• 비파괴검사학회지
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• 제32권3호
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• pp.269-275
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• 2012

Carbon-fiber reinforced plastic(CFRP) laminates made of nano-particle-coated carbon fibers and damaged by a simulated lightning strike were tested under compression-after-impact(CAI) mode, during which the damage progress due to compressive loading has been monitored by acoustic emission(AE). The impact damage was induced not by mechanical loading but by a simulated lightning strike. Conductive nano-particles were coated directly on the fibers, from which CFRP coupons were made. The coupon were subjected to the strikes with a high voltage/current impulse of 10~40 kA within a few ${\mu}s$. The effects of nano-particle coating and the degree of damage induced by the simulated lightning strikes on AE activities were examined, and the relationship between the compressive residual strength and AE behavior has been evaluated in terms of AE event counts and the onset of AE activity with the compressive loading. The degree of impact damage was also measured in terms of damage area by using ultrasonic C-scan images. The assessment during the CAI tests of damaged CFRP showed that AE monitoring appeared to be useful to differentiate the degree of damage hence the mechanical integrity of composite structures damaged by lightning strikes.

• 대한금속재료학회지
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• 제50권6호
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• pp.427-432
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• 2012

This paper presents the material properties of carbon steels for ships, and offshore structures (ASTM A131) are tested under a series of arctic and cryogenic temperature conditions. For material tension tests, among the ASTM 131 steels, Grades A and B of mild steel and Grade AH of high tensile steel have been used. The obtained mechanical properties of the materials from the material tension tests were applied in a 13,000TEU class container ship to define the effect of low temperature on the ultimate longitudinal strength of the target structure by using the ALPS/HULL intelligent supersize finite element method. The tensile coupon test results showed increased strength and nonuniform fracture strain behaviors within different grades and temperatures. Increasing the material strength resulted in increasing the ultimate longitudinal strength of the ship.

• 한국항공우주학회지
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• 제50권6호
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• pp.377-384
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• 2022

복합재 항공기 구조물의 설계 시 인증을 고려한 재료 허용치와 설계치의 설정이 매우 중요하다. 그리고 복합재 구조물의 재료 허용치와 설계치의 설정은 정적강도, 손상허용 요구 조건 및 환경효과가 고려되어야 한다. 빌딩블록 접근법은 오랫동안 민간 및 군수 항공 산업에 적용되어 왔으며 중요한 인증 방법론을 제공하였다. 현재의 인증 방법은 시편, 요소, 부구성품 및 전기체 시험을 포함하는 광범위한 실험을 기반으로 한다. 본 논문에서는 복합재 허용치 실험 사례가 제시되며 빌딩 블록 접근 방식의 중요한 배경 및 적용방법이 제시된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.692-697
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• 2005

좋은 날개 실속특성 및 실속/스핀의 특성이 입증된 선미익형 항공기를 현재 개발중에 있다. 전에 개발된 1호기 및 2호기 시제기는 코어 샌드위치 형식으로 날개 전체가 채워지고 고정식 착륙장치로 제작되었다. 새로이 개발될 반디호는 접개식 착륙장치와 날개와 동체에 일반적인 폼 코아 샌드위치층이 장착될 예정이다. 제작을 위해 시편 시험을 포함한 복합 소재 제작 공정이 연구되었고 적층 몰드를 이용하여 유리 섬유 천으로 폼 코어 위로 상온 적충하는 방식이 채택되었으며, 복합소재 부품들은 실온과 대기압하에 경화시킨다. 일반적으로, 몰드부품들은 양산에 적합한 매끄러운 표면 조도와 표준 품질을 보여주었다. 본 연구에서는 소형 항공기 반디호 몰드 기술과 개발 상황을 기술하였다.

