Advertisement

Journal of Failure Analysis and Prevention

, Volume 6, Issue 4, pp 17–22 | Cite as

Metallurgical failure analysis of fasteners in an impeller assembly

  • L. R. Curtis
Case Histories

Abstract

This paper examines a failure analysis of the bolts from a failed joint between an impeller blade and a rotating assembly unit. The bolts failed due to poor thread manufacture and installation. Sharpened thread roots led to high stress concentrations that favored crack initiation. An oddly shaped thread profile allowed friction between mismatched thread surfaces. Poor installation procedures allowed for the possibility of overtightening to nucleate cracks in the head-to-shank interface (which had a smaller radius and therefore a higher stress concentration) and possibly also in the thread roots. Each of these influences contributed to crack initiation in the bolts. After cracks had formed, bending fatigue then propagated the nucleated cracks to final fracture. The failure analysis also recommended using bolts with rolled threads, which allow a more complete fit between mating male and female threads, and assuring that an appropriate preload is placed on bolts during installation.

Keywords

austenitic stainless steel EDS fasteners fatigue failure fractography metallography SEM 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    R.I. Stephens, A. Fatemi, R.R. Stephens, and H.O. Fuchs: Metal Fatigue in Engineering, John Wiley & Sons, 2001, pp. 40–43.Google Scholar
  2. 2.
    J.I Goldstein, D.E. Newbury, P. Echlin, D.C. Joy, A.D. Roming, Jr., C.E. Lyman, C. Fiori, and E. Lifshin: Scanning Electron Microscopy and X-Ray Microanalysis, Plenum Publishing Corp., 1992, pp. 509–10.Google Scholar
  3. 3.
    S. Kalpakjian and S.R. Schmid: Manufacturing Engineering and Technology, Prentice Hall, Upper Saddle River, NJ, 2001, pp. 57–58, 332–33.Google Scholar
  4. 4.
    W.J. Jensen: “Failures of Mechanical Fasteners,” Failure Analysis and Prevention, vol. 11, Metals Handbook, 9th ed., American Society for Metals, 1986, p. 531.Google Scholar
  5. 5.
    R.C. Tucker, Jr.: “Wear Failures,” Failure Analysis and Prevention, vol. 11, Metals Handbook, 9th ed., American Society for Metals, 1986, p. 148.Google Scholar
  6. 6.
    “Thread Rolling,” Machining, vol. 16, Metals Handbook, 9th ed., ASM International, 1989, p. 281.Google Scholar
  7. 7.
    R.B. Waterhouse: “Fretting Wear,” Friction, Lubrication, and Wear Technology, vol. 18, ASM Handbook, ASM International, 1992, p. 253.Google Scholar

Copyright information

© ASM International 2006

Authors and Affiliations

  • L. R. Curtis
    • 1
  1. 1.The M&P LabSchenectady

Personalised recommendations