• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 영호남학술대회 논문집
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• pp.250-253
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• 2000

The fiber orientation in FRP has a great effect on the strength of FRP because the strength of FRP mainly depends on the strength of fiber. Unidirectional FRP made by pultrusion method has comparatively lower compressive strength than tensile strength. Compressive strength of unidirectional FRP may be increased by filament winding layer which has tensile stress when compressive stress was loaded. In this study, compressive strength and stresses of FRP rods were simulated according to the winding orientation of glass fiber. Inner part of FRP was made unidirectionally by pultrusion method and outer part of FRP was made by filament winding method. Simulated value and real evaluated compressive strength were compared to investigate stresses which is prominent to the fracture of FRP. The shear stresses had a great effect on the strength of FRP although the stress of parallel direction of FRP was much higher.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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• pp.53-58
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• 2000

During the curing process of thick glass/epoxy laminates, a substantial amount of temperature lag and overshoot at the center of the laminates is usually experienced due to the large thickness and low thermal conductivity of the glass/epoxy composites. Also, it requires a longer time for full and uniform consolidation. In this work, temperature, degree of cure and consolidation of a 20mm thick unidirectional glass/epoxy laminate were investigated using an experiment and a 3-dimentional numerical analysis considering the exothermic reaction. From the experimental and numerical results, it was found that the experimentally obtained temperature profile agreed well with the numerical one and the cure cycle recommended by the prepreg manufacturer should be modified to prevent a temperature overshoot and to obtain full consolidation.

• 대한기계학회논문집A
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• 제24권11호
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• pp.2853-2865
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• 2000

During the curing process of thick glass/epoxy laminates, a substantial amount of temperature lag and overshoot at the center of the laminates is usually experienced due to the large thickness and low thermal conductivity of the glass/epoxy composites. Also, it takes a longer time for full and uniform consolidation. In this work, temperature, degree of cure and consolidation of a 20 mm thick unidirectional glass/epoxy laminate were investigated using an experiment and a 3-dimentional numerical analysis. From the experimental and numerical results, it was found that the experimentally obtained temperature profile agreed well with the numerical one, and the cure cycle recommended by the prepreg manufacturer should be modified to prevent a temperature overshoot and to obtain full consolidation.

• Journal of Korean Vacuum Science & Technology
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• 제4권1호
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• pp.18-22
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• 2000

For the enhancement of the nucleation density of the diamond film, we introduced the cyclic process. The cyclic process was carried out by the on/off control of CH$_4$ flow rate for a relatively short time (10 min), compared with the total reaction time (6 h). Prior to depositing the diamond film, we made the pretreated glass substrate via the unidirectional scratch using ∼l $\mu\textrm{m}$ size diamond powders. Diamond films were deposited on the pretreated glass substrate in a microwave plasma enhanced chemical vapor deposition (MPECVD) system. We observed the enhancement of the nucleation density of the diamond films caused by the cyclic process. Detailed surface morphologies of the substrate were investigated after the cyclic process. Based on these results, we discussed the cause for the enhancement of the nucleation density on the pretreated glass substrate by the cyclic process.

• 한국음향학회지
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• 제13권6호
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• pp.50-59
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• 1994

유리판과 단일방향(unidirectional) 탄소섬유 강화 복합재료(CFRP)판의 표면에서 연필심을 부러뜨려 발생된 과도적 탄성파를 음원으로부터 멀리 떨어진 서로 다른 위치에 둔 두개의 탐촉자로 검출하였다. 탐촉자에 검출된 과도적 신호의 스펙트럼 분석에 의해 판에서 pulse 형태로 발생된 신호는 Lamb파 분산관계를 따르며 전파하고, 유리판과 단일방향 CFRP판에서의 과도적 신호는 최저 대칭$(S_{0})$, 1차 대칭$(S_{1})$, 1차 비대칭$(A_{l})$ 모드의 최대 군속도 주변의 성분들로 형성되었다. 이러한 최대 군속도 주변 성분은 분산이 비교적 적기 때문에 과도적 신호의 초기부분은 크게 변화되지 않았으며, $A_{1}$ 모드 단절 (cut-off)주파수 이하 영역의 $S_{0}$ 모드가 가장 빠른 군속도로 전파되고 과도적 신호 형성에 크게 기여하는 모드이었다.

