• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2001년도 추계학술발표대회 논문집
• /
• pp.9-12
• /
• 2001

Composite materials can be used economically and efficiently in broad civil engineering applications when standards and processes for analysis, design, fabrication, construction and quality control are established. Many of the bridge systems, including the girders and cross-beams, and concrete decks behave as the special othotropic plates. Such systems with boundary conditions other than Navier or Levy solution types, or with irregular cross sections, analytical solution is very difficult to obtain. Numerical method for eigenvalue problems are also very much involved in seeking such a solution. A method of calculating the natural frequency corresponding to the first mode of vibration of beam and tower structures with irregular cross-sections was developed and reported by the author in 1974 Recently, this method was extended to two dimensional problems including composite laminates, and has been applied to composite plates with various boundary conditions with/without shear deformation effects and reported at several international conferences including the Eighth Structures Congress of American Society of Civil Engineers in 1990. In this paper, the result of application of this method to the special orthotropic plates with various boundary condition is presented.

• 전산구조공학
• /
• 제10권1호
• /
• pp.149-158
• /
• 1997

본 논문은 첨가질량이 있는 양단 단순지지 타단 자유단의 경계조건을 갖는 특별 직교 이방성 적층복합판에 대한 적용례로 제시한다. 구조물 설계시 설계자들은 구조물의 정확한 고유진동수를 계산할 필요성을 느끼나 정확한 해답을 얻기란 매우 어렵다. Pretlove는 유효질량 개념을 사용하여 첨가질량을 갖는 보의 해석 방법을 발표하였다. 그러나 이 방법은 단순보의 경우에만 유용할 뿐이다. 그러므로 본 논문에선 해석법이 간단하고, 정확하며, 임의의 경계조건과 단면을 가진 판의 해석에 매우 효과적인 김덕현의 방법으로 첨가질량이 있는 적층복합판의 고유진동수를 계산하였다.

• Journal of Mechanical Science and Technology
• /
• 제18권2호
• /
• pp.240-245
• /
• 2004

A modeling method for the modal analysis of a rotating composite cantilever beam is presented in this paper. Linear differential equations of motion are derived using the assumed mode method. For the modeling, hybrid deformation variables are employed and approximated to derive the equations of motion. Symmetrical laminated composite beams are considered to obtain the numerical results. The effects of the dimensionless angular velocity, the hub radius and the fiber orientation angle on the variations of modal characteristics are investigated.

• Composites Research
• /
• 제13권3호
• /
• pp.9-20
• /
• 2000

모든 층을 한 방향으로 적층하여 횡방향 굽힘과 축방향 인장운동이 연성되어 나타나는 복합재료 외팔보에 다중횡방향 개구형 크랙이 있는 경우에 대하여 자유진동 특성을 고찰하였다. 모든 크랙 위치에서의 파괴역학적 특성을 스프링 상수로 변환하여 산출하고 크랙사이 구간의 보를 전단변형 및 회전관성효과를 포함하여 해밀톤 원리로부터 운동방정식 및 경계조건을 유도하고, 라플라스 변환법을 사용하여 자유진동 특성에 관한 해를 구하였다. 복합재료의 설계 변수로서 섬유 체적비와 적층각을 설정하였으며, 크랙의 외형적 변수로서 크랙의 갯수, 분포 위치 및 크랙 깊이를 설정하여 이들 변수에 대한 고유진동수 및 모드형상의 변화 경향을 도출함으로써 임의의 다수 크랙이 분포되어 있는 보다 실제적인 상황에서의 진동변화에 근거를 둔 비파괴 검사가 이루어질 수 있는 방안에 대하여 연구하였다. 해석 결과 복합재료 보에 단일 크랙이 있는 경우에 비해 다중 크랙이 있는 경우가 여러 가지 변수에 대해 훨씬 복잡한 형태로 나타나고 있음을 보여준다.

• Steel and Composite Structures
• /
• 제34권2호
• /
• pp.299-308
• /
• 2020

This study aims to carry out the experimental and numerical investigation on the flexural behavior of sandwich honeycomb composite (SHC) beams reinforced with novel triaxially woven fabric composite skins. Different stacking sequences of the carbon fiber reinforcement polymer (CFRP) laminate; i.e., 0°-direction of TW (TW0), 0°-direction of UD (UD0), and 90°-direction of UD (UD90) were studied, from which the flexural behavior of SHC beam behaviors reinforced with TW0/UD0 or TW0/UD90 novel laminated skins were compared with those reinforced with UD0/90 conventional laminated skins under four-point loading. Generally, TW0/UD0 SHC beams displayed the same flexural stiffness as UD0/90 SHC beams in terms of load-deflection relationships. In contrast, TW0/UD90 SHC beams showed a 70% lower efficiency than those of UD0/90 SHC. Hence, the TW0/UD0 laminate arrangement is more effective with a mass reduction of 39% compared with UD0/90 for SHC beams, although their stiffness and shear strength are practically identical.

