This work is concerned with a semi-infinite interface crack between a
thin film and a substrate. The two materials are assumed to be linearl
y elastic and orthotropic. A solution is presented for the stress fiel
d due to an edge dislocation on the interface which is valid for any c
ombinations of material parameters. It is found that the behavior of s
uch a bi-material system is governed by 6 independent material paramet
ers. The stress intensity factor is computed for general edge loadings
by solving integral equations numerically, and the size of the K-domi
nant zone is also studied for a residually stressed thin film. The sit
uations in which the K-field zone of dominance is very small are ident
ified and discussed.