Fracture toughness of JLF-1 by miniaturized 3-point bend specimens with 3.3-7.0 mm thickness

Abstract

A small specimen test technique is required to evaluate the fracture toughness values of several millimeter thick plates of structural materials and to maximize the use of very limited space for materials irradiation in intense neutron sources like IFMIF. In view of several advantages of three-point bending (3PB) over compact tension (CT), miniaturized 3PB specimens with 7.0, 5.0 and 3.3mm thickness were prepared from a Japanese low activation ferritic steel, JLF-1, which is a candidate first wall and fusion blanket material.Elastic- plastic fracture toughness tests by the unloading compliance method at room temperature and plane-strain fracture toughness tests at 77 K were conducted in general accordance with the ASTM standards. Emphasis was focused on the determination of the actual J-value for crack initiation, JIN, for reliable fracture toughness evaluation with the 3PB specimens. The obtained values of JIN at room temperature and KIC at 77 K were 100-120 kJ/m2 and 20-22MPam1/2, respectively, exhibiting little dependence on specimen size. By combining the experimentally obtained data with the plane-strain FEM analysis, a method was proposed to estimate JIN from a load-displacement curve measured for a single specimen. The method is applicable to heavily irradiated materials with little ductility.