• Journal of Advanced Marine Engineering and Technology
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• v.28 no.7
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• pp.1165-1171
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• 2004

The free vibration analyses of the isotropic and CFRP laminated composite rectangular plates with point supports at the fix edge is performed by FEM. We showed optimal position and mode shape of point supports that maximized fundamental natural frequency of the isotropic and CFRP laminated composite rectangular plates by each aspect ratio and the number of point supports.

• Advanced Composite Materials
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• v.16 no.4
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• pp.335-347
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• 2007

Green composites composed of long maize fibers and poly $\varepsilon$-caprolactone (PCL) biodegradable polyester matrix were manufactured by the thermo-mechanical processing termed as 'Sequential Molding and Forming Process' that was developed previously by the authors' research group. A variety of processing parameters such as fiber area fraction, molding temperature and forming pressure were systematically controlled and their influence on the tensile properties was investigated. It was revealed that both tensile strength and elastic modulus of the composites increase steadily depending on the increase in fiber area fraction, suggesting a general conformity to the rule of mixtures (ROM), particularly up to 55% fiber area fraction. The improvement in tensile properties was found to be closely related to the good interfacial adhesion between the fiber and polymer matrix, and was observed to be more pronounced under the optimum processing condition of $130^{\circ}C$ molding temperature and 10 MPa forming pressure. However, processing out of the optimum condition results in a deterioration in properties, mostly fiber and/or matrix degradation together with their interfacial defect as a consequence of the thermal or mechanical damages. On the basis of microstructural observation, the cause of strength degradation and its countermeasure to provide a feasible composite design are discussed in relation to the optimized process conditions.

• Advanced Composite Materials
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• v.18 no.4
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• pp.297-314
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• 2009

A design method is proposed to optimize the stacking sequence of laminated composite plates for desired vibration characteristics. The objective functions are the natural frequencies of the laminated plates, and three types of optimization problems are studied where the fundamental frequency and the difference of two adjacent frequencies are maximized, and the difference between the target and actual frequencies is minimized. The design variables are a set of discrete values of fiber orientation angles with prescribed increment in the layers of the plates. The four lamination parameters are used to describe the bending property of a symmetrically laminated plate, and are optimized by a gradient method in the first stage. A new technique is introduced in the second stage to convert from the optimum four lamination parameters into the stacking sequence that is composed of the optimum fiber orientation angles of all the layers. Plates are divided into sub-domains composed of the small number of layers and designed sequentially from outer domains. For each domain, the optimum angles are determined by minimizing the errors between the optimum lamination parameters obtained in the first step and the parameters for all possible discrete stacking sequence designs. It is shown in numerical examples that this design method can provide with accurate optimum solutions for the stacking sequence of vibrating composite plates with various boundary conditions.

• Journal of Aerospace System Engineering
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• v.13 no.1
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• pp.69-76
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• 2019

In this study, resin flow analysis of resin transfer moulding (RTM) method was performed for mould design of composite structure. The target composite structure was a tank used for fluid storage. Natural c fiber composite was adopted for composite structural design of the fluid storage tank. RTM was adopted for manufacturing of the tank using natural fiber composites. Resin flow analysis was performed to find the proper RTM conditions of the tank. The resin flow analysis was performed using the commercial FEM flow simulation software. After repeated analysis while changing the location of resin inlet and outlet, the proper resin filling time and pattern were found.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.40 no.1
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• pp.62-67
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• 2008

Biocomposite was fabricated with biodegradable polymer and natural fiber that has potential to be used as replacement for glass fiber reinforced polymer composite with the benefits of low cost, low density, acceptable specific strength, biodegradability, etc. Until now, mostly natural cellulosic fibers on land have been used as reinforcement for biocomposite. The present study focused on investigating the fabrication and the characterization of biocomposite reinforced with red algae fibers from the sea. The bleached red algae fiber (BRAF) showed very similar crystallinity to the wood cellulose. It has high stability against thermal degradation (maximum thermal decomposition temperature of 359.3$^{\circ}C$) and thermal expansion. Biocomposites reinforced with BRAF have been fabricated by a compression molding method and their mechanical and thermal properties have been studied. The storage modulus and the thermomechanical stability of PBS (polybuthylenesuccinate) matrix are markedly improved by reinforcing with the BRAF. These results indicate that red algae fiber can be used as an excellent reinforcement of biocomposites, which are sometimes called as "green-composites" or "eco-composites".

