• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2003.05a
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• pp.345-353
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• 2003

탄소강은 가공성과 용접성이 우수하기 때문에 각종 산업설비의 배관재로 많이 사용되고 있으며, 특히 가압중수로형 원전의 1차측 배관과 가압경수로형 원전의 2차측 배관에 주로 사용되고 있다. 그러나 탄소강 배관은 부식에 취약하므로 유동가속부식(FAC, Flow Accelerated Corrosion) 현상에 의한 배관의 두께가 감소하는 감육 손상이 중요하게 대두되고 있는 실정이다. 이러한 감육현상은 다른 어떤 설비보다 안전성의 확보가 강조되고 있는 원전 배관의 경우에 있어서는 특히 중요한 건전성 저해요인으로 인식되고 있다.(중략)

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.369-376
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• 1998

원자로 압력용기는 원자력발전소의 일차 압력경계를 구성하는 핵심 부품으로 이의 건전성은 원전의 안전성과 수명관리에 결정적인 영향을 미친다. 탄소강으로 구성된 압력용기는 노심에 근접하게 위치하여 운전중 계속되는 고속중성자 조사로 인하여 인성이 감소한다. 운전중 비상노심 냉각수가 주입되어 압력용기가 급격하게 냉각되면서 압력이 높게 유지되거나 재가압이 되는 가압열충격 현상이 발생하는 경우 조사취화된 압력용기가 적절한 안전여유를 가지지 못할 수도 있다. USNRC에서는 이에 대한 종합적인 연구결과를 바탕으로 가압열충격 규정을 제정하여 가압열충격 기준온도(RT$_{PTS}$)의 계산 방법과 심사기준온도를 제시하였다. 가압열충격 심사기준온도의 결정근거가 기술되어 있는 SECY 82-465에 의하면 축방향 용접부에 대한 위험도를 평가하여 270℉를 심사기준온도로 정하고 원주방향 용접부에 대해서는 30℉를 더하여 300℉를 심사기준온도로 제시하였다. 이 연구에서는 이렇게 제정된 원주방향 용접부에 대한 심사기준온도의 적정성을 평가하기 위하여 균열방향에 따른 가압열충격 위험도를 VISA-II 코드로 평가하였다. 우선 가압열충격 기준온도 제정 시 사용된 방법과 결과들을 검토하고 NRC의 계산결과를 재현하였다. 이를 바탕으로 원주방향 용접부에 대한 위험도를 평가한 결과 균열방향의 차이를 고려하기 위해 적용된 기술적 여유도인 30℉는 과도한 보수성을 내포하고 있음을 알 수 있었다. 원주방향 용접부가 축방향 용접부와 동일한 수준의 가압열충격 위험도를 가지기 위한 심사기준온도 차이는 50℉ 이상인 것으로 평가되었다.을 수 있었다.ngineering because this field has large uncertainties on predicting the effect of earthquake on structures. This paper is based on the presented paper at the Bertero Symposium held in January 31an4 February 1 at Berkeley, California, USA which was entitled "Needs to Evaluate Real Seismic Performance of Buildings-Lessons from 1995 Hyogoken-Nambu Earthquake-". The lessons for buildings from the damage due to the Hyogoken-Nambu Earthquake are necessity to develop more rational seismic design codes based upon a performance-based design concept, and to evaluate seismic performance of existing buildings. In my keynote lecture at the Korean Association for Computational Structural Engineering, the history of seismic design and use of structural analysis in Japan, the lessons for buildings from

• Journal of Welding and Joining
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• v.16 no.6
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• pp.44-51
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• 1998

It is well known that the fine bainitic microstructure obtained by TMCP(thermo-mechanical control process) secures the high toughness of base metal. Besides, TMCP steel is very suitable for high heat input in welding as it has low carbon equivalent. In HAZ, however, the accelerated cooling effect imparted on the matrix by the weld thermal cycles is relieved and thus the weldment of TMCP steel has softening zone which shows low fracture toughness compared with base metal. Therefore, PHWT of weldment is carried out to improve the fracture toughness in weldment of TMCP steel which has softening zone. In this study, the effects of PWHT on the weldment of AH36-TMCP steel are investigated by the small punch (SP) test. From the several results such as SP energy and displacement at room temperature, the behavior of transition curves, the fracture strength at -196$^{\circ}C$, distribution of (DBTT)sp and (DBTT)sp, the PWHT condition of A.C. after 85$0^{\circ}C$-1 sec W.C. was suitable condition for recovering a softening zone of HAZ as welded.

