• Journal of Welding and Joining
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• v.17 no.2
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• pp.91-96
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• 1999

The problems of welding distortion in a welded structures are major concern in heavy industry. Weld-induced angular distortion's formula, composed weld parameter such as heat input and plate thickness, is developed analytically by the use of an elliptic cylindrical inclusion with an eigenstrain in an infinite laminated plate theory. The source of angular distortion in weldments is the plastic strains, which are caused by non-uniform temperature gradient. The distributions of the plastic strain corresponding eigenstrain are assumed by the use of Rosenthal's solution expressing thermal history. Comparison of calculated results with experimental data shows the accuracy and validity of the proposed method.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.1
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• pp.139-146
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• 2001

This paper presents a study on heat transfer and residual distortion analysis of laser welded EDFA(Erbium Doped Fiber Amplifier) LD(Laser Diode) Pump using the finite element method. In the production process of LD Pump in light-wave communication system, ferrule and saddle are welded by Nd-YAG laser. These parts experience thermal and mechanical effect during heating and cooling cycle with the laser welding. Thus distortion happens in the laser-welded packaging, and it makes an error in detecting the light signal translate through optical fiber in LD Pump. The amount of final displacement produced by the laser welding is predicted using the finite element method. And the optimal shape of saddle is proposed with the results of numerical analyses to minimize the displacement.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.304-307
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• 2006

Recently, as the global warming by fossil fuels and the steep rise of the oil price become social issues, the interest for renewable energy producing system is increasing rapidly. Among these, the wind turbine is most highlighted because of its economic competitiveness. The tower is one of the main components of wind turbine, which occupying about 20% of overall turbine costs. The tower access door located to base part of the tower, is used to enter the tower. This is the main structural weak points because of door hole, weldment, etc. And so are the weldments between the cans and the flanges. In this study, for the top flange part of the tower, by FEM using ANSYS, we retrieved the maximum von Mises stress on that and carried out fatigue analysis using stresses at such weak points.

• Laser Solutions
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• v.11 no.2
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• pp.1-7
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• 2008

The integrity of laser welded structures is decided in fracture strength and fatigue strength. This study made an effort to understand the fracture behavior considering residual stress. Experiments are conducted and analyses are performed to explore the influence of residual stress on fracture behavior of bead-on laser welded compact specimen. Fracture experiments are performed using ASTM 1820. The performed analyses included thermo-elasto-plastic analyses for residual stress and subsequent J-integral calculation. A modified J integral is calculated in the presence of residual stresses. The J-integral is path-independent for combination of residual stress field and stress due to mechanical loading. The results indicates that the tensile residual stress near crack front bring the low fracture load while the compressive residual stress bring the high fracture load compared to no residual stress specimen. These results quantitatively understand the influence of residual stress on fracture behavior.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.298-302
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• 2011

티타늄 용접부는 수소취성과 잔류응력에 대한 영향을 최소화 하기 위해 용접 후 잔류응력 제거 열처리 작업을 수행하고 있다. 하지만, 현재 항공 분야에 널리 사용하고 있는 규격에 따라 열처리 온도가 다양하게 설정되어 있어 현장에 적용하기에는 어려움이 있다. 이에 규격 별로 대표하고 있는 열처리 조건을 선정하여 열처리 조건에 따른 용접부에 대한 잔류응력, 잔류수소량을 확인하였고, 용접부에 대한 강도와 충격 인성을 확인하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.303-306
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• 2011

티타늄 용접부의 기공 형성은 용접 중 대기중으로부터 유입되거나 모재 표면의 산화막으로부터 확산과정을 통해 유입되는 산소 혹은 수소로 인해 형성된다고 알려져 있다. 용접부 기공은 용접부의 피로 수명과 인성을 저하시키며 취성 파괴의 원인이 된다. 이에 용접 후 비파괴 검사를 통해 용접부 기공을 확인하고 있으며 확인된 기공등의 결함은 재용접을 통해 제거하고 있다. 이번 연구에서는 기계적 가공 방법에 의해 기공을 제거한 후 재용접 하는 기존의 방식에서 벗어나 TIG Dressing 공법을 이용하여 용접부에 형성된 기공을 제거하고자 하였으며 이에 따른 용접부 노치 인성을 확인하였다. 시험 결과 TIG Dressing에 의한 기공 제거 효과와 노치 인성을 확인하였다.

• International Journal of Korean Welding Society
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• v.2 no.1
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• pp.33-39
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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 Korean Welding Society
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• v.2 no.1
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• pp.29-32
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• 2002

In previous study, the decrease and recovery of total stiffness in welded structure was discussed on the basis of experimental examination through tensile loading and unloading test of welded specimen. The recovery of structure stiffness was caused by the release of welding residual stress through mechanical loading. In this study, analysis model that is indispensable for the effective application of MSR method was established on the basis of test and measurement result. Thermal elasto-plastic analysis for welding process was performed by non- coupled analysis. Analysis results of welding process were transfer to elasto-plastic model for tensile loading & unloading by restart technique. In elasto-plastic analysis model for mechanical loading & unloading, hardening appearance of weld metal was considered by rezoning technique and tying technique was used for JIG condition of test machine.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.29-37
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• 2002

High alloyed stainless steels stand out for a high corrosion resistance due to a protective passive layer which is formed when the content of chromium exceeds 13%. When welding these steels, heat tints arise in the area of the weldment. They may occur from flint yellow to intensive blue in the spectrum depending on the applied welding process and the quality of the backing gas used. Due to their structures, they partly drastically reduce the corrosion resistance of stainless steels so that they may lead to damages of the technical application of welded components. In the following the pitting resistance by different backing gases and the chemical composition of the stainless steel itself are described.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.37-37
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• 2009

Due to their high corrosion resistance and improved mechanical properties super-duplex stainless steel (SDSS) are extensively used in petrochemical plants such as facilities in modern oil platform and off-shore process equipment. It is well known that the best mechanical and corrosion resistance properties of super-duplex stainless steel are obtained with a microstructure having approximately equal amounts of austenite and ferrite. And it is also known that sigma($\sigma$), chi($\chi$), secondary austenite(${\gamma}2$), chromium carbides and nitride affected adversely their properties. Therefore these phases must be avoided. However, effects of succeeding weld thermal cycle on the change of microstructure of weldment at multi-pass weld were not seldom experimentally researched. Therefore in the present work, the change of weldmetal microstructure and the effect of microstructure on pitting corrosion property at $40^{\circ}C$ by succeeding each weld thermal cycle were researched. The thermal history of root side was measured experimentally and the change of microstructure of root weld according to thermal cycle of each weld layer was evaluated. And the relationship between microstructure of root weld and pitting corrosion property at $40^{\circ}C$ was also investigated. Results of the present work are show as below. 1. The ferrite contents of root weld are gradually reduced by succeeding weld thermal cycle. 2. The 2nd phases such as sigma($\sigma$), chi($\chi$), secondary austenite(${\gamma}2$), chromium carbides and nitride are increased gradually by succeeding weld thermal cycle. 3. The pitting corrosion was detected in root weld part and weight loss by pitting corrosion is increased in proportional to the time exposed over $600^{\circ}C$ of the root weld. 4. The succeeding weld thermal cycles affect the microstructure of the former weldments and promote the formation of 2nd phases. That is, the more succeeding welds are added, the more 2nd phases are gradually increased. Consequently, it is thougth that this adversely affects pitting corrosion property.