• 대한토목학회논문집
• /
• 제13권1호
• /
• pp.65-74
• /
• 1993

중립축에 대하여 대칭인 보강된 적층평판의 좌굴하중을 극대화 하는 최적설계를 시도하였다. 전체 평판의 무게가 일정한 가운데 적층평판을 이루는 각기 판의 두께와 보강재의 단면을 이루는 두께와 높이를 설계변수로 취하였다. 유한요소법을 이용하여 평판의 좌굴하중이 계산되었으며 최적설계는 IMSL program routine을 사용하였다. 최적설계시 나타나는 optimality condition이 고도의 비선형 연립방정식이 되므로 이경우 여러개의 국부 최적점이 발견되었다. 보강재와 평판의 각층에서의 보강섬유의 방향을 달리하며 각자의 효율성을 연구 조사하였으며 이중($0^{\circ}Beam/0^{\circ}/90^{\circ}$)s인 경우에 사장 우수한 설계를 할수 있는것으로 나타났다.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2000년도 춘계학술대회논문집
• /
• pp.1222-1227
• /
• 2000

The optimization study are carried out for helicopter rotor blades with composite box-beam spar. The objective function is to minimize the weight of rotor blades subject to frequency, aeroelastic stability and failure constraints. Design variables include the number of ply and ply angles of the laminated walls. The beam model of a hinge less rotor blade is based on a large deflection beam theory to describe the arbitrary large deflections and rotations. The p-k method and unsteady two dimensional strip theory are used to calculate aeroelastic stability boundary.

• Structural Engineering and Mechanics
• /
• 제55권1호
• /
• pp.79-92
• /
• 2015

In this study, free vibration analyses of symmetric laminated cantilever and simply supported damaged composite beams are investigated by using finite element method (FEM). Free vibration responses of damaged beams are examined using Euler Bernoulli beam and classical lamination theories. A computer code is developed by using MATLAB software to determine the natural frequencies of a damaged beam. The local damage zone is assumed to be on the surface lamina of the beam by broken fibers after impact. The damaged zone is modeled as a unidirectional discontinuous lamina with $0^{\circ}$ orientations in this study. Fiber volume fraction ($v_f$), fiber aspect ratio ($L_f/d_f$), damage length ($L_D$) and its location (${\lambda}/L$), fiber orientation and stacking sequence parameters effects on natural frequencies are investigated. These parameters are affected the natural frequency values significantly.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1997년도 가을 학술발표회 논문집
• /
• pp.163-170
• /
• 1997

The present paper describes an investigation into the application of the genetic algorithm(GA) in the optimization of structural design. Stochastic processes generate an initial population of designs and then apply principles of natural selection/survival of the fittest to improve the designs. The five test functions are used to verify the robustness and reliability of GA, and as a numerical example, minimum weight of a cantilever composite laminated beam with a mix of continuous, integer and discrete design variables is obtained by using GA with exterior penalty function method. The design problem has constraints on strength, displacements, and natural frequencies, and is formulated to a multidimensional nonlinear form. From the results, it is found that the GA search technique is very effective at finding the good optimum solution as well as has higher robustness.

• 대한기계학회논문집
• /
• 제19권3호
• /
• pp.615-622
• /
• 1995

It may be inefficient to conduct the aeroelastic analysis by using full-scale conventional finite-element analyses or experiments, from the initial design phase, for an aircraft wing which can be considered as the discontinuum complex structure with composite laminated skins. In this paper, therefore more efficient aeroelastic analysis has been conducted for a box-beam typed aircraft wing by using the equivalent continuum beam-rod model which is derived from the concept of energy equivalence. Equivalent structural properties of the continuum beam-rod model are obtained from the direct comparison of the finite-element matrices of continuum beam-rod model with those of box-beam typed aircraft wing. Numerical results by the continuum beam-rod model approach are compared with those by the conventional finite-element analysis approach to show that the continuum beam-rod model proposed herein is quite satisfactory as a simplified model of aircraft wing structure for aeroelastic analyses.