• Structural Engineering and Mechanics
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• 제45권5호
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• pp.677-691
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• 2013

A semi-analytical finite strip method is developed for analyzing the post-buckling behavior of rectangular composite laminated plates of arbitrary lay-up subjected to progressive end-shortening in their plane and to normal pressure loading. In this method, all the displacements are postulated by the appropriate harmonic shape functions in the longitudinal direction and polynomial interpolation functions in the transverse direction. Thin or thick plates are assumed and correspondingly the Classical Plate Theory (CPT) or Higher Order Plate Theory (HOPT) is applied. The in-plane transverse deflection is allowed at the loaded ends of the plate, whilst the same deflection at the unloaded edges is either allowed to occur or completely restrained. Geometric non-linearity is introduced in the strain-displacement equations in the manner of the von-Karman assumptions. The formulations of the finite strip methods are based on the concept of the principle of the minimum potential energy. The Newton-Raphson method is used to solve the non-linear equilibrium equations. A number of applications involving isotropic plates, symmetric and unsymmetric cross-ply laminates are described to investigate the through-thickness shearing effects as well as the effect of pressure loading, end-shortening and boundary conditions. The study of the results has revealed that the response of the composite laminated plates is particularly influenced by the application of the Higher Order Plate Theory (HOPT) and normal pressure loading. In the relatively thick plates, the HOPT results have more accuracy than CPT.

• 한국추진공학회지
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• 제2권3호
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• pp.1-9
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• 1998

풍력에너지는 자연의 에너지를 이용하므로써 환경문제와 경제적 측면에서 다른 대체 에너지보다 훨씬 유리하여 세계 여러 나라에서 각광을 받고 있다. 경제적인 이유로 풍력발전을 위한 회전날개가 대형화 되고 있으며, 경량화를 위해 복합재 구조등의 첨단 항공기술이 적용되고 있는 추세이다. 본 연구에서는 500㎾급 중형 풍력 발전시스템을 개발함에 있어, 적합한 공력 성능을 갖는 경량화 복합재 회전날개의 개선 설계를 수행하였다. 회전날개의 경량화를 위해 기 설계된 쉘-스파 구조물을 쉘-스파-샌드위치 구조물로 설계를 수정하였고, 배선형 해석을 통해서 경량화에 따른 대변형 문제를 검토하였으며, 파괴응력보다 낮은 상태에서 발생되는 국부좌굴에 의한 구조물의 안전성을 검토하였다. 또한, 허브의 금속재 삽입부분의 전단핀에 의한 핀 홀 주위의 응력해석을 수행하여 충분히 안전함을 확인하였고, 수정 설계된 구조물이 운용구간내에서 공진이 발생하지 않음을 확인하였다.

• Structural Engineering and Mechanics
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• 제68권5호
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• pp.603-619
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• 2018

In this research, an effective computational technique is carried out for nonlinear and post-buckling analyses of cracked imperfect composite plates. The laminated plates are assumed to be moderately thick so that the analysis can be carried out based on the first-order shear deformation theory. Geometric non-linearity is introduced in the way of von-Karman assumptions for the strain-displacement equations. The Ritz technique is applied using Legendre polynomials for the primary variable approximations. The crack is modeled by partitioning the entire domain of the plates into several sub-plates and therefore the plate decomposition technique is implemented in this research. The penalty technique is used for imposing the interface continuity between the sub-plates. Different out-of-plane essential boundary conditions such as clamp, simply support or free conditions will be assumed in this research by defining the relevant displacement functions. For in-plane boundary conditions, lateral expansions of the unloaded edges are completely free while the loaded edges are assumed to move straight but restricted to move laterally. With the formulation presented here, the plates can be subjected to biaxial compressive loads, therefore a sensitivity analysis is performed with respect to the applied load direction, along the parallel or perpendicular to the crack axis. The integrals of potential energy are numerically computed using Gauss-Lobatto quadrature formulas to get adequate accuracy. Then, the obtained non-linear system of equations is solved by the Newton-Raphson method. Finally, the results are presented to show the influence of crack length, various locations of crack, load direction, boundary conditions and different values of initial imperfection on nonlinear and post-buckling behavior of laminates.

