• Composites Research
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• v.28 no.4
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• pp.168-175
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• 2015

Recently, the applications of carbon fiber reinforced plastics (CFRPs) have become broader than ever when it comes to such industries as automotive, ships, aerospace and military because of their lightweight-ness and high mechanical properties. Thermosetting plastics like epoxy are frequently used as the binding matrix in CFRPs due to their high hardness, wetting characteristics and low viscosity. However, they cannot melted and remolded. For this reason, thermosetting plastic wastes have caused serious environmental problems with the production of fiber reinforced plastics. Thus, many studies have focused on the carbon fiber reinforced thermoplastics (CFRTPs) and recycling carbon fiber. In this study, recycled carbon fiber (RCF) was prepared from CFRPs using a pyrolysis method, which was employed to separate resin and carbon fiber. The degree of decomposition for epoxy resin was confirmed from thermal gravimetric analysis (TGA) and scanning electron microscope (SEM). The RCF was cut and ground to prepare a carbon fiber composite sheet (CFCS). CFCS was manufactured by applying recycled carbon fibers and various thermoplastic fibers. Various characterizations were performed, including morphological analyses of surface and cross-section, mechanical properties, and crystallization enthalpy of CFCS at different cooling conditions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.1111-1112
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• 2012

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.121.2-121.2
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• 2005

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.747-748
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• 2010

• Composites Research
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• v.18 no.1
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• pp.38-44
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• 2005

In this paper, the group velocity dispersion curves of the $S_o$ symmetric mode in unidirectional CFRP plate was calculated as varying the propagating direction. The group velocity curve was obtained with the group velocities of the $S_o$ symmetric mode corresponding to 0.2 MHz-mm under the first cut-off frequency in the dispersion curves, and corrected by introducing the slowness curve. The velocities of the $S_o$ symmetric mode in the unidirectional CFRP plate were measured as varying the propagating direction and compared with the col?rotted group velocity curve. The measured velocities were good agreement with the corrected group velocity curve except near the fiber direction which was called the cusp region. It implies that the direction of the group velocities incline toward the fiber direction of the unidirectional CFRP plates when the propagation direction is not accorded with the principal axis. It is supposed that this phenomenon rerults from the preferential propagating the energy toward the direction with the faster propagation velocity.

• Composites Research
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• v.12 no.4
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• pp.42-54
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• 1999

FMLC(Fiber-Metal Laminate Composites) is a new structural material combining thin metal laminate with adhesive fiber prepreg, it nearly include all the advantage of metallic materials, for example: good plasticity, impact resistance, processibility, light weight and excellent fatigue properties. This research studied the optimum design of the FMLC subject to various loading conditions using genetic algorithm. The finite element method based on the shear deformation theory was used for the analysis of FMLC. Tasi-Hill failure criterion and Miser yield criterion were taken as fitness functions of the fiber prepreg and the metal laminate, respectively. The design variables were fiber orientation angles. In genetic algorithm, the tournament selection and the uniform crossover method were used. The elitist model was also used to be effective evolution strategy and the creeping random search method was adopted in order to approach a solution with high accuracy. Optimization results were given for various loading conditions and compared with CFRP(Carbon Fiber Reinforced Plastic). The results show that the FMLC is more excellent than the CFRP in point and uniform loading conditions and it is more stable to unexpected loading because the deviation of failure index is smaller than that of CFRP.

• Composites Research
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• v.12 no.3
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• pp.8-16
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• 1999

Carbon woven fabric/C/SiC composites were fabricated by multiple impregnations of carbon woven fabric/carbon preform with the polymer precursor of SiC, i.e., polycarbosilane. In addition, two kinds of low density carbon/carbon preforms which had different fiber volume fraction and fiber orientation, i.e., a carbon woven fabric(${\thickapprox}$55 vol%)/carbon and a chopped carbon fiber${\thickapprox}$40 vol%)/carbon composites, were reaction-bonded with a silicon melt at 1$700^{\circ}C$ in a vacuum to fabricate dense carbon fiber/Si/SiC composites. The reaction-bonding process increased the density to ~2.1 g/$cm^3$ from 1.6 g/$cm^3$ and 1.15 g/$cm^3$ of a carbon woven and a chopped carbon preforms, respectively. All of the composites fractured with extensive fiber pull-out. The higher the density the higher the stiffness and proportional limit stress. The mechanical properties obtained from a three-point bend and tension tests were compared. The ratios of the peak tensile stresses to the bending strengths of a carbon woven and a chopped carbon composites were about one-third, respectively. The carbon woven fabric/Si/SiC composites with density of 2.06 g/$cm^3$ showed ~120 MPa of ultimate strength and ~80 MPa of proportional limit in bend testing.

• Composites Research
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• v.36 no.4
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• pp.246-252
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• 2023

A secondary barrier made of glass fiber reinforced composites has been installed infinitely using automatic bonding machine(ABM) in membrane type LNG cargo containment system (CCS). At the same time, significant thermal stress due to cryogenic heat shrinkage has occurred in the composite on the non-bonding area between the adhesive fixation at both ends. There have been studies from the perspective of structural safety evaluation taking this into account, but none that have analyzed mechanical property taking an prolonged length into account. In this study, 2-parameter Weibull distribution statistical analysis was used to standardize reliable mechanical property for actual length, taking into account the composite's brittle fracture of ceramic material with wide fracture strength dispersion. Related experimental data were obtained by performing uniaxial tensile tests at specific temperatures below cryogenic condition considering LNG environment. As a result, the mechanical strength increased about 1.5 times compared to -20℃ at -70℃ and initial non-linear behavior of fiber stretched was suppressed. As the temperature decreased until the cryogenic, the mechanical strength continued to increase due to cold brittleness. The suggested mechanical property in this study would be employed to secure reliable analysis support material property when assessing the safety of secondary barrier's structures.

• Composites Research
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• v.34 no.2
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• pp.136-142
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• 2021

3D printing technology has the advantage of easy to make various shapes of products without a mold. However, it has a problem such as mechanical properties vary greatly depending on materials and manufacturing conditions. Thus, the need for research of 3D printing technology on ways to reduce manufacturing cost compared to physical properties is increasing. In this study, a 3D printing thermoplastic structure was fabricated using short fiber carbon fiber reinforced nylon filaments. And a method of improving mechanical properties was proposed by reinforcing the outer surface using pultruded continuous fiber-type carbon fiber or glass fiber-reinforced thermosetting composite material. It was confirmed that the bending properties were improved according to the reinforcing position of the stiffener and the type of fiber in the stiffener.

• Composites Research
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• v.33 no.1
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• pp.30-37
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• 2020

Stress distributions dependent on fiber arrangements are studied using the two-dimensional representative volume element (RVE) model for uni-directionally continuous fiber-reinforced composites subjected to transverse tensile loading. It is easily expected that the stresses around the fibers are concentrated mainly due to the stiffness mismatch between the fiber and matrix materials. In this presentation, it is shown that the stresses are not always increased although the distance between two fibers is shortened. The 2D RVE models, originally having a regular hexagonal fiber array, is utilized to study the effect of the fiber locations on the stress distributions. As the central fiber is relocated, the stress distributions around the fiber are obtained through finite element analysis. It is found that the stresses around the fiber are strongly dependent on the fiber distance as well as the angle between the loading direction and the line connecting two fibers.