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오병덕,이용복,Oh, Byung-Duck,Lee, Yong-Bok 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.3
SM45C steel rods being used generally for power transmission shafts and machine components was selected and welded by Butt-GMAW(Gas Metal Arc Welding) method. An estimation of fatigue life was studied by constructing S-N curve. Fatigue strength of base metal zone showed higher values than one of weld zone in low cycles between $10^4$ and $10^6$cycles. However, significant decrease in fatigue strength of base metal was found around $10^6$cycles, which were almost same as one of heat affected zone. This decrease was attributed that initial residual stress of the steel rods distributed by drawing process was diminished by continually applied load, and resulted in softening of base metal. The fatigue limit of the weld zone was highest in the boundary between deposited metal zone and heat affected zone, and followed by in the order of deposited metal zone, base metal zone, and heat affected zone. Based on these results, it is revealed that the stress for safety design of machine components using SM45C butt-welded steel rods must be selected within the region of the lowest fatigue limit of heat affected zone.
李喆求,吳炳德 서울産業大學校 1992 논문집 Vol.36 No.1
The study is experimentally investigated for the effects of solid wire(S.W) and flux cored wire(F.C.W) of the workability and weldability by welding conditions in the mixed active gas arc welding of the general structural steel. In order to investigate the each workability and weldability of wire, bead apperaance, tensile strength test, hardness test, impact test, bending test were comparatively performed. The results from the comparative analysis of experiments by various welding conditions are as follows. That is, the influences of the mixed active gas welding in S.W. and F.C.W. were almost similar in mechanical properties, while S.W. was observed better in deposition efficency and effectiveness and F.C.W. in arc stability, spatter, bead apperances. Also, Both S.W. and F.C.W. were observed superior in weldability and workability when they were welding the general structural steel under the conditions of welding velocity 20cm/min, and mixed gas CO₂ 25%-Ar 75%, Current 200(A), and Voltage 25(V).
李龍福,吳炳德 弘益大學校 科學技術硏究所 2001 科學技術硏究論文集 Vol.12 No.-
The influence of weld size(l/t) and specimen geometry(a/w) on fatique life and fatique crack growth rate of flux cored arc welded(FCAW) cruciform joints, containing lack of penetration(LOP) defects, has been studied experimentally. It was found that fatique life of the weld joint increases with the larger weld size(l/t) and the smaller specimen geometry(a/w) and exhibits significant variations in low stress region. the crack growth rates are relatively higher with the smaller weld size(l/t) for a constant stress intensity factor range(AK), and are faster with the larger stress intensity factor range. The longer weld leg length appears to be beneficial for the fatigue life in an allowable range of weldment size.
용접방법에 따른 하중전달 십자형 필렛 용접부의 피로특성
이용복,오병덕 한국공작기계학회 2003 한국생산제조학회지 Vol.12 No.1
In this study, endurance limit and fatigue behavior of load carrying fillet welded cruciform joints depending on commonly used welding methods such as SMAW, SAW, MIG and FCAW are investigated. In respect of endurance limit, SMAW specimen showes highest result, and then MIG, SAW, FCAW in descending order. However, SMAW specimen showes lowest crack growth rate and it followed by MIG, FCAW, SAW. By these results, it is needed to use SMAW or MiG welding methods for welding structures with small welding capacity and SAW or FCAW methods for large welding structures with respect to economic benefits and operation efficiency of welding. It was also shown fatigue crack growth rate was more influenced by the strenght of welding materials than the endurance limit of welding materials.
용접방법에 따른 하중전달 십자형 필렛 용접부의 피로특성
李龍福,吳炳德 한국공작기계학회 2002 한국공작기계학회 춘계학술대회논문집 Vol.2002 No.-
In this study, it was investigated about endurance limit and fatigue behavior of load carrying fillet welded cruciform joints according to welding methods of SMAW, SAW, MIG and FCAW commonly using for welding structures in present. Endurance limit carried out highly in the order of SMAW, MIG, SAW, FCAW and fatigue crack propagation ratio carried out lowly in the order of SMAW, MIG, FCAW, SAW. By these results, it is needed to use SMAW or MIG welding methods for welding structures with small welding capacity and SAW or FCAW methods for large welding structures after due consideration about economic gains and operation efficiency of welding. Fatigue crack propagation ratio is more effected by strength of welding materials than endurance limit of welding materials according to welding methods.
압연 및 용접방향이 같은 맞대기 용접강판의 하중방향에 따른 피로균열 진전특성
이용복,김성엽,오병덕,Lee Yong-Bok,Kim Sung-Yeup,Oh Byung-Duck 대한용접접합학회 2005 대한용접·접합학회지 Vol.23 No.6
Most of the welding steel plate structures have complicated mechanical problems such as rolling directional characteristics and residual stresses caused by manufacturing process. For the enhancement of reliability and safety in those structures, therefore, a systematic investigation is required. SS400 steel plate used for common structures was selected and welded by FCAW butt-welding process for this study, and then it was studied experimently about characteristics of fatigue crack propagations with respect to rolling direction and welding residual stress of welded steel plates. When the angles between rolling direction and tensile loading direction in base material are increased, their ultimate strength not show a significant difference, but yielding strength are increased and elongations are decreased uniformly. It is also shown that fatigue crack growth rate can be increased from those results. When the angles between welding bead direction and loading direction in welded material are increase, fatigue crack growth rate of them are decreased and influenced uniformly according to the conditions of residual stress distribution. In these results, it is shown that the welded steel plate structures are needed to harmonize distributed welding residual stress, rolling direction and loading direction fur the improvement of safety and endurance in manufacture of their structures.
이용복(Yong-Bok Lee),오병덕(Byung-Duck Oh),정재근(Jae-Keun Jung),김성엽(Sung-Yeup Kim) 한국생산제조학회 2006 한국생산제조시스템학회 학술발표대회 논문집 Vol.2006 No.5
For the improvement of safety and endurance in welded steel structure, it is needed to consider welding residual stress distribution and rolling directional characteristics of materials. In this study, it was investigated experimentally about characteristics of fatigue crack propagation according to welding residual stress and rolling in FCAW(flux cored arc welding) butt-jointed steel plates. SS400 steel plates of 3㎜ thickness were selected and tested for this study. When the angles between tensile loading direction and rolling direction in welded materials are increased from 0° to 90°, their fatigue crack propagation rates are increased. These results are same as predicted increments of fatigue crack propagation rate when stress ratio is increased from 0 to 0.5. When the angles of rolling direction and welding direction to tensile loading direction are 0° and 90° respectively, fatigue crack propagation rate in welded material is lowest. In these results, it is shown that welded steel plate structures are needed to harmonize distributed welding residual stress, rolling direction and loading direction for the improvement of safetyand endurance in manufacture of their structures.
이용복(Yong-Bok Lee),오병덕(Byung-Duk Oh),김성엽(Sung-Yeup Kim) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.8
All of steel plates using for common structures are manufactured by rolling. Traces of rolling direction in materials caused by this process affect in mechanical properties and fatigue crack behavior. In this reason, it is important that understand exactly mechanical properties and fatigue crack behavior according to rolling direction in these materials for the improvement of usefulness and safety in structures. In this research(study), it was selected SS400 steel plate with 3㎜ thickness and researched(studied) about the method for the improvement of fatigue strength and safety in structures considering rolling direction in the material. Consequently, for the improvement of fatigue strength and safety in structures it is needed to lie the rolling direction to loading direction by 90°