• Applied Chemistry for Engineering
• /
• v.32 no.6
• /
• pp.664-670
• /
• 2021

Stainless steel was applied as bipolar plate (BP) of polymer electrolyte membrane fuel cell (PEMFC) due to high mechanical strength, electrical conductivity, and good machinability. However, stainless steel was corroded and increased contact resistance resulting PEMFC performance decrease. Although the corrosion resistance could be improved by surface treatment such as noble metal coating, there is a disadvantage of cost increase. The stainless steel corrosion behavior and passive layer influence on PEMFC performance should be studied to improve durability and economics of metal bipolar plate. In this study, SUS316L bipolar plate of 25 cm² active area was manufactured, and experiments were conducted for corrosion behavior at an anode and cathode. The influence of SUS316L BP corrosion on fuel cell performance was measured using the polarization curve, impedance, and contact resistance. The metal ion concentration in drained water was analyzed during fuel cell operation with SUS316L BP. It was confirmed that the corrosion occurs more severely at the anode than at the cathode for SUS316L BP. The contact resistance was increased due to the passivation of SUS316L during fuel cell operation, and metal ions continuously dissolved even after the passive layer formation.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.5
• /
• pp.651-657
• /
• 2010

A composite piston with a crown made of steel and a skirt made of NCI is used in a marine diesel engine, which has a maximum firing pressure of over 180 bar and a high thermal load. In the fatigue design of the composite piston, the fatigue is influenced by factors such as the load type, surface roughness, and temperature; further, the distribution ratio of the firing force from the crown to the skirt is important for optimizing the design of the crown and skirt. In this study, the stress gradient method was used to consider the effect of the load type. The temperature field on the piston was predicted by cocktail-shaking cooling analysis, and influence of high temperature on fatigue strength was investigated. The load transfer ratio and contact pressure were optimized by design of the surface shape and accurate tolerance analysis. Finally, the cooling performance and durability design of the composite piston were verified by performing a long-term prototype test.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.7 no.2
• /
• pp.143-152
• /
• 2005

Shotcrete for support of tunnel structures may contact with groundwater. The hazardous components in groundwater may cause corrosion of shotcrete. Also, the hazardous components may deteriorate the engineering properties of shotcrete, such as compressive strength, bond strength, flexural strength and so forth. The more the effect of the hazardous components on the shotcrete may increase, the more the stability of tunnel structure may decrease. The specimens were artificially immersed in various chemical solutions including hazardous components after the specimens were made at the tunnel construction site. It was performed to analyze the effect of the hazardous components in ground water on the engineering properties of shotcrete. The uniaxial compressive strength test, XRD, SEM were conducted to evaluate the durability and corrosion of shotcrete.

• Journal of Adhesion and Interface
• /
• v.6 no.2
• /
• pp.13-20
• /
• 2005

Interfacial shear strength (IFSS) of environmentally friendly natural fiber reinforced polymer composites plays a very important role in controlling the overall mechanical performance. The IFSS of various Ramie and Kenaf fibers/epoxy composites was evaluated using the combination of micromechanical test and nondestructive acoustic emission (AE) to find out optimal conditions for desirable final performance. Dynamic contact angle was measured for Ramie and Kenaf fibers and correlated the wettability properties with interfacial adhesion. Mechanical properties of Ramie and Kenaf fibers were investigated using single-fiber tensile test and analyzed statistically by both uni-and bimodal Weibull distributions. An influence of clamping effect on a real elongation for both Ramie and Kenaf fibers were evaluated as well. Two different microfailure modes, axial debonding and fibril fracture coming from fiber bundles and single fiber composites (SFC) were observed under tension and compression.

• Polymer(Korea)
• /
• v.25 no.3
• /
• pp.435-440
• /
• 2001

The objective of this study was to examine the effect of oxidation inhibitor contents on the work of adhesion, fracture toughness, and impact strength of the unidirectional carbon-carbon composites (C/C composites). The molybdenum disilicide ($MoSi_2$) used as an oxidation inhibitor was impregnated with phenolic resins to improve the anti-oxidation properties of the composites in different concentrations of 4, 12 and 20 wt%. Based on Wilhelmy equation, the work of adhesion of C/C composites was calculated by contact angle methods. Fracture toughness and impact strength were pressured by three-point bending test for the critical intensity factor ($K_IC$) and Izod test method, respectively. As a result, the composites made with $MoSi_2$ resulted in an increasing of both fracture toughness and impact strength. Especially, the composites made with 12 wt% $MoSi_2$ content showed the highest value of London dispersive component, $W_A\;^L$, in work of adhesion, resulting from improving the interfacial adhesion force among fibers, filler, and matrix in this system.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2017.05a
• /
• pp.110-110
• /
• 2017

