• 대한조선학회논문집
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• 제44권5호
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• pp.496-503
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• 2007

Although weld-induced deformation is inevitable in shipbuilding, it is important to reduce it as low as possible during fabrication for a more efficient production of ships' blocks. The weld-induced deformation is more serious in thin plates than in thick plates because heat affect zone of thin plates is wider than that of thick plates, and in addition internal and external constraints much more influence upon weld-induced deformation of thin plates. This paper deals with the application of the mechanical tensioning method to butt weld of thin plates to reduce the transverse and longitudinal deformation. in order to investigate the quantitative effect of tensioning method upon the reduction of angular deformation and shrinkage in longitudinal and transverse direction of weld line, butt welding test have been carried out for several thin plate specimens with varying plate thickness and magnitude of tensile load. Numerical simulation has been also carried out to compare the weld-induced deformation and residual stress. From the present study, it has been found that the tensioning method is very effective on reduction of weld-induced residual stress as well as weld-induced deformation.

• Journal of Ship and Ocean Technology
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• 제12권3호
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• pp.1-13
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• 2008

In shipbuilding, diverse manufacturing techniques for automation have been developed and used in practice. Among them, however, the hull forming automation is the one that has not been of major concern compared with others such as welding and cutting. The basis of the development of this process is to find out how to extract thermal forming information. There exist various methods to obtain such information and the 3D design shape that needs to be formed should be extracted first for getting the necessary thermal forming information. Except well-established shipyards which operate 3D design systems, most of the shipyards only rely on 2.5D design systems and do not have an easy way to obtain 3D surface design data. So in this study, various shipbuilding design systems used by shipyards are investigated and a 3D design surface data extraction method is proposed from those design systems. Then an example is presented to show the extraction of real 3D surface data using the proposed method and computation of thermal forming information using the data.

• 대한기계학회논문집A
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• 제39권7호
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• pp.707-712
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• 2015

용접변형은 용접 시 구조물 내에서의 불균일한 온도분포특성으로 인하여 필연적으로 유발되는 현상이다. 또한 용접변형이 발생된 용접구조물의 일부를 제거하는 과정에서 구조물내의 용접잔류응력과 강성의 연속적인 변화에 따라 추가적인 변형이 발생하여 변형의 재분포가 이루어진다. 특히, 이러한 현상은 선박의 제조과정 중 대형블럭을 옮기기 위해 설치된 러그의 절단과정에서 살펴볼 수 있다. 용접구조물의 부분 제거 시 발생되는 변형의 재분포는 절단공구의 파손 등의 문제를 야기하기도 한다. 본 논문은 실험을 통하여 용접구조물의 부분 제거에 따른 용접변형의 재분포가 어떠한 양상으로 발생되는지 연구하기 위한 것이다. 실험을 위해 필릿용접을 실시하였고, 용접된 리브의 일부를 제거함에 따라 발생되는 종굽힘과 각변형을 측정하여 비교 및 분석하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제36권8호
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• pp.1069-1075
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• 2012

레이저는 고밀도 열원으로써, 입열을 최소화하면서 고속용접이 가능한 장비이다. 특히 최근 상업화된 고출력 파이버 레이저는 특유의 발진원리 때문에 높은 빔품질과 소형화된 시스템이 가능하다. 이러한 장점들로 인해 파이버 레이저는 LNG 카고탱크에 대해 선박 내부에서 용접이 가능한 가장 적합한 열원이라고 판단된다. 따라서 본 연구에서는 선박산업에 레이저 용접기술을 적용하기 위해 파이버 레이저를 이용하여 LNG 선용 스테인리스강의 용접을 진행하였다. 연구에서 사용한 재료는 카고탱크에 사용되고 있는 오스테나이트계 스테인리스강인 두께 1.2mm의 STS304L였다. 레이저 출력 및 용접속도를 변화시켜가면서 겹치기 및 맞대기 용접을 실시한 후 용입특성을 분석하여 최적의 접합조건을 도출하였다. 그 결과 용접부에서 모재보다 우수한 기계적 성질을 얻을 수 있었다.

