• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2008년도 추계학술대회 논문집
• /
• pp.593-594
• /
• 2008

• 한국해양공학회지
• /
• 제34권6호
• /
• pp.481-488
• /
• 2020

Composite materialsuch as glass-fiber reinforced plastic and carbon-fiber reinforced plastic (CFRP) shows anisotropic property and have been widely used for structural members and outfitings of ships. The structural safety of composite structures has been generally evaluated via finite element analysis. This paper presents a technique for updating the finite element model of anisotropic beams or plates via natural frequencies. The finite element model updates involved a compensation process of anisotropic material properties, such as the elastic and shear moduli of orthotropic structural members. The technique adopted was based on a discrete genetic algorithm, which is an optimization technique. The cost function was adopted to assess the optimization problem, which consisted of the calculated and referenced low-order natural frequencies for the target structure. The optimization process was implemented with MATLAB, which includes the finite element updates and the corresponding natural frequency calculations with MSC/NASTRAN. Material properties of a virtual cantilevered orthotropic beam were estimated to verify the presented method and the results obtained were compared with the reference values. Furthermore, the technique was applied to a cantilevered CFRP beam to successfully estimate the unknown material properties.

• 한국강구조학회 논문집
• /
• 제18권6호
• /
• pp.737-746
• /
• 2006

본 연구에서는 리브로 보강된 GFRP(Glass Fiber Reinforced Plastic) 관로의 탄성 좌굴 강도를 산정하였다. 보강된 리브의 두께, 높이, 배치 간격은 관로의 좌굴 강도에 영향을 미치는 주요 인자이다. 또한, GFRP 재료는 이방성 재료이므로, 재료의 방향별 강성 또한 관로의 좌굴강도에 영형을 미치는 인자로서 고려되어야할 부분이다. 이러한 매개변수를 적용하여, 직교 이방성 재료로 구성된 리브 보강 관로의 좌굴 강도를 유한요소 해석을 이용하여 매개변수를 수행하고, 회귀분석을 통하여 좌굴 강도 산정을 위한 간략식을 제시하였다.

• Structural Engineering and Mechanics
• /
• 제37권5호
• /
• pp.529-542
• /
• 2011

Three dimensional solutions for free vibrations analysis of functionally graded fiber reinforced cylindrical panel are presented, using differential quadrature method (DQM). The orthotropic panel is simply supported at the edges and is assumed to have an arbitrary variation of reinforcement volume fraction in the radial direction. Suitable displacement functions that identically satisfy the simply supported boundary condition are used to reduce the equilibrium equations to a set of coupled ordinary differential equations with variable coefficients, which can be solved by differential quadrature method to obtain natural frequencies. The main contribution of this work is presenting useful results for continuous grading of fiber reinforcement in the thickness direction of a cylindrical panel and comparison with similar discrete laminate composite ones. Results indicate that significant improvement is found in natural frequency of a functionally graded fiber reinforced composite panel due to the reduction in spatial mismatch of material properties.

• Steel and Composite Structures
• /
• 제30권1호
• /
• pp.1-12
• /
• 2019

In this research, an efficient mixed mode I/II fracture criterion is developed for fracture investigation of orthotropic materials wherein crack is placed along the fibers. This criterion is developed based on extension of well-known Maximum Tensile Stress (MTS) criterion in conjunction with a novel material model titled as Equivalent Reinforced Isotropic Model (ERIM). In this model, orthotropic material is replaced with an isotropic matrix reinforced with fibers. A comparison between available experimental observations and theoretical estimation implies on capability of developed criterion for predicting both crack propagation direction and fracture instance, wherein the achieved fracture limit curves are also compatible with fracture mechanism of orthotic materials. It is also shown that unlike isotropic materials, fracture toughness of orthotic materials in mode $I(K)_{IC}{\mid})$ cannot be introduced as the maximum load bearing capacity and thus new fracture mechanics property, named here as maximum orthotropic fracture toughness in mode $I(K_{IC}{\mid}^{ortho}_{max})$ is defined. Optimum angle between crack and fiber direction for maximum load bearing in orthotropic materials is also defined.

