Physics – Condensed Matter – Materials Science
Scientific paper
1996-06-27
Phys. Rev. B 55, 6211 (1997)
Physics
Condensed Matter
Materials Science
12 pages, REVTeX using epsfig.sty. 13 PostScript figures. Final version to appear in Phys. Rev. B. Main changes: Discussion sl
Scientific paper
10.1103/PhysRevB.55.6211
We present a systematic study of the effect of crack blunting on subsequent crack propagation and dislocation emission. We show that the stress intensity factor required to propagate the crack is increased as the crack is blunted by up to thirteen atomic layers, but only by a relatively modest amount for a crack with a sharp 60$^\circ$ corner. The effect of the blunting is far less than would be expected from a smoothly blunted crack; the sharp corners preserve the stress concentration, reducing the effect of the blunting. However, for some material parameters blunting changes the preferred deformation mode from brittle cleavage to dislocation emission. In such materials, the absorption of preexisting dislocations by the crack tip can cause the crack tip to be locally arrested, causing a significant increase in the microscopic toughness of the crack tip. Continuum plasticity models have shown that even a moderate increase in the microscopic toughness can lead to an increase in the macroscopic fracture toughness of the material by several orders of magnitude. We thus propose an atomic-scale mechanism at the crack tip, that ultimately may lead to a high fracture toughness in some materials where a sharp crack would seem to be able to propagate in a brittle manner. Results for blunt cracks loaded in mode II are also presented.
Canel L. M.
Carlsson Anders E.
Schiøtz Jakob
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