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유한요소법에 의한 PREFLEX BEAM의 용접열분포 특성에 관한 연구
방한서(HAN-SUR BANG),주성민(SUNG-MIN JOO),김하식(HA-SIG KIM) 한국해양공학회 2004 韓國海洋工學會誌 Vol.18 No.2
Preflex beam is a method of construction designed to hold the pre-compressive stresses over the concrete pier by the preflexion load. During the fabrication of the girder, welding causes residual stresses. The welding residual stresses must be relieved in order to generate the accurate compressive pre-stresses. In this study, to determine the thermal distribution characteristics on the girder by welding, both three-dimensional finite element analysis and two-dimensional finite element analysis, in a quasi-steady state, is carried out. After comparing each result between the three-dimensional analysis and the two-dimensional analysis, finite element analysis is carried out against the actual girder, and the welding thermal distribution characteristic over the preflex beam is analyzed. It is possible to provide the input data for the analysis of the welding residual stresses.
조선용 극후판 EH36-TMCP강 FCAW 용접부의 역학적 특성에 관한 연구
방한서 ( Han Sur Bang ),고민성 ( Min Sung Go ),김성주 ( Sung Joo Kim ) 조선대학교 공학기술연구원 2009 공학기술논문지 Vol.2 No.3
This work attempts to establish the stability and reliability of welded joint by FCAW for high strength EH32-TMCP ultra thick plate. Experimental results are reported for 37 pass X-groove butt joint of EH32 steel. Abbnevation on Expantion FE analysis has been carried out to simulate the FCA W process on the same specimen model as in experiment. By numerical simulation, thermal and mechanical behavior (residual stress, plastic strain, magnitude of stress and their distribution and production mechanism) has been investigated by heat conduction and thermo elasto-plastic analysis.
고장력강 용접부의 열ㆍ역학적 거동에 관한 수치해석적 연구
방한서(Han-Sur Bang),임래수(Rae-Su Lim),김종명(Jong-Myung Kim) 한국해양공학회 1998 韓國海洋工學會誌 Vol.12 No.4
High tensile steel has been welding in building construction and ship structure to reduce cost as well as weight. Accordingly, welding strength and weldability of high tensile steel is a matter of concern and interest.<br/> In the case of high tensile, brittle fracture and buckling strength are affected by welding residual stresses. For the sound design of structure using high tensile steel, distribution of welding residual stress need to be identified, which should be considered as initial imperfection of welded structure.<br/> Therefore, in this paper, in order to know the thermal and mechanical characteristics of high tensile steel during the welding and the post welding heat treatment, we would be compared with mild steel through numerical analysis of computer program based on the finite element method. The materials, which used study on welding strength, are SWS490, 60㎏f/㎟ class high tensile steel(HT60) and 80㎏f/㎟ class high tensile steel (HT80).
2¼Cr-1Mo강 압력용기 Nozzle 용접이음부의 재열균열에 관한 수치해석적 연구
방한서(HAN-SUR BANG),김종명(JONG-MYUNG KIM) 한국해양공학회 2000 韓國海洋工學會誌 Vol.14 No.1
Recently, various pressure vessels like an atomic reactor and plant facilities become more larger and are needed to bear in both very) high temperature and pressure condition. And, in making such a high pressure vessels, the amount of annual usage of 2¼Cr-1Mo steels which are predominant to resist high temperature, high pressure and corrosive circumstances are increasing. But, despite of this advantages of 2¼Cr-1Mo steel, when PWHT(post welding heat treatment)is carried out lots of reheating cracks are occur. In this reason, it is strongly needed to study and examine the mechanical behavior of welded joints through welding to PWHT process. So, in this study, welded nozzle parts of pressure vessel where reheat cracks are frequently occur are selected for analysis the crack-occurrence mechanism.
용접 공정에 따른 2.25Cr-1Mo강 용접이음부의 특성 변화에 관한 연구
방한서(HAN-SUR BANG),오종인(CHONG-IN OH),방희선(HEE-SUN BANG),김형(HYUNG KIM) 한국해양공학회 2005 韓國海洋工學會誌 Vol.19 No.1
In spite of the merits of laser welding being able to obtain the high welding quality such as smaller width of melting and heat affected zone, smaller welding deformation and fine grains of weldment compared to arc welding, laser welding is mainly used in joining of thin steel parts of electronics industry. Laser welding is getting widely used in joining thick plate and special kinds of steel due to its high power. While the arc welding is still applied for 2.25Cr-1Mo steel which is the essential material of atomic power generation equipment, the laser welding is not yet applied despite its high quality. So it has a trial to a special case demanding high welding quality such as atomic power plant. Accordingly, in this research, the mechanical properties of weldments by arc and laser welding were investigated using FEM to confirm the applicability of laser welding to 2.25Cr-1Mo steel. The Charphy test was carried out to understand the effect on the fracture toughness of weldments. The results of examination and test of the mechanical properties showed the validity of this research.
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.
방한서(Han-Sur Bang),한길영(Gil-Young Han) 한국해양공학회 1994 韓國海洋工學會誌 Vol.8 No.1
Welding of structure produces welding residual stresses which influence buckling strength, brittle fracture strength and cold crack on the weld parts. Therefore, it is very important to accurately analyze the residual stress before welding in order to guarantee the safety of weldment.<br/> If the weld length is long enough compared to the thickness and the breadth of plate, thermal and mechanical behaviors in the middle portion of the plate are assumed to be uniform along the thickness direction(z-axis). Thus, the following conditions(so-called plane deformation) can be assumed for the plate except near its end ; 1) distributions of stress and strain are independent on the z-axis ; 2) plane normal to z-axis before deformation remains plane during and after deformation.<br/> In this paper, plane-deformation thermal elasto-plastic problem is formulated by being based on the finite element method. Moreover special regards are paid to the fact that material properties in elastic and plastic region are temperature-dependence. And the method to solve the plane-deformation thermal elasto-plastic problem is shown by using the incremental technique. From the results of analysis, the characterisics of distribution of welding residual stress and plastic strain with the production mechanism are clarified.