• Composites Research
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• v.34 no.6
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• pp.380-386
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• 2021

This paper aims to improve the critical speed of power-take-off (PTO) shafts by using carbon fiber reinforced plastics (CFRPs). The PTO shaft was designed with titanium-CFRPs hybrid structure in order to compensate the low shear strength of CFRPs. Based on the requirements for PTO shafts, the dimensions of PTO shafts were determined through a parametric study. To evaluate the performance of the PTO shaft, a vibration test, a static torsion test, and a torsion durability test were performed. In the vibration test, the critical speed of PTO shafts was 20570 rpm, which was 7.5% higher than that of titanium shafts. Additionally, it was confirmed that the maximum allowable torque of the PTO shaft was 2300 N·m. Finally, under repeated load in the range of 11.3 to 113 N·m, the fatigue failure in the PTO shaft did not occur up to 10⁶ cycles.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.4
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• pp.180-188
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• 2013

The glass of E-glass fiber composition was fabricated by using refused coal ore which is obtained as by-product from Dogye coal mine in Samcheok. We used silica-alumina refused coal ore which has low carbon content relatively, and the amount of refused coal ore has been changed from 0 to 35 % in batch composition. E-glass was fabricated by the melting of mixed batch materials at $1550^{\circ}C$ for 2 hrs with different refused coal ore composition of 0~35 %. We obtained a transparent and clear glass with high visible light transmittance value of 81~84%, thermal expansion coefficient of $5.39{\sim}5.61{\times}10^{-6}/^{\circ}C$ and softening point of $851{\sim}860^{\circ}C$. The glass fiber samples were also obtained through fiberizing equipment at $1150^{\circ}C$, and tested chemical resistance and tensile strength to evaluate the mechanical property as a reinforced glass fiber of composite material. As the result, we identified the properties of E-glass fiber by using refused coal ore are plenty good enough compare to that of normal E-glass without refused coal ore, and confirmed the possibility of refused coal ore as for the raw material of E-glass fiber.

• Composites Research
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• v.31 no.5
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• pp.186-191
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• 2018

Condition and properties of composites with different chemical structure of epoxy matrix were observed after saline solution treatment. Epoxy was used as matrix and the flexibility was controlled by using 2 typed-epoxies and 3 types hardeners (amine, acid anhydride and amide). Saline water treatment was conducted with 6 wt% NaCl solution at $60^{\circ}C$ for 0, 15, and 30 days. Cross section was observed and interfacial and mechanical and properties was evaluated. Amine type exhibited the highest crosslinking density and mechanical and interfacial properties whereas water absorbance was lowest. It is because that the water molecules can be hardly penetrate into the epoxy matrix or the interface between epoxy and glass fiber and it leads to saline water resistance of composites.

• Composites Research
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• v.32 no.5
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• pp.284-289
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• 2019

In the present paper, the dynamic force-moment equilibrium equations, driving power and energy equations are analyzed to formulate the equation for fuel economy(km/liter) equivalent to the driving distance (km) divided by the fuel volume (liter) of the vehicle, a selected model of gasoline powered KIA K3 (1.6v). In addition, the effects of the dynamic parameters such as speed of vehicle (V), vehicle total weight(M), rolling resistance ($C_r$) between tires and road surface, inclined angle of road (${\theta}$), as well as the aerodynamic parameters such as drag coefficient ($C_d$) of vehicle, air density(${\rho}$), cross-sectional area (A) of vehicle, wind speed ($V_w$) have been analyzed. And the possibility of alternative materials such as lightweight metal alloys, fiber reinforced plastic composite materials to replace the conventional steel and casting iron materials and to reduce the weight of the vehicle has been investigated by Ashby's material index method. Through studies, the following results were obtained. The most influencing parameters on the fuel economy at high speed zone (100 km/h) were V, the aerodynamic parameters such as $C_d$, A, ${\rho}$, and $C_r$ and M. While at low speed zone (60 km/h), they are, in magnitude order, dynamic parameters such as V, M, $C_r$ and aerodynamic ones such as $C_d$, A, and ${\rho}$, respectively.

• Composites Research
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• v.35 no.4
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• pp.255-260
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• 2022

Lightweight hydrant tanks increase the amount of water that can be carried by fire trucks, resulting in longer water spray times during the initial firefighting process, which can minimize human and property damages. In this study, the applicability of carbon-fiber-reinforced polymer (CFRP) composites as a material for lightweight hydrant tanks was investigated. In particular, the resin for manufacturing CFRP hydrant tanks must meet various requirements, such as excellent mechanical properties, formability, and dimensional stability. In order to identify a resin that satisfies these conditions, five commercially available resins, including epoxy(KFR-120V), unsaturated polyesters(G-650, HG-3689BT, LSP8020), vinyl ester(KRF-1031) were selected as candidates, and their characteristics were analyzed to investigate the suitability for manufacturing a CFRP hydrant tank. Based on the analyses, KRF-1031 exhibited the most suitable properties for hydrant tanks. Particularly, CFRP with KRF-1031 exhibited successful results for thermal stability and elution tests.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.617-624
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• 2010

