That paper is discussing honeycomb cores, which behave a
little differently to closed cell foam. The wrinkling
they refer to could be viewed as micro-buckling of the
skin with the skin still adhered to some part of the cells
but the cells have collapsed near the plane of the where
they attach to the core. They distinguish wrinkling from
buckling as they refer to buckling of the cells between
skins due to perpendicular compressive stress.
When I refer to skin buckling with a foam core
it is the failure of the skin in compression in the plane
of the skin due to buckling resulting from core or
adhesion failure enabling the skin to become unstable. It
is more a gross failure than wrinkling. Both are the
result of the in-plane compressive stress on the skin
under compression.
A wrinkled skin on honeycomb core may be still
serviceable but a buckled skin on foam core will rapidly
deteriorate. The composite panel has been reduced to
essentially a single skin on a foam panel so has lost most
of its rigidity. If the outer skin is exposed to water
pressure it will soon delaminate in the failed area. The
honeycomb may leak and take water into the core but it
will survive for longer.
In the oceanskayaks link there were a couple
of images showing buckling failure of the skins on foam
core.
Rick
Rick, about
the buckling, is it what the paper calls "Core
crushing"/"Indentation" or "Face wrinkling"?
See Chapter 2, and especially Figure 2..9
and Table 2.3
Design of Sandwich Structures
Achilles Petras