• Fibers and Polymers
• /
• 제1권2호
• /
• pp.103-110
• /
• 2000

Flow analysis of profile extrusion is essential for design and production of a profile extrusion die. Velocity, pressure, and temperature distribution in an extrusion die are predicted and compared with the experimental results. A two dimensional numerical method is proposed for three dimensional analysis of the flow field within the profile extrusion die by applying a modified cross-sectional numerical method. Since the cross-sectional shape of the die is varied gradually, it is assumed that the pressure is constant within a cross-sectional plane that is perpendicular to the flow direction. With this assumption, the velocity component in the cross-sectional direction is neglected. The exact cross-sectional shape at any position is calculated based on the geometry of standard cross-sections. The momentum and energy equations are solved with proper boundary conditions at a cross-section and then the same calculation is carried out for the next cross-section using the current calculated values. An L-shaped profile extrusion die is produced and employed for experimental investigation using a commercially available polypropylene. Numerical prediction for the varying cross-sectional shape provides better results than the previous studies and is in good agreement with the experimental results.

• Structural Engineering and Mechanics
• /
• 제62권3호
• /
• pp.273-279
• /
• 2017

A meso-scale model is proposed to study filament-wound composites with fiber undulations and crossovers. First, the crossover and undulation region is classified as the circumferential undulation and the helical undulation. Next, the two undulations are separately regarded as a series of sub-models to describe the meso-structure of undulations by using meso-parameters such as fiber orientation, fiber inclination angle, resin rich area, fiber volume fraction and bundle cross section. With the meso-structure model and the classic laminate theory, a method for calculating the stiffness of filament wound composites is eventually established. The effects of the fiber inclination angle, the fiber and resin volume fraction and the resin rich area on the stiffness are studied. The numerical results show that the elastic moduli for the circumferential undulation region decrease to a great extent as compared with that of the helical undulation region. Moreover, significant decrease in the elastic and shear moduli and increase in the Poisson's ratio are also found for the resin rich area. In addition, thickness and bundle section have evident effect on the equivalent stiffness of the fiber crossover and the undulation region.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
• /
• pp.93-96
• /
• 2000

The theory of non-prismatic folded plate structures was reported by the senior author in 1965 and 1966. Fiber reinforced composite materials are strong in tension. The structural element for such tension force is very thin and weak against bending because of small bending stiffnesses. Naturally, the box type section is considered as the optimum structural configuration because of its high bending stiffnesses. Such structures can be effectively analyzed by the folded plate theory with relative ease. The "hollow" bending member with uniform cross-section can be treated as prismatic folded plates which is a special case of the non-prismatic folded plates. Tn this paper, the result of analysis of a folded plates with one box type uniform cross-section is presented. Each plate is made of composite laminates with fiber orientation of [ABBCAAB]$_r$, with A=-B=$45^{\circ}$, and C=$90^{\circ}$. The influence of the span to depth ratio is also studied. When this ratio is 5, the difference between the results of folded plate theory and beam theory is 1.66%. is 1.66%.

• Computers and Concrete
• /
• 제11권6호
• /
• pp.515-529
• /
• 2013

The moment-curvature relation for simple bending is a well-studied subject and the classical moment-curvature diagram is commonly found in literature. The influence of axial forces has generally been considered as compression onto symmetrically reinforced cross-sections, thus strain at the reference fiber never has been an issue. However, when dealing with integral structures, which are usually statically indeterminate in different degrees, these concepts are not sufficient. Their horizontal elements are often completely restrained, which, under imposed deformations, leads to moderate compressive or tensile axial forces. The authors propose to analyze conventional beam cross-sections with moment-curvature diagrams considering asymmetrically reinforced cross-sections under combined influence of bending and moderate axial force. In addition a new diagram is introduced that expands the common moment-curvature relation onto the strain variation at the reference fiber. A parametric study presented in this article reveals the significant influence of selected cross-section parameters.

• 한국전자통신학회논문지
• /
• 제7권4호
• /
• pp.867-871
• /
• 2012

본 논문에서는 폴리머 테이퍼링 도파로 영역을 포함하는 $1{\times}4$ 형태의 플라스틱 광섬유 커플러를 제안하고 구현하였다. 플라스틱 광섬유와 폴리머 사각 도파로의 접속면에서 광 누설 손실을 줄이기 위해 단면이 원형에서 구형으로 천천히 바뀐 플라스틱 광섬유를 도입하였다. 실리콘 고무로 만들어진 주형을 이용하여 소자를 제작하였다. 제작된 소자는 1.33 dB의 삽입손실과 2.2 dB의 평탄도를 보였다.