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.206-210
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• 2003

Machining of deep holes with conventional boring bars frequently induce chatter vibration because of their low dynamic stiffness which is defined as the product of static stiffness and damping of conventional boring bar materials. In addition, the specific stiffness ($E/{\rho}g$) of boring bars is more important than the static stiffness to increase the fundamental natural frequency of boring bars in high speed machining. Therefore, boring bar materials should have high static stiffness and high damping as well as high specific stiffness. The best way to meet requirements is to employ fiber reinforced composite materials for high speed boring bars because composite materials have high static stiffness, high damping and high specific stiffness compared to conventional boring bar materials. In this study, the dynamic characteristics of carbon fiber epoxy composite boring bars were investigated. From the metal cutting test, it was found that the chatter was not initiated up to the ratio of length to diameter of 10.7 at the rotating speed of 2,500 rpm.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.3
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• pp.269-277
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• 2015

Compressed natural gas (CNG) composite vessels for vehicles have been generally made of 34CrMo4 for a inner liner part and E-glass/epoxy for a composite layer part. But, there is a problem of material loss of CNG composite vessels used in vehicles due to the design of excessive thickness of the liner. And, light weight of the CNG composite vessel is required for improving fuel efficiency. In this study, optimal design for CNG composite pressure vessel was performed by using basalt fiber, which is the environment-friendly material having a good mechanical strength. The optimal thickness of each part (inner liner and composite layer) was determined by theoretical analysis and FEA for satisfying structural safety and lightweight of the vessel. Also, for improving fatigue life, optimal autofrettage pressure was derived from FEA results.

• Composites Research
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• v.12 no.1
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• pp.47-58
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• 1999

This paper describes the results of experiments to analyze the free vibration of the laminated composite and hybrid composite plates with various shapes and boundary conditions. The materials of specimens were the carbon fiber reinforced plastic (CFRP), the glass fiber reinforced plastic (GFRP), the GFRP-Aluminum hybrid composite and the CFRP-CFRP hybrid composite. The natural frequencies and nodal patterns of plates with various shapes were experimentally obtained by impact exciting test using an impact hammer and an accelerometer. The experimental results were presented with normalized frequency parameters. The effects of composite material properties, fiber orientation angles, various geometrical shapes and boundary conditions on the vibration characteristics of composite plates were evaluated. To compare and verify these experimental results, the finite element analysis was carried out, and was well agreed with experimental results.

• Advanced Composite Materials
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• v.16 no.4
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• pp.283-298
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• 2007

Environment-friendly composites reinforced with bagasse fiber (BF), a kind of natural fiber as the remains from squeezed sugarcane, were fabricated by injection molding and press molding. As appropriate matrices for injection molding and press molding, polypropylene (PP) and polycaprolactone-cornstarch (PCL-C) were selected, as a typical recyclable resin and biodegradable resin, respectively. The mechanical properties of BF/PP composites were investigated in view of fiber mass fraction and injection molding conditions. And the mechanical properties and the biodegradation of BF/PCL composites were also evaluated. In the case of injection molding, the flexural modulus increased with an increase in fiber mass fraction, and the mechanical properties decreased with an increase in cylinder temperature due to the thermal degradation of BF. The optimum conditions increasing the flexural properties and the impact strength were $90^{\circ}C$ mold temperature, 30 s injection interval, and in the range of 165 to $185^{\circ}C$ cylinder temperature. On the other hand, as to BF/PCL-C fully-green composites, both the flexural properties and the impact strength increased with an increase in fiber mass fraction. It is considered that the BF compressed during preparation could result in the enhancement in mechanical properties. The results of the biodegradability test showed the addition of BF caused the acceleration of weight loss, which increased further with increasing fiber content. This reveals that the addition and the quantities of BF could promote the biodegradation of fully-green composites.

• International Journal of Aerospace System Engineering
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• v.3 no.1
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• pp.17-20
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• 2016

In this work, a structural design on horizontal axis wind turbine blade using natural flax fiber composite is performed. The structural design results of flax/epoxy composite blade are compared with the design results of glass/epoxy composite blade. In order to evaluate the structural design of the composite blade, the structural analysis was performed by the finite element method. Through the structural analyses, it is confirmed that the designed blade using natural composite is acceptable for structural safety, blade tip deflection, structural stability, resonance possibility, and weight. Finally, structural test of manufactured blade was performed. Through the structural test, it is confirmed that the designed blade is acceptable.