• 비파괴검사학회지
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• 제9권1호
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• pp.83-89
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• 1989

Effects of the microstructure and the testing conditions for the detectability of the small flaw in ultrasonic testing have been studied. The detectability of the flaw was influenced not only by the grain size but also by the microstructure of the test piece. This is considered to be caused by randomization of the matrix which influences the elastic anisotropy of the grain. It was found that the detectability was improved as the frequence became higher and the beam size became smaller. The experimental results indicate that ultrasonic backscattering measurement is one of the promising methods to evaluate the detectability of the flaw indirectly.

• 한국결정성장학회지
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• 제6권3호
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• pp.392-398
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• 1996

$Si_{3}N_{4}$에 평균입경이 다른 SiC 분말을 0, 10, 20, 30, 40 vol% 첨가하여 고온가압소결법으로 초미립복합재료를 제조하였다. SiC의 첨가량에 따라 $Si_{3}N_{4}$의 결정립성장이 억제되어 원형의 미세한 결정립들이 많아졌다. 이러한 경향은 평균입경이 작은 SiC를 사용한 조성에서 현저하게 나타났다. 이에 따라 파괴강도와 경도는 작은 SiC를 첨가한 시편에서 높은 값을 나타냈으며, 파괴인성은 낮았다.

• 한국세라믹학회지
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• 제29권3호
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• pp.211-215
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• 1992

Crack free PbTiO3 ceramics were produced by sol-gel processing using alkoxide, which has not been reported to be successful. The PbTiO3 gels were prepared from Ti alkoxide and lead acetate without any dopants. They were calcined at $600^{\circ}C$ and miled to produce fine PbTiO3 powder. It was pressed into discs and they were sintered at 110$0^{\circ}C$ for a few hours. The sintered ceramics were relativley hard and dense as having about 96% of theoretical density of PbTiO3. Fabrication of pure PbTiO3 ceramics by sol-gel processing is possibly due to their small grain size and uniform distribution of residual stress created during cubic-tetragonal transition over large number of small grains in fine grain PbTiO3 ceramics.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.155-159
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• 2002

This paper has studied to obtain the grinding characteristics and optimal grinding conditions of ceramics in the grinding with diamond wheel by Taguchi method. Feed rate was most important factor to the surface roughness. In the case of 4{Si_3}{N_4}$ and ${A1_2}{O_3}$, surface roughness value were small at 3m/min of feed rate. In the case of $ZrO_2$. surface roughness value was small at 4m/min of feed rate. Surface roughness have much influenced by major load for the :ii3N4 and $ZrO_2$. On the other hand, ${A1_2}{O_3}$ have more influenced by grain shedding of brittle fracture phenomenon. The major factors affecting the surface roughness and the optimum grinding conditions were obtained with minimum experiment using Taguchi method.

• E2M - 전기 전자와 첨단 소재
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• 제10권10호
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• pp.995-999
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• 1997

For melt-spun Fe-Nd-C alloy variation of phase development and magnetic properties with the variety of small Al addition was investigated. As the amount of Al addition increased the amorphization of Fe$_{14}$/Nd$_{2}$/C or $\alpha$-Fe was retarded and the residual Fe$_{14}$/Nd$_{2}$/C or $\alpha$-Fe did not eliminated after heat treatment resulting in poor coercivities of the ribbons. The grain size of Fe$_{14}$/Nd$_{2}$/C increased with the increase of Al addition and the abnormal grain was often found out in the ribbon heat treated for more then 10 min. The enhancement of coercivity was the highest with the addition of 0.5at%Al. As the amount of Al addition increase the coercivities dropped rapidly. The highest coercivity obtained so far is 13.9kOe which about 16% higher than that(11.2kOe) obtained from the Al-free specimen.

• Journal of Welding and Joining
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• 제16권3호
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• pp.121-128
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• 1998

The degradation of mechanical properties in the high nitrogen steel HN3 developed for nuclear fusion reactor has been evaluated quantitatively using the small punch(SP) test, X-ray diffraction (XRD) analysis has also been conducted to identify carbides or nitrides precipitated on grain boundaries of the heat treated samples. Mechanical properties of the steel HN3 significantly decreased with increasing heat treatment time and temperature or with decreasing testing temperature. Combination of XRD and metallurgical observation, revealed that the material degradation in the thermally aged steel was caused by precipitation of carbides on the grain boundaries. While the weld metal showed the lowest mechanical properties among various microstructures in GTA weldments. By combining SP test and XRD analysis, cryogenic fracture behaviors and aging degradation for high nitrogen steel could be successfully evaluated in nondestructive manner.

