Fracture toughness evaluation and specimen size effect

This paper reviews specimen size effect which significantly affects fracture toughness and fracture behavior of materials mainly based on the present authors' research works. After introducing controversial scale problems on fracture and fracture toughness, various actual examples of the scale problems are presented from a viewpoint of the effects of specimen size on dynamic fracture toughness values in various materials, such as steel for nuclear pressure vessel designated as A508cl.3, ductile cast iron, AC4CH aluminum casting alloy and silicon nitride ceramic. Then, the γ factor which has been introduced by Atkins et al. to interpret differences in fracture behaviors between a specimen (i.e. model) and the actual structure (i.e. prototype) and the Q factor which expresses the discrepancy between the HRR solution and the actual stress distribution at a crack-tip, are described for recognition of the scale problems.