Hee Jae Shin

A Study on Impact Strength of CFRP Using Infrared Thermography

Of the advanced composite materials for aerospace structures such as aircrafts and space devices, the carbon fiber reinforced plastics (CFRP) is applied to many sectors that require lightweight materials for its high strength and stiffness. One of the disadvantages of the CFRP, however, is that it is weak against impact. In this study, impact test specimens were manufactured with five fiber stacking angles (0°/0°, 0°/15°, 0°/30°, 0°/45°, 0°/90°) according to ASTM D7136[15], and a falling weight test was performed to analyze the correlation between their mechanical and thermal characteristics. As a result, the impact energy applied to the five test specimens with different fiber stacking angles was almost constant at 30.63 J - 30.78 J. The absorbed energy increased with the increase in the fiber stacking angle, and decreased after 0°/45°. The average temperature on the fractured surface increased with the increase in the fiber stacking angle in all specimens other than the 0°/0° specimen.

Electromagnetic interference shielding characteristics for orientation angle and number of plies of carbon fiber reinforced plastic

Recently, methods that usea carbon-based filler, a conductive nanomaterial, have been investigated to develop composite fillers containing dielectric materials. In this study, we added geometric changes to a carbon fiber, a typical carbon-based filler material, by differentiating the orientation angle and the number of plies of the fiber. We also studied the electrical and electromagnetic shield characteristics. Based on the orientation angle of , the orientation angle of the carbon fiber was changed between 0, 15, 30, 45, and , and 2, 4, and 6 plies were stacked for each orientation angle. The maximum effect was found when the orientation angle was , which was perpendicular to the electromagnetic wave flow, as compared to , in which case the electrical resistance was small. Therefore, it is verified that the orientation angle has more of an effect on the electromagnetic interference shield performance than the number of plies.

A Study on the Bending Analysis of the Al Honeycomb Core Sandwich Composite Panel Bearing Large Bending Load

Al honeycomb core sandwich composite panels have different core and plate materials. The core is the Al honeycomb core, and the thin plate is GFRP sheets with fibers laminated in the 0°/90° symmetric structure. The Al honeycomb core sandwich composite panel is used for structures, which involve relatively high bending load. Before designing the structures, their stability is evaluated via the finite element analysis. In this study, an analysis method that is closest to the reality was proposed for designing the structures with Al honeycomb core sandwich composite panels. For that purpose, the modulus was reviewed. In the finite element analysis, the tensile modulus is generally used. In the results of this study, however, the tensile modulus led to significant deviations from the test results, whereas the bending modulus led to a closer value to the test results.

Stability Evaluation for Polymer Electrolyte Membrane Eletrolyzer

Recently, polymer electrolyte membrane (PEM) electrolyzers consist of the layered structure of membrane and electrode assembly (MEA), titanium flow field plate, gasket, end plate, and others. Among these components, MEA and titanium flow field plate take account for most of the device cost. The cost and time for manufacturing device can be reduced with the gasket-integrated 3-D mesh-applied PEM electrolyzer (Fig. 3), while maintaining the same performance as that of the existing titanium flow field plate devices. The 3-D mesh is found to perform the roles of the existing flow plate which ensures the smooth fluid flow and uniform power supply. The voltage shows 19.3V at current density (0.5 A/cm2), a little lower than 19.6V that is 10 times of 1.96V which is the average cell voltage at the same current density. In addition, hydrogen production and stability for performance are equal to or higher than that of the device for titanium flow field plate.

Biomass Fly Ash as an Alternative Approach for Synthesis of Amorphous Silica Nanoparticles with High Surface Area

In this study, the monodisperse amorphous silica nanoparticles (SiO2 NPs) with uniform size distribution and high surface area were successfully synthesized from fly ash as a silica source by chemical sol-gel method. The influence of reaction conditions such as surfactant concentration, aging temperature (Ta), and aging time (Ta) on formation of SiO2 NPs was investigated. Through SEM characterization, it was founded that the uniform and small spherical SiO2 NPs with diameter of 20-30 nm could be synthesized at the appropriate CTAB content of 3 wt%, Ta of 60 °C, and Ta of 8 h. In addition, XRD and nitrogen adsorption-desorption measurements indicated that the SiO2 NPs were obtained under amorphous structure, which possesses a high specific surface area of 408 m2 g-1. The obtained results imply that the successful synthesis of SiO2 NPs from fly ash not only displays an effectively alternative approach to provide high quality SiO2 NPs for various necessary applications but also help solving environmental issues due to large amount of fly ash waste each year.

