• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.8 no.3
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• pp.589-596
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• 2018

Transportation or structure has the important role at clothing, food, and housing at modern society. If even the small crack happens and propagates at transportation or structure, the parts are fractured and they can cause a disaster. CT specimen was used in order to investigate the damage trend due to the crack propagation at this study to prevent this situation. As the material of CT specimen, the unidirectional carbon fiber reinforced plastic of the composite material in the limelight nowadays. The laminate angle designated in order of [60/-60/60/-60] was applied to the specimen model with the unidirectional fiber. As the analysis condition, the forced displacement was applied to the hole of upper part after fixing the hole of lower part. At the result of this study, the equivalent stress and shear stress was shown to be higher in order of the structural steel, copper, titanium and aluminum. This study result is thought to be utilized usefully at verifying the damage of CT specimen made of inhomogeneous material.

• Korean Journal of Optics and Photonics
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• v.31 no.5
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• pp.205-212
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• 2020

In the performance of a wind turbine system, the blades play a vital role. However, they are susceptible to damage arising from complex and irregular loading (which may even cause catastrophic collapse), and they are expensive to maintain. Therefore, it is very important both to find defects after blade manufacturing is completed and to find damage after the blade is used for a certain period of time. This study provides a new perspective for the detection of internal defects in glass-fiber- and carbon-fiber-reinforced panels, which are used as the main materials in wind turbine blades. A gap or fracture between fiber-reinforced materials, which may occur during blade manufacturing or operation, is simulated by drilling a hole 5 mm in diameter in the middle layer of the laminated material. Then, a digital-image-correlation (DIC) method is used to detect internal defects in the blade. Tensile load is applied to the fabricated specimen using a tensile tester, and the generated changes are recorded and analyzed with the DIC system. In the glass-fiber-reinforced laminated specimen, internal defects were detected from a strain value of 5% until the end of the experiment, while in the case of the carbon-fiber-reinforced laminated specimen, internal defects were detected from 1% onward. It was proved using the DIC system that the defect was detected as a certain level of strain difference developed around the internal defects, according to the material properties.

• Polymer(Korea)
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• v.25 no.4
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• pp.575-586
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• 2001

Stabilized polyacrylonitrile (PAN) fibers can be transformed into quasi-carbon fibers with different properties depending on heat-treatment processing parameters at lower temperatures than temperature for the fabrication of carbon fibers. It has been investigated from the preliminary work that appropriate quasi-carbonization processes at about 1100$^{\circ}C$ strongly influence various properties of quasi-carbon fiber/polymer composite as well as quasi-carbon fiber itself. The objective of the present work is to prepare quasi-carbon fibers from stabilized PAN fibers using various quasi-carbonization cycles and to examine their properties. Two temperature regions, up to 800$^{\circ}C$ and above 1000$^{\circ}C$, were used for quasi-carbonization processes. The chemical composition, physical properties, thermal stability, microstructure, mechanical properties and electrical resistivity of the quasi-carbon fibers prepared with different final heat-treatment temperatures, heating rates, holding times, heating steps, and purging gas purity were extensively examined. The results were also compared with those from stabilized PAN fiber and commercial PAN-based carbon fiber. The present study showed that a variety of properties of quasi-carbon fibers significantly depended on several quasi-carbonization process parameters.

• Composites Research
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• v.32 no.5
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• pp.265-269
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• 2019

The direct spinning of carbon nanotube (CNT) fibers is a promising method in the high performance composite materials. However, most of the reported CNT arrays do not have spinning properties because of their limited synthesis conditions. In this study, we investigate the properties of spinnable CNT arrays, which is closely related to the morphology of CNT array. The array morphology controlled by controlling the conditions of catalyst, carbon source, etc. By additional carbon source of ethylene and changing the composition of the catalyst, the waviness of the CNT array can be remarkably reduced, which leads to improve of the spinning properties. The synthesized CNT arrays were well aligned along c-axis and the synthesis conditions of the spinning array could be derived.

• Composites Research
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• v.35 no.2
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• pp.106-114
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• 2022

Carbon fiber-reinforced plastic, well known high specific strength and high specific stiffness, have been widely used in the aircraft industry. Mostly the CFRP structure is fabricated by lamination of carbon fiber or carbon prepreg, which has major disadvantage called delamination. Delamination is usually produced due to absence of the through-thickness direction fiber. In this study, three-dimensional carbon preform woven in three directions is used for fabrication of aircraft wing unit structure, a part of repeated structure in aircraft wing. The unit structure include skin, stringer and rib were prepared by resin transfer molding method. After, the 3D structure was compared with laminate structure through compression test. The results show that 3D structure is not only effective to prevent delamination but improved the mechanical strength. Therefore, the 3d preform structure is expected to be used in various fields requiring delamination prevention, especially in the aircraft industry.

