• Composites Research
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• 제20권4호
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• pp.25-30
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• 2007

The advanced fiber-reinforced laminated composites are widely used in a variety of engineering applications such as aerospace, marine, mechanical and civil engineering for weight savings because of their high specific strength and stiffness. The material properties of ply is known to have larger variations than that of conventional materials and very sensitive to the loading direction. Therefore, it is important to consider the variations on designing the laminated composite. This paper demonstrates the importance of considering uncertainties through examining the effect of material properties variations on various design requirements such as tip deflection, natural frequency and buckling stress using COMSOL-MATLAB interface.

• Composites Research
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• 제18권6호
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• pp.1-8
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• 2005

The fiber-reinforced composite materials have been advanced for various applications because of their excellent mechanical and electromagnetic properties. On their manufacturing processes, however, thermo-curing inherently produces the undesired thermal deformation mainly from temperature drop from the process temperature to the room temperature, so called spring-back. The spring-back must be understood especially in the hybrid composites in order to design and fabricate desired shape. In this research, (glass fiber / epoxy) + (carbon fiber / epoxy) unsymmetric hybrid composites were fabricated under various conditions such as cure cycle, laminate thickness, stacking sequence and curing sequence. Coupons were made and spring-back were measured using coordinate measuring machine (CMM). Using the Classical Lamination Theory (CLT) and finite element analysis (ANSYS), the behavior of spring-back were predicted and compared with the experimental data. The results from CLT and FEA agreed well with the experimental data. Although, the spring-back could be reduced by lowering curing temperature, at any case, the spring-back could not be removed completely.

• Composites Research
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• 제23권6호
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• pp.61-66
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• 2010

In this paper, the variation of mechanical properties of T800 carbon/epoxy composites according to the forming pressure, which was referred to previous studies on a filament winding process, were investigated. The specimens of all the tests were fabricated by an autoclave de-gassing molding process controlling forming pressure (absolute pressures of 0.1MPa, 0.3MPa, 0.7MPa including vacuum) and water jet cutting after fabricating composite laminates. Various tensile tests were performed for in-plane properties and interlaminar properties were also measured by using Iosipescu test jig. Fiber volume fraction was measured to correlate the property variation and the forming pressure. This properties are expected to be utilized in the design of Type III pressure vessel for hydrogen vehicles which uses the same carbon fiber (T800 carbon fiber) for the filament winding process.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제32권8호
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• pp.91-100
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• 2004

A Green's function approach is adopted for analyzing the thermoelastic deformations and stresses of a plate made of functionally graded materials(FGMs). The solution to the 3-dimensional unsteady temperature is obtained by using the laminate theory. The fundamental equations for thermoelastic problems are derived in terms of out-plane deformation and in-plane force, separately. The thermoelastic deformation and the stress distributions due to the bending and in-plane forces are analyzed by using a Green's function based on the Galerkin method. The eigenfunctions of the Galerkin Green's function for the thermoelastic deformation and the stress distributions are approximated in terms of a series of admissible functions that satisfy the homogeneous boundary conditions of the rectangular plate. Numerical analysis for a simply supported plate is carried out and effects of material properties on unsteady thermoclastic behaviors are discussed.

• Journal of Korea Foundry Society
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• 제27권6호
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• pp.255-257
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• 2007

최근에는 탄소섬유복합재료(CFRP)는 우주 및 민간 항공산업분야에 널리 활용이 되고 있는 실정이다. CFRP 복합재는 적층구성에 따라 기계물성치 및 강성에 크게 영향이 미치므로 가장 대표적인 직교이방성 적층재의 적층배향을 비파괴 탐상하는 것은 중요하다. 본 연구에서는 CFRP 적층재의 섬유배향에 가장 민감한 초음파 전단파를 활용하기 위해 2개의 종파 초음탐촉자를 이용하는 새로운 기법을 제안하였다. 또한 초음파 전단파를 발생하기 위해서는 탐촉자 밑면에 접촉매질인 태운꿀을 사용하는데 초음파시험하는 도중에 물성치중에 하나인 즉 점성이 상당히 변하게 된다. 이러한 문제를 해결하기 위해 2개의 종파용 초음파탐촉자를 이용해 전단파를 발생시킴으로써 접촉매질문제를 상당히 경감할 수 있는 것으로 나타났으며 여기에서 발생한 전단파가 CFRP 복합적층판의 섬유배향에 매우 민감함을 알 수 있었다.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• 제7권11호
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• pp.925-932
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• 2017

