• 한국강구조학회 논문집
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• 제24권6호
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• pp.711-723
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• 2012

플랜지와 웨브에 서로 강도가 다른 이종강재를 사용한 CFT 합성구조의 거동특성을 파악하기 위하여, 플랜지는 건축용 800MPa급 강재인 HSA800, 웨브에는 일반강도 강재인 SM490 강재를 사용하여 실험연구를 수행하였다. 주요실험 변수는 강관의 강도 조합, 충전된 콘크리트의 강도, 콘크리트 충전효과이다. 이종강재간의 용접접합부는 낮은강도 강재에 적합한 용접부를 사용하여 접합부 성능을 검증하였다. 실험체의 거동특성을 평가하기 위해 편심압축 실험을 수행하였으며, 현행 설계기준들에 따른 예측결과와 비교하였다. 플랜지에 고강도 강재를 적용함에 따라 단면의 축강도 및 휨모멘트강도가 증가하였으며, 부재 강도를 충분히 발현한 이후 용접부에서 파괴가 일어났다. 실험결과 현행 설계기준을 적용하여 합성단면의 축력-모멘트 상관관계 및 유효휨강성을 안전측으로 예측 가능하였다.

• 한국분말재료학회지
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• 제18권1호
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• pp.64-72
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• 2011

Nondestructive instrumented indentation test is the method to evaluate the mechanical properties by analyzing load - displacement curve when forming indentation on the surface of the specimen within hundreds of micro-indentation depth. Resistance spot welded samples are known to difficult to measure the local mechanical properties due to the combination of microstructural changes with heat input. Particularly, more difficulties arise to evaluate local mechanical properties of resistance spot welds because of having narrow HAZ, as well as dramatic changed in microstructure and hardness properties across the welds. In this study, evaluation of the local mechanical properties of resistance spot welds was carried out using the characterization of Instrumented Indentation testing. Resistance spot welding were performed for 590MPa DP (Dual Phase) steels and 780MPa TRIP (Transformation Induced Plasticity) steels following ISO 18278-2 condition. Mechanical properties of base metal using tensile test and Instrumented Indentation test showed similar results. Also it is possible to measure local mechanical properties of the center of fusion zone, edge of fusion zone, HAZ and base metal regions by using instrumented indentation test. Therefore, measurement of local mechanical properties using instrumented indentation test is efficient, reliable and relatively simple technique to evaluate the tensile strength, yield strength and hardening exponent.

• Journal of Advanced Marine Engineering and Technology
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• 제38권10호
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• pp.1190-1199
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• 2014

As a considerable, experimental approach, an autocarriage type of $CO_2$ welding machine and a MIG(metal inert gas) welding robot in the inert gas atmosphere were utilized in order to realize Al 5083 welding to hull and relevant components of green leisure ships. This study aims at investigating the effect of welding conditions(current, voltage, welding speed, etc.) on thermal deformation that occurs as welding operation and tensile characteristics after welding, by using Al 5083, nonferrous material, applied to manufacturing of eco-environmental leisure ships. With respect to welding condition to minimize the thermal deformation, 150 A and 16 V at the wire-feed rate of 6 mm/sec were acquired in the process of welding Al 5083 through an auto carriage type of $CO_2$ welding feeder. As to tensile characteristics of Al 5083 welding through a MIG welding robot, most of tensile specimens showed the fracture behavior on HAZ(heat affected zone) located at the area joined with weld metal, except for some cases. Especially, for the case of the Al specimen with 5 mm thickness, 284.62 MPa of tensile strength and 11.41 % of elongation were obtained as an actual allowable tensile stress-strain value. Mostly, after acquiring the optimum welding condition, the relevant welding data and technical requirements might be provided for actual welding operation site and welding procedure specification (WPS).

