• Geomechanics and Engineering
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• 제1권4호
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• pp.323-335
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• 2009

Gravels forming part of the base of flexible pavements experience abrasion and crushing as a result of static and dynamic loads. Abrasion takes place when the sharp corners of the particles of gravel are removed as a result of compressive and shear loads. As a result of abrasion, the particles change in shape. Crushing is caused by the fragmentation of the particles into a mixture of many small particles of varying sizes. In this study, the abrasion and crushing of gravels are evaluated experimentally and analytically. The laboratory component of this study involves gravels that were subjected to abrasion and dynamic compression tests. The evaluation of the abrasion and crushing experienced by the gravel was carried out using fractals. In this study, the fractal dimension concept from fractal theory is used to evaluate: (a) the changes in shape, and (b) the crushing (fragmentation) of the original particles of gravel. It was determined that the fractal dimension of the profile of the particles decreased as a result of abrasion. With respect to crushing, the fragmentation fractal dimension was found to increase with the degree of breakage of the gravel. To understand the influence of crushing on the permeability of the gravels, the hydraulic conductivity of the gravels was measured before and after crushing. The hydraulic conductivity of the gravels was found to decrease with an increase in their level of crushing. Also, changes in the angle of friction of the granular materials as a result of abrasion was calculated using the Krumbein's roundness chart. The angle of friction of the granular materials was found to decrease as a result of abrasion.

• 한국결정성장학회지
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• 제31권6호
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• pp.264-269
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• 2021

본 연구는 공침법을 통하여 비정질 알루미늄 실리케이트 분말을 제조하였으며, 슬러리의 알루미늄 실리케이트 분말 함량 및 분산제 첨가량을 조절하여, 슬러리의 특성에 따른 분무 건조 알루미늄 실리케이트 과립 분말 제조의 영향 분석 및 최적화 연구를 진행하였다. 연구 결과, 알루미늄 실리케이트 슬러리의 분말 함량 27.5 wt% 이하, 슬러리의 분산제 첨가량 0.8 wt% 이상, pH 6~9의 중성 분위기의 슬러리에서 안정적으로 과립 분말이 제조되었으며, 슬러리의 분말 함량 20, 22.5 wt%에서 과립 분말의 평균 입도는 약 14 ㎛, 슬러리의 분말 함량 25, 27.5 wt%에서 과립 분말의 평균 입도가 약 19 ㎛인 것을 확인하였다. 분무 건조 과립 분말의 형상은 슬러리의 분산안정성 및 점도 영향을 받으며, 분말 함량이 높을수록 평균 입자 사이즈가 증가하는 것을 확인하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2002년도 춘계학술대회 논문집
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• pp.289-294
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• 2002

Sand Compaction Pile (SCP) method, which uses sand material, is frequently used in Korea. However, the use of sand for SCP faces environmental and economical problems with the shortage of its resources. Therefore, it is necessary to substitute other materials for compaction piles. One of the alternatives is using gravel in lieu of sand. Granular Pile, constituted with sand and crushed-stone, is one of the methods to improve soft clay and loose sandy ground. In this study, modeled pile load tests are performed in test cell. The observations are made on the consolidation and the variation of water table of three different grounds, original, sand pile installed, and granular pile installed ground. In addition, engineering characteristics such as bearing capacity, settlement and drainage are investigated. The test results show that Gravel Compaction Pile (GCP) is more efficient for increasing bearing capacity and reducing settlement than SCP and had similar pore water pressure dissipation to sand. Therefore, the results show that GCP can be a good substitution for SCP.

• 한국지반환경공학회 논문집
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• 제5권1호
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• pp.13-25
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• 2004

조립토 다짐말뚝 공법은 비교적 강성이 큰 쇄석, 자갈 및 모래 등과 같은 조립질 재료를 사용하여 원지반을 치환하여 보강하는 공법으로, 기초지반의 침하를 감소시키며, 연약지반의 지지력 증가 및 압밀배수를 촉진하고, 또한 지진에 의한 액상화의 방지에도 효과가 큰 공법으로 알려져 있으나, 국내에서는 아직 널리 사용되지 않고 있다. 본 연구에서는 유전자 알고리즘을 이용하여 군형태의 조립토 다짐말뚝에 대한 최적배치 기법을 제시하고자 한다. 분석결과, 조립토 말뚝의 배치가 중앙부에 집중될 때 조립토 군말뚝의 지지력은 증가하는 것으로 나타났다. 또한 경제적인 측면을 고려하여 조립토 군말뚝의 총중량에 대한 최적설계를 수행하였으며, 조립토 군말뚝 설계변수의 변화가 최적설계에 미치는 영향을 알아보기 위해 parametric study를 수행하였다.

