• 한국주조공학회지
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• 제33권4호
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• pp.157-161
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• 2013

A ribbon-type polycrystalline silicon wafer was directly fabricated from liquid silicon via a novel technique for both a fast growth rate and large grain size by exploiting gas pressure. Effects of processing parameters such as moving speed of a dummy bar and the length of the solidification zone on continuous casting of the silicon wafer were investigated. Silicon melt extruded from the growth region in the case of a solidification zone with a length of 1cm due to incomplete solidification. In case of a solidification zone wieh a length of 2 cm, on the other hand, continuous casting of the wafer was impossible due to the volume expansion of silicon derived from the liquid-solid transformation in solidification zone. Consequently, the optimal length of the solidification zone was 1.5 cm for maintaining the position of the solid-liquid interface in the solidification zone. The silicon wafer could be continuously casted when the moving speed of the dummy bar was 6 cm/min, but liquid silicon extruded from the growth region without solidification when the moving speed of the dummy bar was ${\geq}$ 9 cm/min. This was due to a shift of the position of the solid-liquid interface from the solidification zone to the moving area. The present study reports experimental findings on a new direct growth system for obtaining silicon wafers with both high quality and productivity, as a candidate for an alternate route for the fabrication of ribbon-type silicon wafers.

• 한국결정성장학회지
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• 제22권2호
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• pp.105-113
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• 2012

정밀주조기술은 수공예에 의한 일품장신구가 규격화, 표준화된 제품으로 대량 생산될 수 있는 기틀을 만들어 주었고 또한 생산라인의 시스템 개선으로 업무의 분업화와 장비의 첨단화로 명실상부한 장신구가 산업으로서의 면모를 갖추는데 지대한 기여를 하였다. 본 연구자는 주조장비가 국내 도입된 이래 약 30여 년 동안 주조장비의 고급화와 업그레이드에 따른 제품의 질이 향상되었다고 볼 수 있으나 주조장비가 100 % 해결해 줄 수 없는 생산 프로세스를 직시하면서 정밀주조 과정에서 매우 중요하다고 판단되는 왁스트리(Wax Tree)공정 시 수행되는 장신구 사출물과 금속이 용해되어 흘러 들어가는 스프루(Sprue)의 연결은 여전히 수작업에 의해 진행이 되고 있고 이 과정에서 원하는 결과물이 나오는데 많은 영향을 미칠 수 있다는 문제점을 실험데이터를 바탕으로 하여 좀더 완벽한 정밀주조의 프로세스를 수행하기 위한 방안 제시를 하고자 한다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.1057-1060
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• 2008

고강도 콘크리트는 낮은 물-시멘트 비와 혼화제의 첨가로 인해 타설 후 극 초기재령에서 큰 자기수축과 온도변형이 발생한다. 이것은 고강도 콘크리트 구조물의 초기재령에서의 균열을 초래할것이고, 고강도 콘크리트의 내구성에 영향을 미칠 것 이다. 그러므로 고강도 콘크리트의 초기재령 특성에 집중할 필요가 있다. 이 논문에서는 매설형 FBG 센서를 이용하여 고강도 콘크리트의 초기재령 특성을 모니터링 하였다. 결과에서는 고강도 콘크리트 타설 후 하루동안 변형이 급격히 증가함을 보여 주었다. 그리고 변형량의 값은 $85{\mu}{\varepsilon}$ 이상이며, 두달간의 변형량($280{\mu}{\varepsilon}$)의 30%에 해당한다. 고강도콘크리트의 내구성과 침투성을 고려하면, 첫째날의 변형률은 꽤 높아 무시할 수 없는 수치이다. 또한 연속성, 안정성, 다양한 복합기술 등 FBG 센서의 보다 높은 성능이 증명 되었다.

• 한국세라믹학회지
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• 제37권1호
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• pp.21-25
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• 2000

Gas pressure sintered silicon nitride based composites with 5 wt% $\beta$-Si3N4 whiskers were prepared, and the variations depending on sintering additives and sintering temperature were studied. Sintering additives were 6 wt% Y2O3-1 wt% MgO(6Y1M), 6 wt%Y2O3-1 wt% Al2O3(6Y1A), 6 wt% Y2O3-1 wt% SiO2(6Y1S), and whiskers were unidirectionally oriented by a modified tape casting technique. Samples were fully densified by gas pressure sintering at 2148 K and 2273 K. As the sintering temperature increased, the size of large elongated grains was increased. Three point flexural strength of 6Y1M and 6Y1M samples was higher than that of 6Y1S sample, and the strength decreased as the sintering temperature increased. The indentation crack length became shorter for the sample sintered at higher temperature, and the difference between the cracks length parallel to and normal to the direction of whisker alignment was decreased. In case of cracks 45$^{\circ}$off the whisker alignment direction, the crack length anisotropy disappeared.

