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The noncontinuum crack tip deformation behavior of surface microcracks

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Abstract

The crack tip opening displacement (CTOD) of small surface fatigue cracks (lengths of the grain size) in Al 2219-T851 depends upon the location of a crack relative to the grain boundaries. Both CTOD and crack tip closure stress are greatest when the crack tip is a large distance from the next grain boundary in the direction of crack propagation. Contrary to behavioral trends predicted by continuum fracture mechanics, crack length has no detectable effect on the contribution of plastic deformation to CTOD. It is apparent from these observations that the region of significant plastic deformation is confined by the grain boundaries, resulting in a plastic zone size that is insensitive to crack length and to external load.

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Abbreviations

a:

Crack depth

c :

Half crack length measured perpendicular to the stress axis

CTOD:

Crack tip opening displacement measured at maximum cyclic tensile stress

CTOD:

Average of the CTOD values of the two crack tips at the surface

CTOD e :

Elastic component of CTOD

CTOD p :

Plastic component of CTOD

R p :

Plastic zone radius

z0 :

Distance of crack tip to grain boundary, measured perpendicular to the stress axis

α:

Material parameter relating closure stress to crack size and location

δ:

Crack opening displacement at any location along crack, measured parallel to the stress axis

δ(σ) :

Crack opening displacement at crack center for surface stress, σ

ε:

Strain in the plastic zone

σ :

Surface stress

σ cc :

Crack tip closure stress

σcc :

Average of σcc for two surface tips of a microcrack

σmax :

Maximum tensile surface stress

σyieid :

Macroscopic surface stress at 0.2 pct yield

CTOD/δ(σmax):

Ratio of crack tip opening displacement to opening at crack center both measured for σ = σmax. Used as an indirect measure of plastic zone size and of crack tip closure stress

CTOD/δ(σmax):

Average of CTOD/δ(σmax) for the two surface crack tips

z0/2c:

Ratio of distance of crack tip to grain boundary to microcrack length. Used to estimate crack closure stress from microscopic parameters

References

  1. J. Lankford and D. L. Davidson:Int. J. Fract., 1978, vol. 14, pp. R87–89.

    CAS  Google Scholar 

  2. W. L. Morris:Met. Trans. A, 1979, vol. 10A, pp. 5–11.

    CAS  Google Scholar 

  3. C. Y. Kung and M. E. Fine:Met. Trans. A, 1979, vol. 10A, pp. 603–10.

    CAS  Google Scholar 

  4. C. G. Bowles and J. Schijve:Int.J. Fract., 1973, vol. 9, pp. 171–79.

    Article  Google Scholar 

  5. W. L. Morris:Met. Trans. A, 1978, vol. 9A, pp. 1345–48.

    Article  CAS  Google Scholar 

  6. W. Elber: ASTM STP 486, p. 230, Am. Soc. Test, and Mat., Philadelphia, PA, 1971.

    Google Scholar 

  7. W. L. Morris and O. Buck:Met. Trans. A, 1977, vol. 8A, pp. 597–601.

    CAS  Google Scholar 

  8. C. K. Clark and G. C. Cassait:Eng. Fract. Mech., 1977, vol. 9, pp. 675–88.

    Article  Google Scholar 

  9. J. R. Rice: ASTM STP 415, Am. Soc. Test and Mat., pp. 247–309, 1967.

  10. W. L. Morris:Met. Trans. A, 1977, vol. 8A, pp. 1087–93.

    CAS  Google Scholar 

  11. A. E. Green and I. N. Sneddon:Proc. Cambridge Phil. Soc, 1950, vol. 46, pp. 159–64.

    Article  Google Scholar 

  12. N. J. I. Actams:Eng. Fract. Mech., 1972, vol. 4, pp. 543–54.

    Article  Google Scholar 

  13. O. Buck, J. D. Frandsen, C. L. Ho, and H. L. Marcus:The Microstructure and Design of Alloys Vol. 1, p. 462, The Institute of Metals and Iron and Steel Institute, 1973.

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Authors and Affiliations

  1. member of the Technical Staff, Science Center, Rockwell International, 91360, Thousand Oaks, CA

    W. L. Morris

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  1. W. L. Morris
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Morris, W.L. The noncontinuum crack tip deformation behavior of surface microcracks. Metall Trans A 11, 1117–1123 (1980). https://doi.org/10.1007/BF02668135

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