• 한국추진공학회지
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• 제18권4호
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• pp.61-66
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• 2014

본 연구의 흑연은 로켓 노즐목 재료로 많이 사용되는 것으로써 온도, 가공성 및 무게 측면에서 유리하다. 하지만 고온 및 고압상태에서 고속으로 취성파괴 되므로 설계 시 구조적 안정성을 충분히 확보해야 한다. 본 연구에서는 로켓 노즐목에 이용되는 ATJ 흑연의 압축 파괴 거동에 대해 연구했다. 상온 및 고온에서 ASTM C 695에 준하여 일축 압축 시험을 수행하였다. 또한 시편의 단면적 변화에 의한 압축강도 및 파단특성을 분석하였다.

• 한국주조공학회지
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• 제25권1호
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• pp.40-50
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• 2005

A series of heavy section ductile cast iron ingots with the cube length of 250mm were systematically investigated as functions of casting parameters of sand casting. Abnormal graphite formation was specially observed with the variation of Si content and Bi or Sb addition. Effects of chilling during casting and adaptation of riserless system were also examined, and proved to be effective for the prevention of both shrinkage and abnormal graphite such as chunky one. The formation of chunky graphite was effectively prevented by low Si content despite the promotion of pearlite matrix structure. The ferritic matrix was encouraged to form by high Si content and chunky graphite formation was effectively suppressed by the addition of Bi and Sb. Bi addition, however, was not good enough to control the microstructure owing to the sensitive cooling rate dependent inoculation behavior and relative low ability of nodulization. Sb addition, on the other hand, was proved to be effective for the microstructural control and enhancement of various mechanical properties such as strength, elongation, and impact energy. It may be suggested that optimized casting parameters should be applied to produce heavy section ductile cast iron with reliability.

• Composites Research
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• 제16권4호
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• pp.10-21
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• 2003

본 논문에서는 특성길이 결정을 위해 시편에 가해지는 하중과 내부 응력분포의 관계가 거의 선형적으로 변한다는 특성을 이용하여. 실험을 수행하지 않고 복합재 체결부 파손해석을 위한 특성길이를 결정할 수 있는 방법을 제안하였다. 제안된 방법을 사용할 경우 특성길이 결정을 위한 실험 없이도 실험값을 사용한 결과와 동일한 압축특성길이를 얻을수 있음을 보였다. 압축특성길이 결정에서와 마찬가지로 실험 없이 인장특성길이를 결정하기 위해, 기존의 방법에서와 달리, 인장특성길이의 정의를 위해 사용하는 적층판의 강도값을, 원공이 없는 적층판의 값이 아닌 원공을 가진 적층판의 값을 사용하였다. 유한요소해석은 MSC/NASTRAN을 이용하였고, 체결재와 복합재의 접촉부는 접촉면 요소를 사용하여 모델링하였다. 제안된 방법으로 해석한 복합재 체결부의 파손하중은 Graphite/Epoxy 복합재료 체겯부의 실험 견과와 매우 잘 일치함을 확인하였다

• 한국표면공학회지
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• 제49권1호
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• pp.104-109
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• 2016

Graphite's thermal stability facilitates its widespread use as crucibles and molds in high temperatures processes. However, carbon atoms can be rather easily detached from pores and outer surfaces of the graphite due to the weak molecular force of the c axis of graphites. Detached carbon atoms are known to become a source of dust during fabrication processes, eventually lowering the effective yield of products. As an effort to reduce these problems of dust scattering, we have fabricated SiC composites by employing Si vapor infiltration method into the pores of graphites. In order to understand the diffusion process of the Si vapor infiltration, Si and C atomic percentages of fabricated SiC composites are carefully measured and the diffusion law is used to estimate the diffusion coefficient of Si vapor. A quadratic equation is obtained from the experimental results using the least square method. Diffusion coefficient of Si vapor is estimated using this quadratic equation. The result shows that the diffusion length obtained through the Si vapor infiltration method is about 10.7 times longer than that obtained using liquid Si and clearly demonstrates the usefulness of the present method.