• 한국공간구조학회논문집
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• 제20권4호
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• pp.149-158
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• 2020

The governing equation for a dome-type shallow spatial truss subjected to a transverse load is expressed in the form of the Duffing equation, and it can be derived by considering geometrical non-linearity. When this model under constant load exceeds the critical level, unstable behavior is appeared. This phenomenon changes sensitively as the number of free-nodes increases or depends on the imperfection of the system. When the load is a periodic function, more complex behavior and low critical levels can be expected. Thus, the dynamic unstable behavior and the change in the critical point of the 3-free-nodes space truss system were analyzed in this work. The 4-th order Runge-Kutta method was used in the system analysis, while the change in the frequency domain was analyzed through FFT. The sinusoidal wave and the beating wave were utilized as the periodic load function. This unstable situation was observed by the case when all nodes had same load vector as well as by the case that the load vector had slight difference. The results showed the critical buckling level of the periodic load was lower than that of the constant load. The value is greatly influenced by the period of the load, while a lower critical point was observed when it was closer to the natural frequency in the case of a linear system. The beating wave, which is attributed to the interference of the two frequencies, exhibits slightly more behavior than the sinusoidal wave. And the changing of critical level could be observed even with slight changes in the load vector.

• Structural Engineering and Mechanics
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• 제90권1호
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• pp.83-96
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• 2024

This paper suggests an analytical approach to investigate the free vibration and stability of functionally graded (FG) beams with both perfect and imperfect characteristics using a quasi-3D higher-order shear deformation theory (HSDT) with stretching effect. The study specifically focuses on FG beams resting on variable elastic foundations. In contrast to other shear deformation theories, this particular theory employs only four unknown functions instead of five. Moreover, this theory satisfies the boundary conditions of zero tension on the beam surfaces and facilitates hyperbolic distributions of transverse shear stresses without the necessity of shear correction factors. The elastic medium in consideration assumes the presence of two parameters, specifically Winkler-Pasternak foundations. The Winkler parameter exhibits variable variations in the longitudinal direction, including linear, parabolic, sinusoidal, cosine, exponential, and uniform, while the Pasternak parameter remains constant. The effective material characteristics of the functionally graded (FG) beam are assumed to follow a straightforward power-law distribution along the thickness direction. Additionally, the investigation of porosity includes the consideration of four different types of porosity distribution patterns, allowing for a comprehensive examination of its influence on the behavior of the beam. Using the virtual work principle, equations of motion are derived and solved analytically using Navier's method for simply supported FG beams. The accuracy is verified through comparisons with literature results. Parametric studies explore the impact of different parameters on free vibration and buckling behavior, demonstrating the theory's correctness and simplicity.

• Steel and Composite Structures
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• 제14권5호
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• pp.409-429
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• 2013

A composite box-girder with corrugated steel webs has been used in civil engineering practice as an alternative to the conventional pre-stressed concrete box-girder because of several advantages, such as high shear resistance without vertical stiffeners and an increase in the efficiency of pre-stressing due to the accordion effect. Many studies have been conducted on the shear buckling and flexural behavior of the composite box-girder with corrugated steel webs. However, the torsional behavior is not fully understood yet, and it needed to be investigated. Prior study of the torsion of the composite box-girder with corrugated steel webs has been developed by assuming that the concrete section is cracked prior to loading and doesn't have tensile resistance. This results in poor estimation of pre-cracking behaviors, such as initial stiffness. To overcome this disadvantage of the previous analytical model, an improved analytical model for torsion of the composite box-girder with corrugated steel webs was developed considering the concrete tension behavior in this study. Based on the proposed analytical model, a non-linear torsional analysis program for torsion of the composite box-girder with corrugated steel webs was developed and successfully verified by comparing with the results of the test. The proposed analytical model shows that the concrete tension behavior has significant effect on the initial torsional stiffness and cracking torsional moment. Finally, a simplified torsional moment-twist angle relationship of the composite box-girder with corrugated steel webs was proposed based on the proposed analytical model.

