• Composites Research
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• 제30권2호
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• pp.149-157
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• 2017

본 논문에서는 응집영역 모델링 기법을 사용하여 노치가 있는 적층복합재료의 파괴거동을 연구하였다. 먼저 노치가 있는 적층복합재료 시편형상에 대해 일반 3차원 고체요소로 모델링 한 후 요소들 사이에 섬유파괴, 기지파괴 및 층간분리 파괴를 담당하는 응집요소를 삽입하여 유한요소 메쉬를 제작하였다. 다음으로 일축인장 시험을 모사하는 하중 및 경계조건을 가하여 점진적 파괴해석을 수행하고 해석결과를 참고문헌의 실험결과와 비교하여 해석의 타당성을 검증하였다. 수치해석 결과로부터 노치가 있는 적층복합재료 인장시편의 파괴시작 및 진전거동을 분석하였으며 파괴모드의 진전을 체계적으로 조사하였다.

• 한국항공우주학회지
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• 제32권3호
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• pp.74-81
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• 2004

복합재 주익을 실험용 경항공기급에 적용하기 위하여, 복합재료의 특성과 제작공정을 고려한 일련의 기본 설계와 해석과정을 보이고 그 결과를 수록하였다. Schrenk 방식 (NACA TM No. 948) 과 FAR part 23 Appendix A의 근사방법을 이용하여 공력하중해석을 수행하였으며, 이에 의거한 구조하중 조건을 만족함과 동시에 복합재 구조의 장점을 반영할 수 있도록 주요 부재를 배치하였다. 제작공정과 동일한 조건에서 성형된 시편들에 대해 실험을 수행하여 선정재료의 설계기준치를 확보하였고, 단순화된 상자형 날개보에 대해 최대 변형 률 파괴기준식을 적용하여 구조의 안전도를 평가하였다.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1653-1665
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• 2002

One of the most significant problems in the processing of composite materials is residual stresses. The residual stresses may be high enough to cause cracking in the matrix even before external loads are applied and can degrade the integrity of composite structures. In this study, thermo-viscoelastic residual stresses occurred in the polymeric composite cylinder are investigated. This type of structure is used for the launch vehicle fuselage. The time and degree of cure dependent thermo-viscoelastic constitutive equations are developed and coupled with a thermo-chemical process model. These equations are solved with the finite element method to predict the residual stresses in the composite structures during cure. A launch vehicle experiences high thermal loads during flight and re-entry due to aerodynamic heating or propulsion heat, and the thermal loads may cause thermal buckling on the structure. In this study the thermal buckling analysis of composite cylinders are performed. Two boundary conditions such as all clamped and all simply supported are used for the analysis. The effects of laminates stacking sequences, shapes and residual stresses on the critical buckling temperatures of composite cylinders are investigated. The thermal buckling analysis is performed using ABAQUS.

• 대한기계학회논문집A
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• 제21권3호
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• pp.423-429
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• 1997

A simplified method for determining the mode components of the strain energy release rate of free-edge delaminations in laminated composite is proposed. The interlaminar stresses are evaluated as an interface moment and interface shear forces that are obtained from the equilibrium equations at the interface between the adjacent layers. Deformation of an edge-delaminated laminate is calculated by using a generalized quasi-three dimensional classical laminated plate theory developed by the authors. The analysis provides closed-form expression for the three components of the strain energy release rate. Comparison of results with a finite element solution using the virtual crack closure technique shows good agreement. In the present study, laminated composite with stacking sequences of [30/-30/90]$_{s}$ were examined. The simple nature of the method makes it suitable for primary design analysis for the delaminations of laminated composite.e.

• 한국생물정보학회:학술대회논문집
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• 한국생물정보시스템생물학회 2005년도 BIOINFO 2005
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• pp.287-293
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• 2005

Predicting RNA secondary structure as accurately as possible is very important in functional analysis of RNA molecules. However, different prediction methods and related parameters including terminal GU pair of helices, minimum length of helices, and free energy systems often give different prediction results for the same RNA sequence. Then, which structure is more important than the others? i.e. which combinations of the methods and related parameters are the optimal? In order to investigate above problems, first, three prediction methods, namely, random stacking of helical regions (RS), helical regions distribution (HD), and Zuker's minimum free energy algorithm (ZMFE) were compared by taking 1139 tRNA sequences from Rfam database as the samples with different combinations of parameters. The optimal parameters are derived. Second, Zuker's dynamic programming method for prediction of RNA secondary structure was revised using the above optimal parameters and related software BJRNAFold was developed. Third, the effects of short-range interaction were studied. The results indicated that the prediction accuracy would be improved much if proper short-range factor were introduced. But the optimal short-range factor was difficult to determine. A user-adjustable parameter for short-range factor was introduced in BJRNAFold software.

