• Journal of Korea Foundry Society
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• v.20 no.5
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• pp.300-306
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• 2000

The objective of this work was to investigate the effects of SiC particle size(50, 100 ${\mu}m$) and additional elements such as Si, Cu and Ti on aging behavior in Al-5Mg-X(Si,Cu,Ti)/SiCp composites fabricated by pressureless infiltration method using hardness and wear test, scanning electron microscopy(SEM) and differential scanning calorimetry(DSC). The peak aging time in Al-5Mg-X(Si, Cu, Ti)/SiCp(50, 100 ${\mu}m$) composites is shorter than Al-5Mg-0.3Si alloy.The peak aging time of 50 ${\mu}m$ SiC particle reinforced Al-5Mg-X(Si,Cu,Ti) composites is shorter than those of 100 ${\mu}m$ SiC particle reinforced of Al-5Mg-X(Si,Cu,Ti) composites. The Al-5Mg-0.3Si-0.1Cu-0.1Ti/SiCp(50 ${\mu}m$) composites aged at $180^{\circ}C$ has higher hardness and better wear resistance than any other aged composite.The aging effect is promoted by the addition of Si and Cu in Al-5Mg/SiCp composites, so the wear resistance of Al-5Mg/SiCp composites with Si and Cu elements is enhanced by the aging treatment.

• Korean Journal of Metals and Materials
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• v.49 no.8
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• pp.589-595
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• 2011

Laminated glass fiber-reinforced plastic (GFRP) composites were applied to an insulating structure of a magnet system for a nuclear fusion device. Decreased inter-laminar strength by a strong repulsive force between coils which is induced a problem of structural integrity in laminated GFRPs. Therefore, it is important to investigate the inter-laminar characteristics of laminated GFRP composites in order to assure more reliable design and better structural integrity. Three types of the laminated GFRP composites using a high voltage insulating materials were fabricated according to each molding process. To evaluate the grade of the fabricated composites, mechanical tests, such as hardness, tensile and compressive tests,were carried out. The autoclave molding composites satisfied almost of the mechanical properties reguested at the G10 class standard, but the vacuum impregnation (VPI) and Prepreg composites did not.

• Korean Journal of Materials Research
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• v.31 no.6
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• pp.339-344
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• 2021

Composite materials offer distinct and unique properties that are not naturally inherited in the individual materials that make them. One of the most attractive composites to manufacture is the aluminum alloy matrix composite, because it usually combines easiness of availability, light weight, strength, and other favorable properties. In the current work, Powder Metallurgy Method (PMM) is used to prepare Al2024 matrix composites reinforced with different mixing ratios of yttrium oxide (Y₂O₃) particles. The tests performed on the composites include physical, mechanical, and tribological, as well as microstructure analysis via optical microscope. The results show that the experimental density slightly decreases while the porosity increases when the reinforcement ratio increases within the selected range of 0 ~ 20 wt%. Besides this, the yield strength, tensile strength, and Vickers hardness increase up to a 10 wt% Y₂O₃ ratio, after which they decline. Moreover, the wear results show that the composite follows the same paradigm for strength and hardness. It is concluded that this composite is ideal for application when higher strength is required from aluminum composites, as well as lighter weight up to certain values of Y₂O₃ ratio.

• Elastomers and Composites
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• v.46 no.3
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• pp.186-194
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• 2011

Natural fiber/natural rubber composites were fabricated by uniformly compounding natural rubber and cellulose- based natural fiber kenaf and then by compression molding. The effect of kenaf fiber content on their vulcanization behavior, hardness, tensile properties, tear strength and static and dynamic properties was investigated. The contents of kenaf fiber in the composites were 0, 5, 10, 15, and 20 phr, compared to natural rubber and additives. The result indicated that various properties of natural rubber depended on the kenaf fiber content. With increasing kenaf fiber content, the torque for vulcanization of natural rubber was increased whereas the vulcanization time was reduced as well. The hardness, tensile modulus and tear strength of kenaf/natural rubber composites were gradually decreased with the fiber content whereas the tensile strength and elongation at break were decreased. Also, with increasing the kenaf fiber content the dynamic property of natural rubber was changed more greatly than the static property. The loss factor, which is closely related with the damping or absorption of the energy given to natural rubber, was proportionally increased with the fiber content.

• Macromolecular Research
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• v.13 no.3
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• pp.194-205
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• 2005

The network structure of Ni-coated carbon black (NCB) composites filled with phenolic resin was investigated by means of using scanning electron microscopy, viscosity, interfacial tension, shrinkability, Flory-Huggins interaction parameters, and swelling index. The electrical properties of the composites have been characterized by measurement of the specific conductivity as a function of temperature. Additionally, the variation of conductivity with temperature for the composites has been reported and analyzed in terms of the dilution volume fraction, relative volume expansion, and barrier heights energy. The thermal stability of phenolic-NCB composites has been also studied by means of the voltage cycle processes. The experimental data of EMI wave shielding were analyzed and compared with theoretical calculations. The mechanical properties such as tensile strength, tensile modulus, hardness and elongation at break (EB) of NCB-phenolic resin composites were also investigated.