• 한국강구조학회 논문집
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• 제21권6호
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• pp.597-608
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• 2009

본 연구에서는 접합부 특성이 고려된 공간프레임의 대변형 탄소성해석법에 관한 내용을 기술한다. 이 해석법은 유한변형을 고려한 대변형 탄성해석법에 기초한 것으로 부재의 재료적 탄소성, 접합부 반강접 특성을 추가적으로 고려하였다. 절점의 유한변형은 오일러의 개념으로 부터 유도되었으며, 부재좌표계에서 계산된 부재변형은 보-기둥식에 대입하여 부재력을 계산하였다. 부재변형은 부재축변형과 휨에 의한 축변형효과를 함께 고려하여 계산하였으며, 부재축력의 휨강성, 비틀림강성에 대한 효과를 고려하여 항복함수를 계산하였다. 재료는 완전 탄소성으로 가정하였고, 항복은 부재 양단부에서 집중하여 발생하는 소성힌지의 개념을 사용하였다. 부재 접합부 반강접 특성은 지수모델이나 선형모델을 적용하였고, 접합부 특성이 고려된 탄소성 후좌굴해석을 수행하기 위해 호장법을 사용하였다. 본 연구내용의 정확성 및 효율성을 검증하기 위해 공간프레임에 대한 해석을 수행하였다.

• 한국강구조학회 논문집
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• 제19권4호
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• pp.367-381
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• 2007

전력 수요의 증가로 인해 송전철탑의 고용량, 대용량화가 요구되어왔지만 아직 대부분을 차지하고 있는 345kV급 송전철탑에 대한 연구는 미흡한 실정이다. 현재 해석 설계되고 있는 방식은 2차원 트러스요소를 사용하여 양단은 힌지접합으로 축력만 작용하고 있는 것으로 가정한다. 이러한 방식을 3차원 트러스 요소에 적용하였을 때, 면 외로 작용하는 하중에 대해 무한변위가 발생하는 구조해석적인 문제점을 가지고 있다. 이에 본 연구는 보다 합리적인 요소 선택을 통한 구조해석 방식을 제안하기 위해 기존의 3차원 트러스요소 모델, 보요소 모델, 주주재와 수평재는 보요소로 모사하고 사재 및 기타 복재는 트러스로 모사한 보-트러스요소 모델 등 세 모델을 실제 설계 시공된 345kV급 송전철탑에 대해 설계하중 내에서 구조해석프로그램을 이용한 정적해석, 자유진동해석, 선형좌굴해석을 수행하였다. 구조해석 결과, 세 모델 모두 축력 및 축응력, 변위에서는 큰 차이가 나타나지 않았으나 보요소모델과 보-트러스요소 모델에서 휨응력의 비율이 축응력에 대해 크게 나타났다. 자유진동해석과 탄성좌굴해석의 결과를 통해 보-트러스요소 모델이 송전철탑 설계 및 해석에 있어서 더 안전측으로 고려될 수 있음을 확인하였다.

