Transactions of the Korean Society of Mechanical Engineers A (대한기계학회논문집A)

The Korean Society of Mechanical Engineers (대한기계학회)
권호 표지
DOI QR코드

DOI QR Code

Fracture Behavior of Graphite Material at Elevated Temperatures Considering Oxidation Condition

산화환경을 고려한 흑연 내열재의 고온파단특성

  • Choi, Hoon Seok (Dept. of Mechanical Design Engineering, ChungNam Nat'l Univ.) ;
  • Kim, Jae Hoon (Dept. of Mechanical Design Engineering, ChungNam Nat'l Univ.) ;
  • Oh, Kawng Keun (Dept. of Mechanical Design Engineering, ChungNam Nat'l Univ.)
  • 최훈석 (충남대학교 기계설계공학과) ;
  • 김재훈 (충남대학교 기계설계공학과) ;
  • 오광근 (충남대학교 기계설계공학과)
  • Received : 2015.01.07
  • Accepted : 2015.08.24
  • Published : 2015.11.01
Download PDF
⟨ Previous Next ⟩

Abstract

Graphite material has been widely used for making the rocket nozzle throat because of its excellent thermal properties. However, when compared with typical structural materials, graphite is relatively weak with respect to both strength and toughness, owing to its quasi-brittle behavior, and gets oxidized at $450^{\circ}C$. Therefore, it is important to evaluate the thermal and mechanical properties of this material for using it in structural applications. This study presents an experimental method to investigate the fracture behavior of ATJ graphite at elevated temperatures. In particular, the effects of major parameters such as temperature, loading, and oxidation conditions on strength and fracture characteristics were investigated. Uniaxial compression and tension tests were conducted in accordance with the ASTM standard at room temperature, $500^{\circ}C$, and $1,000^{\circ}C$. Fractography analysis of the fractured specimens was carried out using an SEM.

흑연은 우수한 열특성을 지니기 때문에 로켓 노즐목 재료로 많이 이용된다. 하지만 흑연은 소성영역을 동반하지 않으며 파괴되는 준취성 특성을 보이므로 일반구조재료와 비교해 보았을 때, 강도 관점에서 상대적으로 취약하며, $450^{\circ}C$ 이상에서 산화가 발생한다. 따라서 흑연 재료의 실구조체 적용을 위하여 이 재료에 대한 기계적 열적 특성 평가가 요구된다. 본 논문에서는 ATJ 계열 흑연의 고온파단특성에 대한 실험적인 연구를 수행하였다. 특히, 온도와 하중, 그리고 산화조건을 변수로 두어 강도 및 파단특성에 대한 상관관계를 연구하였다. 이를 위하여 ASTM 규정을 준수하여 상온, 500, $1,000^{\circ}C$에서 일축 압축 및 인장시험을 수행하였으며, 파단면은 SEM 촬영을 통하여 분석하였다.

Keywords

References

  1. Page, D. J., 1991, The Industrial Graphite Engineering Handbook, UCAR Carbon Company Inc.
  2. Choi, W. K., Kim, B. J., Chi, S. H. and Park, S. J., 2009, "Nuclear Graphite (I) : Oxidation Behaviors," Carbon Letters, Vol. 10, No. 3, pp. 239-249. https://doi.org/10.5714/CL.2009.10.3.239
  3. Kawakami, H., 1986, "Air Oxidation Behavior of Carbon and Graphite Material for HTGR," Tanso, No. 124, pp.26-33.
  4. Wang, Z., Qu, Q., Wu, Z. and Shi, G., 2011, "Effect of Oxidation at $1100^{\circ}C$ on the Strength of $ZrB_2$-SiC-Graphite Ceramics," Journal of Alloys and Compounds, Vol. 509, Issue 24, pp.6871-6875 https://doi.org/10.1016/j.jallcom.2011.03.163
  5. Cho, K.Y., Kim, K.J., Lim, Y.S., Chung, Y.J. and Chi, S.H., 2006, "Specimen Geometry Effects on Oxidation Behavior of Nuclear Graphite," Carbon Letters, Vol. 7, No. 3, pp. 196-200.
  6. Nemeth, N.N. and Bratton, R.L., 2011, "Statical Models of Fracture Relevant to Nuclear-Grade Graphite: Review and Recommendation," NASA/TM 2011-215805
  7. ASTM standard C695-91, 2010, "Standard Test Method for Compressive Strength of Carbon and Graphite," ASTM International.
  8. ASTM standard C749-92, 2002, "Standard Test Method for Tensile Stress-Strain of Carbon and Graphite," ASTM International.
  9. Neighbour, G.B. and Hacker, P.J., 2001, "The Variation of Compressive Strength of AGR Moderator Graphite with Increasing Thermal Weight Loss," Materials Letter, Vol. 51, Issue. 4, pp.307-314. https://doi.org/10.1016/S0167-577X(01)00309-3
  10. Choi, W. K., Kim, B. J., Kim, E. S., Chi, S. H. and Park, S. J., 2010, "Nuclear Graphites (II) : Mechanical Properties," Carbon Letters, Vol. 11, No. 1, pp.41-47. https://doi.org/10.5714/CL.2010.11.1.041