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안규백,배홍열,노병두,안영호,최종교,우완측,박정웅,An, Gyubaek,Bae, Hong-Yeol,Noh, Byung-Doo,An, Young-Ho,Choi, Jong-Kyo,Woo, Wanchuck,Park, Jeong-Ung 대한용접접합학회 2015 대한용접·접합학회지 Vol.33 No.1
Recently, there have been the increase of ship size and the development of oil and gas in arctic region. These trends have led to the requirements such as high strength, good toughness at low temperature and good weldability for prevent of brittle fracture at service temperature. There has been the key issue of crack arrestability in large size structure such as container ship. In this report for the first time, crack arrest toughness of thick steel plate welds was evaluated by large scale ESSO test for estimate of brittle crack arrestability in thick steel plate. For large structures using thick steel plates, fracture toughness of welded joint is an important factor to obtain structural integrity. In general, there are two kinds of design concepts based on fracture toughness: crack initiation and crack arrest. So far, when steel structures such as buildings, bridges and ships were manufactured using thick steel plates (max. 80~100mm in thickness), they had to be designed in order to avoid crack initiation, especially in welded joint. However, crack arrest design has been considered as a second line of defense and applied to limited industries like pipelines and nuclear power plants. Although welded joint is the weakest part to brittle fracture, there are few results to investigate crack arrest toughness of welded joint. In this study, brittle crack arrest designs were developed for hatch side coaming of large container ships using arrest weld, hole, and insert technology.
안규백(Gyubaek An),홍승래(Seunglae Hong),박정웅(Jeongung Park),노찬승(Chanseung Ro),한일욱(Ilwook Han) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.3
Recent trends in shipbuilding and offshore industries are a huge increase in the ship size and the exploration and production of oil and natural gas in the arctic offshore region. High performance steel plates are required by these industrial trends. Also in IMO(International Maritime Organization) has begun to regulate of fuel of ship to environmental protection, therefore it is little bit difficult to use bunker-C oil to working ship. As the problem of environmental change such as global warming is emerged, the operation of the ship is considered to be involved in the environmental change problem, and the regulation of environmental pollution is gradually strengthened. As these environmental regulations are strengthened demand for LNG fuel ships is rapidly increasing. Currently, cryogenic steels used in LNG tanks include aluminum alloy, SUS 304, and 9%-Ni steel. Those steels are has high cost to construction of large LNG carrier. The new materials were suggested several steel mills to decrease construction cost and easy construction. The new cryogenic steel should be evaluate safety to applied real structure include LNG ship. Therefore, in this study, fracture toughness of weld joints were investigated with cryogenic steel for application of LNG tank.
안규백(Gyubaek An),배홍열(Hong-Yeol Bae),박정웅(Jeong-Ung Park) 대한용접·접합학회 2020 대한용접·접합학회지 Vol.38 No.6
This study evaluated the brittle crack arrest temperature (CAT) through an isothermal crack arrest test. The concept of evaluating CAT by an isothermal crack arrest test was proposed by C. Wiesner for application to low temperature steels for LPG tanks. The proposed test method consists of arresting a double-tension-type brittle crack with EB melt-run, which acts as a crack initiator and crack runway. There are some disadvantages when evaluating CAT with electron beam welding (EBW), which requires a local brittle zone to initiate a brittle crack. A local temperature gradient (LTG) system is developed to overcome the limitations of the EBW method. LTG systems do not require additional EBW to develop a brittle zone to initiate brittle crack. Recently, brittle crack arrest (BCA) steels are being used in large container ship such as in the upper deck or hatch side coaming of 22,000 twenty-foot equivalent units to prevent fatal brittle fracture accident of those ships. The International Association of Classification Societies (IACS) defined BCA steels using Kca requirement or CAT requirement in their unified rule (UR) S33. Therefore, when a shipyard uses BCA steel in the construction of large container ships, CAT or Kca should be evaluated. In this study, a new CAT test method is introduced to evaluate brittle crack arrest temperature more easily. Furthermore, both test methods were compared for the same specimens to verify the validity of the test method.
고강도강 용접부의 소성변형 정도에 따른 파괴안전성 평가
안규백(Gyubaek An),박정웅(Jeongung Park),Mituru Ohata,Fumiyoshi Minami 대한용접·접합학회 2019 대한용접·접합학회지 Vol.37 No.6
Fracture toughness of plastic strain (pre-strain) effect was determined as a function of the temperature in structural steels of the 600 to 780 MPa class. Cyclic loading during earthquakes produces plastic strain in the component, which is enhanced at the region of strain concentration. When the great earthquake occur, the steel structure 10-15% strain deformation was recorded at the beam-to-column connection. The steel structure fracture was more likely to occur. Therefore evaluate of plastic stain effect in steel structure to avoid unstable fracture especially in the weld joint (heat-affected zone; HAZ). The critical fracture toughness value (crack tip opening displacement, CTOD) in a large structure with plastic strain, which was applied to the HAZ region, was estimated from a small-scale plastic stained three-point bend specimen. The critical fracture toughness value is a very useful parameter to evaluate the safety of huge structural to avoid unstable fracture. In this study, it was proposed to critical fracture toughness value (CTOD) to avoid unstable fracture with each plastic strain effect.
안규백(Gyubaek An),한일욱(Illwook Han),박정웅(Jeongung Park),우완측(Wan Chuck Woo) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.6
As the recession in shipbuilding industry became longer, domestic shipbuilders focused on the need for high value added and high technology, and strived to build safer vessels. There are LNG carriers and container ships that require representative technologies. Both ship types are rapidly increasing ship size in the 2000s. Recently, there have been the increase of ship size and the development of oil and gas in arctic region. These trends have led to the requirements such as high strength, good toughness at low temperature and good weldability for prevent of brittle fracture at service temperature. Studies on unstable fracture have mainly been conducted to evaluate the brittle crack stopping properties of the high strength steel welded joints through large scale fracture tests, and studies on the difficulty of stopping brittle cracks in welded joints. It is known that BCA (Brittle Crack Arrest) steel has recently been developed to prevent unstable fracture if cracks propagate toward the BCA steel even if brittle cracks occur. Therefore, it is considered that the ship can be dried more easily if a technology capable of inducing the brittle crack to the BCA steel is developed. In this study, we describe a technique for securing unsafe fracture safety by inducing cracks toward the BCA steel, which has excellent brittle crack stopping ability, regardless of the welding process when brittle cracks occur in the superstructure of super large container ships.
대형 강구조블록의 최소 용접변형의 용접순서 결정 및 변형예측
박정웅(Jeong-ung Park ),안규백(Gyubaek An),양승현(Seung-hyun Yang) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.6
In order to minimize the effect of weld deformation on the preceding equipment during Pre-erection joint welding, the optimal welding sequence by unit load method was derived. And the weld deformation was predicted by the equivalent load method considering the constraint according to the derived welding sequence. For this purpose, the restraint coefficient was derived by conducting experiments and elastic FEM analysis on various welded specimens in order to derive the restraint of butt welds. In addition, the welding sequence that can minimize the welding deformation was derived by calculating the constraint by the unit load method in steel block structure. According to the derived welding procedure, the welding deformation near the preceding equipment during the pre-erection joint welding was predicted within 4 mm by using the equivalent load method considering the constraint. Specifically, the deformation in the lower part with the block supports occurred about 2 mm, and the deformation of 3~4 mm occurred at the upper part of block.