Size effects on the load-displacement curves of compact specimens of SUS 316 steel

Austenitic stainless steel is an ideal material because of its very large ductility or toughness. The fracture toughness of this material is more than 1 MJ/m2, but in order to obtain the value effective as a material constant, the large test pieces with the smallest dimension more than 10 cm are required. According to the experimental results on the thickness effect (thickness 4 -- 24 mm) in the breaking of the compact test pieces of SUS 316 steel carried out recently, it was clarified that the point of maximum load on load-displacement curves was the point at which the steady development of ductile cracks started, and the apparent fracture toughness increased monotonously with plate thickness. In order to clarify the whole aspect of size effect in crack development, the systematic data on the test pieces with constant thickness, of which the plane dimensions are proportionally changed, are necessary. In this study, the effect of the plane dimensions of test pieces on crack development in austenitic stainless steel was examined, and the importance of true fracture stress as a factor controlling ductile fracture was studied. (Kako, I.)