For current containership designs actually a new material class with minimum yield strength of 460 N/mm2, called YP47 steel, is considered. In connection with big plate thicknesses and high static and dynamic loads at the upper hull girder area e. g. the coaming and the coaming top plate brittle fracture is a factor which has to be deeply investigated. This paper describes development of a safety concept based on a brittle fracture avoidance strategy using fracture mechanics methods. Finally, this safety concept results in toughness and quality requirements, which are practically applicable in shipbuilding industry. Effects of different influence parameters are discussed, such as design temperature, fracture toughness, initial defect size, and shape of load spectra. Furthermore, prospective inspection and assessment strategies are presented.
Mainly driven by economy of scale, the size especially of containerships increased during the past years. This development is accompanied by using steels of increased plate thickness up to 85 and even 100 mm in some cases and higher yield strength exceeding 390 N/mm2. Currently, a new material class with a nominal yield strength of 460 N/mm2, called YP47 steel, is considered for latest containership designs. This development is mainly driven to reduce the plate thickness to gain the benefit of thinner plate thickness and to reduce welding work. It is the challenge for classification societies to consider all point of views and to ensure a safe application of this new material. Actually plate thickness up to 80 mm is designated in conjunction with this material. By utilizing the higher static load carrying capacity of the material, it is intended to achieve a limitation of the plate thickness. Otherwise, utilization of high permissible static loads results also in high dynamic loads.