• Journal of Welding and Joining
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• v.6 no.2
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• pp.56-63
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• 1988

The effects of PWHT (poste weld heat treatment) and stress simulating the residual stress during PWHT in weld HAZ of low and high strength steels on corrosion fatigue crack growth were evaluated. The obtained results are summarized as follows. 1. Fatigue crack growth rate of HAZ in air and 3.5% NaCl solution was slower than that of parent due to the signgularity in weld HAZ. 2. In the case of HT-80, 3.5% NaCl solutio nacts to accelerate the crack growth for all specimens, and the sensitivity of as-weld to corrosion environment was the greatest among other PWHT specimens. 3. Corrosion fatigue crack growth of parent, as-weld and PWHT speciments ofr SS41 as well as SM53B was retarded in comparison with the fatigue crack growth in air. 4. There was a tendency that crack growth of PWHT specimens subjected $10kg/mm^2$ was faster than that of PWHT specimens without stress during PWHT. 5. The retardation phenomenon of crack growth in corrosion environment is attributed to the crack branching decreased .DELTA.K due to the corrosion products and multi-cracks.

• Journal of Welding and Joining
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• v.16 no.3
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• pp.111-120
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• 1998

To predict and evaluate metallurgical and mechanical behavior of th welds, it is essential to understand solidification behavior and microstructural evolution experienced in the welds, neither of which follows the equilibrium phase diagram because of rapid heating and cooling conditions. Metallurgical phenomena in austenitic stainless steel fusion welds, types 304, 309S, 316L, 321 and 304N, were investigated in this study. Autogenous GTA welding was performed on weld coupons, and primary solidification mode and phase distribution were investigated from the welds. Varestraint test was employed to evaluate solidification cracking susceptibilities of the alloys. GTA weld fusion zones in type 304, 321 and 304N stainless steels experienced primary ferrite solidification while those in type 309S primary austenite solidification. Type 316L exhibited a mixed type of primary ferrite and primary austenite solidification. The primary solidification mode strongly depended on $Cr_{eq}/Ni_{eq}$ ratio. In terms of solidification cracking susceptibility, type 309S that solidified as primary austenite exhibited high cracking susceptibility while the alloys experienced primary ferrite solidification showed low cracking susceptibility. The relative ranking in solidification cracking susceptibility was type 304=type 304N < type 321 < type 316L < type 309S.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.30-30
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• 2009

GTA 용접에서 용입, 용접부의 크기와 형상이 형성되는 아크 물리학적 현상을 이해함에 있어서 에너지 분포특성은 매우 중요한 인자이다. GTA 용접에서 아크 길이의 변화와 사용된 실드 가스 종류에 따라 음극인 텅스텐 전극 팁의 아크 루트 직경에 큰 변화를 주며, 양극인 모재 쪽의 에너지 분포에 영향을 미치며 된다. 기존의 연구자들은 저전류나 중전류 영역의 GTA 용접에서 텅스텐 전극의 선단각과 용입 형태와 의 관계를 plasma 기류 등에 의해 고찰하거나, 최대 아크압력에 미치는 전극형상의 영향에 대하여 연구하였다. 용접부에 작용하는 아크 압력의 분포는 결국 운동 에너지의 분포이다. 기존의 연구자들에 비하여 보다 간편한 실험을 통하여 양극 모재위의 아크 압력에 의한 에너지 분포특성을 규명하는 연구가 필요하다. 본 연구의 목적은 GTA 용접의 용접전류 100A~200A 영역에서 아크 길이 변화와 Ar 가스에 $H_2$ 혼합에 따른 측정된 아크 압력으로부터 기존연구자들의 아크 물리학적 결과들을 활용하여 양극 모재 위에 작용하는 전류밀도 분포를 유도하는 것이다. GTA 용접에서 아크 길이의 변화와 Ar 가스에 $H_2$ 혼합은 아크 압력분포에 큰 영향을 미치며, 이에 따라 에너지 분포특성에 많은 영향을 미친다. 아크 길이가 증가함에 따라 Ar가스와 $H_2$ 혼합가스의 에너지 분포는 감소하였고, Ar가스에 $H_2$ 혼합에 의해 아크 에너지가 증가하여 용입형상에 큰 영향을 미칠 것으로 판단된다. 이에 대한 연구는 향후 GTA 용접 응용분야 확대 적용될 것이며, 아크 물리학 연구에 기초적이고 아주 중요한 과학적인 자료가 될 것으로 판단된다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.7-13
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• 2019

