• 한국재료학회지
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• 제30권1호
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• pp.38-43
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• 2020

Sand casting 3D printing uses a binder jetting method to produce a mold having complicated shape by spraying a binder on sand coated with activator. Appropriate heat treatment process in sand mold fabrication can increase the degree of polymerization to improve flexural strength. However, long heat treatment of over 24 hours decreases flexural strength and reliability due to chemical bond decomposition through thermal degradation. The main role of the activator is to control the reaction rate between the polymer chains. As a result, when the activator composition is increased from 0.15 wt% to 0.25 wt%, the flexural strength is increased by 218 N/㎠. However, excess activator (0.40 wt%) has been shown to decrease reliability without increasing flexural strength. The main role of the binder is to control the flexural strength of the specimen. As the binder composition is increased from 2.00 wt% to 4.00 wt%, the flexural strength increases to about 255 N/㎠, indicating the maximum flexural strength increase. Finally, the reliability of the flexural strength of the fabricated specimens is evaluated by a Weibull plot. Weibull modulus calculations are used to evaluate the flexural strength reliability of the specimens, and maximum reliability value of 11.7 is obtained at 0.20 wt% activator composition. Therefore, it is confirmed that this composition has maximum flexural strength reliability.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1992년도 가을 학술발표회 논문집
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• pp.1-4
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• 1992

This paper deals with the effect of siliceous slurry coating on concrete microstructure under damp environment. This material is mixed inorganic powder consisted of silica, cement and fine sand and water. Water pressure was given on the coated surface of concrete. for estimation on effect of siliceous slurry coating, microstructure of coated concrete was observed through SEM, and chemical components of crystals were analyzed with X-ray diffraction and EDX. A number of needle and fibrous crystals were produced in microstructure. And based on X-ray diffraction and EDX, needle crystal mainly consist of Al, Si, and Ca, and it is concluded to be ettringite. Fibrous crystals consist of Ca and Si, and it to be calcium silicate hydrate.

• 대한기계학회논문집A
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• 제22권3호
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• pp.529-539
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• 1998

A quantitative study of impact damage of ${Al_2}}O_3}-TiO_2$ plasma coated soda-lime glasses was carried out and compared with that of the uncoated smooth glass specimen. The shape of cracks by the impact of steel ball was observed by stereo-microscope and the decrease of the bending strength due to the impact of steel ball was measured through the 4-point bending test. At the low velocity, cone cracks were occurred. As the impact velocity increases, initial lateral cracks were propagated on the slanting surface of a cone crack, and radial cracks were generated at the crushed site. When the impact velocity of steel ball exceeds the critical velocity, the contact site of specimen was crushed due to plastic deformation and then radial and lateral cracks were largely grown. Crack length of coated specimens was smaller than that of uncoated smooth specimen due to the effect of coating layer on the substrate surface. According to impact velocity, the bending strength of coated specimens had no significant difference, compared with that of the uncoated smooth specimen. But this represents that the bending strength of coated specimens was increased, considering the effect of sand blasting damage which was performed to increase the adhesion force of coating layer.

• 대한자원환경지질학회:학술대회논문집
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• 대한자원환경지질학회 2005년도 춘계 학술발표회 논문집
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• pp.141-145
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• 2005

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.309-312
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• 2006

An experimental study for bond slip behavior of concrete and a FRP plank was used as the both formwork and the tensile reinforcement for a concrete structural member is described. For the FRP plank and the concrete to act as a composite structural member a satisfactory bond at the interface between the smooth surface of the FRP and the concrete must be developed. This study focuses on investigation of the bond slip behavior of sand coated interface between FRP and cast-in-place concrete experimentally.

• KSBB Journal
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• 제21권4호
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• pp.317-323
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• 2006

본 연구는 다가올 물 부족에 따른 하나의 대안으로서 중수도 시스템에 초점을 맞추어, 생활오수를 이용하여 혐기/무산소/호기조의 $A^2O$ 생물막 공법으로 구성된 상향류식 고정상 담체 반응기로 처리한 오수를 하향류식 은나노 모래여과 반응기에 다시 연속 통과시켜 이중 처리하여 얻은 처리수를 중수도에 활용이 가능하지에 대하여 연구하였다. 이중 공정 후 배출수의 pH는 $7.39{\sim}8.06$(평균 7.84) 범위이었고, $COD_{Mn}$은 $8{\sim}18mg/L$(평균 12.1 mg/L), $BOD_5$는 $2.1{\sim}10mg/L$(평균 4.9 mg/L)로 중수도 수질 기준에 적합하였다. SS는 $3{\sim}9mg/L$의 범위로 평균 농도가 4.95 mg/L를 나타내면서 SS 제거율이 94.8%로 대부분 법적 기준치 5 mg/L 이하로 처리되어 가능성을 보여 주었다. 대장균군 수의 평균 제거율이 99.1%이었으며, 배출수의 평균 대장균 군수는 65 MPN/100mL이 검출되었으나 중수도 수질 기준에는 불검출로 되어 있으므로 완벽한 제거를 위해서는 0.2 mg/L 이상의 결합잔류염소의 양을 고려한 염소 처리를 하여야 한다. SEM 사진으로부터 은모래 표면에서는 박테리아가 존재하지 않음을 알 수 있었다. 이 외에 중수도 수질 기준에 포함될 가능성이 있는 총질소 및 총인의 제거율은 각각 50.3%와 27.2%이었다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2003년도 추계학술발표회초록집
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• pp.134-135
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• 2003

