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Materials Science and Engineering Laboratory,
National Institute of Standards and Technology,
Gaithersburg, MD 20899
The Intrinsic Ductility Criterion for Interfaces in Solids
Robb Thomson, NIST Fellow Emeritus
Thu May 4 14:27:50 EDT 1995
Abstract:
This paper explores the cleavage vs. blunting dislocation emission
from a crack on an interface in a 2D simple hexagonal lattice for a
variety of nearest neighbor central force laws, and compares the
results with elastic predictions of the criteria couched in terms of
the interfacial surface energy, 
, and the unstable stacking
fault, 
. The
mode conversion characteristic of interfacial cracks is interpreted in
terms of a local phase at the core of the crack, with a cut-off at
the force law range parameter. Results are that the emission
criterion has two regimes. When 
the emission
criterion is proportional to the product, 
, while
when 
, the criterion is proportional to
. Chemical embrittlement of a crack is a direct
consequence of these results, and is discussed. It is shown, however,
that the localized interactions associated with chemical effects at a
crack tip are inherently too complex to be encompassed in simple
criteria such as these, and that quantitative predictions for chemical
effects will require more detailed considerations of the specific
lattice and bonding configurations in hand. But these results should serve
usefully as ``rule of thumb'' guides.
PACS numbers: 07.05.T, 62.20.M, 61.72.B, 61.72