When you overstress a sandwich , very often the first failure is the delamination of the skin facing, followed by a buckling of the side of the face in compression, the other failure is deformation of the foam again allowing the compression side to buckle into it. There are other failure modes like peeling.
You explore and investigate these all failure modes to see how closely you can load your structure, or even to see if you are using the best foam for the job.
B.E.
You are judged not by what you know, but by what you can do.
NASA CR 1457 analysis of sandwich panels.
Skin wrinkling is often most critical. You also have honeycomb (and very coarse foam) skin dimpling and also core shear failure with both skins in compression (shear crimping). Note the two types of skin wrinkling with honeycomb and foam core. Skin wrinkling occurs with the lower of core compression or core tension or core/skin bond tension. Core compression is often lower than core tension with hot wet foam core (but always check foam tension which will have a low skin-bond tension compared with honeycomb). Lessons to be learned? Check and avoid all local stability failures as well as overall panel stability. Note that foam has lower specific strengths than honeycomb so foam will always make a slightly heavier structure.
