• Applied Chemistry for Engineering
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• v.27 no.3
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• pp.285-290
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• 2016

To improve properties of epoxy composites, surfaces of the illite and carbon nanotube (CNT) were treated by fluorine gas. The fluorinated illite and CNT were then characterized by X-ray photoelectron microscopy (XPS) and the mechanical and thermal properties of their composites were evaluated. The tensile and impact strengths and thermal stability of the composites increased upto about 59%, 18% and 124%, respectively compared to those of the neat epoxy. Improvements of mechanical and thermal properties in the composites were attributed that the fluorination of illite and carbon nanotube helps to enhance the dispersion in epoxy resin and interfacial interaction between them.

• Composites Research
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• v.36 no.4
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• pp.259-263
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• 2023

This study investigated the open hole tensile (OHT) properties of carbon fiber/epoxy composites and compared them to bolt joint tensile (BJT) properties. The net nominal modulus and strength (1376 MPa) were found to be higher than the gross nominal strength (1041 MPa), likely due to increasing hole size. The OHT and BJT specimens exhibited similar stiffness, as expected without bolt rotation causing secondary bending. OHT specimens experienced a sharp drop in stress indicating unstable crack propagation, delamination, and catastrophic failure. BJT specimens failed through shear out on the bolt side and bearing failure on the nut side, involving fiber kinking, matrix splitting, and delamination, resulting in lower strength compared to OHT specimens. The strength retention of carbon fiber/epoxy composites with open holes was 66%. Delamination initiation at the hole's edge caused a reduction in the stress concentration factor. Filling the hole with a bolt suppressed this relieving mechanism, leading to lower strength in BJT specimens compared to OHT specimens. Bolt joint efficiency was calculated as 15%. The reduction in strength in bolted joints was attributed to fiber-matrix splitting and delamination, aligning with Hart Smith's bolted joint efficiency diagram. These findings contribute to materials selection and structural reliability estimation for carbon fiber/epoxy composites. They highlight the behavior of open hole and bolt joint configurations under tensile loading, providing valuable insights for engineering applications.

• Journal of Power System Engineering
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• v.19 no.5
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• pp.12-16
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• 2015

$TiO_2$ nanoparticle can be used for the improvement of performance of the epoxy resin composites. In this study, the effect of the size of $TiO_2$ nanoparticle on the mechanical properties for the epoxy resin composites was investigated. The size of $TiO_2$ nanoparticle was easily controlled by heat treatment. The heat treatment of $TiO_2$ nanoparticle was conducted between $700^{\circ}C$ and $900^{\circ}C$. The obtained size of $TiO_2$ nanoparticle was 20 nm, 100 nm and 200 nm respectively. As the diameter of $TiO_2$ nanoparticle is smaller, the epoxy resin composite specimen showed higher tensile strength. It was also found that Vickers hardness of epoxy resin was increased by the addition of $TiO_2$ nanoparticle. But the size of $TiO_2$ nanoparticle did not strongly affected to the Vickers hardness of this material. The fracture surface of epoxy resin showed clear difference by the size of $TiO_2$ nanoparticlet.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.199-202
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• 2002

Interfacial properties and electrical sensing for fiber fracture in carbon and SiC fibers/epoxy composites were investigated by the electrical resistance measurement and fragmentation test. As fiber-embedded angle increased, interfacial shear strength (IFSS) of two-type fiber composites decreased, and the elapsed time was long to the infinity in electrical resistivity. The initial slope of electrical resistivity increased rapidly to the infinity at higher angle, whereas electrical resistivity increased gradually at small angle. Furthermore, both fiber composites with small embedded angle showed a fully-developed stress whitening pattern, whereas both composites with higher embedded angle exhibited a less developed stress whitening pattern. As embedded angle decreased, the gap between the fragments increased and the debonded length was wider for both fiber composites. Electro-micromechanical technique can be a feasible nondestructive evaluation to measure interfacial sensing properties depending on the fiber-embedded angle in conductive fiber reinforced composites.

• Composites Research
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• v.30 no.6
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• pp.406-409
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• 2017

The thin-walled cylindrical tubes are frequently used for the evaluation of fatigue property of composites. But the curvature of the tubular specimen induces interlaminar normal stress which may affect the fatigue property. In this paper interlaminar normal stress effect on the fatigue behaviour of thin-walled graphite/epoxy tubes $[{\pm}45]_s$ composites was studied experimentally. It was concluded that the interlaminar normal stress induced by the curvature of the cylinder has no discernible effect on the fatigue life. But excessive internal pressure can produce the stiffness increase and this affects the fatigue life of the cylindrical tubular composite.