• 대한기계학회논문집A
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• 제37권6호
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• pp.775-782
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• 2013

본 연구에서는 마찰교반용접재의 피로균열전파 거동의 공간적 불규칙성을 고찰하기 위한 연구의 일환으로써, 최적의 조건에서 마찰교반용접된 7075-T651 알루미늄 합금 용접부의 LT-방향의 각각 5개의 피로균열전파 시험편에 대하여 일정 응력확대계수범위 제어하의 피로균열전파 실험을 수행하여 마찰교반용접부의 교반용접부재(WM)와 열영향부재(HAZ) 그리고 모재(BM)에 대한 피로균열전파 거동을 실험적으로 고찰하였다. WM재의 피로균열전파율이 가장 빠르게 나타났으며, 그 다음 HAZ재와 WM재 순으로 나타났다. 게다가 시험편간 피로균열전파율의 변동성은 WM시험편에서 가장 높았고, 반면 BM재에서 가장 낮게 나타났다.

• 한국자동차공학회논문집
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• 제20권5호
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• pp.53-64
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• 2012

Deep and narrow welds can be produced by laser welding at high welding speeds with a narrow heat-affected zone (HAZ) and little distortion of the workpiece. This study aims to evaluate the usefulness of laser welding at automobile component manufacture. Microstructure observation, hardness test, tensile test and fatigue life test are performed by using the fiber laser welded SPFC590 steel sheets which is used widely in the manufacture of automotive seat frame. Three kinds of specimens are only a SPFC590 steel plate, quasi-butt joint plate and lap joint plate by laser welding. The following results that will be helpful to understand the static strength, fatigue crack initiation and growth mechanism were obtained. (1) The tensile strength of quasi butt joint specimens nearly equal to base metal specimens, but lap joint specimens fractured in shear area of weld metal. (2) The fatigue strength of quasi-butt joint specimen was approximately 8 percent lower than that of the base metal specimens. Furthermore, the lap joint specimens were less than 86 percent of the base metal specimens. (3) The lap joint fatigue specimens fractured at shear area in high level stress amplitude, while fractured at normal area in low level stress amplitude. From these results, the applicability of the laser welding to the automobile component is discussed.

• 한국강구조학회 논문집
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• 제12권2호통권45호
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• pp.197-207
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• 2000

본 연구는 유한요소법을 이용해서 시간이력 열전도해석과 열탄성해석을 통해 필렛용접 이음부에서의 잔류응력분포를 측정하였다. 필렛용접은 1패스 용접이며, 경계조건으로는 표면유속조건과 온도에 의존하는 재료의 특성치를 고려하여 잔류응력을 평가하였다. 여기서, 용접입열양을 변수로 하였다. 그리고, 열탄성해석에 의해 잔류응력 평가할 때 중요한 문제로 언급되고 있는 cut-off 온도 설정에 대해 조사하였다. 또한, 시험체에서 구멍뚫기 방법에 의해 잔류응력분포를 측정하여 유한요소법에 의한 잔류응력분포와 비교하였다. 그 결과, 용접부에서는 재료의 항복강도 수준에 해당하는 인장잔류응력이 측정되었으며, 유한요소해석에 의한 수치해석 결과는 구멍뚫기 방법에 의한 측정치 및 다른 연구자의 측정치와 비교적 일치하는 것으로 나타났다. 그리고, Cut-off 온도는 재료의 항복강도가 나타나는 온도로 설정하는 것이 효과적임을 알 수 있었다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.4-4
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• 2009

Polycarbonate (PC) and Acrylonitrile Butadiene Styrene (ABS) was welded through a combination of a diode laser and CNC. Laser beam passed the transparent PC and was absorbed in an opaque ABS. Polymers were melted and welded by absorbed and conducted heat. Experiments were carried out by varying working distance from 44mm to 50mm for the focus spot diameter control, laser input power from 10W to 25W, and scanning speed from 100 to 400mm/min. The weld bead size and the specimen cross-section were analyzed, and tensile results were presented through the joint force measurement. With focus distance at 48mm, laser power with 20W, and welding speed at 300mm/min, experimental results showed the best welding quality which bead size was 3.75mm and the shear strength was $22.8N/mm^2$. Considering tensile strength of ABS is $43N/mm^2$, shear strength was sufficient to hold two materials. A single process was possible in CNC machining processes, surface processing, hole machining and welding. As a result, the process cycle time was reduced to 25%. Compared to a typical process, specimens were fabricated in a single process, with high precision. By combining two operations processes developed process gained 50% more efficiency.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.247-250
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• 2005

