Modeling of Wrinkling in Sandwich Panels under Compression

A wrinkling model for sandwich panels in compression is developed with the assumption of a continuous isotropic linear elastic core. Wrinkling stresses for the three modes, defined in a well-known book by H. G. Allen, are expressed by a unified, single expression. The expression depends linearly on a case parameter η, defined to specify the three cases of wrinkling: η = 0 for single-sided face wrinkling (case 1), η = 1 for in-phase wrinkling (case 2), and η = −1 for out-of-phase wrinkling (case 3). It is shown that the stresses in all three cases are almost identical for short wavelength wrinkling and can be expressed by a single simplified analytical expression; however, they may differ significantly in moderate and long wavelength wrinkling, and for these cases they are given by simplified analytical expressions. It is proved that the in-phase wrinkling stress is the lowest among the three cases. Based on the analysis conducted, limitations of the commonly used Winkler and two-parameter models are discussed. Finally, engineering design procedures are recommended for the wrinkling effect in sandwich panels under compression.