조선용 후판 AH32 강에 대한 SAW 및 Hybrid(CO₂ Laser+MIG) 맞대기 용접부의 열 및 역학적 특성 비교

방한서,오종인,방희선,노찬승,이윤기,봉현수,이정수,Bang, Han-Sur,Oh, Chong-In,Bang, Hee-Seon,Ro, Chan-Seung,Lee, Yoon-Ki,Bong, Hyun-Soo,Lee, Jeong-Soo 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.5

In this paper concentrate on the comparison of the thermal and mechanical characteristics in Butt joint of ship structure AH32 steel by using hybrid welding and conventional SAW. For this purpose, fundamental welding phenomena of hybrid process using $CO_2$ Laser and MIG is investigated by the experiments and characteristics of thermal and welding residual stress distribution of welded joint in SAW and hybrid welding are understood from the result of FE numerical simulation and experimental values. From the result of this study, it is understood that Laser-MIG hybrid welding have high potential, make substantial saving of time and manufacturing cost and may proves its self robust in the butt joining of thick AH32 steel ship structural plate in the near future.

필릿용접 루트부 Gap의 영향에 관한 연구

방한서,김성환,김종명 조선대학교 생산기술연구소 1998 生産技術硏究 Vol.20 No.2

The groove for proper welding joints is required to obtain a complete joint penetration However, fillet joint welding without edge preparation is often adopted to save coats and manhours. In this case, gaps of root may occurs, which cause stress concentration around gaps of root and compromises structural safety. In this paper, double fillet welded T-joints are selected for investigation. The welding residual stresses on the plate, web and notches of roots are calculated under two dimensional heat conduction and plane deformation thermal elasto-plastic theory are applied. It is found that multi pass welding alleviates stress concentration on the notch tips of roots by distributing the compressed residual stresses and external tensile forces in the direction of the width of web may restrict the occurrence of root-crack since the compressive residual stresses is expected in that direction. Through this results, in case of acting tensile force for the direction of the width of web, we supposed that occurrence of root-crack is restricted under the influence of compressed residual stress around notch-tip of root.

T-joint 용접부의 형상에 따른 역학적 메카니즘에 관한 연구

방한서,김종명 대한용접접합학회 1999 대한용접·접합학회지 Vol.17 No.6

The use of thick plate in increasing in recent years due to the rapid expansion of chemical plants, nuclear plants, ships and other industrial plants. Welding is the most popular joining techniques employed in manufacturing industrial machineries and structures. Normally, Groove shapes are prepared according to appropriate rules and regulations such as KS, JIS, AWS, LR, DNV and etc. for various thicknesses of plate. However those groove angles tend to be too large. As a result of large groove angle, residual stress, deformation of material and strength reduction is obtained. Therefore, the reliability and safety of structures and machinery tend to be decreasing. Therefore, in this paper, theoretical as well as experimental study are carried out to find optimum groove shapes for T-welded joint of mild steel. The test specimen are made in same condition with simulation model. Welding residual stresses measurement by sectional cutting method. ⅰ) The mechanical difference for change the thickness of plate and groove angle are not appeared. ⅱ) In a mechanical point of view minimum preparation angle(40°) is more suitable than maximum groove angle(60℃). ⅲ) The measurement value and distribution of welding residual stresses are not effected largely by groove angle. It is mechanical restraint that mainly affect welding residual stresses distribution. In mechanical point of view minimum groove angle is more suitable than maximum groove angle. Therefore, it is appropriate to minimize the size of groove shape in strength and safety.

$2\frac{1}{4}Cr-1Mo$강 압력용기 Nozzle 용접이음부의 재열균열에 관한 연구

방한서,김종명 대한용접접합학회 2000 대한용접·접합학회지 Vol.18 No.2

Pressure vessels usually consist of main body and pipes which are connected with the main body. And as joining method of such main body and pipes, welding is carried out. After welding, welding residual stresses inevitably occur around welded joints. As residual stresses act harmfully on fatigue strength, corrosion and buckling strength of structure, PWHT is carried out for the purpose of removing the residual stress. But, during PWHT process, $2\frac{1}{4}Cr-1Mo$ steels are frequently apt to generate reheat crack. For this reason, it is strongly needed to analyze and examine the mechanical behavior of welded joints before and after PWHT process. So, in this study, welded nozzle parts of pressure vessel where reheat cracks frequently occur are selected for examining the mechanism of crack-occurrence.

필립용접 루트부 Gap의 Notch효과에 관한 연구

방한서,김종명 전남도립대학교 1999 전남도립대학교 논문집 Vol.S No.-

The groove welding for proper joint design obtain complete joint penetration. But, fillet joint welding is likely to produce inadequate joint penetration, i.e. gap(or slit) of root. Nevertheless, this process is often carried out. Because edge preparation in welding is complained with the increasement of preparation-time and consumption of welding rod. But, welding structures are apt to bring about root failure by the stress concentration which will occur by external force. Therefore, in the safety and reliability of structure, groove welding is generally required. The focus of this study is to investigate the welding residual stresses is distributed on the plate, web and, especially, around notch of root in the double fillet welded joint which have root gap due to incomplete joint penetration So, in this paper, the double fillet welded joint by the single and multi-pass welding which are acted submerged arc welding process is selected for analysis and used the finite element computer programs based on the two dimensional heat conduction and plan-deformation thermal-elastic-plastic theory. The result of this study represent that the multi-pass welding have the advantage of welding residual stress. Also, the notch-tip of the root generally distributed the compressed residual stress. Through this results, in case of acting tensile force for the direction of the width of web, we supposed that occurrence of root-crack is restricted under the influence of compressed residual stress around notch-tip of root.