• 한국의류학회지
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• 제14권4호
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• pp.252-261
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• 1990

This study intends to provide a beneficial foundation which can aid our understanding of how a clothing consumer group can be classified according to the clothing buying motives, and what differences are there about the importances of stroe image attribute among them and how consumer's preferences to the store image are shown differently among them and ultimately, some concrete data which can be useful in establishing efficient store image strategies for clothing stores. 413 subjects were gathered through convenience sampling method and, for data analysis, cronbach'$\alpha$, frequency, percentage, mean, $x^{2}-text$, 1-test, ANOVA, Duncan Multiple Range Test, Factor Analysis, Cluster Analysis were conducted. The results are as follows; 1. Three kind of factors in the clothing buying motives were determined for analysis of consumers group and by which it was revealed as to be significant for us to classify them four subdivisions; those of fashion pursuit group, self display group, financial utilitarian group, individual group. 2. Importance on store image attribute was revealed then the middle aged women regarded quality, price, service in order as more important factors than others. 3. Store image preferences show significantly when concerned with quality, price, fashion, impression and age of store personnel, convenience for exchanging and returning goods, credit, delivery and repair, mailing of catalogue and discount coupon, exit from, brightness of store among consumer groups. From these findings, concretely store image strategies are proposed.

• 자동차안전학회지
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• 제13권2호
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• pp.30-34
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• 2021

Electrical failures and reliability problems of electronic components by ionic migration between adjacent device terminals have become an issue in automotive electronics. Especially unlike galvanic corrosion, ionic migration is occurred at high temperature and high humidity under applied electric field condition. Until now, although extensive studies of the ionic migrations dealing with PCBs, electrodes, and solders were reported, there is no study on the effect of insulation polymers and metallic fillers for ionic migration. In this research, therefore, ionic migration induced by the types and contents of polymers and metallic fillers, and variety conditions of temperature, humidity, and applied voltage was studied in detail. Ester and amide types of liquid crystal polymer (LCP) and poly (phthalamide) (PPA) were used as base polymers, respectively and compounded with the metallic fillers of Copper iodide (CuI), Zinc stearate (Zn-st), or Calcium stearate (Ca-st) in various compositions. The compounding polymers were fabricated in IPC-B-24 of SIR test coupon according to ISO 9455-17 with Cu electrodes for ionic migration test. While there is no change in LCP-based samples, ionic migration in PPA compounding sample with a high water absorption property was accelerated in the presence of 0.25 wt% or above of CuI at the environmental conditions of 85℃, 85% RH and 48V. The dendritic short-circuit growth of Cu caused by ionic migration between the electrodes on the surface of compounded polymers was systematically observed and analyzed by using optical microscopy and SEM (EDX).

• Steel and Composite Structures
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• 제39권4호
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• pp.401-417
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• 2021

This study experimentally reveals the influence of welding on grade S690Q high strength steel (HSS) butt joints from both micro and macro levels. Total eight butt joints, taking plate thickness and welding heat input as principal factors, were welded by shielded metal arc welding. In micro level, the microstructure transformations of the coarse grain heat affected zone (CGHAZ), the fine grain heat affected zone (FGHAZ) and the tempering zone occurred during welding were observed under light optical microscopy, and the corresponding mechanical performance of those areas were explored by micro-hardness tests. In macro level, standard tensile tests were conducted to investigate the impacts of welding on tensile behaviour of S690Q HSS butt joints. The test results showed that the main microstructure of S690Q HSS before welding was tempered martensite. After welding, the original microstructure was transformed to granular bainite in the CGHAZ, and to ferrite and cementite in the FGHAZ. For the tempering zone, some temper martensite decomposed to ferrite. The performed micro-hardness tests revealed that an obvious "soft layer" occurred in HAZ, and the HAZ size increased as the heat input increased. However, under the same level of heat input, the HAZ size decreased as the plate thickness increased. Subsequent coupon tensile tests found that all joints eventually failed within the HAZ with reduced tensile strength when compared with the base material. Similar to the size of the HAZ, the reduction of tensile strength increased as the welding heat input increased but decreased as the thickness of the plate increased.

