Journal of Materials Science

, Volume 21, Issue 8, pp 2881–2888 | Cite as

An examination of the role of flaw size and material toughness in the brittle fracture of polyethylene pipes

  • G. J. Sandilands
  • J. Bowman
Papers

Abstract

At low temperatures and hoop stresses, polyethylene pipes fail by the time-dependent propagation of a crack. These brittle, fissure-like failures have been observed to initiate from adventitious flaws, and the concepts and methods of fracture mechanics indicate that flaw size should determine stress rupture lifetime. A number of controlled model experiments have therefore been undertaken to assess the influence of flaw size and material toughness on the stress rupture lifetimes of polyethylene pipes. To two different pipe grade polyethylene resins (one shorter, one longer lifetime resin) flaws of varying sizes have been added. For the shorter lifetime resin small flaws were, in addition, purposely excluded by the use of fine melt filtration techniques. Pipes containing added flaws or pipes where flaws were excluded were then stress rupture tested under those conditions designed to induce brittle failure by slow crack growth. The stress rupture lifetimes of the various pipes are then correlated with flaw size. The results of the tests using the shorter lifetime resin show that flaw size does have a significant influence. It is particularly interesting to note that melt filtration, which removes large inherent flaws, substantially improved the stress rupture lifetime. With respect to material toughness, the longer lifetime pipe grade polyethylene resin showed a healthy tolerance to included flaws. In respect of the stress rupture test preferred resins can therefore be identified in terms of their tolerance to included flaws.

Keywords

Brittle Brittle Fracture Flaw Size Brittle Failure Hoop Stress 

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References

  1. 1.
    E. Gaube, G. Diedrich and W. Muller, Kunststoffe 66 (1976) 2.Google Scholar
  2. 2.
    A. Gray, J. N. Mallinson and J. B. Price, Plast. Rubb. Process. Appl. 1 (1981) 51.Google Scholar
  3. 3.
    M. K. V. Chan and J. G. Williams, Polymer 24 (1983) 234.Google Scholar
  4. 4.
    R. W. Hertzberg and J. A. Manson, “Fatigue of Engineering Plastics” (Academic Press, London, 1980).Google Scholar
  5. 5.
    Plastics and Rubber Institute, “Triannual Conference on Deformation, Yield and Fracture of Polymer”, (1973, 1976, 1979, 1982).Google Scholar
  6. 6.
    S. H. Joseph and P. S. Leevers, J. Mater. Sci. 20 (1985) 237.Google Scholar
  7. 7.
    R. J. Young, “Introduction to Polymers”, (Chapman and Hall, London, 1981).Google Scholar
  8. 8.
    J. M. Greig, Plast. Rubber Prcoess. Appl. 1 (1981) 43.Google Scholar
  9. 9.
    C. S. Lee and M. M. Epstein, Polym. Eng. Sci. 22 (1982) 549.Google Scholar
  10. 10.
    D. P. Rooke and D. J. Cartwright, “Compendium of Stress Intensity Factors” (HMSO, London, 1976).Google Scholar
  11. 11.
    G. C. Ford, M. B. Barker, S. Bentley, K. Batchelor and J. Bowman, Polymer Testing 3 (1983) 161.Google Scholar
  12. 12.
    M. B. Barker, J. Bowman and M. J. Bevis, J. Mater. Sci. 18 (1983) 1095.Google Scholar
  13. 13.
    E. J. Hearn, “Mechanics of Materials”, Vol. 1 (Pergamon Press, Oxford, 1977).Google Scholar
  14. 14.
    J. M. Hodgkinson and J. G. Williams, Plast. Rubber Process Appl. 3 (1983) 37.Google Scholar
  15. 15.
    C. G. Bragaw, Proceedings of the 4th International Conference on Deformation, Yield and Fracture of Polymers, Cambridge (April 1979) (The Plastics and Rubber Institute, London) Paper 1.Google Scholar
  16. 16.
    C. G. Bragaw, Proceedings of the American Gas Association, VIth Plastics Pipes Symposium, Ohio, USA (1978).Google Scholar

Copyright information

© Chapman and Hall Ltd. 1986

Authors and Affiliations

  • G. J. Sandilands
    • 1
  • J. Bowman
    • 1
  1. 1.Department of Materials TechnologyBrunel UniversityUxbridgeUK

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