• Composites Research
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• v.35 no.1
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• pp.13-17
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• 2022

RADAR Absorbing Structure (RAS), one of stealth technologies, is a multifunctional composite that is capable of supporting load and absorbing electromagnetic waves. In order to supplement the shortcomings of the existing RAS, a hybrid RAS in which the short carbon fiber layers were inserted has been proposed. However, the inserted short carbon fiber layers may affect the mechanical properties of the structure. Therefore, this study measured the interlaminar shear strength (ILSS) of the hybrid RAS with the inserted short carbon fiber layer. The ILSS of hybrid composite with different areal densities of the short carbon fiber layer was measured to investigate the effect of changes in the areal density of the short carbon fiber layer on the ILSS of the structure. In addition, the ILSS of the 4 kinds of the hybrid RAS were measured and compared with the ILSS of glass/epoxy. As a result of the measurement, it was confirmed that the short carbon fiber layer did not significantly affect the ILSS of the hybrid composite and the hybrid RAS.

• Composites Research
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• v.36 no.3
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• pp.211-216
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• 2023

When designing ships and aircraft structures, it is important to design them to satisfy weight reduction and strength. Currently, studies related to topology optimization using 3D printed composite materials are being actively conducted to satisfy the weight reduction and strength of the structure. In this study, structural analysis was performed to analyze the applicability of 3D printed composite materials to the flight control surface, one of the parts of an aircraft or unmanned aerial vehicle. The optimal topology shape of the flight control surface for the bending load was analyzed by considering three types (hexagonal, rectangular, triangular) of the topology shape of the flight control surface. In addition, the bending strength of the flight control surface was analyzed when four types of reinforcing materials (carbon fiber, glass fiber, high-strength high-temperature glass fiber, and kevlar) of the 3D printed composite material were applied. As a result of comparing the three-point bending test results with the finite element method results, it was confirmed that the flight control surface with hexagonal topology shape made of carbon fiber and Kevlar had excellent performance. And it is judged that the 3D printed composite can be sufficiently applied to the flight control surface.

• Composites Research
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• v.37 no.2
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• pp.59-67
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• 2024

Research was conducted on a PA material-based composite material manufacturing method for application to engine mount brackets. Engine mount brackets must have heat resistance, impact resistance, and damping performance. PA66 resin was used as the base material for the composite material. The glass fiber was used as the reinforcement material. The composite material was manufactured using the injection molding method. The thermal, mechanical, and morphological characteristics were analyzed depending on the content of glass fiber. 3D model was created using the property evaluation database of composite materials(input data). The damping performance of the generated 3D model was extracted as out-put data. The reason for evaluating the characteristics of PA-based composite materials and conducting simulations on the damping performance of 3D models of engine brackets is because product performance can be predicted without manufacturing actual automobile parts and conducting damping performance tests. As a result of the damping simulation, damping performance tended to increase proportionally as the mass fraction of the reinforcement increased. But above a certain level, it no longer increased and slightly decreased. As a result of comparing the actual experimental values a nd the simulated values, the approximate value was within ±5%.

• Journal of Aerospace System Engineering
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• v.13 no.6
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• pp.52-59
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• 2019

The rotor blade is a key component that generates the lift, thrust, and control forces required for helicopter flight by the torque transmitted through the hub and the blade pitch angle control, and should be designed to factor vibration characteristics so that there is no risk of resonance with structural safety. In this study, the structural design of the main rotor blade for MPUH(Multi-Purpose Unmanned Helicopter) was conducted and the sectional stiffness measurement of the fabricated blade was performed. The evaluation of the vibration characteristics of the main rotor system was then conducted factoring the measured stiffness distribution. The interior of the rotor blade comprised of the skin, spar, and torsion box, and carbon and glass fiber composites were applied. The Ksec2D program was applied to predict the stiffness of blade, and the results were compared to the measured data. CAMRADII, a comprehensive rotorcraft analysis program, was applied to investigate the natural frequency trends and resonance risks due to the rotor rotation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.1002-1008
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• 2001

The absorbing structure composed of multi-layered fiber reinforced composite materials was designed and microwave absorbing properties are investigated. On the basis of transmission line theory, the theoretical equations to predict the reflection loss and the appropriate composite material for each functional layer are suggested. The most significant result of this study is the successful design and fabrication of triple-layered composite laminates which has the superior microwave absorbing porperties (more than 10 dB in 4∼12 GHz range), without using the ferrite filler in the impedance transforming layer. In the two-layered composite laminate (absorber/substrate), however, the use of ferrite filler (about 40 wt %) in the absorbing layer is necessary to obtain the certain level of microwave absorbance. By combining the glass-fiber composite with ferrite filler and carbon-fiber composite substrate, the microwave absorbing properties more than 10 dB in 4∼12 GHz frequencies than be obtained.

