• Composites Research
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• v.19 no.1
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• pp.15-21
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• 2006

It is very difficult to make complex 3 dimensional curved-shape composite laminates using the advanced unidirectional composite prepregs. This study shows development process of subscale composite parabolic antenna reflector using unidirectional AS4/PEEK prepreg tapes. The AS4/PEEK thermoplastic composite materials are known to have good thermal and chemical stabilities in addition to their high specific strength and modulus. Various lamination methods were investigated through finite element analyses to make up the laminate design of the reflector. The automated fiber placement method was used to fabricate the reflector. The thermal expansion test using full-bridge strain gage circuits was done to verity the performance of the composite product.

• 기계와재료
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• v.14 no.1 s.51
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• pp.113-120
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• 2002

• Composites Research
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• v.18 no.3
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• pp.38-46
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• 2005

In order to characterize the outstanding performance of three-dimensional (3D) composites, the low velocity impact test has been carried out. 3D fiber structures have been achieved by using the automated tape placement (ATP) process and a stitching method. Materials for the ATP and the stitching process were carbon/epoxy prepreg tapes and Kevlar fibers, respectively. Two-dimensional composites with the same stacking sequence as 3D counterparts have also been fabricated for the comparison of damage tolerance. For the assessment of damage after the impact loading, specimens were subjected to C-Scan nondestructive inspection. Compression after impact (CAI) tests were conducted to evaluate residual compressive strength. The damage area of 3D composites was greatly reduced $(30-40\%)$ compared with that of 2D composites. Although the CAI strength did not show drastic improvement for 3D composites, the ratio of retained strength was $5-10\%$ higher than 2D samples. The effect of stitching on the impact performance was negligible above the energy level of 35 Joules.

• Composites Research
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• v.32 no.5
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• pp.229-236
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• 2019

In this study, the effects of the additional processing parameters on the mechanical properties of thermoplastic composites fabricated with automated fiber placement (AFP) were evaluated. Annealing and vacuum bag only processes were then performed on the manufactured thermoplastic composites, respectively. For verification, the crystallinity was measured by differential scanning calorimetry (DSC), confirming the variation of semi-crystalline thermoplastic composite according to the process conditions. The void content of thermoplastic composites was evaluated by matrix digestion method while microscopic examination confirmed the porosity distribution. The interlaminar shear strength test was conducted for three different process parameters (VBO, annealing, and no treatment). A comparison of the three tested strengths was made, revealing that the porosity value had larger effect on the mechanical properties of the thermoplastic composite compared to the degree of crystallinity. Additionally, when thermoplastic composite melted up, the pores were continuously removed under vacuum process; the removal of the pores resulted in an increase of the interlaminar shear strength.

• Journal of the Korean Institute of Gas
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• v.15 no.1
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• pp.35-39
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• 2011

The purpose of this paper is to analyze affecting ratios of strength safety in carbon fiber layer thickness of a composite fuel tank for FEV vehicles. To investigate affecting ratios by FEM modeling, the equivalent von Mises stress has been computed on the aluminum liner and carbon fiber layers of composite fuel tanks in hoop and helical directions respectively. According to the FEM results, the affecting ratios of an aluminum liner on the equivalent stress are 77.5% in hoop direction, 18.11% in $70^{\circ}C$ winded helical direction and 4.39% in $12^{\circ}C$ winded helical direction. These trends on the strength safety of carbon fiber layers have been shown as those of an aluminum liner even though the layer thickness ratio of $12^{\circ}C$ inclined carbon fiber is very high of 42% compared with that of hoop layer thickness. Thus, the computed results show that the strength safety of a carbon fiber fuel tank is more influenced by the winding angle rather than the fiber thickness of carbon fiber layers.

• Proceedings of the Korea Information Processing Society Conference
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• 2019.10a
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• pp.1090-1093
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• 2019

유리섬유강화복합재료로 제작된 배관/덕트 조인트의 오버레이 자동접합을 할 수 있는 로봇이 개발되고 있으며 로봇의 구성 중 하나인 자동적층장치의 작업 시작 위치와 제자리 회전 오차를 극복할 수 있는 기준선에 대한 실시간 영상처리가 필요하다. 기존의 선 검출 알고리즘들은 연산량이 많아 실시간 처리가 어렵거나 전체 영상에서 잡음에 취약한 단점이 있다. 본 논문은 이러한 FRP 배관 및 덕트 내 색상 실선 인식 알고리즘의 효율적인 실시간 영상처리 방법에 관하여 소개하고 배관 내 라인 제어를 위한 선의 실제 거리를 계산하고 출력하는 방법을 나타내었다.

