Experimental Proof of Brittle Crack Arrestability by Large Scale Structural Model Test Simulating Ultra Large Container Ship

摘要

On the background of increasing demand in ship transportation,capacity of container ship is recently growing to achieve low costshipping. The use of extremely thick steel plates is recently requiredaround hatch side structure to realize ultra large container ships. Brittlecrack arrest design concept in container ships has been already commonin the last decade, but the rule revision in brittle crack arrest designdoesn’t catch up with a demand for thicker plates. Industries of shipbuilding and steel manufacturer in Japan have collaborativelyinvestigated about brittle crack arrest toughness, Kca, and alreadyestablished Kca test procedure. The recent program of the jointresearch activity focuses on the required Kca value in brittle crack steelplates over 80mm thickness, which has not been prescribed in any shipclassification rules, yet. In this project, the required Kca, with which arunning brittle crack can be arrested, is experimentally investigatedwith steel plates of 100mm thickness. A large scale structural models,which simulate a cruciform joint of hatch side coaming and strengthdeck, were exposed to brittle crack propagation test. In the presentwork, a part of the research program was picked up. It was supposedthat a brittle crack initiated at butt weld of strength deck propagatedinto hatch side coaming. Two different scales of the structural modelspecimens, denoted as large-scale specimen and ultra large-scalespecimen, were prepared. A brittle crack runway plate simulated asstrength deck was designed over 1000mm in ultra large-scale specimen.A running brittle crack at a specific test temperature was examined tobe arrested or not in the test plate subjected to a specific tensile stress.Brittle crack behavior was discussed considering the balance of crackpropagation driving force and crack arrest toughness based on fracturemechanics. The required Kca value in steel plates over 80mmthickness for hatch side coaming was also discussed.