• Composites Research
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• v.16 no.2
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• pp.33-40
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• 2003

In order to overcome one of the most pronounced shortcomings of conventional laminated composites, such as the low damage tolerance due to delamination, the thermoplastic materials and 3D (three-dimensional) preforms have been utilized in the manufacture of composite materials. From the newly developed process termed as the co-braiding, hybrid yarns of the thermoplastic fibers (PEEK) and reinforcing fibers (carbon) have been fabricated. In order to further enhance the delamination suppression, through thickness fibers have been introduced by way of 3D weaving technique in the fabrication of textile preforms. The preforms have been thermoformed to make composite materials. Complete impregnation of the PEEK into the carbon fiber bundles has been confirmed. For the comparison of mechanical performance of 3D woven composites, quasi-isotropic laminates using APC-2/AS4 tapes have been fabricated. Tensile and compressive properties of both the composites have been determined. Furthermore. the open hole, impact and CAI(Compression After Impact) tests were also carried out to assess the applicability of 3D woven textile reinforced thermoplastic composites in aerospace structures.

• Composites Research
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• v.35 no.4
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• pp.269-276
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• 2022

In this paper, a composite stiffened panel was fabricated using a three-dimensional weaving method that can reduce the risk of delamination, and mechanical properties such as buckling load and natural frequency were investigated. The preform of the stringer and skin of the stiffened panel were fabricated in one piece using T800 grade carbon fiber and then, resin (EP2400) was injected into the preform. The compression test and natural frequency measurement were performed for the stiffened panel, and the results were compared with the finite element analyses. In order to compare the performance of 3D weaving structures, the stiffened panels with the same configuration were fabricated using UD and 2D plain weave (fabric) prepregs. Compared to the tested buckling load of the 3D woven panel, the buckling loads of the stiffened panels of UD prepreg and 2D plain weave exhibited +20% and -3% differences, respectively. From this study, it was confirmed that the buckling load of the stiffened panel manufactured by 3D weaving method was lower than that of the UD prepreg panel, but showed a slightly higher value than that of the 2D plain weave panel.

• Composites Research
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• v.32 no.1
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• pp.65-70
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• 2019

The aircraft composites wing parts are usually integrated with adhesive or fastener. These laminated composites have weak interlaminar strength, which can lead to delamination. In order to compensate the disadvantages of laminated composites, it is possible to improve the strength, durability, shock and fatigue resistance by reinforcing the fiber in the thickness direction. In addition, using a single structure near-net-shape saves the manufacturing time and the number of fasteners, thus can reduce the overall cost of the composite parts. In this study, compression test, tensile test and open-hole tensile test are carried out for three structural architecture of 3D (three-dimensional) textile preforms: orthogonal(ORT), layer-to-layer(LTL) and through-the-thickness(TTT) patterns. Among these, the orthogonal textile composite shows the highest Young's modulus and strength in tensile and compression. The notch sensitivity of the orthogonal textile composite was the smallest as compared with UD (unidirectional) and 2D (two-dimensional) fabric laminates.

• Composites Research
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• v.30 no.5
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• pp.297-302
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• 2017

Finite element analysis of T-beam laminate structure under bending-torsional loading was conducted to prevent the delamination which is the major failure behavior on laminated composites. Three-dimensional preform, which is that fabric is braided through thickness direction, is suggested from the laminate analysis. The analysis aimed to optimize the fiber ratio in laminated composites. After it is suggested that guideline for design of T-beam structure using commercial software ANSYS Composites PrePost. The results show that strength of T-beam structure is increased 21.6% when the fiber density along with beam length direction is two times bigger than transverse direction. It is expected that development of high strength T-beam structure using designed three-dimensional preform.

