• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.4
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• pp.329-336
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• 2000

Welding is a important technological method in mechanical engineering. $CO_2$MAG(metal active gas) welding means that metal part in double capstan drum for the inshore and costal vessels are joined by melting(with or without a filler material) or that new material is added to a metal part by melting. The thermal stresses appear due to a non-uniform temperature field, inhomogeneous material properties, external restraint and volume changes during phase transformations. In this study analysis the elasto-plastic thermal stresses distribution of welding part in double capstan drum for the inshore and costal vessels using finite element method (FBM). Therefore it calculates the numerical value that can be applied to the optimum design of welding parts and the shapes. The significant results obtained in this study are summarized as fellows. At early stage of the cooling after welding process, the abrupt thermal stresses gradient has been shown in the vicinity of welding part. In the thermal stresses analysis due to temperature gradient and heat shocking maximum stress was occurred of welding part and stresses were distributed from 54MPa~48MPa.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.68-76
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• 1997

The welding-induced initial imperfections such as residual stresses and initial strains in plated structures of ships and offshore structures can be effectively evaluated by the thermal elasto-plastic analysis method proposed in this paper. In the analysis of heat conduction of plate structures, both the analytical method and the numerical method are used. For the thermal elasto-plastic analysis of plates, the finite element analysis is performed, based on the initial strain method. In the plastic domain during incremental process, the 2nd order terms of stress increments and yield stress increments were considered, so that time increment could be controlled for more stable solution. To measure temperature distribution and angular distortion of plates during welding, bead-on-plate experiment are perform with various heat input and plate thickness. Measured data show good agreement with the calculated results.

• Journal of Korean Port Research
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• v.14 no.3
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• pp.331-340
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• 2000

For the rational and economic design of the structural elements of ships which is built using welding, the ultimate strength analyses of the plates having initial imperfections, such as welding residual stresses and strains, are needful. The welding deformation usually relied on approximative equations or based on expert's experience. But in this paper, for the thermal elasto-plastic analysis of plates, the finite element analysis was performed, based on initial strain method. In formulating the incremental analysis, unbalanced force terns were included. In the plastic domain during the incremental process, the 2nd order terns stress increment and yield stress increment were considered, so that time increment could be controlled for a more stable solution. The ultimate strength analysis program of the plates having initial imperfections was made. The ultimate strength analysis was carried out based on the results of the welding deformations of this paper. In the ultimate strength analysis the Rayleigh-Ritz method based on the minimum potential theory was used.

• Journal of Welding and Joining
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• v.20 no.4
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• pp.414-422
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• 2002

일본에 있어서 용접역학분야의 연구추이, 연구동향, 전망 등의 문헌을 충실히 소개했다. 연구추이로부터 추측하면. 역학현상의 해명뿐만 아니라 용접에 관련한 연구전체에 있어서 계산기의 지원은 현 연구수단의 주류로부터 옮겨져 왔으며. 이러한 경향은 더욱더 증가할 것으로 예상된다. 이 분야는 저자의 전문분야로서 일본, 세계에 있어서 용접관린학회등에 참가한 경험을 기초로 정리한 것이다. 용접역학 중에서도 용접변형 잔류응력을 대상으로 하는 분야에서는 범용프로그램이 시판되고 있으며 이러한 것은 데이터 작성으로부터 결과의 표시까지 간단히 얻어낼 수 있다. 이와 같은 장점을 보유하고 있기 때문에 일반적으로 널리 이용되고 있지만, 큰 결점 또한 갖고 있는 것을 말하고 싶다. 즉, 범용프로그램에서도 결과의 정당성을 평가하는 기능은 없으며, 결과의 평가는 해석자 자신에 맡겨지는 것이 사실이다. 이것을 충분히 인식할 필요가 있다. 이와 관련해서 실험을 행하고, 해석해를 도출하고, 이러한 결과와 범용프로그램에서 얻어진 결과와 비교 검토하는 등. 반드시 프로그램을 바르게 사용하는 있는 일의 인식을 행하는 일을 강조하고 싶다. 특히, 모델링, 시뮬레이션에 종사하는 연구자 기술자는 실험을 행하고 거기서 일어나는 어떤 사실을 감지하는 일을 권하고 싶다.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.98-103
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• 2008

