• 수산해양기술연구
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• 제32권4호
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• pp.402-410
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• 1996

Recently carbon fiber reinforced plastic(CFRP) has been used structural materials in corrosive environment such as for water, chemical tank and chemical pipes. However, mechanical properties of such materials may change when CFRP are exposed to corrosive environment for long periods of time. Therefore, it is important to understand the effect of moisture absorption on mechanical properties of the CFRP. In this study, degradation behavior of immersed carbon fiber/epoxy resin composite material was investigated using acoustic emission(AE) technique. Fracture toughness test are performed on the compact tension(CT) test specimens that are pilled by two types of laminates $[0^{\circ}_2$/$90^{\circ}_2]_3s$ and $[0^{\circ}_2$/$90^{\circ}_2]_6s$During the fracture toughness test, AE test was carried out to monitor the damage of CFRP by moisture absorption. In spite of the change of moisture absorption rate, the fracture toughness of CFRP was not change. As immersion time increased, AE event count numbers decreased in low amplitude range of AE for amplitude distribution histogram. The event in low amplitude range was known to be generated by debonding of matrix-fiber interface. Therefore, decrease of AE event count numbers in low amplitude range represents that debonding of matrix-fiber interface which was probably generated by moisture absorption.

• 한국해양공학회지
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• 제12권3호통권29호
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• pp.31-41
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• 1998

Single fiber fragmentation technique was used to evaluate the change of interfacial properties by degradation of fiber tensile strength in the fiber reinforced composites. The influences of fiber tensile strength on the interfacial properties have been evaluated by the fragmentation specimens(weak fiber samples) of glass fiber/epoxy resin that was made using the pre-degraded glass fiber in distilled water at $80^{circ}C$ for specified periods. The effects of the immersion time on the interfacial properties in the distilled water at $80^{circ}C$ also have been evaluated by the fragmentation specimens(original fiber samples) of glass fiber/epoxy resin that was made using the received glass fiber. As the result, the tensile strength of glass fiber was decreased with the increasing of the treatment time in the distilled water at $80^{circ}C$ and the interfacial shear strength was independent of the change of the glass fiber strength in the single fiber fragmentation test. But in the durability test using the single fiber fragmentation specimen, interfacial shear strength decreased with the increasing of the immersion time in distilled water ar $80^{circ}C$. And it turned out that the evaluating of interfacial shear strength using original fiber tensile strength was valuable in the durability test for the water environment by the single fiber fragmentation technique.

• 한국환경농학회지
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• 제24권3호
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• pp.289-294
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• 2005

The toxic effects of 12 commercially available insecticides on the earthworm, Eisenia fetida (Savigny), were evaluated using artificial soil, surface sprayed soil, immersion, and contact filter tests. The risk to earthworm was assessed by the TER (toxic exposure ratio) value, which was calculated by the formula, TER=NOEC/PEC (predicted environmental concentration). TER was 3 for methomyl SL, 20 for carbaryl WP, 20 for phosphamidon SL, 30 for imidacloprid WP, and 60 for dichlorvos EC the in artificial soil test. At recommended, the earthworm mortality to methomyl SL reached 50% in the surface sprayed soil test, 72% in the immersion test, 30% in the contact filter paper test, whereas that to imidacloprid WP reached 56, 32, and 100 respectively. As a result of the four methods, methomyl SL and imidacloprid WP would be toxic insecticides to earthworm.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2002년도 춘계공동학술발표회요약집
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• pp.291.1-291
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• 2002

• Corrosion Science and Technology
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• 제6권4호
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• pp.147-153
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• 2007

This study sought to investigate the reaction of Co-binder containing tungsten with molten zinc. Four kinds of Co-W alloys (pure, 10%W, 20%W, 30%W) were prepared using the powder metallurgy method. The specimens were immersion-tested in molten pure zinc baths at $460^{\circ}C$. To evaluate the corrosion property in molten zinc, the weight loss of the specimen was measured after the immersion tests at different immersion times (10~300 min.). Co-10%W alloys, compared with pure cobalt, showed no effect of tungsten addition on the reaction rate in molten zinc. The relationship between the weight loss and the square root of immersion period represents a straight line in both pure cobalt and Co-10%W alloy. The Co-Zn reaction layer in Co- 1O%W alloy consists of $\gamma2$, $\gamma1$, $\gamma$ and ($\beta1$ phases. The rate of weight loss significantly increases and the weight loss behavior is not well accord with the linear relationship as the tungsten content in the Co-W alloy increases. The $\beta1$ layer was not formed on the Co-20%W alloy and neither was a stable Co-Zn intermetallic compound layer found on the Co-30%W alloy. The main cause of increase in reaction rate with increasing tungsten content is related with the instability of the Co-Zn reaction phases as seen on micro-structural analysis.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
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• pp.145-149
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• 2006

The effect of alkaline environmental condition on durability of GFRP composites according to additives has been investigated. Additives used were polyvinyl alcohol (PVA), kaolin and alumina powder. Weight gains increased with immersion time in all GFRP composites at $80^{\circ}C$. But weight gain of specimen added PVA did not differ through the whole immersion time in both tap water and alkaline solution at 20 and $80^{\circ}C$. Tensile strength decreased with immersion time in all environment conditions. Tensile strength of GFRP composites regardless of additives decreased rapidly up to 5 days of immersion and then decreased slowly up to 30 days in alkaline solution environment at $80^{\circ}C$. The weight gains were not much difference in both tap water and alkaline solution at $20^{\circ}C$. But the ones of GFRP composites added PVA was smaller than the composites without additive in all aqueous at $20^{\circ}C$. Test strength of GFRP composites added polyvinyl alcohol has improved through the whole immersion time in both tap water and alkaline solution environment at $20^{\circ}C$.

