• 한국군사과학기술학회지
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• 제19권3호
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• pp.311-318
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• 2016

This paper shows storage life estimation of next IR(infrared) flare material through accelerated degradation tests. Three temperature conditions for the accelerated degradation tests are 55, 65 and $75^{\circ}C$. Six performances of IR flare material are burning time, IR peak/continuous Intensity, total energy of near/mid-IR and color ratio, and they were measured after the tests. Storage life of the IR flare material was estimated through both analyzing the degradation data of those performances and applying distribution-based degradation models to the data. Over 30 years of storage life at $20^{\circ}C$ is estimated in terms of IR peak intensity with reliability 0.99 and confidence level 99 %. Additionally, 10 years of storage period at $21^{\circ}C$ would be equivalent to 68 days of accelerated test at $65^{\circ}C$ from the activation energy in Arrhenius model.

• 한국정밀공학회지
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• 제15권7호
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• pp.91-97
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• 1998

The analysis model is the infinite body consisted of power law creep material containing a rigid inclusion with line crack shape subjected to the arbitrarily directional stress on an infinite boundary. The crack analysis is performed using the complex pseudo-stress function. The strain rate intensity factor is determined in the closed form as new fracture mechanics parmeter which represents the magnitudes of stress and strain rate near the tip in power law creep material.

• 한국결정성장학회지
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• 제29권1호
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• pp.32-38
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• 2019

서비스디자인 방법론을 통해 사용 편의성에 중점을 둔 신개념의 모듈형 자전거 액세서리를 탄소 소재를 이용하여 개발하였다. 기존의 탄소 재질을 사용할 경우 자전거 주행 중 충격에 견디지 못하거나, 파손 현상이 발생하였으며, 이러한 문제점을 해결하고자 새로운 소재(S Foam Core 소재)를 적용 하였다. 기존 탄소 재질과 S Foam Core 소재의 강도, 뒤틀림 강도, 충격흡수 및 진동감쇄 측정을 하였고, S Foam Core가 적용된 제품이 기존 탄소 소재 보다 더 우수한 결과를 얻었다. 본 연구에서는 S Foam Core 소재로 프로토 타입을 제작하여, 자체 실험을 통해 검증하였고, 이를 보고하고자 한다.

• 한국재료학회지
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• 제21권7호
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• pp.396-402
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• 2011

In this study, by using tin chloride solution as a raw material, a nano-sized tin oxide powder with an average particle size below 50 nm is generated by a spray pyrolysis process. The properties of the generated tin oxide powder depending on the inflow speed of the raw material solution are examined. When the inflow speed of the raw material solution is 2 ml/min, the majority of generated particles appear in the shape of independent polygons with average size above 80-100 nm, while droplet-shaped particles show an average size of approximately 30 nm. When the inflow speed is increased to 5 ml/min, the ratio of independent particles decreases, and the average particle size is approximately 80-100 nm. When the inflow speed is increased to 20 ml/min, the ratio of droplet-shaped particles increases, whereas the ratio of independent particles with average size of 80-100 nm decreases. When the inflow speed is increased to 100 ml/min, the average size of the generated particles is around 30-40 nm, and most of them maintain a droplet shape. With a rise of inflow speed from 2 ml/min to 5 ml/min, a slight increase of the XRD peak intensity and a minor decrease of specific surface area are observed. When the inflow speed is increased to 20 ml/min, the XRD peak intensity falls dramatically, although a significant rise of specific surface area is observed. When the inflow speed is increased to 100 ml/min, the XRD peak intensity further decreases, while the specific surface area increases.

• 한국안전학회지
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• 제32권4호
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• pp.1-6
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• 2017

Functionally Graded Materials (FGM) as advanced heterogeneous composite materials have a higher performance than a conventional composite or bimaterial composite under some severe environments. As a heterogeneous material, FGM is commonly used in spacecraft, defense, nuclear and automotive industries due to its excellent properties. The purposes of this study are to evaluate the stress distribution and crack behaviors by the multiscale simulation. FGM contains two or more than two materials that the composition is structured continuously. Two types of FGM model are suggested, which are created by arbitrary prediction of the volume fraction and the exponential function. Aluminum as the metal matrix constituent and silicon carbide as the ceramic particle constituent are structured gradually by two types and the three point bending test also estimated. Moreover, two kinds of crack location were introduced in order to get the influences of material property distribution on the stress intensity factor. From the results we found that the stress intensity factors are increased in the case from softer to stiffer material, while vice versa.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.817-820
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• 2011

