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
On 16 Nov 2018, at 11:13 pm, Björn bjornmail@gmail.com [harryproa] <harryproa@yahoogroups.com.au> wrote: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 2.3Design of Sandwich StructuresAchilles Petras
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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