• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 추계학술발표대회 개요집
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• pp.79-81
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• 2005

Bridges constructed recently are preferred to have long spans and simple structure details considering not only the function as bridge but scenic beauty, maintenance, construction term and life cycle cost, etc. Therefore, they require high performance steels like extra-thick plate steels and TMCP steels. A TMCP steel produced by themo-mechanical control process is now spot lighted due to the weldability for less carbon equivalent. It improved at strength and toughness in microstructure. Recently, the SM570-TMC steel which is a high strength TMCP steel whose tensile strength is 600MPa has been developed and applied to steel structures. But, for the application of this steel to steel structures, it is necessary to elucidate not only the material characteristics but also the mechanical characteristic of welded joints. In this study, the characteristics of residual stresses in welded joints of SM570-TMC steel were studied through the three-dimensional thermal elastic-plastic analyses on the basis of mechanical properties at high temperatures obtained from the elevated temperature tensile test.

• 한국소음진동공학회논문집
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• 제12권3호
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• pp.195-203
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• 2002

In the engine room and the aft part areas of the ship, there exist so many tank structures contacting with fresh water or sea water or oil. If these structures exhibit excessive vibrations during the sea trials, it takes a lot of cost, time and effort to improve vibration situation because the reinforcement work requires emptying the fluid out of the tanks, additional welding and special painting. It is therefore very important to predict a precise vibration characteristics of the tank structures at the design stage, however it is not easy to estimate vibration characteristics of the structures because of difficulties for accurate evaluation of the added (or virtual) mass effect due to the fluid inside the tank. In this paper, numerical and experimental approaches have been performed to present same fundamental data necessary for anti-vibration design of tank structures contacting with fluid, by investigating vibration behaviors of rectangular tank structure for various water depths.

• Corrosion Science and Technology
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• 제16권2호
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• pp.85-89
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• 2017

One of the most challenging issues in the oil and gas industry is corrosion assessment and management in subsea structures or equipment. At present, almost all steel pipelines are sensitive to corrosion in harsh working environments, particularly in salty water and sulphur ingress media. Nowadays, the most commonly practiced solution for a damaged steel pipe is to entirely remove the pipe, to remove only a localized damaged section and then replace it with a new one, or to cover it with a steel patch through welding, respectively. Numerous literatures have shown that fiber-reinforced polymer-based composites can be effectively used for steel pipe repairs. Considerable research has also been carried out on the repair of corroded and gouged pipes incorporated with hybrid natural fiber-reinforced composite wraps. Currently, further research in the field should focus on enhanced use of the lesser and highly explored hybrid-biocomposite material for the development in corrosion prevention. A hybrid-biocomposite material from renewable resource based derivatives is cost-effective, abundantly available, biodegradable, and an environmentally benign alternative for corrosion prevention. The aim of this article is to provide a comprehensive review and to bridge the gap by developing a new hybrid-biocomposite with superhydrophobic surfaces.

• Corrosion Science and Technology
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• 제14권2호
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• pp.47-53
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• 2015

Recently, the bending process is greatly applied to fabricate the pipe line. Bending process can reduce welding joints and then decrease the number of inspection. Thus, the maintenance cost will be reduced. Induction heat bending process is composed of bending deformation by repeated local heat and cooling. By this thermal process, corrosion properties and microstructure can be affected. This work focused on the effect of induction heating bending process on the properties of ASME SA106 Gr. C low carbon steel pipes. Microstructure analysis, hardness measurements, and immersion corrosion test were performed for base metal and bended area including extrados, intrados, crown up, and down parts. Microstructure was analyzed using an optical microscope and SEM. Hardness was measured using a Rockwell B scale. Induction heat bending process has influenced upon the size and distribution of ferrite and pearlite phases which were transformed into finer structure than those of base metal. Even though the fine microstructure, every bent area showed a little lower hardness than that of base metal. It is considered that softening by the bending process may be arisen. Except of I2, intrados area, the others showed a similar corrosion rate to that of base metal. But even relatively high rate of intrados area was very low and acceptable. Therefore, it is judged that induction heat bending process didn't affect boric acid corrosion behaviour of carbon steel.

• 한국산학기술학회논문지
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• 제16권7호
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• pp.4398-4404
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• 2015

스테인리스 강판은 동적기계구조물을 제작하기 위한 구조용 재료로 널리 사용된다. 또한 이들을 일체화 시키는 방법으로 가스용접을 많이 사용하게 되는데 가스용접에는 다양한 종류에 의해 구조물을 일체화 시킨다. 따라서 부재와 부재를 연결하는 용접부에 대한 응력분포 및 피로강도평가는 구조물의 건전성 및 수명을 연구하는데 매우 중요한 요소가 된다. 그래서 본 연구에서는 피로시험에 의해서 얻어지는 ${\Delta}P-N_f$ 관계를 유한요소해석법에 의해서 최대주응력으로 ${\Delta}{\sigma}-N_f$ 관계로 나타내어 피로설계기준을 정하였고, 이 결과를 이용해서 확률론적 통계해석기법을 적용해서 가속식을 추정하여 임의의 목표수명을 예측할 수 있는 신뢰성설계기술기법을 제시하고자 하였다.

