연료전지분리판의 제조 및 기계적 특성 연구

주원경(Wonkyung Joo),송정일(Jungil song),최환석(Hwansuk Choi) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

Considering diverse needed conditions, so far many materials have been studied as materials of bipolar plate for the fuel cell. At the first, plate which was made from graphite flat board having channel is that manufacturing cost of channel is high and due to the high brittleness, it is hard to reduce the thickness of plate. On the case of using a metal like stainless steel, there are some disadvantages such as high material density, high manufacturing cost and corrosion. To make a completion of disadvantages, we are researching on a carbon conductive polymer composite material. A carbon conductive polymer composite material has advantages like taking low-cost manufacturing and making light weight and reducing the manufacturing time. And due to using polymer fiber, higher ductilities is possible. On account of the fact that PEMFC is working on low temperature (approximately 80℃) comparing with other fuel cell plate, carbon conductive polymer composite material can be used for the plate. On this study, the goals are of establishing the manufacturing process of carbon conductive polymer composite material which is used for PEMFC and examining of mechanical characteristics of carbon conductive polymer composite material having superior electrical conductivity according to the change of fillers and forming conditions. And compression molding technique was used for processing, and graphite powder and carbon fiber was used as fillers. As a result of the research, through the optimization of molding conditions using compression molding technique I made carbon conductive polymer composite material for fuel cell plate having superior electrical conductivity which is up to 180 S/㎝. on the case of powder/epoxy composite material, according to the increasing forming pressure, electrical conductivity and bending strength were increased and optimal forming pressure was 1000~1500psi that carbon powder's degree of fineness was fully made. Maximum impact load and absorbing energy of carbon fiber reinforced composite material were better than those of graphite powder/epoxy composite material. This shows that degree of fineness was fully made and strength was increased.

Prediction of Material Properties of Ceramic Composite Material by Porous Structure and Porosity Using the Finite Element Method

이동규,김수현,김세영,유지행,조성욱 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.5

Recently, the use of ceramic composite materials in various areas has been increasing. However, since detailed structures have various porous structures according to the characteristics of the ceramic composite material, it is difficult to predict material properties through simple material experiments. If the detailed structure of ceramic composite materials were metal or other simple and regular forms, it would be possible to predict material properties through experiments or analysis. However, as porous ceramic materials have an irregular structure and random form, it is very difficult to predict their material properties through simple methods and actual material experiments must be conducted several or even dozens of times to predict the material properties with statistical analysis techniques. Therefore, this study uses FEM to predict the porous type or pore ratio of ceramic composite materials and the changes in material properties according to their detailed structure. It attempt to predict the maximum and minimum values of actual material properties. Through the results of this study, it is possible to more easily predict the material properties of ceramic composite materials by porosity and pore dispersity or adjacency. The results can be applied to the manufacturing of parts and structural analysis of models made from ceramic composite materials.

Comparative analysis of shear bond strength and quality of interface at novel bioactive material or Biodentine

Ivanka Dimitrova,Desislava Tsanova-Tosheva 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.2

The quality and durability of the adhesion between calcium-silicate cements and the restorative material are important, bothfor the durability of the healing and the clinical success outcome. The aim is to analyze the shear bond strength and qualityof the interface between composite restorative material and new bioactive material and Biodentine at the same conditions. Theused pulp-capping materials: conventional Biodentine and the new hybrid biomaterial BioCal-Cap. In this study, only one typeof adhesive system and one resin-based composite have been used. For this purpose, 60 molds were prepared and divided intofour groups. Half of them were filled with Biodentine and the other 30 with BioCal-Cap. The shear bond strength betweencalcium-silicate cements and the composite material was investigated. The Mann-Whitney test and the Wilcoxon Signed RanksTest were used for statistical analysis of the results. The results of the analyses show a statistically significant difference in shearbond strength between the two groups (p<0.05). In all selected specimens with Biodentine, upon immediate restoration withcomposite material, cracks of different lengths and sizes were observed in the pulp capping material. Fewer cracks wererecorded in the samples with delayed restoration using composite material. The data clearly show that the time of thecomposite material placement does not affect the shear bond strength in each of the observed groups. In selected specimenswith Biodentine, upon immediate restoration with composite material, cracks of different lengths and sizes were observed inthe pulp capping material. Fewer cracks were recorded in the samples with delayed restoration using composite material.

카울크로스빔용 PA/GF복합재료의 기계적 특성 분석에 관한 연구

김환국,박종빈,이지훈,정헌규 한국염색가공학회 2023 韓國染色加工學會誌 Vol.35 No.1

This study is about a hybrid lightweight cowl crossbeam structure with high rigidity and ability to absorb collision energy to support the cockpit module, which is an automobile interior part, and to absorb energy during a collision. It is a manufacturing process in which composite material bracket parts are inserted and injected into existing steel bars. When considering the mounting condition of a vehicle, the optimization of the fastening condition of the two parts and the mechanical properties of the composite material is acting as an important factor. Therefore, this study is about a composite material having a volume content of Polyamide(PA) and Glass Fiber used as a composite material for a composite material-metal hybrid cowl crossbeam. As a result of analyzing the physical properties of the PA/GF composite material, experimental data were obtained that can further enhance tensile strength and flexural strength by using PA66 rather than PA6 used as a base material for the composite material. And based on this, it contributed to securing the advantage of lightening by using high-stiffness composite material by improving the high disadvantage of the weight of the cowl crossbeam material, which was made only of existing metal materials.

