• Polymer(Korea)
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• v.33 no.5
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• pp.420-428
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• 2009

In this study, the composites containing carbon black (CB) or carbon fibers were prepared, and the microwave absorbing properties and the absorption mechanism of them were investigated and discussed in the frequency range of 2-18 GHz, respectively. The optimum mass fraction of CB has been found as 6%, and the carbon fibers were discovered to absorb radar wave either under parallel or vertical polarization, the suitable gap distance between each bundle of which was 5 mm. According to the results of the single constitute absorber samples, the structured composites with the two kinds of absorbers combination were fabricated and studied at 2-18 GHz. The top layer absorbers affect the absorption performance a lot; the maximum reflection loss of composites with CB as top layer absorbers was -31.8 dB with the frequency range of 2.4 GHz below -10 dB, and the other type with CFs as the top layer absorbers obtained the reflection loss peak value of -31.4 dB with 2 GHz below-10 dB.

• Composites Research
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• v.28 no.3
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• pp.130-135
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• 2015

This study investigates the property of graphene filled polymer nanocomposites in LEO(Low Earth orbit) environment conditions. In order to improve compatibility with polymer matrices and resistance of carbon material against AO(Atomic oxygen) attack, silanization of graphene oxide with organosilane was carried out. The corresponding moieties were characterized through X-ray photoelectron spectroscopy (XPS). Graphene oxide filled nanocomposites were prepared using solution based processing methods. The sets of specimen series were tested in an accelerated LEO simulated space environment facility. Graphene oxide and silane treated graphene oxide reinforced nanocomposites were compared with neat epoxy. The comparison revealed that the silane treated graphene filled polymer composite shows inherent resistance against atomic oxygen attack while the lack of silane treatment resulted in a reduction in performance.

• Composites Research
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• v.29 no.6
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• pp.336-341
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• 2016

This paper conducted the study on the electromagnetic and mechanical applicability of CNT-coated glass fiber for wind blades. Large-size wind blade has the serious pending problems to meet the target, such as interfering radar signals, increasing weights, and increasing repair costs. In this paper, we are suggesting the CNT-coated glass fiber in order to overcome these problems. First, the CNTs were strongly coated on the surfaces of glass fiber by suggested coating process, and the CNT-coated glass fiber/epoxy composites were fabricated by Va-RTM process. We designed and fabricated a radar absorbing structure using the CNT-coated glass fiber, which showed over 90% radar absorbing performance between 8.3 and 12.1 GHz frequency. In addition, we confirmed the improvement of mechanical properties on the strength and modulus of tensile, compressive, and in-plane shear.

• Composites Research
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• v.23 no.3
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• pp.13-18
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• 2010

One of the biggest challenges in the nano-field is how to effectively disperse nano-scale particles, especially CNTs, which are strongly agglomerated by intermolecular van der Waals forces. This study suggests a new method, discharge flocking, in order to disperse nano-scale particles effectively, which combines corona discharge phenomenon and a traditional electrostatic flocking process. In order to evaluate the discharge flocking process, composite specimens were fabricated by the process and RFI(resin film infusion) process, and then the mechanical and electrical properties of the specimens were measured and compared. Moreover, the evaluation of gas discharge effect on the CNTs and epoxy was performed to compare the mechanical and electrical properties of the composite specimens including the plasma treated CNTs. The experimental results showed that the electrical and mechanical properties of the specimens fabricated by the discharge flocking process were similar to those of the RFI process. In addition, plasma treated CNTs were not affected by gas discharge during the discharge flocking process.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.9
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• pp.25-32
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• 2006

In this study, the characteristics of filament wound composite/aluminum ring specimens were investigated at cryogenic temperature. The ring specimens were manufactured using carbon fibre and Type B epoxy resin which had been developed for cryogenic use. As a result of measuring thermal strains at -150℃, it was found that compressive thermal stress was induced in composite part on the contrary, tensile thermal stress in aluminum part which was about 32% of yield stress and in turn, caused aluminum to be yielded at lower load level. In addition, Thermal strains which resulted from finite element analysis showed good agreement with those of the experiment. After 6 mechanical loading cycles had been applied to the ring specimen at -150℃, tensile tests were performed at -150℃ using a split disk fixture. As a result, it was shown that composite strength in a liner-composite tank structure which is for the use of cryogenic propellant tank would be decreased by auto-frettage pressure which is applied to it.