• Composites Research
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• v.30 no.2
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• pp.102-107
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• 2017

The preceramic polymer can realize a variety of complex ceramic structures that can not be obtained by conventional ceramic processes. Polycarbosilane, which is a typical preceramic polymer, can control the molecular structure, molecular weight and molecular weight distribution for preparing complex morphology and microstructure of SiC ceramics, including SiC fiber. In this paper, synthesis and molecular structure control technique of polycarbosilane is explained. The silicon carbide fiber prepared by melt spinning, stabilization and heat treatment, and ceramic fiber composites technology made by PIP process are also discussed. In addition, we introduce an example of the development of a complex silicon carbide material such as a silicon carbide hollow fiber having a nanoporous structure.

• Composites Research
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• v.31 no.6
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• pp.421-428
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• 2018

In order to optimize the prepreg compression molding (PCM) process, the forming simulation is required to cope with any problems that may be raised during the process. For the improvement of simulation accuracy, the input data of material property should be measured accurately. However, most studies assume that the compressive properties of the prepreg are identical to the tensile properties without quantifying them separately. Therefore, in this study, the in - plane compressive properties of the prepreg are presented to improve the accuracy of the forming simulation. As a result, the compressive modulus of the fibers was measured to be about $10^{-2}$ times lower than the tensile modulus. Also we designed a square-cup mold with a tilting angle of $110^{\circ}$ to simulate the prepreg formability during the high temperature compression mold process. Shear angles were measured at each corner, which were compared with the simulation results. It was observed that the simulation results using the accurate compressive properties of the prepreg showed a similar trend with the experimental results. It was confirmed that the measured data of the in-plane compression property improved the accuracy of the forming simulation results.

• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.798-803
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• 2018

In order to use Si as an anode material for lithium-ion battery, the particle size was controlled to less than $0.5{\mu}m$ and carbon was coated on the surface with the thickness less than 10 nm. The carbon fiber was grown on the Si surface with 50~150 wt%, and the carbon coating was carried out once again. The Si composite material was mixed with dissimilar metals to increase the conductivity, and graphite was mixed to improve cyclic life characteristics. The physical and electrochemical characteristics of composite materials were measured with XRD, SEM, TEM and coin cell. The discharge capacity of Si/PC/CNF/PC was lower than that of Si/PC (Pyrolytic Carbon)/CNF (Carbon Nano Fiber). However, the cyclic life of Si/PC/CNF/PC was higher. Initial discharge capacity of 1512 mA h g-1 at 0.2 C rate and initial efficiency of 78% were shown. It also showed a capacity retention of 94% in 10 cycles.

• Composites Research
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• v.35 no.1
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• pp.47-51
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• 2022

In order to efficiently control the heat generation of electronic devices, many research has been conducted on thermally conductive composite materials. In this study, milled carbon fiber was dispersed in four solvent to investigate the relationship of carbon fiber alignment according to dispersion by solvents, and carbon fiberreinforced composite material(CFRP) was manufactured using vacuum filtration. To evaluate the arrangement of CFRP the arrangement of the prepared specimen was observed under an optical microscope, and thermal conductivity was measured by Laser Flash Analysis. The Through-plane thermal conductivity of CFRP using NMP and Ethanol was 10.79 W/mK and 10.57 W/mK respectively, which were improved by 218% and 209% compared to the In-plane thermal conductivity. The high viscosity of the solvent greatly affects the shear of the fluid, and it seemed to determine the alignment of the filler.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4A
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• pp.279-286
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• 2011

FRP (Fiber Reinforced Polymer) tendons can be used as an alternative to solve the corrosion problem of steel tendons. Material properties of FRP tendons-bond strength, transfer length, development length-must be determined in order to apply to concrete structures. First of all, in case of application for pretension concrete members with CFRP tendons, transfer length is an important characteristic. The bond of the material characteristics should be demanded clearly to apply to PSC structures prestressed with FRP tendons. This paper investigated on the bond characteristics of FRP reinforcements with various surface-type. To determine the bond characteristics of FRP materials used in place of steel reinforcement or prestressing tendon in concrete, pull-out testing suggested by CAN/CSA S806-02 was performed. A total of 40 specimens were made of concrete cube with steel strands, deformed steel bar and 6 different surface shape FRP materials like carbon or E-glass. Results of the bonding tests presented that each specimen showed various behaviors as the bond stress-slip curve and compared with the bond characteristic of CFRP tendon developed in Korea.