Session: 02-10-02 Fatigue and Fracture Reliability 2

Submission Number: 180793

Brittle Crack Arrest Technology Using Surface Layer With High-Toughness Steel for Large Container Ships 

To prevent large-scale failure due to brittle crack propagation, steel plates used for hatch side coamings and upper decks on container ships require brittle crack arresting properties. In recent years, container ships have grown larger, ultra-thick high-strength steel plates exceeding 80mm in thickness are used in the large container ships. The rules of the International Association of Classification Societies (IACS) require steel plates over 80 mm thick used for hatch side coamings to have an extremely high arrest toughness, with Kca value of 8000 N/mm^3/2 or higher. This study proposes a new arrest structure utilizing surface layer with high-toughness steel plate. By combining the surface layer with high-toughness steel plate and partial penetration welding, the propagation path of brittle crack is confined to the high-toughness region, effectively arresting brittle crack propagation. It is expected that brittle crack arrest can be achieved even when the Kca value of steel plates is less than 8000 N/mm^3/2. To demonstrate the effectiveness of the new brittle crack arrest technology, large-scale structural model tests simulating brittle crack propagation from the upper deck to the hatch side coaming were conducted. Two tests were performed, using test plates with thicknesses of 90 mm and 100 mm, respectively. To investigate the effect of partial penetration weld depth, multiple test plates with varying penetration depths were prepared by controlling the welding conditions. Test results showed that when the penetration depth was shallow, the brittle crack arrested immediately after entering the test plate, demonstrating the effectiveness of the proposed brittle crack arrest technology utilizing the surface layer with high-toughness steel.

Presenting Author: Teppei Okawa NIPPON STEEL CORPORATION

Presenting Author Biography: Dr. Teppei Okawa is a senior researcher at Nippon steel corporation. His research interests include fracture and fatigue of steel materials. His recent work focuses on fracture evaluation of steel structures such as ships, tanks and wind power.

Authors:

Teppei Okawa NIPPON STEEL CORPORATION
Takayuki Yonezawa NIPPON STEEL CORPORATION
Kiyotaka Nakashima NIPPON STEEL CORPORATION
Saho Sugasawa NIPPON STEEL CORPORATION
Shigenobu Sato IMABARI SHIPBUILDING CO., LTD.
Hiroto Nishiyama IMABARI SHIPBUILDING CO., LTD.
Yasuyuki Kan IMABARI SHIPBUILDING CO., LTD.
Kenji Kamita IMABARI SHIPBUILDING CO., LTD.