• Journal of the Korean Institute of Gas
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• v.18 no.6
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• pp.27-31
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• 2014

This paper presents a study on the strength safety of the weak parts at Part 1, Part 2 and Part 3 in the valve structure for LPG cylinder by using the finite element method. The maximum Von Mises stress of 27.5MPa was occurred at the corner edge of a valve Part 1 for the valve thickness of 1.5mm and LPG pressure of 3.5MPa. And the maximum Von Mises stresses for the valve thickness of 1.5mm and LPG pressure of 3.5MPa were 41.5MPa at Part 2 and 46.5MPa at Part 3. The FEM computed results show that the maximum Von Mises stresses at Part 1, Part 2 and Part 3 are very low value of 9.2~15.5% compared with the yield strength of a copper alloy, C3604. This means that the valve thickness for LPG cylinder is so over designed for the conventional valve. Thus, this paper recommends that the thickness at Part 1 and Part 2 is reduced for a light weight of a copper valve. But, the thickness at Part 3 may be better for a thick valve as a conventional valve for high torque strength.

• Journal of the Korean Institute of Landscape Architecture
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• v.32 no.6 s.107
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• pp.103-108
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• 2005

It was aimed to promote as a material for interior landscape by validating Rumohra aristata, in an indoor environment, especially irrigation interval, medium composition and drainage at indoor. 1. The result of physico-chemical analysis of medium composition showed that porosity, pH and Ex-Ca, Ex-Mg and Ex-K were high with peatmoss: vermiculite: perlite(1:1:1) and water contents, organic matter content, total nitrogen and cation exchange capacity were high with sand: leaf mold(1:1). 2. Growth and indoor adaptability of Rumohra aristata were better with irrigation at 2 interval per week than irrigation at 7 interval per week regardless of drainage. 3. In the case of medium composition, of growth and indoor adaptability were higher with sud: leaf mold (1:1) than peatmoss: vermiculite: perlite(1:1:1). 4. Fronds fresh weight and dry weight decreased when irrigation interval increased and were higher with sand: leaf mold(1:1) than peatmoss: vermiculite: perlite(1:1:1) treatment.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.9
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• pp.527-533
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• 2017

Environmental concern about smart phone is growing because it has short product life span while having intensive production technology and cost. In this study environmental impact of the smart phone is quantified using the LCA methodology based on the ISO 14040 series standards. The assessment considers potential environmental impacts across the whole life cycle of the smart phone including; pre-manufacturing; manufacturing; distribution; product use; and end-of-life stages. The pre-manufacturing stage is the most dominant life cycle stage causing the highest environmental impacts among all 10 impact categories assessed. The global warming impacts of the smart phone in the pre-manufacturing, distribution, use, manufacturing, and end-of-life stages were 52.6% 23.9%, 15.7%, 7.0%, and 0.8%, respectively. Sensitivity of the life cycle impact assessment results to the system boundary definition and assumptions made were quite high. Three components of the smart phone, PCB, battery, and display module were identified as the key components causing majority of the potential environmental impact in the pre-manufacturing stage. As such the slim and light-weight design and the use of environmental friendly materials are important design factors for reducing the environmental impact of the smart phone.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.677-681
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• 2015

Aluminum alloy was examined as a material of low weight reactor for hydrolysis of $NaBH_4$. Aluminum is dissolved with alkali, but there is NaOH as a stabilizer in $NaBH_4$ solution. To decrease corrosion rate of aluminum, decrease NaOH concentration and this result in loss of $NaBH_4$ during storage of $NaBH_4$ solution. Therefore stability of $NaBH_4$ and corrosion of aluminum should be considered in determining the optimum NaOH concentration. $NaBH_4$ stability and corrosion rate of aluminum were measured by hydrogen evolution rate. $NaBH_4$ stability was tested at $20{\sim}50^{\circ}C$ and aluminum corrosion was measured at $60{\sim}90^{\circ}C$. The optimum concentration of NaOH was 0.3 wt%, considering both $NaBH_4$ stability and aluminun corrosion. $NaBH_4$ hydrolysis reaction continued 200min in aluminum No 6061 alloy reactor with 0.3 wt% NaOH at $80{\sim}90^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.40 no.8
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• pp.777-783
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• 2003