• Composites Research
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• v.32 no.5
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• pp.206-210
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• 2019

As the use of composite materials of woven structure has expanded to various fields such as automobile and aviation industry, there has been a need for reliability problems and prediction of mechanical properties of woven composites. In this study, finite element analysis for predicting the mechanical properties of composite materials with different weaving structures was conducted to verify similarity with experimental static properties and an effective modeling method was developed. To reflect the characteristics of the weave structure, the meso-scale representative volume element (RVE) was used in modeling. Three-dimensional modeling was carried out by separating the yarn and the pure matrix. Hashin's failure criterion was used to determine whether the element was failed, and the simulation model used a progressive failure model which was suitable for the composite material. Finally, the accordance of the modeling and simulation technique was verified by successfully predicting the mechanical properties of the composite material according to the weave structure.

• Journal of Aerospace System Engineering
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• v.16 no.6
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• pp.8-17
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• 2022

This paper presents a novel geometric modeling technique to predict the mechanical properties of an aircraft wing's skin-stringer integrated panel. Due to mechanical and adhesive fastening, this panel is vulnerable to stress concentration and debonding, so we designed it to integrate the skin and stringer using three-dimensional woven composites. Geometric modeling was conducted by measuring the geometric parameters of the specimen and defining the pattern of the yarns as functions. We used a weighted average model with iso-strain and iso-stress assumptions to predict the mechanical properties of the panel parts. We then compared the results of a finite element analysis with a compression test to verify the accuracy of our model. Our proposed technique proved to be more efficient than the traditional experimental method for predicting the mechanical properties of skin-stringer integrated panels.

• Composites Research
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• v.33 no.3
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• pp.115-124
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• 2020

Laminate composites, especially Carbon fiber-reinforced composites are wide used in various industry such as aerospace and automotive industry due to their high specific strength and specific stiffness. However, the laminate composites has a big disadvantage that delamination occurs because the arrangement of the fibers is all arranged in the in-plane direction, which limits the field of application of the laminate composites. In this study, we first developed a laminate composites T-beam in which π-beam and flat plate were combined and optimized the design parameters through structural analysis and mechanical tests. Afterwards, 3D weave preform T-beam was developed by applying the same design parameters of laminate composites T-beams, and improved mechanical strength was achieved compared to laminated structures. These findings are expected to be applicable to existing laminated composite structures that require increased strength.

• Composites Research
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• v.35 no.2
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• pp.106-114
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• 2022

Carbon fiber-reinforced plastic, well known high specific strength and high specific stiffness, have been widely used in the aircraft industry. Mostly the CFRP structure is fabricated by lamination of carbon fiber or carbon prepreg, which has major disadvantage called delamination. Delamination is usually produced due to absence of the through-thickness direction fiber. In this study, three-dimensional carbon preform woven in three directions is used for fabrication of aircraft wing unit structure, a part of repeated structure in aircraft wing. The unit structure include skin, stringer and rib were prepared by resin transfer molding method. After, the 3D structure was compared with laminate structure through compression test. The results show that 3D structure is not only effective to prevent delamination but improved the mechanical strength. Therefore, the 3d preform structure is expected to be used in various fields requiring delamination prevention, especially in the aircraft industry.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1410-1415
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• 2007

Recently introduced WBK(Wire-wounded Bulk Kagome) shows relatively superior mechanical properties compared to other types of PCM. WBK is fabricated by assembling helical wires in 6 directions. Wire being a helix, the wire's geometric properties like pitch and helical radius shows certain geometric characteristics which can play some critical role in setting up an automatic fabrication process. In this study, geometry of WBK is modeled by various transformations of a piece of helical wire and the characteristics of the geometry of an element of WBK truss are discussed. In addition, the roles of pitch and helical radius of wire in optimizing the assembling process are described and the derivation of criteria is attempted to decide proper helical radius which would maintain minimal interference between wires at the crossings.