This paper reports on a comprehensive study on the mechanical properties of expansive fiber-reinforced strainhardening cement composite (SHCC) materials containing various replacement levels (0, 8, 10, 12 and 14%) of an expansive admixture and 1.5% polyethylene (PE) fibers volume fraction. A number of experimental tests were conducted to investigate shrinkage, compressive strength, flexural strength, and direct tension behavior. Test results show that as expected, the different replacement levels of an expansive admixture have an important effect on the evolution of the free shrinkage of SHCC with a rich mixture. At the volume fraction of 1.5%, PE fibers in normal SHCC reduce free shrinkage deformation by about 30% in comparison to plain mortar. The replacement of an expansive admixture in SHCC material has led the SHCC to a better initial cracking behavior. Enhanced cracking tendency improved mechanical properties of SHCC materials with rich mixtures. Note that an increase in the replacement of expansive admixture from 10% to 14% does not lead to a significant improvement for mechanical properties; this implies that the replacement of 10% expansive admixture is sufficient.

• Polymer(Korea)
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• v.39 no.3
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• pp.382-387
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• 2015

The dispersion of calcium carbonate ($CaCO_3$) in polypropylene (PP) and the effect of $CaCO_3$ size on the crystallinity of PP were studied. Polymer composite usually suffers from the brittleness when reinforced with inorganic fillers. The problem is generally related to the size and dispersion of fillers. First, the dispersion was studied for the nanosize $CaCO_3$ with 15~40 nm average diameter. To enhance the dispersibility in PP, the surface of the $CaCO_3$ was treated with sodium lignosulfonate (SLS). $CaCO_3$/PP composites were prepared via melt compounding. The $CaCO_3$ coated with more than 3 wt% SLS was uniformly distributed within the PP matrix, while the uncoated $CaCO_3$ formed aggregated structures in the PP. Even with 30 wt%, the SLS-$CaCO_3$ was well dispersed in the PP matrix. Also, the transition enthalpy of $CaCO_3$/PP increased and the full-width of half maximum of the crystallization peak decreased regardless of SLS coating and size of $CaCO_3$. However, the crystallinity of PP was more influenced by nano $CaCO_3$. These results imply that the nano $CaCO_3$ coated with SLS may reduce the brittleness of polymer composites.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.59-60
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• 2009

Steel fibers are recently well recognized for good composite/strengthening materials because of their ductile behavior and good performance on crack control and shear behavior compared to concrete materials. Especially, the great improvement in shear strength by steel fibers led researchers to be involved in many experimental studies. However, our understanding on the complex shear behavior of the steel fiber reinforced concrete(SFRC) members are still very limited, and the fundamental test data are also not enough. In this study, therefore, 4 SFRC specimens were fabricated and tested, from which the effectiveness of steel fibers as shear reinforcement were evaluated. The test results shows that the shear strength of SFRC members increases as the amount of steel fibers increases.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.234-238
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• 2008

The efficiency of fiber reinforced CMC(ceramic matrix composite) on the SiC materials have been investigated, in conjunction with the fabrication process by liquid phase sintering and the characterization. LPS-$SiC_f$/SiC composites was studied with the detailed analysis such as the microstructure, sintered density, flexural strength and fracture behavior. The applicability of carbon interfacial layer has been also investigated in the LPS process. Submicron SiC powder with the constant total amount and composition ratio of $Al_2O_3,\;Y_2O_3$ as sintering additives was used in order to promote the performance of the SiC matrix material. LPS-$SiC_f$/SiC composites were fabricated with hot press under the sintering temperature and applied pressure of $1820^{\circ}C$ and 20MPa for 1hr. The typical property of monolithic LPS-SiC materials was compared with LPS-$SiC_f$/SiC composites.

• Journal of the Korean Society of Clothing and Textiles
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• v.41 no.4
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• pp.771-781
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• 2017

The helmet is an imperative personal protective equipment. This protective device must be able to guard the human head against potential risks. Helmets are classified according into the purpose of use; therefore, the required performance and specifications depend on the type of products. Military helmets are intended to protect the wearer's head from bullets and shrapnel. Generally, lightweight super fibers and fiber reinforced composite materials are used as helmet shell materials, and NIJ STD of U.S. Department of Justice is most widely used as international standard related to bulletproof helmets. Safety helmets are widely used for industrial application and sports leisure. In general, the performance of shock absorption must be ensured, and various lining systems are applied in material, design, and combination methods. Evaluation standards have also been classified and strictly controlled for each purpose; therefore, it is difficult to certify with the existing standards such as the recently developed convergence helmets. However, it is possible to launch the product through a separate national integrated certification procedure.