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Butt 용접에서 횡구속과 휨구속에 고려한 용접잔류응력 예측
박정웅(Park Jeongung),안규백(An Gyubaek) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.6
용접에 의해 발생하는 잔류응력은 구조물의 피로, 파괴 뿐아니라 좌굴강도 등에 영향을 준다. 따라서 용접부의 잔류응력을 예측하고 이를 설계에 적용하거나 구조물의 안전성 평가에 사용하는 것은 매우 중요하다. 또한 기존 연구에서는 잔류응력의 분포를 표면에 국한하여 측정하고 평가 하였으나 구조물의 안전성을 평가하기 위해서는 표면뿐 아니라 내부에 발생하고 있는 잔류응력을 예측 및 측정해야 한다. 최근 열탄소성해석 기법과 내부 잔류응력 측정장비가 개발되어 다양한 코드에서 잔류응력을 제시하고 있다. 그러나 이것은 구조물에 구속이 없는 자유상태의 용접잔류응력이다. 그러나 구조물 제작 과정에서 필연적으로 발생하는 구속은 구조물에 아무런 구속이 없는 상태의 잔류응력과 다르고, 코드에서는 구속이 있는 경우 사용된 재료의 항복응력을 사용하도록 하고 제시하고 있다. 본 연구에서는 횡구속과 굽힘구속에 따른 잔류응력에 미치는 영향을 고찰하고, 실 구조물에서 부재의 두께, 항복 강도 그리고 구속도로부터 용접잔류응력을 예측하는 회귀식을 제시하였다. [그림 본문 참조]
와이블 응력 해석법을 이용한 극저온용강의 파괴특성 평가
박정웅(Jeongung Park),안규백(Gyubaek An) 대한용접·접합학회 2019 대한용접·접합학회지 Vol.37 No.6
The standardized three-point bending CTOD test as a fracture toughness test of materials has established a system in which the safety evaluation of brittle fracture of welded steel structures can be reasonably handled from the viewpoint of design, manufacture, and inspection. However, the evaluation system, which has been applied to the design, has been thoroughly examined for its validity by various experiments, analysis, and various problems have been found as a result of the application to the thick and high strength steel sheet. In particular, the concept that the failure limit evaluated by three-point bending CTOD is the same in the real structural members has been applied to the design. However, experimental and analytical results have been reported that the CTOD results do not satisfy the mechanical parameters that govern the fracture limit of cracked members. In this study, evaluated the suitability of 9% Ni steel as the inner tank material of LNG storage tank using weibull stress. For this purpose, we calculated the weibull stress from the CTOD test and predicted the failure stress and load of the real structure in consideration of the restraining effect.
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),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),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.