• Composites Research
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• v.14 no.6
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• pp.16-23
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• 2001

Analysis of mechanical behavior for a pultruded-wound hollow rod is presented. For this purpose, the pultruded-wound hollow rod is manufactured by the new winder attached to the conventional pultrusion system. And the conventional pultrusion process is newly altered to manufacture pultruded-wound specimens. A computer program, POST II, is modified to perform this study, In the nonlinear finite element formulation, the updated Lagrangian description method based on the second Piolar-Kirchhoff stress tensor and the Green strain tensor are used. For the finite element modeling of the composite hollow rod, the eight-node degenerated shell element is utilized. In order to estimate the failure, the maximum stress criterion is adopted to the averaged stress in the each layer of the finite elements. As numerical examples, the behavior of glass/up composite hollow rod is investigated from the initial loading to the final collapse. Present finite element results considering stiffness degradation and stress unload due to failure shows excellent agreement with experiments in the ultimate load, failure and deformations.

• 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.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.2
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• pp.81-93
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• 2020

The fatigue characteristics of glass fiber reinforced plastic (GFRP) composites were studied under repeated loads using the finite element method (FEM). To realize the material characteristics of GFRP composites, Digimat, a mean-field homogenization tool, was employed. Additionally, the micro-structures and material models of GFRP composites were defined with it to predict the fatigue behavior of composites more realistically. Specifically, the fatigue characteristics of polybutylene terephthalate with short fiber fractions of 30wt% were investigated with respect to fiber orientation, stress ratio, and thickness. The injection analysis was conducted using Moldflow software to obtain the information on fiber orientations. It was mapped over FEM concerned with fatigue specimens. LS-DYNA, a typical finite element commercial software, was used in the coupled analysis of Digimat to calculate the stress amplitude of composites. FEMFAT software consisting of various numerical material models was used to predict the fatigue life. The results of coupled analysis of linear and nonlinear material models of Digimat were analyzed to identify the fatigue characteristics of GFRP composites using FEMFAT. Neuber's rule was applied to the linear material model to analyze the fatigue behavior in LCF regimen. Additionally, to evaluate the morphological and mechanical structure of GFRP composites, the coupled and fatigue analysis were conducted in terms of thickness.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.512-519
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• 2002

본 연구에서는 임의의 형상의 다중세포 단면을 갖는 복합재료 블레이드에 대한 유한요소 구조해석을 수행하였다. 보 해석 모델은 구조연성 효과와 단면 벽의 두께, 횡 전단변형, 비틀림과 연관된 워핑 및 워핑구속효과 등을 고려하고 있다. 블레이드 힘-변위 관계식은 Reissner의 반복족에너지 함수를 이용한 혼합이론을 적용하여 유도하였다. 이 관계식은 굽힘 및 전단에 대해서는 Timoshenko 보의 형태로 그리고 비틀림 변형은 Vlasov 이론으로 근사하고 있다. 결과적인 [7×7] 구조강성 행렬은 전단변형 및 전단강성계수들을 특이한 가정에 의존하지 않고도 해석적으로 기술하고 있다. 본 정식화 과정을 통해서 구한 보 이론을 이중세포로 구성된 에어포일 형상의 복합재료 블레이드에 적용하였으며, 기존의 실험 연구 및 다차원 유한요소해석 결과들과 비교 연구를 수행하여 본 해석모델의 타당성을 보이고자 하였다.

• Composites Research
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• v.23 no.6
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• pp.7-13
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• 2010

Type3 cylinder is a composite pressure vessel fully over-wrapped with carbon/epoxy composite layers over an aluminum liner, which is the most ideal and safe high pressure gas container for CNG vehicles due to the lightweight and the leakage-before-burst characteristics. During service in CNG vehicle, if a fiber cut damage occurs in outer composite layers, it can degrade structural performance, reducing cycling life from the original design life. In this study, finite element modeling and analysis technique for the composite cylinder with fiber-cut crack damage is presented. Because FE analysis of type3 cylinder is path dependant due to plastic deformation of aluminum liner in autofrettage process, method to introduce a crack into FE model affect analysis result. A crack should be introduced after autofrettage in analysis step considering real circumstances where crack occurs during usage in service. For realistic simulation of this situation, FE modeling and analysis technique introducing a crack in the middle of analysis step is presented and the results are compared with usual FE analysis which has initial crack in the model from the beginning of analysis. Proposed analysis technique can be used effectively in the evaluation of influence of damage on composite layers of type3 cylinder and establish inspection criteria of composite cylinder in service.