• Composites Research
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• 제15권4호
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• pp.23-31
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• 2002

시편 게이지 면적($길이{\;}{\times}{\;}폭$)의 이차원 크기효과가 T300/924 $[45/-45/0/90]_3s$ 탄소섬유/에폭시 적층판의 압축거동에 대해 조사하였다. 개조된 압축시험치구(ICSTM)와 좌굴방지장치가 $30mm{\;}{\times}{\;}30mm,{\;}50mm{\;}{\times}{\;}50mm,{\;}70mm{\;}{\times}{\;}70mm,{\;}90mm{\;}{\times}{\;}90mm$의 게이지 길이와 폭을 가진 시편들의 압축시험에 사용하였다. 모든 경우의 파괴들은 시편 게이지 길이 내에서 주로 갑자기 발생하였다. 파괴 후 분석결과는 $0^{\circ}$층의 섬유의 미소좌굴에 의해 파괴를 시작하여 최종파괴를 일으키는 임계파괴기구일 것으로 생각되었다. 이것은 매트릭스 지배적인 파괴를 의미하며, 초기섬유굴곡에 따라 파괴가 지배적으로 시작된다는 것을 말한다 이것은 또한 제작공정과 품질이 압축강도를 결정하는 중요한 역할을 한다고 볼 수 있다. 좌굴방지장치를 장착하고 시험할 때 장치의 볼트 조임 토크에 따라 시편과의 접촉마찰 등에 의해 실제 압축강도 보다 크게 나타나는 결과를 보였다. 좌굴방지장치의 영향을 유한요소법을 이용하여 해석한 결과 실제 압축강도 보다 7% 정도 크게 나타남을 확인하였다. 부가적으로 홀을 갖는 시편들의 압축시험도 수행되었다. 홀에 의한 국부응력집중이 적층판 강도에 지배적 요인이었다. 파괴강도는 홀 크기와 시편 폭이 증가할수록 감소하였으나 탄성응력집중계수로 예측된 값보다는 일반적으로 크게 나타났다. 이것은 사용된 복합재가 이상적인 취성재질이 아니라는 것을 의미하며 홀 주위에서 다소간의 응력이완이 발생한다고 볼 수 있다. X선 검사 사진분석에서 섬유좌굴과 층간분리형태의 손상이 파괴하중의 약 80%에서 홀 가장자리로부터 시작되었고 임계파괴크랙길이인 2-3mm의 불안정한 상태에 도달하기 전까지는 하중 증가와 더불어 안정되게 파괴가 진전되었다(시편의 기하학적 크기에 의존함). 이 손상과 파괴는 선형 cohesive zone 모델로 해석되었다. 노치없는 시편의 압축강도와 평면 파괴인성의 측정된 적층판 변수들을 사용하여 홀의 크기와 시편 폭의 함수로서 홀을 갖는 적층판의 압축강도를 성공적으로 예측하였다.

• Advances in aircraft and spacecraft science
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• 제3권4호
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• pp.427-445
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• 2016

Star sensors are the attitude estimation sensors of the satellite orbiting in its path. It gives information to the control station on the earth about where the satellite is heading towards. It captures the images of a predetermined reference star. By comparing this image with that of the one captured from the earth, exact position of the satellite is determined. In the process of imaging, stray lights are eliminated from reaching the optic lens by the mechanical enclosures of the star sensors called Baffles. Research in space domain in the last few years is mainly focused on increased payload capacity and reduction in launch cost. In this paper, a star sensor baffle made of Aluminium is considered for the study. In order to minimize the component weight, material wastage and to improve the structural performance, an alternate material to Aluminium is investigated. Carbon Fiber Reinforced Polymer is found to be a better substitute in this regard. Design optimisation studies are carried out by adopting suitable design modifications like implementing an additional L-shaped flange, Upward flange projections, downward flange projections etc. A better configuration of the baffle, satisfying the design requirements and achieving manufacturing feasibility is attained. Geometrical modeling of the baffle is done by using UNIGRAPHICS-Nx7.5(R). Structural behavior of the baffle is analysed by FE analysis such as normal mode analysis, linear static analysis, and linear buckling analysis using MSC/PATRAN(R), MSC-NASTRAN(R) as the solver to validate the stiffness, strength and stability requirements respectively. Effect of the layup sequence and the fiber orientation angle of the composite layup on the stiffness are also studied.