• Advances in concrete construction
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• 제2권3호
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• pp.177-192
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• 2014

One of the main applications of FRP composites is confining concrete columns. Hence identifying the cyclic and monotonic stress-strain behavior of confined concrete columns and the parameters influencing this behavior is inevitable. Two significant parameters affecting the stress-strain behavior are aspect ratio and corner radius. The present study aims to scrutinize the effects of corner radius and aspect ratio on different aspects of stress-strain behavior of FRP confined concrete specimens (rectangular, square and circular). Hence 44 FRP confined concrete specimens were tested and the results of the tests were investigated. The findings indicated that for specimens with different aspect ratios, the relationship between the ultimate stress and the corner radius is linear and the variations of the ultimate stress versus the corner radius decreases as a result of an increase in aspect ratio. It was also observed that increase of the corner radius results in increase of the compressive strength and ultimate axial strain and increase of the aspect ratio causes an increase of the ultimate axial strain but a decrease of the compressive strength. Investigation of the ultimate condition showed that the FRP hoop rupture strain is smaller in comparison with the one obtained from the tensile coupon test and also the ultimate axial strain and confined concrete strength are smaller when a prism is under monotonic loading. Other important results of this study were, an increase in the axial strain during the early stage of unloading paths and increase of the confining effect of FRP jacket with the increase and decrease of the corner radius and aspect ratio respectively, a decrease in the slope of reloading branches with cycle repetitions and the independence of this trend from the variations of the aspect ratio and corner radius and also quadric relationship between the number of each cycle and the plastic strain of the same cycle as well as the independence of this relationship from the aspect ratio and corner radius.

• 한국강구조학회 논문집
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• 제24권4호
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• pp.443-450
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• 2012

이 연구에서는 내진구조용 강재(SN)의 냉강롤성형된 각형강관을 사용한 CFT 부재의 중심축하중에 대한 구조성능을 평가한다. 일반적으로 냉간롤성형 및 냉간프레스형성으로 인하여 각형강관의 코너부와 평판부 모두 SN강재에 비해 재질변화가 발생하며, 항복강도와 인장강도 및 항복비의 상한치가 높아지는 경향을 나타낸다. 이러한 현상은 강관의 국부좌굴 이후의 비선형거동에 의해 영향을 주며, 이는 CFT 합성 부재와 같이 비선형해석모델에 대하여 영향을 미친다. 따라서 각형강관의 가공열화도를 평가하기 위하여 각형강관의 재료시험을 수행하였고, 세장비 및 판-폭두께비를 실험변수로 하여 일축 압축력을 받는 CFT부재의 구조성능을 평가하였다.

• 미생물학회지
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• 제31권3호
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• pp.255-260
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• 1993

Enterobacter cloacae 를 이용하여 슬라이드 (slide glass) 와 아연도강관조각 (galvanized-iron coupon) 상에 생물막을 형성시킨 후 부착생장세균의 염소에 대한 내성을 측정한 결과 부유생장세균에 비해 각각 14배와 380배의 내성증가를 나타내었다. 또한 입자에 부착된 세균군집의 경우 부유세균군집에 비해 48배로 내성이 증가되었다. 슬라이드와 아연도강관조각을 수돗물에 75일간 접촉하였을때 각각 $4.75 {\times} 10^{4}$ cfu/$cm^{2}$, $1.12 {\times} 10^5 cfu/cm^{2}$의 생물막이 형성되는 것을 관찰하였다. 따라서 수돗물에서의 장내세균과 종속영양세균 입자에 부착 혹은 흡착되거나 응집된 상태로 존재함으로써 잔류염소에 대한 내성을 가지게 되며, 또한 정수과정에서 염소살균을 피하여 비급수계통으로 유입되면 배급수관 내벽에 생물막을 형성하여 잔류업소에 대한 내성을 가지게 됨으로써 배급수계통에서 생장하는 것으로 판단된다.