• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 춘계학술대회 논문집
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• pp.3-8
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• 2003

In this study, using linear and nonlinear deformation theories and by closed-form analysis and finite difference energy methods, respectively, various buckling load factors are obtained for stiffened laminated composite panel with trapezoidal type stiffeners and various longitudinal length to radius ratios, which are made from Carbon/Epoxy USN 125 prepreg and are simply-supported on four edges under uniaxial compression, and then for them, optimal design analyses are carried out by the nonlinear search optimizer, ADS.

• 한국공작기계학회논문집
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• 제12권5호
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• pp.88-93
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• 2003

Buckling behavior of stiffened laminated composite cylindrical panel was studied using linear and nonlinear deformation theory. Various buckling load factors are obtained for stiffened laminated composite cylindrical panels with rectangular type longitudinal stiffeners and various longitudinal length to radius ratio, which made from Carbon/Epoxy USN150 prepreg and are simply-supported on four edges under uniaxial compression. Buckling behavior design analyses are carried out by the nonlinear search optimizer, ADS.

• 대한기계학회논문집A
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• 제26권5호
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• pp.960-968
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• 2002

In this research, the effects of fiber stacking sequence on damage behaviors of FML(Fiber Metal Laminates) subject to indentation loading. SOP (Singly Oriented Ply) FML and angle ply FML were fabricated to study fiber orientation effects and angle ply effects. FML were fabricated by using 1050 aluminum laminate and carbon/epoxy prepreg. To increase adhesive bonding strength, Al laminate was etched using FPL methods. The static indentation test were conducted by using UTM under the 2side clamped conditions. During the tests, load and displacement curve and crack initiation and propagation behaviors were investigated. As fiber orientation angle increases, the crack initiation load of SOP FML increases because the stiffness induced by fiber orientation is increased. The penetration load of SOP FML is influenced by the deformation tendency and boundary conditions. However, the macro-crack of angle ply FML was initiated by fiber breakage of lower ply because angle plies in Angle ply FML prevents the crack growth and consolidation. The Angle ply FML has a critical cross-angle which prevent crack growth and consolidation. Damage behavior of Angle ply FML is changed around the critical cross-angle.

• 대한기계학회논문집A
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• 제30권12호
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• pp.1603-1610
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• 2006

In this paper compressive characteristics of composite egg-box panels were investigated and energy absorption was calculated from the nominal stress-strain relations obtained by the compressive tests. Several different stacking sequences and number of plies were introduced for investigation of static compression characteristics and the energy absorption rates of composite egg-box panels. The compressive stress-strain relation and energy absorption of various composite egg-box panels were compared with those of aluminium egg-box panels. From the test results it was found that the fracture behavior of composite egg-box panel was affected by stacking angle causing different local deformation, during lay-up and draping processes and types of prepreg; that is, plain weave carbon/epoxy and 4-harness satin glass/epoxy. The energy absorption capacity of composite egg-box panels were proved to be higher than that of aluminium egg-box panels with low mass.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.12-16
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• 2000

This study is about the effect of braiding on the 2-D biaxial braided hollow composite(BD) compared with unidirectional hollow composite(UD). The specimens were made of T700S Carbon/Epoxy prepreg and T700S dried Carbon yarns. Fiber volume fraction of UD and BD was obtained experimentally and analytically. Fiber volume fraction of BD was derived based on unit cell of braiding yarn section. Bending test was executed to investigate the effect of braiding part. The result of experiment and analysis of fiber volume fraction has good agreement. Bending strength of BD is about 20% higher than that of UD.

• 폴리머
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• 제24권1호
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• pp.105-112
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• 2000

본 연구에서는 항공기 구조용 재료로 쓰이는 탄소섬유/에폭시 복합재료 프리프레그(DMS 2224)를 모델시스템으로 하여 등온환경과 등속도 가열환경에서 경화반응 속도를 연구하였다. 이 복합재료의 공정온도에서의 가공공정을 묘사할 수 있는 현상학적인 반응속도 모델을 differential scanning calorimetry (DSC)와 이론을 통하여 제안하였다. 등온환경에서의 실험으로부터 반응특성곡선을 관찰한 결과 경화반응이 1차 반응함수임을 확인하였고, 활성화 에너지는 78.43 kJ/mo1을 얻었다. 이 프리프레그는 경화온도에 따라 한계경화도를 보여주어 유리화가 존재함을 확인하였고 이를 1차 반응속도 모델에 적용시킨 결과, 유리화 이후의 확산우세현상을 포함한 반응속도 모델을 제안하였다. 제안된 모델식을 이용하여 등온/등속도 가열환경을 포함한 실제 경화공정을 성공적으로 표현할 수 있었다.

