• Composites Research
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• v.22 no.6
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• pp.18-22
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• 2009

In this paper, we examined impact force and impact behavior through low velocity impact tests of composite laminates. And through c-scan as nondestructive inspection, explored the damaged area being difficult to examine with the visual inspection. Through CAI tests, we also measured the compression strength of composite laminates subjected to low velocity impact. To examine the characteristics of impact behavior measured from low velocity impact test, nondestructive inspection, and CAI test, the simulated data are generated from the test data using Monte-Carlo simulation, then represented it by probability distribution. The testing results using visible stochastic distribution were examined and compared.

• Journal of the KSME
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• v.34 no.7
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• pp.517-526
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• 1994

복합재료가 점차 최근에 항공기에서 이차적인 구조요소에서 일차적으로 힘을 받는 구조물에 사 용됨으로써 두꺼운 복합재료 구조판과 셸의 정확한 동적, 정적거동을 예측하는 것이 중요한 문 제가 되었다. 특히 전산구조역학의 한 분야로서 복합재료 적층판의 문제는 inhomogeneity와 anisotropy 문제를 가지고 있어서 복잡하며 일차구조 (primary structrue)에서는 100장-200장의 적층도 드물지 않게 볼 수 있어서 정확한 계산을 위해서는 방대한 기억용량과 빠른 계산속도를 요구한다. 그러므로 복합재료 적층판의 거동을 정확하고 값싸고 빠르게 계산할 수 있는 이론과 수치방법의 개발이 중요한 문제이다. 이 문제는 E. Reissner, R. K. Kapania & S. Raciti, A. K. Noor & W. S., Burton, L. Librescu & J. N. Reddy, J. N. Reddy 등에 의해서 review가 행하 여졌고 이 분야의 모든 paper들의 비교적 현재까지 연구동향을 잘 묘사하고 있다. 여러 review paper들이 시간흐름상으로 여러 연구들을 잘 정리하고 있으므로 이 글에서는 논문들을 다시 review하는 것이 아니라 지난 20여 년간 이 분야에서 계속되어 온 연구중 주요한 것을 고찰하고 소개하는 것을 그 목적으로 한다.

• Journal of the Korean Society for Advanced Composite Structures
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• v.1 no.2
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• pp.1-13
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• 2010

Delamination reduces an elastic buckling load of the laminated composite structures and lead to global structural failure at loads below the design level. Therefore, the problem of the delamination buckling of laminated composite structures has generated significant research interest and has been the subject of many theoretical and experimental investigations. However, questions still remain regarding a complete understanding and details of the phenomena involved. In this paper an efficient finite element model is presented for analyzing the elastic buckling behavior of laminated composite plates with square embedded delamination using a solid element based on a three-dimensional theory. The solid finite element, named by EAS-SOLID8, based on an enhanced assumed strain method is developed. The study for elastic buckling behavior of laminated composite plates with embedded square delaminations are focused on various parameters, such as support condition and width-to-thickness ratio. Both graphs and buckling modes in this paper are good guide for design of the laminated composite plates with embedded square delamination.

• Journal of Aerospace System Engineering
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• v.16 no.5
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• pp.35-42
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• 2022

This paper deals with predicting comparable mechanical properties of laminated composite plates. The stiffness of an equivalent anisotropic composite plate is derived based on classical lamination theory. A novel failure criterion is defined to describe the failure behaviour of laminated composite plates based on micro-mechanics failure criteria. Finally, the theory's validation of finite element analysis results was verified. We concluded that this theory is very suitable for failure analysis of laminated composite plates for aerospace applications due to their relative simplicity and computational efficiency.

• Composites Research
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• v.18 no.3
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• pp.7-13
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• 2005

This paper presents a study on the low velocity impact response of the woven fabric laminates for the hybrid composite bodyshell of a tilting railway vehicle. In this study, the low velocity impact tests for the three laminates with size of $100mm\times100mm$ were conducted at three impact energy levels of 2.4J, 2.7J and 4.2J. Based on the tests, the impact force, the absorbed energy and the damaged area were investigated according to the different energy levels and the stacking sequences. The damage area was evaluated by the visual inspection and the C-scan device. The test results show that the absorbed energy of [fill]8 laminate is highest whereas (fill2/warp2)s is lowest. The [fill]8 laminate has the largest damage area because of the highest impact energy absorption.

