• Journal of the Korean Vacuum Society
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• v.9 no.2
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• pp.110-115
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• 2000

Deposition conditions of diamond thin films were optimized using hot-filament chemical vapor deposition (HFCVD). Boron-doped diamond thin films with varying boron densities were then fabricated using B4C solid pellets. Current-voltage responses and field emission currents were measured to test the characteristics of field emission display (FED). With the increase of boron doping, the crystal size of diamond decreased slightly, but its quality was not changed significantly in case of small doping. The I-V characterization was performed for Al/diamond/p-Si, and the current of doped diamond film was increased $10^4\sim10^5$ times as compared with that of undoped film. In the field emission properties, the electrons were emitted with low electric field with the increase of doping, while the emission current increased. The onset-field of electron emission was 15.5 V/$\mu\textrm{m}$ for 2 pellets, 13.6 V/$\mu\textrm{m}$ for 3 pellets and 11.1 V/$\mu\textrm{m}$ for 4 pellets. With the incorporation of boron, the slope of Fowler-Nordheim graph was decreased, revealing that the electron emission behavior was improved with the decrease of the effective barrier energy.

• Journal of Korea Foresty Energy
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• v.25 no.2
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• pp.28-33
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• 2006

This study was conducted to find potentialities of the leaves of gingko tree (Gingko biloba L.) which has been planted as a roadside tree in Korea because of its resistance on air pollution, insect, fungi, etc. Various amounts of the leaves were mixed with wasted wood particles to manufacture particleboard. Their influences on physical and mechanical properties and the formaldehyde emission of PB were investigated. Physical and mechanical properties, such as density, modulus of rupture (MOR), and internal bond (IB) strength, of manufactured particleboard were not much different from those of control board. Formaldehyde emission values were decreased with increasing amount of leaves in PB prepared. Especially, particleboard made with 3 percent of leaves was decreased to $1.66mg/{\ell}$ in formaldehyde emission, which is about 40% lower emission than that of control. From these results, the leaves of gingko tree may be considered as a formaldehyde emission lowering additive in a functional PB manufacturing process.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.2
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• pp.31-38
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• 2013

This research analyzed the acoustic emission signals collected from the pin loading tests and investigated the effect of hygrothermal exposure on the fracture behavior of the pin-jointed carbon fiber/epoxy composites. The composite specimens include: the Base specimen that has not been exposed to any environments, the RT specimen that has been immersed in room temperature water, and the HT specimen that has been immersed in high temperature water. According to the pin loading test, the RT and the HT specimens showed 2.2% and 13% decreases in the bearing strength compared to the Base specimen, respectively. The analysis of the acoustic emission signals showed different fracture acceleration points for three types of the specimens. Furthermore, for the RT and the HT specimens, the event from the matrix crack signals in the composites decreased. This shows the effect of the hygrothermal conditions on the acoustic emission signals. Additionally, upon investigating the fracture behaviors of the pin-jointed composites, the exposing specimens to hygrothermal environments decreases the interfacial characteristics of the composites.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.381-389
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• 2000

Metal matrix composite(MMCs) have been rapidly becoming one of the strongest candidates for structural materials for high temperature application. It is well recognized that MMCs always experience at least one large cool-down from processing temperature before my significant applied service loading. Due to the large difference in thermal expansion coefficient between the fiber and matrix, large thermal residual stresses generally develop in composites. It was reported from many previous studies that the effects of thermal residual stress on mechanical properties and fracture behavior were much more complex and dramatic than conventional engineering materials. Therefore it is crucial to evaluate the effect of heat treatment which changes the characteristic of distribution of thermal residual stress in MMCs. Single fiber composite(SFC) test based on the balance in a micromechanical model is a quite convenient method to evaluate interfacial shear strength(IFSS) and the failure mode of composite. In this study the effect of heat treatment on IFSS and the microscopic failure mechanism of MMC is investigated by combining acoustic emission(AE) technique with SFC test. The characteristic of AE signal, IFSS and microscopic failure mechanism due to heat treatment condition is discussed.

• Composites Research
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• v.20 no.3
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• pp.55-62
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• 2007

Interfacial evaluation and durability of Jute and Hemp fibers/polypropylene (PP) composites were investigated. Moisture content of various treated conditions were measured by thermogravimetic analyzer (TGA). After boiling water test, mechanical properties and IFSS between Jute, Hemp fibers and PP matrix decreased. On the other hand, work of adhesion increased due to swelled fibril by water. Surface energies of Jute and Hemp fibers before and after boiling water test were obtained using dynamic contact angle measurement. IFSS was not always consistent with thermodynamic work of adhesion. In boiling water case, since Jute and Hemp fibers could be swelled by water, surface area and moisture infiltration space increased. Environmental effect on microfailure modes of Jute or Hemp fibers and Jute or Hemp fibers/PP composites were obtained by observing via optical microscope and by monitoring acoustic emission (AE) events and their AE parameters. After boiling water test, unlike Hemp fiber, microfailure process of Jute fiber could occur due to low tensile strength by swelled fibril. In addition, AE events occurred more and AE amplitude and energy became lower than those of before boiling water test.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.5
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• pp.418-428
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• 2003

