Specimen size effects on fracture toughness of JLF-1 reduced-activation ferritic steel

Four different sizes of compact tension (CT) specimens of a reduced activation ferritic steel, JLF-1 steel, were fabricated and the fracture toughness was measured at room temperature by means of the unloading compliance method referring to in the ASTM E1820-99a. The JQ values obtained for the 1T–1CT and 1/2T–1CT specimens were 404 and 623 kJ/m2, respectively, indicating that the JQ value increased with decreasing the specimen thickness. On the other hand, the JQ value decreased when specimens were miniaturized while maintaining the similar proportions. The JQ values for the 1/2CT and 1/4CT specimens were 371 and 321 kJ/m2, respectively. Specimen size effects are interpreted in terms of an increase in the plain stress state region and plastic zone size at the crack tip in the specimen.