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 $30^{\circ}$.

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.

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.

저항 다점용접부의 역학적 특성에 관한 연구

방한서,방희선 대한용접접합학회 2001 대한용접·접합학회지 Vol.19 No.5

In order to classify the mechanical phenomena of thermal elasto-plastic behavior on the multi-spot welded joints, this study has tried to carry out three-dimensional thermal elasto-plastic analysis on them. However, because the shape of multi-spot welded joints is not taxi-symmetric, unlike the cafe of single-spot welded joint, the solution domain for simulation should be three dimension. Therefore, in this paper, firstly, the three-dimensional thermal elasto-plastic program is developed by an iso-parametric finite element method. Secondly, from the results analyzed by developed program, this has clarified mechanical characteristics and their production mechanism on single and multi-spot waled joints. Moreover, it has been intended to make clear effects of pitch length on welding residual stresses, plastic strain of multi-spot welded joints.

FSW에 대한 수치 Simulation 연구 동향 - 용접 강도 -

방한서,김흥주,김영표,장웅성 대한용접접합학회 2001 대한용접·접합학회지 Vol.19 No.6

후판 용접부의 역학적 특성 -유한요소법에 의한 3차원 열탄소성 해석-

방한서 대한용접접합학회 1992 대한용접·접합학회지 Vol.10 No.4

In order to clarify the mechanical behavior of welding crack and to evaluate the mechanical characteristics of welded parts in thick plate, it is very important to accurately predict the welding deformation and residual stress including transient state before welding. In this paper, the theory of a three-dimensional elasto-plastic problem for the analysis of mechanical phenomenon of welding joint on the plate is developed into an efficient and accurate method based on the finite element method, and then several examples are considered by using the proposed model. The results of numerical analyses are discussed in the viewpoint of the mechanical characteristics of the distribution of three-dimensional welding residual stresses, plastic strains and their production mechanism on the thick plate.

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$^{\circ}$).

厚板熔接部의 應力除去 熱處理時의 力學的 擧動에 關한 硏究

방한서 대한용접접합학회 1993 대한용접·접합학회지 Vol.11 No.4

Recently, several high-tensile steels(e.g. 80kg and above, $2^{1/4}Cr$-1Mo)having good quality to high temperature and pressure-resistance are widely used to construct petroleum-plant and pressure vessel of heat or nuclear-power plant. However, in the steels, reheating crack at grain boundaries of the heat affected zone(HAZ) occures during post welding heat treatment(PWHT)to remove welding residual stress. In order to study theoretically the characteristics of reheating crack created by PWHT, the computer program of three-dimensional thermal-elasto-plasto-creep analysis based on finite element method are developed, and then the mechanical behavior(history of creep strain accumulation and stress relaxation, etc)of welded join in thick plate during PWTH is clarified by the numerical results.

자동차용 강판의 MAG 용접시 최적용접조건 선정에 관한 연구

방한서,방희선,주성민,노찬승,성보람,석한길,Bang, Han-Sur,Bang, Hee-Seon,Joo, Sung-Min,Ro, Chan-Seung,Sung, Bo-Ram,Suk, Han-Gil 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.3

The optimization of the welding parameters was studied to maximize the weldability and minimize the amount of spatter in the MAG welding of automotive steel sheets under different shielding gas composition ratio. JS-EFSC, JS-SPHC steel plates and Ar mixture gases were used as a substrate and shielding gas for welding respectively. The five welding parameters were selected through preliminary experiments and their effects on the weldability were analyzed. Experiments were performed using the Taguchi experimental method. As results, appropriate range for welding could be achieved. Amount of spatter in 80%Ar+20%$CO_2$ shielding gas was 20% of that of $CO_2$welding. Therefore, in terms of high productivity and welding cost, Ar mixture gas(80%Ar+20%$CO_2$) was recommended as a shielding gas for application of MAG process, indicating the low spatter and good weld quality.

$2\frac{1}{4}Cr-1Mo$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.