• Composites Research
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• v.16 no.5
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• pp.7-14
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• 2003

Modeling of thick composite structures for finite element analysis is relatively complicated. 2-D plane elements may cause inaccurate result since the plane stress condition cannot be applicable in these structures. Therefore a 3-D modeling should be used. However, the difficulty to model all the layers with different material properties and ply orientation arise in this case. In this paper, an equivalent modeling is proposed and numerically tested for analysis of thick composite structures. By grouping layers with same material and ply orientation, number of elements through the thickness is remarkably reduced and still the result is close enough to the one from a detail finite element model. MSC/NASTRAN and PATRAN are used for the analysis. The proposed modeling technique has been applied for analysis of composite rotor hub system designed by Korea Aerospace Research Institute(KARI). Using the proposed equivalent modeling technique, we could conduct stress analysis for the hub system and check the safety factor of each part.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.101-106
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• 1999

Fiber reinforced plastic composites is widely used to make be lightening of aircraft and automotive owing to having high specific strength and specific modulus. And it is very important to know a charge shape in order to have good products in the compression molding. In particular, the product such as a bumper beam is composed of the random and unidirectional composite mats. Its deformation and charge shape are very different by stack type of random and unidirectional mats. In this paper, the characteristics of flow fronts such as a bulging phenomenon for step-type random/unidirectional composite mats and slip parameters are studied numerically. And the effects of viscosity ratio and stack type on the mold filling parameters are also discussed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.519-525
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• 2009

In this study a cohesive zone model was used to simulate the delamination phenomena which occurs by a successive crack initiation and propagation in composite laminates. The cohesive zone model was incorporated to the classical finite element method via cohesive element formulation and then implemented into the user-subroutine UEL of a commercial finite element program Abaqus. To validate the formulation and implementation of the cohesive element the finite element results were compared with the experimental data of double cantilever beam and end notched flexure tests. The numerical results well agree with the experimental load-displacement curves. Also the effect of the elastic stiffness and the size of the cohesive element on the global load-displacement curves were studied numerically. To minimize the mesh-dependency of the crack propagation path and eliminate the zig-zag patterns in the load-displacement curve, cohesive elements should be refined at the crack-tip.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.236-240
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• 2017

다양한 분야에서 복합재료의 중요성이 강조되면서 각각의 재료 특성에 따른 물성을 미시역학적으로 구하는 것에 대한 다양한 방법이 제시되고 있다. 본 논문에서는 5개의 혼합 법칙을 선정하여 전산구조해석을 통한 유한요소해석을 비교 검증한다. 그 과정에서 산출된 결과를 통하여 복합재료의 탄성거동의 오차가 1% 미만인 것을 확인하였고, 프로그램의 해석이 적절하다는 것을 검증하였다. 또한 프로그램과 가장 유사한 혼합 법칙이 무엇인지 확인하고, 체적 비에 따른 오차를 비교하여 가장 적합한 체적 비를 선정하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.1
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• pp.51-61
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• 2000

This paper discusses the homogenization method to determine effective average elastic constants of a linear structure by considering its microstructure. A detailed description on the homogenization method is given for the linear elastic material and then the finite element approximation is performed for an investigation of elastic properties. An asymptotic expansion is carried out in the cross-section area, or in the unit cell. Two and three lay-up structures made up of individual isotropic constituents are chosen for numerical examples to check discrepancies between results generated by this theoretical development and the conventional approach. Asymptotic characteristics of the process in extracting the stiffness of structure locally formed by spatial repetitions yield underestimated values of stiffness. These discrepancies are detected by the asymptotic corrective term which is ascribed to considerations of microscopic perturbations and proved in the finite element formulation. The asymptotic analysis is the more reasonable in analysing the composite material, rather than the conventional approach to calculate the macroscopic average for elastic properties.