Fracture Toughness of Nuclear Graphites

Abstract

Nuclear graphite materials behave as a brittle material during their fracture, so that, properties of higher fracture toughness and crack extension resistance have been required for graphites. The knowledge of fracture behavior of graphites must be needed for its modification, however, those behavior of graphites has not been examined in detail considering to its mechanical and physical properties.In this paper, fracture toughness tests were performed for nuclear graphites and properties of fracture toughness and crack extension resistance of graphites were examined as a function of mechanical and physical properties of graphites. From the results, the following conclusions were derived:(1) 3-point strength of graphites increases as Young's modulus increases.(2) Relationship between density and Jic was not found.(3) Jic increases as Young's modulus increases for lower Young's modulus materials, however, for high Young's modulus materials, Jic decreases as Young's modulus increases.(4) The graphites consisted of larger grain have larger crack extension resistance.(5) The value of JICE/π σsb2 is related to mean grain size of graphites, where E and σsb were Young's modulus and 3-point bending strength respectively.