Buckling of Honeycomb Sandwiches: Periodic Finite Element Considerations
D. H. Pahr and F.G. Rammerstorfer

Source CMES: Computer Modeling in Engineering & Sciences, Vol. 12, No. 3, pp. 229-242, 2006
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Keywords Sandwich Buckling, Wrinkling, Dimpling, Periodic Unit Cells, Finite Element Method
Abstract Sandwich structures are efficient lightweight materials. Due to there design they exhibit very special failure modes such as global buckling, shear crimping, facesheet wrinkling, facesheet dimpling, and face/core yielding. The core of the sandwich is usually made of foams or cellular materials, e.g., honeycombs. Especially in the case of honeycomb cores the correlation between analytical buckling predictions and experiments might be poor (\relax \begingroup \catcode `\ 12\relax \catcode `\\12\relax \catcode `\$12\relax \catcode `\&12\relax \catcode `\#12\relax \catcode `\^12\relax \catcode `\_12\relax \catcode `\%12\relax \catcode `\~12\relax \endgroup \relax \cite *{ley99}). The reason for this lies in the fact that analytical formulae typically assume a homogeneous core (continuous support of the facesheets). This work highlights problems of honeycomb core sandwiches in a parameter regime, where the transition between continuous and discrete support of the facesheets is studied. Periodic finite element unit cell models are utilized for this task, which offer the big advantage of a homogeneous load introduction to the structure. The finite element models are found to be well suited for all kinds of buckling predictions. Different uni- and bi-axial loadings are considered as well as influences of core height, core material, core geometry, and facesheet thickness are investigated. Finally, a new analytical approach is introduced for the unexpected core cell wall buckling under in-plane compression of the sandwich, which predicts the critical load very accurately.
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