• Composites Research
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• v.14 no.6
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• pp.32-37
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• 2001

It is known that recoating or protection with glass-tube can prevent FBG sensor from being affected by birefringence. However, the effect on the strain transfer of such treatment has not been verified yet. Three types (uncoated, recoated and glass-tube protection) of FBG sensors are fabricated to verify the effect on the strain transfer of each treatment. The strain from each sensor embedded into a graphite/epoxy composite specimen was compared with that of ESG attached on the surface through the tensile test. And the signal characteristics of each sensor were also compared using the tensile test of a tapered aluminum specimen which was under the state of strain gradient.

• Composites Research
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• v.37 no.2
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• pp.132-138
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• 2024

In this study, a molecular dynamics simulation study was performed to investigate the size-dependent electroelastic properties of single-walled boron nitride nanotubes(BNNT). To describe the elasticity and polarization of BNNT under mechanical loading, the Tersoff potential model and rigid ion approximation were adopted. For the prediction of piezoelectric constants and Young's modulus of BNNTs, piezoelectric constitutive equations based on the Maxwell's equation were used to calculate the strain-electric displacement and strain-stress relationships. It was found that the piezoelectric constants of BNNTs gradually decreases as the radius of the tubes increases showing a nonnegligible size effect. On the other hand, the elastic constants of the BNNTs showed opposites trends according to the equivalent geometrical assumption of the tubular structures. To establish the structure-property relationships, localized configurational change of the primarily bonded B-N bonded topology was investigated in detail to elucidate the BNNT curvature dependent elasticity.

• Composites Research
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• v.34 no.6
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• pp.387-393
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• 2021

This paper investigated the electrical properties of multiwall carbon nanotube reinforced polydimethylsiloxane (CNT-PDMS) strain sensors with copper electrodes on the wet-etched surface. MWCNT-PDMS strain sensors were fabricated according to the wt% of MWCNT. Surfaces on the electrode area were wet-etched with various etching duration and silver epoxy adhesives were spread on the wet-etched surface. Finally, we attached the copper electrodes to the MWCNT-PMDS strain sensors. We checked the electric conductivities by the two-probe method and sensing characteristics under the cyclic loading. We observed the electric conductivity of MWCNT-PDMS strain sensors increased sharply and the scattering of the measured data decreased when the surface of the electrode area was wet-etched. Initial resistances of MWCNT-PDMS strain sensors were inversely proportion to wt% of MWCNT and the etching duration. However, the resistance changing rates under 30% strain increased as wt% of MWCNT and the etching duration increased. Decreasing rate of the electric resistance change after 100 repetitions was smaller when wt% of MWCNT was larger and the etching duration was short. This was due to the low initial resistance of the MWCNT-PMDS strain sensors by the wet-etching.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.67-67
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• 2013

그래핀과 탄소나노튜브와 같은 탄소나노재료는 우수한 물성으로 인하여 다양한 분야에 응용이 가능할 것으로 예측되고 있으며, 더욱이 이러한 특성은 구조변형, 화학적 도핑뿐만 아니라 표면처리를 통해서 제어가 가능하다고 알려져 있다. 본 연구에서는 기존의 진공 공정이 아닌 상온 상압 환경에서 그래핀과 탄소나노튜브를 효율적으로 표면 처리하기 위하여 대기압 플라즈마장치를 제작하였고, 질소플라즈마를 이용하여 그래핀과 탄소나노튜브의 표면을 처리하였다. 대표적인 결과로는 소수성이었던 그래핀 및 탄소나노튜브의 표면을 친수성으로 개질하였으며, 플라즈마 처리에 의한 결함을 최소화시킬 수 있는 최적의 표면처리 조건을 도출하였다.

• Journal of the Korean Society for Railway
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• v.13 no.2
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• pp.147-151
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• 2010

Since the kinetic energy is dissipated through plastic deformation energy generated in expanding process of the tube by a die. In order to successfully absorb the kinetic energy there should be no buckling in the expansion tube during expanding process. The buckling instability of the expansion tubes is affected by the initial boundary conditions, tube thickness and length. In this study, the effects of the tube thickness except length and initial boundary condition on the buckling instability are studied using a finite element method. In addition, Analysis procedure for nonlinear post-buckling analysis of expansion tube is established. There are three kinds of finite element analysis procedures for buckling analysis of expansion tube, quasi-static analysis, linear buckling analysis and nonlinear post-buckling analysis. The effect of the geometry imperfections defined as linear superimposition of buckling modes is considered in the nonlinear post-buckling analysis. The results of finite element analysis indicate that the buckling load increase with increase of thickness of tube and geometry imperfection. Finial buckling shapes are changed with respect to the geometry imperfection.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6A
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• pp.861-872
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• 2008

