• Journal of the Korea Convergence Society
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• v.8 no.7
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• pp.231-236
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• 2017

In this study, the inhomogeneous material composed of CFRP(carbon fiber reinforced plastic) and structural metal of SM45C is used for the light material. The finite element analysis on the basis of compact tension test was carried out by using the composite material for sandwich type bonded with the unidirectional CFRP that differs in fiber stacking angle at both sides with the core of SM 45C. CT test is the representative method to confirm the fracture behaviour due to crack in material under the load. The effect on crack and hole must be investigated in order to apply inhomogeneous material to mechanical structure. As the result of this study, the fracture behaviour by CT test of the composite material for sandwich was studied by simulation analysis. The sandwich composite of unidirectional CFRP with the stacking angle of [0/60/-60/0] has the superior strength and the maximum equivalent stress of about 182GPa.Also, the esthetic sense can be shown as the designed factor of shape with composite material is grafted onto the convergence technique.

• Composites Research
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• v.19 no.3
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• pp.23-28
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• 2006

Carbon nanotubes reinforced copper matrix laminated nanocomposites were developed and the mechanical properties were evaluated by using micro-tensile testing system. Sandwich-type laminated structure constituted with carbon nanotube layers as a reinforcement and electroplated copper matrix were fabricated by a new processing approach based on selective dip-coating of carbon nanotubes. The mechanical properties of nanocomposites were improved due to an enhanced load sharing capacity of carbon nanotubes homogeneously distributed within the in-plane direction, as well as a bridging effect of carbon nanotubes along the out-of-plane direction between the upper and lower matrices. The universality of the layering approach is applicable to a wide range of functional materials, and here we demonstrate its potential use in reinforcing composite materials.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5979-5986
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• 2013

This study carried out a geometrical nonlinear dynamic analysis of laminated composite shell structures. Based on the first-order shear deformation shell theory and nonlinear formulation of Sanders, the Newmark method and Newton-Raphson iteration are used for dynamic solution considering nonlinear effects. The effects of radius, fiber angles, and layup sequences on the nonlinear dynamic response for various parameters are studied using a nonlinear dynamic finite element program developed for this study. The several numerical results were in good agreement with those reported by other investigators for square composite plates, and the new results reported in this paper show the significant interactions between the radius, fiber angles and layup sequence in the laminate. Key observation points are discussed and a brief design guideline of laminated composite shells is given.

• Journal of the Korean Society for Railway
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• v.13 no.4
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• pp.382-388
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• 2010

This paper describes the standardized finite element model for carbody structures of railway vehicle made of sandwich composites. Recently, sandwich composites were widely used to railway vehicle due to the improvement of energy efficiency, high specific stiffness and strength, weight reduction and space saving in korea. Therefore, structural integrity should be verified using finite element analysis prior to the manufacture of composite railway vehicle. The standardized finite element model for composite carbody structures was introduced through comparing the results of real structural test under vertical, compressive, twisting load and natural frequency test of various railway vehicles in this study. The results show that the quadratic shell element is suitable to model the reinforced metal frame used to improve the flexural stiffness of sandwich panel compared to beam element, and layered shell and solid element are recommended to model the skin and honeycomb core of sandwich panel compared to sandwich shell element. Also, the proposed standard finite element model has the merit of being applied to crashworthiness problem without modifications of finite element model.

• 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.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.4
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• pp.67-80
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• 1989

This Paper is concerned with the fracture behavoir of Unidirectional Laminate(UD) and the characteristic length of Multidirectional Laminate(MD) around hole under the Uniform Tensial Strain. Two fracture mechanical concepts of the Waddoups-Eisenman-Kaminski(WEK) model based on the Linear Elastic Fracture Mechanics(LEFM) and the Whitney-Nuismer Model based on Point and Average Stress Criteria were applied. The characteristic length of a laminate with a hole is then obtained using the coefficient of stress reduction and the experimental results, and it can be utilized in predicting the stress level at which the specimen will fracture. The results of the fracture characteristics and the strength of the specimens having a hole in the center can be used as the important experimental data in the research branch of the mechanical fastening of laminated structures. The Ultrasonic scanning and the Acoustic Emission(AE) method were utilized in order to find out the initial defects and the fracture behavior, respectively.

• Composites Research
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• v.12 no.4
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• pp.42-54
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• 1999

FMLC(Fiber-Metal Laminate Composites) is a new structural material combining thin metal laminate with adhesive fiber prepreg, it nearly include all the advantage of metallic materials, for example: good plasticity, impact resistance, processibility, light weight and excellent fatigue properties. This research studied the optimum design of the FMLC subject to various loading conditions using genetic algorithm. The finite element method based on the shear deformation theory was used for the analysis of FMLC. Tasi-Hill failure criterion and Miser yield criterion were taken as fitness functions of the fiber prepreg and the metal laminate, respectively. The design variables were fiber orientation angles. In genetic algorithm, the tournament selection and the uniform crossover method were used. The elitist model was also used to be effective evolution strategy and the creeping random search method was adopted in order to approach a solution with high accuracy. Optimization results were given for various loading conditions and compared with CFRP(Carbon Fiber Reinforced Plastic). The results show that the FMLC is more excellent than the CFRP in point and uniform loading conditions and it is more stable to unexpected loading because the deviation of failure index is smaller than that of CFRP.

• Composites Research
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• v.36 no.1
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• pp.25-31
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• 2023

Composite structures have been designed by stacking the laminae with different stacking angles to meet the required mechanical performance. Although the induced stresses on the composite structures under the external loads usually differ depending on the location, we determined the stacking sequence based on the maximum stress, which leads to low efficiency and generally is not the optimum design. Recently, piecewise integrated composites (PICs) were suggested for solving this inefficiency. PICs assume the perfect bonding between adjacent pieces, but this is ideal and hard to accomplish. Therefore, the overlap at the boundary is essential to prevent separation from each other. In this study, we investigated the effect of the overlap design on the impact failure mode of PIC plates. We fabricated the sample composite plates with different overlap designs using the fast curing carbon prepreg and conducted the impact tests according to ASTM D 7136. We found that PICs had different failure modes according to the overlap design, which lead the changes of absorbed impact energies as well as impact load curves.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.10
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• pp.959-965
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• 2017

In recent years, major airplane manufacturers have been using the laminate failure theory to estimate the strain of composite structures for airplanes. The laminate failure theory uses the failure strain of the laminate to analyze composite structures. This paper describes a procedure for the experimental assessment of laminate tensile failure characteristics. Regression analysis was used as the experimental assessment method. The regression analysis was performed with the response variable being the laminate failure strain and with the regressor variables being two-ply orientation ($0^{\circ}$ and ${\pm}45^{\circ}$) variables. The composite material in this study is a carbon/epoxy unidirectional (UD) tape that was cured as a pre-preg at $177^{\circ}C(350^{\circ}F)$. A total of 149 tension tests were conducted on specimens from 14 distinct laminates that were laid up at standard angle layers ($0^{\circ}$, $45^{\circ}$, $-45^{\circ}$, and $90^{\circ}$). The ASTM-D-3039 standard was used as the test method.

• 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.