• 대한금속재료학회지
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• 제49권10호
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• pp.766-773
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• 2011

In this study, three kinds of linepipe steels were processed by changing the amount of Mo and Nb to investigate the effects on microstructures, tensile and Charpy impact properties. All the specimens consisted of acicular ferrite, granular bainite and secondary phases such as martensite and austenite constituents (MA). The increase in Mo raised the volume fractions of the granular bainite and MA, and raised the number of fine precipitates, which increased the yield and tensile strengths and decreased the upper self energy and energy transition temperatures. In the steel having less Mo and more Nb, the volume fractions of the granular bainite and MA decreased, and a finer microstructure was observed. This microstructure suppressed the formation of separation during Charpy impact testing and led to a higher upper shelf energy and lower energy transition temperature, while the yield and tensile strengths were lower than those of the steels with more Mo and less Nb.

• Carbon letters
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• 제4권3호
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• pp.126-132
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• 2003

Granular Activated Carbon (GAC) has been proven to be an excellent material for many industrial applications. A systematic study has been carried out of the kinetics of physical as well as chemical activation of phenolic resin chars. Physical activation was carried out using $CO_2$ and chemical activation using KOH as activating agent. There are number of factors which influence the rate of activation. The activation temperature and residence time at HTT varied in the range $550{\sim}1000^{\circ}C$ and $\frac{1}{2}{\sim}8$ hrs respectively. Kinetic studies show that the rate of chemical activation is 10 times faster than physical activation even at much lower temperature. Above study show that the chemical activation process is suitable to prepare granular activated carbon with very high surface area i.e.$ 2895\;m^2/g$ in short duration of time i.e. 1 to 2 hrs at lower temperature i.e. $750^{\circ}C$ from phenolic resins.

• 한국재료학회지
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• 제31권3호
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• pp.139-149
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• 2021

In this study, three kinds of bainitic steels are fabricated by controlling the contents of vanadium and boron. High vanadium steel has a lot of carbides and nitrides, and so, during the cooling process, acicular ferrite is well formed. Carbides and nitrides develop fine grains by inhibiting grain growth. As a result, the low temperature Charpy absorbed energy of high vanadium steel is higher than that of low vanadium steel. In boron added steel, boron segregates at the prior austenite grain boundary, so that acicular ferrite formation occurs well during the cooling process. However, the granular bainite packet size of the boron added steel is larger than that of high vanadium steel because boron cannot effectively suppress grain growth. Therefore, the low temperature Charpy absorbed energy of the boron added steel is lower than that of the low vanadium steel. HAZ (heat affected zone) microstructure formation affects not only vanadium and boron but also the prior austenite grain size. In the HAZ specimen having large prior austenite grain size, acicular ferrite is formed inside the austenite, and granular bainite, bainitic ferrite, and martensite are also formed in a complex, resulting in a mixed acicular ferrite region with a high volume fraction. On the other hand, in the HAZ specimen having small prior austenite grain size, the volume fraction of the mixed acicular ferrite region is low because granular bainite and bainitic ferrite are coarse due to the large number of prior austenite grain boundaries.

• 한국임상수의학회지
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• 제27권4호
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• pp.491-493
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• 2010

Granular cell tumor was described in a 7-year-old male Miniature Pinscher. Sublingual mass was surgically removed and submitted for diagnosis. The mass was about 1.8 cm in diameter, firm, tan, and ulcerated. On histopathology, the mass was unencapsulated and infiltrated adjacent tissue and consisted of nest or sheet of round to polygonal, and occasional spindle-shaped cells. The neoplastic cells contain large amount of eosinophilic granular materials in the cytoplasm. Immunohistochemically, the neoplastic cells were positive to neuron-specific enolase but were negative to S-100. The cytoplasmic eosinophilic granules were positive to PAS but were negative to PTAH methods. Based on these results, the mass was diagnosed as sublingual granular cell tumor. No recurrence or metastasis was noted so far since surgery.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2007년도 추계학술발표대회 및
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• pp.154.1-154.1
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• 2007

• 한국재료학회:학술대회논문집
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• 한국재료학회 1998년도 추계학술발표강연 및 논문개요집
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• pp.75-75
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• 1998