Journal of Materials Science

, Volume 17, Issue 7, pp 1871–1879 | Cite as

The competition between shear deformation and crazing in glassy polymers

  • Athene M. Donald
  • Edward J. Kramer
Papers

Abstract

Whereas thin films of some polymers such as polystyrene readily form crazes when strained in tension, thin films of other polymers such as polycarbonate rarely exhibit crazing under the same testing conditions; the polymers that rarely craze tend to form regions of shear deformation instead. Polymers such as polystyrene-acrylonitrile which lie between these two extremes of behaviour may exhibit both modes of deformation. Thin films suitable for optical and transmission electron microscopy (TEM) of six such co-polymers and polymer blends have been prepared. After straining, the nature of the competition between shear deformation and crazing is examined by TEM. It is found that in these polymers many crazes have tips which are blunted by shear deformation. This process leads to stress relaxation at the craze tip, preventing further tip advance. In this way short, but broad, cigar-shaped crazes are formed. Examination of the deformation at crack tips in the same polymers shows more complex structures, the initial high stress levels lead to chain scission and fibrillation but as the stress drops, shear becomes the dominant mechanism of deformation and the stress is relieved further. Finally, at long times under stress, chain disentanglement may become important leading to fibrillation and craze formation again. The nature of the competition is thus seen to be both stress and time dependent. Physical ageing of these polymers, via annealing below Tg, suppresses shear leading to the generation of more simple craze structures.

Keywords

Polymer Transmission Electron Microscopy Polycarbonate Scission Shear Deformation 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    A. M. Donald and E. J. Kramer, J. Polymer Sci. Polymer Phys. Edn, in press.Google Scholar
  2. 2.
    P. B. Bowden and S. Raha, Phil. Mag. 22 (1970) 463.Google Scholar
  3. 3.
    E. J. Kramer, J. Macromol. Sci. B10 (1974) 191.Google Scholar
  4. 4.
    S. T. Wellinghoff and E. Baer, J. Appl. Polymer Sci. 22 (1978) 2025.Google Scholar
  5. 5.
    A. M. Donald and E. J. Kramer, J. Mater. Sci. 16 (1981) 2967.Google Scholar
  6. 6.
    Idem, Polymer in press.Google Scholar
  7. 7.
    J. H. Golden, B. L. Hammant and E. A. Hazell, J. Appl. Polymer Sci. 11 (1967) 1571.Google Scholar
  8. 8.
    T. E. Brady and G. S. Y. Yeh, J. Appl. Phys. 42 (1971) 4622.Google Scholar
  9. 9.
    L. C. E. Struik, “The Physical Aging of Amorphous Polymers and Other Materials” (Elsevier, Amsterdam, 1978) p. 279.Google Scholar
  10. 10.
    P. B. Bowden, in “The Physics of Glassy Polymers” edited by R. N. Haward (Applied Science Publishers, London, 1973).Google Scholar
  11. 11.
    G. Adam, A. Cross and R. N. Haward, J. Mater. Sci. 10 (1975) 1582.Google Scholar
  12. 12.
    A. Cross, R. N. Haward and N. J. Mills, Polymer 20 (1979) 288.Google Scholar
  13. 13.
    P. Beahan, M. Bevis and D. Hull, ibid. 14 (1973) 96.Google Scholar
  14. 14.
    A. M. Donald and E. J. Kramer, ibid. 23 (1982) 461.Google Scholar
  15. 15.
    B. D. Lauterwasser and E. J. Kramer, Phil. Mag. 39A (1979) 469.Google Scholar
  16. 16.
    A. M. Donald, E. J. Kramer and R. A. Bubeck, J. Polymer Sci. Polymer. Phys. in press.Google Scholar
  17. 17.
    P. Beardmore and S. Rabinowitz, J. Mater. Sci. 10 (1975) 1763.Google Scholar
  18. 18.
    C. B. Bucknall, “Toughened Plastics” (Applied Science Publishers, London, 1977) p. 193.Google Scholar
  19. 19.
    C. B. Bucknall, D. Clayton and W. E. Keast, J. Mater. Sci. 7 (1972) 1443.Google Scholar
  20. 20.
    A. M. Donald, E. J. Kramer and R. P. Kambour, J. Mater. Sci. 17 (1982).Google Scholar
  21. 21.
    M. T. Takemori and R. P. Kambour, J. Mater. Sci. 16 (1981) 1108.Google Scholar

Copyright information

© Chapman and Hall Ltd 1982

Authors and Affiliations

  • Athene M. Donald
    • 1
  • Edward J. Kramer
    • 1
  1. 1.Department of Materials Science and Engineering and the Materials Science CenterCornell UniversityIthacaUSA

Personalised recommendations