• Composites Research
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• v.21 no.5
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• pp.15-22
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• 2008

This paper describes the results of structural integrity and crashworthiness of Automatic Guideway Transit(AGT) vehicle made of sandwich composites. The applied sandwich composite of vehicle structure was composed of aluminum honeycomb core and WR580/NF4000 glass fabric/epoxy laminate composite facesheet. Material testing was conducted to determine the input parameters for the composite facesheet model, and the effective equivalent damage model fer the orthotropic honeycomb core material. The finite element analysis using ANSYS v11.0 was dont to evaluate structural integrity of AGT vehicle according to JIS E 7105 and ASCE 21-98. Crashworthiness analysis was carried out using explicit finite element code LS-DYNA3D with the lapse of time. The crash condition was frontal accident with speed of 10km/h at rigid wall. The results showed that the structural integrity and crashworthiness of AGT vehicle were proven under the specified loading and crash conditions. Also, the modified Chang-Chang failure criterion was recommended to evaluate the failure modes of composite structures after crashworthiness event.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.1
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• pp.46-53
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• 2008

Ultrasonic C-scan technique is one of very popular techniques being used for detection of flaws in polymer matrix composite(PMC). However, the application of this technique is very limited for evaluation of defects in PMC fabricated by the automated fiber placement process. The purpose of this study is to develop a novel ultrasonic hybrid system based on nondestructive and non-contact ultrasonic techniques for evaluation of delamination in carbon/epoxy and carbon/PPS composite laminates. It was shown that the newly developed ultrasonic hybrid system based on dual air-coupled pitch-catch technique with ultrasonic scattering reflection concept could provide excellent image with higher resolution of delamination in PMC compared with the conventional pitch-catch method. It is expected that this ultrasonic hybrid technique can be applied for on-line inspection of flaws in PMC during the fabrication process.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2010.04a
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• pp.43-43
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• 2010

국내에 천연가스버스가 보급된 이래 5차례의 용기파열 사고가 발생하였는데 그중 2005년 8월 전주 덕진충전소에서 발생한 용기파열사고는 CNG용기의 라이너를 감싸고 있는 복합재료가 손상되어 발생한 사고로 보고되었다. 복합재료용기의 외피손상이 원인이 되어 발생한 사고사례는 해외에서 약 13건이 보고되었다. CNG용기 외피손상은 용기룰 고정하는 스트랩과 밀접한 관련이 있다. 용기고정이 불완전하면 슬립이 발생하고 이는 복합재의 손상으로 이어진다. 본 연구에서는 ISO 19078, CGA C6.4 등 국제코드의 규정을 고려하여 국내에서 제조된 Type 2, 3, 4 용기와 외국에서 생산된 Type 3 용기를 대상으로 결함깊이, 길이, 넓이에 따른 복합재료 결함 내구성시험을 수행하여 CNG용기의 내구성능을 평가하였고, 시험과 동일한 조건으로 복합재료 손상결함 조건을 컴퓨터로 전산모사하여 시험결과의 타당성과 유효성을 비교 검증하였다. 실험결과, Type 2 용기의 경우, 11,250회의 최소반복가압 회수를 충족하였으나 외피손상부와 반복가압에 따른 실제누출부위가 일치하지 않아 실험조건을 달리한 추가실험이 요구되었다. Type 3 용기의 경우에는 복합재 결함부위와 누수부위가 일치된 시험용기의 수는 67%정도로, 복합재료 용기의 수명을 저하시키는 원인으로 라이너와 외피손상이 서로 밀접한 관련이 있음을 확인하였다. Type 4 용기는 국제기준에서 요구하는 반복횟수를 만족하였고, 손상깊이 0.75mm와 1.25mm에서 반복가압회수가 60,000회 이상이 되어도 누설이 발생되지 않았다. 이는 라이너의 재질이 폴리머로서 균일한데다 탄소섬유 복합재료층 위에 유리섬유 복합재료 층이 1.5mm 정도 추가로 적층되어 있어서 3등급의 손상결함(결함깊이 1.25mm)에서도 구조 층이 전혀 손상되지 않은 것으로 판단되며, 이는 Type 2 용기의 강재라이너나 Type 3의 알루미늄 라이너와 비교하여 Type 4 용기의 폴리에틸렌 라이너의 물성이 반복성능이 탁월함을 확인할 수 있었다.

• Composites Research
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• v.28 no.4
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• pp.212-218
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• 2015

A large composite spar was manufactured using an automatic fiber placement (AFP) machine. To verify its structural performance, the weakest part of the structure, which is called 'corner radius', was tested under bending and examined by finite element analysis. Since the application of AFP machine to composite structure fabrication is still in early stage in Korea, this paper presents the summary of whole process for manufacturing composite spar using AFP machine from mandrel design and analysis to verification test. The deflection and stress by mandrel weight and AFP machine force, thermal deformation and natural frequency were all examined for mandrel design. The target structure was composite C-spar and cured in an autoclave. Test results were compared with nonlinear finite element analysis results to show that the structure has the strength close to the theoretical value. It was confirmed that the corner radius of the spar manufactured by AFP process showed deviation less than 20% compared with first ply failure strength. The results indicate that the AFP technology could be used for large scale composite structure production in the near future.