• 방송공학회논문지
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• 제25권1호
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• pp.113-116
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• 2020

본 논문은 360도 동영상과 감각효과(Sensorial Effects)가 피실험자의 몰입도, 만족도, 실재감에 미치는 영향을 측정하기 위한 사용자 경험(Quality of Experience: QoE) 평가 실험 방법을 제안한다. 피실험자는 발향장치가 부착된 헤드 마운티드 디스플레이(Head Mounted Display: HMD)를 착용한 상태에서 감각효과가 동반된 360도 동영상을 경험한 후, 몰입도, 만족도, 실재감에 대한 설문에 응답한다. 응답 분석 결과 제안된 실험방법이 360도 VR 동영상과 감각효과에 대한 피실험자의 몰입도, 만족도, 실재감 등을 측정하기에 적합한 실험 방법임을 확인하였다. 반면, 360도 동영상을 시청하는 도중 비교 실험을 위한 회색 화면을 삽입하게 되면 몰입도와 실재감에 상당한 저하를 일으키는 것으로 파악되었다.

• 한국표면공학회지
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• 제54권5호
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• pp.238-247
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• 2021

PEO (plasma electrolytic oxidation) was applied to modify the surface of AZ31 magnesium alloy in this study. The mixed solution of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) was used as the electrolyte, and 0 - 0.05 g/L of Ca-GP (Glycerol Phosphate Calcium salt) was added in the electrolyte as an additive. PEO treatment was conducted at a current density of 30mA/cm² for 5 minutes using a DC power supply. The surface properties were identified by SEM, XRD and surface roughness analyses, and the corrosion resistance was evaluated by potentiodynamic polarization and immersion tests. In addition, the biocompatibility was evaluated by immersion test in SBF solution. As the concentration of Ca-GP was increased, the surface morphology was denser and more uniform, and the amount of Ca and the thickness of oxide layer increased. Only Mg peak was observed in XRD analysis due to very thin oxide layer. The corrosion resistance of PEO-treated samples increased with the concentration of Ca-GP in comparision with the untreated sample. In particular, the highest corrosion resistance was identified at the group of 0.04g Ca-GP through potentiodynamic polarization and immersion tests in saline solution (0.9 wt.%NaCl). During the immersion in saline solution, pH rapidly increased at the beginning of immersion period due to rapid corrosion, and then increase rate of pH decreased. However, the pH value in the SBF temporarily increased from 7.4 to 8.5 during the day, then decreased due to the inhibition of corrosion with HA(hydroxyapatite) formation.

• Journal of the Korean Data Analysis Society
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• 제20권6호
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• pp.3127-3137
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• 2018

본 연구는 대학생들을 대상으로 교수의 리더십 유형이 전공만족과 학습몰입에 어떠한 영향을 미치는지 확인하는데 목적이 있다. 이러한 목적을 달성하기 위하여 2017년 9월부터 11월까지 계열 전공학생 543명의 자료를 최종 분석에 사용하였다. 자료처리는 IBM SPSS Statistics 25 프로그램을 사용하였고, 조사대상자 특성을 파악하기 위한 빈도분석, 조사도구의 타당도 및 신뢰도 검정을 위한 요인분석, 요인 간의 차이 및 영향력을 알아보기 위해서 t-검정, 다중회귀분석을 실시하였다. 분석결과 첫째, 전공만족에 대해서 성별과 학년별로 차이가 있는 것으로 나타났으나 전공별로는 차이가 없는 것으로 나타났다. 둘째, 학습몰입은 전공별, 성별, 학년별로 차이가 있는 것으로 나타났다. 셋째, 리더십 유형이 전공만족에 유의한 영향을 미치는 요인은 비전과 사명감, 개별적 고려, 상황적 보상은 유의한 영향을 미치는 것으로 나타났으나, 예외적 관리에서는 유의하지 않은 것으로 나타났다. 넷째, 리더십 유형이 학습몰입에 미치는 영향에서 비전과 사명감, 상황적 보상은 유의한 영향을 미치는 것으로 나타났으나, 개별적 고려, 예외적 관리는 유의하지 않은 것으로 나타났다.

• Composites Research
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• 제21권3호
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• pp.1-8
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• 2008

본 연구에서는 염수환경이 탄소-에폭시 복합재의 기계적 물성치에 미치는 영향을 살펴보았다. 시편은 USN125 복합재로 제작하였고, 3.5% 염수에 0, 0.5. 1, 2, 3, 6, 9, 12 개월간의 침수 후 면내 인장시험과 전단시험을 수행하였다. 실험에서 염수로부터 시편을 보호하기 위한 방수페인트나 시간을 절약하기 인한 특별한 가속방법은 사용하지 않았다. 섬유방향 및 기지방향 인장강도와 강성의 경우 12개월 동안의 침수에도 불구하고 특별한 물성치의 변화를 발견할 수 없었다. 반면 전단강도와 강성은 염수환경에 민감하게 반응하며. 12개월 침수 후의 물성치는 염수에 노출되지 않은 시편에 비해 전단강도 30%, 전단강성 46%의 저하를 보였다.