• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 추계학술발표대회 논문집
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• pp.57-60
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• 2001

In order to extend the life time of building and civil infra-structure, nowadays, patch type fibrous composite materials are widely used. Retrofitted concrete columns and beams gain the stiffness and strength, but they lose toughness and show brittle failure. Usually, the cracks of concrete structures are visible with naked eyes and the status of the structure in the life cycle is estimated with visible inspection. After retrofitting of the structure, crack visibility is blocked by retrofitted composite materials. Therefore, structural monitoring after retrofitting is indispensible and self diagnosis method with optical fiber sensor is very useful. In this paper, We try to detect peel out effect and find the strain difference between main structure and retrofitting patch material when they separate each other.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.502-507
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• 2008

An entire composite structure satellite is developing for the first time in Korea. All of the structure is made of CFRP-composite faced aluminum honeycomb sandwich structure. Here the random and sinusoidal spectrum analysis of the satellite was carried out by using the finite element method. The general spectrum analysis was herein performed but also the PSD (power spectrum density) function for random vibration analysis had been transformed into equivalent time domain function and then transient analysis is conducted. The time history of displacement, acceleration, stress and velocity responses with respect to the PSD input has been achieved by the time dependent transient function transformed from frequency PDS function. It enables one to perform dynamic durability analysis and then expect the life time of the composite structure. The composite faced sandwich structure's spectrum analysis of a domestically-developed satellite, STSAT-3, has been discussed in the present study.

• Advanced Composite Materials
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• 제17권3호
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• pp.215-224
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• 2008

The present study aims to design a multilayer microstrip antenna with composite sandwich construction and investigate fatigue behavior of this multilayer SAS (surface antenna structure) that was asymmetric sandwich structure for the next generation of structural surface technology. This term, SAS, indicates that the structural surface becomes an antenna. Constituent materials were selected considering electrical properties, dielectric constant and tangent loss as well as mechanical properties. For the antenna performance, antenna elements inserted into structural layers were designed for satellite communication at a resonant frequency of 12.2 GHz. From electrical measurements, it was shown that antenna performances were in good agreement with design requirements. In cyclic 4-point bending, flexure behavior was investigated by static and fatigue test. Fatigue life curve of the SAS was obtained. The experimental results of bending fatigue were compared with single load level fatigue life prediction equations and in good agreement. The SAS concept is can be extended to give a useful guide for manufacturers of structural body panels as well as antenna designers.

• Journal of Magnetics
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• 제16권3호
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• pp.271-275
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• 2011

This paper proposes a magnetoelectric (ME) composite transducer structure consisting of a magnetostrictive H-type Fe-Ni fork substrate and piezoelectric PZT plates. The fork composite structure has a higher ME voltage coefficient compared to other ME composite structures due to the higher quality (Q) factor. The ME sensitivity of the fork structure reaches 12 V/Oe (i.e., 150 V/cm Oe). The fork composite with two PZT plates electrically connected in series exhibits over 5 times higher ME voltage coefficient than the output of the rectangle structure in the same size. The experiment shows the composite of a Fe-Ni fork substrate and PZT plates has a significantly enhanced ME voltage coefficient and a higher ME sensitivity relative to the prior sandwiched composite laminates. By the use of a lock-in amplifier with 10 nV resolution, this transducer can detect a weak magnetic field of less than $10^{-12}$ T. This transducer can also be designed for a magnetoelectric energy harvester due to its passive high-efficiency ME energy conversion.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.207-211
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• 2005

The Korean Tilting Train eXpress (TTX) with service speed of 180km/h have been developing using hybrid design concept combined with a sandwich composite structure for the carbody and stainless steel structure for the underframe to match the challenging demands with respect to cost efficient lightweight design for railway carriage structures. The sandwich composite structure was used to minimize the weight of the carbody, while the metal underframe was used to modify the design easily and to keep the strength of underframe for the installation of the electrical equipments. The sandwich composite structure was 23 meters long, 3 meters wide and 2.7 meters high, and cured as one body in a large autoclave equipment with the length of 30 meters and the diameter of 5 meters. The joint part between the carbody structure made of sandwich composites and the metal underframe was joined by the proposed design.

• Composites Research
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• 제25권4호
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• pp.105-109
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• 2012

최근 국내에서 미국과 상호항공안전협정 체결을 위한 소형 항공기가 연구 개발 중이다. 연구 대상 항공기는 경량화 하여 연료 절감을 위해 전기체 복합재료가 적용되었다. 그러나 복합재 구조는 외부의 충격 손상에 취약한 구조이다. 따라서 항공기 구조물은 충격 손상에 대한 압축 파손 강도를 고려하여 손상 허용 설계가 반드시 수행되어야 한다. 이는 복합재 구조 항공기 인증에 매우 중요한 요소이다. 본 연구에서는 항공기 복합재 구조에 적용된 두꺼운 적층판에 대한 손상 허용 연구를 수행하였다. 두꺼운 적층판의 세 가지 형태인 손상이 없는 시편, 구멍 손상 및 충격 손상이 적용된 시편의 압축 하중 하에서 손상 허용 기준이 평가되었다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.247-250
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• 2005

This study has evaluated the analysis results for the under structure of Korean tilting train(TTX). TTX has many equipments which are attached below the composite carbody. Loads due to equipments on the under structure are very complex and various types as operating condition. So applied loads are considered weight of equipments and acceleration. From the analysis, the structural safety of under structure was assessed.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 추계학술발표대회 논문집
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• pp.272-276
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• 1999

The present paper proposes design and manufacturing methods of the carbon/epoxy square grid structure with near zero-CTE in three geometrical principal directions. Bonding strength of the grid structure is examined for different bonding methods. Numerical examples show that maximum displacement of the composite grid structure is almost zero comparing with that of aluminum grid structure with same dimension under thermal loading.

• 한국철도학회논문집
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• 제9권1호
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• pp.43-49
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• 2006

We have evaluated the structural integrity of a sandwich composite train roof structure that can be a lightweight, cost saving solution to large structural components for rail vehicles in design stages. The sandwich composite train roof structure was 11.45 meters long and 1.76 meters wide. The finite element analysis was used to calculate the stresses, deflections and natural frequencies of the sandwich composite train roof against the weight of air-conditioned system. The 3D sandwich finite element model was introduced to examine the structural behavior of the hollow aluminum extrusion frames joined to both sides of the sandwich composite train roof. The results shown that the structural performance of the sandwich composite train roof under loading conditions specified is satisfaction and the use of aluminum reinforced frame and aluminum honeycomb core is beneficial with regard to weight saving and structural performance in comparison with steel reinforced frame and polyurethane foam core. Also, we have manufactured prototype of sandwich composite train roof structure on the basis of analysis results.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.220-223
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• 2004

The weight reduction of carbody structures is of great concern in developing high speed tilting train for the normal operation of tilting system. The use of composite materials for the carbody structures has many advantages due to their excellent material properties. In this paper, finite element analysis was conducted to analysis and design the composite structure of Tilting Train eXpress(TTX). According to JIS E 7105, static load tests were performed and the structural safety of the composite carbody structure was verified by conducting finite element analysis of the model to which reinforcing frame are added in the composite carbody structure. In addition, modal analysis was conducted to estimate the natural frequency of a train.