• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.67-70
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• 2005

The carbon fiber reinforced/epoxy laminated composites were fabricated with initial fiber failures within the unidirectional fiber pre-pregnated ply. The fiber failures were made intentionally either parallel to and/or perpendicular to the unidirectional fibers within the ply. The pre-made clear-cut cracks were found to be healed partially after laminating process. The laminates were impacted with or without initial fiber failures within the laminates. The force versus deflection curves were compared. The partially healed laminates showed the reduced laminate stiffness as compared to those without any intentional fiber failures. The impact curves were compared with size and the location of the initial failures varied.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.410-414
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• 2004

Under longitudinal loading continuous fiber reinforced metal matrix composite(MMC) have interpreted an outstanding performance. However, the applicability of continuous fiber reinforced MMCs is somewhat limited due to their relatively poor transverse properties. Therefore, the transverse properties of MMCs are significantly influenced by the properties of the fiber/matrix interface. In this study, elastic-plastic behavior of transversely loaded unidirectional fiber reinforced metal matrix composites investigated by using elastic-plastic finite element analysis. Different fiber placement(square and hexagon) and fiber volume fractions were studied numerically. The interface was treated as three thin layer (with different properties) with a finite thickness between the fiber and the matrix. The analyses were based on a two-dimensional generalized plane strain model of a cross-section of an unidirectional composite by the ANSYS finite element analysis code.

• Fibers and Polymers
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• 제7권4호
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• pp.380-388
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• 2006

Fully biodegradable and environment-friendly green composite specimens were made using ramie fibers and soy protein concentrate (SPC) resin. SPC was used as continuous phase resin in green composites. The SPC resin was plasticized with glycerin. Precuring and curing processes for the resin were optimized to obtain required mechanical properties. Unidirectional green composites were prepared by combining 65% (on weight basis) ramie fibers and SPC resin. The tensile strength and Young's modulus of these composites were significantly higher compared to those of pure SPC resin. Tensile and flexural properties of the composite in the longitudinal direction were moderate and found to be significantly higher than those of three common wood varieties. In the transverse direction, however, their properties were comparable with those of wood specimens. Scanning electron microscope (SEM) micrographs of the tensile fracture surfaces of the green composite indicated good interfacial bonding between ramie fibers and SPC resin. Theoretical values for tensile strength and Young's modulus, calculated using simple rule of mixture were higher than the experimentally obtained values. The main reasons for this discrepancy are loss of fiber alignment, voids and fiber compression due to resin shrinking during curing.

• 한국재료학회지
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• 제23권9호
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• pp.531-536
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• 2013

This paper investigates the effect of prolonged high temperature exposure on concentric laminated $Al_2O_3-ZrO_2$ composites. An ultrafine scale microstructure with a cellular 7 layer concentric lamination with unidirectional alignment was fabricated by a multi-pass extrusion method. Each laminate in the microstructure was $2-3{\mu}m$ thick. An alternate lamina was composed of 75%$Al_2O_3$-(25%m-$ZrO_2$) and t-$ZrO_2$ ceramics. The composite was sintered at $1500^{\circ}C$ and subjected to $1450^{\circ}C$ temperature for 24 hours to 72 hours. We investigated the effect of long time high temperature exposure on the generation of residual stress and grain growth and their effect on the overall stability of the composites. The residual stress development and its subsequent effect on the microstructure with the edge cracking behavior mechanism were investigated. The residual stress in the concentric laminated microstructure causes extensive micro cracks in the t-$ZrO_2$ layer, despite the very thin laminate thickness. The material properties like Vickers hardness and fracture toughness were measured and evaluated along with the microstructure of the composites with prolonged high temperature exposure.

• 한국항공우주학회지
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• 제34권10호
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• pp.24-31
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• 2006

본 논문에서는 유연수지 복합재료에 대하여 기하학적 비선형해석을 수행하였다. 실제 랜덤한 섬유배열을 사각배열과 육각배열로 가정하고 각각에 대해 단위구조를 정의하였다. 다양한 하중상태를 수치적으로 모사하여 단위구조해석을 통해 전체 구조물의 응력-변형률 선도를 예측하였고 이로부터 등가물성치를 계산하였다. 해석시 유연수지의 초탄성 성질을 정의하기 위해 Mooney-Rivlin모델을 사용하였다. 계산결과, 유연수지 복합재료 구조물은 변형률 증가에 따라 비선형의 응력-변형률 관계를 보였다. 비선형성은 횡방향 하중 상태에서 더욱 두드러지게 나타났으며, 이 경우 복합재 단면의 섬유배열 형태에 따라 상당한 차이를 보여주었다.

• 한국군사과학기술학회지
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• 제9권3호
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• pp.88-94
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• 2006

In order to substitute current aluminum sabot and to increase the penetration performance of the kinetic energy projectiles, the research and development program for composites sabot has been conducted. For carbon/epoxy composites sabot, unidirectional carbon fiber reinforced epoxy prepreg was chosen and thick sectioned composites preforms with the different fiber angles along the circumferential direction of sabot were prepared by compression molding under the careful processing conditions at $150^{\circ}C$ for 1hour with $70kgf/cm^2$ curing pressure. The composites sabot demonstrated a weight reduction by approximately 30% than that of current aluminum sabot. The muzzle velocity of a kinetic energy projectile with composites sabot was measured to be about 63m/s higher than that with aluminum sabot. These results imply that the penetration performance is expected to be considerably increased when the composite sabot is applied to the kinetic energy projectiles.