• 융합정보논문지
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• 제9권7호
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• pp.94-99
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• 2019

마찰교반용접법(Friction Stir Welding, FSW)은 1991년에 영국 용접연구소 TWI(The Welding Institute)에서 최초 개발된 후 여러 산업분야에 걸쳐 적용연구가 활발히 진행되고 있다. 본 연구에서는 철도차량 차체의 주요 구성 소재인 알루미늄 합금 (Al-6005-T6) 평판 압출재에 대한 마찰교반접합 적용 기초연구를 수행하였다. 접합속도를 500 mm/min으로 고정한 채 회전공구의 회전속도를 600-1600 rpm으로 변화될 때 미세구조와 기계적 물성 변화에 미치는 영향에 대해 평가하였다. 경도 측정 결과 nugget부는 모재의 70% 수준의 경도값을 가지며 설정된 범위 내의 공구 회전속도와 연관성은 관찰되지 않았으며 용접계면에서 약 5 mm 벗어나게 되면 모재의 경도값을 가지는 것으로 확인되었다. 인장시험 결과 회전속도가 올라갈수록 항복강도와 인장강도가 소폭 하락하는 경향을 보였으며 연신률의 변화는 관찰되지 않았다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.113-120
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• 2002

The effect of out-of-plane loads on the fatigue strength of welded steel structures is examined through fatigue tests with weldment of two fillet weld joint types. The results of the fatigue tests are compared with those under axial loads, on the basis of the hot spot stress range at the weld toe. From the result of the comparison, a method on how to incorporate the effect of the out-of-plane bending stress is proposed using design S-N curves derived from fatigue tests under the axial load. The proposed method is useful for rational assessment of the fatigue strength of fillet-welded structures, where combined stresses of the in-plane axial stress and the out-of-plane bending stress are induced simultaneously due to the complexity of applied loads and structural geometry.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.784-798
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• 2020

This paper presents the results of research on transverse shrinkage of welded butt joints conducted according to the principles of experimental design and under production conditions for two main welding techniques used in shipbuilding (FCAW and SAW). Analysis took into account the technological and structural parameters influencing the assembly suitability of a large steel structure. The presented method of evaluation makes it possible to apply approximation formulae to predict transverse shrinkage in real sections of a ship hull. The determined predictive formulae were verified to actual transverse shrinkage measurements during prefabrication of hull sections at a shipyard as well as the equations referring to the analyzed form of deformation available in the literature.

• 한국표면공학회지
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• 제42권6호
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• pp.294-300
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• 2009

The Friction Stir Welding (FSW) has mainly been used for making butt joints in Al alloys. The development of Friction Stir Lap Welding (FSLW) would expand the number of applications. In this study, for effective application on thin aluminum alloy lap joint, non-heat treatment A5052 alloys were joined by FSLW with the length of probe 2.3 mm and 3.0 mm. Investigating the characteristics of joint area showed the results were as below ; When the length of probe was 2.3 mm, good joint area was formed at all welding condition except for 600 rpm-700 mm/min. In the case of 3.0 mm probe length, there was formed good joint area without defects at 1500 rpm-100 mm/min. The width of joint area, position and size of defects were very important factors for FSLW, due to heat input and stirring intensity.

• 한국해양공학회지
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• 제28권5호
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• pp.452-465
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• 2014

The application of friction stir welding (FSW) technology has been extended to all industries, including shipbuilding. A heat transfer analysis evaluates the weldability of a welded work piece, and elasto-plastic analysis predicts the residual stress and deformation after welding. A thermal elasto-plastic analysis based on the heat transfer analysis results is most frequently used today. However, its application to large objects such as offshore structures and hulls is impractical owing to its long computational time. This paper proposes a new method, namely an equivalent strain method using the inherent strain, to overcome the disadvantages of the extended analysis time. In the present study, a residual stress analysis of FSW was performed using this equivalent strain method. Additionally, in order to reflect the external constraints in FSW, the reaction force was predicted using a neural network, Finally, the approach was verified by comparing the experimental results and thermal elasto-plastic analysis results for the calculated residual stress distribution.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.151-155
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• 2002

In GMA(Gas Metal Arc)Welding, the weld size that is a locally melted area of a workpiece is one of the most important considerations in determining the strength of a welded structure. Variations in the weld power and the welding heat flux may affect the weld pool formation and ultimately the size of the weld. Therefore, an accurate prediction of the weld size requires a precise analysis of the weld thermal cycle. In this study, a model which can estimate the weld bead geometry and a method for thermal analysis, including the model, are suggested. In order to analyze the weld bead geometry, a mathematical model was developed with transformed coordinates to apply to the horizontal fillet joints. A heat flow analysis was performed with a two dimensional finite element model that was adopted for computing the base metal melting zone. The reliability of the proposed model and the thermal analysis was evaluated through experiments, and the results showed that the proposed model was very effective for predicting the weld bead shape and good correspondence in melting zone of the base metal.