Journal of Failure Analysis and Prevention

, Volume 15, Issue 4, pp 555–562 | Cite as

Failure Analysis of Micro Cracks and Alumina Inclusions Induced Insulator Pin’s Low Stress Mode of Fracture

  • Qiangyun Yang
  • Hui Zhao
  • Wuqian Chai
  • Chuan Yang
Technical Article---Peer-Reviewed


A tensile test must be conducted for each finished insulator in which a common but significant problem is a low stress mode of fracture. In order to investigate the cause of the low stress fracture in a batch of insulators, a series of failure analysis methods were carried out. As described in this paper, macro-fracture analysis, SEM observation, EDS examination, metallographic structure analysis, hardness test, and inclusion rating were all conducted on the investigation. The results of this investigation show that the major cause of incident fracture is micro cracks in the pin, which are the result of both the molding method and the heating treatment. However, the major reason for the macro cracks lies in the induction heating process, which lacked the accurate temperature control method and using of higher electric power. Furthermore, alumina inclusions in the pin were in excess of standard, so they may also have contributed to the low stress fracture of the pin.


Insulator pin Low stress fracture Micro cracks Alumina inclusions Induction heating 



This paper is supported by the National Demonstration Central of Experimental Education of Materials Science and Engineering and the Key Lab of Advanced Technologies of Materials in Southwest Jiaotong University.


  1. 1.
    N.S. Negmatov, ZhZ Abdullaev, Wollastonite-based high-voltage electric insulators. Steklo Keram. 11, 29–30 (2001)Google Scholar
  2. 2.
    A. Phillips, Electric field distribution and their impact on transmission line composite insulators, in Proceedings of the IEEE Power Engineering Society Transmission and Distribution Conference, 2012Google Scholar
  3. 3.
    V.A. Aleko, E.B. Kozhelupenko, Effective technologies and equipment for the continuous forming of screw-type electric insulators. Int. Ceram. Rev. 6(52), 352–354 (2003)Google Scholar
  4. 4.
    C.R. Murakami, R.A.C. Altafim, A. Bonomo, P.E. Cruvinel, G.O. Chierice, J.A.M. Agnelli, Study of pin-type polymeric electric insulators: manufacturing process, tomographic analysis, and electrical and mechanical tests, in Proceedings of the 7th International Conference on Properties and Applications of Dielectric Materials, vol. 2, 2003, pp. 824–827Google Scholar
  5. 5.
    ISO6892-1:2006, Metallic Materials—Tensile Testing—Part 1: Method of Test at Room Temperature (ISO, Geneva, 2006)Google Scholar
  6. 6.
    ISO4499-1:2008, Hard Metals—Metallographic Determination of Micro-structure—Part 1: Photomicrographs and Description (ISO, Geneva, 2008)Google Scholar
  7. 7.
    ASTM E45-97:2002, Standard Test Methods for Determining the Inclusion Content of Steel (ASTM, West Conshohocken, 2002)Google Scholar
  8. 8.
    F. Li, H. Huang, Analysis on the deformation and fracture behavior of carbon steel by in situ tensile test. J. Univ. Sci. Technol. Beijing Miner. Metall. Mater. 6(13), 504–507 (2006)Google Scholar
  9. 9.
    ASM CS-44:1971, AISI 1045—Medium Carbon Steel (ASM, Materials Park, 1971)Google Scholar
  10. 10.
    D.Z. Lu, A. Irons, W.K. Lu, Kinetics and mechanisms of calcium dissolution and modification of oxide and sulfide inclusions in steel. Ironmak. Steelmak. 5(21), 362–371 (1994)Google Scholar

Copyright information

© ASM International 2015

Authors and Affiliations

  • Qiangyun Yang
    • 1
  • Hui Zhao
    • 1
  • Wuqian Chai
    • 1
  • Chuan Yang
    • 1
  1. 1.College of Materials Science and EngineeringSouthwest Jiaotong UniversityChengduChina

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