• 한국해양공학회지
• /
• 제18권3호
• /
• pp.13-19
• /
• 2004

The structural behavior of a worn tire, attached to carbon fiber steel pile by current and wave forces, has been investigated through the numerical method. The finite element model has been developed, by considering that the composite material of rubber and cord is orthotropic, the rubber is isotropic, and that all the material behaves as linear elastic. The pressure distribution by wave and current, around the worn tire, has been estimated through the adjustment for the concept of flow separation. Also, the structural behavior of the worn tire has been examined, by comparing the situation wherein the space between the pile is reinforced, and tire as elastic and isotropic material, with the one left empty. Through this comparison, it is determined that the space between pile and tire has to be filled with elastic and isotropic material, in order to avoid the failure by wave and current action.

• Wind and Structures
• /
• 제3권2호
• /
• pp.83-96
• /
• 2000

Due to their high corrosion and chemical resistance, fiber reinforced plastics (FRP) are becoming widely used as the main structural material for industrial chimneys. However, no national code currently exists for the design of such type of chimneys. The purpose of this study is to investigate analytically the response of FRP chimneys to wind loads. The classical lamination theory is used to substitute the angle-ply laminate of a FRP chimney with an equivalent orthotropic material that provides the same stiffness. Dynamic wind loads are applied to the equivalent chimney to evaluate its response to both along and across wind loads. A parametric study is then conducted to identify the material and geometric parameters affecting the response of FRP chimneys to wind loads. Unlike the across-wind response, the along-wind tip deflection is found to be highly dependent on the angle of orientation of the fibers. In general, the analysis shows that FRP chimneys are very vulnerable to across-wind oscillations resulting from the vortex shedding phenomenon.

• Structural Engineering and Mechanics
• /
• 제57권1호
• /
• pp.105-126
• /
• 2016

In the present study, modelling and vibration control of axially moving laminated Carbon nanotubes/fiber/polymer composite (CNTFPC) plate under initial tension are investigated. Orthotropic visco-Pasternak foundation is developed to consider the influences of orthotropy angle, damping coefficient, normal and shear modulus. The governing equations of the laminated CNTFPC plates are derived based on new form of first-order shear deformation plate theory (FSDT) which is simpler than the conventional one due to reducing the number of unknowns and governing equations, and significantly, it does not require a shear correction factor. Halpin-Tsai model is utilized to evaluate the material properties of two-phase composite consist of uniformly distributed and randomly oriented CNTs through the epoxy resin matrix. Afterwards, the structural properties of CNT reinforced polymer matrix which is assumed as a new matrix and then reinforced with E-Glass fiber are calculated by fiber micromechanics approach. Employing Hamilton's principle, the equations of motion are obtained and solved by Hybrid analytical numerical method. Results indicate that the critical speed of moving laminated CNTFPC plate can be improved by adding appropriate values of CNTs. These findings can be used in design and manufacturing of marine vessels and aircrafts.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 1999년도 추계학술발표대회 논문집
• /
• pp.211-214
• /
• 1999

The stress distribution around the cutout of composite cylindrical shells with a circular or elliptical reinforced cutout subjected to axial compression or tension is studied by asymptotic method. Analytical solutions used a Donnell type orthotropic shell theory are presented by the defined stress concentration factor and are compared to experimental results. The experiment used the universal testing machine (UTM), strain gage and fixtures designed/manufactured for axial tension test of a cylindrical shell is carried and the composite material used in the experiment is plain weave glass fiber reinforced plastic (GFRP).

• 비파괴검사학회지
• /
• 제13권1호
• /
• pp.7-14
• /
• 1993

In order to analyze the stress distribution and stress concentration factors in composite materials, especially, in the short fiber of the reinforced composite materials by photoelastic method, it is necessary to develop the photoelastic model material having short fibers with arbitrary size and orientation. In this paper, the orthotropic photoelastic model material having short fibers for the transparent type photoelastic device was developed by the embedded corrosion fiber method. It was found that the model material was satisfactory to the properties of photoelastic model material, and also that the embedded corrosion fiber method can be employed for developing a model material with arbitrary size and direction to analyze the stress distribution and crack problems of composite materials.