This paper is to discuss distribution of welding residual stresses of a ferritic low alloy steel nozzle with dissimilar metal weld using Alloy 82/182. Two dimensional (2D) thermo-mechanical finite element analyses are carried out to simulate multi-pass welding process on the basis of the detailed and fabrication data. On performing the welding analysis generally, the characteristics on the heat input and heat transfer of weld are affected on the weld residual stress analyses. Thermal analyses in the welding heat cycle process is very important process in weld residual stress analyses. Therefore, heat is rapidly input to the weld pass material, using internal volumetric heat generation, at a rate which raises the peak weld metal temperature to $2200^{\circ}C$ and the base metal adjacent to the weld to about $1400^{\circ}C$. These are approximately the temperature that the weld metal and surrounding base materials reach during welding. Also, According to the various ways of appling the weld heat source, the predicted residual stress results are compared with measured axial, hoop and radial through-wall profiles in the heat affected zone of test component. Also, those results are compared with those of full 3-dimensional simulation.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.1
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• pp.8-18
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• 2012

In early constructed nuclear power plants, Ni-based Alloys 82/182 had been widely used for dissimilar metal welds (DMW) as a weld filler metal. However, Alloys 82/182 have been proven to be susceptible to primary water stress corrosion cracking (PWSCC) in the nuclear primary water environment. The formation of crack due to PWSCC is also influenced by weld residual stresses. Thus, the accurate estimation of weld residual stresses of DMW is crucial to investigate the possibility of PWSCC and instability behaviors of crack due to PWSCC. In this context, the present paper investigates weld residual stresses of nuclear reactor piping nozzles based on 2-D axi-symmetric finite element analyses based on layer-based approach using maximum molten bead temperature. In particular, the effect of analysis parameters, i.e., a thickness of weld layer, an initial molten bead temperature, convection heat transfer coefficient, and geometric constraints on predicted weld residual stresses was investigated.

• 한국가스학회:학술대회논문집
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• no.5
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• pp.97-104
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• 2002

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.5
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• pp.713-723
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• 2003

In this study, a state of art review of existing residual stress analysis techniques and representative solutions is presented in order to develope the residual stress analysis procedure for fitness-for-service (FFS) assessment of welded structure. Critical issues associated with existing residual stress solutions and their treatments in performing FFS are discussed. It should be recognized that detailed residual stress evolution is an extremely complicated phenomenon that typically involves material-specific ther-momechanical/metallurgical response, welding process physics, and structural interactions within a component being welded. As a result, computational procedures can vary significantly from highly complicated numerical techniques intended only to elucidate a small part of the process physics to cost-effective procedures that are deemed adequate for capturing some of the important features in a final residual stress distribution. Residual stress analysis procedure for FFS purposes belongs to the latter category. With this in mind, both residual stress analysis techniques and their adequacy for FFS are assessed based on both literature data and analyses performed in this investigation.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.5
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• pp.113-117
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• 2011

The frame for automotive assembly can be deformed and remained on the residual stress due to high temperature thermal attacks when in welding. The frame deformation can be made to problems when in assembly with body and the residual stress can affect the negative effect on durability performance of the automobile. In order to analyze the frame deformation, the simplified test frame which had the similar shape (form) of the real automotive frame was fabricated. The contactless optical 3D scanner was used for the shape difference measurement of the frame between before and after the welding. The FE-model of the test frame was composed and the heat transfer and thermal stress simulation were performed. The simulated results were compared with the measured results for the reference of the frame design. The deformation shape of the frame by simulation was in good agreement with that by the experimental measurement.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.385-390
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• 2005

A specimen with residual stress due to welding was analyzed by three-dimensional cohesive zone model. The residual stress distribution was calculated by simulating welding process, and cohesive elements were located along crack propagation planes. Crack growth is possible since two planes of the cohesive element are separated beyond a maximum load carrying capacity. Stress fields around a crack tip are compared for specimens with and without residual stresses. Load-displacement curves and crack growth behaviors are also examined.