• Journal of the Korean Society for Railway
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• v.12 no.5
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• pp.719-724
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• 2009

In this study, DCB(double cantilever beam) specimens of woven fabric carbon/epoxy and glass/epoxy were manufactured and mode I fracture toughness of specimen was measured according to ASTM 5528-01. And FE analysis was conducted in the same condition and evaluated the behavior of delamination analytically. Mode I fracture toughness measured by test was $845.7\;J/m^2$ in the case carbon/epoxy and that of glass/epoxy was $1,042\;J/m^2$. FE analysis was conducted using cohesive elements for adhesive layer and applied measured fracture toughness. To verify the result of analysis, the reaction force measured at the end of specimen and that calculated by Timoshenko beam theory were compared. The numerical results show good agreements with the measured one.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.31 no.3
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• pp.272-278
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• 1995

In this paper to investigate mode I and mode II critical energy release rates, G sub(IC) and G sub(IIC), three prepregs which are domestic products are used. Those are used for the unidirectional composites, but only one is used for the cross-ply laminate composites which is molded [0/90] sub(6s), [0/45] sub(6s) and [0/45/90] sub(6s). The value of G sub(IC) is almost same when modified three calculating methods are applied. The highest value of G sub(IC) at crack initiation is obtained at the [0/90] sub(6s) interlaminar and the lowest one is at the [0/45/90] sub(6s) interlaminar.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.11
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• pp.1265-1272
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• 2014

This study performed the progressive failure analysis of adhesive joints of a composite pressure vessel with a separated dome by using a cohesive zone model. In order to determine the input parameters of a cohesive element for numerical analysis, the interlaminar fracture toughness values in modes I and II and in the mixed mode for the adhesive joints of the composite pressure vessel were obtained by a material test. All specimens were manufactured by the filament winding method. A mechanical test was performed on adhesively bonded double-lap joints to determine the shear strength of the adhesive joints and verify the reliability of the cohesive zone model for progressive failure analysis. The test results showed that the shear strength of the adhesive joints was 32MPa; the experiment and analysis results had an error of about 4.4%, indicating their relatively good agreement. The progressive failure analysis of a composite pressure vessel with an adhesively bonded dome performed using the cohesive zone model showed that only 5.8% of the total adhesive length was debonded and this debonded length did not affect the structural integrity of the vessel.

• Composites Research
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• v.19 no.2
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• pp.20-27
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• 2006

The hybrid composite materials with non-woven tissue (NWT) was developed to improve the mechanical properties of conventional FRP composite materials. The hybrid prepreg with NWT consists of FRP prepreg and NWT prepreg. The NWT prepreg consists of NWT and polymer resin. The NWT has short fibers, discretely distributed with in-plane random orientation fibers. The purposes of this study of hybrid prepreg with NWT are (i) to increase the interlaminar properties(the fracture toughness and strength), (ii) to improve the mechanical properties and reliability, while maintaining a low cost, (iii) to introduce a tough and strong interlayer at critical positions to be required of strength in the laminate. To accomplish the above purposes, a production technique to decrease voids in NWT layers was proposed in this paper. The interlaminar failure characteristics of laminated composite materials was tremendously improved by hybrid concept with NWT.

• Textile Coloration and Finishing
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• v.29 no.1
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• pp.37-44
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• 2017

An issue of major concern in the utilization of laminated composites based epoxy resin is associated with the occurrence of delaminations or interlaminar cracks, which may be related to manufacturing defects or are induced in service by low-velocity impacts. A strong interfacial filament/brittle epoxy resin bonding can, however, be combined with the high fracture toughness of weak interfacial bonding, when the filaments are arranged to have alternate sections of shear stress. To improve this drawback of the epoxy resin, UV-thermal dual curable resin were developed. This paper presents UV-thermal dual curable resin which were prepared using epoxy acrylate oligomer, photoinitiators, a thermal-curing agent and thermoset epoxy resin. The UV curing behaviors and characteristics of UV-thermal dual curable epoxy resin were investigated using Photo-DSC, DMA and FTIR-ATR spectroscopy. The mechanical properties of UV-thermal dual curable epoxy resin impregnated CF prepreg by UV curable resin content were measured with Tensile, Flextural, ILSS and Sharpy impact test. The obtained results showed that UV curable resin content improves the epoxy toughness.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.11
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• pp.885-890
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• 2015

Nanomaterials possess unique mechanical, physical, and chemical properties. They are small, and have an ultrahigh surface area, making them suitable for air filter applications. Electrospinning has been recognized as an efficient technique for fabricating polymer nanofibers. In order to determine the optimum manufacturing conditions, the effects of several electrospinning process parameters on the diameter, orientation, and distribution of polyacrylonitrile (PAN) nanofiber are analyzed. To improve interlaminar fracture toughness and suppress delamination in the form of laminated non-woven fibers by using a heat roller, the performances of filter efficiency and pressure drop achieved with PAN nanofiber air filter are evaluated experimentally.

• Composites Research
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• v.18 no.3
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• pp.31-37
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• 2005

In this work, poly(ethylene oxide) (PEO) nanofibers were fabricated by electrospinning to prepare the nanofibers-reinforced composites. And the PEO powders-impregnated composites were also prepared to compare the mechanical interfacial behaviors of the composites. Morphology and fiber diameter of PEO nanofibers were determined by SEM observation. Mechanical interfacial properties of the composites were investigated in fracture toughness $(K_{IC})$ and interlaminar shea. strength (ILSS) tests. As a result, the fiber diameter was decreased with increasing the applied voltage. And optimum condition for the fiber formation was 15 kV, resulting from increasing of jet instability at high voltage. The PEO-based nanofibers-reinforced epoxy composites showed the improvements of both $K_{IC}$ and ILSS, compared to the composites impregnated with PEO powders. These results indicated that the nanofibers had higher specific surface area and larger aspect ratio than those of the powders, which played an important role in improving the mechanical interfacial properties of the composites.