• Journal of Magnetics
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• 제4권1호
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• pp.33-37
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• 1999

Unidirectional magnetic anisotropy field ($H_an$) was investigated for thin films of $CdCr{2-2x}In_{2X}Se_4 (0$\leq$x$\leq$0.2). This anisotropy originates from the microscopic anisotropic Dzyaloshinskii-Moriya (DM) interaction which arise from the spin-orbit scattering of the conduction electrons by the nonmagnetic impurities. This interaction maintains the remanent magnetization in the direction of the initial applied field. Then the single easy direction of the magnetization is parallel to the direction of the magnetic field. The anisotropy produced by field cooling is unidirectional I.e. the spins system deeps some memory of the cooling field direction. The chalcogenide spinel of$ CdCr_{2-2x}In){2X}Se_4$belongs to the class of the magnetic semiconductors. The magnetic disordered state is obtained when ferromagnetic structure is diluted by In. Then we have the mixed phase characterised by coexistence the magnetic long range ordering (IFN-infinite ferromagnetic network) and the spin glass order (Fc-finite clusters). The total magnetic anisotropy energy depends on the state of magnetic ordering. In our study we concentrated on the magnetic state with reentrant transition and spin glass state. The polycrystalline $ CdCr_{2-2x}In){2X}Se_4$ thin films were obtained by rf sputtering technique. We applied the ferromagnetic resonance (FMR) and M-H loop techniques for determining the temperature composition dependencies of Han. From the experimental data, we have found that Han decreases almost linearly when temperature is increased and in the low temperature is about three times bigger at SG state with comparison to the state with REE.

• 대한치과보철학회지
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• 제40권5호
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• pp.429-440
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• 2002

Current dental restorations present a relatively weak resistance to fracture. Owing to their unique mechanical properties, fibre-reinforced polymers are now being considered. Unidirectional or woven continuous fibres, made of glass, polyethylene, carbon or Kevlar, have been evaluated. This study focused on the use of glass fibre knitted fabrics to reinforce acrylate resins, in order to investigate the possibility to construct single crowns as well as three unit bridges. Some points affecting the final composite system were tested ; 1) static strength, with focus on the stress transfer under a occlusal contact point ; 2) modelling of a three nit bridge ; 3) fatigue strength as a posterior three unit bridge material. The study demonstrated that knitted fabric reinforcements are showing an interesting compromise between stiffness, static strength for single crown. For three unit bridge applications in the posterior arch, however knitted glass fabric reinforcements were not strong enough in fatigue An additional reinforcement in the posterior arch fixed partial denture design was recommended.

• 한국생산제조학회지
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• 제26권4호
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• pp.395-401
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• 2017

Energy absorption capabilities and failure modes of circular tubes made of glass/epoxy with two trigger mechanisms were evaluated. Three types of glass/epoxy tubes were fabricated using a hand lay-up method with unidirectional and woven fabric prepregs tapes, and a filament winding method. The one end of the fabricated tubes was machined for the bevel trigger and tulip trigger. Then, crush tests were conducted at 10 mm/min loading speed, wherein the glass/epoxy tubes were crushed by a brittle fracturing mode combined with fragmentation and lamina-splaying modes. The UD glass/epoxy tubes with a bevel trigger and the filament winded tubes with a tulip trigger showed the maximum and minimum specific energy absorptions, respectively, with a difference of 9.3%. The tube with a tulip trigger exhibited a maximum reduction of 5.7% in the initial peak load; the tube with a bevel trigger showed a maximum increase of 2.9% in the specific energy absorption.

• Advances in aircraft and spacecraft science
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• 제3권4호
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• pp.379-397
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• 2016

In this manuscript, free vibrations of a unidirectional composite orthotropic Timoshenko beam based on finite strain have been studied. Using Green-Lagrange strain tensor and comprising all of the nonlinear terms of the tensor and also applying Hamilton's principle, equations of motion and boundary conditions of the beam are obtained. Using separation method in single-harmonic state, time and locative variables are separated from each other and finally, the equations of motion and boundary conditions are gained according to locative variable. To solve the equations, generalized differential quadrature method (GDQM) is applied and then, deflection and cross-section rotation of the beam in linear and nonlinear states are drawn and compared with each other. Also, frequencies of carbon/epoxy and glass/epoxy composite beams for different boundary conditions on the basis of the finite strain are calculated. The calculated frequencies of the nonlinear free vibration of the beam utilizing finite strain assumption for various geometries have been compared to von Karman one.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.175-179
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• 2004

Since the electromagnetic properties of fiber reinforced polymeric composites can be tailored effectively by adding small amount of electromagnetic powders to the matrix of composites, they are plausible materials for fabricating the radar absorbing structures (RAS) of desired performance. In order to design the effective electromagnetic wave (EM) absorber with the fiber reinforced polymeric composites, the electromagnetic characteristics with respect to the constituents of the composite should be available in the target frequency band. In order to describe the dielectric behavior of low loss unidirectional fiber reinforced composite, theoretical models and mixture equations for estimating its dielectric constant were proposed with respect to the fiber, matrix volume fractions and fiber orientations, and verified by the experiments. From the investigation, it was found that the suggested binary mixture rules agreed well with the experimental results.