• 한국안전학회지
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• 제25권3호
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• pp.34-39
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• 2010

Unidirectional Carbon Fiber Reinforced Plastics (CFRP) are advanced materials which combine the characteristics of the light weight, high stiffness and strength. For those reasons, the use of the unidirectional CFRP has increased in jet fighters, aerospace structures. However, unidirectional CFRP composites have a lot of problems, especially delamination, compared with traditional materials such as steels and aluminums, and so forth. Therefore, the interlaminar fracture toughness for a laminate CFRP composite is very important. In this study, The mode II interlaminar fracture toughness was measured by using center notched flexure(CNF) test specimen. The CNF specimens using unidirectional carbon prepreg were fabricated by a hot-press with the gage pressure and temperature controller. And three kinds of a/L ratio was applied to these specimens. Here, we discuss the relations of the crack growth and the mode II interlaminar fracture under the four point bending CNF test. From the results, we shows that mode II interlaminar was occurred when the more $a_0$/L ratio, the less load. And $G_{IIC}$ also were obtained as 5.33, 2.9 and $0.58kJ/m^2$ according to $a_0$/L ratio=0.2, 0.3 and 0.4.

• 대한금속재료학회지
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• 제50권9호
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• pp.697-702
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• 2012

In this study, unidirectional and plain woven carbon fiber reinforced magnesium matrix composite laminates were fabricated by the liquid pressing infiltration process, and evolutions of the microstructure and compressive strength of the composite laminates under corrosion were investigated by static immersion tests. In the case of the unidirectional composite laminate, the main microstructural damage during immersion appeared as a form of corrosion induced cracks, which were formed at both CF/Mg interfaces and the interfaces between layers. On the otherhand, wrap/fill interface cracks were mainly formed in the plain woven composite laminate, without any cracks at the CF/Mg interface. The formation of these cracks was considered to be associated with internal thermal residual stress, which was generated during cooling after the fabrication process of these materials. As a consequence of the corrosion induced cracks, the thickness of both laminates increased in directions vertical to the fibers with increasing immersion time. With increasing immersion time, the compressive strengths of both composite laminates also decreased continuously. It was found that the plain woven composite laminates have superior corrosion resistance and stability under a corrosive condition than unidirectional laminates.

• 폴리머
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• 제25권3호
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• pp.435-440
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• 2001

본 연구에서는 일방향 탄소/탄소 복합재료에 산화억제제로 사용된 $MoSi_2$의 첨가량에 따른 복합재료의 부착력, 파괴인성 그리고 충격강도와의 관계를 고찰하였다. 산화억제제로 사용한 이규화 몰리브덴 (MoSi$_2$)은 복합재료의 내산화 특성을 향상시키기 위하여 각각 4, 12, 20wt%의 중량비로 페놀수지에 함침시켰다. 본 연구에 있어서 복합재료의 부착력은 접촉각 측정에 의한 Wilhelmy 방정식을 사용하여 계산하였다. 파괴인성과 충격강도는 임계 세기인자 측정을 위한 3점 굴곡 시험 방법과 Izod 충격시험에 의해 각각 측정하였다. 그 결과, $MoSi_2$가 첨가된 탄소/탄소 복합재료의 파괴인성과 충격강도는 증가하였다. 특허 l2wt%의 $MoSi_2$가 첨가된 복합재료가 London dispersive 요소($W_A\;^L$)의 증가에 의한 가장 큰 부착력을 나타내었으며, 이는 복합재료의 각 구성요소간의 계면결합력 증가에 따른 결과라 사료된다.

• Structural Engineering and Mechanics
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• 제34권4호
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• pp.525-539
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• 2010

Polymer matrix composites are widely used in many engineering applications as they can be customized to meet a desired performance while not only maintaining low cost but also reducing weight. Polymers can experience viscoelastic-viscoplastic response when subjected to external loadings. Various reinforcements and fillers are added to polymers which bring out more complexity in analyzing the timedependent response. This study formulates an integrated micromechanical model and finite element (FE) analysis for predicting effective viscoelastic-viscoplastic response of polymer based hybrid composites. The studied hybrid system consists of unidirectional short-fiber reinforcements and a matrix system which is composed of solid spherical particle fillers dispersed in a homogeneous polymer constituent. The goal is to predict effective performance of hybrid systems having different compositions and properties of the fiber, particle, and matrix constituents. A combined Schapery's viscoelastic integral model and Valanis's endochronic viscoplastic model is used for the polymer constituent. The particle and fiber constituents are assumed linear elastic. A previously developed micromechanical model of particle reinforced composite is first used to obtain effective mechanical properties of the matrix systems. The effective properties of the matrix are then integrated to a unit-cell model of short-fiber reinforced composites, which is generated using the FE. The effective properties of the matrix are implemented using a user material subroutine in the FE framework. Limited experimental data and analytical solutions available in the literatures are used for comparisons.