• Steel and Composite Structures
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• 제28권1호
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• pp.111-121
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• 2018

It has been argued that fracture energy of composite laminates depends on their thickness and number of layers. In this paper a modified direct energy balance approach (DEBA) has been developed to evaluate the mode-II shear fracture energy for E-glass/Epoxy laminates from finite element model at an arbitrary thickness. This approach considers friction and damage/plasticity deformations using cohesive zone modeling (CZM) and nonlinear finite element modeling. The presence of compressive stress and resulting friction was argued to be a possible cause for the thickness dependency of fracture energy. In the finite element modeling, CZM formulation has been developed with bilinear cohesive constitutive law combined with friction consideration. Also ply element have been developed with shear plastic damage model. Modified direct energy balance approach has been proposed for estimation of mode-II shear fracture energy. Experiments were performed on laminates of glass epoxy specimens for characterization of material parameters and determination of mode-II fracture energies for different thicknesses. Effect of laminate thickness on fracture energy of transverse crack tension (TCT) and end notched flexure (ENF) specimens has been numerically studied and comparison with experimental results has been made. It is shown that the developed numerical approach is capable of estimating increase in fracture energy due to size effect.

• 한국항공우주학회지
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• 제37권11호
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• pp.1089-1095
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• 2009

태핑 테스트 시 방사되는 음압을 Rayleigh 적분식을 이용하여 해석하였다. 구조물에 의해 방사되는 음은 구조물의 거동과 직접적으로 연관되므로 충격응답해석이 수행되어야 한다. 본 논문에서는 층간분리가 존재하는 적층판의 해석을 위하여 층간분리 모델을 사용하였으며, 해머 형상의 충격체를 모사할 수 있는 효과적인 스프링-질량모델을 제시하였다. 예측된 음압이력과 시험결과와 비교하였으며, 음압이력과 충격하중이력에 손상이 주는 영향을 검토하였다. 방사되는 음압과 충격하중이력은 적층판에 존재하는 손상에 영향을 주는 것을 보였다. 결과적으로 제안된 음을 이용한 태핑실험은 복합재에 존재하는 손상을 검출하는데 신뢰성 있는 방법임을 알 수 있었다.

• Steel and Composite Structures
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• 제21권1호
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• pp.57-72
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• 2016

The Poisson ratio reduction of symmetric hygrothermal aged $[{\theta}_m/90_n]_s$ composite laminates containing a transverse cracking in mid-layer is predicted by using a modified shear-lag model. Good agreement is obtained by comparing the prediction models and experimental data published by Joffe et al. (2001). The material properties of the composite are affected by the variation of temperature and transient moisture concentration distribution in desorption case, and are based on a micro-mechanical model of laminates. The transient and non-uniform moisture concentration distribution give rise to the transient Poisson ratio reduction. The obtained results represent well the dependence of the Poisson ratio degradation on the cracks density, fibre orientation angle of the outer layers and transient environmental conditions. Through the presented study, we hope to contribute to the understanding of the hygrothermal behaviour of cracked composite laminate.

• Composites Research
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• 제16권2호
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• pp.48-53
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• 2003

본 논문에서는 카본 블랙의 함유율에 따른 유리섬유/에폭시 직조 복합재료 적층판의 유전율에 대한 실험 및 예측방법에 대한 연구를 수행하였다. 유전율 측정은 5 GHz∼18 GHz의 주파수 영역에서 수행하였으며, 복합재료의 유전율은 카본 블랙의 함유율과 주파수의 함수로 얻을 수 있었다. 카본 블랙의 함유율에 따른 복합재료의 유전율을 모사하는 혼합법칙을 얻기 위한 새로운 방법이 제시되었으며. 이 방법에서는 실험적으로 얻기 어려운 카본 블랙 자체의 유전율도 얻을 수 있다. 혼합법칙으로 계산된 복합재료 유전율 결과는 실험적으로 얻은 유전율을 비교적 잘 모사하는 결과를 얻을 수 있었다.