• 한국세라믹학회지
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• 제50권4호
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• pp.263-268
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• 2013

Porous biphasic calcium phosphate scaffolds were fabricated by a freeze-gel casting technique using a tertiary-butyl alcohol (TBA)-based slurry. After sintering, unidirectional macropore channels of scaffolds aligned regularly along the TBA ice growth direction were tailored simultaneously with micropores formed in the outer wall of the pore channels. The crystallinity, micro structure, pore configuration, bulk density, and compressive strength for the scaffolds were investigated with X-ray diffractometery, scanning electron microscopy analysis, a water immersion method, and a universal test machine. The results revealed that the sintered porosity and pore size generally resulted in a high solid loading which resulted in low porosity and small pore size, which relatively increased the higher compressive strength. After being sintered at $1100-1300^{\circ}C$, the scaffolds showed an average porosity and compressive strength in the range 35.1-74.9% and 65.1-3.0 MPa, respectively, according to the processing conditions.

• 한국주조공학회지
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• 제41권5호
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• pp.445-453
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• 2021

다양한 합금계에 대한 계산열역학은 CALPHAD 기법으로 잘 알려져있다. 실험적으로 측정된 열역학 특성들을 활용하여 각 상에 대한 Gibbs 에너지 모델 파라미터들을 구하여, 주로 실험적으로 측정되지 못한 영역에 대한 예측이나 실험 결과에 대한 열역학 해석에 활용되고 있다. 본 연구에서는 내열 주조 합금 (IN-657)이 장시간 사용 후에 일정 영역에서 파괴되는 현상의 열역학적 해석을 위해 Ni-Cr-Nb-C 사원계 시스템의 열역학 모델링을 수행하였고, Cr 함량에 따른 시스템의 안정상, 온도에 따른 상분율 및 Ni₂Cr상의 long range ordering 파라미터를 계산하였고 실험결과와 비교하였다. 계산된 열역학 물성들은 실험으로 보고된 파괴온도 영역 및 해당 영역에서 생성된 안정상에 대한 결과를 잘 설명한다. CALPHAD 기법을 통한 열역학 모델링은 다양한 주조 합금의 열역학적 거동을 해석하고 예측하는데 유용하게 사용될 수 있을 것으로 기대된다.

• 대한치과기공학회지
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• 제45권1호
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• pp.1-7
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• 2023

Purpose: To evaluate the marginal and internal fit of metal coping fabricated by a metal three-dimensional (3D) printer that uses selective laser melting (SLM). Methods: An extraoral scanner was used to scan a die of the prepared maxillary right first molar, and the coping was designed using computer-aided design software and saved as an stereo lithography (STL) file. Ten specimens were printed with an SLM-type metal 3D printer (SLM group), and 10 more specimens were fabricated by casting the castable patterns output generated by a digital light processing-type resin 3D printer (casting the 3D printed resin patterns [CRP] group). The fit was measured using the silicon replica technique, and 8 points (A to H) were set per specimen to measure the marginal (points A, H) and internal (points B~G) gaps. The differences among the groups were compared using the Mann-Whitney U-test (α=0.05). Results: The mean of marginal fit in the SLM group was 69.67±18.04 ㎛, while in the CRP group was 117.10±41.95 ㎛. The internal fit of the SLM group was 95.18±41.20 ㎛, and that of the CRP group was 86.35±32 ㎛. As a result of statistical analysis, there was a significant difference in marginal fit between the SLM and CRP groups (p<0.05); however, there was no significant difference in internal fit between the SLM group and the CRP group (p>0.05). Conclusion: The marginal and internal fit of SLM is within the clinically acceptable range, and it seems to be applicable in terms of fit.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.313-314
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• 2002

SiCp-reinforced metal matrix composites (MMCs) containing 8 wt % and 16 wt % of $SiC_p-reinforced$ with 30 and $45\;{\mu}m$ in sizes were prepared by a melt stirring-squeeze casting technique. Microstructural observation showed that particle distributions were reasonably well. Turning experiments were carried out on the composites using uncoated and triple-layer coated carbide tools at various cutting speeds under a constant feed rate and depth of cut. Coated tools indicated better performance than uncoated tools for all the materials while the poor surface finish was obtained for coated tools.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -1
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• pp.54-57
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• 2002

In this paper, an adaptive beam tracing method with revised subdivision technique is proposed, in which the beam is generated by a set of three rays. According to reflection and/or refraction of the rays on the buildings and/or ground, additional rays are generated adaptively and the beam is subdivided efficiently and automatically. After generation of the set of beams, we transform the electromagnetic wave propagation data into volume data. Then one can visualize the data of propagation with reflection, refraction and interaction in full three dimensional space at any viewpoint by the so-called ray casting algorithm, which is one of the most useful methods in compute. graphics(CG).

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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• pp.31-37
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• 2000

Metal matrix composites(MMCs) are rapidly becoming one of the strongest candidates for structural materials for many high temperature application. Among the high temperature environment, thermal shock is known to cause significant degradation in most MMC system. Therefore, the nondestructive evaluation on thermal shock damage behavior of SiC/A16061 composite has been carried out using ultrasonic surface and SH-waves. For this study, Sic fiber reinforced metal matrix composite specimens fabricated by a squeeze casting technique were thermally cycled in the temperature range 25~$400^{\circ}C$ up to 1000 cycles. Three point bend test was conducted to investigate the effect of thermal shock damage on mechanical properties. The relationship between thermal shock damage behavior and the change of ultrasonic velocity and attenuation were discussed by considering SEM observation of fracture surface.