• Composites Research
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• v.20 no.5
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• pp.20-25
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• 2007

Cyclic heating method is useful method for measuring the thermal diffusivity of porous materials. The main object of this paper is to develop and verify the thermal diffusivity measuring system of porous materials under vacuum condition. To verify this method, thermal diffusivities of the alumina ($Al_2O_3$) specimen and polystyrene foam were measured. Thermal diffusivities of these specimens were agreed with reference values. Thermal diffusivities of carbon/epoxy and porous insulation material were measured at atmospheric room temperature condition and vacuum condition respectively. Thermal diffusivities of carbon/epoxy and porous insulation material under vacuum are reduced by 66.4% and 64.9% compared to the thermal diffusivities under the atmospheric condition. These differences are considered the effect of the porous insulation material with an air.

• Composites Research
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• v.20 no.5
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• pp.1-6
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• 2007

This study was performed to make a comparison on low-velocity impact behavior between graphite/epoxy composite laminate and steel plate. In order to validate the proposed scheme fur the impact behavior of the plate, the Karas's impact model was used. The impact models for this comparative study are the graphite/epoxy composite plate having $[0/90/45/-45/-45/45/90/0]_{8S}$ laminate sequence and the steel plate with a steel ball impactor. The low-velocity impact behaviors for two types of plates were comparatively investigated and performed by considering different impactor velocities and weights respectively. In this investigation, it was found that the composite laminate has impact energy absorption effect due to more flexible behavior than the steel plate, and also it has better characteristics on impact damage and weight.

• Journal of the Korean Wood Science and Technology
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• v.50 no.2
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• pp.93-103
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• 2022

Currently, biofibers are used as a reinforcement in polymer composites for structural elements and construction materials instead of the synthetic fibers which cause environmental problems and are expensive. One of the chemicals with a pH close to neutral that can be potentially used as a modified fiber material is sodium chloride (NaCl). Therefore, this study aims to investigate the characteristics of a composite board made from NaCl-treated kenaf fiber. A completely randomized design method was used with consideration of two factors: the content of NaCl in the treatment solution (1 wt%, 3 wt%, and 5 wt%) and the duration of immersion of fibers in the solution (1 h, 2 h, and 3 h). The NaCl treatment was conducted by soaking the fibers in the solution for different durations. The fibers were then rinsed with water until the pH of the water reached 7 and subsequently dried inside an oven at 80℃ for 6 h. Kenaf fiber and epoxy were mixed manually with the total loading of 20 wt% based on the dry weight of the fiber. Physical and mechanical properties of the fibers were then evaluated based on JIS A 5908 particleboard standards. The results showed that increasing NaCl content in the fiber treatment solution can increase the physical and mechanical properties of the composite board. The properties of fibers treated with 5 wt% NaCl for 3 h were superior with a modulus of elasticity of 2.085 GPa, modulus of rupture of 19.77 MPa, internal bonding of 1.8 MPa, thickness swelling of 3%, and water absorption of 10.9%. The contact angle of untreated kenaf fibers was 104°, which increased to 80° and 73° on treatment with 1 wt% and 5 wt% NaCl for 3 h, respectively.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.3
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• pp.191-198
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• 2008

Pot life of two-component adhesives such as epoxy resin used in saturating FRP composite is defined as a certain time periods which can guarantee the bond performance and workability of epoxy resin. Therefore, adhesion procedure in strengthening RC members should be completed before chemical hardening is going on at job site. It has been known that there are two types of test method to evaluate the pot life of structural adhesive based on apparent viscosity or temperature change. This study is to verify the test methods how to assess pot life of structural adhesive for FRP composites by means of changing in apparent viscosity and means of exothermic reaction temperature proposed in existing test standards. Results of each test method were compared and analyzed, and reasonable test and evaluation method were suggested.