The mechanical properties of B$_4$C/Al composites normally depend on the species and quantity of reaction products between B$_4$C and Al and then the control of reaction products is necessary to make desirable composites for lightweight advanced or armor materials. TiB$_2$ is chemically inert with aluminum and has a lower contact angle (85$^{\circ}$ at 100$0^{\circ}C$) to liquid aluminum than B$_4$C. Thus, TiB$_2$ coating on B$_4$C may lower infiltration temperature of aluminum when the B$_4$C/Al composites is fabricated by infiltration process. In this study, the effects of TiB$_2$ on the microstructure and mechanical properties of the B$_4$C/Al composites have been investigated. TiB$_2$ coated B$_4$C powder was prepared using the sol-gel technique. It was found that the B$_4$C surface is homogeneously covered with TiB$_2$ having a particles size of 20-50 nm. While the B$_4$C/Al composites prepared by infiltration after TiB$_2$ coating had 17 wt% of unreacted Al, on the other hand, the B$_4$C/Al composites without coating included 14 wt% of Al. As a result, the composites infiltrated after the coating showed higher fracture toughness and lower hardness. This strongly suggests that TiB$_2$ not only lowers the infiltration temperature, but also inhibits the reaction between B$_4$C and Al.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.18-18
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• 2010

전기적 에너지를 기계적 에너지로 변환하고 또한, 기계적 에너지를 전기적 에너지로 변환할 수 있는 압전 세라믹스는 압전 변압기 (piezoelectric transformer), 초음파 모터, 센서 등과 같은 응용분야에 광범위하게 사용되고 있다. 특히, 전원장치에 있어서 현재 주요 전자제품에 사용되고 있는 권선형 변압기와 같은 전자 변환기의 대체품으로 압전 세라믹스 소재의 특성을 이용한 압전변압기의 개발과 응용연구는 국내외적으로 활발히 연구되어왔다. 압전변압기는 권선형 변압기와 비교 하였을 때 누설자속이 없어 노이즈 발생이 없고, 공진주파수만을 이용하므로 출력의 파형이 정현파에 가까워 고조파 잡음이 없으며, 불연성의 특징을 가지고 있다. 추가적으로 압전 변압기는 소형화, 슬림화, 경량화가 가능하며 90%이상의 높은 효율을 얻을 수 있다. 또한, 단판형 압전변압기의 출력한계를 개선하기 위해 높은 승압비와 고출력을 갖는 적층타입의 압전변압기가 제안되었다. 압전변압기용 조성 세라믹스는 높은 에너지 변환효율을 위해서 전기기계결합계수 ($k_p$)가 커야 하며, 발열에 의한 온도 상승을 억제하기 위하여 기계적 품질계수(Qm)가 큰 것이 바람직하다. 또한, 높은 전류를 발생하기 위해서는 유전상수가 커 압전변압기의 출력측 정전용량을 크게 하여야한다. 이러한 압전변압기의 제작 조건을 위해 우수한 압전 및 유전특성을 갖는 PZT계 세라믹스가 주로 사용 되어져 왔다. 그러나, PZT계 세라믹스의 우수한 압전 및 유전특성에도 불구하고 $1000^{\circ}C$에서 급격히 휘발하는 PbO의 성질 때문에 환경적으로나 인체의 건강문제로 인해 전세계적으로 그 사용량을 제한하고 있다. 또한 적층 압전변압기의 구조적 특성상 내부전극과 함께 소결하여야 하는데, 이때 소결온도가 높으면 값비싼 Pd합량이 높은 전극을 사용하여야 한다. Pd함량이 10%미만인 Ag/Pd 전극을 사용하기 위해서는 $950^{\circ}C$ 이하에서 저온소결이 가능한 세라믹스 제조가 필수적이라 할 수 있다. 소결온도를 낮추는 방법으로는 다른 물질들을 치환하여 소결온도를 낮추는 방법과 미세분말을 만들어 그레인사이즈를 미세화 하는 방법들이 있다. 많은 미세 분말 제조 방법 중에서 Attrition mill은 일반적인 ball mill에 비해 분말의 입도를 미세하게 할 수 있어 증가된 분말의 비표면적에 의하여 반응을 촉진시킴으로써 저온소결이 가능한 세라믹스를 만들 수 있다. 따라서 본 연구에서는 소결온도가 낮으면서도 유전 및 압전특성이 우수한 조성을 사용하여 적층 압전변압기를 제작하여 전기적 특성을 조사하였다.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.27-27
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• 2010

