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. Alien, are expressed by a unified, single expression. The expression depends linearly on a case parameter eta, defined to specify the three cases of wrinkling: eta = 0 for single-sided face wrinkling (case 1), eta = 1 for in-phase wrinkling (case 2), and eta = -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.