The evaluation of electromagnetic shielding properties of CFRP/metal mesh hybrid woven laminated composites:

Carbon fiber-reinforced plastic (CFRP) composites, owing to their lightweight and strength-weight ratio, are being used in many applications to replace traditional metallic materials and their alloys. The combination of polymeric composites with metallic materials can provide a significant impact in engineering applications. This paper evaluates electromagnetic interference shielding of bimetal-carbon prepreg fibers textile composite materials. Prepreg carbon fibers and metal wire mesh are used to make electromagnetic interference shielding samples. The material samples consist of making plain weaves of metal wire mesh and carbon prepreg and stack them with prepreg carbon fiber layers. In order to produce plain woven fabrics, wefts were made of prepreg carbon fibers and warps were made of wire meshes. In each woven fabric, two yarns of different metal wire meshes were alternated one after another. The combination of conductive wire meshes such as stainless steel-copper, stainless steel-nickel, and copper-nickel in a woven fabric was considered. The electromagnetic shielding effectiveness was evaluated for each textile composite material based on ASTM 4935-99. Results showed a possible application of these materials for electromagnetic interference shielding with higher absorption. The best electromagnetic interference shielding performance was obtained for a combination of stainless steel-copper-CFRP with a shielding effectiveness of 131.6u2009dB. The absorption losses for all samples were about 82% of electromagnetic interference shielding effectiveness. The mechanical properties and scanning electron image of fabricated samples were also investigated.

The Design and Performance Study of Polymer Electrolyte Membrane Using 3-D Mesh

The production of hydrogen and oxygen using the water electrolysis technology is mostly influenced by the performance and efficiency of the components that are used in the production systems. In this study, the flow field’s channels of the bipolar plates of polymer electrolyte membrane electrolyzer were replaced by 3-D titanium mesh, and the polymer electrolyte membrane (PEM) electrolyzer cell that uses 3-D titanium mesh was designed. A numerical analysis was conducted to study the performance of the designed model. By comparing the results with the electrochemical performance of PEM electrolyzer cell with flow field channels on the plates, it was found that the cell with 3-D titanium mesh has greater performance and higher total power dissipation density. Therefore, the use of 3-D mesh can be used instead of machining the flow field channels on the bipolar plates.

A Study on the Efficiency Improvements of the Modified Design Propeller Pump Using Numerical Methods

Typically, in order to prevent the rainwater flooding of populated areas and limit the large water circulation in pumps for power plants, flooding of farmland, the propeller pumps used primarily introduced for drainage and sewage treatment are consist of large suction casing, impeller, discharge casing, and motor. When the main shaft and the impeller rotate and driven by an electric motor, the fluid sucked through the suction casing has the principle to be sent to the outside through the impeller and the guide vane. At this time most of the propeller pump that have T shape, severe vibration and vortex the drop of efficiency of the pump. Therefore, in this paper, we increased the mechanical efficiency through the change of the design and through the numerical methods for the impact and efficiency on the lift flow characteristics, the Reynolds number was derived and the feasibility of reducing turbulence and vibration was analyzed.

Numerical Simulation of the Polymer Electrolyte Membrane Electrolyzer

In the development of renewable energy, polymer electrolyte membrane(PEM) electrolyzer has shown an impressive impact on the production of pure hydrogen gas, that can be used as fuel and energy storage, and oxygen gas. In this study, the numerical simulation was conducted in order to investigate I-V characteristic of PEM electrolyzer. Moreover, the electromechanical performance that is characterized by the polarization curve depends on many parameters. Therefore, the impact of the membrane and electrodes thicknesses and electrodes porosities are presented.

The Design and Performance Evaluation of a Parallelogram Type Magnetic Spring Suspension for Commercial Vehicle Seat

* Dept. of Carbon and Nano Engineering, Jeonju Univ., **Dept. of Mechanical and Vehicle Engineering, Jeonju Univ.,***Dept. of Mechanical Engineering, Graduate School, Jeonju Univ., **** TOP Co., Ltd.(Received July 9, 2014 ; Revised February 3, 2015 ; Accepted February 3, 2015)Key Words: Commercial Vehicle Seat(상용차 시트), Magnetic Spring Suspension(마그네틱 현가기구), Transmissibility(진동전달률), Vertical Vibration(수직진동), Seat Factor(승차감지수), Weighted Root Mean Square Value(WRMS:가중 유효치)초록: 상용차 운전자들은 운전시간이 길고, 엔진폭발에 의한 아이들 진동 등으로 인하여 일반인보다 많은 피로감을 느낀다. 본 논문에서는 아이들 진동에 의해 상용차 운전석에 전달되는 진동을 줄여 승차감을 향상시키기 위하여, 마그네틱 스프링을 이용한 시트현가장치를 제안하였다. 또한 최적설계를 통해 평행사변형 마그네틱 현가기구를 설계하였으며 이 제안된 시트를 장착한 차량의 진동 및 성능을 연구하였다. 그 결과 진동 전달률은 코일스프링 현가기구가 0.990, 평행사변형 마그네틱 현가기구는 0.823로 우수한 성능을 보여주었다. Abstract: Commercial drivers feel tired more than the general public, because their driving times are long and they experience more idle vibration. In this study, we developed a nonlinear model of a magnetic, linear spring seat suspension to determine the optimal design to improve ride comfort. The resonant frequency for the optimal design of the suspension was found to be 3.5 Hz, and the stiffness was analyzed through displacement-load experiments. Additionally, the vibration transmissibility was analyzed by the suspension stiffness, and the existing coil spring type vibration transmissibility was found to be 0.99. A parallelogram type magnetic spring was determined to result in a better performance than the existing spring with a vibration transmissibility of 0.823.