• Composites Research
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• v.25 no.3
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• pp.65-69
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• 2012

The main objective of this study is to investigate the effect of metal z-pinning on the failure behavior of cocured composite single-lap joints. Three different pin diameters (0.3, 0.5, and 0.7 mm) and three pin areal densities (0.5, 2.0, and 4.0%) were examined. The specimens were fabricated by T700-12K-31E#2510 unidirectional prepreg from Toray. Stainless steel pins were used for z-pinning. Test results showed that except one case with extremely low pin density of 0.5%, all other z-pinned joints exhibited lower initial crack stresses than those of the unpinned joint. However the ultimate strength of the z-pinned joint increased up to 45% at most. Furthermore, even after the complete failure of the joint, the z-pins sustained the carried load to a certain degree experiencing large deformation and provided the stable fracture behavior for the composite joint.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.3
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• pp.205-214
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• 2018

This paper deals with the experimental study on the hygrothermal ageing effect to the strength of Carbon Fiber Reinforced Plastics (CFRP) materials for marine leisure boat manufactured by vacuum assisted resin infusion method. The experiments performed consist of tensile, flexural and shear tests according to American Society for Testing and Materials (ASTM) and Korean Industrial Standards (KS) test methods. Test coupons are varied from uni-directional(UD, $0^{\circ}$, $90^{\circ}$), Bi-Directional (BD), and Double-Bias (DB) carbon fiber fabrics in conjunction with epoxy resin. The results of tensile test show that tensile strength reduces significantly while not the same degree of reduction is observed for elasticity modulus with respect to the existence of hygrothermal ageing effect. This implies that the tensile strain induced from external load holds steady values but ultimate strength values change widely under hygrothermal ageing effect. In case of the flexural test, $0^{\circ}$ UD shows more strength reduction than $90^{\circ}$ UD while BD has reduced values in both flexural strength and elasticity modulus under hygrothermal ageing effect. It is learned that the bending strain induced from external load and ultimate strength values are reduced with respect to hygrothermal ageing effect. Shear test performed only on DB materials, and the results show marginal reduction in ultimate strength and moderate reduction in elasticity modulus. This means that the shear strain varies more than ultimate shear strength with respect to hygrothermal ageing effect. The experiment conducted in this paper clearly demonstrates the differences in material properties of the CFRP for the consideration of hygrothermal ageing effect. Findings obtained from this experimental study can serve as a fundamental input data for the realistic structural responses of marine leisure boat built in CFRP materials.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.251-259
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• 2006

In some cases, wooden structures are used for medium-rise buildings. It is therefore necessary to develop and test a new structural system for medium-rise buildings using wooden structures. This study deals with high-performance, laminated, timber-based composite members, which consist of structural laminated timber and H-beam. Simple beam tests were performed to determine the strength, stress distributions, and failure patterns of laminated timber. The main parameters are the insertinglength (1, 1.5, and 2 times the H-beam height) and the epoxy between the top/bottom flange of the H-beam and the top/bottom flange of the laminated timber. The results of the test show that the specimen with an inserting length that is 2 times the H-beam height was characterized by fairly god strength and stiffness.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.6
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• pp.74-86
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• 2021

The composite lattice structure is a structure that supports the required load with the minimum weight and thickness. Composite lattice structure is manufactured by the filament winding process using impregnating high-strength carbon fiber with an epoxy resin. Filament winding process can laminate and manufacture only structurally necessary parts, composite lattice structure can be applied to aircraft fuselages, satellite and launch vehicles, and guided weapons to maximize weight reduction. In this paper, the development and evaluation of the composite lattice structure corresponding to the entire process from design, analysis, fabrication, and evaluation of large-scale cylindrical and conical composites lattice structure were performed. To be applicable to actual projectiles and guided weapons, we developed a cylindrical lattice structure with a diameter of 2,600 mm and a length of 2,000 mm, and a conical lattice structure with an upper diameter of 1,300 mm, a lower diameter of 2,500 mm, and a length of 900 mm. The performance of the developed composite lattice structure was evaluated through a load test.

• Composites Research
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• v.37 no.2
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• pp.76-85
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• 2024

In this paper, a composite maintenance robot using carbon fiber spray method was developed that automatically sprays mixture was created for repair to damaged areas to repair them. To develop a robot, a repair process was developed in which a mixture of milled carbon fiber, epoxy resin, and hardener is sprayed and consolidated on the damaged area. To automate the repair process, an EOAT based on a collaborative robot was developed that can automatically suction and spray the mixture onto the damaged area. To evaluate the repair performance of the robot, 0° and 90° unidirectional specimens were manufactured and tested in accordance with ASTM D3039. Tests were performed on undamaged specimen, damaged specimen, and repaired specimen by a robot after damaged. As a result of the specimen test, the tensile strength of the 0° and 90° specimens was recovered by 10% and 90% after repair. Based on the test results, the repair performance of the developed composite maintenance robot was verified.