The need for improved fuel efficiency, weight reduction has motivated the automotive industry to focus on aluminum alloys as a replacement for steel-based alloy. To cope with the needs for high structural rigidity with low weight, it is forecasted that substantial amount of cast components will be replaced by tubular parts which are mainly manufactured by the extruded aluminum tubes. The extrusion process is utilized to produce tubes and hollow sections. Because there is no weld seam, the circumferential mechanical properties may be uniform and advantageous for hydroforming. However the possibility of the occurrence of a surface defect is very high, especially due to the temperature increase from forming at high pressure when it comes out of the bearing and the roughness of the bearing, which cause the surface defects such as the dies line and pick-up. And when forming a extruded aluminum tube, the free surface of the tube becomes rough with increasing plastic strain. This is well known as orange peel phenomena and has a great effect not only on the surface quality of a product but also on the forming limit. In an attempt to increase the forming limit of the tubular specimen, in the present paper, surface asperities generated during the hydroforming process are polished to eliminate the weak positions of the tube which lead to a localized necking. It is shown that the forming limit of the tube can be considerably improved by simple method of polishing the surface roughness during hydroforming. And also the extent of the crack propagation caused by dies lines generated during the extrusion process is evaluated according to the deformed shape of the tube.

• 열처리공학회지
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• 제9권1호
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• pp.34-44
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• 1996

Austenite stainless steel was produced by arc welding with current 650A, voltage 50V and welding speed 10cm/min. It was post-welded and then heat treated at $1,050^{\circ}C$ for 120min. And then it was immersed in water or in air. The microstructural changes, ferrite contents, mechanical properties, and stress corrosion cracking(SCC) were investigated. The SCC was studied in 42wt% boiling $MgCl_2$($140^{\circ}C$) under the constant stress using SCC elongation curve. The results showed that; 1. The as-welded spedimen seemed to increase ${\delta}$-ferrite content largely, and revealed continuous network of lathy and vermicular type. The post-welded heat treatment changed the morphologies of ferrite from continuous type to island type. 2. The as-welded, air and water quenched specimens had the ${\delta}$-ferrite content 9.7%, 3.2% and 2.1% respectively. We also showed that ${\delta}$-ferrite was Cr-rich and Ni-poor by EPMA. 3. The time of failure on the SCC was measured and it was used for corrosion elongation curve. The condition of SCC was investigated under $35kgf/mm^2$ load and the results were as follows; 4. The intergranullar cracking by stress corrosion was most distinct in weld metal while the transgranular cracking occurred in the air cooled specimen.

• 대한조선학회논문집
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• 제47권6호
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• pp.821-830
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• 2010

Deck plates and hatch coming of large container carrier and offshore structures are joined by ultra-thick plates whose thickness is more than 60mm. Traditionally FCAW has been used to join the thick plates in butt joint. However, FCAW has been replaced with EGW since the welding efficiency of EGW is higher than that of FCAW. Tandem EGW using two electrodes has been applied to vertical position welding by several shipyards. EGW requires one or two layers of bead whereas FCAW requires more than 20 layers of weld bead in thick welding. However, high welding residual stresses are generated by EGW since it uses higher heat input than FCAW. In the present study, a finite element model is suggested to predict the residual stresses induced by the tandem EGW. Butt specimen of EH40 TMCP shipbuilding steel plates vertical welding was modeled by a three-dimensional model. Residual stresses were measured by X-ray diffraction method and to verify the numerical result. The results show a good agreement with experimental result.