• Journal of Power System Engineering
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• v.20 no.5
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• pp.14-19
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• 2016

This study is about the effect of nitrogen gas pressures during manufacturing process on the mechanical properties of composite materials. $TiO_2$/epoxy resin nanocomposites and carbon fiber reinforced epoxy resin(CFRP) composites were fabricated under various nitrogen gas pressures. Tensile strength test, vicker's hardness test and fracture surface observation were carried out to investigate the effect of nitrogen gas pressure. As a result, the tensile strength of nanocomposite and CFRP composites showed clearly increasing tendency by a change in the nitrogen gas pressure up to 3.0 atm and then the tensile strength decreased a little. However, the vicker's hardness of $TiO_2$/epoxy nanocomposites showed same hardness values regardless of the nitrogen gas pressures.

• Restorative Dentistry and Endodontics
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• v.46 no.4
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• pp.51.1-51.13
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• 2021

Objectives: This study aimed to evaluate the effect of improper positioning single-peak and multi-peak lights on color change, microhardness of bottom and top, and surface topography of bulk fill and incremental composites after artificial aging for 1 year. Materials and Methods: Bulk fill and incremental composites were cured using multi-peak and single-peak light-emitting diode (LED) following 4 clinical conditions: (1) optimal condition (no angulation or tip displacement), (2) tip-displacement (2 mm), (3) slight tip angulation (α = 20°) and (4) moderate tip angulation (α = 35°). After 1-year of water aging, the specimens were analyzed for color changes (ΔE), Vickers hardness, surface topography (Ra, Rt, and Rv), and scanning electron microscopy. Results: For samples cured by single-peak LED, the improper positioning significantly increases the color change compared to the optimal position regardless of the type of composite (p < 0.001). For multi-peak LED, the type of resin composite and the curing condition displayed a significant effect on ΔE (p < 0.001). For both LEDs, the Vickers hardness and bottom/top ratio of Vickers hardness were affected by the type of composite and the curing condition (p < 0.01). Conclusions: The bulk fill composite presented greater resistance to wear, higher color stability, and better microhardness than the incremental composite when subjected to improper curing. The multi-peak LED improves curing under improper conditions compared to single-peak LED. Prevention of errors when curing composites requires the attention of all personnel involved in the patient's care once the clinical relevance of the appropriate polymerization reflects on reliable long-term outcomes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.11
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• pp.1757-1764
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• 1997

The geometric and elastic models based on the unit cell have been proposed to predict the geometric characteristics and the engineering constants of plain and satin woven composites. In the geometric model, length and inclined angle of the yarn crimp and the fiber volume fraction of woven composites have been predicted. In the elastic model, the coordinate transformation has been utilized to transform the elastic constants of the yarn crimp to those of woven composites, and the effective elastic constants have been determined from the volume averaging of the constituent materials. Good correlations between the model predictions and the experimental results of carbon/epoxy and glass/epoxy woven composites have been observed. Based on the model, the effect of various geometric parameters and materials on the three-dimensional elastic properties of woven composites can be identified.

• Elastomers and Composites
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• v.52 no.1
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• pp.17-21
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• 2017

The optimum mixing conditions of silica and silane containing rubber composites were evaluated by investigating the properties of rubber composites prepared with a silica composition of 10, 20, 40, 60, and 80 g, respectively. The crosslinking rate decreased with increasing silica content, with he promoters being adsorbed on the silica surface with in the rubber composite. As a result, the increase in crosslinking time resulted in the destruction of the silica structure. The increase of the bound rubber content due to the destruction of the silica structure inhibited the chain motion of the polymer molecules and reduced the cohesion of the silica itself. Finally, the increase of silica content showed the increase of hardness, tensile strength, and storage modulus of rubber composites.

• Elastomers and Composites
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• v.53 no.4
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• pp.202-206
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• 2018

Five solution styrene butadiene rubber/neodymium butadiene rubber (SSBR/NdBR) composites were manufactured using different ratios of SSBR and NdBR. In this study, the composites were reinforced with NdBR and silica to confirm the physical properties of SSBR used for treads of automobile tires and the dispersibility with silica. The morphologies of the rubber composites were observed using field-emission scanning electron microscopy (FE-SEM). The crosslinking behaviors of the composites were tested using a rubber process analyzer (RPA), and the abrasion resistances were tested using a National Bureau of Standards (NBS) abrasion tester. The hardness values, tensile strengths, and cold resistances of the composites were also tested according to ASTM standards. Increased NdBR content yielded composites with excellent crosslinking properties, abrasion resistances, hardnesses, tensile strengths, and cold resistances. The crosslinking point increased due to the double bond in NdBR, thereby increasing the degree of crosslinking in the composites. The NdBR-reinforced composites exhibited excellent abrasion resistances, which is explained as follows. In SSBR, a breakage is permanent because a resonance structure between styrene and SSBR forms when the molecular backbone is broken during the abrasion process. However, NdBR forms an additional crosslink due to the breakdown of the molecular backbone and high reactivity of the radicals produced. In addition, the low glass transition temperature (Tg) of NdBR provided the rubber composites with excellent cold resistances.