• KCI Concrete Journal
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• 제12권1호
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• pp.91-99
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• 2000

A new type of retrof=t anchor bolt that uses deformed reinforcing bars and a commercial adhesive was developed and then an experimental study was carried out to determine the behavior of the anchors in direct shear. The steel-to-concl몫ete interface was tested. Plain concrete slabs with about 20-MPa compressive strength were used for 23 direct shear tests performed Test variables were anchor diameters (D16, D22. and D29) and edge effect. Three different shear tests were completed: simple shear, edge shear where anchors were pulled against the concrete core, and edge shear where anchors were pushed against the concrete cover In the simple and the edge shear tests where the anchors were pulled against the core, the theoretical dowel strength determined by (equation omitted) was achieved but with relatively large displacements. The shear resistances increased with the increasing displacements. In the edge shear test where the anchors were pushrd against the cover, the peak shear strengths signif=cantly lower than the theoretical dowel strength were determined due to cracks developed in concrete when the edge distance was 80 mm. The peak strengths were about 50% of the dowel strength for Dl6 bar. and about 25% or less of the dowel strength for D22 and D29 bars. Test results revealed that the edge shear where the anchor was pushed against the cover controled.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.86-91
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• 2005

The stack, the core unit of the MCFC system, is composed of the three main parts which are the electrodes, the matrix keeping the electrolyte and the separator. Among these, the separator made of low carbon steel is manufactured by some sheet metal forming processes. The flatness of flange of the mask plate of the separator is crucial not only to enhance the stack performance but also to reduce the production cost. This study has focused on the enhancement of flatness of the mask plate flange by controlling some process parameters like the punch and die comer radii, the blank holding force, the friction coefficient and so on. The springback phenomenon occurring in the flange drawing process has been studied first using the finite element method (FEM) in order to understand what causes the springback. The distribution pattern of local longitudinal stress in the flanged part has been revealed very important in predicting the final shape of the flange. This fact has been backed up by the experimental results carried out with the developed test dies.

• 한국건설순환자원학회논문집
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• 제11권3호
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• pp.161-168
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• 2023

전로슬래그는 용광로에서 생산된 선철을 용융강으로 정제하는 과정에서 배출되는 부산물로, 컨버터에서 생산되는 양의 약 15 %가 배출된다. 이 전로슬래그는 유리 CaO 함량이 높아 콘크리트 골재로 사용 시 팽창균열 가능성이 있어 재활용이 어렵다. 이를 해결하기 위해 전로슬래그를 야드에서 숙성시키지만 완벽하게 제어하기는 어렵다. 본 연구에서는 전로슬래그에 모르타르 제제를 혼합하여 연구를 수행함으로써 골재가 아닌 시멘트 대체재로 전로슬래그를 사용할 수 있는 가능성을 검토하였다. 실험에 사용된 전로슬래그의 EDS 결과, 분말상 대비 골재상일 때 자력선별을 진행하는 것이 T.Fe를 제거하는데 더 효과적인 것을 확인하였다. 분쇄효율 실험은 T.Fe가 많이 분류된 비자착분이 가장 높은 분말도를 나타내었다. 이런 고분말도로 인해 전로슬래그를 15 % 치환했을 때 Plain 대비 비자착분의 플로가 가장 많이 감소하였다. 전로슬래그를 혼입한 모르타르의 길이변화는 재령이 증가할수록 변화율이 커지지만 Plain 대비 유사한 변화율이 나타났다. 압축강도에서는 Plain 대비 비자착분은 치환율 15 %까지 91.9~97.1 %의 강도 발현을 나타내었다. 추후 전로슬래그 미분말을 시멘트 대체재로 활용할 경우, 분쇄 전 자력(Gauss) 조절을 통한 최적의 자력선별 조건을 찾아 더 효율적인 T.Fe 선별 방법이 필요할 것으로 판단되며, EDS 및 Mapping은 국부적인 분석방법으로 큰 편차율을 보이기 때문에 다수의 시료 평가가 필요할 것으로 판단된다.