厚板 鋼構造物 熔接이음부의 熱分布 特性에 關한 硏究

방한서,김종명 대한용접접합학회 1995 대한용접·접합학회지 Vol.13 No.1

Recently, as the industrial structure tends to become large, the thickness of structural plate becomes thicker. Therefore, the thicker the plate of welded structure is, the larger the shape of welded joint. The effect of large heat input makes large heat affected zone(HAZ). These bring to complict welding residual stress and to weaken material, which may cause extremely harm to the safety of structures. Nevertheless, welding is design is regulated by the KS, JIS or standard in the resister of shipping such as KR, ABS or LR. However, these rules are based on rather experimental than theoretical. In this study, the computer program of heat conduction, considering un-steady state and quasi-steady state, is developed for optimizing(minimizing) a shape of welded joint. The characteristics of heat on the welded joints with various shapes are clarified by the results of the analyses.

溶接이음부 形狀變化에 따른 後熱處理時의 力學的 特性에 關한 硏究

방한서,강성원,김기성,김종명,노찬승 대한용접접합학회 1997 대한용접·접합학회지 Vol.15 No.2

In order to define the effects on shapes of welding joint, during Post Welding Heat Treatment (PWHT), we have carried out numerical analysis on the several test pieces by using computer program which was based on thermal-elasto-plastic-creep theories for the study. And then, welding residual stresses after PWHT were measured same test-pieces to compare with the results of numerical analysis. The main results obtained from this study is as follows: 1) The distribution modes of welding residual stresses are same on the all test pieces after and during PWHT by the both sides (measurement and numerical analysis). 2) The mechanical difference for change the thickness of plate and bevel angle are not appeared. 3) In a mechanical point of view (like material quality test, welding deformation etc.), manimum bevel angle (40$^{\circ}$.) is more suitable than maximum bevel angle (70$^{\circ}$).

극후판 Box Column 코너이음부의 용접잔류응력 및 Groove형상 특성에 관한 연구

방한서,안규백,김종명,석한길,장웅성 대한용접접합학회 1999 대한용접·접합학회지 Vol.17 No.1

Ships, structures on the ocean, bridges, and other structures tend to be large by the development of industry. These ultra thick plate were welded with large heat input, which causes welding stresses, deformation and buckling, so it has to be considered the weld design, safety, reliability. The welded residual stresses were produced and redistributed due to the effect of large heat input. The mechanical phenomenon has not been surely identified yet. In spite of the lack of the study on the box column, there are various types of steel frame such as I type, H type, + type and $\bigcirc$ type, used in high story building. In this study, we performed computer simulation with two dimensional heat conduction and plane deformation thermal elasto-plastic finite element computer program as changing the plate thickness to 100mm, 150mm and groove angle to $60^{\circ}C$, $45^{\circ}C$, $30^{\circ}C$ of corner joint in box column. And then, to identify mechanical phenomenon such as the phenomenon of thermal distribution, welding residual stresses and deformation and to decide optimum groove angle and welding condition. The main conclusion can be summarized as follows: 1) Since the groove angle has became cooling down rapidly due to its smaller value, the temperature slope was steeped somewhat. 2) The tensile stress within the welding direction stresses was somewhat decreased at the weld metal and HAZ, increasing of the groove angle. 3) The local stress concentration of the groove angle $60^{\circ}C$ was appeared smaller than groove angle $30^{\circ}$.

有限要素法에 依한 厚板熔接時의 3次元 非定常熱傳導解析

방한서,김유철 대한용접접합학회 1991 대한용접·접합학회지 Vol.9 No.2

In order to analyze the mechanical phenomena of three dimensional elato-plastic behavior caused by welding of thick plate, it is necessary to solve exactly the three dimensional unstationary heat conduction problem considering the moving effect of heat source and the temperature-dependence of material properties. In this paper, the three-dimensional unstationary heat conduction problem is formulated by using an isoparametric finite element method. Thereafter, the transient temperature distributions, according to time, of thick plate during welding are defined from the results calculated by the developed computer program.

熔接이음부의 形象 最適化에 關한 硏究

방한서,강성원 대한용접접합학회 1997 대한용접·접합학회지 Vol.15 No.4

Welding is one of the most important and popular joining techniques employed in structures. In spite of, weld designs depend on the rules and regulations. Moreover, the study to optimize a shape of welding joint not may be sufficient and systematic on the theoretical and experimental sides. Therefore, in this study, a computer program based on thermal elasto plastic theory is developed for optimizing(minimizing) shape of weld joints. By the results, study is made on the characteristics of the distributions of welding residual stresses and plastic strains, and their production mechanisms. Also, Various kinds of tests are carried out to find out mechanical characteristics due to shape of weld joints. As a result of this optimization(minimization) of weld joints, the productivity and the reliability will be improved.