• Steel and Composite Structures
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• 제34권6호
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• pp.837-851
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• 2020

This study aims to examine the interface shear behavior between precast high-strength concrete slabs with pockets and steel beam to achieve accelerated bridge construction (ABC). Twenty-six push-out specimens, with different stud height, stud diameter, stud arrangement, deck thickness, the infilling concrete strength in shear pocket (different types of concrete), steel fiber volume of the infilling concrete in shear pocket concrete and casting method, were tested in this investigation. Based on the experimental results, this study suggests that the larger stud diameter and higher strength concrete promoted the shear capacity and stiffness but with the losing of ductility. The addition of steel fiber in pocket concrete would promote the ductility effectively, but without apparent improvement of bearing capacity or even declining the initial stiffness of specimens. It can also be confirmed that the precast steel-concrete composite structure can be adopted in practice engineering, with an acceptable ductility (6.74 mm) and minor decline of stiffness (4.93%) and shear capacity (0.98%). Due to the inapplicability of current design provision, a more accurate model was proposed, which can be used for predicting the interface shear capacity well for specimens with wide ranges of the stud diameters (from13 mm to 30 mm) and the concrete strength (from 26 MPa to 200 MPa).

• Steel and Composite Structures
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• 제50권6호
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• pp.659-674
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• 2024

Casting Ultra High-Performance Concrete (UHPC) on an orthotropic steel deck and forming a composite action by connectors could improve the steel deck fatigue performance. This study presents the mechanical performance of a proposed post-combination connection between UHPC and steel, which had a low constraint effect on UHPC shrinkage. A total of 10 push-out tests were conducted for static and fatigue performance investigations. And the test results were compared with evaluation methods in codes to verify the latter's applicability. Meanwhile, nonlinear simulation and parametric works with material damage plasticity models were also conducted for the static and fatigue failure mechanism understanding. The static and fatigue test results both showed that fractures at stud roots and surrounding local UHPC crushes were the main failure appearances. Compared with normally arranged studs, group arrangement could result in reductions of static stud shear stiffness, strength, and fatigue lives, which were about 18%, 12%, and 27%, respectively. Compared with the test results, stud shear capacity and fatigue lives evaluations based on the codes of AASHTO, Eurocode 4, JSCE and JTG D64 could be applicable in general while the safety redundancies tended to be smaller or even insufficient for group studs. The analysis results showed that arranging studs in groups caused obviously uneven strain distributions. The severer stress concentration and larger strain ranges caused the static and fatigue performance degradations of group studs. The research outcome provides a very important basis for establishing a design method of connections in the novel post-combination steel-UHPC composite deck.

• 한국재료학회지
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• 제22권4호
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• pp.169-173
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• 2012

Recently, various attempts to produce a heat sink made of Al 6xxx alloys have been carried out using die-casting. In order to apply die-casting, the Al alloys should be verified for die-soldering ability with die steel. It is generally well known that both Fe and Mn contents have effects on decreasing die soldering, especially with aluminum alloys containing substantial amounts of Si. However, die soldering has not been widely studied for the low Si aluminum (1.0~2.0wt%) alloys. Therefore, in this study, an investigation was performed to consider how the soldering phenomena were affected by Fe and Mn contents in low Si aluminum alloys. Each aluminum alloy was melted and held at $680^{\circ}C$. Then, STD61 substrate was dipped for 2 hr in the melt. The specimens, which were air cooled, were observed using a scanning electron microscope and were line analyzed by an electron probe micro analyzer. The SEM results of the dipping soldering test showed an Al-Fe inter-metallic layer in the microstructure. With increasing Fe content up to 0.35%, the Al-Fe inter-metallic layer became thicker. In Al-1.0%Si alloy, the additional content of Mn also increased the thickness of the inter-metallic layer compared to that in the alloy without Mn. In addition, EPMA analysis showed that Al-Fe inter-metallic compounds such as $Al_2Fe$, $Al_3Fe$, and $Al_5Fe_2$ formed in the die soldering layers.

• 대한전자공학회논문지TE
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• 제37권3호
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• pp.30-36
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• 2000

본 논문에서는 결함신호의 신호 대 잡음비를 높이기 위해 최소진복선택 알고리즘과 극 문턱치(PT : polarity threshold) 알고리즘을 결합한 최소극 문턱치(MPO : minimum polarity threshold) 알고리즘을 이용한 원전 고감쇠 용접부 초음파 검사방법을 제안하였다. 제안된 알고리즘의 유용성을 확인하기 위한 실험에서는 ASME Xl 코드에 준하는 원전의 실제 모재와 동일한 용접방법으로 제작된 대비 시험편과 4종류의 개선된 탐촉자를 이용하였다. 실험 결과, SE(safeend)와 CCSS(centrifugal casting stainless steel) 재료는 조직의 구조적 특성 때문에 산란신호가 발생하고, 용접 내부에서는 높은 감쇠 현상이 발생하여 정확한 결합검출 능력이 저하되며, 이러한 결함신호에 최소극 문턱치 알고리즘을 적용하면 신호 대 잡음비가 2.6배 개선됨을 확인하였다.

• 한국주조공학회지
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• 제41권2호
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• pp.139-143
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• 2021

타이타늄 합금 중 페로-타이타늄은 철강 업계에서 철강과 스테인리스강을 생산하는데 사용되는 주요 첨가물이다. 본 연구에서는 고품질의 페로-타이타늄 합금을 주조하기 위해 경제적인 면을 고려한 저비용 타이타늄 스크랩을 활용하고자 하였다. 먼저 재활용 타이타늄 스크랩의 표면에 형성되어 있는 절삭유 및 불순물을 제거하기 위한 최적의 전처리 공정을 연구하였다. 일반적인 세척 방법인 산이나 유기용제는 세척이 용이하나 환경적으로 문제가 되므로 친환경적인 방법을 고안하여 적용하고자 하였다. 또한, 타이타늄 스크랩을 활용하여 고품질의 페로-타이타늄 잉곳을 제조하고 성분 분석을 통해 불순물과 특성을 상용 소재 규격과 비교 분석하였다.