The dental implant materials required good mechanical properties, such as fatigue strength, combined with a high resistance to corrosion. For increasing fatigue resistance and delaying onset of stress corrosion cracking, shot peening has been used for > 50 years to extend service life of metal components. However, there is no information on the electrochemical behavior of shot peened and hydroxyapatite(HA) coated Ti-6Al-4V alloys. To increase fatigue strength, good corrosion resistance, and biocompatibility, the electrochemical characteristics of Ti/TiN/HA coated and shot peened Ti-6Al-4V alloys by electron beam physical vapor deposition(EB-PVD) have been researched by various electrochemical method in 0.9%NaCl. Ti-6Al-4V alloys were prepared under the condition of hydrogen and vacuum arc furnace. The produced materials were quenched at 1000$^{\circ}C$ under high purity dried Ar atmosphere and were hold at 500$^{\circ}C$ for 2 hrs to achieve the fatigue strength(1140㎫) of materials. Ti-6Al-4V alloys were prepared under the condition of hydrogen and vacuum arc furnace. Shot peening(SP) and sand blasting treatment was carried out for 1, 5, and 10min. On the surface of Ti-6Al-4V alloys using the steel balls of 0.5mm and alumina sand of 40$\mu\textrm{m}$ size. Ti/TiN/HA multilayer coatings were carried out by using electron-beam deposition method(EB-PVD) as shown Fig. 1. Bulk Ti, powder TiN and hydroxyapatite were used as the source of the deposition materials. Electrons were accelerated by high voltage of 4.2kV with 80 - 120mA on the deposition materials at 350$^{\circ}C$ in 2.0 X 10-6 torr vacuum. Ti/TiN/HA multilayer coated surfaces and layers were investigated by SEM and XRD. A saturated calomel electrode as a reference electrode, and high density carbon electrode as a counter electrode, were set according to ASTM GS-87. The potentials were controlled at a scan rate of 100 mV/min. by a potentiostat (EG&G Co.273A) connected to a computer system. Electrochemical tests were used to investigate the electrochemical characteristics of Ti/TiN/HA coated and shot peened materials in 0.9% NaCl solution at 36.5$^{\circ}C$. After each electrochemical measurement, the corrosion surface of each sample was investigated by SEM.

• Design & Manufacturing
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• 제7권1호
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• pp.45-49
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• 2013

Since the shell-molds are used to make casting the metal parts for the automobile industry, the quality may well be inconsistent with the lower productivity, increasing the cost of the end products. The primary elbow design shell molded steel castings being produced through extrusion process has $180^{\varnothing}$ O.D., $150^{\varnothing}$ I.D., 14mm thickness and 400mm length, while being processed onto the left side of the tubing. The primary cause for the poor processing is the uneven manual shell molding. If the manual shell molds should be produced to have even quality, they would not be processed for tube linking. The purpose of this study was to develop the flask-molds for manufacturing of the shell molds to ensure mass-production, consistent quality, ommission of processing and comfortable working environment. For this purpose, four flask-molds were produced and thereby, four shell molds were assembled. In particular, the shell molds for processing were formed of the fine coated sand to be blown. As a result, productivity increased about three times, while a consistent quality was ensured. Furthermore, the tubes could be linked with each other without being processed, while pallets could be stacked, stored, transported and managed more easily. In a nut-shell, the molding theory could be applied more effectively. However, it is conceived that this study should be followed up by future studies which will research into reliability and endurability of the end products.

• 한국건설순환자원학회논문집
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• 제9권4호
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• pp.499-505
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• 2021

이 연구의 목적은 거푸집 종류별로 콘크리트 표면의 물리/화학적 특성을 실험적으로 조사하는 것이다. 이를 위하여 건설공사에 일반적으로 사용되는 합판 거푸집과 코팅된 합판 거푸집을 준비하였고, 추가로 콘크리트 표면 열화나 거친 표면을 모사하기 위해 사포를 부착한 합판 거푸집을 준비하였다. 콘크리트는 일반 콘크리트를 사용하였다. 콘크리트 표면 특성은 육안관찰, 주사전자현미경 관찰, 성분 이미지 맵핑, 화학성분 분석, 2차원과 3차원 표면 형상 분석, 그리고 제타 전위 측정을 통해 조사하였다. 실험결과 코팅된 거푸집과 접한 콘크리트 표면이 가장 매끄럽고, 사포를 부착한 거푸집과 접한 콘크리트 표면이 가장 거친 것으로 나타났다. 이외에도 거푸집 종류별로 표면 특성에 뚜렷한 차이가 나타났다. 다만 표면 거칠기가 화학 성분이나 제타 전위에 비하여 차이가 크게 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제11권5호
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• pp.114-122
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• 2007

강구조물의 고력볼트 마찰접합부에 있어서 마찰면의 부식은 장기적으로 마찰력 감소와 접합부 내력저하를 초래한다. 본 연구는 고력볼트 접합부의 부식을 방지하고 소요 역학적 성질을 만족시키기 위해 접합부의 마찰면에 Zn/Al 금속용사 방청처리 한 고력볼트 접합부를 대상으로 마찰면의 표면처리방법과 피막두께를 주요 변수로 하여 인장시험을 실시하였고, 실험으로 부터 마찰면 표면거칠기와 미끄럼계수를 측정하였다. 무도장 샌드블라스트 처리한 접합부 및 샌드블라스트 처리 후 금속용사를 실시한 볼트 접합부의 미끄럼 계수는 국내 규준의 규정 값과 비교하여 동등 이상의 우수한 미끄럼계수 값을 나타냈다.