• 한국강구조학회 논문집
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• 제13권3호
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• pp.233-244
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• 2001

본 연구에서는 다층 층간분리된 복합보의 휨강성 감소를 고찰하였다. 휨강성 감소를 평가하기 위해서 이론해석을 수행하였다. 층간분리가 복합보에 휨강성 감소에 주는 영향을 고찰하기 위해서 지배운동방정식이 유도되었고, 층간분리된 각각의 분할보는 연속조건을 이용한 반복관계를 이용하여 구해졌다. 복합적층보에 층간분리가 여러 층에서 발생한 경우에 대해 다양한 적층순서와 여러 가지 형태의 층간분리 형상으로 모델링하여 결과를 비교하였다. 다층 층간분리가 존재하는 적층복합보의 휨강성을 평가하는데 있어서 본 연구는 유용하게 활용될 수 있다.

• Composites Research
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• 제12권4호
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• pp.17-24
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• 1999

프리프레그 덧대기 방법을 이용하여 복합재료 쉘 구조물을 수리할 때 발생하는 잔류 변형을 고찰하기 위해서 유한요소해석과 실험을 수행하였다. 삼차원 응축 쉘 요소와 일차 전단변형 이론에 기초하여 유한요소 프로그램을 개발하였다. 자유 경계조건을 갖는 적층 쉘에 대한 해석결과를 프리프레그 덧대기 수리과정을 통해 측정된 변형률과 비교 검토하였다. 네 변이 고정된 적층 쉘을 프리프레그 덧대기로 수리할 경우 최종 잔류응력이 덧대기 부근에서 크게 발생하였다. 적층 쉘과 덧대기의 적층순서는 잔류응력에 크게 영향을 미치고, 또한 적층 쉘과 덧대기의 적층 순서가 동일해도 잔류응력이 발생하였다.

• Steel and Composite Structures
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• 제15권4호
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• pp.379-397
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• 2013

Conoidal shells are doubly curved stiff surfaces which are easy to cast and fabricate due to their singly ruled property. Application of laminated composites in fabrication of conoidal shells reduces gravity forces and mass induced forces compared to the isotropic constructions due to the high strength to weight ratio of the material. These light weight shells are preferred in the industry to cover large column free open spaces. To ensure design reliability under service conditions, detailed knowledge about different behavioral aspects of conoidal shell is necessary. Hence, in this paper, static bending, free and forced vibration responses of composite conoidal shells are studied. Lagrange's equation of motion is used in conjunction with Hamilton's principle to derive governing equations of the shell. A finite element code using eight noded curved quadratic isoparametric elements is developed to get the solutions. Uniformly distributed load for static bending analysis and three different load time histories for solution of forced vibration problems are considered. Eight different stacking sequences of graphite-epoxy composite and two different boundary conditions are taken up in the present study. The study shows that relative performances of different shell combinations in terms of static behaviour cannot provide an idea about how they will relatively behave under dynamic loads and also the fact that the points of occurrence of maximum static and dynamic displacement may not be same on a shell surface.

• Advances in aircraft and spacecraft science
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• 제5권6호
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• pp.633-652
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• 2018

The present paper focuses on the development of a model for simulating the thermoelectric behavior of CNTs/CFRP Organic Matrix Composite (OMC) laminates for aeronautical applications. The model is developed within the framework of the thermodynamics of irreversible processes and implemented into commercial ABAQUS Finite Element software and validated by comparison with experimental thermoelectric tests on two types of composites materials, namely Type A with Carbon Nanotubes (CNT) and Type B without CNT. A simplified model, neglecting heat conduction, is also developed for simplifying the identification process. The model is then applied for FEM numerical simulation of the thermoelectric response of aircraft panel structures subjected to electrical loads, in order to discuss the potential danger coming from electrical solicitations. The structural simulations are performed on quasi-isotropic stacking sequences (QI) $[45/-45/90/0]_s$ using composite materials of type A and type B and compared with those obtained on plates made of metallic material (aluminum). For both tested cases-transit of electric current of intermediate intensity (9A) and electrical loading on panels made of composite material-higher heating intensity is observed in composites materials with respect to the corresponding metallic ones.

• 한국자동차공학회논문집
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• 제11권1호
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• pp.151-159
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• 2003

The front 2 pieces of the 3-piece steel propeller shaft installed on a 8.5-ton truck were redesigned with a 1 -piece composite propeller shaft with steel yokes and spline parts to get the reduction of weight and the improvement of NVH characteristics. Based on the analysis of bending vibration, strength and cure-induced residual stresses of the composite propeller shaft, proper composite materials and stacking sequences were selected. The composite propeller shaft requires a reliable joining method between the shaft and steel end parts through a steel connector. From 3-D contact stress analyses of the laminated composite shaft with bolted Joints, the 3-row mechanical joint which satisfies the torque transmission capability has been designed. Several full-scale composite shafts were fabricated and tested to verify the design analyses. The design requirements are shown to be satisfied. With the newly designed composite shaft, the weight reduction more than 50% and improvements in NVH characteristics have been achieved.