• Composites Research
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• v.30 no.5
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• pp.316-322
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• 2017

Carbon fiber is a material with excellent mechanical, electrical and thermal properties, which is widely used as a composite material made of a polymer matrix. However, this composite material has a weak point of interlaminar delamination due to weak interfacial bond with polymer matrix compared with high strength and elasticity of carbon fiber. In order to solve this problem, it is essential to use reinforcements. Due to excellent mechanical properties, graphene have been expected to have large improvement in physical properties as a reinforcing material. However, the aggregation of graphene and the weak interfacial bonding have resulted in failure to properly implement reinforcement effect. In order to solve this problems, dispersibility will be improved. In this study, functionalization of graphene nanoplatelet was proceeded with melamine and mixed with epoxy polymer matrix. The carbon fiber reinforced polymer composites were fabricated using the prepared graphene nanoplatelet/epoxy and flexural properties and interlaminar shear strength were measured. As a result, it was confirmed that the dispersibility of graphene nanoplatelet was improved and the mechanical properties of the composite material were increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.259-259
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• 2009

Surface contamination and leakage current have caused operating problems. A flashover in a substation may result in destruction of an insulator or many others electrical equipment. Engineering plastics have good characteristic (light weight, good productivity and little of void) as compare with epoxy or porcelain insulators. Outdoor insulator must have resistance to contamination. However, they are not suited to outdoor insulator by reason of being not good hydrophobic. RTV has a good property of hydrophobic and ATH has characteristic obstructing exothermic reaction. In order to reduce the incidence of insulator flashover and damage, the silicon rubber contained nano size ATH coat on surface of engineering plastics. In this paper, it compares resistance tracking of the engineering plastic coated RTV with that of non-coated engineering plastic and ATH filled composites performed much better than non-filled composites.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.159-162
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• 2000

Interfacial and microfailure properties of carbon fiber/epoxy matrix composites were evaluated using both tensile fragmentation and compressive Broutman tests with acoustic emission (AE). Amino-silane and maleic anhydride polymeric coupling agents were used via the dipping and electrodeposition (ED), respectively. Both coupling agents exhibited higher improvements in interfacial shear strength (IFSS) under tensile tests than compressive cases. However, ED treatment showed higher IFSS improvement than dipping case under both tensile and compressive test. The typical microfailure modes including fiber break, matrix cracking, and interlayer failure were observed during tensile test, whereas the diagonal slippage in fiber ends was observed during compressive test. For both the untreated and treated cases AE distributions were separated well under tensile testing. On the other hand, AE distributions were rather closer under compressive tests because of the difference in failure energies between tensile and compressive loading. Under both loading conditions, fiber breaks occurred around just before and after yielding point. Maximum AE voltage fur the waveform of carbon or basalt fiber breakage under tensile tests exhibited much larger than those under compressive tests.

• Composites Research
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• v.12 no.3
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• pp.26-35
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• 1999

The static strength and fatigue life of repaired graphite/epoxy laminates are observed using tensile coupon. The lay-up of investigated laminates was [$0^{\circ}$/$\pm$$45^{\circ}$/$90^{\circ}$]$_s$. Static strength was measured from the specimens prepared by various repair techniques such as precured-single patch, precured-double patch and cure-in-place methods. The strength was recovered to the extent of 60~80 % of unnotched case. Fatigue life was also measured from the laminates repaired with cure-in-place method. Hwang and Han's MFLPE 1(modified fatigue life prediction equation 1), which was based on the fatigue modulus degradation model and reference modulus, was chosen for fatigue life prediction of repaired specimen and compared with the conventional fatigue life equation such as S-N curve and Basquin's relation. The MFLPE 1 has better agreement with experimental data than S-N curve and Basquin's relation.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.750-752
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• 1992

The paper presents the effects of environment on glass-cloth/epoxy composites exposed to humid air were investigated. Tests were performed at temperature 40$^{\circ}C$ and 70$^{\circ}C$ with the materials exposed to humid air at 76% and 90% relative humidity. This investigation surveyed include (a) the moisture absorption and desorption characteristics of single and multi layered composites exposed to steady and to transient ambients, and (b) the resulting changes in tensile strength, dielectric strength, tan $\delta$ and $\varepsilon_{\tau}$ and the effects of environment on these parameters were assessed.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1449_1450
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• 2009

Surface contamination and leakage current have caused operating problems. A flashover in a substation may result in destruction of an insulator or many others electrical equipment. Engineering plastics have good characteristic (light weight, good productivity and little of void) as compare with epoxy or porcelain insulators. Outdoor insulator must have resistance to contamination. However, they are not suited to outdoor insulator by reason of being not good hydrophobic. RTV has a good property of hydrophobic and ATH has characteristic obstructing exothermic reaction. In order to reduce the incidence of insulator flashover and damage, the silicon rubber contained nano size ATH coat on surface of engineering plastics. In this paper, it compares resistance tracking of the engineering plastic coated RTV with that of non-coated engineering plastic and ATH filled composites performed much better than non-filled composites.