• 대한조선학회논문집
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• 제52권2호
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• pp.143-152
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• 2015

In the present study, the fiber and matrix failure of composite laminates under arbitrary biaxial stresses were evaluated based on separate mode criteria such as Hasnin and Puck theories. There is a limitation to predict the fiber-dominant and/or matrix-dominant failures under arbitrary stress states using limit criteria (maximum stress and maximum strain theories) and interactive criteria (Tsai-Hill and Tsai-Wu theories). There is little literature for failure analysis of ships and offshore composite structures considering advanced failure theories such as Hashin and Puck theories. Furthermore, there is not enough practical commercial finite element analysis (FEA) code which is basically adopted the separate mode criteria. Hence, in the present study, the user-defined subroutine of commercial FEA code ABAQUS for evaluation of fiber and matrix failures of composite structures was developed based on Hashin and Puck failure criteria. And then, the proposed subroutine was validated by comparing with a series of experimental results of carbon- and glass-implemented composite laminates to guarantee the reliability and usefulness of the developed method.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.420-425
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• 2000

The room-temperature shapes of cured unsymmetric composite laminates have out-of-plane warping after autoclave processing. In addition, they exhibit two stable room-temperature configurations due to snap-through phenomena when the side length of laminates exceeds a critical value. The cured shapes of unsymmetric laminates are influenced by many environmental factors. Experiments show that the effect of too-plate cannot be ignored and has significant influence on the cured shape of unsymmetric laminates. In this present study, approximations to the strain fields are used in the expression for the total potential energy and the Rayleigh-Ritz method is applied. The slippage effects resulting from the interaction between the laminates and the tool-plate are considered. By introducing a dimensionless slippage coefficient and correlating the corresponding value with experimental results, the influence of processing parameters is investigated. Modeling is extended to predict curvatures of plate configurations with various aspect ratio.

• 대한기계학회논문집A
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• 제26권3호
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• pp.553-559
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• 2002

Carbon-fiber which has very small radial dimension makes us difficult to measure it's properties. So in this paper, we suggest a simple method to measure the thermal conductivity of a carbon-fiber's and carbon-fiber-reinforced-plastics(CFRP) laminates. The thermal conductivity of CFRP laminates was measured experimentally at the same time analytically. The experimental model is based on the one-dimensional analysis of fin sample because CFRP laminates has a thin geometric configuration. The analytical model to measure the thermal conductivity of carbon-fiber is expressed by use of mean-field model which is based on Eshelby's elliptical inclusion problem. Therefore the thermal conductivity of angle-ply laminates can be computed by use of effective longitudinal and transverse thermal conductivities of unidirectional composite of the constituents.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.50-53
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• 2001

An experimental research work for the fracture and notch strength of thick laminates has been performed to develop high quality composite notches for structural use. Thus, the multi-directional laminates are designed and compared to the baseline aluminum. The difference of notch strength caused by manufacturing techniques is also discussed. The notches of selected materials are evaluated by the static test and low-velocity impact test. Failure modes are also observed and assessed. Material design is evaluated by the FEA(finite element analysis) and confirmed by experiments. The successful results are obtained for thick composite notches, which shows higher strength than aluminum notches.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.155-158
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• 2001

The layup optimization by genetic algorithm (GA) for the strength of laminated composites with free-edge is presented. For the calculation of interlaminar stresses of composite laminates with free edges, extended Kantorovich method is applied. In the formulation of GA, repair strategy is adopted for the satisfaction of given constraints. In order to consider the bounded uncertainty of material properties, convex modeling is used. Results of GA optimization with scattered properties are compared with those of optimization with nominal properties. The GA combined with convex modeling can work as a practical tool for light weight design of laminated composite structures since uncertainties are always encountered in composite materials.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 추계학술발표대회 논문집
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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.