Thin films and coatings bonded to substrates often sustain high levels of
in-plane stress. If the stress is tensile, the film is susceptible to cracking
or interface delamination, depending on the relative toughness of the film and
interface. If the stress is compressive, the film can delaminate by either an
edge mode or a mode driven by buckling. All of these failure modes are
sensitive to the ratio of the film modulus to that of the substrate. In
particular, the driving forces for these failure modes are significantly
enhanced when the compliance of the substrate is large compared to the film. The
most striking instances are for metal or ceramic films on polymer substrates,
which, typically, are under compressive stress. Results illustrating the
phenomena for each of the failure modes will be presented and discussed.
Several of these results are not intuitive. In particular, it will be shown
that edge delamination is highly dependent on details of edge geometry. Some
edge geometries provide an intrinsic barrier to the nucleation of delamination
while others offer none at all.
