• 한국분말재료학회지
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• 제19권3호
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• pp.189-195
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• 2012

A novel PM (powder metallurgy) steel for automotive power-train gear components was developed to reduce manufacturing cost, while meeting application requirements. The high-density PM steel was manufactured by mixing using special Cr-Mo atomized iron powders, high-pressure compaction, and sintering. Tensile strength, charpy impact, bending fatigue, and contact fatigue tests for the PM steel were carried out and compared to conventional forged steel. Pinion gears for auto-transmission were also manufactured by helical pressing, sintering, and surface densification process. In order to evaluate the durability of the PM parts, auto-transmission durability tests were performed using dynamometer tests. Results showed that the PM steel fulfilled the requirements for pinion gears indicating suitable tensile, bending fatigue, contact fatigue strengths and improved gear tooth profile. The PM gears also showed good performance during the transmission durability tests. As a result, the PM gears showed significant potential to replace the conventional forged steel gears manufactured by tooth machining (hobbing, shaving, and grinding) processes.

• 한국농공학회논문집
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• 제57권1호
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• pp.11-23
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• 2015

In this study the laboratory test for hydraulic conductivity and the seepage analysis with finite element method on measurement section of sea dike embankment were performed for the purpose of estimating the relative density of embankment from the measured pore water pressures, and both results of the test and the analysis were coupled with the method of estimating seepage blocking state with the hydraulic head loss rate in sea dike embankment. The relationship of void ratio vs hydraulic head loss rate was obtained by setting hydraulic conductivity as common ordinate on the relationships between the void ratio and the hydraulic conductivity and between the hydraulic conductivity and the hydraulic head loss rate. The void ratio on the segment between measuring points was calculated from the coupled relationship of the void ratio vs the hydraulic conductivity. The allowable upper and lower limits of hydraulic head loss rate and those of void ratio on the safety were generated from the coupled relationship between the laboratory compaction test and the sedimentation test. Current hydraulic head loss rate and void ratio were evaluated in the allowable range between upper and lower limits.

• Geomechanics and Engineering
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• 제8권2호
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• pp.173-186
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• 2015

The rapid urbanization in Pakistan is creating a shortage of sustainable construction sites with good soil conditions. Attempts have been made to use rice husk ash (RHA) in concrete industry of Pakistan, however, limited literature is available on its potential to improve local soils. This paper presents an experimental study on engineering properties of low and high plastic cohesive soils blended with 0-20% RHA by dry weight of soil. The decrease in plasticity index and shrinkage ratio indicates a reduction in swell potential of RHA treated cohesive soils which is beneficial for problems related to placing pavements and footings on such soils. It is also observed that the increased formation of pozzolanic products within the pore spaces of soil from physicochemical changes transforms RHA treated soils to a compact mass which decreases both total settlement and rate of settlement. A notable increase in friction angle with increase in RHA up to 16% was also observed in direct shear tests. It is concluded that RHA treatment is a cost-effective and sustainable alternate to deal with problematic local cohesive soils in agro-based developing countries like Pakistan.

• Geomechanics and Engineering
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• 제11권5호
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• pp.639-655
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• 2016

The effect of particle breakage and intermediate principal stress ratio on the behaviour of crushable granular assemblies under true triaxial stress conditions is studied using the discrete element method. Numerical results show that the increase of intermediate principal stress ratio $b(b=({\sigma}_2-{\sigma}_3)/({\sigma}_1-{\sigma}_3))$ results in the increase of dilatancy at low confining pressures but the decrease of dilatancy at high confining pressures, which stems from the distinct increasing compaction caused by breakage with b. The influence of b on the evolution of the peak apparent friction angle is also weakened by particle breakage. For low relative breakage, the relationship between the peak apparent friction angle and b is close to the Lade-Duncan failure model, whereas it conforms to the Matsuoka-Nakai failure model for high relative breakage. In addition, the increasing tendency of relative breakage, calculated based on a fractal particle size distribution with the fractal dimension being 2.5, declines with the increasing confining pressure and axial strain, which implies the existence of an ultimate graduation. Finally, the relationship between particle breakage and plastic work is found to conform to a unique hyperbolic correlation regardless of the test conditions.

• 한국분말재료학회지
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• 제17권6호
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• pp.482-488
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• 2010

In this study, $FeSi_2$ as high temperature performance capable thermoelectric materials was manufactured by powder metallurgy.The as-casted Fe-Si alloy was annealed for homogenization below $1200^{\circ}C$ for 3 h. Due to its high brittleness, the cast alloy transformed to fine powders by ball-milling, followed by subsequent compaction (hydraulic pressure; 2 GPa) and sintering ($1200^{\circ}C$, 12 h). In order to precipitate ${\beta}-FeSi_2$, heat treatment was performed at $850^{\circ}C$ with varying dwell time (7, 15 and 55 h). As a result of this experiment thermoelectric phase ${\beta}-FeSi_2$ was quickly transformed by powder metallurgical process. There was not much change in powder factor between 7h and 55h specimens.

