Advertisement

Journal of Materials Science

, Volume 31, Issue 17, pp 4483–4492 | Cite as

Influence of stress intensity and crack speed on fracture surface topography: mirror to mist to macroscopic bifurcation

Article

Abstract

The development of roughness on the fracture surfaces of a brittle, glassy, epoxy resin from the mirror-to-mist transition to macroscopic bifurcation has been investigated using optical microscopy, scanning electron microscopy (SEM) and contact and non-contact laser profilometry. Most of the observations were made on specimens fractured in edge-notched tension. In a series of tests the initial crack length was varied to obtain fracture surfaces formed by accelerating and decelerating cracks without macroscopic bifurcation (specimen A) and by cracks which accelerated continuously to macroscopic bifurcation (specimen B). Some observations were made on specimens tested in compact tension to study changes in fracture surface topography associated with crack arrest in stick-slip fracture. There was a close correlation between the topographical detail revealed by the different techniques. In specimen A the roughness increased progressively from the mirror-to-mist transition and reached a maximum before decreasing as the crack decelerated. The topographical features revealed by optical microscopy and SEM were the same for accelerating and decelerating cracks at the same roughness value. In specimen B the roughness increased continuously to macroscopic bifurcation. There was a close similarity between the topographical features at all levels of roughness. A simple model for the basic step involved in roughness formation is presented which involves an element of the crack tip tilting out of the plane of the main crack before stopping (micro-bifurcation). The scale of micro-bifurcation ranged from 3 μm in the early stages of mist, when the crack velocity was close to 10% of the shear wave velocity, to the full width of the specimen (6 mm) at macroscopic bifurcation. The micro-bifurcation process develops from crack surface undulations and does not involve micro-crack nucleating ahead of the main crack. It is concluded that the relationships between crack velocity and dynamic stress intensity, and the value of the limiting crack velocity, must be interpreted in terms of micro-mechanical processes at the crack tip which are strongly dependent on specific material characteristics.

Keywords

Shear Wave Stress Intensity Mist Shear Wave Velocity Topographical Feature 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    D. Hull, J. Mater. Sci. 31 (1996) 1829.CrossRefGoogle Scholar
  2. 2.
    K. Takahashi and K. Arakawa, Expt. Mech. 44 (1987) 195.CrossRefGoogle Scholar
  3. 3.
    Idem, Int. J. Fract. 48 (1991) 103.CrossRefGoogle Scholar
  4. 4.
    Idem, Photomechanics and Speckle Metrology 814 (1987) 670.Google Scholar
  5. 5.
    D. Hull, Int. J. Fract. 66 (1994) 295.CrossRefGoogle Scholar
  6. 6.
    Idem, ibid. 70 (1995) 59.CrossRefGoogle Scholar
  7. 7.
    K. Ravi-Chandar and W. G. Knauss, ibid. 26 (1984) 65.CrossRefGoogle Scholar
  8. 8.
    Idem, ibid. 247.CrossRefGoogle Scholar
  9. 9.
    Idem, ibid. 26 (1984) 141.CrossRefGoogle Scholar
  10. 10.
    Idem, ibid. 26 (1984) 189.CrossRefGoogle Scholar
  11. 11.
    J. R. Rice, Y. Ben-Zion and K. S. Kim, J. Mech. Phys. Solids 42 (1994) 813.CrossRefGoogle Scholar
  12. 12.
    H. Gao, ibid. 41 (1993) 457.CrossRefGoogle Scholar
  13. 13.
    L. B. Freund, “Dynamic fracture mechanics” (Cambridge University Press, Cambridge, 1990).CrossRefGoogle Scholar
  14. 14.
    E. H. Yoffe, Phil. Mag. 42 (1951) 739.CrossRefGoogle Scholar
  15. 15.
    D. Hull, Int. J. Fract. 62 (1993) 119.CrossRefGoogle Scholar
  16. 16.
    J. W. Dally, W. L. Fourney and G. R. Irwin, ibid. 27 (1985) 159.CrossRefGoogle Scholar
  17. 17.
    B. Cotterell, ibid. 4 (1968) 209.CrossRefGoogle Scholar
  18. 18.
    P. D. Washabaugh and W. G. Knauss, ibid. 65 (1994) 97.Google Scholar
  19. 19.
    D. Hull and P. Beardmore, in Proceedings of the First International Conference on Fracture, Sendai, 12–17 September 1965, edited by T. Yokobori, T. Kawasaki, J. L. Swedlow (Japan Society for Strength and Fracture of Materials, Sendai, 1966) Vol. 2, pp. 629–645.Google Scholar
  20. 20.
    J. E. Field, Contemp. Phys. 12 (1971) 1.CrossRefGoogle Scholar

Copyright information

© Chapman & Hall 1996

Authors and Affiliations

  • D. Hull
    • 1
  1. 1.Department of Materials Science and EngineeringUniversity of LiverpoolLiverpoolUK

Personalised recommendations