샌드위치 구조를 가지는 복합재의 손실계수 향상을 위한 설계

이창민(Lee Chang-Min),전관수,강동석(Kang Dong-Suk),신영훈(Shin Young-Hoon),김종훈(Jong-Hoon Kim),강명환(Myunghwan Kang),서영수(Youngsu Seo) 한국소음진동공학회 2015 한국소음진동공학회 학술대회논문집 Vol.2015 No.10

Underwater weapon system, because it is directly exposed to external impact, structurally strong material is required. Moreover, it is necessary to use a light material in order to take advantage of buoyancy. Satisfying material to both at the same time is a composite material. Particularly in the case of submarine composite it is often used. It is important to have a high strength enough to be able to withstand large impact, but it is also important to attenuate it. In many cases the viscoelastic damping material in a sandwich structure is inserted between the high strength composite material in accordance with the part of the submarine. The degree of attenuation due to the impact from the outside is evaluated by the loss factor. It is possible to evaluate the damping coefficient through the cantilever specimen before fabrication of large structures made up of composite material. In ASTM(American Society of Testing Materials), the cantilever pieces and test methods have been explicit. In this paper, run mode testing of the cantilever by the ASTM standard, in order to calculate the loss factor of the viscoelastic damping material by the specified expression to verify the validity of the calculated loss factor and loss of the composite beam the coefficient test it was performed. In addition, the characteristics of the material were analyzed the effect on the loss factor.

Interactions between ZnO nanoparticles and amorphous g-C₃N₄ nanosheets in thermal formation of g-C₃N₄/ZnO composite materials: The annealing temperature effect

Jung, Haewon,Pham, Thanh-Truc,Shin, Eun Woo Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.458 No.-

<P><B>Abstract</B></P> <P>In this study, C<SUB>3</SUB>N<SUB>4</SUB>/ZnO composite materials were prepared at various annealing temperatures and systematically characterized to investigate the role of ZnO in the thermal formation of graphitic C<SUB>3</SUB>N<SUB>4</SUB> (g-C<SUB>3</SUB>N<SUB>4</SUB>), and to understand effect of annealing temperatures on the interaction between g-C<SUB>3</SUB>N<SUB>4</SUB> and ZnO in the composite materials. ZnO nanoparticles in the composite materials facilitated the thermal formation of the g-C<SUB>3</SUB>N<SUB>4</SUB> structure due to the strong interaction between g-C<SUB>3</SUB>N<SUB>4</SUB> and ZnO nanoparticles, resulting in a decrease in thermal polymeric condensation temperatures. Moreover, the morphological structure of g-C<SUB>3</SUB>N<SUB>4</SUB> was significantly influenced by the presence of ZnO nanoparticles with an amorphous g-C<SUB>3</SUB>N<SUB>4</SUB> nanosheet structure in the composite materials and a crystalline interlayered g-C<SUB>3</SUB>N<SUB>4</SUB> structure in g-C<SUB>3</SUB>N<SUB>4</SUB> only. The higher annealing temperatures for composite materials induced the stronger interaction between ZnO nanoparticles and g-C<SUB>3</SUB>N<SUB>4</SUB> nanosheets. The strong interaction in a core-shell g-C<SUB>3</SUB>N<SUB>4</SUB>/ZnO structure not only gradually decreased the electronic density of ZnO nanoparticles but also proportionally inhibited the recombination of photo-generated electron-hole pairs in the composite materials, with increasing the annealing temperature. The g-C<SUB>3</SUB>N<SUB>4</SUB>/ZnO composite material prepared at 500 °C exhibited the highest photocatalytic reaction rate constant for photocatalytic degradation of methylene blue, which might be caused by the slowest recombination rate.</P> <P><B>Highlights</B></P> <P> <UL> <LI> g-C<SUB>3</SUB>N<SUB>4</SUB>/ZnO composite materials were prepared at various annealing temperatures. </LI> <LI> Non-crystalline g-C<SUB>3</SUB>N<SUB>4</SUB> nanosheets were formed from DCDA over ZnO nanoparticles. </LI> <LI> The strong interaction between ZnO and g-C<SUB>3</SUB>N<SUB>4</SUB> decreased the electron density of ZnO. </LI> <LI> The g-C<SUB>3</SUB>N<SUB>4</SUB>/ZnO composite prepared at 500 °C showed the slowest recombination rate. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Development of DLP 3D Printer with Multiple Composite Materials

황소리(SoRee Hwang),이종원(JongWon Lee),이소향(SoHyang Lee),홍대기(DaeGi Hong),박민수(MinSoo Park) Korean Society for Precision Engineering 2020 한국정밀공학회지 Vol.37 No.5