• 한국항공우주학회지
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• 제32권6호
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• pp.126-133
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• 2004

현재 개발중인 다목적실용위성은 자세제어 등에 필요한 추력과 모멘트를 발생하기 위해 NASA의 1lbf급 표준 추력기인 MRE-1을 사용할 예정으로 신뢰도 향상을 위해 이중추력기 모듈의 형태로 장착된다. 열차폐막의 국산화를 위해 기존의 용접 대신 전기주형법을 적용 할 예정이다. 하지만 열차폐막 내경이 기존의 용접으로 제작된 형상보다 불가피하게 감소됨으로 인해 열차폐막 끝단과 추력기 노즐 사이에 간섭이 발생할 우려가 제기되었다. 따라서 본 논문에서는 두 가지 다른 공정으로 제작될 열차폐막에 대해 구조해석을 수행하여 위성의 발사환경에서 추력기와 열차폐막의 간섭 여부 및 구조적 거동을 해석 및 비교하였고, 그 결과를 토대로 새로운 형상의 열차폐막에 대한 타당성을 검증하였다.

• Steel and Composite Structures
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• 제33권6호
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• pp.823-836
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• 2019

Spiral welded tubes (SWTs) are fabricated by helically bending a steel plate and welding the resulting abutting edges. The cost-effectiveness of concrete-filled steel tube (CFST) columns can be enhanced by utilising such SWTs rather than the more conventional longitudinal seam welded tubes. Even though the steel-concrete interface bond strength of such concrete-filled spiral-welded steel tubes (CF-SWSTs) is an important consideration in relation to ensuring composite behaviour of such elements, especially at connections, it has not been investigated in detail to date. CF-SWSTs warrant separate consideration of their bond behaviour to CFSTs of other tube types due to the distinct weld seam geometry and fabrication induced surface imperfection patterns of SWTs. To address this research gap, axial push-out tests on forty CF-SWSTs were carried out where the effects of tube material, outside diameter (D), outside diameter to wall thickness (D/t), length of the steel-concrete interface (L) and concrete strength grade (f'_c) were investigated. D, D/t and L/D values in the range 102-305 mm, 51-152.5 and 1.8-5.9 were considered while two nominal concrete grades, 20 MPa and 50 MPa, were used for the tests. The test results showed that the push-out bond strengths of CF-SWSTs of both mild-steel and stainless-steel were either similar to or greater than those of comparable CFSTs of other tube types. The bond strengths obtained experimentally for the tested CF-SWSTs, irrespective of the tube material type, were found to be well predicted by the guidelines contained in AISC-360.

• 대한조선학회논문집
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• 제51권3호
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• pp.246-253
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• 2014

Liquid natural gas is stored and transported inside cargo tank which is made of specially designed cryogenic materials such as 9% Ni steel, Al5083-O alloy and SUS304 and so on. The materials have to keep excellent ductile characteristics under the cryogenic environment, down to -163oC, in order to avoid the catastrophic sudden brittle fracture during the operation condition. High manganese steel is considered to be the promising alternative material that can replace the commonly used materials mentioned above owing to its cost effectiveness. In line with this industrial need, the mechanical properties of the high manganese steel under both room and cryogenic environment were investigated in this study focused on its tensile and fatigue behavior. In terms of the tensile strength, the ultimate tensile strength of the base material of the high manganese steel was comparable to the existing cryogenic materials, but it turned out to be undermatched one when welding is involved in. The fatigue strength of the high manganese steel under room temperature was as good as other cryogenic materials, but under cryogenic environment, slightly less than others though better than Al 5083-O alloy.

• 동력기계공학회지
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• 제13권5호
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• pp.95-102
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• 2009

A steam generator (boiler) in thermal power plants, consisting of more than 30,000 parts and components, can lead to the plant shutdown with damage to even the small part of the components; esp., like weld failures on boiler tubes. Consequently it is greatly demanded to improve the quality of the weld on the boiler tube for the stable operation of the power plants. Because of the feature of the welding, which is done past by melting the work pieces and adding a filler material that cools to become a strong coalescence, there is a great possibility that weld failures take place. As a result, it is regulated to make a non-destructive testing, like radiography test, to detect defects and flaws in the weld. The current film radiography test provides a lower image quality exceeding 2.0% of a basic quality level for a penetrameter, it is very likely to fail to detect micro defect. As a result, the prevention for the boiler tube failure has not been made effectively. In this study, computed radiography technology has been applied as a digital radiography test to the boiler tube weld, and Se-75 radiation source was used to improve the image quality, instead of Ir-192 source. As a result of this study, it is proven to save the time and cost for test and to enhance the quality level of penetrameter penetrating image, which enables to upgrade the quality of radiography test to the boiler tube weld.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2010년도 춘계학술발표대회 초록집
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• pp.60-60
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• 2010

Since the curved hull plate was made by a series of manufacturing process including cold bending, manual local heating and correction work, the accuracy of curved plate strongly depends on the proficiency of worker. So the demands on the automatic local heating system for curved hull plate have continuously increased and the various researches relevant to it have been performed. Generally, the heat sources used for local heating were flame and induction heat. In terms of initial cost, flame heating is in a better favorable position than induction heating. However, from the viewpoint of the control of heat, induction heating has more advantage. So the various researches related to apply the induction heating to the automatic forming system has been performed. The purpose of this study is to establish the proper capacity of high frequency induction heating system for forming the curved hull plate. In order to do it, the proper coil shape for local heating was designed and the efficiency of induction heating system was determined by comparing of temperature results obtained by FEA and experiment. With the results, the extensive FEA was performed to identify the effect of heated plate dimension, cooling method and the capacity of induction heating system on the amount of heat loss introduced by induction heating. Based on the results, the proper capacity of high frequency induction heating system was proposed.