• Advanced Composite Materials
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• v.16 no.2
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• pp.83-94
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• 2007

Woven sisal textile fiber reinforced composites were used to evaluate fracture toughness, tensile and three-point bending. The water absorption testing of all specimens was repeated five times in this study. All specimens were immersed in pure water during 9 days at room temperature, and dried in 1 day at $50^{\circ}C$. Two kinds of polymer matrices such as epoxy and vinyl-ester were used. Fractured surfaces were taken to study the failure mechanism and fiber/matrix interfacial adhesion. It is shown that it can be enhanced to improve their mechanical performance to reveal the relationship between fracture toughness and water absorption fatigue according to different polymer matrices. Water uptake of the epoxy composites was found to increase with cycle times. Mechanical properties are dramatically affected by the water absorption cycles. Water-absorbed samples showed poor mechanical properties, such as lower values of maximum strength and extreme elongation. The $K_{IC}$ values demonstrated a decrease in inclination with increasing cyclic times of wetting and drying for the epoxy and vinyl-ester.

• Composites Research
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• v.26 no.6
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• pp.337-342
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• 2013

The good dispersion of nano-materials in epoxy matrix was important parameter for the reinforcement effect, and the evaluation of dispersion degree was to prove it. This work was studied to predict the dispersion condition of nano-SiC powders in SiC/epoxy composites using capacitance measurement. Capacitance was defined to be the electric capacity in proportional to electron charge of the measuring section. In case of nano-SiC powders, the electron charge of SiC/epoxy composites was higher than that of neat epoxy resin. Capacitance was evaluated for each section of SiC/epoxy composites. The prediction of dispersion condition was verified by using capacitance measurement. Dispersion condition of nano-SiC powders in epoxy matrix was evaluated with two different dispersion methods, i.e., sonication and stirring methods. The dispersion degree was also verified with the tensile strength correlating to capacitance.

• Transactions on Electrical and Electronic Materials
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• v.13 no.5
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• pp.248-251
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• 2012

In order to develop a high voltage insulation material, epoxy/micro-silica composites (EMC) and epoxy/micro-silica/nano-silica composites (EMNC) with three different particle sizes in ${\mu}m$ and one particle size in nm were prepared and their tensile and flexural tests were carried out and the data was estimated by Weibull statistical analysis. The tensile strength of the neat epoxy was 82.8 MPa and those of the EMCs were larger than that of the neat epoxy, and they were much more advanced by the addition of 10 nm sized nano-silica to the EMCs. Flexural strength showed the same tendency of the tensile strength. As the micro-particle size decreased, tensile and flexural strength increased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.9
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• pp.793-797
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• 2007

In this paper, the long time breakdown characteristic of the epoxy composite, which is widely used in the insulation system for high voltage application, was estimated with Weibull distribution. In the procedure of the estimation, the short time breakdown characteristics for the epoxy composite specimens, which were made with the variation of hardener and/or filler, were tested firstly. Then the long time voltage-to-time test was implemented. Finally, the long time breakdown voltage of each specimen was estimated with the parameters obtained from the statistical treatment with Weibull distribution. Base on the results, it has been found that the optimal weight ratio of epoxy resin/hardener/filler that has the excellent long time breakdown characteristic was 100/100/65. It was due to the silane treatment which relieves the electric field at the interface between filler and epoxy.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.1
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• pp.88-93
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• 2001

Carbon fiber epoxy composite are widely used in airframe structures, space vehicles, sports equipment, and high speed reciprocating parts for industrial machinery. In this paper, the groove processing characteristics of carbon fiber epoxy com-posite was experimentally investigated in order to study the endmill operation of fiber reinforce epoxy composites. Followings are main finding from the experimental results. First, the cutting and bending force in groove processing of the carbon fiber epoxy composite increased as the spindle speed deceased. They also deceased as the table feed increased. Second, the good cutting status obtained at the entrance of groove while delamination occurred at the exit of groove, Third, the regular high speed steel endmill was not efficient, thus the new endmill such as coated carbide rooter endmill or dia-mode endmill should be used for the effective endmll operation of carbon filber epoxy composites.