• Fibers and Polymers
• /
• 제7권4호
• /
• pp.372-379
• /
• 2006

The surface topography, tensile properties, and thermal properties of ramie fibers were investigated as reinforcement for fully biodegradable and environmental-friendly 'green' composites. SEM micrographs of a longitudinal and cross sectional view of a single ramie fiber showed a fibrillar structure and rough surface with irregular cross-section, which is considered to provide good interfacial adhesion with polymer resin in composites. An average tensile strength, Young's modulus, and fracture strain of ramie fibers were measured to be 627 MPa, 31.8 GPa, and 2.7 %, respectively. The specific tensile properties of the ramie fiber calculated per unit density were found to be comparable to those of E-glass fibers. Ramie fibers exhibited good thermal stability after aging up to $160^{\circ}C$ with no decrease in tensile strength or Young's modulus. However, at temperatures higher than $160^{\circ}C$ the tensile strength decreased significantly and its fracture behavior was also affected. The moisture content of the ramie fiber was 9.9 %. These properties make ramie fibers suitable as reinforcement for 'green' composites. Also, the green composites can be fabricated at temperatures up to $160^{\circ}C$ without reducing the fiber properties.

• 대한토목학회논문집
• /
• 제26권3A호
• /
• pp.457-464
• /
• 2006

화이버로 보강된 복합재료는 비강성과 강도가 높을 뿐만 아니라 경량화를 위한 작업이 가능한 재료로써, 항공, 선박 그리고 토목분야와 같은 많은 산업분야에서 계속적으로 사용이 증대되고 있다. 본 연구는 전단변형을 고려한 타원단면을 갖는 복합적 층 구조물의 좌굴하중 및 모드형상을 분석하였다. 좌굴해석을 수행하기 위해, 면내회전자유도를 갖는 평면응력 요소와 휨 요소를 결합하여 무결점 4절점 쉘요소를 작성하였다. 이때 추가변형률과 대체전단변형률을 도입함으로써 요소의 거동을 개선하였다. 해석모델에 대해 쉘의 기하학적 형상, 종횡비, 화이버 보강각도, 그리고 적층배열에 따른 영향을 고찰하였다. 본 연구에서 제시한 타원단면을 갖는 적층관의 임계좌굴하중과 모드형상은 여러 가지 설계변수에 의한 거동에 대한 정확한 이해로부터 효율적인 설계방향을 제시하고자 하였으며, 추후 적층관의 좌굴해석시 좋은 참고자료로 활용할 수 있으리라 기대된다.

• Steel and Composite Structures
• /
• 제14권5호
• /
• pp.453-472
• /
• 2013

This paper presents the structural behavior of CFRP (carbon fiber reinforced polymer) strengthened CFT (concrete-filled steel tubes) columns under axial loads. Circular and square specimens were selected to investigate the retrofitting effects of CFRP sheet on CFT columns. Test parameters are cross section of CFT, D/t (B/t) ratios, and the number of CFRP layers. The load and ductility capacities were evaluated for each specimen. Structural behavior comparisons of circular and rectangular section will be represented in the experimental result discussion section. Finally, ultimate load formula of CFRP strengthened CFT will be proposed to calculate the ultimate strength of CFRP strengthened circular CFT. The prediction values are in good agreement with the test results obtained in this study and in the literature.

• 한국식품조리과학회지
• /
• 제17권6호
• /
• pp.549-554
• /
• 2001

Thermal measurements were made for connective tissues of 5 different fish muscles by using a differential scanning calorimeter(DSC), and connective tissues between muscle fibers and the cross sections of muscle fibers were observed by a light microscope. Red sea bream(cultured and wild) and flounder(cultured, cultured with obosan and wild) were used in this study. It was found that the connective tissues of cultured and frozen fish muscle required less endothermic enthalpy and the endothermic peak temperature was lower than those of wild and fresh ones when they were shrunken and denatured. Therefore, it is likely that the former are more unstable to heat than the latter. The cultured flounder fed with obosan and wild flounder which contained more collagen than cultured flounder and the wild red sea bream showed clear connective tissues between fibers. The cross-section of cultured fish muscle fiber was larger than that of wild one. From these results, collagen content and thermal properties of collagen, cross section of muscle fibers seemed to contribute to the textural difference between wild and cultured fish.

• Composites Research
• /
• 제31권4호
• /
• pp.161-170
• /
• 2018

원통형 복합재 격자 구조체는 필라멘트 와인딩 기법으로 제작되며 제작 공정에서 발생할 수 있는 섬유체적비 불균일과 수지응집층은 구조체의 강성도 및 강도에 영향을 줄 수 있다. 구조체의 주요 요소인 후프 및 헬리컬 리브의 단면 분석을 통해 섬유체적비 불균일 및 수지응집층의 존재 여부를 확인하였으며, 단면 분석 결과를 바탕으로 후프 및 헬리컬 리브에 대한 실험 및 이론적 접근을 통해 섬유체적비 불균일 및 수지응집층이 리브 요소의 강성도에 미치는 영향을 분석하였다. 섬유체적비 불균일이 후프 리브의 굽힘 거동에 영향을 미치는 것을 확인하였으며 헬리컬 리브의 경우 섬유체적비 불균일 및 수지응집층에 의해 강성도에 변화가 있음을 확인하였다.