  Cavitation has long been recognized as a crucial predictor, or precursor, to
the ultimate failure of various materials, ranging from ductile metals to soft
and biological materials. Traditionally, cavitation in solids is defined as an
unstable expansion of a void or a defect within a material. The critical
applied load needed to trigger this instability - the critical pressure - is a
lengthscale independent material property and has been predicted by numerous
theoretical studies for a breadth of constitutive models. While these studies
usually assume that cavitation initiates from defects in the bulk of an
otherwise homogeneous medium, an alternative and potentially more ubiquitous
scenario can occur if the defects are found at interfaces between two distinct
media within the body. Such interfaces are becoming increasingly common in
modern materials with the use of multi-material composites and layer-by-layer
additive manufacturing methods. However, a criterion to determine the threshold
for interfacial failure, in analogy to the bulk cavitation limit, has yet to be
reported. In this work we fill this gap. Our theoretical model captures a
lengthscale independent limit for interfacial cavitation, and is shown to agree
with our observations at two distinct lengthscales, via two different
experimental systems. To further understand the competition between the two
cavitation modes (bulk versus interface) we expand our investigation beyond the
elastic response to understand the ensuing unstable propagation of delamination
at the interface. A phase diagram summarizes these results, showing regimes in
which interfacial failure becomes the dominant mechanism.