청정에너지원의 수요가 증가함에 따라 에너지원의 공급로의 역할을 하는 강관의 수요가 증가하고 있다. 소재가공 기술의 발전과 함께 경량의 고장력 강재의 적용은 공급로의 역할을 하는 강관의 비용절감 및 자원의 효율적 이용 측면에서 지속적으로 연구 개발을 이어왔다. 이러한 추세에 따라 구조용 또는 라인파이프용 강관에서도 고장력 강재의 적용과 함께 고인성 그리고 용접성의 향상을 위한 다양한 라인파이프용 강재의 개발과 이의 적용이 그간 활발히 진행되어왔다. 용도상 반드시 필요한 특성인 고장력, 고인성, 용접성 등 외에도 다양한 강재의 사용에 따른 제조공정상 즉 용접공정에서 발생될 수 있는 용접부의 기계적 특성 변화에 대한 특성 연구 및 기술 연구가 계속 되어왔다. 주로 강관을 생산하는데 쓰이는 ERW (Electric Resistance Welding) 공정에서도 이러한 문제점을 해결하기 위해 많은 연구가 진행되고 있다. ERW는 높은 생산성과 낮은 제조비용의 장점을 가지고 있으나 용접 후 용접부의 기계적 특성 감소로 인한 단점이 있다. 때문에 기계적 특성향상을 위해 최적의 용접조건에 대해 연구해야 할 필요가 있다. 본 연구에서는 4가지 합금강관의 ERW 용접시 용접 입열량의 변화와 용접부의 후열처리를 통한 미세조직의 변화와 기계적 특성에 대해서 고찰하였다. 4강종 시편의 미세조직을 OM, SEM을 통한 분석 이후 인장시험 및 경도시험 등을 통해 기계적 특성을 평가하였다. 대부분의 시편에서 입열량의 증가에 따라 Ferrite 분율이 증가하였고 용접중앙부의 Ferrite 양이 용접경계부 보다 많았다. Ferrite 집중부의 분포가 극명하게 관찰되었던 DP780 (적정) 강종과 미세하게나마 Ferrite 집중부가 존재하였던 K55 (과소, 과대) 강종에서 나란히 경도 하락 현상이 관찰되었다. 이는 강종마다 고유의 Ceq, 합금 중 Mn 농도, 입열량 등에 의한 복합적인 이유 때문으로 판단된다. 탄소가 0.3~0.4 wt% 함유된 중탄소강인 S45C, K55의 경우 용접중앙부와 용접경계부의 페라이트 분율 차이가 큰 것을 알 수 있었다. 이는 용접시 열에 의한 탈탄현상으로 인해 나타나는 현상으로 판단된다.

• Resources Recycling
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• v.14 no.2
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• pp.19-27
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• 2005

The recycling possibility of aluminum waste dross(AWD) as a ceramic raw material of porous light-weight material was examined. A aluminum waste dross was washed 4-7 consecutive times and roasted at 900$^{\circ}% for 1hour as pre-treatments. The properties of the pre-treatment of aluminum waste dross was investigated. It was conformed by XRD result that the spinel crystalline was grown in AWD, after roasting. After the roasted AWD was ground in aqueous state, the sodium hexaphosphate(SHP) as a dispersant which is used for stabilizing the concentrated slurry was added to the AWD slurry. The porous material was prepared by slurry foaming method with surfactant at room temperature. The foamed slurry volumes were 2 and 3 times of the original slurry volume. The properties of porous material with extended volume of 3 times was following: the porosity was about 84%, bulk density was 0.59 g/cm$^3$, the range of pore was from 50 ${\mu}m$ to 500 ${\mu}m$ and mean pore size was about 200 ${\mu}m$. AWD porous material was sintered at 1150$^{\circ}C-1250$^{\circ}C. It was colcluded that AWD was sintered well at 1200$^{\circ}C from material surface observation by SEM.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.121-127
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• 2013

With the continuing demand for lightweight bicycles, carbon fiber composite materials have been widely used in manufacturing bicycle frames and components. Unlike general isotropic materials, the structural characteristics of composite materials are strongly influenced by the staking directions and sequences of composite laminates. Thus, to verify the design process of bicycles manufactured using composites, structural analysis is considered essential. In this study, a carbon-fiber-reinforced plastic (CFRP) bicycle frame was designed and its structural behavior was investigated using finite element analysis (FEA). By measuring the failure indices of the fiber and matrix under various stacking sequences and loading conditions, the effect of the stacking condition of composite laminates on the strength of the bicycle structure was examined. In addition, the structural safety of the bicycle frame can be enhanced by reinforcing weak regions prone to failure using additional composite laminates.

• Journal of Adhesion and Interface
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• v.22 no.4
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• pp.136-143
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• 2021

Polyurea has been investigated as a polymer matrix for composite materials because of its high mechanical strength. Although polyurea has a similar chemical structure to polyurethane, it has much higher strength and durability. In this study, the fabrication of polyurea composites reinforced with carbon nanotube (CNT) and graphene oxide (GO) is demonstrated to enhance the tensile strength of the glass fibers composite. Using FTIR and Raman spectroscopies, the chemical structures of polyurea, CNT, and GO are investigated. As a result, spectroscopy analysis reveals that the chemical structure of CNT, GO, and polyurea is maintained during the fabrication of the composite structure. Scanning electron microscopy reveals the uniform distribution of CNT and GO across the polyurea matrix. The reinforcement of 1 wt% CNT in polyurea enhances the tensile strength of CNT/polyurea composites. In contrast, the reinforcement of GO in polyurea induces the degradation of the tensile strength of GO/polyurea composites.