마이크로 플루이딕 디바이스는 화학, 생물학 실험 및 생체 의학 진단을 위한 플랫폼으로 지난 20년간 그 사용 및 연구가 증가되어 왔다. 마이크로 플루이딕 디바이스를 제작하는 데 있어 가장 일반적으로 사용되는 재료는 실리콘이지만 비용이 많이 들고 불투명하므로 광학 검출이 필요한 곳에 적용이 제한된다. 이러한 측면에서 열가소성 플라스틱은 상업화의 중요한 요소인 대량 생산에 있어 큰 잠재력을 가지고 있으며 저렴하고, 가공이 쉽고, 유연하고, 광학적으로 투명하고, 화학적으로 불활성이며, 생체적합성을 가진다. 본 연구에서는 열가소성 플라스틱의 일종인 PMMA Poly(methylmethacrylate)를 효율적으로 접합하기 위해 비교적 낮은 온도와 낮은 압력에서 에탄올을 활용한 접착방식을 개발하였다. 먼저, PMMA 기판의 전체 표면을 $80^{\circ}C$에서 20 분 동안 에탄올로 처리한 후, $60^{\circ}C$에서 20 분간 열 압착하는 방식으로 영구적인 결합이 이루어졌다. 결합 강도 및 채널의 sealing 정도를 확인하기 위해, 인장 강도, 누수 및 파열 테스트를 수행하였다. 결합강도는 약 12.4 MPa로 타 연구와 비교할 때 매우 높았으며 마이크로 채널의 전체 내부 체적보다 거의 450 배 높은 강한 액체 흐름을 견딜 정도로 견고한 결합이 유지되었다. 열가소성 플라스틱의 본딩에 사용되는 유기 용매는 광학 특성을 희생시키지 않으면서 결합 속도를 높일 수 있지만, 결합 공정 중에 용매로 인해 마이크로 채널이 막히는 현상이 발생될 수 있다. 따라서, 견고한 본딩을 유지하면서 채널 막힘을 방지하기 위해 마이크로 채널을 소수성으로 선택적으로 처리하여 내벽의 표면 특성을 튜닝해 주는 기법을 추가로 적용하였다. 본 연구에서 사용한 방법은 아민-PDMS (polydimethylsiloxane) 링커를 적용하여 기판 표면의 극성을 변경시켜 주었다. 아민-PDMS 링커는 PC (polycarbonate), PET (polyethylene terephthalate), PVC (polyvinyl chloride) 및 PI (polyimide)와 같은 다양한 열가소성 플라스틱의 표면 소수성을 현저히 증가시키며 화학적, 열적 안정성이 뛰어나다. 아민-PDMS 링커는 PMMA의 카보닐 그룹과 반응할 수 있는 아민 사이드 그룹을 포함하는 PDMS 백본으로 구성되며 처리된 대상표면을 소수성으로 만든다. 아민-PDMS 링커 처리 이후 채널은 소수성으로 변화되었으며 이는 접촉각(contact angle)의 증가로 확인되었다. 코팅된 채널을 에탄올로 30분간 80도에서 처리하여도 소수성은 그대로 유지되어 마이크로 채널의 선택적인 소수성 코팅이 성공적으로 수행되었다.

• Journal of the Korean Ceramic Society
• /
• v.41 no.1
• /
• pp.69-75
• /
• 2004

The degree of the indentation damage and strength degradation for 3Y-TZP ceramics and (Y,Nb)-TZP/$Al_2O_3$ dental implant composites was investigated under the Hertzian cyclic fatigue. Fatigue tests were conducted at contact loads of 500 to 3000 N and up to $10^6$ cycles in exact in vitro environments. At 500 N, no strength degradation and crack generation was observed up to $5{\times}10^5$ contact cycles. Fatigue properties of 3Y-TZP ceramics was superior to (Y,Nb)-TZP/ㅍ composites due to stress relief caused by the phase transformation from tettagonal to monoclinic phase. As contact load increased, the drastic reduction in strength was found when the damage transition from ring to radial crack occurred. The extent of strength degradation was more pronounced in vitro environments probably due to chemical corrosion of artificial saliva through cracks introduced during large numbers of contacts.

• Journal of the Korean GEO-environmental Society
• /
• v.11 no.3
• /
• pp.23-32
• /
• 2010

In this study, Generally sandbag was used to reinforce slope or restore levee by using the in-situ material. To increase shear strength of sandbag, the Velcro system was effective for geosynthetic interface and make up for the weakness of shear strength between sandbag to sandbag. In this study, shear properties of geosynthetic-geosynthetic and geosynthetic-soil were evaluated from large scale direct shear tests. The cohesion and the angle of internal friction of each interface was evaluated. And laboratory model tests were performed to compare strength of reinforcement with strength of none reinforcement. As a result of this study, the cohesion and the angle of internal friction of each interface was increased, especially the cohesion was increased more than the angle of internal friction. Also according to the result of model test, the bearing capacity was increased by 20%.

• Journal of the Korean Geotechnical Society
• /
• v.20 no.1
• /
• pp.5-12
• /
• 2004

The purpose of this paper is to make an understanding of fundamental mechanism of shear behaviour between rock and concrete interfaces in the pile socketed into granite. The interface of pile socketed in rock can be modeled in laboratory tests by resolving the axi-symmetric pile situation into the two dimensional situation under CNS(constant normal stiffness) direct shear condition. In this paper, the granite core samples were used to simulate the interface condition of piles socketed in granite in our country. The samples were prepared in the laboratory to simulate field condition, roughness(angle and height), stress boundary condition, and then tested by CNS direct shear tests. This paper describes shearing behaviour of socket piles into domestic granite through the analysis of CNS test results. It was found out that the peak shear strength increases with the angle of asperity and CNS value, and also the dilation increases with the angle of asperity but decreases with the CNS value.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.20 no.4
• /
• pp.59-67
• /
• 2016

Concrete is a very useful construction material for the sealing disposal of hazardous substances. In general, mass concrete is applied to these structures. And, the mineral admixtures are recommended for the long term performance. Calcium leaching could be happened due to the contact with pure water in underground structures. Thus, it is needed to evaluate the resistance of calcium leaching for concrete mixed with mineral admixtures. From the test results, the mineral admixtures are effective to the improvement of long term compressive strength and chloride diffusion coefficient in concrete members. When calcium leaching is happened, however, the reduction of compressive strength and chloride penetration resistance is severe than OPC case, the micro pore distribution is adversely affected. Consequently, when the mineral admixtures are applied to underground structures which is exposed to calcium leaching environment, it is desirable to reduce water-to-binder ratio, to expose after the sufficient pozolanic reaction, and to use BFS than FA.