In this study, the analysis of plate under torsion was carried out according to stacking angle at the unidirectional carbon fiber reinforced plastic(UD CFRP) among composite materials. In case of UD CFRP, the material property due to stacking angle becomes different. Also, the stacking angles were designated to 15°, 30°, 45°, 60°, 75° and 90° at the study models. The notch hole was applied at the center part by supposing that rivet or hole was used. The analysis method was used by applying the experimental method at ISO 15310. Two jigs were fixed at the lower part and two jigs were descending at the upper part. As seen by the analysis result values at this study, the shear stress happening at the fracture part was seen with the lowest value in case of the stacking angle of 45°. It is known that the case of the stacking angle of 45°has the structural safety and durability higher than those of the other stacking angles when the torsion applies. It is thought that this result can be applied to the data of basis which can be devoted to the durability when the torsion is applied at CFRP plate.

• Journal of the Computational Structural Engineering Institute of Korea
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• 제27권6호
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• pp.625-633
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• 2014

Mark III CCS plate is considered in this paper to perform its strength assessment. Mark III CCS plate is designed and constructed by stacking various non-metallic engineering materials such as plywood, triplex and reinforced PU foam that are supported by series of mastic upon inner steel hull structure. From the viewpoint of structural analysis, this plated structure is treated as a laminated anisotropic structure. Commercially available general purpose finite element analysis programs such as MSC PATRAN and MARC are used to develop the finite element (FE) model of the Mark III CCS plate. Because of the characteristics of LNG cargo that the Mark III CCS plate deals with, it is subjected to a wide range of temperature variations, i.e. about $-163^{\circ}C$ to $20^{\circ}C$. Different material properties of the Mark III CCS plate at these temperature levels are considered in the FE model. Using the developed FE model, strength assessment procedure is developed incorporating various anisotropic failure criteria such as Hashin, Hill, Hoffman, Maximum stress and Tsai-Wu. The strength assessment is performed within the initial failure state of the Mark III CCS plate and, as a result, failure details such as failure locations and loads are identified.

• Composites Research
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• 제13권1호
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• pp.33-39
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• 2000

A numerical approach for predicting the ultimate strength of laminate composites has been studied using the Weibull distribution of the strengths of lamina plies. The probabilistic initial failure strengths of laminates were calculated using Tsai-Hill failure criterion. The ultimate strength of the laminate composites has been predicted using progressive failure analysis. The experimental results show that the strength prediction based on the Weibull distribution of ply strength reasonably agrees well with the experimentals better than equal strength assumption.

• Proceedings of the Korean Society For Composite Materials Conference
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.169-172
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• 2000

Although extensive efforts have been devoted to the optimal design of composite laminated plates in recent years, some practical issues still need further research. One of them is the handling of the uncertainties in material properties, which were ignored in most researches in the past. In this paper, the convex modeling is used in calculating the failure criterion, given as constraint, to consider the uncertain material properties in the thickness optimization. Numerical results show that the optimal thickness increases when the uncertainties of elastic moduli considered, which shows such uncertainties should not be ignored for safe and reliable designs.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제11권9호
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• pp.3176-3183
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• 2010

A multi-scale fatigue life prediction methodology of composite pressure vessels subjected to multi-axial loading has been proposed in this paper. The multi-scale approach starts from the constituents, fiber, matrix and interface, leading to predict behavior of ply, laminates and eventually the composite structures. The multi-scale fatigue life prediction methodology is composed of two steps: macro stress analysis and micro mechanics of failure based on fatigue analysis. In the macro stress analysis, multi-axial fatigue loading acting at laminate is determined from finite element analysis of composite pressure vessel, and ply stresses are computed using a classical laminate theory. The micro stresses are calculated in each constituent from ply stresses using a micromechanical model. Three methods are employed in predicting fatigue life of each constituent, i.e. a maximum stress method for fiber, an equivalent stress method for multi-axially loaded matrix, and a critical plane method for the interface. A modified Goodman diagram is used to take into account the generic mean stresses. Damages from each loading cycle are accumulated using Miner's rule. Monte Carlo simulation has been performed to predict the overall fatigue life of a composite pressure vessel considering statistical distribution of material properties of each constituent, fiber volume fraction and manufacturing winding angle.