SPECIMEN SIZE EFFECTS ON TENSILE PROPERTIES OF NEUTRON-IRRADIATED STEELS

In the research and development of miniaturized specimen technology, consideration of specimen size effect is the key issue. In this work, tensile tests were studied with variations of specimen size around the standard mini-tensile specimen in the Japanese fusion materials program. The materials used were JPCA (modified 316 SS) and JFMS (modified 10Cr-2Mo dual phase steel). Microstructure has been controlled to clarify the effect of grain size for the former and the effect of ferrite/martensite ratio for the latter. Neutron irradiations of post-irradiation deformation response, microstructure prior to and after deformation were examined by transmission electron microscopy. The effects of specimen thickness and aspect ratio (thickness/width) on tensile properties are studied. New scaling equations to evaluate valid yield strength and tensile strength from small specimens with thickness less than the critical thickness, t(c), are proposed. The origins of specimen size effects from a microstructural viewpoint are also discussed.