• 한국분말재료학회지
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• 제28권6호
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• pp.483-490
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• 2021

A new Fe-Cr-Mo-B-C amorphous alloy is designed, which offers high mechanical strength, corrosion resistance as well as high glass-forming ability and its gas-atomized amorphous powder is deposited on an ASTM A213-T91 steel substrate using the high-velocity oxygen fuel (HVOF) process. The hybrid coating layer, consisting of nanocrystalline and amorphous phases, exhibits strong bonding features with the substrate, without revealing significant pore formation. By the coating process, it is possible to obtain a dense structure in which pores are hardly observed not only inside the coating layer but also at the interface between the coating layer and the substrate. The coating layer exhibits good adhesive strength as well as good wear resistance, making it suitable for coating layers for biomass applications.

• Steel and Composite Structures
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• 제52권2호
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• pp.121-134
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• 2024

To investigate the compressive behavior of partially encased recycled aggregate concrete (PERAC) stub columns after exposed to elevated temperatures, 22 specimens were tested. The maximum temperature suffered, the replacement ratio of recycled coarse aggregate (RCA), the endurance time and the spacing between links were considered as the main parameters. It was found that the failure mode of post-heated PERAC columns generally matched that of traditional partially encased composite (PEC) columns, but the flange of specimens appeared premature buckling after undergoing the temperature of 400℃ and above. Additionally, the ultimate strength and ductility of the specimens deteriorated with the elevated temperatures and extended heating time. When 400℃< T ≤ 600℃, the strength reduction range is the largest, about 11% ~ 17%. The higher the replacement ratio of RCA, the lower the ultimate strength of specimens. At the temperature of 600℃, the ultimate strength of specimens with the RCA replacement ratio of 50% and 100% is 0.94 and 0.91 times than that of specimens without RCA, respectively. But the specimen with 50% replacement ratio of RCA showed the best ductility performance. And the bearing capacity and ductility of PERAC stub columns were changed for the better due to the application of links. When the RCA replacement ratio is 100%, the ultimate strength of specimens with the link spacing of 100 mm and 50 mm increased 14% and 25% than that of the specimen without links, respectively. Based on the results above, a formula for calculating the ultimate strength of PERAC stub columns after exposure to high temperatures was proposed.

• Restorative Dentistry and Endodontics
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• 제25권3호
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• pp.381-389
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• 2000

Lateral condensation with gutta-percha and sealer has been shown to provide an excellent apical seal; however, the lateral condensation technique has demonstrated less favorable apical leakage results in curved canals when compared with straight canals. Placement of endodontic spreaders to within 1 to 2mm of the root canal working length has been advocated for optimum gutta-percha obturation. Due to their stiffness, stainless-steel(SS) spreaders will often fail to achieve this position in curved canals. Newly marketed nickel-titanium(NT) spreaders may offer an advantage in this regard due to the increased flexibility of these instruments. The purpose of this study was to evaluate the effect of NT finger spreader on the sealing ability in lateral condensation technique, compared with conventional SS finger spreader. Twenty four standardized resin models simulating curved canals(30 degree) were randomly placed into 2 groups and instrumented to a #30 master apical file size with Ni-Ti Profile .04 taper series using step down technique. Each groups was obturated with standardized gutta-percha cone by standard lateral condensation technique using SS finger spreader, NT finger spreader. And then, each model was sectioned horizontally with microtome at 1, 2, 3, 4, 5mm levels from the apex. At each of 5 levels, ratio of the area of gutta-percha was obtained by calculating the area of gutta-percha to the total area of the canal. The data collected were then analyzed statistically using a t test for independent samples. The results as follows ; 1. The total mean ratio of area of gutta-percha was 89.20${\pm}$7.00(%) for SS spreader group. 92.20${\pm}$5.17(%) for NT spreader group. There was statistically significant difference between each group(p<0.05). 2. At 3mm level, the mean ratio of area of gutta-percha was 88.32${\pm}$5.41(%) for SS spreader group, 95.25${\pm}$2.60(%) for NT spreader group. There was statistically significant difference between each group(p<0.05). At 1,2,4mm levels, NT spreader group showed greater mean ratio of area of gutta-percha than SS spreader group, too. But there was no statistically significant difference. 3. At 5mm level, the mean ratio of area of gutta-percha was 91.83${\pm}$3.42(%) for SS spreader group, 87.91${\pm}$3.68(%) for NT spreader group. There was statistically significant difference between each group(p<0.05). This study concluded that the NT spreader demonstrated somewhat favorable apical sealing effect than SS spreader in prepared curved canals. The clinical use of NT spreaders may enhance our ability to create better apical seals in curved canals, but further studies in this area will help clarify some of the remaining areas with which practitioners are concerned, such as compaction forces exerted by NT spreaders.