• 대한기계학회논문집
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• 제4권3호
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• pp.113-118
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• 1980

Stresses were calculated for finite-width orthotropic laminates with a circular hole and remote uniaxial loading using a two-dimensional finite-element analysis with both uniform stress and uniform displacement boundary conditions. Five different laminates were analyzed: quasi-isotropic [0.deg./.+-.45.deg./90.deg.].$\_$s/, 0.deg., 90.deg., [0.deg./90.deg.]$\_$s/, and [.+-.45.deg.]$\_$s/, Computed results are presented for selected combinations of hole diameter-sheet-width ratio d/w and length-to width ratio L/w. For small L/w values, the stress-concentration factors K$\_$tn/ were significantly different for the uniform stress and uniform displacement boundary conditions. Typically, for the uniform stress conditions, the K$\_$tn/ values were much larger than for the infinite-strip reference conditions; however, for the uniform displacement conditon, they were only slighty smaller than for this reference. The results for long strips are also presented as width-correction factor. For d/w.leg.33, these width-correction factors are nearly equal for all five laminates.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1390-1393
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• 2003

Work factor approach is conveniently used in metal fracture mechanics to determine fracture toughness from a single fracture test. In this work, we investigated the applicability of the work factor approach in order to determine fracture toughness of thick graphite/epoxy composites in the hydrostatic pressure environment from a single fracture test. The effect of hydrostatic pressure on the elastic work factor was studied, The stacking sequence used was multi-directional, [0$^{\circ}$/${\pm}$45$^{\circ}$/90$^{\circ}$]. The hydrostatic pressures applied were 0.1 MPa, 100 MPa, 200 MPa, and 300 MPa. The results showed that the elastic work factor was not affected by the hydrostatic pressure, The elastic work factor decreased in a linear fashion with crack length.

• 한국재료학회지
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• 제9권2호
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• pp.139-143
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• 1999

Solidification simulation of gray cast iron sheave product was conducted with the consideration of graphite precipitation during solidification, and of casting processes such as post-inoculation method, treatment and rate, the result of which was aimed to be adopted in the field. In risering design(I), shrinkage cavities were predicted to occur in the part below the risers and center part of the product. While the former defect was considered to be due to the solidification behaviour of riser neck, the latter was due to the feeding channel. In design(II), the length of the riser neck was reduced and one top open riser was attached in the center of the product to prevent the formation of shrinkage cavities, whereby defect-free product was produced.

• Bulletin of the Korean Chemical Society
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• 제34권4호
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• pp.1039-1042
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• 2013

Polyynes were prepared by liquid laser ablation of a graphite target in deionized water at various physical conditions such as laser power (20 and 40 mJ/pulse) and ablation wavelengths (355, 532, and 1064 nm). The effects of physical parameters on the linear carbon chain length were examined by analyzing the densities of polyynes with different carbon numbers ($C_6H_2$, $C_8H_2$, and $C_{10}H_2$) as well as their branching ratios. We concluded the photophysical processes turned out to play a more significant role than thermal ones in the formation of polyynes.

• 대한기계학회논문집
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• 제13권4호
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• pp.625-635
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• 1989

본 논문에서는 이 방법을 사용하여 glass/epoxy와 graphite/epoxy 유한평판이 균일응력과 균일변위 경계조건을 받을 때 평판 종횡비 H/W를 1,2,3, 균열길이와 폭의 비 L/W를 0.1부터 0.7까지, 균열각도를 0, 30, 45, 60으로 변화 시키면서 응력강도수정계수를 구하려고 한다.

• 대한금속재료학회지
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• 제50권4호
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• pp.324-330
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• 2012

The microstructural changes of three pieces from an ancient iron pot were studied in order to identify present the material degradation due to repeated heating for one-thousand years. The microstructures of the pieces were divided into the areas of ferrite/graphite, ferrite/pearlite, and corroded oxidation. The area of ferrite/graphite was undergone by severe Galvanic corrosion, but that of ferrite/pearlite was not even during a thousand years' using. The shape of the graphites was coexisted with types of A, B, and C of as modern graphite classification. In the ferrite/pearlite area, abnormal acicula precipitates with a high aspect ratio of $0.2{\mu}m$ thickness and several hundreds ${\mu}m$ length were presented. They might be a kind of carbide in the ferrite matrix with its special precipitate plane.