This study aims to develop a FE Model to simulate dissimilar friction stir welding and to address its potential for fundamental analysis and practical applications. The FE model is based on Coupled Eulerian-Lagrangian approach. Multiphysics systems are calculated using explicit time integration algorithm, and heat generations by friction and inelastic heat conversion as well as heat transfer through the bottom surface are included. Using the developed model, friction stir welding between an Al6061T6 plate and an AZ61 plate were simulated. Three simulations are carried out varying the welding parameters. The model is capable of predicting the temperature and plastic strain fields and the distribution of void. The simulation results showed that temperature was generally greater in Mg plates and that, as a rotation speed increase, not the maximum temperature of Mg plate increased, but did the temperature of Al plate. In addition, the model could predict flash defects, however, the prediction of void near the welding tool was not satisfactory. Since the model includes the complex physics closely occurring during FSW, the model possibly analyze a lot of phenomena hard to discovered by experiments. However, practical applications may be limited due to huge simulation time.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.2
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• pp.133-142
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• 1984

With the weld-joined compact tension specimens compared with each other, that is, transverse and lengthwise about the crack propagation direction, high and low in the input heat level, same as and lower than the base metal in the strength of weld material, the fatigue test were performed. With these data, the log-log curves between the fatigue crack propagation rate ${\frac{da}{dN}}$ and the transition range of the stress intensity factor ${\Delta}K$ ahead the crack tip were drawed. These curves were compared and estimated among each compared specimens, among each zones, that is, the base metal, the heat-affected metal and the weld-mixed metal, and between this study and the past studies. Basically, Little difference in the slope of the $da/dN-{\Delta}K$ relation was showed in all the welded directions, all the input heat levels and all the zones. But, First, to comparison with in the past studies about the base metals, it was showed that da/dN started in the much later rate, increased faster and stoped in the little faster rate. Second, it was showed that, near the time the crack's going from the heat-affected zone to the weld-mixed metal da/dN decreased a little for a while. Third, in the lengthwise weld compared with the transverse weld, in the high input heat weld compared with the low input heat weld in the case used the weld material of the same strength as the base metal, in the opposite case in the case used the one of the lower strength than the base metal, in the case used the weld material of the same strength as compared with the lower strength than the base metal beside the high input heat and the lengthwise weld, it was showed that the crack occured earlier in lower ${\Delta}K$ and later da/dN, the curves went with the same slope. Forth, in the lengthwise weld compared with the transverse weld in the low input heat weld, in the low input heat weld compared with the high input heat weld, it was showed that da/dN went with the lower level.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.331-339
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• 2003

The study discussed in this paper investigated the material characteristics for the Thermo-Mechanical Control Process(TMCP) plates, which are controlled by several factors such as rolling, cold-stripping, cooling rate, and fixed carbon quantity. The suitability of thick TMCP steel plates as structural steel was also estimated through several experiments and with the us of a statistical method to analyze mill certificate sheets provided by the manufacturer. The results of this study are as follows: the TMCP steel plates showed stable values of the composition parameter ($P_cm$) and the carbon equivalents ($C_eq$ ) with satisfied yield strength, ultimate strength, and low-yield ratio.

• Journal of Welding and Joining
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• v.17 no.1
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• pp.104-115
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• 1999

There have been many studies on the two dimensional thermo-elasto-plastic analysis in welding process, mostly from viewpoint of residual stresses. In this study, the temperature distribution, transient thermal stress, and angular distortion during bead-on-plate gas metal arc welding of rectangular plates were analyzed by using the finite element method. A nonlinear heat transfer analysis was first performed by taking account of the temperature-dependent material properties and convection heat losses on the surface. This was followed by a thermo-elasto-plastic stresses and distortion analysis that incorporates the constrained boundary condition of the two dimensional solution domain to get the three dimensional size effect of the plate. The constrained boundary conditions adopted in this study were the constant displacement condition over the whole two dimensional section for axial movement in the welding direction, and the force boundary condition for rotational movementof the domain around the axis of the welding direction. It could be revealed that the theoretical predictions of the angular distortion have an improved agreement with the experimentally obtained data presented in the previous study.