Since most commercialized DLP 3D printers fabricate 3D structures by sinking materials to Vat using a bottom-up method, it is difficult to use various materials simultaneously and there are many restrictions on printing composite materials. Especially, composite resin mixed with various functional powders in photo curable resin generally has high viscosity, causing difficult material flow in the bottom-up method when using Vat. Additionally, most of the previously presented methods for fabricating multi-material structure use individual curing for each material, so the adhesion force at the contact surface is less than 50% compared to single material. Thus, in this paper, we propose a new type of DLP 3D printer that combines Material Extrusion and the DLP system. The proposed equipment can supply high viscosity composite material resins to a specific area to cure various materials simultaneously. This method will enable fabrication of multiple composite material structures with sufficient adhesion force. The tensile test will be performed to verify suitability of the proposed method.

Evaluation of thermal stability of quasi-isotropic composite/polymeric cylindrical structures under extreme climatic conditions

Mohamed Gadalla,Hany El Kadi 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.3

Thermal stability of quasi-isotropic composite and polymeric structures is considered one of the most important criteria in predicting life span of building structures. The outdoor applications of these structures have raised some legitimate concerns about their durability including moisture resistance and thermal stability. Exposure of such quasi-isotropic composite/polymeric structures to various and severe climatic conditions such as heat flux and frigid climate would change the material behavior and thermal viability and may lead to the degradation of material properties and building durability. This paper presents an analytical model for the generalized problem. This model accommodates the non-linearity and the non-homogeneity of the internal heat generated within the structure and the changes, modification to the material constants, and the structural size. The paper also investigates the effect of the incorporation of the temperature and/or material constant sensitive internal heat generation with four encountered climatic conditions on thermal stability of infinite cylindrical quasi-isotropic composite/polymeric structures. This can eventually result in the failure of such structures. Detailed critical analyses for four case studies which consider the population of the internal heat generation, cylindrical size, material constants, and four different climatic conditions are carried out. For each case of the proposed boundary conditions, the critical thermal stability parameter is determined. The results of this paper indicate that the thermal stability parameter is critically dependent on the cylinder size, material constants/selection, the convective heat transfer coefficient, subjected heat flux and other constants accrued from the structure environment.

압전기법을 이용한 복합재료 손상모니터링의 가능성에 관한 연구

황희윤(Hui Yun Hwang) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Since crack detection for laminated composites in-service is effective to improve the structural reliability of laminated composites, it have been tried to detect cracks of laminated composites by various nondestructive methods. An electric potential method is one of the widely used approaches for detection of cracks for carbon fiber composites, since the electric potential method adopts the electric conductive carbon fibers as reinforcements and sensors and the adoption of carbon fibers as sensors does not bring strength reduction induced by embedding sensors into the structures such as optical fibers. However, the application of the electric method is limited only to electrically conductive composite materials. Recently, a piezoelectric method using piezoelectric characteristics of epoxy adhesives has been successfully developed for the adhesive joints because it can monitor continuously the damage of adhesively bonded structures without producing any defects. Polymeric materials for the matrix of composite materials have piezoelectric characteristics similarly to adhesive materials, and the fracture of composite materials should lead to the fracture of polymeric matrix. Therefore, it seems to be valid that the piezoelectric method can be applied to monitoring the damage of composite materials. In this research, therefore, the feasibility study of the damage monitoring for composite materials by piezoelectric method was conducted. Using carbon fiber epoxy composite and glass fiber composite, charge output signals were measured and analyzed during the static and fatigue tests, and the effect of fiber materials on the damage monitoring of composite materials by the piezoelectric method was investigated.

압전기법을 이용한 복합재료 손상모니터링의 가능성에 관한 연구

황희윤(Hui-Yun Hwang) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.11

Since crack detection for laminated composites in-service is effective to improve the structural reliability of laminated composites, it have been tried to detect cracks of laminated composites by various nondestructive methods. An electric potential method is one of the widely used approaches for detection of cracks for carbon fiber composites, since the electric potential method adopts the electric conductive carbon fibers as reinforcements and sensors and the adoption of carbon fibers as sensors does not bring strength reduction induced by embedding sensors into the structures such as optical fibers. However, the application of the electric method is limited only to electrically conductive composite materials. Recently, a piezoelectric method using piezoelectric characteristics of epoxy adhesives has been successfully developed for the adhesive joints because it can monitor continuously the damage of adhesively bonded structures without producing any defects. Polymeric materials for the matrix of composite materials have piezoelectric characteristics similarly to adhesive materials, and the fracture of composite materials should lead to the fracture of polymeric matrix. Therefore, it seems to be valid that the piezoelectric method can be applied to monitoring the damage of composite materials. In this research, therefore, the feasibility study of the damage monitoring for composite materials by piezoelectric method was conducted. Using carbon fiber epoxy composite and glass fiber composite, charge output signals were measured and analyzed during the static and fatigue tests, and the effect of fiber materials on the damage monitoring of composite materials by the piezoelectric method was investigated.