• Tribology and Lubricants
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• 제39권6호
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• pp.235-243
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• 2023

This paper presents the fabrication process of water-lubricated plastic bearings. Plastic bearings require good mechanical properties and tribological properties as well as elasticity and shock resistance, especially when lubricated in dirty water conditions. In this study, sleeve-type plastic bearings are produced by winding a prepreg sheet, which primary contains nitrile rubber (NBR)-modified epoxy, self-lubricating fillers, and various types of lattice-structured reinforcing fibers such as carbon, Aramid, and polyethylene terephthalate. A thermosetting epoxy is chemically modified with NBR to impart elasticity and low-friction characteristics in water conditions. Experimental investigations are conducted to examine the mechanical and tribological characteristics of the developed bearing materials, and the results are compared with the characteristics of a commercial plastic bearing (Thordon SXL), well known as a water-lubricated bearing. A Thordon bearing (mainly composed of polyurethane) exhibits an extremely low load-bearing capacity and is thus only suitable for medium loading (1~10MPa). The tribological characteristics of the test materials are evaluated through Falex block-on-ring (LFW-1) friction and wear tests. The results indicate that friction exhibited by the carbon-fiber-reinforced NBR-10wt.%-modified epoxy composite material, incorporated with the addition of 20wt.% UHMWPE and 6wt.% paraffin wax, is lower than that of the Thorden bearings, whereas its wear resistance surpass that of Thorden ones. Because of these features, the load carrying capacity of the fabricated composite (>10MPa) is higher than that of the Thorden bearings. These results confirm the applicability of water-lubricated plastic bearing materials developed in this study.

• 한국항공우주학회지
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• 제47권1호
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• pp.35-40
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• 2019

본 연구의 목적은 항공기 구조개발에 널리 적용되고 있는 탄소섬유 복합재의 피로특성을 확인하고, 실기체 피로시험에 활용되고 있는 자료를 획득하는 것이다. 복합재 구조의 내구성 및 손상허용성의 평가는 주로 피로시험을 통하여 이루어지며, 실기체 피로시험에 적용되고 있는 파라미터에는 피로수명계수와 하중증대계수가 있다. 탄소섬유/에폭시 일방향 및 직물형 복합재로 시편을 제작하였으며, 응력비와 적층패턴을 달리하여 피로시험을 수행하였다. Sendeckyj 모델을 적용한 와이블 분포와 개별적인 피로수명에 대한 와이블 분포를 이용하여 형상 파라미터를 분석하였다. 또한 신뢰도를 고려한 피로수명계수와 하중증대계수를 평가하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.254-257
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• 2004

An electromagnetic acoustic transducers (EMAT) can usually generate or detect an ultrasonic wave into specimens across a small gap. Especially stiffness of composites depends on layup sequence of CFRP(carbon fiber reinforced plastics) laminates because the layup of composite laminates influences there properties. It is very important to evaluate the layup errors in prepreg laminates. A nondestructive technique can therefore serve as a useful measurement for detecting layup errors. It was shown experimentally that this shear waves for detecting the presence of the errors is very sensitive. It is found that high probability shows between tests and the model developed in characterizing cured layups of the laminates. Also a C-scan method was used for detecting layup of the laminates because of extracting fiber orientation information from the ultrasonic reflection caused by structural imperfections in the laminates. Therefore, it was found that interface C-scan images show the fiber orientation information by using two-dimensional fast Fourier transform(2-D FFT).

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.154-157
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• 2005

This paper aims to investigate the tow deformation pattern with respect to shear angle and mold property during draping of plain weave carbon/epoxy prepreg. Aluminum and PVC foams with different foam density are used for the draping hemisphere molds with 250 mm diameters. Microscopic observation reveals that tow parameters like crimp angle and Y-directional tow intervals are influenced by shear angle and mold density at the same time. The correlation between crimp angle and Y-directional tow interval is also found out.