its use in finite element stress analysis, is discussed. (Author)