• Journal of the Korean Wood Science and Technology
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• v.46 no.4
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• pp.393-401
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• 2018

Natural fibers derived from lignocellulosic materials are considered to be more environment-friendly than petroleum-based synthetic fibers. Several natural fibers, such as seedpod fibers, have a potential for development, including kapok and balsa fibers. The characteristics of both fibers were evaluated to determine their suitability for specific valuable applications. The purpose of this study was to analyze some important fundamental properties of kapok and balsa fibers, including their dimensions, morphology, chemical components, and wettability. The results showed that the average fiber lengths for kapok and balsa were 1.63 and 1.30 cm, respectively. Kapok and balsa fibers had thin cell walls and large lumens filled with air. The kapok fiber was composed of 38.09% ${\alpha}-cellulose$, 14.09% lignin, and 2.34% wax content, whereas the balsa fiber was composed 44.62% ${\alpha}-cellulose$, 16.60% lignin, and 2.29% wax content. The characteristics of kapok and balsa fibers were examined by X-ray diffraction, Fourier-transform infrared spectroscopy and differential scanning calorimetry analyses. The contact angle of the distilled water on kapok and balsa fibers was more than $90^{\circ}$, indicating that both fibers are hydrophobic with low wettability properties because of to the presence of wax on the fiber surface.

• Composites Research
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• v.28 no.6
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• pp.340-347
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• 2015

As resin impregnates through the fiber preform in vacuum assisted resin transfer molding process, the volume of fibers is changed by expansion of fiber mat according to filling time. It causes not only the change in dimension but also the decrease of mechanical properties of the composite product. Moreover, it results in the economic loss by increase of the used amount of resin especially in the large product such as wind turbine blade. In this study, the ways to control fiber volume fraction were investigated by both the experimental and theoretical analyses on the expansion of fiber preform as the preform was impregnated by resin in the VARTM process. Two kinds of swelling stage were observed as flow front progressed, which was analyzed by comparing the experimental and simulation results. The process parameters are expected to be optimized by investigating the swelling behavior of fiber preform in the manufacturing process of the composite product.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.1
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• pp.38-46
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• 2011

A study was performed to investigate the dynamic behaviors of fiber-reinforced composite materials subjected to transversely low-velocity impact. For this purpose, the simulation of modified beam finite element based on higher order beam theory for two(isotropic and anisotropic) materials is carried out according to the changes of material property, stacking sequence, geometric dimension and impact velocity of steel ball, etc. Main composite materials for simulation are composed of $[0^{\circ}/90^{\circ}/0^{\circ}/-90^{\circ}/0^{\circ}]_{2s}$, $[0^{\circ}/90^{\circ}/0^{\circ}/-90^{\circ}/0^{\circ}]_s$ and $[0^{\circ}/45^{\circ}/0^{\circ}/-45^{\circ}/0^{\circ}]_{2s}$, $[0^{\circ}/45^{\circ}/0^{\circ}/-45^{\circ}/0^{\circ}]_s$ stacking sequences. The effectiveness of this simulation for qualitative and quantitative evaluations in composite materials subjected to foreign object impact was established.

• Structural Engineering and Mechanics
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• v.18 no.1
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• pp.21-40
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• 2004

In this paper, we modify the L-L model (Li et al. 2003) and extend the application of this model to concrete confined by both steel reinforcement and CFRP. Thirty-six concrete cylinders with a dimension of ${\varphi}30{\times}60$ cm were tested to verify the effectiveness of the proposed model. The experimental test results show that different types of steel reinforcement have a great effect on the compressive strength of concrete cylinders confined by steel reinforcement, but the different types of steel reinforcement have very little effect on concrete cylinders confined by both steel reinforcement and CFRP. Compared with the stress-strain curves of confined concrete cylinders, we can conclude that the proposed model can provide more effective prediction than others models.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.616-622
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• 2001

In this paper, we analyzed the laminated composite sandwich plate structure of honeycomb core with changing values of the designing parameters. As a result, in designing parameters of that, the more height and thickness of the laminated composite plate's core, the more increase of natural frequency. The laminated angle has the maximum value when the plate of honeycomb core is join to opposite direction. This paper shows that the natural frequency of CFRP is higher than that of GFRP, and also impact strength marks maximum value in case of antisymmetry than symmetry of core. Also it shows that the mode shapes are various along with the angle-ply of laminated composite plate.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.703-709
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• 2001

In this paper, we analyzed the laminated composite sandwich plate structure of truss core with changing values of the designing parameters. As a result, in designing parameters of that, the more height and thickness of the laminated composite plate's core, the more increase of natural frequency. In this type of structure, in the case of applying core of the laminated composite plate and antisymmetric stacking, natural frequency has high value and we calculated the optimum angle-ply making natural frequency maximum. Natural frequency of CFRP is higher than that of GFRP. Both are materials of the laminated composite plate. The mode shapes are various along with the angle-ply of the laminated composite plate.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.710-715
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• 1997

This paper deals with the analysis of the optimum value of honeycomb core considering variable design parameter. As thickness and height of core rises in design parameter, natural frequency of laminated composite plate increases. The angle-phy has the maximum value when the plate of honeycomb core join to opposite direction. This paper shows that the natural frequency of CFRP was higher than that of GFRP and mode shapes were various at angle-ply.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.629-632
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• 2006

The various rib geometry of hybrid fiber reinforced polymer (FRP) reinforcing bars were analyzed by finite element method. From the analysis result, two types of hybrid FRP reinforcing bars such as spiral and cross type with the same dimension of rib geometry were fabricated in this study. To evaluate the bond properties of them, direct pull-out test was performed. All testing procedures including specimens preparation, set-up of test equipments and measuring devices were made in accordance with the recommendations of CSA Standard S806-02. From the test results, it was found that cross type hybrid FRP reinforcing bars showed the highest bond strength than that of the others due to the higher relative rib area.

• Journal of the Korean Society of Safety
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• v.17 no.4
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• pp.31-37
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• 2002

This paper demonstrates the analyses of the interlaminar shear stress of laminated composite plates subjected to transversely impact. For this purpose, a plate finite element model based on the higher order shear deformation plate theory in conjunction with static contact laws is developed. Test materials were CFRP with cross-ply laminate $[O_4/{\theta}_4]_S$, $[90_4/{\theta}_4]_S$ stacking sequences and angle-ply laminate $[{\theta}_4/-{\theta}_4]_S$, $[{\theta}_4/-{\theta}_4]_S$ stacking deguences with $2^t{\times}40^w{\times}100^l(mm)$ dimension. As a result, stacking seguence and fiber orientation were found to have a significant effect on the interlaminar stresses in composite laminates.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.146-152
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• 2001

The fractal geometry is a non-Euclidean geometry which discribes the naturally irregular or fragmented shaps, so that it can be applied to fracture behavior of materials to investigate the fracture process. Fractal curves have a characteristic that represents a self-similarity as an invariant based on the fractal dimension. This fractal geometry was applied to the crack growth of cementitious composites in order to correlate the fracture behavior to microstructures of cemposite composites. The purpose of this study was to find relationships between fractal dimensions and fracture energy. Fracture test was carried out in order to investigate the fracture behavior of plain and fiber reinforced cement composites. The load-CMOD curve and fracture energy of the beams were observed under the three point loading system. The crack profiles were obtained by the image processing system. Box counting method was used to determine the fractal dimension, D$_{f}$. It was known that the linear correlation exists between fractal dimension and fracture energy of the cement composites. The implications of the fractal nature for the crack growth behavior on the fracture energy, G$_{f}$ is appearent.ent.