• Composites Research
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• v.30 no.5
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• pp.297-302
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• 2017

Finite element analysis of T-beam laminate structure under bending-torsional loading was conducted to prevent the delamination which is the major failure behavior on laminated composites. Three-dimensional preform, which is that fabric is braided through thickness direction, is suggested from the laminate analysis. The analysis aimed to optimize the fiber ratio in laminated composites. After it is suggested that guideline for design of T-beam structure using commercial software ANSYS Composites PrePost. The results show that strength of T-beam structure is increased 21.6% when the fiber density along with beam length direction is two times bigger than transverse direction. It is expected that development of high strength T-beam structure using designed three-dimensional preform.

• 대한공업교육학회지
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• v.34 no.2
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• pp.321-330
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• 2009

This study presents the blow molding of injection stretch-blow molding process for PET bottle. The numerical analysis of the blow molding of PET bottle is considered in this paper using CAE with a view to minimize the thickness difference. In order to determine the design parameters and processing conditions in blow molding, it is very important to establish the numerical model with physical phenomenon. In this study, a shell model with thickness has been introduced for the purpose and blow simulations with 3-type blow process condition are carried out. The simulations resulted in the thickness distribution in good agreement with the physical phenomenon. Also, from the result of numerical analysis, we appropriately predicted the thickness distribution along the PET bottle wall and Using the result of numerical analysis we apply the preform design and blow molding process condition for optimization.

• Journal of Korean Ophthalmic Optics Society
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• v.18 no.3
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• pp.241-246
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• 2013

Purpose: The aim of this study was a comparative analysis of the effect of distance contrast sensitivity when wearing free-form progressive lens and conventional progressive lens. Methods: The 20 subjects who do not have any ocular diseases were participated in this study. Contrast sensitivities at 5 different levels of spatial frequency were conducted by using FACT (Stereo Optical, USA). Results: Contrast sensitivity was measured for free-form progressive lens and conventional progressive lens in the order of right eye, left eye and binocular. Right/left/binocular contrast sensitivity values of the free-form progressive lenses compared to the conventional progressive lenses were higher 16%/17%/11% at A(1.5 cpd) of spatial frequency, 11%/5%/5% at B(3 cpd) of spatial frequency, 6%/6%/9% at C(6 cpd) of spatial frequency, 19%/16%/13% at D(12 cpd) of spatial frequency, 4%/3%/18% at E(18 cpd) of spatial frequency. Conclusions: In all the area of spatial frequency, distance contrast sensitivity values were measured highly on free-form progressive lens than on conventional progressive lens.

• Composites Research
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• v.18 no.1
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• pp.10-15
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• 2005

It is useful to detect defects of a preform for resin transfer molding before and after placement into the mold. To conduct this test, the gas flow method has been developed. This method not only measures permeability but also detects defects utilizing the pressure readings obtained from the gas flow test. This paper introduces the methodology and examine the applicability to actual processes.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.467-470
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• 2008

추진기관용 노즐에 사용하는 대표적인 소재로는 흑연소재와 탄소/탄소 복합재료를 들 수 있다. 흑연 소재는 열충격 저항성이 취약하여 사용 중 파손의 발생가능성이 높아 현재는 열축격 저항성이 우수한 탄소/탄소 복합재료를 주로 사용하고 있다. 본 연구를 통하여 수입에 의존하였던 Quasi-3D 구조의 니들펀치(Needle Punch) 프리폼을 국산화 개발하였다. 본 연구에서는 니들펀치 프리폼의 제조 공정 및 밀도화 공정을 다루고자 한다.