• 한국세라믹학회지
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• 제29권4호
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• pp.65-65
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• 1992

12Ce-TZP의 소결에 미치는 CaO의 역할에 대하여 연구하였다. CaO의 첨가는 Ce-TZP의 격자결함구조와 확산의 율속종인 cerium과 zirconium 이온의 확산계수를 변화시켜 치밀화를 촉진시킨다. CaO는 또한 소결과정중 결정립 성장을 억제하며, 이는 소결과정중 임계 이동시 입계로부터의 기공의 분리를 방지함과 동시에 기공으로부터 입계로의 공격자의 빠른 확산을 유지시킴으로써 이론밀도까지의 소결을 가능하게 한다. Ce-TZP의 결정립 성장 억제는 calcium의 입계편석에 의한 입계 이동도의 감소에 의하며, calcium의 입계편석을 AES 분석으로 확인하였다.

• 한국작물학회지
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• 제35권3호
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• pp.211-217
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• 1990

팔당호밀과 신기호밀에 대한 전엽시기와 전엽정도가 종실의 발육에 미치는 영향을 구명코자 시험을 실시한 결과를 요약하면 다음과 같다. 1. 엽신중은 2엽, 3엽, 지엽 경으로 무거웠다. 2. 엽록소함량은 지엽, 2엽, 3엽 순으로 높았으며, 엽소도 같은 경향이었고 신기호밀보다 팔당호밀에서 높았다. 3. 립중은 전엽시기가 늦고 전엽정도가 적을수록 무거웠다. 4. 엽신들의 생산효과는 지엽, 2엽, 3엽 순으로 높았다. 5. 이삭부위별 립중은 중부, 하부, 상부 순으로 무거웠다.

• 한국농공학회지
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• 제22권3호
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• pp.46-59
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• 1980

This study was conducted to obtain the most effective distribution of grain size and the optimum lime content for lime-soil stabilization. To achieve the aim, the change of consistency, the characteristics of compaction and unconfined compressive strength were tested by adding of 0, 4, 6, 8, 10 and 12 percent lime by weight for all soils adjusted by given ratios of sand to clay. The results obtained were as follows; 1. There was a tendency that the plasticity index of lime-soil mixture was decreased by increasing the amount of lime, whereas the liquid limit was varied irregularly and the plastic limit was increased. 2. With the addition of more lime, the optimum moisture content of lime-soil mixture was increased, and the maximum dry density was decreased. 3. The optimum lime content of lime-soil mixture was varied from soil to soil, and the less amount of small grain size, the less value of optimum lime content. 4. The optimum distribution of grain size for lime-soil mixture was in the soil, having the ratio of about 60 percent of cohesive clay and about 40 percent of sand by weight. 5. In the soil having fine grain size, the effect of curing appeared for long periods of time, whereas the increasing rate of unconfined compressive strength was great on the soil of coarse grain size in the earlier stage of curing period.

• 한국환경복원기술학회지
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• 제13권2호
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• pp.95-104
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• 2010

The purpose of this study is to analyze the correlation between physical stream characteristics and bed materials in natural rivers. Accordingly, four natural rivers were selected reference streams, they were Nam river, Sumjin River, Naesung River and Han River. Grain size distributions of bed materials were gravels, cobbles and boulders in Han river and Nam river, were sand, gravels, cobbles and boulders in Sumjin river and were sand in Naesung river. Four reference streams were divided into each two reference reaches (straight and bend) by plan and profile characteristics of naturally meandering stream. Therefore various reference reaches were chosen in the aspect of physical stream characteristics and grain size distributions. The results investigated and analyzed are as follows. The streams that grain sizes distributions of river bed materials were coarse were stable because they had variety of bed slope without sediment deposition, and then the riffles frequency and the physical characteristics were various. Also, velocitydepth regime were various in four kinds, and the response parts for water level change were small, so that channel flow status were stable and excellent condition. On the other hand, sand river that grain sizes distributions of river bed materials were fine had not the variety of parameters as velocity-depth regimes, sediment deposition, channel flow status and riffles frequency, so that the physical stream characteristics were not various.