• 소성∙가공
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• 제32권6호
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• pp.344-351
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• 2023

The use of Zn-Al-Mg alloy coatings for enhancing the corrosion resistance of steel sheets is gaining prominence over traditional Zn coatings. There is a growing demand for the development of thermal spray wires made from Zn-Al-Mg alloys, as a replacement for the existing wires produced using Al and Zn. This is particularly crucial to secure corrosion resistance and durability in the damaged areas of coated steel sheets caused by deformation and welding. This study focuses on the casting and extrusion processes of Zn-2Al-1Mg alloy for the fabrication of such spray wires and analyzes the changes in microstructure during the extrusion process. The Zn-2Al-1Mg alloy, cast in molds, was subjected to a heat treatment at 250 ℃ for 3 hours prior to extrusion. The extrusion process was carried out by heating both the material and the mold up to 300 ℃. Microstructural analysis was conducted using FE-SEM and EDS to differentiate each phase. The mechanical properties of the cast specimen were evaluated through compression tests at temperatures ranging from 200 to 300 ℃, with strain rates of 0.1 to 5 sec^-1. Vickers hardness testing was utilized to assess the inhomogeneity of mechanical properties in the radial direction of the extruded material. Finite Element Analysis (FEA) was employed to understand the inhomogeneity in stress and strain distribution during extrusion, which aids in understanding the impact of heterogeneous deformation on the microstructure during the process.

• 한국주조공학회지
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• 제12권4호
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• pp.305-316
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• 1992

Steel and iron castings made with expandable polystylene (referred to hereafter as EPS) patterns are often affected by distinctive defects associated with incomplete decomposition of the EPS as the molds are filled with metal. The effects of practical factors on carbon pick-up were investigated on the specimens, by taking successive layers of swarf and analysis, whereas the lustrous carbon is determined by using combustion analysis. The quality of the castings, with particular reference to carbon pick-up in low carbon steel and lustrous carbon on gray iron, is further influenced to a significant extent by such practical factors as reduced pressure, the pouring temperature, the density of EPS pattern, the additive in coating and in pattern and the casting thickness. The rate at which carbon pick-up and lustrous carbon deposites are formed can be reduced by reducing the density of the pattern and also reducing pressure, especially by adding $Na_2CO_3$ in coating and in pattern to promote $CO_2$ evolution. The upper parts of castings obtained using EPS patterns are slightly higher in carbon pick-up and in lustrous carbon than other parts.

• 한국강구조학회 논문집
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• 제24권5호
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• pp.571-582
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• 2012

프리스트레스트 합성거더란 합성거더의 하부 콘크리트에 프리스트레싱 강선을 통해 압축력을 도입한 거더형식으로, 본 연구에서는 거푸집을 강재에 매달아 콘크리트의 자중이 강재에 부담된 상태로 합성시켜 단면의 효율을 극대화한 거더를 사용하였다. 이러한 프리스트레스트 합성거더에 대하여 재령보정 유효계수방법을 사용하여 시공단계별로 발생하는 여러 지속하중에 의한 장기거동 효과로 인해 유발되는 프리스트레스의 손실을 산정하고, 실제교량을 대상으로 시공단계별로 계측한 결과에 대해 야쓰미해법을 이용한 결과와 비교하였고, 또한 온도, 습도, 프리스트레스 긴장시기, 바닥판 타설시기를 변수로 한 변수해석을 수행하여 유효성을 검증하였다.

• 한국생산제조학회지
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• 제21권5호
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• pp.797-804
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• 2012

Magnesium has a long tradition of use as a lightweight material in the field of automotive industry. This paper presents the design optimization process of Mg armrest frame to minimize its weight by replacing the steel frame. formerly, the analysis of steel armrest frame was peformed to determine the design specifications for Mg armrest frame. The initial design of Mg armrest frame was carried out by topological optimization technique. After six types of design variables and four types of response variables were defined, DOE(Design of Experiment) and RSM (Response Surface Method) were applied in order to measure sensitivity of design variables and realize optimization through regression model. After design optimization, the weight of the optimized Mg armrest frame was reduced by about 3% compared to the initial design of the Mg frame and was decreased by 41.7% in comparison with that of the steel frame. Some prototypical armrest frames were also made by die casting process and tested. The results were satisfying for its design specifications.

• 한국주조공학회지
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• 제30권4호
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• pp.130-136
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• 2010

Sulfide segregation behavior, characteristics of solidification microstructure and compositional distribution in the riser/castings junction of heavy-section main bearing support (MBS) steel castings were investigated; Sulfide streaks of A segregation were formed in the transitional region from columnar grain to coarse equiaxed grain and floated with aggregation of the dendritic free crystal. Solute segregation behaviors of elements Si, P and S were V shape negative segregation from the bottom of the castings to upper part of the riser with the reference of vertical center-line of the specimen block. Those of elements C and Mn were V shape negative segregation in the main body and A shape positive segregation in the riser of the casting. Just beneath the pipe shrinkage in the riser segregation ratio of each element was the highest, and that of S was 3.6 times higher, C 3.3 times, P 2.1 times, Si 1.6 times and Mn 1.0 times respectively. [Mn/S] ratio of the specimen block was distributed in the wide range of 20~275.