• Corrosion Science and Technology
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• 제14권4호
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• pp.172-176
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• 2015

Austenitic stainless steel was investigated under cyclic loading in electrolytes with different chloride contents and pH and at different temperatures. The testing solutions were 13.2 % NaCl (80,000 ppm $Cl^-$) at $80^{\circ}C$and 43 % $CaCl_2$ (275,000 ppm $Cl^-$) at $120^{\circ}C$. In addition to S-N curves in inert and corrosive media, the fracture surfaces were investigated with a scanning electron microscope (SEM) to analyse the type of attack. The experimental results showed that a sharp decrease in corrosion fatigue properties can be correlated with the occurrence of stress corrosion cracking. The correlation of occurring types of damage in different corrosion systems is described.

• 대한기계학회논문집
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• 제10권6호
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• pp.830-836
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• 1986

본 연구에서는 이러한 사실에 착안하여 프랑스의 Granjon에 의해 이미 개발된 용접부의 재용성이 탁월한 종래의 정적임플란트(implant)시험기를 정한.고안하여 아아 크용접부의 피로특성에 영향을 미칠 수 있는 제영향인자를 재현하여 간편하게 피로시 험을 할 수 있는 동적 임플란트시험기를 개발하였다. 이러한 시험기를 이용하여 저 온.고압력용강재에 대해서 다음과 같은 항목들을 구명할 목적으로 본 연구는 수행된 것이다.

• Advanced Composite Materials
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• 제16권2호
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• pp.83-94
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• 2007

Woven sisal textile fiber reinforced composites were used to evaluate fracture toughness, tensile and three-point bending. The water absorption testing of all specimens was repeated five times in this study. All specimens were immersed in pure water during 9 days at room temperature, and dried in 1 day at $50^{\circ}C$. Two kinds of polymer matrices such as epoxy and vinyl-ester were used. Fractured surfaces were taken to study the failure mechanism and fiber/matrix interfacial adhesion. It is shown that it can be enhanced to improve their mechanical performance to reveal the relationship between fracture toughness and water absorption fatigue according to different polymer matrices. Water uptake of the epoxy composites was found to increase with cycle times. Mechanical properties are dramatically affected by the water absorption cycles. Water-absorbed samples showed poor mechanical properties, such as lower values of maximum strength and extreme elongation. The $K_{IC}$ values demonstrated a decrease in inclination with increasing cyclic times of wetting and drying for the epoxy and vinyl-ester.

• Bulletin of the Korean Chemical Society
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• 제17권4호
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• pp.342-347
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• 1996

Voltammetric determination of phenol derivatives, such as phenol, o-, m-, and p-cresols was studied with a β-Cyclodextrin (β-CD) modified-carbon paste electrode composing of the graphite powder and Nujol oil. Phenol derivatives were chemically deposited via the complex formation with β-CD by immersing the CME into a sample solution. The resulting surfaces were characterized with cyclic and differential pulse voltammetry. Treating the CME with 1 M nitric acid for five sec after a measurement could regenerate the electrode surface. Linear sweep and differential pulse voltammograms were recorded for the above system to optimize the experimental parameters for analysing the phenol derivatives. In this case, the detection limit for phenols was 5.0×10-7M for 25 min of the deposition time with differential pulse voltammetry. The relative standard deviation was ±5.2% of 3.0×10-6M (four repetitions). The interference effect of the following organic compounds was also investigated; Bezoic acid, hippuric acid, o-, m-, and p-methylhippuric acid. Adding the organic compounds into the sample solution reduces the peak current of the phenols to about 25%.