• Design & Manufacturing
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• 제10권2호
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• pp.6-11
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• 2016

Designed patterns of slit are introduced to the uni-directional (UD) prepreg in order to enhance the formability of the carbon/epoxy composites without wrinkling and laddering. Three different types of the slit alignment along the thickness direction are applied to analyse the deformation behavior during the compression moulding process of laminates. Degrees of the slit open and the mechanical strength are evaluated based on the level of the compaction pressure in the course of forming process. Results have shown that the mechanical strength of laminates having slits could attain at least 80% of the conventional ones without slits. However, further studies are required to identify the direct relevance of the slit alignment in laminate to the mechanical properties.

• Geomechanics and Engineering
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• 제11권1호
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• pp.161-175
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• 2016

A series of experimental studies are conducted on the deformation and shear strength property of compacted loess. The results reveal that the relationships of both the initial moisture content (w) and the initial degree of compaction (K) of compacted loess with cohesion (w) and the angle of internal friction (${\varphi}$) are linear. The relationship between the secant modulus ($E_{soi}$) and K is also linear. The relationship between $E_{soi}$ and w can be fitted well by a second-order polynomial. Further, when the influences of w and K are ignored, the relationship between the confined compression strain (${\varepsilon}$) and vertical pressure (p) can be expressed by a formula. A correction formula for the deformation of compacted loess caused by a change in w and K is derived on the basis of the study results.

• 멤브레인
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• 제31권4호
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• pp.282-292
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• 2021

본 연구에서는 Dead-end와 Crossflow 시스템을 사용하여 유기용매 나노여과(Organic Solvent Nanofiltration, OSN) 상용분리막의 성능을 분석하였다. 가교된 polyimide 소재 기반의 Duramem (DM) OSN 분리막의 성능을 ethanol, dimethylformamide (DMF), acetone, acetonitrile 용매에서의 성능을 분석하였다. 네 종류의 분획분자량 성능을 갖는 DM 분리막의 성능을 평가하였을 때 dead-end보다 Crossflow에서 조금 더 정확하고 신뢰성 높은 결과를 얻을 수 있었으며, 동일한 분리막이더라도 용매의 특성에 따라 투과도와 선택도 차이가 크게 난다는 것을 확인할 수 있었다. 이는 압밀화현상으로 인한 초기 안정화 기간의 차이 때문인 것으로 판단되며 분리막마다 안정화기간이 다르므로 신뢰성 높은 결과를 얻기 위해선 Crossflow 시스템을 활용하는 것이 더 적합한 것으로 보인다.

• Nuclear Engineering and Technology
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• 제56권3호
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• pp.873-879
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• 2024

A sodium-cooled fast reactor (SFR) core has a potential of prompt criticality due to a change of core material distribution during a severe accident, and the resultant energy release has been one of the safety issues of SFRs. In this study, the safety assessment of an unprotected loss-of-flow (ULOF) in a small SFR (SSFR) has been performed using the SIMMER-IV computer code, which couples the models of space- and time-dependent neutronics and multi-component, multi-field thermal hydraulics in three dimensions. The code, therefore, is applicable to the simulations of transient behaviors of extended disrupted core material motion and its reactivity effects during the transition phase (TP) of ULOF, including a potential of prompt-criticality power excursions driven by fuel compaction. Several conservative assumptions are used in the TP analysis by SIMMER-IV. It was found out that one of the important mechanisms that drives the reactivity-inserting fuel motion was sodium vapor pressure resulted from a fuel-coolant interaction (FCI), which itself was non-energetic local phenomenon. The uncertainties relating to FCI is also evaluated in much conservative way in the sensitivity analysis. From this study, the ULOF characteristics in an SSFR have been understood. Occurrence of recriticality events under conservative assumptions are plausible, but their energy releases are limited.

• 대한토목학회논문집
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• 제32권1C호
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• pp.1-6
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• 2012

본 논문에서는 이중보온관의 다짐시공 중 안정성 평가 및 되메움 대체재료 제시를 위하여 현장시험을 수행하였다. 현장시험 시 사용된 되메움 재료는 기존 되메움 재료인 중사와 되메움 대체재료 평가를 위한 자연모래 2종(세사, 왕사)과 부순모래, 자갈 2종(10mm, 20mm)을 사용하였다. 현장시험은 되메움재료 별 이중보온관 토압 및 변형, 외관손상 등의 거동 특성 평가를 위하여 수행하였다. 연구결과에 따르면, 부순모래는 5종의 되메움 대체재료 별 평가결과 이중보온관에 미치는 공학적 특성 및 재료의 수급 측면에 있어 기존 중사를 이용하는 이중보온관 되메움재의 대체재료로 가장 합리적인 재료로 평가되었다.