An evaluation of fracture toughness of graphites for High Temperature Gas-Cooled Reactors by the ISRM core testing method used jointly with AE method

The fracture toughness test together with the acoustic emission method (AE) was conducted on a fine-grained isotropic graphite (IG-11) and a coarse-grained near isotropic graphite (PGX) for the core components of High Temperature Gas-Cooled Reactors. Three different kinds of specimens were used: a cylindrical three point bending, a short rod and a round compact tension specimens. These cylindrical specimens were proposed as the standard fracture toughness test method at the International Society for Rock Mechanics (ISRM). We have used the J-integral as a parameter of the fracture mechanics, taking into consideration non-linearity of deformation observed in the graphites used here. The J-integral value (JiAE) which was evaluated by AE method was constant independent of specimen shapes. On the basis of the results, the fracture toughness values KIC of the graphites were evaluated: 1.04 MPa√m for IG-11 and 0.77 MPa√m for PGX. In addition, the effect of specimen size on the JiAE values was examined. (author)