• Polymer(Korea)
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• v.35 no.5
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• pp.467-471
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• 2011

PET bottle is manufactured by blow molding the preform, which is molded by injection molding. The neck part of the preform of PET bottle for juice or grain-based beverage is crystallized before blowing to improve heat resistance at the entrance of the bottle. However, residual stress, developed during injection molding of preform, prevents the crystallization. In order to release the residual stress in the preform, the preform is annealed after the injection molding. If the residual stress is reduced by optimizing the injection molding conditions of preform the annealing time would be shortened. In this study, the optimum conditions for minimizing the residual stress and increasing dimensional accuracy of the injection molded preform are suggested through CAE analysis. In order to optimize the molding conditions, minimizing residual stress and shrinkage, computer simulations have been carried out with help of design of experiment scheduling. Injection temperature, initial packing pressure and filling time were selected for control parameters. Residual stress was affected by injection temperature and filling time. Shrinkage was affected by injection temperature. It was found that maximum residual stress, distribution of residual stress and shrinkage were decreased by 22%, 40% and 25%, respectively at an optimum molding condition compared with the results of previous molding condition.

• Composites Research
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• v.16 no.2
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• pp.33-40
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• 2003

In order to overcome one of the most pronounced shortcomings of conventional laminated composites, such as the low damage tolerance due to delamination, the thermoplastic materials and 3D (three-dimensional) preforms have been utilized in the manufacture of composite materials. From the newly developed process termed as the co-braiding, hybrid yarns of the thermoplastic fibers (PEEK) and reinforcing fibers (carbon) have been fabricated. In order to further enhance the delamination suppression, through thickness fibers have been introduced by way of 3D weaving technique in the fabrication of textile preforms. The preforms have been thermoformed to make composite materials. Complete impregnation of the PEEK into the carbon fiber bundles has been confirmed. For the comparison of mechanical performance of 3D woven composites, quasi-isotropic laminates using APC-2/AS4 tapes have been fabricated. Tensile and compressive properties of both the composites have been determined. Furthermore. the open hole, impact and CAI(Compression After Impact) tests were also carried out to assess the applicability of 3D woven textile reinforced thermoplastic composites in aerospace structures.

• Composites Research
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• v.35 no.2
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• pp.106-114
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• 2022

Carbon fiber-reinforced plastic, well known high specific strength and high specific stiffness, have been widely used in the aircraft industry. Mostly the CFRP structure is fabricated by lamination of carbon fiber or carbon prepreg, which has major disadvantage called delamination. Delamination is usually produced due to absence of the through-thickness direction fiber. In this study, three-dimensional carbon preform woven in three directions is used for fabrication of aircraft wing unit structure, a part of repeated structure in aircraft wing. The unit structure include skin, stringer and rib were prepared by resin transfer molding method. After, the 3D structure was compared with laminate structure through compression test. The results show that 3D structure is not only effective to prevent delamination but improved the mechanical strength. Therefore, the 3d preform structure is expected to be used in various fields requiring delamination prevention, especially in the aircraft industry.

• Journal of Korean Society of Steel Construction
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• v.24 no.1
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• pp.59-71
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• 2012

Results of the analysis of the structural behavior of axially loaded nodes in freeform structure were not fully understood due to certain difficulties, including the application of various welding and bolting types. In this study, a node of single layered freeform structure was tested to determine its structural behavior when subjected to axial loads. The tests were classified into node ball tests to evaluate the center of the node subjected to cyclic and monotonic loading. The node part tests were also conducted to evaluate the whole node subjected to monotonic loading. The test showed that the node ball is safe with the tensile force, but the node ball needs to increase its strength with the node loaded compressive force due to the additional bending moment of the node ball's asymmetric form.

• Composites Research
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• v.33 no.2
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• pp.61-67
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• 2020

Preforming is crucial in resin transfer molding process using woven fabric. When shear deformation exceeds the locking angle, wrinkles are generated in the preform, which causes defects in the RTM process. Therefore, in this study, the allowable shear deformation limit of carbon fiber woven fabrics is quantified and the molding characteristics are verified using the actual fabric forming. As a result, the characteristics of creases according to the layer setups have been examined and the results have been discussed. Numerical analyses have been also performed using measured shear properties. These results have been compared with the experimental results.