• Journal of Magnetics
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• v.3 no.2
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• pp.64-67
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• 1998

Microwave absorbing properties of ferrite-epoxy composite (absorbing layer) attached on the carbon fiber polymer composite (reflective substrate) are analyzed on the basis of wave propagation theory. A modified equation for wave-impedance-matching at the front surface of absorbing layer including the effect of electrical properties of the quasi-conducting substrate is proposed. Based on this analysis, the frequency and layer dimension that produce zero-reflection can be estimated from the intrinsic material properties of the obsorbing layer and the substrate. It is demonstrated that the microwave reflectivity of carbon fiber composite has a strong influence on the microwave absorbance of front magnetic layer.

• Journal of the Korean Society for Railway
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• v.10 no.1 s.38
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• pp.39-44
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• 2007

This rafer explains a durability test of a large train car body made of carbon/epoxy composite material. The composite car body with the length of 23m was manufactured as a sandwich structure composed of an aluminum honeycomb core and CF1263 woven fabric carbon/epoxy faces. In order to evaluate durability of the composite car body, it was excited by two 500kN capacity hydraulic actuators installed underneath the body bolster. The natural frequency of the composite car body under full weight condition was found to be 4.33Hz. Based on this result, the excitation frequency and displacement of 5Hz and ${\pm}1.0mm$, respectively, were used as inputs for the durability test. The test was conducted for $2{\times}10^6$ cycles. During the test, the nondestructive tests using X-ray radiography and dye penetration method was performed to determine the presence of the cracks. Upon completion of the test, no cracks were found.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.04b
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• pp.108-113
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• 1993

The material for the machine tool structure should have high static stiffiness and damping in its property to improve both the static and dynamic performances. The static stiffness of a machine tool can be inceased by using either higher modulus material in the structure of a machine tool. However, the machine tool structrue with high stiffness but low damping is vulnerable to vibration at the resonance frequencies of the structure . For the high precision and highsped machine tool structure, therefore, the high damping capacity is most important in order to suppress vibration. The damping of a machine tool can not be increased by increasing the static stiffness. The best way to increase the damping capacity of the machine tool structure is to use a composite material which is composed of on material with high stiffness with low damping and another material with low stiffness with high damping. Therefore, in this paper, the bed of the ultra high precision grinding machine for mirror surface machining of brittle materials such as ceramics and composite materials was designed and manufactured with the epoxy concrete material. The epoxy concrete material was prepared by mixing epoxy resin with different size sands and gravels. The modulus, compressive strength, coefficient of thermal expansion, specific heat, and damping factor were measured by varying the compaction ratio, sizes and contents of the ingredients to assess the effect of the processing parameters on the mechanical properties of the material. Based of the measured properties, the prototype epoxy resin concrete bed for the mirror surface CNC grinding machine was designed and manufactured.

• Journal of the Korean Society for Railway
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• v.12 no.4
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• pp.590-596
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• 2009

In this study, the failure modes and energy absorption characteristics of four different kinds of circular tubes made of carbon, glass, Kevlar and carbon-Kevlar hybrid fibres composites with epoxy resin have been evaluated. To achieve these goals, compressive tests were conducted for the tubes under 10mm/min loading speed. Based on the test results, the carbon/epoxy tube showed the best energy absorption capability, while carbon-Kevlar/epoxy tubes were worst. In the failure mode during crushing, both of the carbon/epoxy tubes and the glass/epoxy tubes were crushed by brittle fracturing mode. The Kevlar/epoxy tubes were collapsed by local buckling mode like steel, while the carbon-Kevlar hybrid tubes were collapsed by mixed mode of local buckling and lamina bending.

• Composites Research
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• v.32 no.1
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• pp.6-12
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• 2019

This paper describes the characteristics for mode I interlaminar and intralaminar fractures of cross-ply carbon/epoxy composite laminates. We obtained mode I interlaminar fracture toughness and mode I intralaminar fracture toughness based on energy release rate and Finite Element Analysis (FEA). For this purpose, the Double-Cantilever Beam (DCB) test and FEA were performed for cross-ply DCB specimens. Also, the behavior of load-displacement curve at the interlaminar and intralaminar crack was analyzed. The results show that mode I intralaminar fracture toughness was lower than mode I interlaminar fracture toughness in the cross-ply DCB specimen.

