ABSTRACT
The recognition of the basic problem of ‘‘ductile-to-brittle transition’’ in metallic materials dates back to the time when the welded fabrication of World War II ships was plagued by catastrophic failures. The incidents were characterized by almost instantaneous fractures of entire ships. Although Navy records indicate that World War II ship steel exhibited some 40% elongation, there was obviously no beneficial effect of this property on the structural integrity of the ship plate in the particular environment. This experience has not been limited to the Navy materials and structures. At times, other costly failures were observed, such as a sudden burst of a multimilliongallon storage tank or unexpected break of a main aircraft spar in flight. The problems were very serious, of course, and, over the years, many large-scale investigations have been sponsored by the U.S. government and private industry to develop remedial measures. In particular, the Naval Research Laboratory has been very active in the studies of fracture phenomena. This work has provided an excellent theoretical and experimental background for fracture-safe design [1-4], with special regard to low-and medium-strength materials. Normally, this implies ‘‘fracture control’’ in design utilizing steels with the yield strength lower than about 120,000 psi. In this category, we encounter the majority of quenched and tempered steels used in modern applications involving rolling stock, shipping, bridges, lifting gear, storage tanks, and automotive components.