• Restorative Dentistry and Endodontics
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• 제32권2호
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• pp.130-137
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• 2007

본 연구의 목적은 니켈티타늄 전동파일의 피로파절에 있어서 표면 결함의 역할을 규명하고자 fatigue tester에서 반복적 인 fatigue force를 부여한 후 파절된 단면을 주사전자현미 경으로 관찰하여 파절 역학을 규명하는 것이다. 총 45개의 #30/.04 taper와 21 mm의 HEROShaper 니켈-티타늄 전동파일을 15개씩 3개의 군으로 분류하였다. 제 1군은 결함이 없는 새 HEROShaper파일, 제 2군은 제조과정에서 metal rollover나 machining marks와 같은 표면결함을 갖는 HEROShaper파일, 제 3군은 임상에서 4- 6개의 구치부 근관의 확대에 사용한 HEROShaper 파일을 사용하였다. 모든 파일들은 회전속도(300 rpm)와 pecking distance (3 mm)가 일정하게 맞춘 fatigue tester에서 파절될 때까지 시간을 측정한 후 통계분석을 통해 각 군간의 유의성을 분석하였고, 파절 단면의 farctographic analysis를 통해 파절역학을 규명하고자 하였다 실험결과 평균 파절시간에 있어서 group 1과 2, group 1과 3사이에는 통계학적으로 유의할 만한 차이가 있었으나 (p<0.05), group 2와 3사이에는 통계학적인 차이가 없었다. Fractographic analysis 결과 대부분의 파절면에서 microvoid와 dimple 소견을 갖는 ductile fracture양상이 관찰되었다. 또한 brittle fracture가 일어난 파절면에서는 파절선 전방에 수 많은 striation들이 관찰되었고 transgranular 및 intergranular cleavage 소견도 보였다. 표면결함이 있는 제 2, 3 군의 파절단면에서는 모든 시편에서 표면결함이 관찰되었다. 이와 같은 결과로 미루어 보아 표면결함이 반복 피로파절에서 미세균열의 기시점으로 중요한 역할을 하며 fractography분석법은 Ni-Ti 파일의 파절역학을 규명하는데 유용함을 알 수 있었다.

• Journal of Electrochemical Science and Technology
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• 제8권3호
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• pp.206-214
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• 2017

SnS films have been prepared by electrodeposition technique onto Cu and ITO substrates using acidic solutions containing tin chloride and sodium thiosulfate with sodium citrate as an additive. The effects of sodium citrate on the electrochemical behavior of electrolyte bath containing tin chloride and sodium thiosulfate were investigated by cyclic voltammetry and chronoamperometry techniques. Deposited films were characterized by XRD, FTIR, SEM, optical, photoelectrochemical, and electrical measurements. XRD data showed that deposited SnS with sodium citrate on both substrates were polycrystalline with orthorhombic structures and preferential orientations along (111) directions. However, SnS films with sodium citrate on Cu substrate exhibited a good crystalline structure if compared with that deposited on ITO substrates. FTIR results confirmed the presence of SnS films at peaks 1384 and $560cm^{-1}$. SEM images revealed that SnS with sodium citrate on Cu substrate are well covered with a smooth and uniform surface morphology than deposited on ITO substrate. The direct band gap of the films is about 1.3 eV. p-type semiconductor conduction of SnS was confirmed by photoelectrochemical and Hall Effect measurements. Electrical properties of SnS films showed a low electrical resistivity of $30{\Omega}cm$, carrier concentration of $2.6{\times}10^{15}cm^{-3}$ and mobility of $80cm^2V^{-1}s^{-1}$.

• 분석과학
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• 제8권4호
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• pp.675-682
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• 1995

Thin films of buckminsterfullerene($C_{60}$) formed by solution drop casting on Pt foil electrode surfaces were studied by cyclic voltammetry(CV) in acetonitrile(MeCN) containing quaternary ammonium or alkali-metal salts as supporting electrolyte. The electrochemical behaviors of $C_{60}$ films are found to be strongly dependent on the nature of the supporting electrolytes, especially with tetrabutyl ammonium perchlorate (TBAP, $NBu_4ClO_4$), and tetrabutyl ammonium tetrafluoroborate ($TBABF_4$, $NBu_4BF_4$). Reasonably stable films are formed into which electrons can be injected. The interaction of $C_{60}$ film with the quaternary ammonium cation may produce the fulleride salts $(TBA^+)(C{_{60}}^-)$ and $(TBA^+)_2(C{_{60}}^{2-})$. The bulk electroreduction with a controlled potential to generate the soluble $C{_{60}}^{3-}$ anions(dark red-brown color) is followed by electrooxidative deposition to produce a neutral $C_{60}$ film on the surface. The peak currents($I_{pc}$ and $I_{pa}$) of these thin film were dramatically decreased with repetitive potential scanning. These results could be explained by the adsorption-desorption phenomena and ion pairing interaction of reduced species($C{_{60}}^-$, and $C{_{60}}^{2-}$) onto the electrode surface. The peak current changes and peak potential shifts of the thin $C_{60}$ film in cyclic voltammograms formed from solution were observed by varying scan rates.