솔레노이드 밸브는 전기에너지를 기계적인 운동으로 변환하는 장치로, 솔레노이드 코일에 전류를 인가할 때 자기장이 생성된다. 솔레노이드에서 발생하는 자기장의 크기는 코일의 권선 수, 전류의 세기 및 자성소재의 특성과 밀접한 관계가 있다. 자기력을 증가시키기 위해 코일의 권선 수, 전류의 세기를 증가시킬 경우, 밸브의 크기 및 무게가 증가하는 단점이 있다. 따라서 밸브의 크기를 줄이기 위해서는 솔레노이드 밸브 사용 환경에 적합한 자성소재의 선정이 중요하다. 본 연구는 솔레노이드 밸브 개발에 필요한 자성소재의 특성을 정리하였다.

• 한국안전학회지
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• 제24권2호
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• pp.23-29
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• 2009

The hybrid composite materials are recently used in many field as an advanced material due to their high resistance to fracture. However, hybrid composite materials have several problems, especially delamination, compared with homogeneous materials such as an aluminum alloy, etc. In this study, we carried out the tensile test to study the tension failure appearances and tensile ultimate strength of CFRP/Al/CFRP hybrid composite materials. The CFRP material used in the experiment is a commercial material known as CU175NS in unidirectional carbon prepreg. Also Al/CFRP/Al hybrid composites with three kind length of a single edge crack were investigated for the relationship between an aluminium volume fraction and a crack length. The crack length was measured by a traveling microscope under a universal dynamic tester. Futhermore the stress intensity factor behavior was examined according to a volume fraction and an initial crack length ratio to a width.

• 한국재료학회지
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• 제26권11호
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• pp.662-669
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• 2016

In order to identify changes in the nature of the particles due to changes in the inflow rate of the raw material solution, the present study was intended to prepare nano-sized cobalt oxide ($Co_3O_4$) powder with an average particle size of 50 nm or less by spray pyrolysis reaction using raw cobalt chloride solution. As the inflow rate of the raw material solution increased, droplets formed by the pyrolysis reaction showed more divided form and the particle size distribution was more uneven. As the inflow rate of the solution increased from 2 to 10 ml/min, the average particle size of the formed particles increased from about 25 nm to 40 nm, while the average particle size did not show significant changes when the inflow rate increased from 10 to 50 ml/min. XRD analysis showed that the intensity of the XRD peaks increased remarkably when the inflow rate of the solution increased from 2 to 10 ml/min. On the other hand, the peak intensity stayed almost constant when the inflow rate increased from 10 to 50 ml/min. With the increase in the inflow rate from 2 to 10 ml/min, the specific surface area of the particles decreased by approximately 20 %. On the contrary, the specific surface area stayed constant when the inflow rate increased from 10 to 50 ml/min.

• Structural Engineering and Mechanics
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• 제66권1호
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• pp.97-111
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• 2018

Cracking can lead to unexpected sudden failure of normally ductile metals subjected to a tensile stress, especially at elevated temperature. This article is raised to study the application of a composite material instead of the traditional carbon steel material used in the natural gas transmission pipeline because the cracks occurs in the pipeline initiate at its internal surface which is subjected to internal high fluctuated pressure and unsteady temperature according to actual operation conditions. Functionally graded material (FGM) is proposed to benefit from the ceramics durability and its surface hardness against erosion. FGM properties are graded at the radial direction. Finite element method (FEM) is applied and solved by ABAQUS software including FORTRAN subroutines adapted for this case of study. The stress intensity factor (SIF), temperatures and stresses are discussed to obtain the optimum FGM configuration under the actual conditions of pressure and temperature. Thermoelastic analysis of a plane strain model is adopted to study SIF and material response at various crack depths.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.412-414
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• 2003

This paper is about research of scintillator layer, which is used for Hybrid method to increase electric signals in a-Se, the material of Direct method. In case of the thermal evaporation, CsI has column structure which is an disadvantage as scintillator. But it decreases scattering of incident X-ray, has better Light output intensity than other scintillation materials. CsI was made by Thermal evaporation. The Doping material, Na, 0.1, 0.3, 0.5, 0.7g were added in each sample. Analysis of absorbed wavelength, PL(Photoluminescence), Light output intensity, SEM, and XRD analysis were performed to analyze optical characteristics. Doping rate of CsI:Na to use as scintillation layer in a-Se based detector could be optimized.