• Composites Research
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• v.14 no.1
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• pp.8-14
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• 2001

A simplified method for determining the three mode(I, II, III) components of the strain energy release rate of free-edge delaminations in composite laminates is proposed. The interlaminar stresses are evaluated using the interface moment and the interface shear forces which are obtained from the equilibrium equations at the interface between the adjacent layers. Deformation of an edge-delaminated laminate is analysed by using a generalized quasi-three dimensional classical laminated plate theory. The analysis provides closed-form expression for the three components of the strain energy release rate. The analyses are performed for composite laminates subjected to uniaxial tension, with free-edge delaminations located symmetrically and asymmetrically with respect to the laminate midplane. The analysis results agreed with a finite element solution using the virtual crack closure technique.

• Journal of Korean Society of Steel Construction
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• v.13 no.5
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• pp.443-455
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• 2001

An energy method has been used for an elastic formulation of bending vibration and buckling analysis of laminated composite plates on two-parameter elastic foundations. A quasi-elastic method is used for the solution of viscoelastic analysis of the laminated composite plates. The third-order shear deformation theory is applied by using the double-fourier series. To validate the derived equations the obtained displacements for simply supported orthotropic plates on elastic foundations are compared with those of LUSAS program Numerical results of the viscoelastic bending vibration and buckling analysis are presented to show the effects of layup sequence number of layers material anisotropy and shear modulus of foundations.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.29-29
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• 1997

각광 받는 구조재료인 섬유강화 복합적층재에 대한 기계적 체결 거동은 본질적인 재료의 이방성에 의해서 파단강도가 파단 모우드와 매우 밀접한 관련을 갖는 것으로 알려져 있다. 따라서, 복합적층판 체결부의 정밀 구조 설계에서는 단순화에 따른 오차를 줄이고 정밀해에 의한 설계 및 해석이 요청된다. 특히, 층간응력 성분을 무시할 수 없는 두께를 갖는 복합적층 판의 기계적 체결부 해석이나 실제 구조물의 체결부에서 발생하는 굽힘이나 비틀림과 같은 하중 상태를 묘사하기 위해서도 정밀한 3차원 응력 해석은 필요하다. 하지만, 지금까지 기계적 체결부의 거동에 관한 연구는 층간응력 성분들을 어느정도 무시할 수 있는 얇은 평판에 대한 2차원 응력해석에 주로 국한되어 왔으며, 일부 수행된 체결부에 대한 3차원 응력 해석의 경우 여러 단점을 갖는 3차원 연속체 요소에 의한 유한요소 해석이 수행되었을 뿐이다.본 연구는 층간응력 성분들을 무시할 수 없는 두께를 갖는 복합적층판의 기계적 체결부 해석에 지금까지 사용되어온 3차원 연속체 요소에 의한 유한요소 방법이 갖는 단점들을 개선한 Layerwise 유한요소법을 이용하여 3차원 응력해석을 수행하였다. 특히, 선형상보성원리에 근거한 최적설계 기법을 응용하여, 기계적 체결시 핀과 적층판의 홀 사이에 발생하는 하중 전달 과정을 모사하고, 접촉력에 의한 홀 주위의 복잡하고 국부적인 응력 집중현상을 규명하여본다.

• Composites Research
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• v.16 no.5
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• pp.15-20
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• 2003

In this paper, the fracture strength of the surface damaged laminates was predicted by applying the fracture strengths of the unflawed and flawed laminates. For prediction, the theoretical equation about the fracture strength of laminates was simplified applying classical laminate theory and was applied to the surface damaged laminates. Lagace's and Tsai's experimental data were used for verifying the theoretical equation. Moreover, to verify the theoretical prediction, an experiment was performed. Surface unflawed laminate and flawed laminates were fabricated and the experiments were made and these results were compared with theoretical predictions. The specimens' fiber direction was same to the tensile direction and the theoretical predictions and the experimental results were showed good agreement. Therefore, by this equation, the fracture strength of structures made of composites will be able to be predicted when the surface of the structures was damaged.

• Composites Research
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• v.12 no.6
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• pp.1-7
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• 1999

The change of the coefficients of thermal expansion(CTE) of Carbon/Epoxy was investigated for the temperature variation and a prediction model for the change of CTE was proposed. Elastic properties and CTEs in the principal material directions were measured in the range of room temperature to cure temperature and characterized as functions of temperature. By applying the characterized properties to the classical lamination theory, a computational method to predict the change of CTEs of a general laminate for temperature variation was proposed. the coefficients of thermal expansion of laminates with various stacking sequences were measured and compared with those predicted. Good agreements between the predicted results and the experimental data show that the c hanges of CTEs of a general laminate for temperature variation can be predicted well by using the proposed method.