• Journal of the Korean Wood Science and Technology
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• v.50 no.2
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• pp.93-103
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• 2022

Currently, biofibers are used as a reinforcement in polymer composites for structural elements and construction materials instead of the synthetic fibers which cause environmental problems and are expensive. One of the chemicals with a pH close to neutral that can be potentially used as a modified fiber material is sodium chloride (NaCl). Therefore, this study aims to investigate the characteristics of a composite board made from NaCl-treated kenaf fiber. A completely randomized design method was used with consideration of two factors: the content of NaCl in the treatment solution (1 wt%, 3 wt%, and 5 wt%) and the duration of immersion of fibers in the solution (1 h, 2 h, and 3 h). The NaCl treatment was conducted by soaking the fibers in the solution for different durations. The fibers were then rinsed with water until the pH of the water reached 7 and subsequently dried inside an oven at 80℃ for 6 h. Kenaf fiber and epoxy were mixed manually with the total loading of 20 wt% based on the dry weight of the fiber. Physical and mechanical properties of the fibers were then evaluated based on JIS A 5908 particleboard standards. The results showed that increasing NaCl content in the fiber treatment solution can increase the physical and mechanical properties of the composite board. The properties of fibers treated with 5 wt% NaCl for 3 h were superior with a modulus of elasticity of 2.085 GPa, modulus of rupture of 19.77 MPa, internal bonding of 1.8 MPa, thickness swelling of 3%, and water absorption of 10.9%. The contact angle of untreated kenaf fibers was 104°, which increased to 80° and 73° on treatment with 1 wt% and 5 wt% NaCl for 3 h, respectively.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.268-271
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• 1999

Fatigue life Prediction is investigated analytically based on the fatigue modulus concept. Fatigue modulus degradation rate at any fatigue cycle was assumed as a power function of number of fatigue cycles. New stress function describing the relation of initial fatigue modulus and elastic modulus was used to account for material non-linearity at the first cycle. It was assumed that fatigue modulus at failure is proportional to applied stress level. A new fatigue life prediction equation as a function of applied stress is proposed. The prediction was verified experimentally using cross-ply carbon/epoxy laminate (CFRP) tube.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.1
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• pp.87-96
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• 1995

A new fungivle material named Epoxy-Granite composite is applied to the column structure of drilling center in order to investigate the advanced dynamic charateristics comparing with a conventional cast iron material. The dimensions of new column structure are adjusted to keep the same stiffness (EI value) and the manufacturing conditions are formulated based on the preceeding research experience about the development of Epoxy-Granite structural material. The two kinds of experiments are set up, one of which is for the measurement of natural mode and frequency using experimental modal analysis, and the other one is for the measurement of vibration amplitude during idling operation of a machine tool. The comparison of maximum accelerance values at each natural frequency of bending mode shows a Epoxy-Granite column have larger modal damping ratios(over 2times) than a cast iron column. The vibration amplitude of Epoxy-Granite column measrued on the bed, motor base, and top of column are also much smaller (up to 12%) than the case of cast iron column. It is therefore confirmed that a Epoxy-Granite material exhibits a good anti- vibrational propderty even if it is used under the actual operational environments of machine tool as a practical structural element.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1995.03a
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• pp.158-165
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• 1995

A new fungible materal named Epoxy-Granite composite is applied to the column structure of drilling center in order to investigate the advanced dynamic chatateristics comparing with a conventional cast iron material. The dimensions of new colum structure are adjusted to keep the same stiffness (El value) and the manufacturing conditions are formulated based on the preceeding research experience about the development of Epoxy-Granite structural material. The two kinds of experiments are set up. one of which is for the measurement of natural mode and frequency using experimental modal analysis and the other one is for the measurement of vibration amplitude during idling operation of a machine fool. The comparison of maximum, accelerance values at each natural frequency of bending mode shows a Epoxy-Granite column have larger modal damping ratios(over 2times) than a cast iron column. The vibration amplitude of Epoxy-Granite column measued on the bed motor base and top of column are also much smaller (up to 12%) than the case of cast iron column. It is therefore confirmed that a Epoxy-Granite materal exhibits a good anti-vibrational property even if it is used under the actual operational environments of machine eool as a practical structural element.

• Composites Research
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• v.34 no.3
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• pp.180-185
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• 2021

Due to the formation of random three dimensional network structure, which cause a lot of scattering of phonons, the thermal conductivity is low when the liquid crystalline epoxy is cured with amine-based curing agent. This problem is solved by using a cationic initiator that can make mesogen groups to be stacked structure. In this experiment, the thermal stability is compared by investigating the activation energy of isothermal decomposition through TGA of an epoxy using an amine-based curing agent and a cationic initiator. As a result, the energy of the activation of the epoxy using a cationic initiator is high. Compared with the previous experiments, the thermal stability is similar to the thermal conductivity.