Concrete-filled glass fiber reinforced polymer tubes are often used for marine structures with the benefit of good durability and high resistance against corrosion under severe chemical environment. Current research presents results of a comprehensive experimental investigation on the behavior of axially loaded circular concrete-filled glass fiber reinforced polymer tubes. This paper is intended to examine several aspects related to the usage of glass fiber fabrics and filament wound layers used for outer shell of piles subjected to axial compression. The objectives of the study are as follows: (1) to evaluate the effectiveness of filament winding angle of glass fiber layers (2) to evaluate the effect of number of GFRP layers on the ultimate load and ductility of confined concrete (3) to evaluate the effect of loading condition of specimens on the effectiveness of confinement and failure characteristics as well, and (4) to propose a analytical model which describes the stress-strain behavior of the confined concrete. Three different types of glass fiber layers were chosen; fabric layer, ${\pm}45^{\circ}$ filament winding layer, and ${\pm}85^{\circ}$ filament winding layer. They were put together or used independently in the fabrication of tubes. Specimens that have various L:D ratios and different diameters have also been tested. Totally 27 GFRP tube specimens to investigate the tension capacity, and 66 concrete-filled GFRP tube specimens for compression test were prepared and tested. The behavior of the specimens in the axial and transverse directions, failure types were investigated. Analytical model and parameters were suggested to describe the stress-strain behavior of concrete under confinement.

• Composites Research
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• v.30 no.3
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• pp.193-201
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• 2017

Molecular dynamics simulation and the Mori-Tanaka micromechanics study are performed to investigate the effect of the covalent grafting between CNT and polyester on the mechanical behavior and load transfer of nanocomposites. The transversely isotropic stress-strain curves are determined through the tension and shear simulations according to the covalent grafting. Also, isotropic properties of randomly dispersed nanocomposites are obtained by orientation averaging the transversely isotropic stiffness matrix. By addressing the grafting, the transverse Young's modulus and shear moduli of the nanocomposites are improved, while the longitudinal Young's modulus decreases due to the degradation of the grafted CNT.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.2
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• pp.57-60
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• 2005

Semiconductor carbon nanotube was grown on oxided silicon wafer with atmosphere pressure chemical vapor deposition (APCVD) method and investigated the electrical property after thermal oxidation at $300^{\circ}C$ in air. The electrical property was measured at room temperature in air after thermal oxidation at $300^{\circ}C$ for various times in air. Semiconductor carbon nanotube was steadily changed to metallic carbon nanotube as increasing of thermal oxidation times at $300^{\circ}C$ in air. Some removed area of carbon nanotube surface was shown with transmission electron microscopy (TEM) after thermal oxidation for 6 hours at $300^{\circ}C$ in air.

• Journal of the Korean Geosynthetics Society
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• v.13 no.2
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• pp.1-10
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• 2014

In this study, two different types of dredged fill injection methods are introduced and filling experiments were conducted to analyze the impact of each technique to the distribution and deposition of dredged soil fill and how it influence the final tube shape. Two transparent plastic tubes were fabricated to observe the deposition behavior of the deposited fill material. Both tubes measured 4.0 meters in length (L) and has vinyl tube diameters (D) of 0.5m and 0.7m. T-type and I-type inlet system are also introduced in this paper. The influence of this inlet systems to the distribution and deposition behavior of dredged soil fill inside the vinyl tubes were observed during the experiment. After the sedimentation of the slurry mixture, the water on top of the soil sediments are removed and the slurry mixture was re-injected into the vinyl tube, this process was carried out repeatedly. The shape changes of the vinyl tube, e.g. the changes in both tube height and width, are constantly monitored after each slurry injection and water draining phases. Crater formation was observed in the case of I-Type inlet system and a non-uniform sediment distribution occurred. For the diffusion deposit of soil particles to long distance are minimal shape technique using the T-Type inlet system. Therefore the undrain filling height ratio ($H/D_0$) was found to be around 0.54 to 0.64 and the horizontal strain ratio ($W/D_0$) ranges from 1.45 to 1.54. The filling soil height is proportional to dredged-material filling phases, but, horizontal strain ratio is constant or inversely reduced so that the center of tube body is raised in the upward direction.

• Journal of Power System Engineering
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• v.7 no.2
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• pp.56-60
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• 2003

Recently the plastic fuel tube is usually used to reduce production cost and weight in automobiles. These days, material used to plastic fuel tube is the polyamide12. The fuel tube is made of the PA12. Post deformation of the tube has been changed by environmental temperature. So, it is important to prevent post deformation. The experiment is performed to investigate post deformation of the tube produced by each bending process. In this study, the results we obtained are used to bending process system for post deformation as the environmental temperature of the tube. It turned out that the method of steam heating and air cooling was shown less deformation than other methods.