• Composites Research
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• v.17 no.1
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• pp.10-17
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• 2004

In this work, the blend system prepared from epoky(DGEBA)/polymethylmethacrylate(PMMA) was investigated in thermal and mechanical interfacial property measurements. The thermal properties were carried out by DSC, DMA, and TGA measurements. Also, the surface free energy and fracture toughness were determined by contact angle and critical stress intensity factor($K_{IC}$), respectively. And the fracture surface was observed by SEM after $K_{IC}$ tests. As experimental results, the curing temperature and glass transition temperature were slightly increased in addition of PMMA. Surface free energy of the blends showed an improved value at low contents of PMMA which could be attributed to the both increasings of London dispersive and polar components. From measurement of $K_{IC}$ of the blends, the highest value was found at 5 phr. This was due to the increasing of compatibility or physical interaction in macromolecular chains between DGEBA and PMMA of the blends.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1700-1711
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• 2015

In the last decade it has been witnessed significant developments in the area of nano particles and nano scale fillers on electrical, thermal, and mechanical properties of polymeric materials such as resins, varnishes, enamel and bakelites. The electric and thermal properties were more important in the electrical equipments for both steady state and transient state conditions. This paper deals with the characterization of the electric and thermal properties of the pure varnish and zirconia (ZrO₂) filler mixed varnish. The electric properties such as dielectric loss (tan δ), dielectric constant (ε), dielectric strength and partial discharge voltage were analyzed and detailed for different samples. It was observed that zirconia nano filler mixed varnish has the superior dielectric and thermal properties when compared to those of standard varnish. It has shown that at power frequency the 1wt% nano composite sample has the higher permittivity value when compared to other samples. It has been examined that the 1wt% sample was having higher inception and extinction voltages when compared to other samples. It has been observed that 1wt% sample has higher dielectric strength when compared with other samples. There has been an improvement of thermal property by adding few weight percent of zirconia nano fillers. There was not much variation in glass transition among the nano mixed composites. The weight loss was improved at 1wt% of the zirconia nano fillers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.39-44
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• 2005

Due to mismatch of thermal expansion coefficients between aluminum sheet and glass/epoxy sheet, thermal residual stresses generally appear in the FML. These stresses will affect the yield and fatigue strength of the FML. The numerically determined residual stresses in the Fiber-Metal-Laminates(FML) have been compared to the residual stresses measured from the curvature and tensile test methods. These two experimental methods have been developed for assessing the influence of residual stress in FML. Post-stretching process has been applied to remove the thermal residual stress and reverse the stress distribution. After post-stretching process, the residual stress has been measured from experiments. The results obtained show that analytical and experimental data are well agreed. The thermal residual stress can be removed by post-stretching process and it will increase the yield strength of FML.

• Journal of Powder Materials
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• v.26 no.6
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• pp.455-462
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• 2019

ZrB₂ ceramic and ZrB₂ ceramic composites with the addition of SiC, WC, and SiC/WC are successfully synthesized by a spark plasma sintering method. During high-temperature oxidation, SiC additive form a SiO₂ amorphous outer scale layer and SiC-deplete ZrO₂ scale layer, which decrease the oxidation rate. WC addition forms WO₃ during the oxidation process to result in a ZrO₂/WO₃ liquid sintering layer, which is known to improve the anti-oxidation effect. The addition of SiC and WC to ZrB₂ reduces the oxygen effective diffusivity by one-fifth of that of ZrB₂. The addition of both SiC and WC shows the formation of a SiO₂ outer dense glass layer and ZrO₂/WO₃ layer so that the anti-oxidation effect is improved three times as much as that of ZrB₂. Therefore, SiC- and WC-added ZrB₂ has a lower two-order oxygen effective diffusivity than ZrB₂; it improves the anti-oxidation performance 3 times as much as that of ZrB₂.

• Korean Journal of Materials Research
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• v.20 no.9
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• pp.483-487
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• 2010

To fabricate $TiO_2$ nanoparticle-based dye sensitized solar cells (DSSCs) at a low-temperature, DSSCs were fabricated using hydropolymer and ZnO nanoparticles composites for the electron transport layer around a low-temperature ($200^{\circ}C$). ZnO nanoparticle with 20 nm and 60 nm diameter were used and Pt was deposited as a counter electrode on ITO/glass using an RF magnetron sputtering. We investigate the effect of ZnO nanoparticle concentration in hydropolymer and ZnO nanoparticle solution on the photoconversion performance of the low temperature fabricated ($200^{\circ}C$) DSSCs. Using cis-bis(isothiocyanato)bis(2,20 bipyridy1-4,40 dicarboxylato) ruthenium (II) bis-tetrabutylammonium (N719) dye as a sensitizer, the corresponding device performance and photo-physical characteristics are investigated through conventional physical characterization techniques. The effect of thickness of the ZnO photoelectrode and the morphology of the ZnO nanoparticles with the variations of hydropolymer to ZnO ratio on the photoconversion performance are also investigated. The morphology of the ZnO layer after sintering was examined using a field emission scanning electron microscope (FE-SEM). 60 nm ZnO nanoparticle DSSCs showed an incident photon-to-current conversion efficiency (IPCE) value of about 7% higher than that of 20 nm ZnO nanoparticle DSSCs. The maximum parameters of the short circuit current density ($J_{sc}$), the open circuit potential ($V_{oc}$), fill factor (ff), and efficiency ($\eta$) in the 60 nm ZnO nanoparticle-based DSSC devices were 4.93 mA/$cm^2$, 0.56V, 0.40, and 1.12%, respectively.