• Journal of the Korean Society of Costume
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• v.45
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• pp.5-16
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• 1999

본 연구의 목적은 Navajo 직물의 역사적 발달을 고전시대를 중심으로 살펴보고 특히 외부영향에 따른 직물의 변화를 고찰하는데 있다. 구체적으로 1) 고전시대의 전통적인 직물은 어떻게 발달하였는가\ulcorner 2) 고전시대 직물의 전통적 요소와 외부영향요인은 어떤 점이 다른가\ulcorner 예 초점을 맞추었다. 연구방법은 아메리카 인디언의 이동,문화 Navajo 직조 및 직물에 대한 문헌을 바탕을 조사하였고 아리조나 주립박물과 아리조나 역사 박물관을 방문하였으며 박물관 안에 있는 전문가들의 조언을 듣고 연구의 자료를 보완하였다. 또 비교 미학적 차원에서 고전시대 navajo 직물의 전통적 요소와 외부영향 요인을 분석하였고 외부영향을 받은 직물의 예를 시각적자료로 제시하였다. 이연구는 인디언직물에 대한 이해, 고전시대. Navajo 직물의 문헌고찰을 통한 민족의복의 문화적측면에 기여할수 이고 현대적 감각을 지닌 Navajo 직물을 한국직물에 접목 응용하는데 도움을 줄수 있다 본 연구의 결과는 다음과 같다. 1. Navajo 직물을 고전, 전환, 양탄자 시대로 구분되었고. 이중에서 고전시대가 navajo 직물의 특성을 가장 잘 나타내었으며 발달된 직조기술을 보였다. Navajo인들의 직조기술은 1863년경 최고조에 달했다. Navajo 직물의 디자인 주제로 주로 인간을 둘러싸고 있는 환경에서 얻어졌고 이것들은 직선의 기하학적 형태로 구체화되었다. 또한 직물에 표현된 색도 자연과 밀접한 관련성을 갖는 있었다. 2. Navajo 직물의 주용한 용도는 여성용 드레스, 남성용 셔츠는 어깨에 걸치는 두르개였다. 여성용 드레스는 동일한 크기의 직물의 두장을 직조한 후에 꿰매었고 남성용 셔츠는 머리가 들어갈수 있는 구멍이 있는 장방형 판쵸 스타일이었다. 어깨에 걸치는 두르개는 여성의 경우 가운데가 검은색이고 가장자리가 푸른색인형태오 흰색과 붉은 색이 교대로 나타나는 형태의 2가지가 있었고 남성용은 고전시대의 대표라고 일컬어지는 족장 두르개였다. 3. Navajo 직물은 외부의 영향을 받아 많은 변화를 가져왔다. 즉 스페인 사람들로 인하여 면 섬유대신 양모섬유를 사용하게 되었고 전통적 모양과 다른직물이 출현하게 되었다. 또한 인디고 염류, 색소니 실, 바에타 직물의 도입으로 다양한 색상의 표현이 가능해졌고 이와 관련하여 다이아몬드 십자형 톱니형 무늬드이 나타나게 되었다. 4, 고전시대를 대표하는 직물로 족장 두르개, 쇼올, 안장덮개를 들수 있으며 이 직물들에서 뚜렷하게 외부영향 요인을볼수 있다. 즉 족장 두르개의 가장 정교한 단계에서 다이아몬드 무늬가 가장가리 가운데 모서리에 위치하여 9지점 배치를 이룬 것 쇼올의 경우 폭보다 길이가 긴 형태의 비전통적 모습을 나타낸 것 안장덮개에서 보여지는 여덟포인트 별 무늬도 외부의 영향을 받은예이다. 뛰어난 직조기술로 유명한 navajo인들은 변화에 잘 적응하는 특성을 갖고 있었다. 외부의 영향을 그들은 긍정적으로 받아들였고 자기 자신들의 필요에 맞도록 수정하여 정체감을 잃지 않으면서도 문화를 발전시켰다. 따라서 고전시대의 Navajo 직물은 고유적 요인과 외래적 요인의 조화를잘 나타내고 있으며 디자인의 탁월함이 세련됨 천연염료와 인조염료의 배\ulcorner에 의한 색상의 우월성 등으로 오늘까지 높이 평가되고있다.