• 공업화학
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• 제9권4호
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• pp.463-468
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• 1998

알루미늄의 부식에 있어서 HCI 용액내에 황산을 첨가하는 경우 황산이온의 화학적 흡착에 의한 부식억제 효과가 나타나며, CV (cyclic voltammetry) 실험결과 황산이온은 핏트내부에 보호성 산화피막을 생성함으로서 에치핏트가 핏트내부와 알루미늄 표면에 함께 생성되어 핏트의 밀도가 증가하였다. 알루미늄 교류에칭시에 핏트분포는 황산이온의 농도와 환원전류량에 의하여 크게 영향을 받으며, 환원전류인가시 $0.8mC/cm^2$ 이하의 전하량에서 핏트내부에 생성된 산화피막은 황산이온 농도의 증가에 따라 핏트발생에 대한 저항성이 중가하였으나, $0.8mC/cm^2$ 이상에서는 산화피막내에 국부적인 구조변화가 발생하며 황산이온 농도에 관계없이 산화피막의 파괴가 빠르게 진행되었다.

• Nuclear Engineering and Technology
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• 제40권3호
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• pp.225-232
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• 2008

To understand the effect of the cyclic strain rate on the environmentally assisted cracking behaviors of SA508 Gr.1a low alloy steel in deoxygenated water at $310^{\circ}C$, the fatigue surface and a sectioned area of specimens were observed after low cycle fatigue tests. On the fatigue surface of the specimen tested at a strain rate of 0.008 %/s, unclear ductile striations and a blunt crack tip were observed. Therefore, metal dissolution could be the main cracking mechanism of the material at this strain rate. On the other hand, on the fatigue surfaces of the specimens tested at strain rates of 0.04 and 0.4 %/s, brittle cracks and flat facets, which are evidences of the hydrogen induced cracking, were observed. In addition, a tendency of linkage between the main crack and the micro-cracks was observed on the sectioned area. Therefore, at higher strain rates, the main cracking mechanism could be hydrogen induced cracking. Additionally, evidence of the dissolved MnS inclusions was observed on the fatigue surface from energy dispersive x-ray spectrometer analyses. Thus, despite the low sulfur content of the test material, the sulfides seem to contribute to environmentally assisted cracking of SA508 Gr.1a low alloy steel in deoxygenated water at $310^{\circ}C$.

• 한국산학기술학회논문지
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• 제18권6호
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• pp.464-469
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• 2017

유도전동기 회전자는 rotor core를 일정한 높이로 쌓은 후 rotor core slot에 Cu bar를 열박음(shrinkage fit)작업으로 고정한 후 Cu bar 표면을 punch로 길이방향, 원주방향으로 순차적으로 압입(swaging)하여 제작된다. 본 연구에서는 Cu bar 표면을 압입할 때 Cu bar 표면에 발생하는 압입깊이, 잔류응력 분포 그리고 rotor core slot과 Cu bar 접촉면에 작용하는 접촉력(contact force)을 평가하고자 하였다. 한편 실제의 압입작업은 복잡한 3차원 문제이나 수치해석적인 접근을 위하여 단순화된 2차원 cyclic symmetry 해석모델을 개발하였으며 이러한 해석모델을 사용하여 일정한 압입압력에서 4가지 종류의 Cu bar 형상에 대하여 압입량과 접촉력을 평가하였다. 탄소성 수치해석 결과 1) sample Cu bar block model을 사용하여 단순화된 2차원 수치해석 모델을 개발하였고 2) rotor core 압입작업시 일정한 압입압력에서 Cu bar 표면의 압입량은 Cu bar 형상에 크게 관계없이 거의 일정하며 3) 압입작업시 punch에 가해지는 압입압력으로부터 rotor core slot과 Cu bar 접촉면에 작용하는 총 접촉력을 추정할 수 있는 근사식을 제안하였다.