Fiber fracture is one of the dominant failure phenomena affecting the total mechanical Performance of the composites. Fiber fracture locations were measured through the conventional optical microscope and the nondestructive acoustic emission (AE) technique and then were compared together as a function of the epoxy matrix modulus and the fiber surface treatment by the electrodeposition method (ED). Interfacial shear strength (IFSS) was measured using tensile fragmentation test in combination of AE method. ED treatment of the fiber surface enlarged the number of fiber fracture locations in comparison to the untreated case. The number of fiber fracture events measured by the AE method was less than optically obtained one. However, fiber fracture locations determined by AE detection corresponded with those by optical observation with small errors. The source location of fiber breaks by AE analysis could be a nondestructive, valuable method to measure interfacial shear strength (IFSS) of matrix in non-, semi- and/or transparent polymer composites.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2009.04a
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• pp.204-207
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• 2009

The purpose of this study was to evaluation of impact factors, which are temperature and relative humidity on formaldehyde emission from MDF(Medium Density Fiberboard). The test was carried out at 4 specimens that were different of temperature and humidity by using small chamber system. Formaldehyde was sampled and analyzed by HPLC. The results of this study were as follows; 1) When the temperature increased from 25 to $35^{\circ}C$ at 50%, the emission rate of formaldehyde increased 1.0-1.6 times. 2) When the RH increased from 50% to 80% at $25^{\circ}C$, the emission rate of formaldehyde decreased 0.6 times. 3) The enhancement effect of temperature on Formaldehyde under RH of 50% was more significant than under RH of 80%.

• Korean Journal of Environment and Ecology
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• v.13 no.2
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• pp.101-108
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• 1999

이산화탄소는 기후변화를 야기시키는 주요 온실가스이다. 본 연구는 춘천시, 강릉시, 서울시 강남구 및 중랑구를 대상으로 토지이용유형별 식생관리에 기인한 에너지소비 및 탄소방출을 잔디깎기, 전정, 관수, 시비, 살충제시용 등의 식생관리실태를 면담설문 및 일부 실측을 통해 파악하였다. 동일 토지이용유형 내 식생관리강도는 대체로 도시간 및 구간 통계적으로 유의한 차이가 없었다. 수목관리에 의한 연간 총탄소방출량은 토지이용유형에 따라 단위피도면적당 36.0~209.7g/m2로서 교통용지에서 가장 많았다. 잔디관리에 의한 연간 총탄소방출량은 단위잔디면적당 7.4~69.3g/m2로서 공원에서 가장 많았다. 이들 총탄소방출량 중 수목의 경우 전정이 토지이용유형에 따라 96.8~99.7%를, 잔디의 경우 잔디깎기가 91.9~100%를 각각 차지하였다. 도시식생의 연간 순탄소흡수를 최대화하기 위해서 가로수의 전정과 공원 내 잔디깎기에 의한 탄소방출을 최소화할 식재계획 및 관리가 요구된다.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2009.04a
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• pp.548-556
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• 2009

본 연구에서는 산불발생 시 삼림 내 가연물의 화재강도 및 산불위험성을 예측하기 위하여 영동지역에서 자생하는 관목류 가운데 주요 분포수종으로 생강나무와 초피나무를 대상으로 생엽과 가지부위를 채취하여 착화특성, 화재전파특성, 피난특성을 고찰하였다. 발화온도 범위는 400$^{\circ}C$${\sim}$440$^{\circ}C$로 확인되었으며 생강나무의 생엽은 착화가 가장 빠르게 개시되었으며 가지부위는 생엽보다 착화는 늦으나 착화 후 화염유지시간이 길고 비교적 빠른시간에 많은 열량을 방출하는 것으로 나타났으며 초피나무의 가지부위는 연기방출량과 CO 및 $CO_2$의 방출량이 많은 것을 확인할 수 있었다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2007.12a
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• pp.125-126
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• 2007

In this paper, the floating body with vertical plate is introduced with a study on the flow patterns and characteristics in around the floating body by using 2 frame particle tracking method. This paper introduce an analysis method to predict the characteristics if flow around the neighboring fields if Floating Body with vertical plate in order to investigate a high performance model. Flow visualization has conducted in a drcu1ating water channel by a high speed camera and etc. Flow phenomena according to turbulence intensity distribution and flow separation around the floating body with vertical plate were obtained by two-dimensional PIV system.